Paper Mill Lime Sludge Valorization as Partial Substitution of Cement in Mortar

Abstract

The solid waste accumulation from industries is becoming the cause of environmental concerns. Millions of tons of lime sludge are generated by the Pulp and paper and other industries all over the world. For the reduction of the solid waste threat to the environment, its application as a raw material in other industries could be the suitable option. In this study, lime sludge from recovery section of the paper mill is used in mortar in its as-received condition and in calcined condition to partially substitute cement. Calcination of lime sludge is performed at the relatively lower temperature of 650–750 °C, which takes less energy input than the industrial process of calcination. The M25 grade of mortar is prepared, with the substitution of cement by as received lime sludge in the range of 10, 20, 30 and 40% by weight. These blends of mortars are also prepared with calcined lime sludge. Produced mortar mixtures are tested for compressive strength and also compared with conventional mortar. Compressive strength is evaluated with 7, 28 days of curing. As a result, the compressive strength of mortar with as received lime sludge, match with the M25 grade of mortar up to 10% addition of lime sludge, after that compressive strength of mortar decreased with the further addition of lime sludge. Mortar blends with calcined lime sludge achieved the M25 grade compressive strength till 30% replacement of cement in mortar blends. Lime sludge after calcination produced more compressive strength in mortar than as received lime sludge due to the presence of reactive lime and pozzolanic materials. This study helps in developing the sustainable utilization of large amount of lime sludge, produced from paper industries ended up in landfills.