Civil Engineering Materials (Kelli)
On average, how do the stresses that coarse aggregates experience relate to those experienced by concrete?
On average, coarse aggregates experience higher stresses than concrete.
Why is density important?
Permanent loads from structure weight account for a large percentage of the loads that the structure carries. It is also important for purchasing materials.
What is self-consolidating concrete?
SCC; self-leveling and non-segregating flowable concrete; requires no or minimal vibration; high dosage of superplasticizer, higher sand and cement contents
What does the gradation band help ensure?
That the aggregate selection will produce good materials that perform well
What's the difference between center point loading and third-point loading for flexural testing?
The center point loading is loaded in the center of the beam, and the third-point loading is loaded at two points, where the increment between loads is equally divided in thirds. Third-point loading allows for constant moment to be applied over a larger part of the beam.
What mechanical properties do reinforcing bars rely on?
adequate tensile properties and strong bonding with concrete
For higher water-cement ratios (greater than 0.40), how does aggregate strength affect concrete?
aggregate strength does not make much difference
For lower water-cement ratios (less than 0.40), how does aggregate strength affect concrete?
aggregate strength may be similar to paste strength
An increase in aggregate size causes...
aggregate volume to increase and paste content to decrease, along with cracking, creep, and shrinkage; less paste -> less cement -> lower cost
What is the ASR process?
alkali + silica = gel; gel + moisture = expansion; absorption-swelling theory & osmotic pressure theory
What is a target value?
an acceptable value for controlling characteristics of a product
What is the Rolling Thin Film Oven Method?
an aging method that simulates construction aging
What is the Pressure Aging Vessel Method?
an aging method that simulates long-term pavement aging
What is a moving average?
an average computed based on a fixed set of continuous data points
Fineness Modulus
an index of the fineness of an aggregate; higher means coarser; particularly useful for sand
What is a lot?
an isolated quantity of material which is produced from a single source under similar condition
What type of material is lumber?
an orthotropic material
Aesthetics
appearance of the material; selected by the architect, who should work with the civil engineer
What are cutback asphalts composed of?
asphalt cement with petroleum solvent
What are emulsified asphalts composed of?
asphalt cement, water, and an emulsifying agent
What are two Superpave aggregate criteria?
based on aggregate blend and based on traffic and depth into pavement
What does a Superpave specification for aggregates look like?
based on the nominal maximum aggregate size; Ex. SM 12.5 means nominal maximum aggregate size is 12.5mm
What do all QA specifications require?
basic knowledge of statistics
When are admixtures added to concrete?
before or during mixing
How is the TxDOT Mix Design completed?
by Excel; requires inputting of: sieve analysis for each sieve, aggregate specific gravities, theoretical maximum specific gravity (Gr), percent density (Ga), and asphalt content (%); plots properties to ensure they satisfy specifications; aids in the selection of optimum asphalt content; prepares data in standard format for submittal
What factors are considered when selecting the PG grade in the superpave grading system?
-reliability -geographic location -loading type (time and amount) -temperature (air and pavement)
What are the major components of the preparation of laboratory samples?
-separate material into individual sieves for each stockpile -batch samples -mixing and compacting -determine percent density (Ga) at each asphalt content and input all data into TxDOT Mix Design program
What are the goals of compaction?
-simulate field densification (traffic & climate) -accommodate large aggregates -measure compactibility -conducive to quality control
How can a source of asphalt be identified?
by solubility tests
What component of concrete is most susceptible to shrinkage?
cement paste; water experiences drying shrinkage and cementitious material experiences chemical shrinkage
What affects the Superpave specification? How does it affect it?
climate; the first number is the average 7-day maximum pavement temperature, and the second number is the minimum pavement temperature
Control Charts
contain tolerances and averages of a production process over time
What does hydration require?
continuous moisture
What causes creep?
crystalline flow in aggregate and cement paste, plastic flow of cement paste, exudation of cement gel water, closing of internal voids
What is creep?
deformation from a sustained load
What is involved in the RV Test?
determine viscosity at both 135 degrees C and 165 degrees C; check for handling and pumping; develop a temperature-viscosity relationship
What is effective specific gravity?
excludes absorbed asphalt volume; includes the volume of solid particle and the volume of the pore volume that is not filled with asphalt
What is apparent specific gravity?
excludes the water permeable pore volume; includes only the volume of solid particle
What are some properties of uniformly-graded aggregates?
few points of contact; poor interlock (depending on shape); high permeability; not strong
Concrete Uses
foundations, columns, beams, slabs, roads, cooling towers, etc.
How is low-temperature cracking addressed in the superpave binder specifications?
from BBR or DTT Tests; a minimum m value and a maximum S value OR a minimum failure strain because we want a soft and elastic binder that relaxes OR a stiff binder that will stretch
Type I Portland Cement Use
general
What is tar?
generally a by-product of coal (coke) production; resistant to petroleum products
What is asphalt?
generally a by-product of petroleum distillation; a complex hydrocarbon; soluble in petroleum products; can be naturally-occuring
What do emulsifiers do?
give surface charge to asphalt droplets suspended in water medium; anionic (limestone compatible) or cationic (siliceous gravel compatible); allow for bitumen to be mixed at lower temperatures; cheaper, safer, and better for the environment compared to cutbacks.
Why is gradation of aggregates important for HMA?
gradation determines packing; dense packing means lower permeability; permeable mix requires voids
How is the concept of aggregate grading taken into consideration when proportioning?
grading to produce the densest packing is desired; most specifications include gradation limits for aggregates
How are mineral admixtures, such as fly ash and GGBFS added?
ground with clinkers
What mechanical properties do bridge wires rely on?
high strength, high toughness, fatigue resistance, and corrosion resistance
How is pavement deformation addressed in the superpave binder specifications?
high temperature stiffness from DSR Test; early part of service life; a minimum value exists because a stiff, elastic binder is the goal
What mechanical properties do prestressing steels rely on?
high yield stress in tension so that a high elastic strain can be induced; no excessive relaxation and good bond
What is self-consolidating concrete (SCC)?
highly flowable, non-segregating concrete requiring no manual consolidation; flowability due to superplasticizers and stability due to high cement content
What does the stress-strain relationship for low-carbon steel look like?
https://upload.wikimedia.org/wikipedia/commons/f/f1/Stress_v_strain_A36_2.svg
What can be determined from the normal distribution?
if the mean and/or scatter is acceptable
How is concrete with admixtures tested? Why?
in large batches with actual equipment because performance will vary as site and material conditions change
Portland Cement Chemical Composition
in order of decreasing percentage: 1. lime (CaO) 2. iron oxide (SiO2) 3. silica (Fe2O3) 4. alumina (Al2O3)
What is bulk specific gravity?
includes the bulk volume, which is the solid volume and the water permeable pore volume
Increased aggregate volume...
increases density, when the aggregate is denser than the paste; increases strength, when the aggregate is stronger than the paste
What is independent assurance?
independent, third-party assessment of the product; method specification
What is the maximum density line?
indicates the densest packing of aggregate particles; closer to line indicates denser packing
What is precision?
indicates values that are close together
What is accuracy?
indicates values that are near the target
What happens with fatigue?
inelastic slip in crystals due to repeated load and local strain concentration may form a nucleus for damage that gradually spreads until the whole member fractures or fails; deformation due to repeated loading
What ideas are involved in acceptance?
inspection; process control monitoring; monitor testing; acceptance testing (by state/agency & contractor)
How is fatigue cracking addressed in the superpave binder specifications?
intermediate temperature stiffness from DSR Test; later part of service life; a maximum value exists because a soft, elastic binder is the goal
What two criteria should questionable water be subjected to before use in concrete?
1. 7-day compressive strength of mortar cubes made with questionable water should be 90%+ of those made with potable water 2. neither setting time (initial or final) should not be adversely affected
What are some characteristics of entrapped air?
1. coarse 2. rain drops 3. inefficient 4. less protection per unit volume 5. more impact on strength
What are four consensus properties of aggregates?
1. coarse aggregate angularity (CAA) 2. fine aggregate angularity (FAA) 3. flat, elongated particles (causes segregation) 4. clay content (want minimum for maximum bonding)
What quality control issues are associated with the use of pozzolans?
1. composition 2. impurities 3. gradation 4. variability
What are the six tests performed on hardened concrete?
1. compressive strength 2. split tension 3. flexural strength (center point or third-point) 4. rebound hammer 5. penetration resistance 6. maturity test
Economic Factors
1. cost of raw material (production & purchase, transport & storage) 2. cost of construction 3. construction time 4. maintenance & life-cycle cost 5. environmental impact
Non-Mechanical Properties
1. density/unit weight 2. thermal expansion 3. surface characteristics, including a) corrosion & deterioration b) abrasion & wear resistance c) surface texture
What are some benefits of control charts?
1. early detection of trouble 2. decreased variability 3. establish process capability 4. reduce price-adjustment costs 5. decrease inspection frequency 6. provide a basis for altering specification limits 7. provide a permanent record of quality 8. provide a basis for acceptance 9. instill quality awareness
What are four major factors that you must consider when designing PCC mixes?
1. economy 2. workability 3. strength 4. durability
What effect can impurities in mixing water have on concrete?
1. efflorescence (salt-coating) 2. corrosion 3. volume instability 4. reduced durability
What are two types of polymer modifiers?
1. elastomers (stiff, but flexible) 2. plastomers (higher stiffness, but not as flexible)
What types of specifications exist?
1. end-result 2. quality assurance 3. performance-related 4. performance-based 5. warranty
What characteristics of the mixing procedure affect admixture behavior?
1. equipment 2. how admixtures are added 3. when admixtures are added 4. sequence of admixture addition 5. concentration of admixture
Aggregate Production
1. excavation 2. transport 3. crushing 4. sizing 5. washing
What are some characteristics of entrained air?
1. fine 2. fog droplets 3. efficient 4. more protection per unit volume 5. less impact on strength
What factors affect flexural testing?
1. flaws 2. preexisting stresses 3. temperature & moisture conditioning
What tests are performed on hardened concrete?
1. modulus of elasticity 2. compression 3. shear 4. bond 5. direct tension 6. flexural
What strength properties are taken into consideration when designing with timber?
1. modulus of rupture (in bending) 2. maximum crushing strength 3. compression perpendicular to grain 4. shear strength parallel to grain
What are the two types of pozzolans?
1. natural 2. synthetic
Aggregate Types/Sources
1. natural 2. manufactured 3. recycled
Why were the Romans successful builders?
1. not a lowest bid contract 2. relatively benign environment 3. not probably reinforced with steel
What are three reasons for blending aggregates?
1. obtain desirable gradation 2. single natural or quarried material not enough to satisfy requirements 3. economical to combine natural and processed materials
In what ways can pozzolans differ?
1. particle size and shape 2. impurities 3. uniformity 4. reactivity
What specifications for petroleum asphalts developed?
1. penetration grade (scale of hardest to softest) 2. viscosity-graded specifications (scale of softest to hardest) 3. Superpave binder specification
What factors affect aggregate reactivity?
1. percent aggregate in mix 2. size gradation 3. dispersion 4. moisture content 5. temperature 6. time (delayed reaction)
How can you determine the reactivity of an aggregate to alkakis?
