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