Ult PCC Exam Prep
Strain
(Delta L)/(Unit length)
Strength (f'c), test cylinder =
(Load, P) / (Area)
Consistency
(slump) how easy to flow
Factors affecting concrete Flow Ability
- Cement Characteristics (composition and fineness) - Water content, or paste content, and water-to-cementitious material ratio (w/cm) - Admixtures - Aggregate properties, size and gradation - Time and temperature
Upright Slump flow test methods
- Raise cone: 3 (+/-) 1 sec - Measure largest diameter to the nearest 1/4 inch - Measure second diameter - Slump flow = (d1-d2)/2 - Complete test within 2.5 min
J-ring Test
- Slump cone is lifted allowing the concrete to flow until it stops. - largest diameter measured J-ring Flow = (d1+d2)/2
Inverted Cone Test - Slump Flow
- T20 or T50 measurement - Time taken for the concrete to reach a spread of 20in or 50cm form the moment the slump cone is lifted up. High T20 - more viscous - god for congested reinforcement Low T20 - less viscous - good for long horizontal distance
Type 2 Cement (Moderate Heat and Sulfate Resistance)
- composition of C3S+C3A<58% and C3A <8% - generates less heat at a slower rate and has a moderate resistance to sulfate attack
Superplasticizer concrete
- high range water reducing admixture - More homogeneous than normal concrete
Advantages of mineral admixtures
- improve concrete workability - Lower heat of hydration - lower concrete permeability - improve resistance to sulfate and acid attack
Main benefits of mineral admixtures
- reduction in heat of hydration - reduction in concrete permeability - improvements in workability - improvements in long term strength - improvements in durability
Mineral Admixtures are
- used as cement replacement - Improve workability, ult strength, impermeability, durability - Reduce heat of hydration and concrete cost Can be divided into three categories: - Cementitious Materials - Pozzolanic Materials - Inert
History
-Aspdin named the product Portland Cement -The hardened cement paste resembled a famous stone quarried on the Isle of Portland of the British coast -He laid the foundation for todays portland cement industry
Why concrete cal flow at the beginning but hardens with time?
-At beginning , water in concrete separates cement particles -With time, hydration products fill spaces and glue particles together, and densify the concrete causing stiffening
Water Reducing Agents (WRA)
-Charged cement particles cling togher and form flocs with trap water -Water reducers sepreactes flocs into individual grains. Thus, trapped water is released and the grains slip by each other like ball bearings - improving the workability of the concrete
How does air entraining agent work?
-Entrapped air bubbles coalesce and then expelled from the mixture surface -Surface of cement particles has opposite charges from sir bubbles on surface, thus stabilizing the air bubbles in the system
Type 1 Cement (General Purpose)
-General purpose cement suitable for all uses - General construction projects such as buildings, bridges, floors, pavements, and other precast products
Superplasticizers
-High range water-reducing admix -consist lonf long chain, high molecular-weight anionic surfactants with large number of polar group in the hydrocarbon chain -Superplasticized concrete are more homogenous than normal concrete
Role of Air Voids (AEA)
-Provide space for water, ice or other substances -cut flow path=reduce hydraulic pressure -lubricate mixture=improve concrete workability -reduce effective cross area of concrete elements
What are the important properties of cement? why?
-Setting time, heat of hydration, strength, & other (consistency, soundness...)
Why use admixtures
-To enhance properties (workability, strength, and durability) of a given mixture -To overcome difficulties in construction (such as hot or cold weather concreting, pumping and early strength requirement) - To reduce cost and save energy
What can WRA do for concrete?
-To increase workability/slump with out changing the mix proportion (w/b=constant) -To reduce the mixing water and/or water to binder ratio in order to increase strength and durability (slump=constant) -To reduce cement content in order to reduce cost, heat of hydration, and/or shrinkage (strength=constant)
Type 3 ( High Early Strength)
-Used for accelerated construction and/or concreting in cold weather (short term frost) condition
Surfactants
-are compounds that lower the surface tension of a liquid, between two liquids, or between a liquid and a solid -Surfactants may act as detergents, wetting agents, emulsifiers, foaming agents, and dispersnats
Pozzolanic materials
-siliceous materials with no cementation value alone -will react with lime and water to form calcium silicate hydration (cement) -need reactive silica, finely divided -natural or synthetic
Concrete should be filled in slump cone in how many layers for the upright slump flow test (Procedure A) of SCC?
