Cement

cement

cementBuilding materialscementTHE NAME CEMENT REFERS TO THE MATERIAL MANUFACTURED FROM LIMESTONE AND CLAY AND MADE AVAILABLE IN POWDER FORM, WHICH WHEN MIXED WITH WATER CAN SET TO A HARD DURABLE MASS EVEN UNDER WATER.

CEMENTS ARE ADHESIVE AND COHESIVE MATERIALS WHICH ARE CAPABLE OF BONDING TOGETHER PARTICLES OF SOLID MATTER INTO A COMPACT DURABLE MASS.

ASSYRIANS AND BABYLONIANS WERE PERHAPS THE FIRST TO USE CLAY AS CEMENTING MATERIAL.RECORDS SHOW THAT EGYPTIANS HAVE USED LIME AND GYPSUM AS CEMENTING MATERIALS IN THE FAMOUS PYRAMIDS.TYPES OF CEMENTNATURAL CEMENTS

PORTLAND CEMENT

HIGH ALUMINA CEMENT

SUPER SULPHATE CEMENT

SPECIAL CEMENTSNATURAL CEMENTSNATURAL CEMENTS ARE THOSE CEMENTS WHICH ARE MANUFACTURED BY BURNING AND CRUSHING THE STONES CONTAINING CLAY, CARBONATE OF LIME AND SOME AMOUNT OF CARBONATE OF MAGNESIA. THE CLAY CONTENT IN NATURAL CEMENTS IS ABOUT 20 TO 40%.

SOME OF THE IMPORTANT NATURAL CEMENTS ARE ROMAN CEMENTPOZZOLANE CEMENTMADINA CEMENTARTIFICIAL CEMENTARTIFICIAL CEMENT IS MANUFACTURED BY CALCINING AT HIGH TEMPERATURE, PROPORTIONED MiXTURES OF CALCAREOUS MATERIALS (LIME) AND ARGILLACEOUS SUBSTANCES (SILICA, ALUMINA) WITH IRON OXIDE AND THEN CRUSHING THE RESULTANT PRODUCT KNOWN AS CLINKER. ABOUT 3 TO 4% OF GYPSUM IS ADDED TO CLINKER DURING GRINDING TO REGULATE THE SETTING TIME. CLINKER IS GROUND TO A FINE POWDER. LIME (CaO) AND SILICA (SiO2) MAKE UP ABOUT 85% OF THE MASS.CALCAEOUS MATERIALS + ARGILLACEOUS SUBSTANCES + IRON OXIDEHIGH TEMPERATURECRUSHEDCLINKERCLINKER + GYPSUMGRINDINGCEMENTPORTLAND CEMENTIn india, from very early times, hydraulic lime was produced by burning kankar nodules (which is lime mixed with clay). Such hydraulic lime was used for the construction of ancient irrigation works in india. John smeaton, A british engineer, who in 1756, patented the artificial production of cement obtained by heating a mixture of lime and clay (Portland cement).The modern method of manufacture was later patented by joseph aspdin in leeds (england) in 1824.Manufacturing of cement was started in india in 1904 but was fully established only in 1912.

PORTLAND CEMENTOrdinary Portland cement (o.p.c.) (80 to 90% of construction work is done with the o.p.c.)Rapid hardening cementExtra rapid hardening cementQuick setting Portland cementLow heat Portland cementPortland blast furnace slag cementPortland pozzolana cementSulphate resisting Portland cementWhite and coloured Portland cementAir entraining Portland cementHydrophobic Portland cement

Ingredients of Portland cementPrincipal raw materials: argillaceous or silicates of alumina in form of clay and shales. calcareous or calcium carbonate in form of lime stone, chalk and marl which is a mixture of clay and calcium carbonate. IngredientNormal range (%)Typical composition (%)Lime (CaO)60 7062Silica (SiO2)17 2522Alumina (Al2O3)3 85Iron oxide (Fe2O3)0.5 63Magnesia (MgO)0.1- 4 2Sulphur Trioxide (SO3)1 31Soda and/or Potash (Na2O + K2O)0.5 1.31Calcium sulphate (CaSO4) (gypsum)3 - 54Total100Functions of the ingredientsLime:It controls strengthit is a major ingredient of cement and constitutes about two-third of cement. Its quantity should be maintained very carefully, as excess quantity and low quantity of lime are both harmful to cement.if it is used in excess quantity, some of lime remains un-used or uncombined or as free lime. This free lime takes more time to hydrate which cause more expansion of hardened cement leading to cracks.If lime is low in quantity, the mix will be improper which will lead to low strength of cement as this cement will set quickly.SilicaIt gives strengthIt constitutes about one-fifth of cement.Its presence in proper quantity forms calcium silicates which give strength to cement.If silica is used in excess quantity, the setting time of cement is increased and the strength is increased.

