Effect of sulfate activator on mechanical and durability properties of concrete incorporating low calcium fly ash

Abstract

The use of fly ash as a cement replacement material brings economy and sustainability in the concrete construction. Despite economic and environmental benefits, fly ash incorporation in concrete reduces its early age performance. Therefore, the main objective of this research is to increase the incorporation level of fly ash in the hybrid binder (cement plus fly ash) utilizing the sulfate activation technique to overcome the issue of inferior performance at an early age. Replacement levels of fly ash with cement were kept as 20 %, 40 %, and 60 %. 2 % sodium sulfate (Na2SO4) by weight of binder was utilized as an activator. Compressive strength and flexural strength tests on standard samples were carried out at the age of 3, 28 and 90 days. Durability tests namely apparent porosity, sorptivity coefficient and chloride penetration tests were also conducted. Experimental results showed sulfate activation increased the early age strength at all levels of fly ash. After activation, concrete mix with 20 % and 40 % fly ash showed better strength performance than that of the conventional concrete at all ages. Concrete with 20 % and 40 % fly ash upon activation showed lower sorptivity and porosity than control mix at all ages. Similarly, chloride penetrations of concrete with 20, 40 and 60 % activated fly ash was noticeably lower than that of the control concrete. Chemical activation is also beneficial in reducing the cost and carbon footprint per unit strength of the fly ash mixes.