Strength Improvement of Strain-Hardening Cementitious Composites with Ultrahigh-Volume Fly Ash

Strain-hardening cementitious composites (SHCCs) exhibiting tensile strain-hardening and multiple cracking are attractive for many structural applications. However, the high cement content makes typical SHCCs less ecofriendly than conventional concrete. One possible approach to improve the sustainability is to substitute cement with industrial wastes such as fly ash. This paper presents an attempt to develop SHCCs with ultrahigh-volume fly ash (HVFA, 80% by weight of binder) for structural applications. From the literature, polyvinyl alcohol (PVA) fiber reinforced HVFA-SHCCs often exhibit low compressive strength, which limits the material to nonstructural applications. The focus of this work was on improving the compressive strength and maintaining the excellent tensile characteristics of PVA fiber reinforced HVFA-SHCCs by a simple and practical method of reducing the water/binder ratio and adding a small amount of silica fume. The selection of fly ash for making such a material is also discussed. With suitable fly ash, HVFA-SHCCs could achieve a compressive strength of 49.4 MPa at 7 days and 69.2 MPa at 28 days, with the corresponding ultimate tensile strain more than 3.5% at 28 days. This kind of HVFA-SHCC is applicable for many structural applications, and the substitution of high percentages of cement with industrial wastes reduces the material cost and the environmental impact significantly.