Mechanical performance of structural lightweight concrete with metallurgical coal aggregates

Many studies have investigated industrial by-products as alternatives to natural aggregates; however, little attention has been given to metallurgical coal (MC). This study evaluates MC as a replacement for coarse aggregate to develop structural lightweight concrete (SLWC), using five mixtures with MC contents of 0%, 25%, 50%, 75%, and 100% by weight. To this end, an experimental program on testing the microstructural and chemical analysis of MC and the mechanical properties of fresh and hardened concrete was conducted. The results showed that increasing MC reduced mechanical performance; compressive (flexural) strength decreased from 37.6 (5.17) MPa at 0% MC to 20.7 (2.75) MPa at 100% MC. Furthermore, increasing the MC content reduced the elastic modulus per four international codes. On the other hand, the results showed that MC significantly decreased density, achieving up to a 24.3% reduction relative to normal-weight concrete and satisfying lightweight classification. Moreover, concrete mixtures with 25% and 50% MC maintained adequate structural performance when subjected to elevated temperatures. From an economic perspective, 75% MC lightweight concrete was more cost-effective and required 12% less reinforcing steel than normal-weight concrete. These findings indicate that MC can improve natural resource sustainability and offer a cost-effective route for sustainable construction.