1. petrographic examination 2. rock cylinder test 3. quick chemical test 4. mortar bar test
What are the three categories of mineral admixtures?
1. pozzolanic 2. cementitious 3. non-reactive
What are the two Air Content Tests?
1. pressure meter 2. roll-a-meter
What are the three components of quality assurance?
1. process control 2. independent assurance 3. acceptance
What characteristics of the mix affect admixture behavior?
1. proportions 2. water-cement ratio 3. slump
What are the basic steps of refinery operation?
1. pumping 2. storage 3. heating 4. distillation 5. condensing and cooling 6. separation
In what ways can a mineral admixture affect concrete?
1. rate of strength gain 2. water demand 3. lower heat of hydration 3. makes it behave like Type II or Type IV Portland cement 4. increased long-term strength (at the expense of early strength) 5. reduced permeability 6. sulfate and alkali-aggregate reaction susceptibility
What are the requirements for ASR to happen?
1. reactive forms of silica or silicates in aggregate 2. sufficient alkalis 3. sufficient moisture
What are some problems associated with set-accelerating admixtures?
1. reduced sulfate resistance 2. increased alkali-aggregate reaction 3. increased corrosion
What does a smaller maximum aggregate size cause?
1. reduces segregation 2. reduces road noise 3. decreases tire wear
How does fly ash affect fresh concrete?
1. reduces water demand 2. reduces air content; compensate with air-entraining 3. increases workability 4. reduces heat of hydration 5. increases set time; compensate with accelerator
How does the Texas Gyratory Press operate?
4": -6 degree angle -compact to given resistance, not fixed effort 6": -6 degree angle -compact with constant pressure until rate of height change per revolution drops to specified level
What is the air void requirement for Superpave Mix Design?
4%
What are the desirable properties of aggregates for asphalt?
1. sharp edges (interlock) 2. size distribution (within gradation band) (permeability) 3. strong 4. durable 5. clean & free of organic material (for bonding) 6. round in shape (not flat or elongated) 7. cheap & locally available 8. chemical characteristics 9. good adhesion with the binder
In what three ways does a concrete cylinder fail during the compression test?
1. shear or "core" 2. combination shear & splitting 3. splitting or "columnar"
Methods to Create Good Stockpiles
1. short drop distances 2. minimize moving 3. don't use "single cone" method 4. separate stockpiles
List six types of variety concrete.
1. shotcrete 2. soil-cement 3. self-consolidating concrete (SCC) 4. roller-compacted concrete (RCC) 5. lightweight concrete 6. heavyweight concrete
What should be done before starting a mix design?
1. sieve analysis for coarse and fine aggregates 2. unit weight and bulk specific gravities 3. aggregate absorption 4. required strength 5. eventual exposure conditions
What are the three main cementitious materials used as admixtures?
1. silica fume 2. ground granulated blast furnace slag (GGBFS) 3. fly ash & natural pozzolans
What are the four tests performed on fresh concrete?
1. slump 2. air content 3. temperature 4. unit weight
What are the steps in a PCC mix design?
1. slump 2. water and air content 3. water-cement ratio 4. cement 5. maximum size, volume, and weight of coarse aggregate 6. weight of sand by absolute volume method 7. admixtures (chemical and/or mineral) 8. trial mixes
How does silica fume affect hardened concrete?
1. small effect on the rate of strength gain 2. may reduce shrinkage 3. reduces permeability and absorption 4. reduces alkali-aggregate reactivity 5. reduces corrosion induced by deicing or marine salts 6. improves sulfate resistance
What are the five parts of quality management?
1. specification development 2. process control/quality control 3. lab and technician certification 4. product acceptance 5. training and communication
Loading Conditions
1. static 2. dynamic
What types of fibers are used in fiber-reinforced concrete?
1. steel 2. glass 3. synthetic 4. natural
Why would polymer modifiers be used?
1. stiffer mixes at high temperatures 2. softer mixes at low temperatures 3. improved fatigue resistance 4. reduced life-cycle costs
What are some concerns associated with the use of water-reducing admixtures?
1. temporary effect 2. retardation 3. stickiness/elasticity 4. air bubble stability
Why are admixtures used?
1. to enhance concrete properties 2. to modify fresh concrete behavior 3. to compensate for cement characteristics 4. to make concrete economic
What are three source properties of aggregates?
1. toughness 2. soundness 3. deleterious materials
Source Aggregate Properties
1. toughness 2. soundness 3. deleterious materials 4. gradation
Concrete Chemical Composition
1. tri-calcium silicate (C3S) 2. di-calcium silicate (C2S) 3. tri-calcium aluminate (C3A) 4. tetra-calcium aluminoferrite (C4AF); also gypsum, alkalis, magnesia, sulfur tri-oxide
What characteristics of cement affect admixture behavior?
1. type 2. chemistry 3. fineness 4. impurities
What characteristics of aggregates affect admixture behavior?
1. type 2. chemistry 3. gradation
What are the three types of gradations for aggregates?
1. uniformly-graded 2. well-graded 3. gap-graded
What are some characteristics of polymer modifiers?
1. used because of increased demand on HMA pavements (wider range of binder performance required) 3. disposal of waste products 4. willingness to pay more upfront for long-term benefit
What are some other admixtures?
1. viscosity modifiers 2. anti-freezing admixtures 3. expansion-producing admixtures 4. corrosion-inhibitors 5. alkali-aggregate reaction inhibitors 6. shrinkage-reducing admixtures 7. damp-proofing admixtures
What factors affect the compressive strength of concrete?
1. water-cement ratio 2. cement type 3. admixtures 4. aggregate type & grading 5. curing 6. temperature & moisture content at time of testing
Other Cement Types
1. white Portland cement 2. blended hydraulic cement 3. masonry cement 4. expansive cement (type K) 5. specialty cement
What is ACR?
Alkali-Carbonate Reactivity; carbonate in aggregates reacts with the alkali in cement
Asphalt cement and base courses require what shape and texture of aggregate?
Angular and rough, because of aggregate interlock; increases stability and reduces rutting
What were the early specification for lake asphalts and for petroleum asphalts?
lake asphalts: -appearance -solubility in carbon disulfide petroleum asphalts: -consistency
What does finer cement do?
leads to earlier strength but requires higher water content
What does a high cement factor do?
leads to higher early strength, but requires smaller aggregates and more air
What does more cement do?
leads to higher strength but requires higher water content
What does a lower water-cement ratio do?
leads to higher strength but requires more mixing time
What does specific gravity do?
like density, it relates mass and volume
Production & Construction Limitations
limitations due to local availability of materials, equipment, experienced producers, environmental impact, etc.
C2S Contribution to Concrete
long term strength
What are the typical properties of timber?
low specific gravity, low maximum deflection, high compressive strength parallel to the grain, low compressive strength perpendicular to the grain (modulus of rupture and elasticity? comparative)
The cost of producing concrete is ____________ than the cost of ready-mix concrete
lower
Increasing the size of test specimens for compressive strength tests has what effect?
lower relative strength
What is involved in the production of ferrous materials?
produced by the reduction of iron ores in a blast furnace ("cooking" with iron ore, coke, and limestone in a blast furnace) to pig iron, and the subsequent treatment of pig iron to various metallurgical processes
What is proportioning, and what is the goal of proportioning?
proportioning is determining relative quantities to use; the goal is to economically produce a concrete of appropriate workability, strength, and durability
What is the best way to prevent carbonation?
protection
What ideas are involved in process control?
quality is either there or not, not affected by inspection; must control the production process; "do it right the first time".
How does heat evolution relate to the time of setting and hardening of concrete?
rate of heat evolution: (stage 1) high at the beginning, sloping down to the initial set (stage 2), then up to C3S hydration, then slightly down to C3A hydration (stage 3), then down to near 0.
What is RAP?
reclaimed asphalt pavement (RAP) is recycled asphalt pavement; Superpave transition was difficult due to grading difficulties and mixing difficulties, but partial blending occurs to a significant extent; may have to adjust the performance grade.
(Water) Absorption
(SSD weight-oven dry weight)/oven dry weight
What types of properties are considered when working with timber?
-3 moduli of elasticity -3 moduli of rigidity -6 Poisson's ratios (9 are independent)
Freeze-Thaw Durability
resistance of concrete to freeze-thaw damage
What is chemical durability?
resistance to chemical reaction
Natural Aggregates
result from the breakdown of large rock masses
Coarse Aggregate
retained on No. 4 (4.75mm) sieve
Why is gypsum added to Portland cement?
retards early setting and hardening
Aggregate Shapes
rounded, angular, subrounded, subangular
How does testing for performance grade work?
test the same type of asphalt for multiple temperatures until the sample fails to meet the specification requirement; the asphalt belongs to the grade based on the last temperature that passed the specification
What is the dust proportion (DP)?
the % weight of the <0.075 (#200 sieve) material divided by the % weight of effective asphalt (should be between 0.8 and 1.6
What does the shear strength parallel to grain tell you?
the ability to resist internal slipping of one part upon another along the grain
Toughness
the ability to withstand loading
Soundness
the ability to withstand weathering
What is quality assurance?
the activities that have to do with making sure that the quality of a product is what it should be
What is quality control?
the activities that have to do with making the quality of a product what it should be
Modulus of Resilience
the area under the elastic portion of the stress-strain diagram
What is an average or mean?
the arithmetic average is determined for a number of variables
What is hydration?
the chemical and physical process that takes place between Portland cement particles and water, resulting in the setting and hardening of cement
What is the maturity concept?
the concept based on the fact that the hydration of cement is greatly affected by both the time and temperature of hydration; determines the minimum strength needed to continue construction; helps you estimate minimum project time
What is the range?
the difference between the largest and smallest values
What is the limiting tensile strain?
the flexural or tensile expansion of concrete at failure; approximately equal to the values for expansion at failure in compression
How is the weight or volume design different between TxDOT and Superpave Mix Designs?
the function of specific gravity of stockpiles is different (labeling). Additionally, TxDOT has the option of using a weight design or using a volume design; Superpave is purely volumetric.
How does the rate of growth affect timber strength?
the greater the number of rings per inch (the slower it grows), the stronger it is
What relationship exists between the temperature and the yield stress of steel?
the higher the temperature, the lower the yield stress
What is the fiber saturation point (FSP)?
the level of saturation at which the cell walls are completely saturated but no free water exists in cell cavities
What is the lower specification limit (LSL)?
the lower boundary beyond which a sample (an average of samples) characteristics may not deviate
What is the relationship between water-cement ratio and compressive strength?
the lower the water-cement ratio, the higher the compressive strength
Strength
the maximum stress a material can withstand
What is N design based on?
-average design high air temperature -traffic level
What is the metal structure?
-crystalline -space lattices or unit cells
What types of wood products are produced?
-dimentional lumber -heavy timber -round stock -engineered wood (including structural panels, glued laminated timber, structural composite timber, and composite structural members) -specialty items
What are the Superpave Mixture Requirements?
-specimen height -mixture volumetrics (air voids, voids in the mineral aggregate (VMA), voids filled with asphalt (VFA), and mixture density characteristics) -dust proportion -moisture sensitivity
What is the selection of mix type based on?
