ConcreteConcrete

Concrete Main Primary Concrete Main Primary IngredientsIngredients

CementCement AggregateAggregate WaterWater

CementCement

Been around for at least 2 thousand Been around for at least 2 thousand yrsyrs

Romans used them – found cements Romans used them – found cements from natural mixtures of limestone from natural mixtures of limestone and clayand clay

Portland CementPortland Cement 1824 the first modern step was taken 1824 the first modern step was taken

by Joseph Aspdin – produces a powder by Joseph Aspdin – produces a powder from limestone and clayfrom limestone and clay

Called it Portland Cement because it Called it Portland Cement because it resembled a stone quarried near resembled a stone quarried near Portland, EnglandPortland, England

Been improved since then and Been improved since then and produces under strict guidelines todayproduces under strict guidelines today

Portland Cement Portland Cement IngredientsIngredients

Lime, silica, alumina and ironLime, silica, alumina and iron 4 parts limestone to 1 part clay4 parts limestone to 1 part clay

Portland Cement TypesPortland Cement Types

1.1. 10 Normal – general work10 Normal – general work

2.2. 20 Moderate – better resistant to sulfate – 20 Moderate – better resistant to sulfate – lower temp riselower temp rise

3.3. 30 – high early strength – fast curing (cold 30 – high early strength – fast curing (cold weather)weather)

4.4. 40 – low heat – lower heat – slower curing40 – low heat – lower heat – slower curing

5.5. 50 – sulfate resistant – subject to attack 50 – sulfate resistant – subject to attack from sulfate (salt)from sulfate (salt)

Portland Cement PackagingPortland Cement Packaging

Bags – 94 pounds Bags – 94 pounds per bag – equal to per bag – equal to one cubic foot one cubic foot volumevolume

Or by the truck Or by the truck loadload

Cement AdmixturesCement Admixtures

Air entraining – contains small amounts Air entraining – contains small amounts of additives that case microscopic air of additives that case microscopic air bubbles to form the concretebubbles to form the concrete 2 to 8 percent finished volume2 to 8 percent finished volume Give improved workabilityGive improved workability Gives better resistance to freeze and thaw Gives better resistance to freeze and thaw

cyclecycle With same structural strengthWith same structural strength

AggregatesAggregates

Makes up ¾ of concrete Makes up ¾ of concrete mixturesmixtures

QualitiesQualities StrongStrong Resistant to freeze thaw Resistant to freeze thaw

cyclecycle Chemically stableChemically stable Properly sizedProperly sized

In general aggregate In general aggregate size must be no greater size must be no greater then ¾ size of the then ¾ size of the opening it needs to be opening it needs to be placed in including placed in including reinforcementreinforcement

Typical Aggregated sizesTypical Aggregated sizes

¾” –thin slabs¾” –thin slabs ¾” to 1 -1/2” – slabs structural work¾” to 1 -1/2” – slabs structural work Up to 6 in – Dams and other large Up to 6 in – Dams and other large

projectsprojects

Making and placing Making and placing ConcreteConcrete

Rules for making high quality concreteRules for making high quality concrete Use clean sound ingredientsUse clean sound ingredients Mix them in the correct proportionsMix them in the correct proportions Handle the wet concrete properly to avoid Handle the wet concrete properly to avoid

segregationsegregation Cure the concrete carefullyCure the concrete carefully

Water to cement ratio – major factor in Water to cement ratio – major factor in strength of concrete – less water strongerstrength of concrete – less water stronger

But water is needed to hydrate the mixture – But water is needed to hydrate the mixture – gives necessary fluidity and plasticity for gives necessary fluidity and plasticity for placing and finishingplacing and finishing

Absolute water-cement ratio under .60 – Absolute water-cement ratio under .60 – weight of water in mixtureweight of water in mixture

Handling and Placing Handling and Placing ConcreteConcrete

Wet concrete is not Wet concrete is not a liquid – but a slurry a liquid – but a slurry – unstable mixture of – unstable mixture of solids and liquidsolids and liquid

Segregate – move Segregate – move horizontally any horizontally any distance in formworkdistance in formwork Dropped from heightDropped from height Vibrated excessivelyVibrated excessively

Curing ConcreteCuring Concrete

Concrete cures Concrete cures through hydrationthrough hydration Must be kept moist Must be kept moist

until its required until its required strength is achievedstrength is achieved

Takes a long timeTakes a long time 28 days typically28 days typically If allowed to dry If allowed to dry

during the time it during the time it will lose strengthwill lose strength

Concrete WeightsConcrete Weights

Normal weight concretesNormal weight concretes 135 to 160 lb/ft3135 to 160 lb/ft3 Made with sand and gravel and crushed stoneMade with sand and gravel and crushed stone

