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68 Cards in this Set
- Front
- Back
What is durability? (In terms of material life) |
ability to last for the servce life without unacceptable performance related to materials |
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Durability of materials contributes to the environment by: |
conserving natural resources, reducing green house gases |
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What is the number one cause of concrete deterioration? |
Corrosion of rebar in concrete |
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What is carbonation induced corrosion? |
Atmospheric CO2 diffuses the concrete, reacting with Ca(OH)2, lowering the pH |
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Why does entrained air limit freeze-thaw damage? |
lets water expand into entrained air voids and/or eliminating saturation with water |
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What is acid attack of concrete? |
corrosion through H2SO4 bacteria in sewage. H2S emission |
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What is sulphate attack of concrete? |
sulphur from groundwater reacts with aluminate phases- creates softening, expansion and cracking |
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What is Akali Aggregate Reaction (AAR)? |
Akali aggregates exposed to atmosphere reacts to create spalling and cracks |
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What are general solutions to improve durability in concrete? |
low w/c by using super-P SCM Admixtures proper placement and curing practices |
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Name five types of targeted solutions to a specific problem: |
Air entrainment (freeze thaw) cement/aggregate selection (AAR) Shrinkage reduction (crack reduction) absorption reduction (surface properties) coatings, cathodic protection (steel corrosion) |
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What are the design criteria for proportioning concrete mixtures? |
strength, durability, workability, sustainability, economy, appearance |
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What are the exposure classes of CSA A23.1 |
C1- strucural concrete with or without freeze thaw conditons; exposed to chlorides C2- non-structural, freeze thaw, exposed to chloride F1- freeze thaw, saturated, no chloride F2- freeze thaw, unsaturated, no chloride |
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What are the three phases of concrete? |
aggregate, cement paste, ITZ |
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Why is concrete weaker than the aggregate and cement paste separately? |
ITZ is in concrete. creates weak points for cracks to propogate |
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Why is load control testing less effective than displacement control? |
load control only gets a portion of a displacement curve (stops at failure), as displacement control goes past failure load. |
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What are main differences between ITZ and bulk paste? |
ITZ - less hydrated cement - higher porosity - less CSH - more ettringite |
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Explain the weakness of the ITZ. |
the mortar and aggregate have different responses |
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Describe the relationship between strength and W/C |
as w/c increases, strength decreases |
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Describe the relationship between permeability and W/C |
as w/c increases, coefficient of permeability exponentially increases |
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What is mortar volume fraction? |
(Volume of cement, water, fine aggregate, and sometimes air)/ Total volume (1m3) |
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What are the main primary strength producing minerals of clinker? |
C3S and C2S |
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What are the hydration reactions of C3S and C2S? |
Hydrates with water to create CSH |
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What are the elements in cement? |
Oxygen, Si, Ca, Al, Fe |
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What is the nature of CSH? |
"glue" that provides strength (from VDW forces) - poorly crystallized, porous |
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What does Calcium Hydroxide provide to concrete |
- large crystal structure, however has a low strength - forms around ITZ reacts with pozzolanic SCM to form more CSH |
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Why is gypsum added to cement? |
to avoid flash set (stiffening and loss of workability) |
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Why is limestone added to cement? |
reduce greenhouse gases |
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What does fineness of cement mean in regards to creating concrete? |
increasing fineness, increase rate of reaction give off more heat earlier in hydration |
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How is HE concrete achieved? |
increasing fineness increasing C3S |
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How is HS cement achieved? |
reduced C3A content blend SCM |
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What is blended cement? |
mixture of portland cement and: fly ash slag silica natural pozzolan limestone |
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What are pozzolans? |
Common name for several SCMs containing amorphous silica |
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What is slag? |
waste slag from iron ore - increases durability -decreases permeability -slow reaction |
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What is fly ash? |
waste ash from burning of coal (reacts with Ca(OH)2 to produce additional CSH - increases durability -decreases permeability-slow reaction ** used to reduce heat of hydration in large structures such as dams, raft foundations, and bridges |
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What does air entrainer do? |
- Improves workability - Lowers comp. strength - Provide durability in terms of freeze thaw |
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Whatis a water reducer? How does it work? |
- Absorbs on surface of cement particle (negativecharge) - Lets particles slide easier - To get to a certain slump |