Functions of the ingredientsAlumina:It is responsible for quick setting.Alumina is about 6-7% of cement.It reacts with water very quickly and makes the cement to set quickly.If it is used in excess quantity it will weaken the cement as it acts as flux which lowers the temperature.But since high temperature is essential for proper cement, it should not be used in excess.Iron oxide:It gives colour and helps in fusion of different ingredients.It reacts with lime and silica during manufacture which reduces the calcination temperature.Its presence also imparts strength to the cement (hardness)Sulphur trioxide:it makes cement sound.It is used upto 3% If it is used in excess it produces expansion of cement thus making it unsound.Also excess of sulphur trioxide increases the setting time.Functions of the ingredientsAlkalies (soda and potash):These are residuesThe quantity of alkali in cement is very less but they cause number of damages mostly by reacting with the aggregates.If it is present in excess in cement they cause efflorescence and staining in concrete, brick work and masonry mortar.Calcium sulphate:It increases the initial setting time of cementIt is about 3% of cementIf gypsum is not added, the cement will set at the moment water is added to it, without giving any time for mixing and placing.Harmful constituents of cement:Only alkali oxides and magnesium oxide adversely affects the quantity of cement.If alkali oxides present in cement is more than 1% it renders cement unsound.It magnesium oxide present in cement exceeds 5%, it leads to crack after hardening of cement mortar or concrete.

COMPOSITION OF CEMENT CLINKERTHE COMPOUNDS FORMED IN THE BURNING PROCESS HAVE THE PROPERTIES OF SETTING AND HARDENING IN THE PRESENCE OF WATER. THEY ARE KNOWN AS BOGUE COMPOUNDS.COMPOUNDCHEMICAL FORMULANAMESYMBOLTRICALCIUM SILICATE3CaO.SiO2

ALITEC3S

DICALCIUM SILICATE2CaO.SiO2

BELITEC2S

TRICALCIUM ALUMINATE3CaO.Al2O3

CELITEC3A

TETRACALCIUM ALUMINO FERRITE4CaO. Al2O3.Fe2O3

FELITEC4AF

Scanning Electron Microscope (SEM)X-ray powder diffraction (XRPD)X-Ray Florescence (XRF)TRICALCIUM SILICATE:IT IS ABOUT 25-50% (NORMALLY ABOUT 40%) OF CEMENT.IT INCREASES RESISTANCE TO FREEZING AND THAWING, HYDRATES RAPIDLY GENERATING HEAT AND DEVELOPES AN EARLY HARDNESS AND STRENGTH.THE RAISING OF ALITE CONTENT BEYOND THE SPECIFIED LIMITS INCREASES THE HEAT OF HYDRATION AND SOLUBILITY OF CEMENT IN WATER.IT IS MAINLY RESPONSIBLE FOR 7 DAY STRENGTH AND HARDNESSDICALCIUM SILICATE:IT IS ABOUT 25-40% (NORMALLY ABOUT 32%) OF CEMENT.IT IMPARTS RESISTANCE TO CHEMICAL ATTACK.RAISING OF BELITE CONTENT REDUCES THE EARLY STRENGTH, DECREASES RESISTANCE TO FREEZING AND THAWING AT EARLY AGES AND DECREASES HEAT OF HYDRATION.THE HYDROLYSIS OF BELITE PROCEEDS SLOWLY.AT EARLY AGES, LESS THAN A MONTH, BELITE HAS LITTLE INFLUENCE ON STRENGTH AND HARDNESS. WHILE AFTER ONE YEAR, IT CONTRIBUTION TO THE STRENGTH AND HARDNESS IS PROPORTIONATELY ALMOST EQUAL TO ALITE.TRICALCIUM ALUMINATE:IT IS ABOUT 5-11% (NORMALLY ABOUT 10.5%) OF CEMENT.CELITE IS RESPONSIBLE FOR THE INITIAL SET, HIGH HEAT OF HYDRATION AND HAS GREATER TENDENCY TO VOLUME CHANGES CAUSING CRACKING.RAISING OF CELITE REDUCES THE SETTING TIME, WEAKENS RESISTANCE TO SULPHATE ATTACK AND LOWERS THE ULTIMATE STRENGTH, HEAT OF HYDRATION.TETRACALCIUM ALUMINO FERRITE:IT IS ABOUT 8-14% (NORMALLY ABOUT 9%) OF CEMENT.IT IS RESPONSIBLE FOR FLASH SET BUT GENERATES LESS HEAT.RAISING OF FELITE CONTENT REDUCES THE STRENGTH SLIGHTLY.MANUFACTURING OF CEMENTThe main operations involve in manufacture of cement are:Mixing of raw materialsBurningGrindingWhen the raw materials are mixed in dry condition, the process of manufacturing is termed as dry processWhen the raw materials are mixed in wet condition, the process of manufacturing is termed as wet processDry process of manufacturing of cementCalcareous matterArgillaceous matterCrushingFine grinding in ball/tube milsStorageCrushingFine grinding in ball/tube milsStorageMixing in correct proportionStorage of raw mixRotary kilnFormation of clinkersCoolersGrinding of clinkerGypsumCoal dustwet process of manufacturing of cementCalcareous matterArgillaceous matterCrushingStorageWashing in wash millsStorageChannelGrinding millFormation of slurryCorrecting basinStorage tankRotary kilnFormation of clinkersCoolingGrinding of clinkerStorage in silosCoal dustgypsumRapid hardening cementThis cement is also known as high early strength cement.The initial and final setting times of this cement are the same as those of OPC.It contains more lime content than the Opc.The cement was burned at high temperatures. It is ground finer, possesses more alite (to the extent of 56%) and less belite than the OPC.The 3-day strength is about the same as 7-day strength of OPC.It is used fro road work where it is imperative to open the road traffic with the minimum delay.It is light in weightIt is not damaged easilyRequires short period of curing