Structural lightweightStructural lightweight 85 to 135 lb/ft385 to 135 lb/ft3 Made with expanded clay shale slate and slagMade with expanded clay shale slate and slag

Insulating concreteInsulating concrete 15 to 85 lb/ft315 to 85 lb/ft3 Made with prumice, scoria, prelite, vemiculite dhatomiteMade with prumice, scoria, prelite, vemiculite dhatomite

Heavy weight concreteHeavy weight concrete 175 to 400 lb/ft3175 to 400 lb/ft3 Made with hernalite, barite, limonite, iron, steelMade with hernalite, barite, limonite, iron, steel

Concrete TestingConcrete Testing

Slump testSlump test Slump cone 12 in high 8 in dia. At bottomSlump cone 12 in high 8 in dia. At bottom The cone is filled in three equal layers each being The cone is filled in three equal layers each being

tampered 25 times with a 5/8 in bullet nose tampered 25 times with a 5/8 in bullet nose tampering rodtampering rod

Cone is filled and level off it is then lifted and Cone is filled and level off it is then lifted and carefully – the amount of slump is then measuredcarefully – the amount of slump is then measured

Compressive Strength TestCompressive Strength Test Concrete specimens are usually cylindrical with a Concrete specimens are usually cylindrical with a

length equal to twice its diameterlength equal to twice its diameter The mold is filled in three equal parts and The mold is filled in three equal parts and

tampered 25 times with standard tamping rod tampered 25 times with standard tamping rod between layersbetween layers

When mold is full it is struck off and level and When mold is full it is struck off and level and covered with a glass or metal plate to prevent covered with a glass or metal plate to prevent evaporationevaporation

The specimens are removed from mold after 24 The specimens are removed from mold after 24 hours and place in the curing locationhours and place in the curing location

At the end of the curing period the specimens are At the end of the curing period the specimens are subject to a compression testsubject to a compression test

Concrete AdmixturesConcrete Admixtures

An admixture which is used to speed up the initial set of concrete is called an An admixture which is used to speed up the initial set of concrete is called an acceleratoraccelerator

Most common is calcium chlorideMost common is calcium chloride The function of a retarded is to delay or extend the setting time of the cement paste in The function of a retarded is to delay or extend the setting time of the cement paste in

concreteconcrete Used when concrete is set in hot, low humidity, and winding conditionsUsed when concrete is set in hot, low humidity, and winding conditions Most common retarders are carbohydrate derivatives and calcium liginsulfonateMost common retarders are carbohydrate derivatives and calcium liginsulfonate

The introduction of controlled amounts of air into a mix has proved to be an important The introduction of controlled amounts of air into a mix has proved to be an important advance in concrete engineeringadvance in concrete engineering

A proper amounts of air improved workability, easier placing, increased durability, better A proper amounts of air improved workability, easier placing, increased durability, better resistance to frost action, improve flow in concrete pump lines and reduction in bleeding and water resistance to frost action, improve flow in concrete pump lines and reduction in bleeding and water gain.gain.

Air entrained concrete contains microscopic bubbles of air formed with the aid of group of Air entrained concrete contains microscopic bubbles of air formed with the aid of group of chemicals called surface active agents, material which have property of reducing the surface chemicals called surface active agents, material which have property of reducing the surface tension of watertension of water

Air entrainment may have adverse effects on the strength of concrete – the decrease in strength is Air entrainment may have adverse effects on the strength of concrete – the decrease in strength is proportional to the amount of air contentsproportional to the amount of air contents

Super plasticizer – is a substance that disperse the clumps by coating each cement Super plasticizer – is a substance that disperse the clumps by coating each cement particle thus separating and dispersing the cement in the water.particle thus separating and dispersing the cement in the water.

