Study on stress-strain-resistivity and microscopic mechanism of red mud waste modified by desulphurization gypsum-fly ash under drying-wetting cycles

Abstract

In order to investigate characteristics of red mud waste modified by desulfurization gypsum-fly ash, an unconfined compressive strength test and a synchronous resistivity test of solidified soil under different contents, curing time and dry-wet cycles were carried out. Moreover, the internal structure change, reaction mechanism, and the hydration characteristics of desulfurization gypsum-fly ash soil were analyzed by XRD and SEM tests. The results show that under the 77% red mud content, the unconfined compressive strength increases with the increase of age. The stress-strain-resistivity curves of the same amount in red mud at different ages are basically consistent with each other. Under different contents, in the first three-stage, stress increases with strain, and the resistivity decreases with increasing strain. In the local deformation stage, the stress decreases rapidly with the increase of strain, and the resistivity keeps decreasing until the specimen is completely destroyed. When the water content is lower, the resistivity is greater. Also, with the increase of number drying-wetting cycles, the strength of the sample mixture is gradually weakened from 1.34 MPa of one drying-wetting cycle to 0.8 MPa of nine drying-wetting cycle. The corresponding resistivity with one drying-wetting cycle continues decreasing slowly about 0.5%, and this trend of decreasing is gradually weakened. When the drying-wetting cycle is more than 5, the resistivity will increase with the increasing of the drying-wetting cycles. The microstructures of red mud waste modified by desulfurization gypsum-fly ash soil were examined by SEM analysis after a different number of dry-wet cycles. The SEM analysis has shown that the sample mixture was initially compacted with homogenous particles, because of the amorphous gel C-S-H and kotoite silicatian which are basically responsible for strength development. With the increases in drying-wetting cycle numbers, there are obvious changes in the characteristics and the structure of the mixture sample, whereas the porosity of the structure of the sample also increases, while the density and the unconfined compressive strength of the structure of the sample decreases. This paper aims to provide an important theoretical application of the comprehensive utilization of red mud as a road base material.