Influence of pulp industry dregs on the physical and mechanical properties of mortar

This study examined the constituents and evaluated the effects of incorporating a pulp industry residue (dregs) on the physical and mechanical properties of mortar. The properties of the mortar constituents were evaluated using thermogravimetry-differential scanning calorimetry (TG-DSC), energy-dispersive spectroscopy (EDS), X-ray Fluorescence spectroscopy (XRF), X-ray diffraction (XRD), and tests specified in standards NBR 16605:2017, NBR 11579:2013, and NM 18:2012. The hardened mortar was evaluated through mechanical testing (NBR 7215:2019), water absorption testing (NBR 9778:2015), and mercury intrusion porosimetry. XRD data from dregs treated at different temperatures were analyzed using the Rietveld refinement method. The specific gravities of the cement, dregs, and sand were 3.13, 2.58 and 2.62 g/cm³, respectively. The main chemical elements detected in the dregs (> 1 atom%) were Ca, Mg, Mn, Si, Na, S, and Al. Thermal analysis revealed two endothermic events: the evaporation of sulfur-containing compounds and the decomposition of calcium magnesium carbonate. Lattice parameters were obtained for the Ca _0.87 Mg _0.13 (CO ₃ ) ₂ phase, observed in the dregs treated at 100 and 500 ^o C, and for the CaO and MgO phases, observed after treatment at 750 ^o C. Incorporating 40 wt% dregs led to a reduction in compressive strength of 73% under the Substitution condition and 52% under the Addition condition, compared with the mortar without dregs. This behavior is associated with increased water absorption and porosity as the dregs content in the mortar increased.