Mechanical Properties and Modulus Correlations of High-Strength Lightweight Concrete with Fly Ash Cenospheres

Abstract Lightweight concrete containing fly ash cenospheres (FAC) approaches a sustainable solution for cutting structural dead loads while maintaining high strength. This study investigates the mechanical properties and hydration behavior of high-strength lightweight concrete (HSLWC) using FAC as a partial sand replacement and supplementary cementitious materials (SCMs), including silica fume (SF), ground granulated blast furnace slag (GGBFS), and nano-silica (nS). Twelve mixes were proposed to evaluate the effects of FAC and SCMs on density, compressive strength, flexural strength, and elastic modulus. The results demonstrated that an increase in FAC content significantly decreased density while enhancing specific strength, highlighting the effectiveness of FAC in lightweight applications. SCMs enhanced the microstructure and mechanical performance via pozzolanic reactions and C─ S─ H formation. The optimal mix, comprising 40% GGBFS and 0.5% nS, achieved a compressive strength of approximately 80 MPa and showed improved flexural strength compared with the control. Thermogravimetric analysis confirmed a marked reduction in Ca(OH) 2 content, indicating active pozzolanic reactions. Unlike previous studies that focused only on strength or density, this work establishes predictive correlations between modulus, strength, and density ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mo>&gt;</mml:mo> <mml:mn>0.94</mml:mn> </mml:mrow> </mml:math> ), enabling engineering-based performance design of FAC HSLWC. These findings provide valuable insights into the design of high-performance, sustainable, and lightweight concrete.