construction for architecture

8/10/2019 construction for architecture

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LECTURE 1SBEA3723

STRUCTURE AND CONSTRUCTION 2

ASSOC. PROF. DR. MAHMUD BIN MOHD JUSAN


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HISTORICAL NOTES

Concrete was used by the ancient Egyptian 4000 years ago,using calcined impure gypsum.

The Greeks and the Romans used calcined limestone. Later,sand and crushed stone or brick and broken tiles were added to

lime and water. For underwater construction the Romans mixed together lime

with a vocanic ash or finely ground burnt clay tiles. The mixturewas known as pozzolanic cement, derived from the name of theplace where it was originated.

The cement was used as mortar for masonry bonding. Now the

name of pozzolanic cement is referring to the naturalcementitious materials ground at normal temperature


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In the 18th, John Smeaton developed the first hydraulic cementby mixing pozzolana with limestone containing high proportionof clay.

In1824 Joseph Aspdin developed a type of cement by heating a

mixture of clay and limestone in a furnace until CO2 had beendriven off. The prototype of modern cement was made in 1845 by Isaac

Johnson by burning a mixture of clay and chalk until clinkering. A strongly cementitious compound was produced.

The name Portland cement, given originally due to the

resemblance of the colour and quality of the set cement toportland stone a limestone quarried in Dorset. In 1854, William Wilkinson introduced the use of reinforcement

bar to overcome the low tensile strength of concrete.


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BINDER

Binder is a substance which sets and hardensindependently, and can bind other materials together

Cement is a binder Cements used in construction are characterized as

hydraulic or non-hydraulic. The most important use of cement is the production

of mortar and concrete.


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BINDER

Hydraulic cements are materials that set and hardenafter being combined with water.

Most construction cements today are hydraulic, andmost of these are based on Portland cement.

Modern cements are made by burning limestone andclay together at very high temperatures ranging from1400 to 1600


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BINDER

Non-Portland Hydraulic Cements Calcium aluminates (CAC) or high alumina

cement (HAC). Calcium aluminate cements

evolved from a drive to develop sulphate resistantcements. Pozzolan-lime cements. Mixtures of ground

pozzolan and lime. Used by the ancient Romans.Develop strength slowly, but their ultimate strengthcan be very high.

Slag-lime cements. Ground granulated blastfurnace slag, activated by addition of alkalis,mostly using lime. They are similar to pozzolanlime cements in their properties.


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BINDER

Supersulfated cements. contain about 80% groundgranulated blast furnace slag (80%) + gypsum (15%)and a little Portland clinker or lime as an activator

non-hydraulic cements Cements that do not setunder water. They were amongst the most commonlyused cement in the ancient Roman, using lime basedcements and mortars (cement + sand). Gypsum, lime, also sulphur cement


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PORTLAND CEMENT

Portland Cement is made by heating limestone withsmall quantities of other materials (such as clay) to1450C in a kiln. The resulting hard substance, called

clinker, is then ground with a small amount ofgypsum into a powder to make Ordinary PortlandCement, the most commonly used type of cement(often referred to as OPC).


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CONSTITUENT OF PORTLAND CEMENT

Cement Compound WeightPercentage Chemical Formula

Tricalcium silicate 50 % Ca 3SiO 5 or 3CaO .SiO 2 (C3S)

Dicalcium silicate 25 % Ca 2SiO 4 or 2CaO .SiO 2 (C2S)

Tricalcium aluminate 10 % Ca 3Al2O 6 or 3CaO .Al2O3 (C3A)

Tetracalciumaluminoferrite 10 %

Ca 4Al2Fe 10 or4CaO .Al2O 3.Fe 2O 3

(C4AF)

Gypsum 5 % CaSO 4.2H 2O


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TYPES OF PORTLAND CEMENT

Ordinary Portland (Type I) Cement Modified Portland (Type II) Cement

Rapid-Hardening Portland (Type III) Cement Low-Heat Portland (Type IV) Cement Sulphate-Resisting (Type V) Cement


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TYPES OF PORTLAND CEMENTS

Ordinary Portland Cement (OPC) suitable for all uses where the special properties

of other types are not required.

It is used where cement or concrete is not subjectto specific exposures, such as sulfate attack fromsoil or water, or to an objectionable temperaturerise due to heat generated by hydration.

