Performance of ultra-fine fly ash blended mixtures towards mechanical and durability properties of ternary concrete

Abstract

With more people throughout the world building homes and infrastructure, the cement and concrete industries are expanding exponentially. The main cement used in the manufacturing of concrete is called ordinary Portland cement (OPC). Environmental damage from cement manufacture is caused by the gaseous CO2 emissions. Therefore, numerous studies have already considered partial OPC replacement with another material. Concrete has been shown to benefit from the inclusion of several industrial wastes, including fly ash (FA) and ground granulated blast furnace slag (GGBS), as a partial substitute for OPC. However, FA or GGBS are not especially effective at imparting early age strengths and also do not appreciably improve durability metrics when added as supplemental cementitious materials (SCM) in concrete. Application of ultra-fine materials like ultra-fine fly ash (UFFA) was thought to be important in order to improve the mechanical and durability aspects of concrete at all ages. The focus of the current work is on employing FA as a binary substitute for OPC in concrete and UFFA as a ternary substitute. This study examines the mechanical and durability properties of four ternary concrete mixtures containing 5% and 15% of ultra-fine fly ash with 30% and 40% of fly ash as a replacement of ordinary Portland cement. The compressive strength for ternary mixture composed of 15% ultra-fine fly ash and 40% fly ash shows up to 24% increment in the later age compressive strength. For the same ternary concrete mix, resistance to chloride migration and water penetration has increased in the range of 84% to 91% as compared to control concrete. This improvement is attributable to refinement of pores and denseness due to presence of ultra-fine fly ash. It has been demonstrated that employing UFFA as a ternary substitute greatly improves the mechanical and durability properties of ternary concrete.