Upcycling of lime mud into lightweight artificial aggregates through the crushing technique

Lime mud (LM), a solid waste generated in the paper-making industry, was proposed to manufacture lightweight artificial aggregates (LAAs) via the crushing technique. LAAs with a loose bulk density of 765-885 kg/m3, an apparent density of 1270-1445 kg/m3, and a strength of 5.7-7.2 MPa were achieved. To optimize the crushingconsumption energy and the mechanical properties, the mix proportions and curing ages of the LAAs before crushing were comprehensively investigated through mineralogy and microstructure analyses. In addition, the embodied carbon and material costs of the manufactured LAAs were estimated. Results showed that the earlycrushed LAAs (curing till 28 days) enabled achieving the higher 28-day strength compared to the 28-day-crushed LAAs; however, the early-crushed LAAs tended to produce more contents of powder. The incorporation of silica fume (SF) reduced the contents of crushing powder and refined the pore characteristics of the LAAs. An optimized mix proportion (LM:cement:SF = 5:3:2) of the LAAs crushed on day 3 showed the best comprehensive properties, considering the mechanical properties, material costs, energy consumption, and embodied carbon. Overall, this study offers insight into the LAA production via the crushing technique and the value-added use of LM in the construction industry.