Development of a concrete set retarder utilizing electric arc furnace dust

Retarding admixtures are used to increase the setting time of concrete, especially under hot weather conditions. They provide longer time for concrete to be transported, placed and consolidated. Several commercial retarders are used to extend the setting time of concrete. However, they have a shorter shelf-life as they are commonly supplied in a liquid form. Consequently, there is a need to develop a solid (powder) set retarder that can be efficient in retarding the setting time of concrete and at the same time have a longer shelf-life. This paper presents the results of a study conducted to assess the possibility of developing a set retarder utilizing electric arc furnace dust (EAFD), a by-product of steel industry. The retardation efficiency of up to 6% EAFD, by weight of cement, was evaluated in comparison with other two commercial retarders. The effect of EAFD addition on the heat of hydration, slump retention, compressive strength, and drying shrinkage was evaluated. The experimental data indicated that EAFD is effective in increasing the initial and final setting time. The calorimetry data indicated that the hydration of cement was delayed due to the addition of EAFD. The 28-day compressive strength of concrete was not adversely affected by EAFD or the commercial retarders, and it was in the range of 46.5 MPa to 50.7 MPa. However, the drying shrinkage strain increased by 24 to 37%. It can be concluded that the performance of the solid retarder developed using EAFD was comparable to that of the commercial retarders. The use of EAFD, an industrial byproduct, as a retarder will result in technical, economic and environmental benefits.