Extra Rapid hardening cementIt is obtained by inter-grinding calcium chloride with rapid hardening cement. The normal addition of calcium chloride is 2% (of the commercial 70% calcium chloride) by weight of the rapid hardening cement.This cement should be placed and fully compacted within 30 minutes of mixingQuick setting cementThis cement is produced by adding a small percentage of aluminium sulphate and by reducing gypsum (or retarder) content and finely grinding the cement.The setting action of cement starts within 5 minutes after addition of water and it becomes hard like stone in less than 30 minutes or so.This cement is used to lay concrete under static water or running water.Low heat Portland cementWhen concrete is poured in any structure , an increase in temperature occurs and a certain amount of heat is generated. This is due to chemical reaction that takes place while the cement is setting and hardening.To reduce the temperature, the celite component in cement is minimized and a high percentage of belite and felite are added.The rate of development of strength is slow but the ultimate strength is same as that of opc.The initial setting time is about 1 hour and the final setting time is about 10 hours.This cement is mainly used for mass concrete work

Portland blast furnace cementThis cement is made by inter grinding Portland cement clinker and granulated blast furnace slag of high lime content. The proportion of slag being not less than 25% or more than 65% by weight of cement. This cement can be used in all places where opc is used. Because of low heat of hydration, it can also be used for mass concreting.The properties may be same as opc.The strength in early stages is less, so requires more curing.Pozzolana cement it is manufactured either by inter grinding Portland cement clinker and pozzolana or intimately and uniformly blending Portland cement and fine pozzolana. The pozzolana used in the manufacturing of pozzolana cement in india is, at present, burnt clay or shale, or fly ash.This cement has higher resistance to chemical agencies sulphates and to attack by sea water, because of absence of free lime.It has lower heat of evolution.Rate of gain of compressive strength is slower.It has higher tensile strength to expansion.It imparts higher degree of water tightness.It is relatively cheaper than opc.Sulphate resisting cementIt is special opc with less than 5% alite and are superior in resisting against sulphates.Cements called birla coastal comes in this category.Hydrophobic cementThus cement contains hydrophobic admixtures (like acidol, naphthene soap, oxidized petrolatum) which forms a thin film around cement particles, thus decreasing the wetting ability of the cement particles. This cement is not damaged during storage even under humid conditions.The rate of gain of strength is low in the initial period, though the 28 day strength is nearly equal to that of opc.The fine pores in concrete are uniformly distributed and thus the frost resistance and the water resistance of such concrete are considerably increased. High alumina cementThis cement is produced by grinding clinkers formed by calcining bauxite and lime. Total alumina content should not be less than 32% The ratio by weight of alumina to the lime should be between 0.85 and 1.30.The initial setting time of this cement is more than 3 hours.The final setting time is about 5 hours.It allows more time for mixing and placing operations.It resists the action of acids.It evolves great heat.Special cementsMasonry cementAccording to wuerpel, most successful masonry cement are composed of Portland cement clinker, lime stone, gypsum and air-entraining agent.The plasticity and workability of masonry cements are imparted by the lime stone and air-entraining agents.Trief cementThis is practically the same as blast furnace cement except that the blast furnace slag is ground wet and separately from the cement.This cement has smaller shrinkage and a smaller heat of evolution while setting than opcExpansive cementExpansive cement expands while hardening. (ordinary concrete shrinks while hardening)Oil well cementsIn the drilling of oil wells, cement is used to fill the space between the steel lining tube and the wall of the well, and to grout up porous strata and to prevent water or gas from gaining access to oil-bearing strata.This cement is capable of being pumped for up to 3 hoursIt hardens quickly after settingThis is manufactured by adjusting the composition of cement and by adding retarders to opc

