Enhancing the Mechanical and Thermal Properties of Lightweight Concrete through Incorporation of Well-Graded Bottom Ash as a Partial Fine Aggregate Replacement

Abstract The use of lightweight concrete is gaining prominence in civil engineering because of its effectiveness in minimizing dead loads. However, the increased reliance on concrete has accelerated the depletion of natural resources, raising environmental concerns. This challenge has led to a growing interest in finding sustainable alternatives within the field of civil engineering. This study focuses on the enhancement of bottom ash (BA) to develop a well-graded version (BAW). It examines the impact of replacing fine aggregates with BAW on the mechanical and thermal characteristics of lightweight concrete. The research experimented with different BAW incorporation levels, ranging from 5 % to 35 % by volume. The results showed a consistent decrease in concrete density with increasing BAW replacement, as well as varying changes in mechanical and thermal performance across the tested range of 0–35 % by volume. Mechanical and thermal properties peaked at 15 % before falling. Compressive strength peaked at 36.7 MPa at 15 % and dropped to 26.9 MPa at 35 %. Flexural strength increased to 2.85 MPa at 15 % and 2.57 MPa at 35 %. Split tensile strength increased to 0.76 MPa at 15 % and decreased to 0.63 MPa at 35 %. Ultrasonic pulse velocity reached a maximum speed of 3.86 km/s at 15 % and 3.18 km/s at 35 %. Thermal conductivity increased to 1.67 W/m·K at 15 % and dropped to 1.06 W/m·K at 35 %. The 15 % BAW level optimizes performance, whereas higher replacement rates increase porosity. These findings indicate that well-graded BA enhances the properties of concrete, offering reliable and sustainable material for use in modern construction.