1
If concrete mixture is required to have 6% air voids, what is the volume of air in one yard of concrete?
1.62 cf
Slump measured to nearest
1/4 of an inch
Test cylinder Loading Rate
20-25 psi/sec
28 Day strength is
25% higher than the 7 day strength
In a SSD mix design, the required water content is 300 pcy. Since the aggregate (coarse and fine) used has a total of short water of 30 lbs, the batch mix design (after water balance) should have water content of:
330 pcy
a structure engineer specified concrete strength on a structural drawing as 4000 psi. what is the required strength you shall use for your concrete mix design?
5200 psi
in a SSD mix design, the concrete has a controlling water-to-cement ratio (w/c) of .5. Based on the ACI Mix design table, the required water content (Wx) is 280 pounds per cubic yard (pcy) of concrete. How much cement (pcy) should be used for the concrete?
560 pcy
LWC
85-115 Lb/Cf
Recommended concrete placement temperature
<12" : 55*F 12-30" : 50*F 36-72" : 45*F
Blending cement
= portland cement (I/II) + byproducts (S,P,L,T)
Accelerator/Retarder
Accelerate/reduce rate of cement hydration Adjust cement setting time and early strength
Superplasticizers
Accelerators and Retarders - To increase workability/slump without changing w/b - To reduce the mixing water and/or w/b - increase strength and durability (slump=constant) - Reduce cement content - reduce cost, heat of hydration, and/or shrinkage (strength constant)
Concrete Mix - Rules of Thumb
Adding 1 gallon of water to cy of concrete - increase slump one inch - decrease compressive strength about 200-300 psi - increase shrinkage potential about 10% If fresh concrete temp increase 10*F - adding 1 gallon per cy of concrete maintains equal slumps - air content decrease about 1% - compressive strength decreases 150-200 psi If air content of fresh concrete - increases 1%, compressive strength decreases 5% - decreases 1%, yield decreases 1/4 cf per cy - decrease 1%, slump decreases 1/2" - decrease 1%, freeze-thaw durability decrease 10%
Concrete Admixtures
Admixtures are materials other than cement, aggregate and water that are added to concrete either before or during its mixing
Most commonly used admixtures
Air Entraining Agents (AEA) Water Reducing Agents (WRA) Setting Control Agents (Accelerator/Retarder) Other commonly used - Corrosion-inhibiting - shrinkage reducing - coloring agents Many are surfactants
Most commonly used admixtures
Air Entraining Agents (AEA) Water Reducing Agents (WRA) Setting Control Agents- Accelerator/Retarder Others : Corrosion-Inhibiting, Shrinkage reducing, coloring agents
Which of the following admixtures did you use in the CE 382 group mix desgin assignment?
Air Entraining agent
Metakaolin
Al2O3 and SiO2
False set/ flash set caused by
Aluminate reactions accelerated by high temperatures
Air Entraining Agent (AEA)
Are primarily used to stabilize tiny bubbles generated in concrete to protect against freezing and thawing cycles -Chemistry: Salts of fatty acids, salts of sulphonated hydrocarbon
How to select cement
Based on purpose of use
Air content measurement Tests
C231 - Normal Strength C173 - Lightweight T-199 - Mortar
Portland cement manufacturing
Calcination of limestone, sand, and clay/shell to form clinker and grinding clinker with gypsum
Paste consists of
Cement and water
Why can cement aggregate together?
Cement hydration produce a gel (CSH) that glues partical together
Why can cement aggregate together
Cement hydration produce a gel (CSH) that glues particles together.
