What type of admixture is commonly used in hot weather concreting?

In hot weather concreting, a set retarding admixture is utilized to extend the time before the concrete begins to set. This is crucial because high temperatures can accelerate the hydration process, leading to rapid setting and difficulties in properly mixing, placing, and finishing the concrete. By using a set retarding admixture, the concrete's workability is prolonged, allowing for adjustments in placement and ensuring that it can be adequately worked and finished without the risk of premature setting.

The need to manage the setting time becomes particularly important during hot weather to prevent issues like cold joints or surface cracking, which can occur if the concrete hardens too quickly. This type of admixture helps to maintain the integrity of the concrete and allows for better overall quality in the construction process.

In contrast, while water-reducing admixtures increase workability without adding extra water, they do not specifically address the issue of rapid set times in hot conditions. Set accelerating admixtures are intended to increase the rate of strength gain, which is counterproductive in hot weather where extended setting times are required. Viscosity-modifying admixtures are designed to enhance the flow and stability of concrete but do not directly address the problem of setting time.