What do retarders do in the context of concrete?

Retarders are chemical admixtures used in concrete mix designs to slow down the rate of hardening or setting of the concrete. This can be particularly beneficial in various construction situations, such as during hot weather or in larger pours where longer working times are needed. By delaying the setting time, retarders help maintain workability and allow for better placement, finishing, and consolidation of the concrete.

This ability to extend the time before the concrete begins to set assists in achieving a more homogenous mix and can lead to improved performance characteristics in the finished product. In environments where transportation and handling of concrete can lead to premature setting, the use of retarders ensures that the materials remain workable and that the quality of the concrete is upheld throughout the application process.

Other options, such as speeding up the hardening process, artificially increasing the temperature of the mix, or enhancing structural integrity, do not accurately describe the role of retarders in concrete formulations. They specifically function to counteract a rapid setting, thus making the correct answer clearly focused on the aspect of slowing down the rate of hardening.