Damage Mode and Energy Consumption Characteristics of Paper-Sludge-Doped Magnesium Chloride Cement Composites

To reduce the pollution caused by paper sludge in the environment and overcome issues of poor water resistance and brittleness in Magnesium Oxychloride Cement (MOC), the MOC was modified by adding different dosages of paper sludge. The mechanical properties and damage modes of composite MOC materials containing paper sludge were studied by uniaxial compression tests. Under cyclic loading conditions, the damage progression of MOC composites was characterised using the tensile-shear conversion factor (Tsc) and by monitoring the energy parameters (elastic strain energy, plastic strain energy and dissipation energy). The results show that the average peak stress drop of MOC composites gradually increases with the increase in paper sludge dosage. Under uniaxial compression conditions, the Tsc of the MOC composites decreases from 0.99 to 0.44, and the damage mode is transitioned from brittle tensile damage to tensile-shear damage, X-shaped conjugate surface shear damage and finally to pure shear damage with an increase in doping. During cyclic loading conditions, the brittleness of MOC composites gradually decreases with an increase in paper sludge doping, which verifies the effect of paper sludge on the mechanical properties of MOC materials and the change in damage modes from the perspective of energy dissipation.