Its uses include pavements and sidewalks,reinforced concrete buildings, bridges, railwaystructures, tanks, reservoirs, culverts, sewers,water pipes and masonry units.


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TYPES OF PORTLAND CEMENTS

Rapid Hardening Portland Cement (RHPC) RHPC is a high-early strength Portland cement

that provides high strengths at an early period,usually a week or less.

It is used when forms are to be removed as soonas possible, or when the structure must be put intoservice quickly.

In cold weather, its use permits a reduction in thecontrolled curing period.


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Low-Heat Portland Cement (LHPC) LHPC is a low heat of hydration cement for use

where the rate and amount of heat generatedmust be minimized. It develops strength at a slower rate than OPC. LHPC is intended for use in massive concrete

structures, such as large gravity dams, where thetemperature rise resulting from heat generatedduring curing is a critical factor.


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Sulphate Resisting Portland Cement (SRPC) SRPC is used only in concrete exposed to severe

sulfate action -- principally where soils orgroundwaters have a high sulfate content. LowTricalcium Aluminate (C3A) content, generally 5%or less, is required when high sulfate resistance isneeded.


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Modified Portland Cement (MPC) MPC is used where precaution against moderate

sulfate attack is important, as in drainage structureswhere sulfate concentrations in groundwaters arehigher than normal but not unusually

generate less heat at a slower rate than OPC. can be used in structures of considerable mass, such

as large piers, heavy abutments, and heavy retainingwalls. Its use will reduce temperature rise, animportant quality when the concrete is placed inwarm weather.


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White Portland Cement For decorative purposes

Used because of its low content of solublealkalis thus able to avoid staining Made from china clay, which contains little

iron oxide and manganese oxide, together

with chalk or limestone free from specifiedimpurities

expensive


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PORTLAND CEMENT BLENDS

Portland Blast furnace Cement contains up to 70% ground granulated blast

furnace slag, with the rest Portland clinker and alittle gypsum. All compositions produce high ultimate strength,

but as slag content is increased, early strength isreduced, while sulfate resistance increases andheat evolution diminishes.


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Portland Flyash Cement contains up to 30% fly ash. The flyash is

pozzolanic, so that ultimate strength is maintained. Because flyash addition allows a lower concretewater content, early strength can also bemaintained.

Where good quality cheap flyash is available, thiscan be an economic alternative to ordinaryPortland cement.


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Portland Pozzolan Cement Other than Flyash, volcanic ashes are also used

for portland cement blend (commonly used incountries where volcanic ashes are easily

available e.g. Italy, Chile, Mexico, the Philippines)

Portland Silica Fume cement. Addition of silica fume can yield exceptionally high

strengths, and cements containing 5-20% silicafume are occasionally produced.

However, silica fume is more usually added toPortland cement at the concrete mixer


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AGGREGATE

Aggregates are chemically inert, solid bodies heldtogether by the cement.

Aggregates come in various shapes, sizes, andmaterials ranging from fine particles of sand to large,coarse rocks.

Cheaper than cement. Aggregates consist of 70 to80% of the volume of concrete thus keeping the costof the concrete low.

Aggregates influence the desired characteristics ofthe concrete e.g, the density of concrete isdetermined by the density of the aggregate.


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class examples ofaggregates used uses

ultra-lightweight

vermiculiteceramic spheresperlite

lightweight concrete which can be sawed or nailed, also for its insulatingproperties

lightweight

expanded clay

shale or slatecrushed brick

used primarily for making lightweight concrete for structures, also usedfor its insulating properties.

normalweight

crushed limestonesandBasaltGranite river gravelcrushed recycledconcrete

used for normal concrete projects / dense concrete

heavyweight

steel or iron shotsteel or iron pellets

used for making high density concrete for shielding against nuclearradiation

CLASSES OF AGGREGATES


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CLASSES OF AGGREGATES

Commonly used aggregates in Malaysia are granite,lime stone and conglomerate


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SIZES OF AGGREGATE

Concretes are made of 10mm to 50mm aggregates. Aggregate sizes are divided into 2 classes :

less than 5 mm : fine aggregate5 mm and above : coarse aggregate


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ADMIXTURE

Admixtures are substances other than the keyingredients or reinforcements which are added duringthe mixing process to change some of the properties

of the plastic or hardened concretes.Types of admixture include: - Accelerators: speed up the hydration (hardening)

of the concrete.