acid resistant cementThis cement is composed of acid resistant aggregates such as quartz, quartzites etc., sodium fluosilicate and aqueous solution of sodium silicate (soluble glass)Kuhl cementThis cement has low silica content, high alumina content, and high iron content.This cement is similar to rapid hardening cements with respect to their strength.Erz and farrari cementThese cements contain high iron oxides.These cements possesses high resistance to chemical attack.Soreloc cements (magnesium oxychloride cements)This cement is obtained by magnesia and reacting magnesium chloride solution.It is not water resistant.Wax protection is given to these cements on the surface when they are used as flooring material.Field testsColoue: uniform, grey colour with a light greenish shadePhysical properties: Smooth, earthy smellIf hand is inserted in a bag or heap of cement, it should feel cool.Presence of lumpsstrength

Laboratory testsChemical compositionFinenessCompressive strengthTensile strengthConsistencySetting timessoundnessStoring of cementMoisture: if moisture is kept away from cement, it is found that cement will maintain its quality for in definite period.an absorption of 1 to 2% of moisture has no appreciable effect on quality of cementIf moisture absorption exceeds 5%, the cement becomes totally uselessPeriod of storageIt is advisable to avoid storage of cement in jute bags for a period longer than 3 monthsPilesIt is economical to form a pile of 10 bags of cement.A distance of about 300mm should be kept between the piles of cement bags and exterior walls of buildingThe passages of width about 900m should be provided between the pilesFor long storage, the top and bottom of piles should be covered with water proof paper.Quality of cementThe cement which is finely ground is more active and consequently, it absorbs moisture rapidly.Removal of cementThe rule of first in, first out should be followedStorage shedsThe walls, roof and floor of sheds should be of water-proof construction.few small windows should be provided and they should be kept tightly shut.The floor should be provided above ground level. Drainage should be provided, if necessary Storage of cementStorage for a long periods should be avoided and storage during rainy season should be as minimal as possible. The shed size is designed usually to hold the maximum quantity of cement to be used in any two consecutive weeks.Godowns should never be damp and cement bags should not be piled against the wall. A space of 60cm all-round should be the left between the exterior walls and the stacks. The distance between two consecutive stacks should be the minimum to reduce circulation of air.They should be piled off the floor on wooden planks so as to be clear of the floor by at least 10 to 20cm.The number of bags in one pile should not usually be more than to 10 to avoid lumping under pressure. Otherwise, it may also become cumbersome to stack or remove them. Owing to pressure on the lower layer of bags, the cement may develop what is known as warehouse pack. This can be removed by rolling the bag when it is taken out of the stack for use. On account of warehouse pack, the bags need not be moved and restacked, as there is no advantage in doing so.If the pile is to be more than 7 bags high, then the bags may be arranged in header and stretcher fashion (that is alternatively lengthwise and crosswise) so as to tie the piles together and to lessen the danger of toppling over.For safety during rains or when storing cement for unusually long periods, the stack should be enclosed completely in 700 gauge polythene sheet, tarpaulin or any other suitable water-proofing material. The flap should be completely closed on top of the stack.While removing bags from storage, the older cement should be removed first. For this purpose, each consignment as it comes should be stacked separately and a placard indicating the date of arrival should be pinned into the pile.Bags should be removed from two or three tiers rather than all from one tier. If the piles are thus stepped back, then there is less chance of overturning to occur. While removing the bags, the first in, first out rule should be applied.If different brands of cement are meant to be used on one work, they should be stacked separately. Cement which has become caked or in any way damaged shall, on no account, be used on the work.The weight of Portland cement for standard data purposes is taken as 1430kg per cubic meter. One tonne of cement shall comprise of 20 bags, each bag weighing 50kg. Each bag can be assumed to contain 0.035 cubic meter or 35 litres and 1.25Cft of cement in volume