Hydration of Cement
Chemical Reactions with Water Cement + H2O = Hydration products + Heat
Effect of Temp on Slump
Concrete needs more water to reach designed slump at high temps quicker slump loss at high temps
Concrete workability (two major parts)
Consistency Cohesiveness
Concrete setting, set time too long
Delayed time for concrete strength gain
Purposes of admixtures
Enhance properties (workability, strength, durability) Overcome difficulties in construction (hot/cold weather, pumping, early strength requirements) Reduce cost and save energy
Causes of ITZ
Extra water - may bleed and accumulate under big agg particles Concrete is exposed to a drying condition - bleed water evaporates, leaving a number of pores, which form ITZ High Porosity in the ITZ - allows crystals to grow. Become orientated to obtain stable state.
Stress
F/A
WRA
Frees up trapped water by use of an anionic polar group on a hydrocarbon increases workability and slump without altering water content. Can then reduce cement and increase aggregate, lowering cost overall
NWC
General purpose, pavement, curbs, anything bro
Type 4 (low Heat)
Generally used for mass concrete (such as damns and foundations
What is cement mostly made of anyway?
Ground clinker, 5%, and gypsum for sulfate (95%)
Types of Mineral Admixtures
Ground/ Granulated Blast-furnace slag Fly Ash Silica fume Limestone Powder Metakaolin Natural Pozzolans Rice Husk Ash Sugar Cane Ash
Hydraulic cement
Harden with water and form water resistant product. Made by pulverizing clinker consisting of hydraulic calcium silicates
Fresh concrete related properties
Heat of hydration Workability Strength development Density Porosity
SCC Applications
Heavily reinforced structures Thin Structures Structures with complicated shapes - Bridges - High-rise buildings - Water/oil tanks Architectural Concrete Columns and beams Pumped concrete Drilled shafts
Segregation of concrete general causes
Heavy aggregate large aggregate Very low fines Too wet Poor mixing
Fast loading
High Strenght
Type III Concrete
High early strength, repairs or cold weather
Type V
High sulfate resistance (By sea or saltwater body)
HWC
High weight, used for radiation shielding. lead is added, for example
Features of ITZ
Higher porosity richer and larger size of calcium hydroxide (CH) crystals. Plate like CH tend to form orientated layers
Mixture proportion of concrete General concepts
Highest density Least cement Acceptable workability ACI Absolute volume method - hand calculations
Pervious concrete
Highly porous concrete that allows water to pass through it. noise reduction, pollution reduction, stromwater collection, heat absorption. High maintenance though.
How specific gravity is found
How much water is displaced by the aggregate when submerged in water
Portland cements are
Hydraulic cements Pulverizing clinker - hydraulic calcium silicates
Portland Cements
Hydraulic cements made by pulverizing clinker consisting essentially of hydraulic calcium silicates
Commonly used cements
I-V
Which cement has more finer particles
III
Which cement may contain fly ash?
IP
What type of portland cement (I to V) would you recommend for a large bridge pier?
IV (4)
Increasing W/C
Increases voids/ porosity, decreases strength
Mineral Admixtures
Industrial by-products Waste materials Pozzolanic Materials Supplementary Cementitious Materials
ITZ
Interfacial Transition Zone Interfacial region between coarse aggregate particles and cement paste. 10-50 micrometers
Slump flow test methods
Inverted and Upright
Passing ability of SCC measured by
J-ring Test
Type IPM
Less than 15% pozzolan
Type ISM
Less than 25% slag
Cement Production
Limestone/Sand, Clay, Shale Grinding/Storage Blending (wet or dry) Preheating Burning Kiln (2600-3000F) Clinker (cooling pulverizing) Final Grinding w gypsum Portland Cement
Slow Loading
Low Strength
Type IV
Low heat of hydration, for large structures.
