“Properties of Concrete” Introduction. Overview What is concrete made of? What Is Concrete Used For? Why Is Concrete Used? Why Do We Reinforce Concrete?

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Properties of ConcreteIntroductionOverviewWhat is concrete made of?What Is Concrete Used For?Why Is Concrete Used?Why Do We Reinforce Concrete?Curing of concreteWhat 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 massWATERWater good for drinking is good for concreteWATERneeded 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 resistanceAGGREGATEAggregate 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 inchCoarse aggregate particles are retained on the #4 sieve and range up to 6 inchesCOARSE AGGREGATEFINE AGGREGATECONSTITUENTSpaste25 to 40%portland cement 7% to 15% by Vol.water 14% to 21% by Vol.Aggregates 60% to 75%coarse aggregatesFine aggregatesAdmixturesCONSTITUENTSCement Water Air Fine Aggregate Coarse AggregateCement paste constitutes about 25% to 40% volume of concreteAIR 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, cementNON-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 AggregateADMIXTURESincrease 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 fumeslagsQUALITY OF CONCRETEQuality of concrete depends on quality of paste and quality of aggregateseach particle of aggregate is completely coated with pasteAll spaces between aggregate is filled with pasteQUALITY OF CONCRETEIs determined by:W/C Ratio Advantage of reducing waterIncreased compressive and flexural strengthlower permeabilityincreased resistance to weatheringreduced shrinkage cracking tendenciesThe 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 shapeWhat Is Concrete Used For?What Is Concrete Used For?Construction MaterialArt WorkPicture of BenchWhy Is Concrete Used?Why Is Concrete Used?EconomicsInexpensive, readily availableMaterial PropertiesLong LastingMolded into a desired shapeGreat insulatorHardMaterial 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 forcesQuestionWhat is the difference between tension and compression?QuestionWhy would concrete never be used in tension?How Do We Reinforce Concrete?Steel rebarExcellent in tension, poor in compressionCURING OF CONCRETECURING 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 curedCuringCritical to durable concreteIncreases strengthDecreases permeabilityIncreases durabilityCuring ConcreteHow concrete is cured:Ponding or ImmersionSpraying or FoggingWet CoveringsImpervious PaperPlastic SheetsMembrane-Forming Curing CompoundsQuestions?Remember:Use Common SenseTemperature effects on your body have very similar effects on concreteIf you are not sure, ASK!!!


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