Effects of Silica Fume and Fly Ash as Partial Replacement of Cement on Water Permeability and Strength of High Performance Concrete

Abstract—Industrial byproducts such as Silica Fume (SF) and Fly Ash (FA) can be utilized to enhance the strength and water permeability characteristics of High Performance Concrete (HPC). The utilization of these industrial by products is becoming popular throughout the world because of the minimization of their potential hazardous effects on environment. This paper investigates the individual effects of Silica Fume and Fly Ash as a partial replacement of Ordinary Portland Cement (OPC) on water permeability, compressive strength, split tensile strength and flexural tensile strength of High Performance Concrete (HPC). To investigate these properties of concrete, the total investigation was categorized into two basic test groups - SF Group for Silica Fume and FA Group for Fly Ash. Seven types of mix proportions were used to cast the test specimens for both groups. The replacement levels of OPC by Silica Fume were 0%, 2.5%, 5%, 7.5%, 10%, 15% and 20% where replacement levels of OPC by Fly Ash were 0%, 5%, 10%, 15%, 20%, 25% and 30%. 1% super-plasticizer was used in all the test specimens for high performance (i.e., high workability at lower water-binder ratio) and to identify the sharp effects of Silica Fume and Fly Ash on the properties of concrete. Water-binder ratio was kept 0.42 for all cases and the specimens were tested at ages of 7, 14 and 28 days.10% Silica Fume and 20% Fly Ash showed the lowest water penetration depth of 11mm and 15 mm respectively. 7.5% Silica Fume and 10% Fly Ash were found to be optimum for maximum compressive strength, maximum split tensile strength as well as maximum flexural tensile strength.