Roller compacted concrete
No slump, used in roads and dams
NMSA
Nominal maximum size aggregate is the smallest sieve 85-95% of the aggregate passes through
Concrete setting behavior
Normal Initial Set False Set Flash Set
Water Reducing Agent types
Normal Water Reducers (WRA) - 5-10% water reduction Mid-Range Water Reducers (MRWRA) High-range water reducers (HRWRA) or superplasticizers - 20-30% water reduction
Type I Concrete
Normal concrete general purpose (Pavement)
Concrete components
Paste (20-35%) Aggregate (60-80%) Voids (2-10%)
Type IS
Portland blast-flumace slag cement, 25%-75% slag
Factors affecting Air Content
Portland cement - fineness, content alkali %, contaminents Supplementary Cementitious material - chemistry, fineness and content Admixtures - type, dosage, and their compatibility with cementitious materials Aggregate - type, size, sand gradation and content Water - water chemistry (recycled gray water) Concrete mix design - w/c slump Construction - mixing, transportation and delivery, retempering, placement, vibration, finishing, temps
Blended cements
Portland cement + by-products
Type IS Concrete
Portland cement with Slag included
Type IL
Portland- limestone cement
Type I(pm)
Pozzolan-modified portland cement (<15% pozz)
Type 5 (High Sulfate Resistances)
Used in concrete under the extreme sulfate exposure conditions (such as marine structures and foundations in soil/ground water with high sulfate content)
From a visual observation of the picture below, determine what should be the visual stability index (VSI) of this SCC mix and what does it tell about the stability of the mix.
VSI=2 and unstable
Silica Fume
Very finely divided silicon dioxide, a pozzolan, used as an admixture in the formulation of high-strength, low-permeability concrete; also called microsilica.
Natural Pozzolans
Volcanic ash - heating and rapid cooling - higher heat => more rapid cooling => more reactive
Factors for working curve
W/C ratio, cement factor, strength
WRA used in
Water reducing agent used in highly reinforced structure, flow around rebars
Factors affecting concrete strength
Water-to-cement ratio - Higher w/c => more porous the ITZ Mineral admixtures - (small particles, reacting with CH, improved CSH) Properties of aggregate - (size, shape, texture, grading, and type) Others - concrete curing and testing conditions
Uniformity of concrete ( two types)
Within-batch uniformity Between-batch uniformity
Fresh Concrete Properties
Workability Consolidation ability Setting behavior
Important Properties of fresh concrete
Workability Setting behavior Air content/ Unit weight Concrete Temperature
Uniformity of concrete
a measure of homogeneity of concrete
Fly Ash
a waste product produced by the burning of coal.
Accelerating Admixtures Purpose
accelerate setting, early strength development Applications - Cold weather concrete - Early exposure to freezing and thawing - Early Start of finishing - Reducing curing time - Accelerating construction Effects on Concrete properties - Fast setting and early age-strength development - Increased drying shrinkage - Potential corrosion of reinforcement - loss of strength at later age - Discoloration (darkening concrete)
optimum air content
air content: 5-8% size/spacing: 200 micrometers
Cementitious materials
alone will hydrate and have cementing properties - blast furnace slag - Class C fly ash
Pozzolanic materials
alone will not hydrate and possess little or no cementing value - Silica Fume - Class F fly ash - Natural Pozzolans
Caps are placed on cylinders for testing to
balance the load evenly over the cylinder
Slag production
blast furnace
Portland cement manufacturing
calcination of limestone, sand and clay/shell to form clinker, grid clinker with gypsum
between batch uniformity is low
caused by consolidation, due to inconsistent materials, mixing and others
Too cold concrete placement temp
cement hydration may be very slow
Effect of one degree change in various materials
cement needs to drop 8 degrees, water 4, aggregate 2
Properties of portland cement
composition and Fineness soundness consistency setting time Heat of Hydration Compressive strength loss on ignition
Surfactants
compounds that lower the surface tension of a liquid. Act as: - detergents - wetting agents - emulsifiers - foaming agents - dispersants
Pull out test
concrete removed. Tests in-situ strength, shows shear strength
Too high concrete placement temp
concrete slump low cause plastic shrinkage cracks
UPV Pulse
detects defects, but nature is not known. Both sides of concrete need to be accessed. Tests interior and is cheap and easy.
