Occurrence and migration laws of water in circulating fluidized bed bottom slag mortar and their influences on mortar properties

The low utilization rate of circulating fluidized bed bottom slag (CFBBS) leads to its serious stacking and induces severe environmental pollution. Fortunately, the CFBBS can be recycled to the maximum extent as aggregate in mortar or concrete. Due to the porous structure of CFBBS, the occurrence and migration of water between CFBBS and the cement paste have some special laws, which are meaningful to the applications of CFBBS in mortar or concrete. In this paper, the water occurrence and migration laws of CFBBS in pure water, fresh mortar, and hardened mortar were explored systematically. The relationships among the effective water-cement ratio, the total water-cement ratio, and the time after adding water in CFBBS mortar were discussed, and the influences of the effective water-cement ratio on the fluidity and compressive strength of mortar were studied. The strengthening mechanism of CFBBS on the interfacial transition zone (ITZ) of mortar was revealed by micro test technology. The results showed that in the fresh stage, water migrated from the cement paste to CFBBS, which reduced the effective water-cement ratio and led to the decrease of mortar fluidity and the increase of compressive strength; in the hardened stage, however, water migrated from CFBBS to the hardened paste, which maintained the internal humidity of mortar, increased the hydration degree of cement, and improved the microstructure of ITZ.