Type of cement to be used in concrete is primarily choosen based on criteria like strength, durability and other specific requirements necessary for various kinds of work.
Cements used in general concrete work are: Ordinary Portland Cement (OPC), Rapid Hardening Portland Cement (RHPC), Portland Slag Cement (PSC), Portland Pozzolana Cement (PPC), Low Heat Portland Cement (LHPC), High Alumina Cement (HAC), Sulphate Resisting Cement (SRC), Super Sulphate Cement (SSC) etc. Of these, first five are widely used in most countries.
Some other cements used in various situations or purposes are Quick Setting cement, Air entraining cement, Hydrophobic cement, White & coloured cement, Oil well cememt, Expansive cement, Water repellent cement, Water proofing cement etc.
In normal condition, rate of development of strength in ascending order are: LHPC, OPC, RHPC, HAC.
In normal condition, long term strength attained in ascending orders are: LHPC/OPC, RHPC, HAC.
Rate of development of strength for PPC is lower than that of OPC, but 28 days strengths are almost same.
RHPC attains strength quite rapidly. It’s 3 & 7 days strength are almost the same as that of 7 & 28 days strength of OPC. Thus RHPC is quite suitable where formwork need to be removed quickly, e.g. highway concrete slab. This cement is also useful in cold wether concreting as well as in precast concrete items.
LHPC is suitable for massive concrete structures like dams, retaining walls, bridge abutments etc. due to it’s low rate of development of heat.
PSC renders concrete well resistant to corrosion in damp environment. It is also ofen used in pre-fabricated reinforced concrete structures.
Cements quite suitable for marine environment are: HAC, OPC & Sulphate Slag cement as these are highly resistant to sulphate attack. These cements, and also SRC, can as well be used in underground concrete work demanding high sulphate resistance.
HAC is also used in heat resistant and refractory concrete. This cement develops strength much faster than most other cements. Strength attained by an ordinary concrete in 28 days is developed by HAC in just about 24 hours. However, it is not quite suitable for mass concrete work as it generates plenty of heat of hydration unlike LHPC.
Quick setting cement is quite suitable for concrete to be laid under normal water. This is because it starts setting within few minutes and becomes sufficiently hard in less than an hour.
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.
Contd. in Part-II….