-traffic volumes -loading characteristics -design speed -desired performance characteristics -cost -previous experience
What are the main differences between TxDOT HMA Mix Design and Superpave Mix Design?
-type of mix -compactor type -weight or volume design; labeling -compaction level also: -evalution -number of control points for grading
What does the maximum crushing strength tell you?
the maximum stress sustained by a compression parallel-to-grain specimen having a ratio of length to least dimension of less than 11
What do the VMA requirements depend on?
the nominal maximum aggregate size
How is the compaction level different between TxDOT and Superpave Mix Designs?
the number of gyrations of the Superpave Gyratory Compactor is different
What is involved in aggregate gradation for Superpave specifications?
0.45 gradation chart; blend different materials to create the proper gradation (3-4 materials)
What are two Superpave specifications of the designing the aggregate structure?
0.45 power chart and control points
What are the steps for Volumetric Superpave Mix Design?
1) Design aggregate structure 2) compute estimated binder content 3) computer design binder content 4) mix evaluation
What can VTM be increased by?
1) reducing asphalt content and 2) reducing dust
What can VMA be increased by?
1) reducing the dust or natural sand or 2) increasing the distance from the middle
Freeze-Thaw Distresses
1. "D" cracking 2. Scaling 3. Popout
How can you identify ASR?
1. "map" cracking 2. aggregate reaction rims 3. field detection using Uranyl Acetate solution
What are the criteria used when selecting water for the production of Portland cement concrete?
1. 7-day strength of mortar cubes at least 90% of that made with potable water 2. setting should not be affected
What is proportion defective?
the percentage of samples from a normal dsitrbution that fall outside of the lower and upper limit; the percentage of samples that does not fall within the limits
What do the mixing and compaction temperatures depend on?
the performance grade (PG grade) of the binder
What do the requirements for the Hamburg Wheel Test depend on?
the performance grade (PG grade) of the binder
Draw the phase volume diagram of asphalt concrete and identify all components.
the phase diagram contains (from the bottom to top): aggregate, binder absorbed by aggregate, effective binder, and air; also label volumes and masses
What happens with slip?
the phenomenon of movement along gliding planes of crystals due to stress
How do defects affect timber strength?
the presence of defects (such as knots, shakes, and checks) decreases strength
What is viscosity?
the ratio between the applied shear stress and the rate of shear strain
What is the maturity index?
the relationship between the temperature history of a concrete and its strength
What is segregation?
the separation of sizes over time; larger aggregates move to the bottom; causes the mix to be not uniform
What is consistency?
the softness or hardness of a liquid; the stiffness; the way a liquid flows
What is combined specific gravity?
the specific gravity of the blend of multiple aggregates
What is variance?
the square of the standard deviation
What is coefficient of variation (COV)?
the standard deviation as a percentage of the mean
Endurance Limit
the stress level below which fatigue does not occur
What is phase angle?
the time difference between the applied shear stress and the resulting shear strain
What do the VFA requirements depend on?
the traffic level
Elastic Limit
the transition between elastic and plastic behavior on a stress-strain diagram (usually not an abrupt point but a transitional phase)
Proportional Limit
the transition point between linear and nonlinear behavior on a stress-strain diagram.
What is the interfacial transition zone (ITZ)?
the transition zone between paste and aggregate
Gradation Band
the upper and lower limits for grading for an aggregate
What are two types of aggregate properties?
1. Consensus Properties (required) 2. Source Properties (optional)
How can you detect ASR?
1. Mortar-Bar Expansion 2. Chemical Method 3. Rapid Immersion Test
Tests on Cement
1. Normal Consistency of Hydraulic Cement (Vicat) 2. Time of Setting of Hydraulic Cement (Vicat or Gillmore) 3. Fineness (Blaine Fineness or Wagner Turbidimeter)
List tests conducted on bitumen (asphalt cement).
1. Rotational Viscometer (RV) 2. Dynamic Shear Rheometer (DSR) 3. Bending Beam Rheometer (BBR) 4. Direct Tension Test (DTT) [with Rolling Thin Film Oven (RTFO) or Pressure Aging Vessel (PAV) aging] 5. Flashpoint Test 6. Penetration Test 7. Absolute Viscosity Test
What is the upper specification limit (USL)?
the upper boundary above which a sample (an average of samples) may not deviate
Grading
the way that sizes are combined or distributed
What are the four performance grade binder tests? What do they help simulate?
1. Rotational Viscometer (RV); temperature-viscosity relationship 2. Direct Shear Rheometer (DSR); rutting & fatigue cracking 3. Bending Beam Rheometer (BBR); low-temperature cracking 4. Direct Tension Tester (DTT); low-temperature cracking
What tests are performed on fresh concrete?
1. Slump 2. Air Content 3. Unit Weight 4. Temperature
What factors affect the strength of concrete?
1. consolidation 2. water-cement ratio 3. cement type 4. admixtures 5. aggregate type & grading 6. curing 7. specimen size (for testing) 8. temperature & moisture content (during testing)
What is required for pozzolans to react?
1. contain reactive silica (glassy) 2. be very finely divided (high surface area)
What are the aggregate specifications based on?
total aggregate blend, not individual aggregate stockpiles
What should be considered when proportioning mixtures, especially when using silica fume?
1. control weights of all ingredients 2. monitor aggregate moisture content 3. control air content 4. don't use chloride or chloride-bearing ingredients as accelerators 5. pay attention to hot and cold weather conditions
What are some other admixtures?
1. corrosion inhibitors 2. shrinkage-reducing 3. anti-wash 4. coloring 5. damp-proofing 6. grouting 7. air-detraining 8. fungicidal
What are the steps of the bitumen production process?
1. drill/pump 2. store 3. heat 4. cool 5. sort
What are the benefits of maturity testing?
1. early application of pre-stress 2. early opening to traffic 3. early form removal 4. curing times cut dramatically 5. non-destructive and inexpensive
What is toughness? What test measures toughness of aggregates?
toughness is resistance to impact; measured by the LA Abrasion Test; minimum value; also the smaller drums and balls in the Micro-Deval Test
Soundness Test
1. estimates resistance to weathering 2. simulates freeze-thaw process
Sampling is important to...
1. evaluate potential quality 2. determine compliance with project specification requirements
What are the tests performed on asphalt?
1. penetration 2. absolute viscosity 3. flashpoint 3. RV 4. DSR 5. BBR 6. DTT with aging methods: a) RTFO b) PAV see: https://engineering.purdue.edu/NCSC/library/video.htm
Use of Aggregates
1. portland cement concrete 2. bituminous concrete 3. base course in pavement (30% of cost)
How are aggregates blending?
trial and error; multiply percent passing by percent of that material in the blend: plot individual gradations, plot specification limits, and use as an initial assessment
What can affect the coarse aggregate size, volume, and weight?
type of structure, form dimensions, space between rebar, space between rebar and form, slab thickness
When are high-range water reducers (superplasticizers) used?
underwater concreting, thin or densely reinforced sections, self-consolidating concrete (SCC)
Good stockpiling creates...
uniform gradation
What are two types of concrete, in reference to the material proportions?
1. rich (more cement) 2. lean (more coarse aggregates)
Material Variability Components
1. sampling 2. quality control scheme 3. control charts 4. experimental error
What are some specialty concrete types?
1. self-consolidating concrete (SCC) 2. lightweight 3. heavyweight 4. high-strength 5. high-workability 6. expansive 7. polymer-modified 8. roller-compacted 9. shotcrete 10. fiber-reinforced 11. high-performance
Work-ability
1. slump 2. pump-ability 3. segregation 4. response to vibrator 5. finish-ability
What are the results for the SGC?
you can determine the %Gmm vs. Log Gyrations
What is necessary to obtain a desirable blend?
you need to at least have one fine material and one coarse material (one above maximum density line and one below)
Hooke's Law
σ=Eε; applies to all materials below the yield stress and to brittle materials before rupture
What are some mechanical properties of concrete?
1. strength 2. modulus of elasticity 3. Poisson's ratio 4. coefficient of thermal expansion 5. shrinkage 6. creep coefficient 7. fracture toughness 8. fatigue behavior
What are the four main uses of steel in construction?
1. structural steel 2. fastening products 3. reinforcing steel 4. forms & pans
What three materials are used to preserve timber?
1. tar oil (cheap, external, odor, painting difficulty) 2. water-soluble (odorless, possible need for redrying, consumer concerns) 3. organic solvent (internal, redrying not necessary)
What can cause flash setting?
1. too little gypsum 2. too much C3A 3. too much surface area
Maximum Aggregate Size
100% passing
Dust
70%+ passing 0.075mm (No. 200) sieve
What percentage of the weight and volume do aggregates make up?
95% and 70%
What is the maximum mixture density at N maximum?
98%
What is air entrainment?
Adding small bubbles by adding a chemical to provide space for water to expand during freezing
What is a deleterious substance?
Any material that adversely affects the quality of Portland cement or asphalt concrete made with the aggregate
What is the relationship between bulk and apparent specific gravity?
Apparent is always greater than or equal to bulk.
___________ Specific Gravity is always larger than ___________ Specific Gravity.
Apparent, Bulk
List the main differences between asphalt/bitumen and tar.
Asphalt is a by-product of the petroleum industry (or naturally occurs) and it is soluble in petroleum products. Tar is a by-product of the coal industry and it is not soluble in petroleum products.
What does a retarder to?
Delays the stength
What does the Vicat test do?
Determines amount of water needed for normal consistency; determines initial and final set times
What does the Blaine Specific Surface test do?
Determines fineness of cement using air permeability measurements; fine particles have less voids, which leads to longer times
What does the Wagner Turbidimeter test do?
Determines fineness of cement using photoelectric cells
What is DTT?
Direct Tension Tester Test
Factor of Safety
FS=σ failure/σ allowable; varies between structures; depends on: 1. cost of unpredictable failures 2. variability of materials 3. degrees of accuracy of loads and responses 4. possible misuse
How should you apply Type III Portland cement?
Fast-track construction (forms need to be removed ASAP or structure needs to be put in service ASAP)
What do repeated loadings lead to?
Fatigue
Types of Portland Cement
I. Normal II. Moderate Sulfate Resistance III. High Early Strength IV. Low Heat of Hydration V. High Sulfate Resistance
Why is cost so important for Civil Engineering materials?
Large volumes of materials are used.
What is scaling?
Layers peeling off
How should you apply Type IV Portland cement?
When mass of structure requires careful control of heat of hydration; suitable for large dams
What does SSD refer to?
When the aggregate's voids are filled with moisture but the main surface of the aggregate particles is dry
How is economy taken into consideration when proportioning?
You can reduce the cost by minimizing the cement content. 1. lowest slump with adequate workability 2. largest practical maximum aggregate size 3. optimum ratio of coarse to fine aggregates 4. appropriate admixtures Minimizing cement content reduces shrinkage and heat of hydration but causes low early strength and high variability.
