This paper describes a laboratory study on the influence of the combination of ultrafine fly ash (UFFA) and silica Fume (SF) on the properties of fresh and hardened concrete. The paper also compares the performance of theconcrete incorporating UFFA and SF (ternary blend of cement), the concrete incorporating UFFA or SF (binary blend of cement), and control Portland cement concrete. The test results show that the incorporation of silica fume or ultrafine fly ash in concrete resulted in higher strength and improved durability (resistance to chloride penetration). These benefits were found to be more pronounced in the SF concrete. However, the SF concrete demonstrated several limitations such as low slump, and high early age shrinkage. These limitations were not observed in the UFFA concrete; addition ofUFFA increased the slump and decreased the early age shrinkage. In order to minimize the shortcomings of SF without loosing its strength and durability benefits, a concrete mixture was prepared incorporating both SF and UFFA. The test results show that the incorporation of both SF and UFFA produced a concrete mixture that demonstrated high early age strength and improved durability similar to the SF concrete. In addition, unlike SF concrete, the new concrete mixture demonstrated higher level of slump and lower level of free shrinkage.
Samenvatting