Presented By:Presented By:Engineer LATIF HYDER WADHOEngineer LATIF HYDER WADHOMehran University of Engg: & Technology KhairpurMehran University of Engg: & Technology KhairpurCivil Engineering MaterialsCivil Engineering Materials11ststTerm 1Term 1ststYear B.E.CivilYear B.E.Civil
Cement:Cement is the mixture ofcalcareous, siliceous, argillaceousand other substances. Cement isused as a binding material inmortar, concrete, etc.
Chemical Composition ofcement is:Lime 63%Silica 22%Alumina 06%Iron oxide 03%Gypsum 01 to 04%
MANUFACTURING OF CEMENT:(1) Mixing and crushing of raw materialsa. Dry processb. Wet process(2) Burning(3) Grinding
(a) Dry process:In this process calcareous material such as limestone (calcium carbonate) and argillaceousmaterial such as clay are ground separately to finepowder in the absence of water and then are mixedtogether in the desired proportions. Water is thenadded to it for getting thick paste and then its cakesare formed, dried and burnt in kilns. This processis usually used when raw materials are very strongand hard.In this process, the raw materials are changed topowdered form in the absence of water.
(b) Wet process:In this process, the raw materials are changed topowdered form in the presence of water.In this process, raw materials are pulverized by usinga Ball mill, which is a rotary steel cylinder withhardened steel balls. When the mill rotates, steelballs pulverize the raw materials which form slurry(liquid mixture). The slurry is then passed intostorage tanks, where correct proportioning is done.Proper composition of raw materials can be ensuredby using wet process than dry process. Correctedslurry is then fed into rotary kiln for burning.
(b) Wet Process: Continued------This process is generally used when rawmaterials are soft because complete mixing isnot possible unless water is added.Actually the purpose of both processes is tochange the raw materials to fine powder.
(2) Burning:Corrected slurry is feed to rotary kiln, whichis a 150-500 feet long, 8-16 feet in diameterand temperature arrangement is up to 1500-1650 degree C.At this temperature slurrylosses moisture and forms into small lumps,after that changes to clinkers. Clinkers arecooled in another inclined tube similar to kilnbut of lesser length.
(3) Grinding:Now the final process is applied which isgrinding of clinker, it is first cooled down toatmospheric temperature. Grinding of clinkeris done in large tube mills. After propergrinding gypsum (Calcium sulphate Ca SO4)in the ratio of 01-04 % is added forcontrolling the setting time of cement.Finally, fine ground cement is stored instorage tanks from where it is drawn forpacking.
TYPES OF CEMENT:1. Ordinary Portland Cement2. Sulphate Resisting Cement3. Rapid Hardening Cement (or) HighEarly Strength cement4. Quick Setting Cement5. Low Heat Cement6. High Alumina Cement7. Air Entraining Cement8. White Cement
(1) ORDINARY PORTLAND CEMENT:It is the variety of artificial cement. It iscalled Portland cement because onhardening (setting) its colour resembles torocks near Portland in England. It was firstof all introduced in 1824 by Joseph Asp din,a bricklayer of Leeds, England.
Chemical Composition of O.P.Cement:O.P.C has the following approximate chemicalcomposition:The major constituents are:1. Lime (CaO) 60- 63%2. Silica (SiO2) 17- 25%3. Alumina (Al2O3) 03- 08%
Chemical Composition of O.P.Cement: Continued-------The auxiliary constituents are:1. Iron oxide (Fe2O3) 0.5- 06%2. Magnesia (MgO) 1.5- 03%3. Sulphur Tri Oxide (SO3) 01- 02%4. Gypsum 01 to 04%
(i) Lime (CaO):Lime forms nearly two-third (2/3) of thecement. Therefore sufficient quantity of thelime must be in the raw materials for themanufacturing of cement. Its proportion hasan important effect on the cement. Sufficientquantity of lime forms di-calcium silicate(C2SiO2) and tri-calcium silicate in themanufacturing of cement.Lime in excess, causes the cement to expandand disintegrate.
(ii) Silica (SiO2):The quantity of silica should beenough to form di-calciumsilicate (C2SiO2) and tri-calciumsilicate in the manufacturing ofcement. Silica gives strength tothe cement. Silica in excesscauses the cement to set slowly.
(iii) Alumina (Al2O3):Alumina supports to set quickly tothe cement. It also lowers theclinkering temperature. Alumina inexcess, reduces the strength of thecement.
(iv) Iron Oxide (Fe2O3):Iron oxide gives colour to thecement.
(v) Magnesia (MgO):It also helps in giving colour to the cement.Magnesium in excess makes the cementunsound.
(vi) Calcium Sulphate (or) Gypsum (CaSO4) :At the final stage of manufacturing,gypsum is added to increase the setting ofcement.
(2) SULPHATE RESISTING CEMENT:It is modified form of O.P.C and is speciallymanufactured to resist the sulphates. In certainregions/areas where water and soil may have alkalinecontents and O.P.C is liable to disintegrate, because ofunfavourable chemical reaction between cement andwater, S.R.C is used. This cement contains a low %ageof C3A not more than 05%.This cement requires longer period of curing. Thiscement is used for hydraulic structures in alkaline waterand for canal and water courses lining. It developsstrength slowly, but ultimately it is as strong as O.P.C.