What is involved in the RTFO?
a bottle is coated through testing; mass loss must be within a certain range
What is ground granulated blast furnace slag (GGBFS)?
a by-product of the iron industry
What is autoclaved cellular concrete?
a concrete produced by a mortar and gas-forming admixture, pressure steam cured (autoclaved)
What is total quality management?
a customer-focused, strategic, and systematic approach to continuous performance improvement
What happens with relaxation?
a decrease in stress that happens when a component is held for a long time in a state of elastic strain; important for steel tendons used in the prestressed concrete; when there is a fixed strain, the stress decreases
What is a quality control plan?
a detailed description of the type and frequency of inspection, sampling, and testing deemed necessary to measure and control the various properties governed by agency
Transient Loading
a dynamic loading that is an impulse loading that is applied and then removed repeatedly
Random Loading
a dynamic loading that never repeats
Periodic Loading
a dynamic loading that repeats with time
How do higher binder contents compare to lower binder contents on the %Gmm vs. Log Gyrations graph?
a higher binder content means a higher y-intercept
What is roller-compacted concrete (RCC)?
a lean concrete with no slump that is almost dry; compacted in place by vibratory roller
What is structural lightweight concrete?
a lightweight concrete with high thermal and sound insulation properties, very absorbent, segregates easily, lower creep
Dynamic Loading
a loading that generates a shock or vibration; includes: 1. periodic 2. random 3. transient
Ductile Material
a material that displays appreciable plastic deformation before failure; excessive deformation can cause failure
Brittle Material
a material that fails suddenly when the static stress reaches the strength of the material; do not undergo plastic deformation prior to failure
What is quality?
a measure of goodness; if a product meets the requirements and satisfies the customer
What is lake asphalt?
a naturally-occurring asphalt on lake surface (Trinidad & Venezuela)
What is the bulking of sand?
a phenomena observed in moist sand when there is an increase in total volume; surface tension pushes the sand particles apart affects batching by volume
Why is viscosity an important test to perform on asphalt?
a relationship between temperature and viscosity can be determined, and there exist ranges of compaction and mixing
What is involved in the DTT Test?
a tension load is applied to a specimen; obtains stress-strain curve, including strain at peak stress and stress at failure; indicates low-temperature capacity to stretch
What is the creep test for concrete?
a test for the deformation over time under a sustained load
What are petroleum-based asphalts?
a waste product from refinery-processing of crude oil; "bottom of the barrel"; properties depend on refinery operations and composition depends on crude source
What percentage of U.S. concrete contains one or more admixtures?
about 70%
Uniformly-graded
aggregate distribution with few contact points and high voids
Well-graded
aggregate distribution with good interlock and low voids
Gap-graded
aggregate distribution with some sizes missing and low voids
Water content increases when...
aggregate size decreases
How does the behavior of aggregates, cement paste, mortar, and concrete compare on a stress-strain curve?
aggregate straight; cement paste slow but gradual then constant; mortar up then down, reaching slightly below cement paste; concrete up then down at a lower level than mortar
What were Superpave specifications developed from?
air temperatures
What is VTM (air voids) most affected by?
asphalt content, dust, and proportions of course aggregate and fine aggregate
What is aging as it relates to asphalt?
asphalt is a petroleum product that oxidizes and hardens over time
What are the three components of asphalt?
asphaltenes, resins, and oils
Portland Cement Manufacturing
can be wet or dry; 1. quarry 2. crusher 3. proportioning 4. grinding 5. blending 6. kiln 7. grinding + gypsum
What is paste?
cement + water
Plot the evolution of strength vs. time for concrete made with cement and for concrete made with cement and fly ash.
concrete made with cement and fly ash will increase the long-term strength but reduce rate of strength gain
What is creep, with respect to concrete?
concrete under sustained stress or load undergoes a gradual increase of strain or deflection with time
Why did Terminal 2E fail?
creep developed and caused the roof to collapse
What are deleterious materials? What test measures the deleterious materials test?
deleterious materials are contaminants such as shale, wood, mica, and coal; wet sieve analysis determines; requirements for maximum
Crushing Equipment
depends on: 1. strength/toughness 2. size of material 3. desired size 4. energy needed
What is the Maturity Test?
determines the relationship between time, temperature, and strength; can be used in the maturity concept
What is the Temperature Test?
determines the temperature of fresh concrete
How is the effective specific gravity defined?
dry mass divided by effective volume
What are the effects that carbonation has on fresh and hardened concrete?
fresh: reduced surface durability hardened: carbonation shrinkage, corrosion of steel
What are some properties of well-graded aggregates?
good interlock; low permeability; "densely-graded"
In what instance would slower setting and slower strength development be desirable?
hot weather
Draw the typical variation of the compressive strength with time for several water-cement ratios for PCC.
lower water-cement ratio results in higher compressive strength
Alkali Contribution to Concrete
may cause reaction with silica (ASR) or dolomite (ACR); 0.6% limit
What are the steps in Portland cement production?
Quarry, crusher, proportioning, grinding, kiln (produces clinker), grinding+gypsum
Explain RCC, its uses and its properties.
RCC stands for roller-compacted concrete; it is used for pavements; it is lean (low cement content), no-slump, almost dry, and compacted in place by a vibratory roller or plate compaction equipment
Portland cement requires what shape and texture of aggregates?
Rounded and smooth, because of workability
What types of protection can be used to prevent carbonation?
Sealants and coverings
What property is buckling related to?
Stability
What does the flakiness test do?
Tests coarse aggregates for flakiness
What does toughness or abrasion resistance refer to?
The ability of aggregates to resist the damaging effect of loads
What does soundness or durability refer to?
The ability of an aggregate to withstand weathering
How does curing affect creep?
The better/longer the curing, the less creep deformation
What does the maximum density line tell you?
The closer the curve is to the maximum density line, the less room between the particles
Why does relaxation occur?
The deformation stays, so stress reduces over time.
What relationship do aggregate size and surface area have?
The larger the aggregate size, the lower the surface area
What does hardening refer to?
The strength gain in a set cement paste
Yield Stress/Yield Strength
The stress associated with the elastic limit
What is the yield stress/strength?
The stress corresponding to the elastic limit
What two phases of concrete exist? What is the zone between them?
The two phases are cement mortar and aggregate. The zone between them is the interfacial transition zone (ITZ). The ITZ plays a role in determining the strength properties of the concrete. Bond failure at ITZ is common.
What does a rich mix require?
There is more cement paste, so more air entrainment is needed.
Why is sampling of stockpiles done?
To observe properties
What are two purposes of control charts?
To observe variability and reduce variability in production by adjusting based on the results
What is the difference between trapped air and entrained air?
Trapped air reduces strength and increases permeability, while entrained air increases durability; entrapped air happens naturally and air is entrained using chemical admixtures
Which types have smaller amounts of C3A?
Type II and type V
Which type has smaller amounts of C3S and C3A?
Type IV
What is the equilibrium moisture content (EMC)?
moisture content for the average atmospheric conditions
What is maximum aggregate size?
one size larger than nominal maximum size
What are pozzolans?
siliceous or siliceous/aluminous materials which have little to no cementitious value alone; react with lime and water to form a product similar to C-S-H.
Aggregate Surface Textures
smooth, rough
How does unit weight affect timber strength?
the denser the wood, the stronger it will be
What is VMA most affected by?
the dust content
What limits the aggregate size?
thickness of layer
Creep/Viscous Flow
time dependent deformations in viscoelastic materials; creep deals with long-term deformations; viscous flow deals with short-term load duration.
Why are set-controlling admixtures used?
to control setting or to induce early hardening
Why are air-entraining admixtures used?
to improve freeze-thaw resistance and to help the concrete to resist surface scaling due to deicing salts
Stockpiling Purpose
to prevent segregation and contamination of aggregates
What is VFA?
voids filled with asphalt; the percentage of the VMA that contain/absorb asphalt
Plastic Behavior
when a material obtains permanent deformation; it does not return to its original shape when the load is removed; strain does not return to 0
Sieve Analysis Types
1. Washed 2. Mechanical
What is the slump test?
1. fresh concrete is placed in the slump cone and rodded 2. settlement when the cone is lifted is known as slump
Rocks
1. igneous 2. sedimentary 3. metamorphic
What is specific surface area?
surface area divided by unit mass or bulk volume
What environmental factor affects admixture behavior?
temperature
What characteristics of mix water affect admixture behavior?
1. chemistry 2. impurities 3. hardness 4. water content
When is type V Portland cement used?
High sulfate resistance; chemical plants
How does shrinkage cracking occur?
1. chemical (materials) 2. water evaporation (mix) 3. restraint (stiffness) 4. stress (strength)
What can contribute to early volume change in concrete?
1. chemical shrinkage 2. autogenous shrinkage 3. plastic shrinkage 4. drying shrinkage
C4AF Contribution to Concrete
"flux"; reduces clickering temperature
How is the specimen prepared for the Superpave Gyratory Compactor (SGC)?
-mechanical mixer -short term oven aging (4 hours at 135 degrees C)
What is the general rule of field management of volumetric properties?
-mix design is only the starting point (adjustments will be necessary)
How is the bulk specific gravity of the compacted HMA defined?
(compacted) mass of aggregates and asphalt divided by the volume of aggregates, asphalt, and air voids
How is the maximum specific gravity of the mixture defined?
(uncompacted) mass of aggregates and asphalt divided by the volume of aggregates and asphalt
How do you determine mixture properties?
-%Gmm at N initial, N design, and N maximum -determine % VTM, % VMA, and % VFA @ N design -determine dust proportion -graph mixture properties vs. asphalt binder content
What is the Moisture Sensitivity Test?
-3 dry specimens -3 conditioned specimens (in water) -80% minimum tensile strength ratio -optional: freeze cycle, hot water soak
What is the Superpave Gyratory Compactor (SGC)?
-Texas equipment -French operational characteristics -150mm diameter (up to 37.5 mm nominal size -height recording -1.25 degrees -30 gyrations per minute
What are the steps in determining design asphalt content?
-compact design aggregate structure specimens -determine mixture properties -graph mixture properties vs. asphalt binder -select design asphalt binder content -check required criteria (VMA, VFA, etc.)
How do you determine the optimum asphalt content?
-determine VMA, Gr, and Ga at optimum asphalt content -if density and VMA are not within allowable, redesign mixture
How do you determine asphalt binder content?
-find design asphalt binder content that corresponds to 4% air voids -check % VMA, % VFA, %Gmm at N initial, %Gmm at Nmax and dust proportion -if satisfactory, proceed with moisture sensitivity test
How are mixtures evaluated in TxDOT Mix Design?
-indirect tensile strength (specimens at 93% density -rut depth and number of passes (specimens at 93% density) by the Hamburg Wheel Test -if they are not within allowable ranges, redesign mixture
How does cracking in concrete occur?
1. ITZ micro cracks 2. mortar micro cracks 3. aggregate micro cracks The above micro cracks coalesce and become visible cracks.
How can alkali reactivity be reduced?
1. Limiting the alkali content of the cement 2. Keeping the concrete structure as dry as possible 3. Admixture 4. Crushed limestone in place of a percentage of the aggregate
What are the four steps of Superpave Mix Design?
1. Materials Selection 2. Design Aggregate Structure (grading) 3. Design Binder Content 4. Moisture Sensitivity
What are the four steps of Superpave Mix Design after determining specification?
1. Materials Selection 2. Design Aggregate Structure (gradation) 3. Design Binder Content 4. Moisture Sensitivity (vertification)
What are three cutbacks?
