Paper Mill Sludge Ash as Supplementary Cementitious Material

Paper mill sludge is often incinerated for heat recovery and volume reduction. In Italy, about 600,000 t of paper mill sludge is produced yearly. About 6 kg of sludge is produced per ton of paper produced. The paper mill sludge is recovered from a primary mechanical separation process. When it is combusted as a single fuel source, it produces paper mill sludge ash (PA). In this project, PA was studied to evaluate its use as a supplementary cementitious material in mortars and concrete manufacturing. On the basis of the data collected, it was concluded that PA, if used to replace up to 10% of the portland cement, shows a positive effect on the mechanical performance of mortars. On the other hand, because of its high fineness and consequently high water absorption, it required a higher amount of water. It was concluded that the use of PA should not be higher than 10% by weight of the cement replaced, unless mortar mixtures are judiciously proportioned.