Use of Dregs as a Replacement for Hydrated Lime in Cement Coating Mortar

The pulp and paper industry generates a significant volume of solid waste during its operations. In order to mitigate the environmental impact caused by this industry, one of its residues was applied in eco-friendly composites. Therefore, this research aims to use green liquor dregs as a partial replacement for lime in coating mortars. Hydrated lime was replaced by dregs in percentages of 10%, 15%, 20%, and 30%, and the manufactured mortar specimens were tested in terms of their flowability, air content, and specific gravity in the fresh state. In the hardened state, physical and chemical characterization was carried out to determine the influence of the introduction of the dregs on the properties of the different types of mortar. Mechanical testing of the mortar specimens' compressive, flexural, and adhesive strengths was carried out, and scanning electron microscopy was performed to evaluate the microstructural features of the cement composites. In general, the types of mortar with dregs showed a high degree of similarity to conventional mortar in all studied aspects, including the 30% replacement group. The obtained SEM images indicated that the presence of dregs in the mortar did not change the formational mechanism of C-S-H crystals, maintaining the mechanical properties of the material even after the accelerated aging procedure was performed, reaching similar levels of flexural, compressive, and tensile bond strengths when compared to the neat mortar. Furthermore, tensile bond levels reached approximately 0.9 MPa for all the studied types of mortar, allowing the material to be used in external applications.

Automated summary

This research aims to use green liquor dregs as a partial replacement for lime in coating mortars in order to mitigate the environmental impact caused by the pulp and paper industry. The results showed that the mortars with dregs exhibited similar properties to conventional mortar in terms of flowability, air content, and specific gravity. Mechanical testing and scanning electron microscopy revealed that the introduction of dregs did not change the formational mechanism of C-S-H crystals and the material maintained its mechanical properties even after accelerated aging, reaching similar levels of strengths. Therefore, the mortar with dregs can be used in external applications.