Retarders: slow the hydration of concrete, and areused in large or difficult pours where partial settingbefore the pour is complete is undesirable.


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ADMIXTURE

Air-entrainers: add and distribute tiny air bubbles inthe concrete, which will reduce damage duringfreeze-thaw cycles thereby increasing the concrete'sdurability.

Plasticizers: (water-reducing admixtures) increasethe workability of plastic or "fresh" concrete, allowingit be placed more easily, with less consolidatingeffort.

Superplasticizers (high-range water-reducingadmixtures) are a class of plasticizers which havefewer deleterious effects when used to significantlyincrease workability. Also able to reduce the watercontent of a concrete while maintaining workability .


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ADMIXTURE

Pigments: can be used to change the color ofconcrete, for aesthetics.

Corrosion inhibitors: are used to minimize the

corrosion of steel and steel bars in concrete. Bonding agents are used to create a bond between

old and new concrete. Pumping aids improve pumpability, thicken the paste,

and reduce dewatering of the paste.


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TYPE FUNCTION

AIR ENTRAINING improves durability, workability, reduces bleeding, reduces freezing/thawingproblems (e.g. special detergents)

SUPERPLASTICI

ZERS

increase strength by decreasing water needed for workable concrete (e.g. special

polymers)

RETARDING delays setting time, more long term strength, offsets adverse high temp. weather(e.g. sugar, lignosulphonic acids)

ACCELERATING speeds setting time, more early strength, offsets adverse low temp. weather (e.g.calcium chloride)

MINERALADMIXTURES

improves workability, plasticity, strength (e.g. fly ash)

PIGMENT adds color (e.g. metal oxides)

SOME ADMIXTURES AND FUNCTIONS


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WATER

Water is the key ingredient, which causes thehardening of concrete through a chemical reactioncalled hydration.

The water needs to be pure, to prevent side reactionsfrom occurring which may adversely affect stengthand durability of the concrete

The role of water is important because the water tocement ratio is the most critical factor in theproduction of "perfect" concrete


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CHEMISTRY OF CONCRETE

When water is added to cement, a chemical reactionbegins immediately and continues a long as water ispresent.

The chemical reaction is known as hydration . In thisprocess cement grains (tricalsium silicate anddicalcium silicate ) are transformed into cement gel(calcium silicate hydrate) which later binds theaggregates. The reaction also produces calcium andhydroxide ions which increases the pH to over 12. There is no (or very little thus negligible) chemical

reaction between aggregate and cement.


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SETTING AND HARDENING In the presence of water, concrete mixture will

undergo 3 different stages: -

Plastic Setting Hardening


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Plastic state is a short moment immediately afterwater is added into the mixture.

Setting takes place around 45minutes (60 minutes forlow-heat Portland cement) after water is added. Atthis stage, concrete begins to stiffen (depending uponthe hydration heat and the surrounding temperature)

This is the stage where formwork plays itsimportant functions to shape and to ensure thequality of the structure.


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cement requires time to acquire strength andhardness, concrete must be cured once it has beenplaced and achieved initial setting.

Curing is the process of keeping concrete under aspecific environmental condition until hydration isrelatively complete.

Good curing is typically considered to provide a moistenvironment and control temperature. A moistenvironment promotes hydration thus ensuresstrength and durability of concrete .


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concrete environment is alkali that is safe forreinforcement bar


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TYPES OF CONCRETE

Based on methods of concrete production :- In-situ- Precast / Prefabricated


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TYPES OF CONCRETE

Based on concrete density Dense concrete

Dense concrete are those exceeding 2000 kg/m 3. lightweight concrete

Lightweight concrete are those with density lessthan1920 kg/m 3

Types of Lightweight concrete

Aerated Concrete (cellular concrete) Light weight Aggregate Concrete No Fine Concrete

http://www casthome com/about html


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http://www.casthome.com/about.htmlWhat is LCM lightweight concrete methods andhow is it produced?

It is Mortar + Foam : It can be produced at the project site likeordinary concrete. The only difference is that it does not usecoarse aggregate, but instead, uses pre-formed foam. This foamhas no chemical action in concrete. It only serves as a temporarywrapping material for the air bubbles till cement mortar developsits own final set and strength. Hydrolysated protein base is mixand mash into a concentrated liquid call LCM Foaming agent isused to make the foam.


