Question

In curing cement plasters water is sprinkled from time to time. This helps in

(a) keeping it cool

(b) developing interlocking needlelike crystals of hydrated  silicates

(c) hydrating sand and gravel mixed with cement

(d) converting sand into silicic acid.

Answer 1

(b) : Water develops interlocking needlelike crystals of hydrated silicates. The reactions involved are the hydration of calcium aluminates and calcium silicates which change into their colloidal gels. At the same time, some calcium hydroxide and aluminium hydroxides are formed as precipitates due to hydrolysis. Calcium hydroxide binds the particles of calcium silicate together while aluminium hydroxide fills the interstices rendering the mass impervious.