Which additive is used to slow surface evaporation and help prevent early plastic shrinkage during finishing?

Which additive is used to slow surface evaporation and help prevent early plastic shrinkage during finishing?

• A. Evaporation retarder
• B. Accelerating admixture
• C. Water-reducing agent
• D. Air-entraining agent

Answer: (A)

Slowing surface evaporation to prevent early plastic shrinkage is achieved by using an evaporation retarder. This additive acts on the surface to reduce how quickly moisture escapes from fresh concrete, which is crucial when finishing soon after placement in hot, windy, or dry conditions. By keeping the surface moist longer, the cement can hydrate more evenly, and bleed water at the surface has time to rise rather than drying out immediately. This reduces the tensile stresses that cause plastic shrinkage cracks during the early finishing period. Accelerating admixtures speed up early strength gain and hydration, not moisture loss control. A water-reducing agent lowers the amount of water while maintaining workability, but it doesn’t specifically slow surface evaporation. An air-entraining agent creates microscopic air voids to improve freeze-thaw durability, and its main function isn’t to slow evaporation either.

Slowing surface evaporation to prevent early plastic shrinkage is achieved by using an evaporation retarder. This additive acts on the surface to reduce how quickly moisture escapes from fresh concrete, which is crucial when finishing soon after placement in hot, windy, or dry conditions. By keeping the surface moist longer, the cement can hydrate more evenly, and bleed water at the surface has time to rise rather than drying out immediately. This reduces the tensile stresses that cause plastic shrinkage cracks during the early finishing period.

Accelerating admixtures speed up early strength gain and hydration, not moisture loss control. A water-reducing agent lowers the amount of water while maintaining workability, but it doesn’t specifically slow surface evaporation. An air-entraining agent creates microscopic air voids to improve freeze-thaw durability, and its main function isn’t to slow evaporation either.