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105 Cards in this Set
- Front
- Back
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What are the four basic chemical compounds that make up Portland cement? (Give the answers as Industry codes, and Chemical Formulas) |
C3S, C2S, C3A, and C4AF (Industry abbreviation codes)
Tricalcium silicate, Dicalcium silicate, Tricalcium aluminate, and Tetracalcium aluminoferrite (Chemical Formulas) |
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What Percentage does each of the following compounds encompass in Portland Cement? Also what is the rate of reaction of water for each of these compounds? C3S C2S C3A C4AF
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C2S: 35-65% and medium rate
C2S: 15-40 % and Slow Rate
C3A: 0-15 % and Fast Rate
C4AF: 6-20 % and Medium Rate |
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What does C3S do for the chemical composition of Portland Cements? |
C3S is the initial strength.
Most stable, 70-80% of the cement (different than chart).
Contributes most to cements physical properties. |
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What does C2S do for the chemical composition of Portland Cement? |
Final Strength (greater resistance to chemical attack and a smaller drying shrinkage) |
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What does C3A do for the chemical composition of Portland Cements? |
Extremely Exothermic, Concrete susceptible to surface attack, least stable, and proportion > 10% |
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What does C4AF do for the Chemical Composition of Portland Cements? |
Less important than other components
Rate of reaction: Medium |
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What are other characteristics of Portland Cement other than Chemical Composition? |
Fineness and Hydration |
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What is fineness and what does it measure? |
Fineness relates to the size of the content particles Greater the Surface area of a given volume, the greater the hydration Fine cements develop strength and heat quickly |
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What is Hydration as it pertains to Portland Cements? |
The chemical combination of cement and water |
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What is the general chemical formula for the combination of cement and water? |
Portland Cement + H20 -> C-S-H + C-H + Heat (Generated) |
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What is the formula for measure of aimness and what are its units? |
(Surface Area)/(Mass)
Units: (m^2)/(kg) or (in^2)/lb |
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What are the properties of C3S2H? (obtained from mixing cement with water) |
Gel, Hydration product, or tobber marite? which is a cementing property |
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What are the properties of CH? |
product of hydration that does not have (or negligible) cementing property |
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What is a pozzolanic material? |
Examples include microsilica and fly ash.
Pozzolan(S) + C-H -> C-S-H + Heat
Generally 10-15 % of Portland cement can be replaced by pozzolans
Added to concrete to convert CH to CSH |
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What is a method that can be used to Convert C-H to C-S-H? |
Adding a pozzolanic material to the concrete mix |
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What are some properties of Head of Hydration? |
Reaches Max in 2 to 4 days after casting
Can be as high as 45 degrees in concrete dams
Poor heat conductivity produced undesirable results such as micro-cracking! |
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What are the four factors that affect Heat of Hydration? |
1. Size of Structure 2. Type of Framework 3. Rate of Placing Concrete 4. Ambient Conditions |
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Review Notes for Diagrams some of them are kind of confusing. |
No doubt |
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How do you define the Initial Set in the Setting and Hardening of Concrete? |
Noticeable stiffening of cement paste |
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How do you define the Final Set in the Setting and Hardening of Concrete? |
Final Hardening process responsible for the strength of concrete. |
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How do you define the Flash Set in the Setting and Hardening of Concrete?
What is the remedy for this? |
Rapid Stiffening with excessive heat generation. Also includes insufficient gypsum that controls the reaction rate of C3A with water.
ADD MORE WATER AND REAGITATE THE MIX |
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How do you define the False Set in the Setting and Hardening of Concrete?
What is the remedy for this? |
Produces rapid stiffening but with no excessive heat
ADD NO MORE WATER BUT REMIXING |
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Compressive Strength (ASTM C-109)
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-Specimen is a 2-in Mortar cube -Ottawa Sand/cement ratio = 2.75:1 -Water/Cement ratio (W/C) = 0.485 (Portland Cement) -Curing Time = 24 Hours |
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Flexural Strength (ASTM C-340) |
-Proportioning and mixing same as last slide (Compressive Strength) -Specimen is a 40x40x40 mm prism -Center point loading |
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What is Soundness of Concrete? |
Excessive Change in volume (expansion) leads to unsoundness. Long term surface cracking and disintegration.
