Investigating the influence of expanded perlite and lime mud on cement-bonded composites containing pulp sludge

This paper presents a comprehensive study on lightweight cement-bonded composites containing pulp sludge (PS). The objective of the study was to evaluate how the incorporation of perlite (a lightweight volcanic glass aggregate) and lime mud (a pulp mill residue) influences composites' properties including mechanical strength, insulation and fire resistance. Up to 50% of the cement binder was replaced with PS (by mass), and small fractions of cement (5-15%) were replaced with perlite or lime mud. A suite of analytical techniques, material characterization and mechanical tests with digital image correlation (DIC) for strain analysis were employed. X-ray analysis showed that the aggregates influenced the composite properties to a considerable extent due to their particle sizes and ability to form hydrated gels with cement. Adding 5% of perlite or lime mud yields optimal strength without compromising weight reduction whereas higher aggregate content (15%) led to reduced strength. The DIC system provided insights into strain distribution during loading, confirming enhanced toughness from the fibrous PS. The composites were significantly lighter (732-749 kg/m³) and showed about 30% lower thermal conductivity (0.17 W/mK) than pure cement composites (0.25 W/mK). The normal incidence sound absorption of the composites was about 0.3 at mid-high frequencies due to their compact structure. The composites demonstrated potential for use as sustainable, lightweight construction materials with good acoustic and thermal insulation, as well as acceptable load-bearing capacity for non-structural applications based on EN 634-1/-2 requirements for cement-bonded particleboards.