When cement and water are mixed the cement particles tend to gather in clumps known as When cement and water are mixed the cement particles tend to gather in clumps known as cement agglomerates, this clumping action prevents through mixing of cement and water cement agglomerates, this clumping action prevents through mixing of cement and water producing a loss in the workability of the concrete mix as well as preventing complete hydration of producing a loss in the workability of the concrete mix as well as preventing complete hydration of the cement producing a less then full potential of strengththe cement producing a less then full potential of strength

To prolong the life expectancy of the concrete surface, in addition to proper curing and To prolong the life expectancy of the concrete surface, in addition to proper curing and finishing concrete hardeners are added to concrete mixfinishing concrete hardeners are added to concrete mix

Reinforcing ConcreteReinforcing Concrete

Concrete has no useful tensile strength shear and bendingConcrete has no useful tensile strength shear and bending Steel and concrete change dimension nearly at the same rateSteel and concrete change dimension nearly at the same rate Steel is protected from corrosion by the alkaline chemistry of Steel is protected from corrosion by the alkaline chemistry of

concrete plus concrete bonds strongly to steelconcrete plus concrete bonds strongly to steel Theory of concrete reinforcing is extremely simpleTheory of concrete reinforcing is extremely simple

Put steel where there is tension in the concrete memberPut steel where there is tension in the concrete member Bars are rolled into 11 standard diameters in numbers of 1/8”Bars are rolled into 11 standard diameters in numbers of 1/8”

Bar size 3 to 18Bar size 3 to 18 Bars come in 3 grades 40 -50-60Bars come in 3 grades 40 -50-60

40,000 psi40,000 psi 50,000 psi50,000 psi 60,000 psi60,000 psi

Reinforcing steel is also produced in sheets or rolls of welded wire Reinforcing steel is also produced in sheets or rolls of welded wire fabricfabric

Used to reinforce slabs on gradeUsed to reinforce slabs on grade Principal advantage is economy of labor (easy to place)Principal advantage is economy of labor (easy to place)

Precast ConcretePrecast Concrete

Advantages of PrecastAdvantages of Precast Casting and curing conditions as well as concrete design can Casting and curing conditions as well as concrete design can

be rigidly controlled, resulting in consistently high quality be rigidly controlled, resulting in consistently high quality concreteconcrete

Close supervision and control of materials and a specialized Close supervision and control of materials and a specialized work force in a centralized plant also help to produce a high work force in a centralized plant also help to produce a high quality productquality product

Finishing work on concrete surfaces can be done more easily Finishing work on concrete surfaces can be done more easily and efficiently in a plant than in position on the siteand efficiently in a plant than in position on the site

The cost of form work is reduced since it can be set up on the The cost of form work is reduced since it can be set up on the ground rather than begin suspended or supported in positionground rather than begin suspended or supported in position

Because of superior reinforcing techniques the load carrying Because of superior reinforcing techniques the load carrying ability of a member may be increase while at the same time ability of a member may be increase while at the same time reducing its dead load by reducing the amount of concrete reducing its dead load by reducing the amount of concrete requiredrequired

Plant production is not normally subject to delays due to Plant production is not normally subject to delays due to adverse weather conditions as are job site operationsadverse weather conditions as are job site operations

Precast ConcretePrecast Concrete

Precast structural members fall into Precast structural members fall into two general classificationstwo general classifications Normally reinforcedNormally reinforced PrestressedPrestressed

Prestressed broken down into two Prestressed broken down into two categoriescategories PretensionedPretensioned posttensionedposttensioned

Pre stressed ConcretePre stressed Concrete

A prestressed concrete unit is one into which A prestressed concrete unit is one into which engineered stresses have been introduced engineered stresses have been introduced before it has been subjected to a loadbefore it has been subjected to a load PretensioningPretensioning

High strength steel strands are stretched tightly then High strength steel strands are stretched tightly then concrete is pour concrete bonds together with the steel concrete is pour concrete bonds together with the steel after it has cured the concrete unit is place in after it has cured the concrete unit is place in compressioncompression

PosttensioningPosttensioning High strength steel strands are stretched tightly then High strength steel strands are stretched tightly then

concrete is poured , cured then the steel is tensioned concrete is poured , cured then the steel is tensioned usually done in placeusually done in place

Pre stressed ConcretePre stressed Concrete

There are some distinct advantages to producing There are some distinct advantages to producing architectural precast units in a central plantarchitectural precast units in a central plant Design freedomDesign freedom High degree of quality control of both the ingredients High degree of quality control of both the ingredients

and the finished techniquesand the finished techniques The shapes, sizes and configurations of units for are The shapes, sizes and configurations of units for are

building may be as diversified or similar as the designer building may be as diversified or similar as the designer wisheswishes

The possibility of including in the precast units some or The possibility of including in the precast units some or all of the services which are normally installed after all of the services which are normally installed after erectionerection

The speed at which a building can be closed in reducing The speed at which a building can be closed in reducing cost and allowing earlier access by the service trades.cost and allowing earlier access by the service trades.