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What causes Soundness of Concrete and what test do you use for it? |
Cause: Slow hydration of MGO or free lime. And/or reaction of gypsum with C3A
Test: ASTM C-151 |
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What are the five types of Portland Cement? |
Normal, Moderate Surface, High early strength, Low heat of hydration, and High sulfate resistance |
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What is the Application of Normal Cement? |
General concrete work when the special properties of other types are not needed. Suitable for floors, reinforced concrete structures, pavements, etc. |
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What is the application of Moderate sulfate resistance Portland Cement? |
Protection against moderate sulfate exposure, 0.1% - 0.2% weight water soluble sulfate in soil or 150ppm - 1500 ppm sulfate in water (seawater). Can be specified with moderate heat of hydration making it suitable for large piers, heavy abutments, and retaining walls. The moderate heat of hydration is also beneficial when placing concrete in warm weather. |
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What is the application of High Early Strength Portland Cement? |
Used for fast track construction when forms need to be removed as soon as possible or structure needs to be put in service as soon as possible. In cold weather, reduces time required for controlled curing. |
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What is the application of Low heat of hydration Portland Cement? |
Used when mass of structure requires careful control of the heat of hydration, such as in large dams. |
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What is the application of High Sulfate Resistance Portland Cement? |
Protection from severe sulfate exposure. 0.2%-2.0% weight water soluble surface in soils or 1500 ppm - 10,800 ppm sulfate in water. |
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What are the three main components of Portland Cement? |
C3S, C2S, and C3A
(find actual names on the other slide, these are industry abbreviations) |
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What are the characteristics of C3S in Portland Cement? |
-High early strength (because of quicker hydration) -Major contribution to strength at all ages and particularly up to 28 days -Restraint to corrosive salts, alkalis, and acids |
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What are the characteristics of C2S in Portland Cement? |
-Show hardening (Contribution to strength from 7 days up to 1 year).
-Good Final Strength, but comparitively small in 1st 28 days |
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What are some characteristics of C3A in Portland Cement? |
-Quick Setting -High Heat Evolution -Poor Chemical Resistance (Sulphide) -Small contribution to strength (principally within 1st 24 hours) -Grind in gypsum to prevent "flash set" |
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What are the mechanical properties of Fresh (plastic) Concrete? |
Includes; air content, slump, harshness, etc. |
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What are the mechanical properties of Hardened concrete? |
Includes strength, durability, skid resistance, etc. |
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What are the 6 properties of Fresh Concrete? |
1. Easily mixed and transported 2. Uniform throughout given Batch and between batches. 3. Should have flow properties to fill up completely the forms. 4. Ability to be compacted fully. 5. Must not segregate during placing and consolidation. 6. Capable of a good finish. |
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What is a Slump Value? |
Indication of the consistency (or workability) of concrete |
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What can you predict using a slump value? |
Can be used to predict the strength of concrete before adding any water reducing agents which will increase the workability of concrete for the same water-concrete ratio. |
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How is the slump value measured? |
Using a slump cone and other apparatus.
other apparatus could include the tamping rod. |
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What is the procedure for a slump test? |
1. Fill the cone using standard procedure 2. Strike of excess. 3. Raise the mold and measure the displacement of the original center of the specimen.
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In general practice a slump value of __ or __ is used |
2 or 4 |
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In slip form construction a ??? to ??? slump may be used to take advantage of the plasticity of concrete. |
0 to 3 |
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Know figure 3.8 in notes determing the type of slump based on the figure.
In hard to reach locations a ??? slump value is needed so that concrete can "flow: to the hard to reach location. |
High |
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What is Consistency as it pertains to concrete? |
Measure of Concrete Wetness or fluidity |
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What are three things that define workability?
What are factors that affect workability? |
1. Consistency 2. Mobility - Transporting, how easily it can fill nooks and corners of formwork 3. Compactibility
1. Constituents 2. Ambient Conditions |
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What are some of the properties of cement & water in fresh concrete? |
1. Relatively insensitive to change in only cement content but depends upon water content (up to 10 - 20%) 2. Greater effect of cement for rich mixtures 3. Workability decreases with increase in the fineness of cement |
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What are some of the Aggregate properties in Fresh Concrete? |
1. Decreases as the specific surface area increases 2. All other conditions being equal, workability, will be increased when the MAXIMUM SIZE of the aggregate increases. 3. I.E. particles rounded, overall grading is coarser. |
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What are ambient conditions of Fresh concrete? |
Reduction in workability with the rise in:
1. Temperature 2. Humidity. 3. Wind Velocity. |
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What are some important parameters of air bubbles in concretes? |
1. Amount of air bubbles. 2. Size of air bubbles. 3. Distribution Density of air-bubble |
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How is Time defined in terms of fresh concrete? |
The time elapsed between mixing of concrete and it's final compaction
More time = Loss of workability |
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What is Stability as it pertains to fresh concrete? |
Maintaining uniformity of composition throughout distribution, compaction, and initial stiffening causing separation of constituent materials. |
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What is Air Content as it pertains to concrete? |
Effective method to use tiny air bubbles as pressure relieve valves to eliminate hydraulic pressure built up of ice formation. |
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Durability of concrete is a function of what three things? |
1. Air content 2. Size distribution of air bubbles 3. Shape & Spacing of air bubbles |
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The optimum spacing for the spacing factors of air bubbles is about ??? mm to ??? mm in order to achieve the optimum durability |
0.1 mm to 0.3 mm |
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Define Harshness as it pertains to concretes.