Concrete workability
determines the ease and homogeneity with which concrete can be mixed, placed, consolidated and finished.
Primary causes of segregation are
differences in specific gravity and, size of constituents of concrete Gsa>Gsm too much water Also improper mixing, placing, consolidation.
Fiber reinforcement
dispersed throughout, controls crack propagation and improves bond between steel and matrix
Hot weather options
dont add water, use retarding mixtures, use class F fly ash, reduce temperature, night construction, reduce moisture loss
Concrete from air test can be used in cylinders
false
Channeled bleeding
form weak plane
cement hydration
grain surfaces react, exothermically. Crystals and gels are formed. Hydration continues as long as moisture reaches unhydrated particles.
concrete that has a lot of bleeding
has a high tendency to segregate
fiber reinforced concrete has advantages in
higher impact and fatigue resistance
Retarding agent used in
hot climates to prevent early hardening
Air entraining agent used
in regions with freeze thaw cycles
Within-batch uniformity is low
indicates inadequate or inefficient mixing
Passing Ability =
inversed slump flow J-ring flow
Specified strength
is less than required strength
Concrete setting, set time too short
little time for concrete casting
a w/c ratio to be chosen if sulfate attack is likely
low w/c ratio
Larger sample size may yield
lower strength result
Concrete admixtures are
materials other than cement, aggregate, and water that are added to concrete either before mixing or during mixing
Hydraulic Cements
Products that not only harden by reacting with water but also from a water-resistant product
Non-Hydraulic Cements
Products that react with water and may harden in air but are not resistant to water
AEA Roles
Provide space for water/ice cut flow path - reduce hydraulic pressure Lubricate mixture - improve concrete workability Reduce effective cross area of concrete elements
AEA use
Provides space for water and ice, reduces hydraulic pressures
Retarding Admixtures
Purpose - Retarding setting time Applications - Hot weather concreting - provide sufficient time for placing and finishing - overcome damaging and accelerating effects of high temp - Incorporate with superplasticizer to reduce slump loss - Large structure construction - prevent cold joints - unexpected placing and finishing problems
Tricalcium Silicate C3S
Rate of Hydration : Mediate Strength early and ultimate: Good, Good Heat of Hydration Mediate
Tetra calcium Aluminoferrite (C4AF)
Rate of Hydration : Mediate Strength early, Ultimate: Good, Mediate Heat of Hydration : Mediate
Tricalcium aluminate C3A
Rate of hydration : fast Strength early, ultimate : Good Mediate Heat of hydration : High
Dicalcium Silicate C2S
Rate of hydration : slow strength early and ultimate : Poor, Excellent Het of hydration : low
SCM's
React after the cement reacts, so the heat given off is more dispersed, lowers peak temp and increasing workability window.
Hydraulic cement
Reacts with water, hardens, and forms water-tight material
Bleeding and Segregation prevention practical methods
Reduce w/c use mineral admixtures - powder materials increase air content increase rate of hydration Add very fine fibers
Potential problems with mineral admixtures
Reduced early-age strength more admixtures required - adsorption of fine particles increased in salt sealing carbonation and drying shrinkage cracking
Bleeding of concrete
Refers to water in the concrete mix rising to the surface due to the settling of heavier particles. Some bleeding is to be expected, but excessive amounts can be problematic.
Retarding Admixture effects on concrete properties
Retarding the rate of concrete No significant effect on ultimate concrete strength function as a water-reducing agent Entraining air into concrete Unpredictable shrinkage behavior
Normal Initial Set
Right amount of gypsum/sulfate - concrete sets 2-4 hours after mixing
Problems caused by bleeding
Rock jams - in pumplines Sand Streaks - in walls Weak horizontal construction joints Excessive voids beneath aggregate and rebar Blistering, scaling, and dusting surfaces
Slump cone test
Rodded 25 times in three lifts, first layer rodded through and then rodded through the first inch of the previous layer. Layers are of equal VOLUME
Accelerator/Retarder
Role: Accelerate/reduce rate of cement hydration Effects: adjust cement setting time and early strength
WRA
Role: Separate cement Particles Effects: Reduce water requirement Improve workability and/or strength Disadvantages: slump loss
AEA
Role: Stabilize air bubbles in concrete Effects: increase F-T resistance and improve workability Disadvantages: Reduce strength
Which of the following is a correct statement on the saturated surface dry (ssd) condition of concrete aggregate?
