Experimental and microscopic analysis of N-(n-butyl) thiophos-phoric triamide on microbial amelioration of red clay properties

Abstract This study aims to analyze the impact of varying dosages of N-(n-butyl) thiophosphoric triamide (NBPT) on the physical and mechanical properties of microbial-induced calcite precipitation (MICP) grouting improved red clay. The research includes XRD and SEM experiments to examine the micro-structural characterization of the specimens and understand the mechanism of NBPT's action on MICP improved red clay. A comprehensive evaluation is conducted to assess the properties of red clay after the introduction of NBPT microbial improvement, the results show that The mechanical properties and peak strength of MICP improved red clay samples showed a tendency to increase and then decrease with the increase of NBPT doping, and the stress-strain curve showed a change from softening to hardening and then back to softening; the improvement effect was in the optimal state at the cut-off point when the doping amount of NBPT was 0.1%. The shrinkage deformation, initial water content, and shrinkage coefficient of the MICP improved red clay samples decreased gradually as the doping amount of NBPT increased. In the residual shrinkage deformation stage (δs2), the water content of the specimen needed to reach the ultimate linear shrinkage gradually increased with NBPT doping, causing it to enter the stable shrinkage deformation stage (δs3) earlier. The difference in CaCO3 content between the upper and lower parts of the specimens gradually decreased with the increase of NBPT doping, and finally tends to be stabilized. The urease inhibitor NBPT can affect the crystal morphology and distribution of the product and intervene in the morphological transformation of vaterite to calcite.