Contd. from Part-I ….
Super Sulphate cement is very much resistant to chemical attack. This cement can be suitably used in concrete to be poured in acidic environment. It is also suitable for mass concrete work due to it’s low heat of hydration. Concrete having this cement tends to shrink or expand depending on whether curing is done in air or underwater.
Portland Pozzolana cement (PPC) generates lower heat of hydration & thus is good for massive concrete work. It’s rate of development of strength is slower than that of OPC and hence is not quite suitable for works where quick stripping of formwork is planned. However, it’s final strength is comparable to that of OPC. PPC & PSC are usually cheaper than most other cement.
Pozzolanas used in PPC are mainly of the following types: Burnt clay, burnt shale and fly ash. Fly ash is a by-product of thermal power plants.
Specific gravity of ordinary cement commonly used in construction project sites is around 3.15.
Some of the important tests done on cement to be used in construction projects are: setting time test, cube compressive strength test ( 3, 7 & 28 days ), soundness test, fineness test, heat of hydration, tests on chemical properties etc. Of these, first three are frequently performed in construction project site laboratories while tests on fineness and heat of hydration are usually done in recognised established laboratories. For chemical test results, manufacturer’s test certificates are often referred to.
Indian codes specify the minimum strength to be attained standard cement cubes of 3, 7 & 28 days ages as 23, 33 & 43 Mpa respectively.
Setting time of cement is determined by Vicat apparatus & soundness by Le Chatelier’s apparatus. Soundness of cement is also tested by Autoclave apparatus.
Determination of fineness of cement is quite important water demand by a cement is a function of it’s fineness. For example, the finer the cement, the more the specific surface and thus the higher it’s water requirement.
Sieve testing method of fineness de