Experimental analysis of cement-treated red sandstone coarse-grained soil and its microstructural evolution

This study purposes to quantify comprehensively the potential of cement-treated red sandstone coarse-grained soil as a subgrade filler in highway engineering. The compaction characteristics and shear strength of the red sandstone coarse-grained soil improved by ordinary Portland cement are main objects in this study. The experimental methods involve two compaction tests (vibration table test and modified Proctor test), the California bearing ratio (CBR) test, the disintegration test, the triaxial test, and the electron microscopy scanning test. The results show that the CBR value and maximum dry density of soil specimens increased with cement content. Moreover, both compaction density and water stability of Proctor specimens are obviously better than that of vibration specimens since the Proctor compaction makes it easier for the particle breakage of coarse-grained soil. The addition of cement increases the shear strength and reduces the dilatancy of soil. Compared with the untreated soil, the cement-treated soil achieves higher peak strength. Meanwhile, the confining pressure helps the soil to obtain better anti-shear retention ability, which shows that the larger the confining pressure is, the slower the decrement of deviator stress after the peak point in stress-strain curves. The electron microscopy scanning results find that the crystallites produced by cement hydration are the main reason to change the microstructure and improve the shear strength of soil. During the triaxial shear process, the soil specimens show that three failure forms, namely, cementations failure, sliding friction, and particles breaking.