What will happen is a fresh concrete is too harsh? |
An indication of the final finish of concrete.
If a fresh concrete is too "harsh" then achieving a good final surface finish will be difficult. |
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Define Shrinkage as it pertains to concretes. What are some types of shrinkage? |
Shrinkage is the volume reduction in concrete due to the settlement of solids and the loss of water. Types of shrinkage include plastic and drying shrinkage. |
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What is Plastic Shrinkage? What are some of the results of Plastic Shrinkage? |
The reduction in volume of plastic (or wet) concrete. -With Quick drying, the plastic shrinkage may lead to surface cracking - Short irregular cracks on the concrete surface, mostly on horizontal surfaces. |
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Plastic Shrinkage during the first day after mixing can be ___ to ___ times the drying shrinkage. |
5 to 10 |
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How do weather conditions affect the plastic shrinkage? |
Hot weather conditions increase the plastic shrinkage due to excessive evaporation loss |
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Where is plastic shrinkage more common? |
In slabs and pavements due to large surface area contributions to high evaporation loss. |
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What does the amount of plastic shrinkage depend largely on? |
1. Type of content 2. Water/Cement Ratio 3. Quantity and size of coarse aggregate 4. Consistency of mix |
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What are five methods of minimizing plastic shrinkage? |
1. Cooling of concrete during mixing 2. Using sunshades 3. Spraying a curing compound 4. Covering the concrete with plastic sheets 5. Water-reducing and air entraining admixtures |
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What is Crazing? |
Hexagonal pattern of surface cracking at an early age.This is due to improper finishing and curing. |
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What is the hexagonal pattern (honey bee hive) caused by crazing known as? |
Binard liquid convection |
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What is Drying Shrinkage? |
Occurs in hardened concrete due to loss of water from the cement gel. |
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What is the range of Drying Shrinkage? |
350 to 650x10^-6 in/in
(Can also be as large as 1500x10^(-6) in/in)
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What are 6 factors influencing drying shrinkage? |
1. Type and amount of cement 2. Mix proportions 3. Size and Shape of structure 4. Curing and Environmental conditions 5. Reinforcement 6. Water/Cement ratio --> increasing will increase drying shrinkage. |
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What are some other aspects of Drying Shrinkage? |
Restraining will cause cracking!!!
It is gradual, about 40-80% of 20 year shrinkage occurs within 3 months
Concrete in 100% relative humidity swells |
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What are 3 means of controlling shrinkage cracks? |
1. High pressure steam cured samples shrink __ than normally called samples 2. Synthetic fibers in concrete 3. Reinforcement controls the location of cracking |
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What are the Compressive Strength guidelines for a Standard Specimen? |
- 6 in and 12 in height cylinders - most cured for 28 days - Unaxial compression test ASTM (469) |
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What is the compressive strength equation? |
fc' = (Pmax)/((pi/4)*D^(2))
where fc' is the compressive load Pmax is the failure load D is the diameter of the cylinder |
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What are three failure modes in compression? |
1. Material Failure, Compressive Strength 2. Structural Failure, or Buckling phenomenon 3. Combined (material + structure)
compressive load and failure modes, in general - Brittle materials |
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What is the specimen design and aspect ratio? |
-L/D ratio -Strength variation due to non-homogenity -Strength depend on size, shape, and moisture conditionings 1. Larger L/D will result in lower fc'
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How is tensile strength measured? |
Direct Tensile Strength is difficult to measure and is usually not done. Instead the use of the indirect tensile test (split cylinder test) is used. |
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What is the Tensile Strength equation? |
ft = (2Pmax)/(pi*L*D)
Tension(T) = (2*P)/(pi*l*D) *minimum permissible diameter is 2 inches Pmax = failure load ft = 10-15% of fc' ft = 6.7*(fc')^(1/2) |
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How do you determine flexural strength? |
Two tests:
1. Third Point Loading (4 point loading) 2. Center Point Loading (3 point loading)
Also known as the bending strength or MODULUS OF RUPTURE (MoR). |
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What is the equation for Bending Strength in a third point loading test (MoR)? |
fr = (MC)/(I)
where Mmax = (P*L)/6 C = distance from the neutral axis to the extreme fiber in tension I = moment of Inertia about the neutral axis P = Failure Load
fr becomes --> (P*L)/(B*d^(2)) = fr MoR ~ 12*SQRT(fc') (estimated value) for a normal weight concrete fc' is in psi |
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What is the the Bending Strength equation for the three point loading test? (center point loading) |
fr = (3/2)*(P*L)/(B*d^(2)) (general equation for the third point (center) loading test
Note: fr(4 point loading) > fr(3-point load test) by about 10-20% |
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What are the three important stress values for concrete? |
1. Compressive Strength 2. Tensile Strength 3. Bending Strength |
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What is the formula for the Modulus of Elasticity in Concretes? |
Ec = w^(1.5) * (33) * (fc')^(0.5) w = unit weight of concrete in pcf fc' in psi Ec in psi |
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What is Durability as it pertains to concretes? |
The capacity to resist detoriation from weathering and traffic (lifespan of trouble free performance). |
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What are the primary causes of deterioration? |
1. Alkali - aggregate reaction 2. Freeze - thaw cycles 3. Sulphate Attack |
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What are two key factors affecting durability? |
1. Permeability 2. Compressive Strength
Low strength and high permeability decrease the durability. Having a w/c ratio <= 0.45 is better |
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What is the Alkali-Aggregate Reaction? |
Chemical reaction between certain natural aggregates containing active silica and alkalis (Na and Potassium oxide) of Portland cement in the presence of water resulting into swelling of aggregates followed by cracking and disintegrating of concrete.
