Mechanical properties of high-volume fly ash self-compacting concrete mixtures

Self-compacting concrete (SCC), a recent addition to the concrete scenario, is gaining popularity worldwide owing to the ease of its placement without any need for compaction. This paper describes the results of an investigation aimed at producing and evaluating SCC mixtures made with high volumes of class F fly ash. Eight fly ash SCC mixtures of various strength grades (20-100 MPa) were designed at the desired fly ash percentages of 0, 10, 30, 50, 70 and 85%, and were compared with five different mixtures of normal vibrated concrete mixtures (20-100 MPa). Tests were carried out on all mixtures to obtain the properties of fresh concretes in terms of viscosity and stability. The mechanical properties of hardened concretes such as compressive strength, splitting tensile strength and elastic modulus were also determined. The different amounts of paste caused differences in the properties of the two types of concrete. Test results indicated that the use of high volumes of class F fly ash in SCC mixtures decreases its 28-day compressive strength. However, the strength results showed continuous and significant improvement at the ages of 90 and 180 days, which was most probably owing to the pozzolanic reaction of fly ash. Self-compacted fly ash concrete mixtures exhibited higher splitting tensile strengths and lower elastic modulus compared with normal vibrated concretes.