1. Rapid Cure (RC); high volatility of solvent; tack coats and surface treatments 2. Medium Cure (MC); moderate volatility; stockpile patching mix 3. Slow Cure (SC); low volatility; prime coat and dust control good for fast projects, but not used because it's harmful for the environment
What are two asphalt binder aging methods?
1. Rolling Thin Film Oven (RTFO); simulates manufacture and construction aging 2. Pressure Aging Vessel (PAV); simulates long-term pavement aging
Tests on Aggregates
1. Washing Sieve Analysis 2. Specific Gravity & Absorption (coarse & fine) 3. Percent Solids and Voids (Coarse) 4. Sieve Analysis (Mechanical) 5. Sand Equivalent 6. LA Abrasion 7. Fine Aggregate Angularity
When are set-accelerating admixtures used?
1. accelerate setting 2. cold weather (increases rate of strength gain)
What are some methods for controlling freeze-thaw damage?
1. air entrainment 2. good drainage 3. smaller maximum size aggregate 4. performance history
What are the three main types of chemical admixtures?
1. air-entraining admixtures 2. set-controlling admixtures 3. water-reducing admixtures
List six desirable characteristics of aggregates to be used in asphalt concrete.
1. angularity (sharp) 2. cheap 3. available 4. good adhesion (chemical) 5. strong (toughness) 6. durable (soundness)
What are the three bituminous material types?
1. asphalt cement/hot mix asphalt 2. emulsified asphalt 3. cutback asphalt
What terms are involved in HMA volumetrics?
1. bulk specific gravity of compacted HMA 2. maximum specific gravity 3. air voids 4. effective specific gravity of aggregate 5. voids in mineral aggregate (VMA) 6. voids filled with asphalt (VFA)
What are the four main ingredients of concrete?
1. cement 2. aggregates 3. water 4. admixtures
What does concrete contain?
1. cement 2. water 3. aggregates (coarse/rock & fine/sand) 4. admixtures
What criteria must be considered when selecting an asphalt binder?
1. geographic area 2. air temperature 3. pavement temperature 4. loading type 5. reliability
What increases carbonation?
1. high W/C ratio 2. low cement content 3. short curing period 4. low strength 5. highly permeable paste
When are set-retarding admixtures used?
1. hot weather 2. unusual placement or long haul distance 3. special finishes
How can you control Alkali-Silica Reactivity?
1. identification of reactive aggregates 2. limiting alkali content of cement (% in cement & total amount in concrete) 3. using a mineral admixture (like fly ash) 4. limestone sweetening 5. air entraining
What can cause poor quality?
1. ignorance 2. carelessness 3. greed 4. negligence
Unique Properties of Concrete
1. in plastic stage, can be molded into virtually any shape 2. manufactured/cast on-site (cannot be previously tested or approved)
Why are water-reducing (or plasticizing) admixtures used?
1. increase workability (same quantities, less water needed for a higher slump) 2. increase strength (less water, lower water-cement ratio, higher strength) 3. reduce cost (less cement and less water, same water-cement ratio, same strength, lower cost)
How does ground granulated blast furnace slag (GGBFS) affect fresh concrete?
1. increased workability 2. enhanced pumpability/finishability 3. reduced water demand 4. requires enhanced curing 5. increases setting time; compensate with accelerator
What are some other ways that the addition of silica fume can affect concrete?
1. increases cohesion (higher slump without segregation) 2. reduces bleeding (more durable to effects of salts) 3. flat work finishing 4. fast-track projects 5. increased hardness, increased compressive strength (high-rise structures)
What does a larger maximum aggregate size cause?
1. increases strength 2. improves skid resistance 3. increases volume and surface area of aggregate which decreases required asphalt cement content 4. improves rut resistance 5. increases segregation
How does fly ash affect hardened concrete?
1. increases strength but reduces rate of strength gain 2. high concentrations may increase shrinkage 3. reduces permeability and absorption 4. reduces alkali-aggregate reactivity 5. improves sulfate resistance
How does silica fume affect fresh concrete?
1. increases water demand 2. reduces air content; compensate with air-entraining 3. reduces workability; compensate with superplasticizer 4. increases heat of hydration only when used with a superplasticizer 5. does not affect set time
What are the three types of atomic bonds?
1. ionic bonds 2. covalent bonds 3. metallic bonds
Mechanical Properties
1. loading conditions 2. stress-strain relations 3. elastic/elastoplastic/viscous 4. work & energy 5. failure mode & safety 6. temperature & time effects
What are the PG grade factors?
1. location 2. depth of pavement 3. traffic speed and volume 4. reliability
What are the two sources of variability?
1. materials 2. testing
How is workability taken into consideration when proportioning?
1. mix must be able to be placed and compacted with equipment available. 2. for mixes without admixtures, workability depends on the aggregates more than on the cement 3. increase the mortar content (not just water) to increase workability
Grading Influences
1. mix proportions 2. water demand 3. packing 4. density & strength 5. work-ability 6. economy
What does the soundness test do?
Tests the cement's ability to retain its volume after setting; limit: 0.8%
What is the minimum mixture density at N initial?
89%
Nominal Maximum Aggregate Size
90-100% passing
What is the principle of the test used for determining the low-temperature stiffness of bitumen with the Bending Beam Rheometer (BBR)?
A beam of asphalt is prepared. Then, a constant load is applied. Deflection is recorded. The BBR Test uses an equation for stiffness, based off of the beam's dimensions, the load, and the deflection. From the deflection, stiffness can be calculated. The negative slope in the graph of stiffness vs. time is due to relaxation. The slope of the graph of the stiffness vs. time is the m-value.
What is an anisotropic material?
A material that has different properties in all directions
What is an isotropic material?
A material that has the same properties in all directions
What is the goal of a control chart?
A material to express the lowest variability as possible (as uniform as possible)
What kind of load is an earthquake?
A random dynamic load
Why are blends of aggregates used for Portland cement concrete and asphalt concrete?
A single aggregate source is generally unlikely to meet gradation requirements.
What kind of load is traffic on a bridge?
A transient dynamic load
What is Alkali-Silica Reactivity?
ASR; results from the reaction between alkali in cement and the silica in aggregates
What are the advantages and disadvantages of using the PG specifications instead of the viscosity or penetration-based specifications for bitumen/asphalt?
Advantages: -performance-based -based on engineering properties (scientific), not empirical tests -adaptable to new applications -allows testing with results applicable to multiple temperatures (both high and low) Disadvantages: -require newer equipment (cost) -time/place for testing
Why would ductile materials be better for use?
Because they undergo plastic deformation and you can observe problems before failure occurs.
Elastoplastic Behavior
Below yield stress, assume linear. Past yield stress, permanent plastic deformation occurs. There are elastic and plastic ranges.
How are flash setting and false setting different?
Besides being caused by different things, flash setting cannot be recovered, and false setting can be recovered by mixing.
What are the two major components of hardened cement paste?
C-S-H (calcium silicate hydrate), calcium hydroxide, and calcium sulfoaluminate hydrates
Why is the dust from the kiln sometimes collected?
Cement kiln dust (CKD) can be recycled if it has high lime content to aid in binding with water.
How does the job of a construction worked compare to that of a civil engineer?
Civil engineer: 41st best job; construction worker: 247th best job
What is the factor of safety determined by?
Codes
What are the bonding components of concrete? What affects the bond strength?
Components: 1. chemical 2. mechanical interlock 3. adhesion and friction Factors: 1. cement chemistry 2. aggregate chemistry, shape, surface texture, cleanness 3. mortar strength
What material is creep particularly detrimental to?
Concrete
How are strength and durability taken into consideration when proportioning?
Concrete specifications may require: 1. minimum compressive strength 2. limits on the water-cement ratio 3. minimum cement content Other requirements may involve: 1. durability 2. freeze-thaw resistance Compromise is key.
What is concrete wash water? What is significant about it?
Concrete wash water is the water and concrete mix that is obtained from washing equipment and tools used to transport and place concrete. It is hazardous, and its disposal is regulated by the EPA.
Why is construction time important?
Contracts have time requirements with possible delay penalties and early-finish bonuses.
What is the best place for obtaining aggregates for sampling?
Conveyor belt
What is the 666 Test?
Deals with fundamental frequency
Why is thermal expansion important?
Deformation occurs under temperature changes. They cause internal stresses.
What does the Gilmore test do?
Determines initial and final set times with weights
What is the main difference between creep and drying shrinkage of concrete?
Drying shrinkage of concrete is an early change in volume due to loss of moisture. Creep is long-term deformation due to sustained load. Time is the main difference.
What are asphalt emulsions and cutbacks? What are the advantages of using emulsions instead of cutbacks?
Emulsions are asphalt binder, water, and an emulsifying agent. Cutbacks are asphalt binder and petroleum solvent. Emulsions are more environmentally-friendly and cheaper than cutbacks.
How is energy related to material deformation?
Energy is stored when a material deforms.
What is D-cracking?
Exposed surface showing ruts
What does flakiness refer to?
Flat and elongated
How are properties of fresh and hardened concrete affected by the use of fly ash and silica fume?
Fly Ash: Fresh: -reduces water demand -reduces air content -increases workability -reduces heat of hydration -increases set time Hardened: -increases strength, but reduces rate of strength gain -high concentrations may increase shrinkage -reduces permeability and absorption -reduces alkali-aggregate reactivity -improves sulfate resistance Silica Fume: Fresh: -increases water demand -reduces air content -reduces workability -increases heat of hydration when used with a superplasticizer -little effect on set time Hardened: -small effect on the rate of strength gain -may reduce shrinkage -reduces permeability and absorption significantly -reduces alkali-aggregate reactivity -reduces corrosion due to salts -improved sulfate resistance
How is a cement's hydration reaction rate related to its fineness?
For a finer cement, the hydration reaction rate is higher.
What effect can the expansion of ettringite have on fresh, recently-set, and hard concrete?
Fresh: pore-filling; no net expansion Recently-Set: expansion without cracking; compensation for shrinkage Hard: expansion and cracking
How is specific gravity reported for superpave specifications?
G _ _ where the first blank is the material type: m-mixture b-binder s-stone and the second blank is the specific gravity type: a-apparent b-bulk e-effective m-maximum
How should you apply Type I Portland cement?
General concrete work; suitable for floors, structures, pavements, etc.
When is type I Portland cement used?
General use; beams, slabs
What is involved in the DSR Test?
Gstar and sin(delta) are determined; rutting: Gstar divided by sin(delta) indicates high temperature stiffness (unaged or RTFO);fatigue cracking: Gstar multiplied by sin(delta) indicates intermediate temperature stiffness (PAV-aged)
What can cause false setting?
Gypsum converts to plaster (hot cement). The hot cement desiccates (takes the moisture from) gypsum.
When is type III Portland cement used?
High early strength; ground finer than type I; faster setting
What can a high percentage of find aggregates cause?
High stability and density; low permeability, frost susceptibility, handling, and cohesion
Blended Hydraulic Cement
IS - slag; IP, P - pozzolan; IPM - pozzolan modified; ISM - slag modified; S - slag cement (not Portland); a mixture of portland cement and other materials (mineral admixtures)
What does the Compressive Strength of Mortar test do?
