Strength and microstructure analysis of subgrade materials containing red sandstone-limestone-cement composites and red sandstone gravel

This study investigated a cement-stabilized macadam (CSM) base composed of red sandstone as gravel and cement, red sandstone, and limestone powder as composite cementitious materials. The mechanical properties, strength formation mechanism, and synergistic effect of cement-red sandstone-limestone mixture stabilized red sandstone gravel are discussed. The hydration mechanism and microstructure were characterized using isothermal calorimetry, thermogravimetric analysis, X-ray powder diffraction, attenuated total reflectanceFourier transform infrared spectroscopy, and scanning electron microscopy-backscattered electron microscopy. The results showed the following: (1) When the replacement amount reached 15 %, the later strength reached 93.6 % of that of the pure cement specimens. The water released from the red sandstone gravel promotes further hydration of the unhydrated cement particles in the later stage. (2) The addition of limestone and red sandstone had a slight accelerating effect on the hydration of cement, and the addition of appropriate amounts of limestone and red sandstone powder increased the compressive strength. (3) Red sandstone and limestone powders had a synergistic effect and generated more carbon aluminates in the later stages of hydration. (4) The combination of limestone and red sandstone powder improved the weak interface transition zone caused by the red sandstone. In summary, the compressive strength of cement-stabilized red sandstone meets the specification requirements, and the synergistic effect between limestone and red sandstone powder can compensate for the adverse effects of dilution and improve the weak interface transition zone.