Reuse of de-inking sludge from wastepaper recycling in cement mortar products

This paper presents results of an investigation into the use of de-inking sludge from a paper recycling mill as feedstock material in the manufacture of cement mortar products, including masonry blocks and mortar renders. Both physical and mechanical properties of mortar specimens containing various amounts of de-inking sludge were investigated. It was observed that the addition of de-inking sludge to cement mortar at a fixed water-to-cement ratio significantly reduced flow properties and increased setting time. Water absorption and volume of permeable voids of cement mortar increased with increased dosage of de-inking sludge, with a corresponding reduction of bulk density. The 91-day compressive strength of mortar samples with 2.5 wt% and 20 wt% de-inking sludge loadings retained 83% and 62% respectively of the reference mortar strength. The corresponding drying shrinkage increased by up to 160% compared to reference samples. However, a de-inking sludge loading of up to 2.5 wt% did not significantly alter measured physical and mechanical properties. The results demonstrate that despite the high moisture absorbance of de-inking sludge due to its organic matter and residual cellulose fibre content, it serves as a potential supplementary additive and its cellulosic content proving to be an active set retardant to cementitious masonry products.