Mechanical properties and microscopic characterization of coal-based synthetic natural gas slag as supplementary cementitious materials

This study investigated the feasibility of using coal-based synthetic natural gas slag (CSNGS) as supplementary cementitious materials in cement-based binders. The effects of different CSNGS/Cement ratios on the slump flow and mechanical strengths of paste and mortar were first analyzed. Subsequently, the mineralogy, morphology, and chemical structure of CSNGS-Cement paste were examined by means of XRD, SEM/EDS, FT-IR, and TG/DTG. The results showed that an appropriate incorporation of CSNGS contributed to the improvement of flowability due to the micro-filling effect. As the CSNGS proportion increased, the compressive strength decreased, while an appropriate amount of CSNGS was conducive to improving the flexural strength of mortar. The 28-day compressive strength of composite mortar reached over 89 % than that of the reference mortar under CSNGS within 0–30 %, possibly due to the increased contents of needle-like ettringite and C-A-S-H. Additionally, a formula considering the effective water absorption rate and pozzolanic activity of CSNGS was developed for predicting the compressive strength of CSNGS-cement mortar, demonstrating a good correlation coefficient (R² > 0.93) between predicted and measured values. Overall, CSNGS proves to be a feasible supplementary cementitious material, offering a promising way for the effective utilization of CSNGS as well as the clean production of concrete. © 2024 Elsevier Ltd. All rights reserved.