Performance evaluation of heavy oil fly ash as a retarder of Portland cement hydration

Retarding admixtures have the ability minimize the adverse effects of concreting under hot weather conditions. Liquid admixtures are generally used for this purpose. However, these have limited shelf-life and therefore there is a need to develop solid retarding admixtures. This paper reports results of a study conducted to assess the performance of solid retarders for retardation of cement. The examined materials included heavy oil fly ash (HOFA) (a byproduct of oil combustion) and chemical retarders (sodium gluconate, sucrose and zinc oxide). The ability of up to 3% HOFA, by weight of cement, to extend the setting time was compared with other chemical retarders. The performance of the selected retarders was evaluated by measuring heat evolution, workability/slump retention, drying shrinkage, and compressive strength. The experimental results indicated that HOFA, sodium gluconate, sucrose and zinc oxide can effectively extend the initial and final setting time of cement. Further, the calorimetric data demonstrated that cement hydration was temporary hindered by the addition of HOFA and the selected chemical retarders. The 28-day compressive strength of concrete with the selected retarders, including HOFA, was similar to that of OPC concrete, and it ranged from 48.4 to 52.6 MPa. However, the rate of early-age drying shrinkage strain increased due to the addition of the selected retarding agents which may necessitate precautionary measures. Finally, it can be concluded that the retarding efficiency of HOFA was generally comparable to that of the selected chemical admixtures.