(3) RAPID HARDENING CEMENT:This cement contains more %age of C3S and less %age ofC2S. This is infact high early strength cement. The highstrength at early stage is due to finer grinding, burning athigher temperature and increased lime content. Thestrength obtained by this cement in 04 days is same asobtained by O.P.C in 14 days. This cement is used inhighway slabs which are to be opened for traffic quickly.This is also suitable for use in cold weather areas. Onetype of this cement is manufactured by adding calciumchloride (CaCl2) to the O.P.C in small proportions.Calcium chloride (CaCl2) should not be more than 02%.When this type of cement is used, shuttering material canbe removed earlier.
(4) QUICK SETTING CEMENT:When concrete is to be laid under water,quick setting cement is to used. This cementis manufactured by adding small %age ofaluminum sulphate (Al2SO4) whichaccelerates the setting action. The settingaction of such cement starts with in 05minutes after addition of water and itbecomes stone hard in less than half anhour.
(5) LOW HEAT CEMENT:In this cement the heat of hydration isreduced by tri calcium aluminate (C3 A )content. It contains less %age of lime thanordinary port land cement. It is used formass concrete works such as dams etc.
(6) HIGH ALUMINA CEMENT:This cement contains high aluminate %ageusually between 35-55%. It gains strengthvery rapidly with in 24 hours. It is alsoused for construction of dams and otherheavy structures. It has resistance tosulphates and action of frost also.
(7) AIR ENTRAINING CEMENT:This type of cement was first of all developed in U.S.Ato produce such concrete which would have resistanceto weathering actions and particularly to the action offrost. It is found that entrainment of air or gas bubbleswhile applying cement, increases resistance to frostaction. Air entraining cement is produced by grindingminute air entraining materials with clinker or thematerials are also added separately while makingconcrete. Entrainment of air also improves workabilityand durability. It is recommended that air contentsshould be 03-04 % by volume.Natural resins, fats, oils are used as air entrainingagents.
(8) WHITE CEMENT:This cement is called snowcrete. As ironoxide gives the grey colour to cement, it istherefore necessary for white cement to keepthe content of iron oxide as low as possible.Lime stone and china clay free from ironoxide are suitable for its manufacturing. Thiscement is costlier than O.P.C. It is mainlyused for architectural finishing in thebuildings.
TO CHECK THE QUALITY OFCEMENT IN THE FILED:1.Colour greenish grey.2.One feels cool by thrusting one’s hand inthe cement bag.3.It is smooth when rubbed in betweenfingers.4.A handful of cement thrown in a bucket ofwater should float.
QUALITY TESTS OF CEMENT:(1) Fineness Test,(2) Consistency test / setting time test(3) Setting Time Test(4) Compressive strength test
(1) Fineness Test:Finer cements react quicker with water anddevelop early strength, though the ultimatestrength is not affected. However finer cementsincrease the shrinkage and cracking of concrete.The fineness is tested by:By Sieve analysis:Break with hands any lumps present in 100 gramsof cement placed in IS sieve No.9 and sieve it bygentle motion of the wrist for 15 minutescontinuously. The residue when weighed shouldnot exceed 10 percent by weight of the cementsample.
(2) Consistency Test /Setting Time Test :This test is performed to determine the quantityof water required to produce a cement paste ofstandard or normal consistency.Standard consistency of cement paste may bedefined as the consistency which permits theVicate’s plunger (10 mm, 40 to 50 mm in length)to penetrate to a point 5 mm to 7 mm from thebottom ( or 35 mm to 33 mm from top) of Vicatmould. When the cement paste is tested withinthe gauging time ( 3 to 5 minutes) after thecement is thoroughly mixed with water.Vicat apparatus is used for performing this test.
(3) Setting Time Test:In cement hardening process, two instants arevery important, i.e. initial setting and finalsetting.
Initial Setting Time:The process elapsing between the timewhen water is added to the cement andthe time at which the needle ( 1 mmsquare or 1.13 mm dia., 50 mm inlength) fails to pierce the test block ( 80mm dia. and 40 mm high) by about 5mm, is known as Initial Setting Time ofCement.
Final Setting Time:The process elapsing between the timewhen water is added to the cement andthe time at which a needle used fortesting final setting upon applying gentlyto the surface of the test block, makes animpression thereon, while the attachmentof the needle fails to do so, is known asfinal Setting Time of Cement.
(4) Compressive Strength test of Cement:This test is very important. In this test, three mouldsof (face area 50 cm2) are prepared and cured understandard temperature conditions and each cubetested by placing it between movable jaws of thecompressive strength testing machine. The rate ofincreasing load is zero in the beginning and varies at350 kg/cm2 per minute. The load at which the cubegets fractured divided by the cross sectional area ofthe cube, is the compressive strength of the cube.The average of the compressive strengths of threecubes is the required compressive strength of thecement sample.