concrete composition

8/8/2019 Concrete Composition

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DefinitionDefinitionConcrete is a composite material composed of coarsegranular materials embedded in a hard matrix of material

that fills the space between aggregate particles and glues

them together.

ConcreteFillerBinder

Concrete

Cement Paste

Cement

(Admixture)

Water

Fine AggregateMortar

Coarse Aggregate22


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Composition of a Portland Cement


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Chemical Name Chemical

Formula

Shorthand

Notation

Percent by

Weight

Tricalcium silicate 3CaO SiO2 C3S 50

Dicalcium silicate 2CaO SiO2 C2S 25

Tricalcium

aluminate3CaO Al2O3 C3A 12

Tetracalcium

aluminoferrite4CaO

Al2O3Fe2O3

C4AF 8

Gypsum CaSO4H2O CSH2 3.5


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Tricalcium silicate. Hydrates and hardens rapidly and is largelyresponsible for initial set and early strength. Portland cementwith higher percentage of C3S will exhibit early strength

Tricalcium aluminate. Hydrates and hardens the quickest.

Liberates a large amount of heat almost immediately andcontributes somewhat to early strength. Gypsum is added toportland cement to retard C3A hydration. Without gypsum,C3A hydration would cause portland cement to set almostimmediately after adding water.


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Tetracalcium aluminoferrite. Hydrates rapidly

but contributes very little to strength. It use

allows lower kiln temperatures in portland

cement manufacturing. Most portland cement

color effects are due to C4AF

Dicalcium silicate. Hydrates and hardens

slowly and is largely responsible for strength

increases beyond one week

Gypsum. Used as a cement retarder


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Types of ConcreteTypes of Concrete

Unreinforced Concrete

A composite material containing aggregates

held together by a cement combined withwater to form paste.

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Reinforced Concrete

A concrete strengthened by the inclusion of metal bars, which increase the tensile strength

of concrete. Both unreinforced concrete can

be either cast in place or precast.

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Cast-in-Place Concrete

Concrete is poured onsite into a previously

erected form that is removed after theconcrete has set.

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Precast Concrete

Concrete is

molded offsite

into building

components.

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AggregatesAggregates

Fine Aggregatesless than 3/8 inch

make up about 60 to 75% ofthe total volume of concrete

becomes mortar whenmixed with cement andwater

Coarse Aggregatesmore than inchbecomes concrete when

mixed with mortar

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WaterWater

Water that is fit to drink is generally regarded

as acceptable for use in mixing concrete.

Sea water may be used for unreinforcedconcrete but never for reinforced concrete.

Should be free from acids, alkalis and organic

materials

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AdmixturesAdmixtures

Increase workability without increasing water contentor decrease water content at the same workability

Retard or accelerate time of initial setting

Reduce or prevent shrinkage or create slight expansion Modify the rate or capacity of bleeding

Reduce segregation

Retard or reduce heat evolution during early hardening

Improve impact and abrasion resistance

Inhibit corrosion of embedded metal

Produce colored concrete or mortar

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Accelerate the rate of strength development at earlyage

Increase strength

Increase durability or resistance to severe conditions ofexposure, including application of deicing salts andother chemicals

Decrease permeability of concrete

Control expansion caused by the reaction of alkaliswith potentially reactive aggregate constituents

Increase bond between existing and new concrete

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Air-entraining admixtures

Water-reducing and set-controlling admixtures

Corrosion-Inhibiting admixtures

Shrinkage-reducing admixtures

Admixtures for controlling alkali-silica

reactivity Admixtures for underwater concreting

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Water Cement RatioWater Cement Ratio

Example: A truck driver arrives on the job site

and the mix contains the following:

F

lyash725

lbs Portland Cement 6,525

lbsWater added at plant 210 gallons Free Moisture 25 gallons

Water added at site 5 gallons

Total cementitious material: 725 + 6,525 = 7,250 lbs

Total water in mix: 210 + 25 + 5 = 240 gallons

Convert gallons of water to pounds 240x8.34 = 2, 001.6 lbs

2, 001.6 (water) divided by 7,250(total cementitious material) = 0.28

0.28 is the water/cement ratio for this load

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Total WaterTotal Water

Total waters consist of: water added on the

job site and free moisture (water associated

with the aggregate)

Oven DriedCompletely dry

Saturated Surface DrySurface

dry but still have moisture inside

SaturatedInterior and

exterior moist, the exterior

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Total WaterTotal Water

Example

(Sand Moisture) 10, 500 lbs/ 1.05= 10, 000 lbs10, 500 lbs-10, 000 lbs = 500 lbs

(Gravel Moisture) 18, 100 lbs/1.01 = 17, 921 lbs

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End of Part IEnd of Part I

2020

concrete composition

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