Aggregates with silica in active state include hard - burned lime, sileceons lime stone, etc. |
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What is the Cure and Control method for Alkali-Aggregate Reaction? |
- Use of low- alkali cement
- Use of fly-ash or ground blast furnace slag. |
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What is the Freeze-Thaw Cycle? |
Entrained air and a low water/cement ratio will improve freeze-thaw resistance.
- Natural mineral aggregates that are porous are susceptible to deterioration in forms of poputs or surface cracking of concrete above particles. |
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What is Scaling? |
The top thin mortar layer may take off from freeze-thaw effects |
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Look over creep phenomenon stuff from first midterm |
Gotcha homedog |
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I will now describe more about Durability ----- mainly the sulphate ATTACK! |
-The potentially aggressive constituents in seawater include: Sulphates, chlorides, carbonates, bicarbonates, alkali metal, and magnesium ions - mg-sulphate --> the most aggresive agent - Sulphates + Calcium Hydroxides --> gypsum --> reacts with Calcium Aluminate to form expansive compounds |
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Where was the first concrete pavement in america? |
Court Avenue, Bellefontaine, Ohio 1892 |
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What is Sulphate Attack? |
Sulphates in the soil and seawater (sodium + sulphate + calcium sulphate) react with aluminates in the cement to produce compounds that have volumes greater than the initial volume.
This causes expansion & Cracking |
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What are some methods of controlling sulphate attack? |
1. Use cement low in tricalcium aluminates. 2. Fly-Ash and other mineral admixtures reduce the amount of calcium aluminate |
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What is Creep? |
The increase in strain (or deformation) with time under constant loading. - Includes compression, tension, and torsion - Generally no appreciable creep in aggregates - Cement paste creeps - Concrete made with SANDSTONE creeps more than that mad with GRANITE or LIMESTONE |
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What are four factors that affect creep? |
1. Higher the aggregate content (for a given water/cement ratio) the lower the creep 2. Increase in w/c ratio --> increase in creep. 3. Rate at creep increases with ambient temperature 4. Higher in wet than in dry conditions.
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What are some properties of creep? |
Properties of creep include: elastic recovery, delayed recovery, reversible creep, and irreversible creep |
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What is the Visco-Elastic Phenomenon? |
Viscous like liquids but also elastic like solids. |
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What are admixtures? |
Any material other than water, aggregates, and cement that is used as an ingredient of concrete or mortar and is added to the batch immediately before or during batching. |
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What are some examples of admixtures? |
ASTM C 260: Air entraining Agents ASTM C 494: Chemical Admixtures Other admixtures |
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What are the types of chemical admixtures? |
Type A - Water Reducing Type B - Retarding Type C - Accelerating Type D - Water Reducing & Reducing Type E - Water Reducing & Accelerating Type F - High Range Water Reducing Type G - HRWR & Retarding |
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What are some types of other admixtures? |
Fly ash, Slag, Microsilica, Fibers, Corrosion Inhibitors, Set Accelerators, Etc. |
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What are some reasons for using admixtures? |
1. Modify fresh concrete properties. 2. Increase workability without increasing water 3. Decrease water without decreasing workability 4. Retard or accelerate setting time 5. Modify the rate and/or capacity for bleeding 6. Improve Pumpability 7. Reduce the rate of slump loss |
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Look at all charts in notes Go through all notes and notecards Go over homework make sure you know it Go over Sieve analysis Go over Concrete Density measurements (1st lab stuff) |
and you shall have the power to ace this exam |
