Micro and macro experimental study of using the new cement-based self-stress grouting material to solve shrinkage problem

Abstract

Self-stress grouting can effectively improve the weak reinforcement caused by shrinkage of the ordinary cement-based grouting materials (OGM). However, the research on self-stressing grouting materials is still not perfect, and the micro and macro performance discrepancies between it and OGM are rarely analyzed. Aiming to this, this paper developed a new cement-based self-stress grouting material (LS-1). By analysing the mechanical mechanism of self-stress reinforcement, it is found that self-stress reinforcement can reduce the effective shear stress of the rock fracture surface, thereby avoiding shear slip failure. Furthermore, by orthogonal testing, the optimal ratio of content of LS-1 was obtained as 10% of U-type expansive agent (UEA), 1.2% of polycarboxylic acid high-efficiency water-reducing agent (PC) and 1.2% of the early-strength concrete agent (EHD). The control experiment was conducted to investigate the performance discrepancy between the two types of grouting materials. The result showed that in terms of longitudinal restricted expansive displacement, under the same experimental conditions, the LS-1 expanded by 1.521 mm while OGM shrunk by 10.374 mm. Then, the damage model of both grouted coal specimens under the impact of acoustic emission (AE) with uniaxial load was established and analyzed. Besides, scanning electron microscope (SEM) was used to verify the effect of LS-1. It was found that for the OGM grouted coal specimen, the damage variable and degree was more extensive, and the bearing capacity is lower, indicating the expansive needle-shaped crystals that are formed after LS-1 solidification are beneficial to improve the density of the grout and avoid the shrinkage. This research will provide a reference for theoretical research and the engineering application of cement-based grouting material.