Indicates durability and helps with design
What is slag?
Iron blast furnace slag, a manufactured aggregate
Where was asphalt obtained from originally?
Island of Trinidad and Venezuela; lakes
Why don't you want dust in your aggregates?
It causes problems in adhering to cement ; can be caused by crushing and transporting
How is the target required compressive strength obtained?
It is obtained based on historical test results (if available). If not available, over-estimations are made.
Why is a denser gradation usually preferred?
It is related to high stability.
What is the basic stress-strain curve?
Linear elastic, proportionality limit, elastic, elastic limit/yield point, plastic, strain hardening/softening, necking
What are two tests to determine resistance to impact or toughness?
Los Angeles Abrasion Test (one large) and Deval Test (multiple small)
What level of absorption is ideal for asphalt concrete?
Low absorption
When is type IV Portland cement used?
Low heat of hydration; use in big projects, such as dams
What material sources should be used to reduce environmental impact?
Manufactured and recycled aggregates
What do the flow of cement pastes and hydraulic cement mortars tests do?
Measure the workability of cement paste
When is type II Portland cement used?
Moderate sulfate resistance; harsh environment
What are the three special points on the %Gmm vs. Log Gyrations?
N initial, N design, and N max
What methods are used to determine the elastic limit?
Offset method and extention method
What does bulking in sand cause?
Problems when finding specific gravity or other mass-volume relationships
How should you apply Type II Portland cement?
Protection against moderate sulfate exposure, moderate heat of hydration; suitable for large piers, heavy abutments, and retaining walls
How should you apply Type V Portland cement?
Protection from severe sulfate exposure
What is soundness?
Resistance to weathering
Segregation
Separation of an aggregate stockpile that occurs naturally, bringing larger particles to the bottom and smaller particles to the top
What does angularity refer to?
Sharp corners and rough textures
What does setting refer to?
Solidification; the stiffening of the cement paste or the change from a plastic state to a solid state
Why is sulfate resistance important?
Sulfate-rich soils can react with paste and destroy concrete
Why is sulfate resistance important in concrete?
Sulfates in the environment react with C3A to form ettringite, an expansive mineral. They also decompose CSH to gypsum.
What methods can be used to estimate the linear elastic portion of the stress-strain curve for brittle materials?
Tangent modulus, secant modulus, initial tangent modulus
Why is heat of hydration important?
Temperature affects concrete pouring (heat=water evaporation; cold=bubbles)
What does life-cycle cost refer to?
The cost of a project over time, taking into account the useful life, required maintenance, and impact on the public.
What is clinker?
The material produced by the kiln in the production of Portland cement
What does maximum density refer to?
The minimum amount of voids; well-grading
What does absorption refer to?
The moisture content in the saturated surface dry (SSD condition)
What does water-cement ratio (W/C ratio) refer to?
The ratio of the weight of water to the weight of cement
What effect do clay lumps, soft or friable particles, and coatings have on asphalt concrete and Portland cement concrete?
These substances decrease the adhesion between asphalt and aggregate particles.
Why is crushing necessary for aggregates?
To bring aggregates to the size needed and to create sharp edges.
Why is blended hydraulic cement used?
To combat cost while retaining properties; uses slag and other mineral admixtures with Portland cement concrete
Which two types are almost identical, except for particle size?
Type I and type III
What are the parts of a control chart?
USL, LSL, and either means or ranges
What does the Pycnometer Test do?
Uses a Pycnometer to determine the specific gravity and absorption of a fine aggregate
What level of absorption is ideal for Portland cement concrete?
Varying; is used to determine the amount of water to mix into the concrete
Why is rate of strength gain important?
You want concrete to set faster (like in road projects, building or bridges to build the next section)
What is fly ash? What classifications of fly ash exist?
a by-product of the coal industry; contains the same active ingredients as Portland cement; can be Class F (low lime, high silica) or Class C (high lime)
What is silica fume? What are some of its properties?
a by-product of the ferro-silicon industry; gray powder; amorphous (not crystalline), which enables it to dissolve into the mix; reacts chemically because of silicon dioxide; extremely lightweight, very low specific gravity, and large specific surface.
What is a control chart?
a chart containing the data collected from a group of samples, with upper and lower specification limits (LSL and USL) and either the means or the ranges
What is shotcrete?
a concrete placed in difficult locations, thin sections, and large areas; good for placing concrete in freeform shapes, repairing structures, and thin linings; skill of equipment-user affects quality of work
What is involved in the BBR Test?
a constant load is applied and increasing deflection is observed; obtains a formula for creep stiffness, depending on load, length, width, thickness, and deflection; relaxation can be observed
Aggregate
a soil that has in some way been processed or sorted
Static Loading
a sustained loading of the structure over a period of time
How does a weak aggregate structure compare to to strong aggregate structure on the %Gmm vs. Log Gyrations graph?
a weak aggregate structure has a shallower slope than a strong aggregate structure
What method of proportioning is the most popular in the U.S.?
absolute volume/ACI method; design used as a starting point; trial batches and observation of performance prompts adjustments; local experience should be used
What is the target gradation?
acceptable gradation band specified, with upper and lower gradation limits; mix design selects a job mix formula (JMF) which falls within band and meets design criteria; Superpave: 5 sieve size gradation specifications;
What is the Direct Shear Rheometer Test?
determines Gstar and delta, where Gstar (complex shear modulus) is the relationship between highest shear stress applied and highest resulting shear strain and delta (phase angle) is the time delay between the applied shear stress and the resulting shear strain; simulates rutting on unaged and RTFO specimens by determining high temperature stiffness and fatigue cracking on PAV specimens by determining intermediate temperature stiffness
Blaine Specific Surface (Fineness) Test
determines fineness of cement using air permeability
Wagner Turbidimeter Test
determines fineness of cement using light and photoelectric cells
Flow of Cement Pastes & Hydraulic Cement Mortars
determines flow; the flow is related to water content of the cement
Vicat Test
determines initial set time and final set time using a needle inserted into a cement-filled mold
Gillmore Test
determines initial set time and final set time using weights
What is the Penetration Test?
determines penetration, which is a measure of consistency
What is the Penetration Resistance Test?
determines penetration, which is used to assess the uniformity and indicate in-place strength
What is the Absolute Viscosity Test?
determines the absolute viscosity at 60 degrees C, which characterizes flow behavior and may be used for specification requirements; measures the time it takes for a fixed volume of asphalt binder to be drawn up through a capillary tube by means of vacuum
What is the Air Content Test?
determines the air content of freshly-mixed Portland cement concrete by a) pressure method or b) roll-a-meter, which is helpful if proportioning a mix as well as indicating fresh workability and hardened durability
Blaine Fineness Test
determines the amount of fine particles in cement
What is the Compressive Strength Test?
determines the compressive strength, which is a universal measure of concrete quality
What is the Bending Beam Rheometer Test?
determines the deflection of an asphalt beam over time, which helps determine the stiffness and relaxation for use in determining low-temperature cracking
What is the Flexural Strength Test?
determines the flexural strength, which is a measure of concrete quality
Sieve Analysis
determines the gradation of aggregates
What is the Rebound Hammer Test?
determines the rebound number, which may be used to assess the uniformity and strength of concrete; can also be used to determine when forms can be removed.
Los Angeles Abrasion Test
determines the resistance of a course aggregate to abrasion and mechanical degradation during handling, construction, and use
What is the Slump Test?
determines the slump of the fresh concrete, which indicates fresh workability
Soundness Test
determines the soundness (durability) of cement; determines a cement's ability to retain its volume after setting; 0.8% limit
What is the Split Tension Test?
determines the splitting tensile strength
What is the Direct Tension Tester Test?
determines the stress-strain curve for asphalt and obtains the strain at peak stress and stress at failure, which helps determine the low-temperature capacity to stretch
What is the Flashpoint Test?
determines the temperature at which the asphalt catches fire; safety test
What is the Unit Weight Test?
determines unit weight of fresh concrete which is used to calculate the volume of Portland cement concrete
What is the Rotational Viscometer Test?
determines viscosity at 135 and 165 degrees C in order to check for handling and pumping and to develop a temperature-viscosity relationship
Quality Control Scheme
determines what is going to be acceptable for the job; agreed upon before production begins
Relaxation
dissipation of stresses with time; occurs in relation to creep/viscous flow
Gradation
distribution of particle sizes expressed as a percent of total weight
C3S Contribution to Concrete
early strength
What is a sublot?
equal divisions (portions) of a lot
How is a job mix formula gradation determined?
make the gradation fall between the control points
How is absorbed asphalt content defined?
mass concentration of asphalt absorbed by aggregate; used as a percentage by mass of total mix
How is asphalt content defined?
mass concentration of asphalt binder; used as a percentage by mass of total mix; effective asphalt+absorbed asphalt
How is effective asphalt content defined?
mass concentration of asphalt not lost to absorption; used as a percentage by mass of total mix
Apparent Specific Gravity
mass of aggregate (oven dry)/volume of solid aggregate
Bulk Specific Gravity
mass of aggregate (oven dry)/volume of solid aggregate and surface voids
Mechanical Aggregate Properties
mass stability (toughness)
Density
mass/volume
What are admixtures?
materials other than water, aggregates, hydraulic cement, or fiber reinforcement; can be liquid or solid
Reduction Ratio
max. size before/max. size after
What is the Flat, Elongated Particles Test?
measured on larger particles; based on dimensional ratio of particles (usually 1:5); requirements of maximum percentage of flat and elongated particles depend on traffic level; flat, elongated particles cause non-uniformity and potential for segregation
What is the Coarse Aggregate Angularity Test?
measured on larger particles; based on fractured faces; requirements of minimum percentages of fractured faces depend on depth of layer within pavement and traffic level; sample grains, identify number of fractured faces (one or two+) because of interlock between grains; new test: funnel, let fall into cylinder, measure percent air voids
What is the Fine Aggregate Angularity Test?
measured on materials smaller than No. 8 sieve; based on air voids in loose sample; requirements of minimum air voids depend on depth of layer within pavement (higher stresses at lower depths) and traffic level; aggregates blended, put into funnel, place cylinder under funnel, let grains fall freely, calculate uncompacted voids; rounded particles pack tighter together, therefore there is less air
What is the Clay Content/Sand Equivalency Test?
measures how clean the sand is; measured on larger particles; based on sand equivalent value; requirements of minimum sand equivalent value depend on traffic level; get the sand reading and clay reading by putting the sand into a cylinder and mix it with calcium chloride solution and shake, then let it sit and measure the top of the coarse particles (sand reading) and the top of the clay particles (clay reading); higher number indicates cleaner sand; another test Methylene Blue Test exists, color of spot indicates higher or lower percentages of sand: 5-18 are acceptable; 20+ fails
Resistance of Concrete to Rapid Freezing & Thawing
measures the deterioration of concrete as a result of freeze-thaw cycles
Explain the Absolute Viscosity Test.
measures the time it takes for a fixed volume of asphalt binder to be drawn up through a capillary tube by means of vacuum, under closely controlled conditions of vacuum and temperature; determines viscosity at 60 degrees C.
