Mechanical properties and drying water loss mechanism of NaOH-activated slag/silica fume solidified waste mud

In this study, the synergistic curing mechanism of sodium NaOH-activated (N) slag (S)/silica fume (S) on waste mud was investigated. In this paper, orthogonal tests were used to analyze the unconfined compressive strength, stress-strain curves, pH, crack development pattern, water content change and microstructure of NSSF-cured mud specimens with different NSSF dosage and at different ages. The results showed that when the NaOH dosage was 1%~5%, the strength of the specimens showed an increasing and then decreasing trend with the increase of silica fume substitution rate; when the dosage reached 7%~9%, the strength continued to decrease with the increase of silica fume substitution rate. The strength of specimens increased with the age of maintenance, in which the enhancement effect was significant from 7 to 14 days, and the increase was weakened from 14 to 28 days. Microanalysis showed that moderate amount of silica fume could fill the pores of matrix and promote the generation of CSH gel, while high dosage of silica fume formed large pore structure with water storage and crack inhibition. When the pH value is stabilized at 12 ± 0.1, the curing agent reaches the optimal proportion. High content of alkali and silica fume can lock water to a certain extent and delay the cracking of the specimen, but the development of cracks is more rapid after cracking. The study reveals the synergistic solidification mechanism of alkali-activated silica fume / slag on slurry, which provides a theoretical basis for the practical application of solidified mud.