If the admixtures are used in concrete for the purpose of delayed setting and hardening of concrete, they are called _____________?

• A. Accelerators
• B. Retarders
• C. Plasticizers
• D. Water reducers

Answer: (B)

Admixtures that delay the setting and hardening of concrete slow the chemical hydration process, extending the time you have to place, finish, and cure the concrete. These are called retarders. They help prevent early stiffening, which is especially useful in hot weather, long-haul transport, or large pours where heat buildup could cause cracking. Accelerators do the opposite, speeding up setting and early strength. Plasticizers (superplasticizers) mainly improve workability without adding extra water, and water reducers lower the water content to improve strength and finishability, not to delay setting.