Mechanical properties and stress-strain relationship of steel fiber reinforced geopolymer recycled concrete

Abstract

Steel fiber reinforced geopolymer recycled concrete (SFGRC) is a low-carbon concrete material which can reduce the consumption of cement and natural aggregate, and alleviate construction and industrial waste accumulation problems. In this experiment, SFGRC was prepared using fly ash, ground granulated blast slag, silica fume, recycled coarse and fine aggregates, and hooked-end steel fibers. The effects of different calcium-silicon ratios, recycled aggregate volume content, steel fiber volume content, alkaline activator modulus, and alkali-cementitious ratio on the physical properties, mechanical properties, and stress-strain relationship of SFGRC were studied. The failure mode and crack development path of SFGRC were obtained. The stress-strain curve of SFGRC was studied, and the characteristic points of the curve were analyzed. Calculation models for the elastic modulus, peak stress, and peak strain of SFGRC were proposed. Based on the classical constitutive model, a two - stage constitutive model for SFGRC considering the damage evolution process was proposed. The microscopic morphology and formation mechanism of SFGRC were studied using XRD, SEM, and EDS techniques. The results show that the slump of SFGRC is 121 mm - 207 mm, the final setting time is less than 65 min, and the dry apparent density is less than 2040 kg/m³. Compared with ordinary concrete, SFGRC has the characteristics of lightweight, fast setting time, and early strength. The increase in the alkali and calcium content in the mixture can improve the mechanical properties of SFGRC, while the increase in the alkaline activator modulus and recycled aggregate volume content will reduce the mechanical properties of SFGRC. With the increase in the content of steel fibers, the tensile strength and flexural strength of SFGRC increase significantly, while the compressive strength first increases and then decreases. The failure process of SFGRC under uniaxial compression includes four stages. The two-stage constitutive model proposed by considering different factors in the ascending and descending sections of the stress-strain curve can better predict the uniaxial compression behavior of SFGRC, providing a theoretical basis for finite element analysis and structural design in practical engineering.