Upgrading and Evaluation of Waste Paper Sludge Ash in Eco-Lightweight Cement Composites

The upgrading and evaluation of waste paper sludge fly ash (PsFA) as a cement substitute in wood-wool composite boards (WWCB) is investigated in the present study. This type of board is widely applied in the building environment because of its excellent thermal and acoustical properties; however, cement is still widely used as a binder although environmentally its use leads to a high ${\mathrm{CO}}_2$ footprint of the composite and is therefore less favorable for sustainable building designs. Paper sludge fly ash could be a feasible replacement of cement; however, its high water demand limits the substitution level to 10% by mass of binder. Therefore, different upgrading methods including water treatment and thermal treatment are performed, and their effects are evaluated using various analytical methods. Afterward, PsFA’s suitability as a binder replacer in WWCB is investigated with the hypothesis to refine the microstructure of the boards, resulting in extra lightweight properties. A substitution level of binder with the upgraded PsFA by 20–60% in WWCB can be achieved and is confirmed by the improved mechanical, thermal-insulating, and sound-absorbing properties.