Evaluation of efficiency factor of fly ash on compressive strength of fly ash-cement paste with age

Abstract

In recent years, fly ash is increasingly used as a partial replacement of cement for concrete production. Effect of effeciency factor (k) of fly ash on compressive strength of fly ash-cement paste was investigated in order to effectively utilize fly ash. In the experiment, fly-ash cement paste with a water-to-cementitious materials (including Portland cement and Class-F fly ash) ratio of 0.40. Two types of cement were prepapred and the replacement ratios of Portland cement by Class-F fly ash were 0, 5, 10, 15, 20, 30, 40 và 50% by mass. Results show that fly ash reduced the compressive strength of the hardened fly-ash cement paste at each age (i.e., at 7, 14, 28, and 56 days). The efficicency factor (k) of fly ash at the age of 7 days was in the range from 0.10 to 0.59 and gradually increased with time. The lower the replacement of cement by fly ash, the higher the value of the efficiency factor (k).