Development of Ca-rich slag-based ultra-high-performance fiber-reinforced geopolymer concrete (UHP-FRGC): Effect of sand-to-binder ratio

Abstract

In this study, a Ca-rich slag-based Ultra-High-Performance Fiber-Reinforced Geopolymer Concrete (UHP-FRGC) with a high compressive strength of over 150 MPa and high tensile ductility (strain energy density of over 50 kJ/m3) was developed. To optimize its mechanical properties, various silica sand-to-binder (S/B) ratios ranging from 0.16 to 0.8 were considered. Geopolymeric and C[sbnd](A)[sbnd]S[sbnd]H gels were produced simultaneously, and silica fume helped to increase the strength through its filler effect and accelerated the reactivity of the slag. The packing density and compressive strength of the UHP-FRGC increased with increasing S/B ratio up to 0.8, and the highest packing density and compressive strength of 0.78 and 160.7 MPa, respectively, were achieved at an S/B ratio of 0.8. Improved tensile performance of UHP-FRGC with an increase in the S/B ratio was also observed, and the best tensile performance resulted in a tensile strength of 10.3 MPa, strain capacity of 0.833%, and strain energy density of 55.0 kJ/m3. Although both the complementary energy (J’b) and crack tip toughness (Jtip) increased with the S/B ratio, the rate of increase of Jtip was much greater than that of J’b, causing a decreased pseudo strain-hardening (PSH) index. The lowest energy PSH index of 8.23 was thus obtained in the UHP-FRGC with an S/B ratio of 0.8, which provided the best tensile performance. Therefore, no correlation between the strain-hardening performance and PSH index was observed for UHP-FRGC with steel fibers.