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Question and Answer on Cement
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-Er.Colonel.P.Nallathambi
Q. What is Portland cement?
Portland cement is composed of calcium silicates, aluminates and aluminoferrite. It is obtained by
blending predetermined proportions of limestone, clay and other minerals in small quantities which is
pulverized and heated at high temperature - around 1500?C to produce 'clinker'. The clinker is then
ground with small quantities of gypsum to produce a fine powder called Ordinary Portland Cement
(OPC).
Q. Is there any shelf life of cement?
cement remains in good condition as long as it does not come in contact with moisture. If cement is
more than three months old, then it should be tested for its strength before to use.
Q. What are Supplementary Cementations Materials (SCM)?
Supplementary Cementations Materials (SCM) like silica fumes, meta-kaolin, fly ash, slag are the
materials which improve the properties of concrete and enhance its durability.
Q. How fineness of cement affect strength gain?
Fineness defines the surface area of cement particles present in per unit weight. This enhances the è
reaction rate which in turn will result in faster gain of strength at earlier stages.
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Blended cement is obtained by either intergrinding pozzolanic material or slag with clinker along with £
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Gypsum or by blending ground pozzolana or slag with Portland cement.
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Q. What is blended cement?
Q. How does blended cement affect durability?
Pozzolana combines with lime and alkalies in the cement and when water is mixed forms compounds ªð
which contribute to strength, impermeability and sulphate resistance It also contributes to £
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workability, reduced bleeding and controls destructive expansion from alkali-aggregate reaction.
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Q. What is Setting Time of Cement?
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When water is mixed with cement, the paste so formed remains pliable and plastic for a short time.
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This early period in the hardening of cement is referred to as 'setting' of cement.
Initial Setting Time – 30min ; Final Setting Time – 10 to 12hrs
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23
- (to be continued)
mf;Nlhgh; 2013