Question

Differentiate between retarding and accelerating admixtures with following points. i) Hydration process ii) Setting time iii) Weather condition iv) Use

Answer 1

The accelerating and retarding admixtures can be compared as follows.

	Accelerating Admixture	Retarding Admixture
Hydration process	Due to accelerating admixture, hydration process completes very quickly. Hence hardening of concrete takes place earlier.	Due to retarding admixture, hydration process completes slowly, hence concrete hardens very slowly.
Setting time	Setting time of concrete reduces due to addition of accelerating admixture.	Setting time of concrete increases due to addition of retarding admixture
Weather condition	It is useful for concreting in cold weather condition.	It is useful for concreting in hot weather condition.
Use	It is applicable where delay in construction is not allowed i.e. road construction. It is useful where quick setting is required i.e. in underwater construction. It is beneficial where rapid hardening of concrete is necessary i.e. in case of high rise structures.	It is applicable where high heat and vibrations are required to reduce i.e. in machine foundations and nuclear power plant. It is useful where slow setting of concrete is required i.e. in extreme hot weather concreting. It is beneficial where slow hardening of concrete is necessary i.e. in mass concrete structures.