Compression and shear properties of OPC-MCA and basalt fiber cured shield waste mud after dry-wet cycles

The large-scale accumulation of shield waste mud (SWM) generated during urban subway construction is prone to cause potential environmental problems. A new low-carbon curing modified material, i.e., OPC-MCA, was firstly prepared to economically and environmentally treat SWM by partially replacing ordinary Portland cement (OPC) with a composite external admixture. Thereafter, laboratory curing experiments of SWM taken from the Jinan Jile Road Yellow River Tunnel were conducted by controlling OPC-MCA at a 20% dosage and basalt fiber (BF) at different dosages (0–1.05%). The appearance, mass and P-wave velocity of the cured specimens were characterized and the compression and shear strength tests were carried out. In addition, X-ray computed tomography (CT) and scanning electron microscope (SEM) analyses were performed to comprehensively assess the resistance of OPC-MCA cured SWM exposed to dry-wet (d-w) cycles with different BF dosages. The results confirmed that the optimal BF dosage for specimens that did not undergo d-w cycles was 0.45%, resulting in a 16.67% increase in compressive strength and a 51.56% increase in shear strength. The addition of BF enhanced the resistance of specimens to d-w cycles and reduced the deterioration rates of mass, P-wave velocity, and mechanical properties. The hydrophilic expansion property of clay minerals significantly contributed to strength degradation and pore deformation of cured SWM specimens. The development degree of microscopic cracks and pores in cured SWM specimens was significantly affected by both the dosage of BF and the number of d-w cycles. By incorporating BF, the volume and connectivity of cracks and pores were reduced, the formation of small-sized pores was decreased, and the expansion of cracks was inhibited throughout the cycling process.