What is concrete?
mortar + coarse aggregates/rocks
The compressive strength follows what distribution?
normal
Construction materials and properties vary according to what?
normal distribution
What is nominal maximum aggregate size?
one size larger than the first sieve to retain more than 10%
What are the two types of Superpave aggregates tests?
ones based on consensus properties and one based on source properties
What are some properties of gap-graded aggregates?
only limited sizes; good interlock; low permeability
What is asphalt aging?
oxidation of asphalt over time; RTFO & PAV; RTFO to simulate construction aging; PAV to simulate long-term aging
Fine Aggregate
passing No. 4 (4.75mm) sieve
What is mortar?
paste + sand
What does ASR mainly affect?
pavement & bridges
What is reliability as it relates to design temperature?
percent probability of not exceeding design temperature; area under the normal distribution curve to the left of the design temperature
How are voids filled with asphalt (VFA) defined?
percentage of VMA filled with asphalt
What is asphalt binder selection dependent on in Superpave specifications?
performance (rutting, fatigue cracking, low temperature cracking)
What is the basic Superpave specification?
performance grade (PG), which is based on physical properties
Specific Gravity Tests
performed separately for coarse and fine aggregates; determines specific gravity
What type of water is ideal for use in concrete?
potable or drinking water
What are the trial and error steps in determining blending?
select critical sieves, determine initial proportions, check against specifications, adjust, repeat
Physical Aggregate Properties
shape, texture, size distribution, porosity, soundness, volume stability (freeze-thaw), and deleterious substances
What is silica fume and why is it used in concrete?
silica fume is a by-product of the ferro-silicon industry (gray powder); used in concrete because silica fume is particularly effective in decreasing the porosity of the ITZ (transition zone between paste and aggregate); also used in concrete because it may reduce shrinkage, reduces alkali-aggregate reactivity, reduces corrosion from salts, and improves sulfate resistance.
What is a pozzolan?
siliceous or siliceous/aluminous materials which have little or no cementatious value alone but that react with lime and water to form calcium silicate hydrate (CSH)
C3A Contribution to Concrete
slight early strength
When are mid-range water reducers used?
slump between 5-8 inches and moderate water-cement ratio
What is soundness? What test measures soundness of aggregates?
soundness is resistance to weathering (freeze-thaw); sodium or magnesium sulfate solution; observe mass loss
What is standard deviation?
standard deviation is the root mean square of the deviation from the mean
How is mortar strength related to concrete strength?
strength of mortar depends on the strength of the Portland cement; variations in cement strength and rate of strength gain result in variations in concrete strength and rate of strength gain
What does Superpave stand for?
superior performing pavement
Rheological Models
used to mechanically model the time-dependent behavior of materials
What is performance history?
using past experiences when making decisions; for example, if problems with freeze-thaw is observed in an aggregate repeatedly, stop using it.
How are air voids defined?
volume concentration of air voids; used as a percentage by volume of total mix
How are voids in mineral aggregate (VMA) defined?
volume concentration of intergranular void space in a compacted mix; used as a percentage by volume of total mix
Chemical Aggregate Properties
volume stability (chemical)
How is the concept of water-cement ratio taken into consideration when proportioning?
w/c determines the porosity of the cement paste, which indicates the paste's durability
Unit Weight
weight/volume
Fatigue
when a material fails at a stress well below the strength of the material due to the repeated stresses
Elastic Behavior
when a material returns to its original shape when the load is removed and reacts instantaneously to changes in load; strain returns to 0
What is soil-cement?
when cement is mixed into soil to act as a stabilizer; spread cement, mix, compact, cure.
Type V Portland Cement Use
when designing in applications requiring high sulfate resistance (for example, chemical factories)
Type II Portland Cement Use
when designing in applications requiring medium sulfate resistance
Type III Portland Cement Use
when early strength is needed; when traffic on a busy road is involved, or when the next floor of a building needs to be build quickly
Type IV Portland Cement Use
when large projects are involved (for example, dams)
Buckling
when long and slender members fail under axial compression due to lateral deflection; will not happen if the members are stable.
When are modified binders used?
when the difference between the higher and lower temperatures is more than 90 or 92; "Rule of 90 or 92"
What is important when selecting materials?
whether the aggregates are available or not
What are the major components of material selection?
-aggregates (coarse/fine/mineral filler) -asphalt binder -recycled asphalt pavement (RAP) -additives (lime, liquid anti-strip) -determine combined gradation using TxDOT Mix Design Program
How is the materials selection process performed?
-check aggregates and gradation for compliance with specification -check additives compliance with specification -determine specific gravity and absorption -use Excel Mix Design Program to develop a proposed blend of aggregate stockpiles -check aggregate classification of the combined blend
What are the mechanical properties associated with the behavior of metals?
-elastic deformation -plastic deformation -fatigue -ductility -impact resistance -flow or creep -relaxation -stress rupture -corrosion & wear
What are some properties of high-performance steel?
-high strength -high fracture toughness -reduced preheat requirement -improved weathering properties
What are covalent bonds?
-involve the sharing of electrons -small electronegativity differences
What are ionic bonds?
-involve the transfer of electrons -involve positively and negatively charged ions -continuous, strong bonding
What are metallic bonds?
-mass sharing of "mobile" electrons (electron clouds) between several atoms -electrons clouds are responsible for the high thermal and electrical conductivity, strength, ductility, and toughness of metals
What do you need to input into the Excel Mix Design Program?
-material properties -bulk specific gravities -aggregate classification -combined gradation
What are the major components of TxDOT Mix Design?
-materials selection -preparation of laboratory samples -determine optimum asphalt content -mixture evaluation
What are the two methods for seasoning timber?
1. air drying (depends on climate) 2. kiln drying (controlled temperature and humidity)
What are the four metallurgical processes?
1. annealing (to soften, by slow cooling) 2. normalizing (to produce a uniform, fine-grained micro-structure, by air cooling) 3. quenching (to harden, by rapid cooling) 4. tempering (to toughen, by reheating)
What are the five classifications for corrosion of metals?
1. atmospheric 2. water immersion 3. soil 4. chemicals other than water 5. electrolytic
What are the three main types of ferrous materials?
1. cast iron 2. wrought iron (iron + slag) 3. steel
What factors affect timber strength?
1. direction of wood fibers 2. moisture 3. unit weight 4. rate of growth 5. defects
What is involved in iron production?
1. iron ore + charcoal (coke) 2. ore reduced 3. waste (slag) floats 4. melted iron (pig iron)
What are the three main ways that timber is cut?
1. plain/slash cut (tangential to annual rings; practical and popular) 2. quartersawing or rift-cut (wood cut parallel to the axis and radially across the annual rings) 3. combination sawing
Explain the Shear Modulus and Phase Angle of Binders (DSR) Test.
Prepare the asphalt binder sample by making sure it is first fluid enough to pour onto the test plate surface or mold. Make sure the plates are preheated prior to the mounting of the specimen. Then, mount the specimen onto the test plate surface. Move the top plate down to the asphalt disc, leaving a gap of approximately 0.05 mm. Trim the specimen, taking care not to scrap material from between the plates. Close the gap between the top plate and the asphalt sample. Bring the temperature to the starting test temperature, and then run the Dynamic Shear Rheometer to obtain values for G* and sin(δ). Based on test results, increase the testing temperature in 6°C increments until the sample fails to meet the specified criteria; determines the shear modulus and the phase angle that can be used to grade the bitumen
How is the compactor type different between TxDOT and Superpave Mix Designs?
TxDOT has both the Texas Gyratory and Superpave Gyratory Compactors; Superpave only has the Superpave.
How is the type of mix different between TxDOT and Superpave Mix Designs?
TxDOT has dense-graded, large stone, performance, permeable friction course, and stone matrix asphalt; Superpave only has dense-graded.
How is testing different between TxDOT and Superpave Mix Designs?
TxDOT tests indirect tensile strength and rutting with the Hamburg Wheel Test; Superpave only tests moisture sensitivity.
How is the number of control points for grading between TxDOT and Superpave Mix Designs?
TxDOT uses control points for all sieve sizes when determining grading, and Superpave only uses 5 sizes
What happens with ductility?
ability to deform permanently under tensile forces prior to fracture (determined from elongation at failure); deformation before fracture
What happens with flow or creep?
at elevated temperature, or at room temperature for some low melting point metals, prolonged loading at stresses below the normal yield point may lead to a process of plastic flow or creep; sustained loading leads to deformation
Explain the Compressive Strength of Brick Prism Test.
brick prism (brick and mortar) into the compression machine. record the peak load and determine the peak stress; determines the compressive strength of the brick prism
How does the strength of timber compare to that of other materials?
comparatively stronger when considered in proportion to weight
What happens with plastic deformation?
displaced atoms remain in deformed position when the load is withdrawn
What happens with elastic deformation?
displaced atoms return to original position when the load is withdrawn
What do the properties of wood depend on?
distance from the center of the tree (the layer that the wood is from)
How does moisture affect timber strength?
drying below fiber saturation point increases strength
What mechanical properties do cladding steels rely on?
ductility, corrosion resistance, and aesthetics
Explain the 7-day Flexural Strength by Simple Beam Third-Point Loading Test.
measure the beam, place in the compressive strength machine, third-point load the beam, compress the beam until failure, record the tensile strength of the beam. failure needs to occur in the middle third, or a corrected formula has to be used; determines the flexural strength of the concrete beam after 7 days
Explain the Tensile Strength of Steel Test.
measure the gage length of the small steel cylinder, put into the tension machine, apply tension until the increase in load stops or hesitates (yield point), and measure the extension of the cylinder after necking and failure; determines tensile strength, elongation, and percent elongation
Explain the Time of Setting of Hydraulic Cement Test.
mix cement of normal consistency as determined in the previous test. form the sample into a ball. drop from hand to hand 6 times from a height of approximately 6 in. press the ball into the larger end of the mold. remove excess material from the mold. after setting the indicator to 0, release the needle into the specimen; determine the penetration every 15 minutes until a penetration of 25 mm or less is obtained; make sure the penetrations are done at different spots of the mold and far from the edges; determines the initial setting time (can also determine the final setting time)
Explain the Normal Consistency of Hydraulic Cement with the Vicat Apparatus Test.
mix cement with a specific quantity of clean water by placing the water into the bowl, adding cement, mixing at slow speed, and then mixing at medium speed. form the sample into a ball. drop from hand to hand 6 times from a height of approximately 6 in. press the ball into the larger end of the mold. remove excess material from the mold. after setting the indicator to 0, release the plunger into the cement paste. normal consistency is indicated when the paste settled to a point of about 10 mm in 30 seconds; determines the correct percentage of water to use for normal consistency
Explain the Mix Design-Batching, Making, Curing Concrete Specimens Test.
mix specific amounts of coarse aggregate, water, and fine aggregate, and cement into the mixer. the order should be coarse, some water, fine, cement, water. mix until homogenous; prepares concrete for use in other tests
Explain the Mixing of Mortar and Building of Brick Prism Test.
mix specified amounts of sand, cement, and lime. then add water little by little until the desired consistency is obtained. place the mortar on the bricks. place 5 bricks on top of each other with mortar in between; the brick prism is used in the compressive strength testing
Explain the Percent Solids and Voids in Coarse Aggregates Test.
