Abstract
Abstract
Lightweight concrete (LWC) is increasingly utilized in sustainable construction because of its ability to reduce structural dead loads while maintaining performance under aggressive environments. Natural pumice, a highly porous volcanic aggregate, has potential as a lightweight coarse aggregate owing to its low density and internal moisture regulation. However, its vesicular structure increases porosity and weakens the interfacial transition zone (ITZ), thereby reducing strength and durability. This study evaluated the combined effects of pumice aggregates, silica fume, and carbon fiber on the mechanical, durability, and microstructural properties of structural lightweight concrete. M30 and M50 concretes were produced with pumice replacement levels of 0–100 %. Based on strength–density considerations, 40 % replacement was selected as the best-performing level, and modified using 10 % silica fume and 1 % carbon fiber. Mechanical properties were assessed through compressive, split tensile, and flexural strength tests, while durability was evaluated under 5 % sulphuric acid exposure for 28, 56, and 90 days using AMLF, AAF, ASLF, and ADLF indices. Compressive strength decreased with increasing pumice content, from 38.07 to 10.37 MPa (M30) and 58.67 to 19.85 MPa (M50). However, the modified mix achieved 37.78 MPa and 57.33 MPa, respectively, with improved tensile and flexural performance. The hybrid system exhibited the lowest deterioration under acid exposure. SEM–EDS analysis confirmed matrix densification and improved ITZ due to the silica fume, while the carbon fibers enhanced crack resistance through bridging action.