SSD aggregate is lighter than wet aggregate
Slump flow test
Self consolidating concrete
How do water reducers work?
Separate flocs into individual grains Trapped water is released - grains slip by each other Improve the workability
Moisture content-Absorption Yields
Short water or free water
Type S
Slag cement (>70% slag)
Type IS Cement
Slag cement, 25-75% (Blast furnace)
Type S
Slag cement, more than 70% slag
Type I (SM)
Slag modified portland cement
Supplementary cementitious materials
Slag, Fly ash, Silica Fume, Calcined clay, volcanic tuff
Standard Flow Tests
Slump Test Slump Flow Test Vebe Test
Problems in hot weather
Slump loss, reduced air content, premature stiffening, shrinkage, cracking
Effect of Test Methods on Concrete Strength
Specimen Size: Fracture mechanics will explain the importance of size effect. Loading Rate: increasing Rates = Increasing Strength
W/C selected based on
Strength Economy Workability Durabiltiy
Hardened Concrete Properties
Strength Unit Weight Permeability Abrasion resistance Durability
Major Properties of Hardened Concrete
Strength (Compression, Tension, Shear, Impact) Elastic Modulus Dimension stability (expansion/shrinkage) Wearing Resistant Durability
Properties of Hardened SCC
Strength - Comparable or Higher Modulus of Elasticity - Comparable Flexural Strength - Comparable or Higher Shrinkage - Generally Higher Bond - generally weaker Cost - 10-15% increase material cost - 50% reduction in labor cost
Effects of Concrete and Test Conditions on Concrete Strength
Stress distribution Test fixture Specimen Aspect ratio Specimen Shape Rate of Loading Moisture Condition of specimens Testing Temperature
Elastic Modulus
Stress/Strain
Please select which one is FALSE for the self-consolidating concrete (SSCC) mix?
Superplasticizer and viscosity modifying agents are generally not used
Fresh concrete basic properties
Temperature slump setting time Unit weight Air content
Type IT
Ternary blended Cements- portland cement with (pozzolan and limestone or with slag and limestone)
From the following options, please select which one is TRUE for the measurements to be taken in the INVERTED slump flow test (Procedure B).
Tfinal ,T20, and spread diameter
In a SSD mix design, the coarse aggregate content is 1744 pcy (i.e. WCA,SSD=1744 lbs) The aggregate moisture content (MC) is +2.0% and its absorption (abs) is 3.0%. Which statement in the following is correct?
The aggregate is short of water (it will absorb water from the concrete mixture)
Which of the following statement is the most appropriate statement for high strength concrete subject to a load?
The interfacial transition zone between cement
Based on which of the following information, you can find bulk volume of SDD aggregate in our lab?
The weight of the aggregate measured in air and in water
Durability
Thermal and Drying Shrinkage Frost Action (F-T, scaling, Salt) Corrosion of Reinforcement Alkali-Silica Reaction Sulfate Attack
Fresh concrete related problems
Thermal cracking difficult to flow Early exposure to load Low density strength loss or gain excessive entrained air
CSH, CAOH2, Entringite, Monosulfate
These are all crystals formed from hydration, except CSH which is a Gel.
False Set
Too much gypsum (high gypsum/sulfate) Early stiffening (within 10 min) workability can be resumed by remixing
What is the major chemical compound in portland cement?
Tri-Calcium Silicate
From the following options, please select which one is TRUE for the diameter measurement in the case of UPRIGHT slump flow test (Procedure A).
