Dynamic responses of a waste sludge modified by magnesium-cement-based multiphase cementitious material under influences of temperature and moisture cycles

Abstract

This paper explores the influences of external stress and moisture and temperature cycles on the microstructure and dynamic responses (including the dynamic shear modulus G, damping ratio λ, and accumulative plastic strain εp) of a waste sludge that is modified by magnesium-cement-based multiphase cementitious material. Experimental results show that (i) freeze–thaw (FT), wet-dry (WD), and wet-dry-freeze–thaw (WD-FT) cycles significantly change the soil’s pore system. Intra-aggregate pores gradually evolve into inter-aggregate pores and cracks develop during moisture and temperature cycles. This leads to the degradation of the pore structure and decrease in the soil stiffness; (ii) during the progress of moisture and temperature cycles, the G decreases, and the λ increases. The effects of WD and WD-FT cycles on the G and λ are more significant compared to FT cycles. The G increases with the confining pressure σc while the λ is not sensitive to the σc. The relationships of the G and λ to the deviator stress σd are generally non-monotonic and the turning point of such relationships is influenced by the moisture and temperature cycles; (iii) the εp increases after moisture and temperature cycles and the development of the εp during cyclic loading gradually evolve from plastic shakedown to plastic creep. Predictive models based on decay laws considering stress states are developed to describe the changes in dynamic shear modulus and accumulative plastic strain.