Influence of expanded perlite and vermiculite pore structures on acoustic and thermal properties of quicklime-activated fly ash composites

Abstract

This study was motivated by the demand for sustainable, cementless building materials that provide both acoustic and thermal efficiency. Fly ash-based composites incorporating 0-10 wt% expanded perlite (EP) or vermiculite (EV) were experimentally evaluated using impedance tube, laser flash, and microstructural analyses. The incorporation of EV (lamellar) demonstrated superior sound absorption performance compared to EP (closed-shell), achieving a maximum NRC of 0.27. This enhancement is likely attributed to the open, lamellar pore structure of EV, which is more effective in dissipating acoustic energy than the closed-cell morphology of EP. Both additives increased porosity and reduced composite density (1.12 g/cm3); 10 % EP mixture achieving the lowest thermal conductivity (0.372 W/m & sdot;K), likely due to air entrapment within closed pores that inhibited heat transfer. The compressive strength ranged from 12.2 to 19.6 MPa and showed a slight decrease with increasing additive content. However, composites incorporating EP consistently exhibited higher strength than those with EV, which may be attributed to the closedshell structure of EP being more favorable for mechanical strength. Leaching tests for Cd, Cr, Cu, Pb, and As confirmed that all heavy metal concentrations remained well below the regulatory limits set by the U.S. EPA. X-ray diffraction analysis revealed no new reaction products, suggesting that the observed improvements were primarily driven by the intrinsic microstructures of EP and EV.