Mechanical properties and microscopic mechanism of paper mill sludge-magnesium oxychloride cement composites

To make use of industrial solid waste from paper mills, namely paper mill sludge (PMS), and to develop green construction materials, the samples were tested by using these methods that include unconfined compressive strength tests, dry density tests, water absorption tests, scanning electron microscopes (SEM), and X-ray diffractometers (XRD). The effects of different dosages, different particle sizes, and different initial water contents of PMS on the strength and microscopic properties of magnesium oxychloride cement were studied. Results show that the compressive strength of the samples decrease with the increasing of particle size and initial water content, and it first increases before decreasing when PMS content increases. PMS can lessen water absorption while having little impact on the dry density. The compressive strength, which can reach 58.47 MPa, is at its highest when the mixing percentage of PMS is 60%. At this point, the composite material's Phase 5 crystal is longer and the water absorption rate is only 6.33%. The obtained conclusions can provide a reference for the engineering application of paper mill sludge-magnesium oxychloride cement composites.