Properties of Concrete
OverviewWhat is concrete made of?What Is Concrete Used For?Why Is Concrete Used?Why Do We Reinforce Concrete?Curing of concrete
What is concrete made of?
What is concrete made of?Concrete is basically a mixture of two components:Paste AggregatesPaste (Portland cement, water, and air) Aggregates (sand, gravel, crushed stone)
CEMENTCement (Dry powder of very fine particles) is a building material made by grinding calcined limestone and clay into a fine powderPortland Cement chemical compositionLimestone, shale and clayCaO (lime)Al2O3 (Alumina)SO3 (Sulfite)
CEMENTWhen mixed with water, forms a pasteit undergoes chemical changes (chemical reaction-Hydration)Glue paste coats all the aggregates togetherhardens and forms a solid mass
WATERWater good for drinking is good for concrete
WATERneeded for two purposes:chemical reaction with cementworkabilityonly 1/3 of the water is needed for chemical reactionextra water remains in pores and holesresults in porosityGood for preventing plastic shrinkage cracking and workabilityBad for permeability, strength, durability.
AGGREGATEScheap fillershard materialprovide for volume stabilityreduce volume changesprovide abrasion resistance
AGGREGATEAggregate are divided into two groups:Fine - AASHTO M-6 or ASTM C-33 Coarse - AASHTO M-80 or ASTM C-33
Fine aggregate consist of natural or manufactured sand with particle size up to 3/8 inch
Coarse aggregate particles are retained on the #4 sieve and range up to 6 inches
CONSTITUENTSpaste25 to 40%portland cement 7% to 15% by Vol.water 14% to 21% by Vol.Aggregates 60% to 75%coarse aggregatesFine aggregatesAdmixtures
CONSTITUENTSCement Water Air Fine Aggregate Coarse AggregateCement paste constitutes about 25% to 40% volume of concrete
AIR ENTRAINED CONCRETEWhy the difference between line #1 and line #2?Line 1, small size CA, increased H2O and cementLine 2, larger CA, less H20, air, cement
NON-AIR ENTRAINED CONCRETESimilar to Air Entrained Concrete slideSee how aggregate size impacts water demand and amount of paste in the mix CementWater Air Fine AggregateCoarse Aggregate
ADMIXTURESincrease set timedecrease set timeincrease workabilityadjust other concrete propertiesreduce water demandentrain airinhibit corrosionPlastic and hardened properties of concrete may be changed by adding admixturesAdmixtures are commonly used to:
ADMIXTURESchemicalretardersacceleratorswater reducingair entrainingmineralfly ashsilica fumeslags
QUALITY OF CONCRETEQuality of concrete depends on quality of paste and quality of aggregates
each particle of aggregate is completely coated with paste
All spaces between aggregate is filled with paste
QUALITY OF CONCRETEIs determined by:W/C Ratio Advantage of reducing waterIncreased compressive and flexural strengthlower permeabilityincreased resistance to weatheringreduced shrinkage cracking tendencies
The less water used, the better quality of concrete, provided it can be consolidated properly.
Ten cement-paste cylinders with water-cementratios from 0.25 to 0.70. The band indicates that eachcylinder contains the same amount of cement. Increasedwater dilutes the effect of the cement paste, increasingvolume, reducing density, and lowering strength.
FORMSA form is the mold for setting concrete into a desired shape
What Is Concrete Used For?
What Is Concrete Used For?Construction Material
Picture of Bench
Why Is Concrete Used?
Why Is Concrete Used?EconomicsInexpensive, readily available
Material PropertiesLong LastingMolded into a desired shapeGreat insulatorHard
Material Properties (cont.)
Great Compressive Strength (up to 8000 psi and even more than that)
Poor Tensile Strength (almost 0)Reinforcement methods ($)
Why Do We Reinforce Concrete?
Why Do We Reinforce Concrete?
Prevent cracking due to tension forces
What is the difference between tension and compression?
Why would concrete never be used in tension?
How Do We Reinforce Concrete?Steel rebarExcellent in tension, poor in compression
CURING OF CONCRETE
CURING OF CONCRETEOver time concrete will cure, which is a hardening process.Concrete has a 28 day curing time, this is the amount of time it takes to be considered completely cured
CuringCritical to durable concreteIncreases strengthDecreases permeabilityIncreases durability
Curing ConcreteHow concrete is cured:Ponding or ImmersionSpraying or FoggingWet CoveringsImpervious PaperPlastic SheetsMembrane-Forming Curing Compounds
Questions?Remember:Use Common SenseTemperature effects on your body have very similar effects on concreteIf you are not sure, ASK!!!