Two readings, perpendicular to each other, should be taken to the nearest 1⁄4 inch
Chemical Admixtures
Type A: Water-reducing Type B: Retarding Type C: accelerating Type D: A and B Type E: A and C Type F: High Range water reducing Type G: HRWR and Retarding
Commonly used cements
Type I-V
Expansive cement
Type K
Two types of bleeding
Uniform bleeding Channeled bleeding
Too little bleeding may cause
plastic shrinkage cracking in concrete
Type IP or Type P
portland-pozzolan cement, 15-40% pozzolan
Pozzolanic reaction
pozoolan SiO2 and AL2 O3 react with CaOH2, a product of hydration.
Type IP
pozzolan cement, 15-40%
Windsor test
probe goes into concrete, tests penetration resistance. This can measure early strength, but the area is small so the test may be higher than that of the cylinder test
Non-hydraulic cements
products that react with water and may harden in air but are not resistant to water
Pozzolanic admixtures will not
react on their own, but react with calcium hydroxide, a portland cement hydration product, and result in cementing properties
Hydraulic cement
reacts with water, hardens in water, and form water tight material
Bleeding and Segregation prevention concepts
reduce the difference between mortar-coarse aggregate density Increase viscosity of mortar/paste
Shotcrete
shot out of a tube, easy to use for tunnel repairs or odd shapes. High waste with rebound.
Commonly used mineral admixtures include
slag fly ash silica fume volcanic ashes metakaolin limestone powder
Pozzolanic Reaction
slow reaction at normal temp lime consuming generates little heat
Uniformity of concrete measurements include
slump temperature air content unit weight yield
Filling ability measured by
slump flow test
Passing ability measured by
slump flow test
Fibers do not have impact on
strength of the concrete
Water Reducing Agents are
surfactants long-chain organic molecules hydrocarbon chain Anionic polar group
Cohesiveness
tendency to bleed and segregate
Bleeding starts when
the water being forced to the surface as the heavier solids begin to settle.
Bleeding ends when
the water movement is blocked by the growth of hydration products and or by the solids effectively coming into contact (concrete setting)
Why maximum temperature should be minimized
to minimize internal stresses and minimize potential for cracking. Hydration reaction doubles with each increase of 20 degrees Fahrenheit.
Flash Set
too little gypsum (low gypsum/sulfate) Early stiffening within 10 min. Concrete cannot return to a fluid state with re-mixing.
Flash set
too little gypsum, permanent and cannot mix through. NOOOO
False set caused by
too much gypsum which can be mixed through, no heat given off
Proper mixing and testing requires
tools and mixer to be damp/ wet.
Uniform bleeding
uniform seepage over entire surface
surface rebound test
used for checking concrete uniformity, indicator of compressive strength and stiffness low strength absorbs more energy, lower rebound simple and inexpensive, but does not characterize interior properties, and can be influenced by many factors
LWC
used for high rises or bridge decks.
Rebar reinforcement
used to carry tensile and shear stresses, placed in specific location
Why AEA
used to stabilize tiny bubbles generated in concrete to protect against freezing and thawing cycles
Maturity method
uses temperature history to observe how hydration progressed, gives a good estimation of strength.
Pozzolans react with
water and cement
Cementitious admixtures will react with
water, harden, and gain strength
Special Cements
Masonry cement (mortar) - Type: N, S, M Expansive cements - Type K High Early Strength - RR, Rapid Set, Fondu, SET-45 Oil-Well Cements - Class: A-G, O Acid Resistant Cements - Silicate based, sulfur White Cements
MSA
Maximum size is the smallest sieve size 100% of aggregate passes through
SSD Condition
Means the permeable voids in the aggregate are filled with water only.
From the J-Ring test, a passing ability of 1.5 inch means that the SCC mix has
Minimal to noticeable blocking
Rate of heat evolution
Mixing Dormancy Hardening Cooling Densification
Type II
Moderate sulfate resistance
From the test of static segregation resistance, a penetration depth of 12.5 mm means that the SCC mix is
Moderately resistant to segregation
8. From the inverted slump flow test, what does a high T20 value suggest about the SCC mix?
More Viscous mix
Masonry cement
Mortar, types N, S, M, for walls or foundations