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Whatis superplasticizer? |
- High range water reducer - Can create flowing concrete without segregation |
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What is retarder? |
- Delay setting or hardening rate - For long delivery times |
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Whatis accelerator? |
- Early hydration (setting) - Early strength gain |
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What is corrosion inhibitor? How does it work? |
- Delays time to corrode steel reinforcement- Increases chloride threshold of steel surface |
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How does shrinkage-reducing admixtures work? |
- Reducing the surface tension of the watermeniscus, reducing internal attractive forces with the pores |
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Howdoes waterproofing admixtures work? |
- Reduces permeability - Reduces absorption |
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How does central plant mixing work? |
- Ingredients mixed in central mixer and wetconcrete added into truck |
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Howdoes transit plant mixing work? |
Ingredientsadded separately in truck and mixed with truck’s drum |
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What are three different types of curing methods? |
- Early protection (misting, evaporation retarder,wind screens - Continuous moist curing (wet burlap andsprinkler, white fabric for reflection of sun) - Curing compounds (polymer film on surface,reflects sunlight) |
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List 5 factors that affect workability? |
- Water content - Aggregate characteristics - Air temp - Concrete temp - Fineness of cementing materials |
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What are advantages of reducing water content? |
- Increase strength - Lower permeability - Increased durability - Better bond between concrete and rebar - - Reduced cracking |
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What are the three different models to predict elastic modulus in concrete? |
Counto Parallel model - predicts high upper bound solution Series model - predicts lower bound solution |
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Describe the stress strain curves of aggregate, cement paste, and concrete |
Aggregate curve very steep (high stress, low strain) Cement paste has much higher strain for a given stress (depends on porosity) Concrete curve is in between (much more non-linear) |
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Typical E values for aggregate, concrete, and paste? |
45-85 GPa for Aggregate 30-50 GPa for concrete 10GPa for paste |
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What are capillary pores? |
a residue of originally filled water spaces in fresh concrete (significantly reduce strength) |
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concrete permeability comes from what factors? |
capillary pores, transition zone porosity (high influence from SCM), and microcracks |
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Three types of tests to type permeability: |
thru-put water permeability absorption tests gas permeability chloride diffusion resistivity strength |
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strength of concrete is a function of: |
strength of the paste, nature of the paste aggregate interface, nature of the microcracks, aggregate and cement characteristics, CM content, rate of loading, porosity |
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What does rate of loading have on concrete strength? |
High rate of loading yields an overestimate of the concrete strength. Normal and slow rates of loading allow microcracks to develop and rearrange the matrix |
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What increases the amount of creep in concrete? |
- high loads combined with drying - lower cement paste content **relative humidity also affects creep |
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What are 5 different crack types in concrete? |
Plastic Autogenous and chemical Drying Thermal Load induced |
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When does chemical shrinkage occur? How about Autogenous shrinkage? |
chemical shrinkage happens when the volume of products is less than the volume of reactants Autogenous shrinkage is a component of chemical shrinkage; results in external volume change (results in cracking, particularly for high cement content mixes) |
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What is plastic shrinkage? |
evaporative loss when concrete is in plastic state water goes into tension creating tensile stress in concrete (at surface) |
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When does plastic shrinkage occur? |
hot, dry, or windy conditions works with autogenous shrinkage to make cracking worse |
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What can plastic and autogenous shrinkage result in? |
reduced durability of structure aesthetic problems |
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How is plastic and autogenous shrinkage mitigated? |
early moist curing slowing rate of reaction less cement in mix |
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What is drying shrinkage? |
time dependent strain due to loss or gain of water |
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How are thermal cracks made? |
heat generated during cement hydration differential thermal expansion between interior and exterior of element |
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Name three different types of concrete cracks? |
surface cracks, shallow v-shaped (plastic) , deep (drying, thermal, load) |
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What are the benefits of silica fume? |
high strength low water permeability improved cohesion or stickiness high chemical resistance |
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What are the main steps to the cement making process? |
Pre heating, dewatering, calcination (Ca(OH)2 converted to CaO) Sintering in kiln to produce clinker Grinding to fine powder, and adding gypsum, limestone, and possible SCM |
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Which elements lower kiln temperature? |
Al and Fe |