Term
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Definition
Tricalcium silicate
3CaO SiO2
initial strength of the cement (first 28 days) |
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Term
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Definition
Dicalcium silicate
2CaO SiO2
Final Strength
greater resistance to chemical attack
less drying shrinkage |
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Term
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Definition
Tricalcium aluminate
3CaO Al2O3
Extremely exothermic
least stable- quick setting
susceptible to surface attack |
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Term
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Definition
Tetracalcium aluminoferrite
4CaO Al2O3 Fe2O3
less important than other compounds
medium rate of reaction |
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Term
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Definition
relates to the size of cement particles
greater surface area of a given volume means greater hydration |
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Term
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Definition
| chemical combination of cement and water |
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Term
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Definition
Hydration products
CH- negligible cementing property |
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Term
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Definition
added to concrete mix to converty CH to CSH
fly ash |
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Term
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Definition
reaches the max 2-4 days after casting
as high as 45F
can result in microcracking. |
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Term
| factors affecting heat of hydration |
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Definition
size of structure
type of formwork
rate of placing concrete
ambient conditions (freezing/high heat) |
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Term
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Definition
| noticeable stiffening of cement paste |
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Term
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Definition
| final hardening process responsible for strength of concrete |
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Term
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Definition
rapid stiffening with excessive heat generation
remedied by addition of water and re-agitating the mixture |
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Term
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Definition
produces rapid stiffening with no excessive heat
remedied by remixing |
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Term
| compressive strength test |
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Definition
24 hour curing time
2in mortar cube |
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Term
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Definition
prism 40x40x40mm
center point loading
"cement biscuit" |
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Term
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Definition
excessive change in volume(expansion) leads to unsoundness
long term surface cracking & disintegration |
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Term
| properties of fresh concrete |
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Definition
easily mixed & transported
uniform within each batch/between batches
flow properties to completely fill forms
ability to be fully compacted
no segregation between placement & consolidation
capable of a good finish |
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Term
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Definition
used to predict strength of concrete
slump cone & apparatus
generally 2-4 inches |
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Term
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Definition
| measure of concrete wetness or fluidity |
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Term
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Definition
| includes: consistency mobility & compact ability |
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Term
| properties of fresh concrete |
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Definition
depends on water content
workability decreases with increase in fineness of cement
workability increased when max size of aggs increase
workability decreased with increased temp, humidity & wind velocity |
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Term
| air content in fresh cement |
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Definition
reduced by use of tiny air bubbles
can lead to micro cracking with freezing/thawing |
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Term
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Definition
function of:
air content
size distribution of air bubbles
shape & spacing of bubbles |
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Term
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Definition
| indication of final finish of concrete |
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Term
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Definition
| volume reduction in concrete due to settlement of solids and loss of water |
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Term
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Definition
reduction of volume of wet concrete
leads to surface cracking, usually over large surface areas |
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Term
| methods of minimizing plastic shrinkage |
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Definition
cooling of concrete during mixing
using sun shades
spraying a curing compound
covering concrete with plastic sheets
h20 reducing and air entraining admixtures |
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Term
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Definition
hexagonal pattern of surface cracking at early age
due to improper finishing & curing |
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Term
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Definition
occurs in hardened concrete due to loss of water from cement gel
gradual shrinkage |
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Term
| influencing factors of drying shrinkage |
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Definition
type & amount of cement
mix proportions
size & shape of structure
curing & environment conditions
reinforcement
water/cement ratio (increased=increased shrinkage) |
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Term
| ways to control shrinkage cracks |
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Definition
high pressure steam
synthetic fibers in concrete
reinforcement controls location of cracking |
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Term
| compressive strength equation |
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Definition
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Term
| failure modes in compression |
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Definition
material failure
structural failure
both |
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Term
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Definition
| usually not measured directly, instead the split cylinder test is used |
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Term
| tensile strength equation |
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Definition
ft=2Pmax/(piLD)
ft=6.7(sqrt(fc')) |
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Term
| flexural strength of hardened concrete |
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Definition
third point loading (4-point loading)
center point loading (3-point loading) |
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Term
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Definition
third point loading
fr=PL/Bd2
MOR= 12(sqrt(fc')) |
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Term
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Definition
center point loading
fr= 3PL/2Bd2 |
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Term
| modulus of elasticity for concretes |
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Definition
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Term
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Definition
| ability to resist deterioration from weathering and traffic |
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Term
primary causes of deterioration
Key affecting factors |
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Definition
alkali-aggretion reaction
freeze thaw cycles
sulphate attack
permeability
compressive strain |
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Term
| alkali-aggregate reaction |
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Definition
chemical reaction resulting in swelling of aggs & cracking
aggregates with silica in active state
controlled by fly ash & ground blast furnace slag |
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Term
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Definition
cracking due to water getting in small cracks and expanding when frozen
can be reduced by scaling-covering in thing mortar layer |
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Term
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Definition
sulphates in soil & water react with cement resulting in expansion and cracking
can be controlled with fly ash and other admixtures
Mg-sulphate-- most aggressive |
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Term
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Definition
increase of strain or deformation with time under constant loading
creep is in the cement, not the aggregates |
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Term
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Definition
higher agg content->lower creep
increase in h20->higher creep
rate of creep increases with increased temp
higher in wet than dry conditions
elastic recovery, delayed recovery & reversible creep |
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Term
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Definition
any material added other than cement, water and aggregates.
used to modify fresh concrete properties |
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Term
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Definition
water reducing
retarding
accelerating
water reducing and retarding
fly ash
slag
fibers |
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Term
| reasons for using admixtures |
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Definition
increase workability without increasing h20
decrease water without decreasing workability
retard or accelerate setting time
reduce segregation
improve pump ability
reduce rate of slump loss |
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