> Introduction
- Cement is a general term given to the powder materials.
- Which intially have plastic flow when mixed with water or other liquids but has the property of setting to ahard solid structure in several hours with varying degrees of strength and bonding propertic
- Greeks,roman & Egyptian used volcanic staf such as pozzuolanic cement a volcanic tufa obtainear pozzuolanic in iatail.
- This types of natural cement may be regardil as a mixture of burnt duplicates & lime.
- The acidic siliceous matter combines with Ca(OH²)during the setting of natural cement.
- Portland cement is chemically defined as the finally ground mixture of calcium aluminates & silicates of varying composition which hydrate when mixed with water to from a rigid solid structure with good compressive strength.
- Portland cement is a mixture of following compound C²S, C³S, C³A, C4AF, MgO, CaO
> There are various types of portland cement some of as following
1.) High Alumina Cement ( Water proof Cement)
- High alumina cement is essentially a calcium aluminate & can be prepared by heating a mixture of lime-Stone & bauxite at 1550 - 1600°C.
- The contituens of the cement are tri calcium aluminate, di calcium silicate and di calcium aluminate.
- HAC has a very rapid rate of development of strength and superier resistance to sea & sulphar water.
2.) Hydralic Hydrated lime ( HHL)
- This cement have low priced & has good strength.
- The main constituents of hhl is C²S and C³A in this cement Ca(OH)² is a magor component while C²S and C³A are minor constituents.
3.) Pozzolan Cement
- This cement is made by 2-4 part of pozzola with one part of hydrated lime in presen of some burnt. it is mixed with portland cement as cheap extender.
> Types of Of Portland Cement
- Portland cement is of various types depending upon the rate of setting heat. evolution & strength characteristics.
- This propertis may be varying by the varying of the percentage of constituent present in cement.
- There are five types of portland cement are recognised which contain varying amounts of the clinker compound like C²S, C³S, C4AF, MgO.
I) Regular Portland Cement
- They are usual product for general concrete construction and harden to full strength in about 28-30 days.
- They contain 40-60% C³S, 10-30% C²A & 7-13% C³A. when cement, oli wall cement, quick setting cement etc also belong to this class.
II) Modified Portland Cement
- These are sulphar resisting cement which are where moderate heat of hydration is requirqd.
- The heat from this cement should exceed 70 and 80 cal/gm after one week & 4weeks respectively.
- This cement charactersed by higher C²S/C³S ratio.
III) High Early Strength Portland Cement
- The cement contain higher percentage of C³S & C³A with finer grinding to increase hydratiorate.
- The high properatio of C³S causes a quikcer hardeing than regular portland cement and thaus attains a strength of type in only three days.
- Road construction from a cement can be put in to serving much sooner than roads constructed from regular basis cement.
IV) Low Heat Portland Cement
- These cement contain a lower percentage of C³S & C³A & thus decrese the heat evolution.
- The heat evolved should not exceed 60 and 70 cal/gm after 7 and 28 days respective.
- These Cement are desingned for massive structured work.
V) Sulphar Resisting Portland Cement
- These are good for sea water contact, resist sulphar. better than than other four types, lower in C³A(<4%) & higher in C4AF it is used for structural purpose.
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