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TYPES OF CONCRETE

Shotcrete is a mortar or concrete that is dispensedfrom a hose onto a surface at a high velocity usingcompressed air Shotcrete is frequently used againstvertical soil or rock surfaces, as it eliminates the needfor formwork. It is sometimes used for rock support,especially in tunnelling.


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TYPES OF CONCRETE

Roller-Compacted Concrete: is a low-cement-contentstiff concrete placed using earthmoving and pavingtechniques. The concrete is placed on the surface tobe covered, and is compacted in place using largeheavy rollers typically used in earthwork. Theconcrete mix achieves a high density and cures overtime into a strong monolithic block. Roller-compactedconcrete is typically used for concrete pavement, buthas also been used to build concrete dams, as the

low cement content causes less heat to be generatedwhile curing than typical for conventionally placedmassive concrete pours.


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TYPES OF CONCRETE

Concrete Pavement: used for paving highways andairports as well as business and residential streets

Concrete Pipe: Used to provide water for people and

farmlands or carries away sewage and drains land.. Precast Concrete: Concrete that is cast outside its

service location


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TYPES OF CONCRETE

Ready Mixed Concrete:refers to concrete that isbatched for delivery from a central plant instead ofbeing mixed on the job site.

Shotcrete: is a mortar or concrete that is dispensedfrom a hose onto a surface at a high velocity.


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USE OF CONCRETE IN STRUCTURES

Mass concrete structuresThese include heavy structures like gravity dams.

Also referring to concrete structures withoutreinforcement bars

Reinforced concrete structuresReinforced concrete contains steel reinforcing that isdesigned and placed in structural members atspecific positions to cater for all the stress conditionsthat the member is required to accommodate.


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USE OF CONCRETE IN STRUCTURES

Prestressed concrete structuresThis structure provides a way to overcome thecombined tensile stresses, due to own weight anddesign loads in beams and slabs, by introducing acompressive stress in the structural element prior tothe superimposed design loads coming into play. Theprestressing is achieved by using steel tendons orbars that are subjected to a tensile force prior tocasting the concrete, in pre-tensioned concrete, or

only later once the concrete has cured, in post-tensioned concrete.


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MANUFACTURE OF CONCRETE

STORAGE OF MATERIALS

Cement should be stored of theground in well aired, clean, dryplace. Paper bags should not bestacked more than 1.2m or 1.5mhigh to avoid warehouse set caused by compaction.

Wrapping the cement bags inplastic sheets gives extraprotection. Cement in bags shouldbe stored not longer than 6 weeks.


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Silos are used to store cement in large quantities

Aggregates should be kept on clean hard surfacesand not directly on the ground. The various sizes ofaggregates should be kept separately.


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BATCHING a process to quantify the amount of materials

(cement, aggregates, water and admixture) forpreparing concrete

2 methods of batching: Volumetric weight


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Weightweighing scale is used. More accurate, and bulkingdoesnt affect the actual content of the mix.


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Mix proportion

The proportion of each material in the mixture.

It affects the properties of the final hardenedconcrete.


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Batching plant


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Batching plant


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Mix proportion 1:2:4

means

1 part of cement : 2 parts of fine aggregates : 4 partsof coarse aggregates.

Mix proportion can also be designed to a specific

strength. In this way the concrete is often recognisedbased on its designed compressive strength.


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Appropriateness of mix proportion to concrete use instructures

Mixprop.

Use

1:2:4 For normal reinforced structural used,(column, floor, beam)

1:1.5:3 For higher strength reinforced

structural used (bridge, retaining wall)

1:3:6 For component without reinforcement( ground floor slab, apron)


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Mixing of concrete Hand mixed pan mixer truck mixer (for ready mixed concrete)

Repeating mixing process Duration time 3-6 hours should be no problem to

the strength and last May cause water reduction which will reduce its

workability


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Pan mixer


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Truck mixer


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Mixing of concrete Retempering (re-adding water) is possible. However

this will reduce concretes quality due to changesin water cement ratio.

After mixing process the concrete should be pouredin formwork as soon as possible (1-2 hours) depends on the temperature of surroundingconstruction site. Hot day may cause concrete to dryfast)

Set retarder will be used to avoid concrete fromdying very fast - if the concrete cant be poureddue to the above duration of time.


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End of lecture

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