The mechanism of silane-grafted sodium polyacrylate on the toughening of slag-based geopolymer: an insight from macroscopic–microscopic mechanical properties

To enhance the toughness of the geopolymer, silane (amino, epoxy, and methacrylate-based)-grafted sodium polyacrylate (PAA-Na) was used as additives. The interfacial features of the polymer slag paste, including the microstructure, physicochemical interaction or bonding, and mechanical properties, are the main determinants of the ductile qualities of the final concrete. This study examined how the polymer affected the evolution of the strain field, fracture characteristics, and micromechanical properties of slag geopolymer. The flexural strength and the fracture toughness of incorporating 5% 3-methacryloxypropyl trimethoxysilane (KH570) + 2% PAA-Na increased by 296.10% and 81.20%, compared with the reference. Additionally, the addition of 5% KH570 + 2% PAA-Na expanded the distribution of the strain field of geopolymer with 2615.89 με, 2300.57 με, and 1821.54 με under the maximum load of 2833 N. The formation of hydration product C–A–S–H/(5% KH570 + 2% PAA-Na) with a high degree of polymerization had a relatively low elastic modulus of 26.17 GPa. The carboxyl and silane groups of methacrylate-based PAA-Na and KH570 were polycondensed with the hydroxyl group on the surface of C–A–S–H resulting in 12.17% Ca (COO) 2 and 65.36% O–Si–O with a higher degree of polymerization. The slag-based geopolymer became more ductile as a result of the generation of the C–A–S–H/polymers, which had an organic–inorganic cross-linked network structure composed of O polymer –Ca–O C–A–S–H and O polymer –Si–O C–A–S–H bonds.