Synergistic effects of vermiculite, pumice stone, and micro-silica on the mechanical and microstructural performance of lightweight concrete

Lightweight concrete (LWC) is widely used in construction due to its lower density, improved thermal insulation, and enhanced fire resistance. This study investigates the utilization of vermiculite and pumice stone as fine and coarse aggregate replacements, respectively, in LWC, together with micro-silica incorporated at 5%, 10%, 15%, and 20% by weight of cement and a superplasticizer dosage of 0.3%. A comprehensive experimental program comprising 32 mix proportions, each tested in triplicate, was conducted to evaluate the influence of these materials on the microstructural and mechanical performance of LWC. The novelty of this study lies in its detailed investigation of the synergistic effects of vermiculite, pumice stone, and micro-silica on key performance parameters, including density, void ratio, water absorption, and mechanical strength. Among all mixtures, mix number 31 (MN31), containing micro-silica, exhibited the best overall performance, achieving the highest compressive strength (CS) of 17.65 N/mm², satisfying the requirements of ASTM C330 for LWC. The MN31 mix also attained a density of 1438.48 kg/m³, a flexural strength (FS) of 2.84 N/mm², and a split tensile strength (STS) of 1.63 N/mm². Furthermore, microstructural characterization using field-emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDS) revealed improved matrix integrity and refined pore structure, which contributed to the enhanced mechanical performance of the developed LWC.