Mechanical Properties and Mechanisms of Polyacrylamide-Modified Granulated Blast Furnace Slag–Based Geopolymer

Abstract

Geopolymers are an environmentally friendly cementitious materials, which have the advantages of high strength, good durability, and stability; however, geopolymers also have some limitations, such as strong brittleness and low toughness. In this experiment, polyacrylamide (PAM) was used to improve the toughness of granulated blast furnace slag (GBFS)–based geopolymers. The water/binder (W/B) ratio was fixed at 0.5; the content of alkaline activator (Na2O wt%) was fixed at 6.0 wt%; and the alkaline activator modulus was fixed at 0.8. The effect of PAM (0, 0.25, 0.5, 0.75, 1.0, 3.0, and 5.0 wt%) was investigated with respect to compressive strength, flexural strength, and bending toughness of GBFS-based geopolymers. To determine the reason the bending toughness of GBFS-based geopolymers can be improved with PAM, microscopic test methods such as Fourier transform infrared (FTIR), Si29 nuclear magnetic resonance (NMR), mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS) were also performed. With an increase in PAM content, the compressive strength, flexural strength, and bending toughness of GBFS-based geopolymers increased initially and then decreased. The compressive strength, flexural strength, and bending toughness of GBFS-based geopolymers reached their maximum value when PAM content was 0.5 wt%. Compared to the control specimen, flexural strength/compressive strength ratio of PAM-modified samples showed an increase of 28.3%. The bending toughness of PAM-modified samples increased by 70.4%. Results of microscopic tests proved that PAM elicited a multiscale modification effect on GBFS-based geopolymers at molecular and submicroscopic levels.