start with dry aggregate. measure the mass of the cylindrical measure. add 1/3 of the sample. rod 25 times. add another 1/3 of the sample. rod 25 times. add the sample until overflowing and rod 25 times. level the surface of the measure and record the mass of the aggregate and measure; determines the bulk density (A/V) and percentage of voids (specific gravity*unit weight of water-bulk density)/(specific gravity*unit weight) * 100%
Explain the Compressive Strength of Hydraulic Cement Mortars Test.
mix specified amounts of standard sand, water, and cement; apply oil to the mold; place all of the water into the mixing bowl, add cement; mix at slow speed for 30 seconds; add sand slowly over 30 seconds; mix at medium speed for 30 seconds; mix again for 1 minute after letting sit fo 1.5 minutes; determine the flow of mortar using the flow mold: place mortar into the mold in 2 layers, tamping 20 times each layer, level the mortar, drop table ½ in. 25 times in 15 seconds. measure the diameters along the 4 scribed lines (percent increase in the original diameter is obtained); remix at medium speed for 15 seconds. place mortar into the cube molds in two layers, tamping 32 times in 10s in 4 rounds for each layer. level mortar; place into curing room for 24 hours; apply a compressive load to a smooth side of the cube in the compression machine until failure; record maximum load to determine compressive strength; determines the flow of mortar and the compressive strength of mortar
What are cladding steels?
non-structural members that are typically used for exterior walls and curtain walls and as coverings for internal and external structural columns
Explain Theoretical Maximum Specific Gravity or Density of HMA Test.
obtain a warm, loose sample and break up clumps. let cool. determine mass of sample (mass in air). put sample into container with water, making sure that all of the asphalt is covered, place onto shaker table with vacuum lid. start vacuum pump (maintain 3.7 kPa) and start shaker table; shake for 15 minutes; measure total weight of bowl and mix underwater (C). measure weight of bowl underwater (D); theoretical maximum specific gravity Mair/(Mair-Mwater) where Mwater is C-D, a reference value
Explain the HMA Specimen Preparation-TX Gyratory Compaction Test.
obtain asphalt mix at proper compaction temperature from the oven. place into mold in 3 equal layers. flatten the top of mold. pump pressure until 50 psi is reached, rotate the mold, and repeat until 150 psi is reached in one full stroke. add pressure until the high-pressure gauge reads 2500 psi. release pressure. pump the ram out of the mold. remove the specimen from the mold; obtains a specimen that can be used for further testing
What is an orthotropic material?
one that has unique and independent mechanical properties in three mutually perpendicular directions: longitudinal, radial, and tangential
Explain the Measuring Temperature by Freshly Mixed Concrete Test.
prepare concrete sample, and put thermometer into the sample, ensuring that it is covered completely with concrete. leave for 2 minutes or until stabilization. read the temperature. must be completed within 5 minutes of obtaining sample; determines the temperature of fresh concrete
Explain the Air Content by the Pressure Method Test.
prepare concrete sample; place concrete into air pressure apparatus in thirds, rodding 25 times for each layer. tap the sides of the measure after each layer. remove excess. clamp on the cover. inject water until all air is forced out. pump air to initial pressure line. bleed off as needed until the gauge reads at initial pressure. press down on the thumb lever to release the air into the bowl. read the apparent air content and record; determines the air content of fresh concrete
Explain the Slump Test.
prepare concrete sample; place concrete into slump cone in thirds, rodding 25 times for each layer. make sure the last layer is overflowing before rodding, and remove excess. remove the mold by pulling straight up in 3 to 7 seconds. measure the slump by flipping the cone over, placing the rod on the top of the cone parallel to the base, and use a tape measure to measure the slump at the center of the specimen; determines the slump of fresh concrete, which indicates workability
What mechanical properties do steel structures rely on?
primarily on the yield stress, but ductility, toughness at normal and subzero temperature, and weldability are often important properties
Explain the Material <0.075mm Sieve by Washing (Decantation) Test.
record total mass of dry aggregate (A), stack sieve #200 on top of either sieve #8 or sieve #16, wash the aggregate over the sieves until the water is reasonably clean, wash any material retained on the sieves into pans, and dry the aggregate overnight and record the mass (B); determines percent fines (A-B)/(B) * 100%
What happens with impact resistance?
resistance of a metal to failure due to brittleness (inability to take strain) under service condition; usually measured by the area under the stress-strain diagram up to the elastic limit; brittleness
Explain the Specific Gravity and Absorption of Fine Aggregates Test.
screen fine aggregate over the 4.75 mm screen and keep material passing screen with 4 percent water by mass of aggregate; spread out damp aggregate; dry with hair drier to SSD condition; place cone and loosely fill with aggregate; tamp with 25 drops; lift mold; at SSD, part of the cone should not be able to hold its shape. measure the mass of SSD aggregate (B). fill a flask with water to the calibration line and determine the mass (C). partially fill with water and add the SSD aggregate; roll the flask and eliminate air bubbles; determine the mass of flask, water, and aggregate (D). dry in oven overnight and determine the mass of aggregate (A); determines the bulk specific gravity A/(B+C-D) and absorption (B-A)/(A) * 100%
Explain the Superpave Gyratory Compaction Test.
short-term aged asphalt is placed into a compaction mold that are both at proper compaction temperature, mix the material and place into the mold; load the specimen mold into the compactor; lower the ram until pressure reaches 600+20 kPa. begin compacting. it compacts in a kneading manner. obtain the printed results for height vs. gyration. remove the specimen from the mold after it cools. (constant pressure is applied; the number of gyrations specified is based on the expected density, and density changes with traffic level); determines the height of the specimen at each gyration, can be used in the determination of bulk specific gravity of compacted HMA
What type of wood is usually used in civil engineering applications?
softwoods
Explain the Specific Gravity and Absorption of Coarse Aggregates Test.
start with coarse aggregate washed and left in pan under water (retained on 4.75 mm (#4) sieve). remove samples from the water and dry to SSD (saturated surface dry) condition (dull appearance). record the SSD mass in air (B). record the underwater mass (C). oven-dry the sample and record the mass in air (A); determines bulk specific gravity (A)/(B-C) * 100% and water absorption (B-A)/(A) * 100%
Explain the Sand Equivalent Test.
start with material passing the No. 4 sieve, place into a cylinder with calcium chloride solution, release air bubbles, let the sample sit of 10 minutes, partially invert the cylinder and shake, then place the cylinder into the mechanical shaker for 45 seconds. rise material from the top of the interior of the cylinder and fill to the 15 in. mark. let sit for 20 minutes. record the top level of the clay suspension as the clay reading, and record the sand reading by using the weighted foot assembly; determines the sand equivalent (sand reading/clay reading) * 100%
Explain the Sieve Analysis Test.
start with oven-dry aggregate samples of various sizes that had previously been washed to get rid of finer particles. stack the sieves from largest on the top to smallest on the bottom. pour the aggregate over the sieves and position into the mechanical shaker for 10 minutes. obtain the mass of material retained on each sieve; determines the gradation of fine and coarse aggregates, type of gradation, maximum and nominal maximum aggregate sizes, and the fineness modulus
How does the direction of wood fibers affect timber strength?
strength properties differ in directions ranging from parallel to perpendicular
What happens with stress rupture?
stress necessary to cause rupture under continued high temperature and loading; important for aircraft or jet propulsion gas turbines
How do the results of the Texas Gyratory Compactor compare to those of the Superpave Gyratory Compactor?
the Texas Gyratory Compactor is more variable and therefore less reliable; field mixes fair better than lab mixes
What does the modulus of rupture in bending tell you?
the maximum load-carrying capacity of a wood specimen and is proportional to the maximum moment carried by the specimen
What does the compression perpendicular to the grain tell you?
the stress at the proportional limit
Explain the Bulk Specific Gravity of Compacted HMA Test.
use HMA cylinder from Superpave compaction; determine the mass of the dry specimen (A), place specimen in water for 3 to 5 minutes; determine mass underwater (B), blot dry to obtain SSD condition and record the mass (C); bulk specific gravity at Nmax: A/(C-B), bulk specific gravity at Ndes: Gmb (at Nmax) * HNmax/HNdes, percentage air voids 100%*(1-(Gmb (at Ndes))/(Gmm)); useful for VTM, VMA, and VFA calculations
Explain the Viscosity of Binders with the Rotational Viscometer (RV) Test.
uses the Rotational Viscometer; place bitumen into a cylinder, heat to 135 degrees C, insert spindle, the RV determines the viscosity based on the amount of torque needed to keep the spindle spinning at the same speed, obtain viscosity; repeat for 165 degrees C; determines the viscosity of the asphalt binder at two temperatures that can lead to a viscosity vs. temperature graph
Explain the 28-Day Compressive Strength of Concrete and ANOVA Analysis Test.
using a 28-day old concrete cylinder with end caps to help distribute the load, place into the compression machine and compress until failure. record the maximum load and determine the compressive strength; determines the compressive strength of hardened concrete
Explain the 28-Day Splitting Tensile Strength Test.
using a 28-day old concrete cylinder, the longer side is place downward under the compression machine. a plate is placed over the cylinder to help distribute the load evenly across the top. compress until failure, and record the maximum load; determines the tensile strength
Explain Blaine Fineness Test.
using a homogenous mix of cement sample, weigh out a specific amount of cement based on density, porosity, and volume. place the cement into the top of the apparatus. level the cement, compress the cement with the plunger. attached the permeability cell; slowly evacuate the air in the right arm of the manometer using the pressure bulb until the liquid reaches the top mark and then close the manometer valve. record the time it takes from the top of one mark to the bottom of the next mark. calculate specific surface area; determines the fineness of cement
Explain the LA Abrasion Test.
wash and dry aggregates passing the ¾ in. sieve and retained on either the ½ in. sieve or 3/8 in. sieve; record the weight (A); place in the Los Angeles testing machine with 11 steel balls; let the machine rotate 500 revolutions at approximately 30 rpm. sieve the material through No. 12 sieve. wash the retained material and dry to a constant weight (B); determines the LA Abrasion Number (A-B)/(A) * 100%, which is related to the toughness of aggregates
Explain the Compressive Strength of Wood Parallel to the Grain Test.
wood specimen into the compression machine with the wood grains parallel to the application of the load. record the peak load and determine the peak stress; determines compressive strength
Explain the Flexural Strength/Modulus of Rupture of Timber Test.
wood specimen with a span length of 18" onto the compression machine. apply a load to the center of the span length and continue until failure. record the maximum load and type of failure; determines the modulus of elasticity and the modulus of rupture (flexural strength)
Explain the Fine Aggregate Angularity Test.
▪ wash and dry sand with specific gradation; mix sample until homogenous. pour the sample into the funnel while it is plugged. level the material. release the material into the measure below. level the aggregate in the measure, taking care not the vibrate and compact the material. tap lightly to compact slightly. pour contents into the volumetric flask. weight the flask and sample (A). add distilled water and removed trapped air by rolling. fill to the calibrated volume mark. weigh flask and contents (B); determines the uncompacted void content, which indicates relative angularity and surface texture (higher U means higher angularity and rougher surface texture)
