Structural Self-Compacting Lightweight Concrete: Effects of Fly Ash and Basalt Fibers on Workability, Thermal and Mechanical Properties Under Ambient Conditions and High Temperatures

Abstract

In today's concrete technology, the use of pumice aggregate (PA) in the production of lightweight concrete is increasingly gaining popularity. This study investigates PA-based self-compacting lightweight concrete (SCLWC), focusing on the effects of fly ash (FA), and single and hybrid basalt (BA) fibers on its fresh and hardened properties under ambient and high-temperature conditions. Replacing 10 % of Portland cement (PC) with FA significantly enhances workability, as shown by improved slump-flow, L-box, and V-funnel test results. The spherical shape of FA enhances fluidity, aiding mixing and placement. However, the addition of macro-BA fibers reduces workability due to their length and frictional resistance during mixing. The inclusion of micro- and macro-BA fibers improves retained splitting tensile strength (RSTS) and compressive strength (RCS) after exposure to high temperatures, which is crucial for maintaining structural integrity despite reduced workability. FA contributes little to strength gains at 7 and 28 days, but by day 120, significant improvements are observed, indicating increased pozzolanic activity. FA and BA fibers enhance the thermal properties of SCLWC. BA fibers improve durability, while FA reduces the thermal conductivity coefficient (TCC), improving insulation. After exposure to 800°C, the compressive strength (CS) of the K0 control specimen decreased by 77.23 %, while for K1-K5 specimens, the decrease ranged from 69.53 % to 78.29 %. Similarly, the splitting tensile strength (STS) of K0 fell by 74.38 %, while for K1-K5, it varied from 62.76 % to 76.58 %. The TCC of K0 was 0.357 W/mK, while for K1-K5, it ranged from 0.282 to 0.323 W/mK. © 2025 Elsevier Ltd