Q No 4 Suggest the type of cement to produce concrete for ea

Q. No. 4: Suggest the type of cement to produce concrete for each of the following works. Briefly state reasons for choice of cement in each case: i) Repair of airport runway ii) Repair of a sewerage line iii) Construction of a 400 ft long, 20 ft high and 10 ft thick member.

Solution

1)For repair of runway, we should use RAPID HARDENING CEMENT because this cement has higher rae of gain of strength (it can be use in almost 3 days equivalent to opc that will attain in 7 days) thus allwing the function of runway in the earliest possible time.

2)For rapair of sewarage line, we should use SULPHATE RESISTING CEMENT because sewage water contain sulphur and it lead to volume change and OPC is highly suseptible to the attack of sulphates especially to that of MgSO4 which reacts with both, calcium hydroxide to form calcium sulphate & calcium aluminate to form calcium sulpho-aluminate, volume of which is approx 227% more than its original volume, that leads to development of the cracks in the structure in which it is used for construction.

In order to avoid this, proportion of lime, and alumina is reduced in the cement (cement called sulphate resisting cement) such that C3A is not greater than 5%.

3)For constuction of 400ft long, 20ft high and 10ft thick member(for such mass concreting), we should use LOW HEAT CEMENT beacause this cement develop slower rate of gain strength thus generate low rate of hydration and hence require less amount of water for curing. But the ultimate strength will be equivalent to that of OPC cement.