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

Influence of pulp industry dregs on the physical and mechanical properties of mortar | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Influence of pulp industry dregs on the physical and mechanical properties of mortar Luis Felipe Moreira Cesar, Agda Eunice de Souza Albas, Nelson Batista de Lima, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8807219/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 4 You are reading this latest preprint version Abstract 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. Dregs waste reuse mortar X-ray diffraction Rietveld refinement thermal analysis pore size distribution Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction Brazil is the second-largest producer of cellulose in the world, with an annual production of over 20 million tons (IBÁ 2025). As a consequence, the Brazilian pulp industry generates large amounts of solid waste, mostly lime mud, dregs, grits, and biomass ash. In modern industries, lime mud is essentially recovered through advanced calcination systems, making dregs the most abundant residue resulting from cellulose production. This waste corresponds to approximately 15 kg per ton of cellulose pulp produced (Torres et al. 2020 ), resulting in nearly 300 thousand tons of dregs annually from Brazilian industries, most of which is disposed of in landfills. Finding sustainable solutions for this waste is a major challenge to reduce damage to the environment and, consequently, impact on the food chain and human health. Different investigations have been carried out using paper pulp residues, such as: (a) the use of dregs as a filler in the production of geopolymeric mortars based on biomass fly ash, which is also generated during cellulose production (Novais et al. 2018 ; Novais et al. 2019 ); (b) the use of dregs as filler to replace commercial calcium oxide in natural rubber composites (Bittencourt et al. 2020 ); (c) use of dregs-grits in mortar for wall and ceiling coating (Zanella et al. 2014 ); (d) the use of dregs-grits as a permeable reactive barrier for the removal of copper and sulfate in mine drainage (Farage et al. 2020 ); (e) the replacement of clinker with dregs-grits in the manufacture of Portland cement (Buruberri et al. 2015 ; Simão et al. 2019 ); and (f) use of dregs-grits for the correction of acidic soils (Medeiros et al. 2009 ; Cabral et al. 2008 ). In the literature, few studies have investigated the replacement of Portland cement with dregs in mortars. Gemelli et al. ( 2001 ) examined mortars containing waste from the pulp and paper industry. They used four different materials: bottom ash, grit, dregs, and fibers. Only one sample was prepared using dregs as a replacement (2.62% relative to the dregs-free composition) for CP I-S32 cement. The incorporation of dregs into the mortar as a cement replacement reduced compressive strength by 20.4%. Zanella et al. ( 2014 ) evaluated the durability of mortars applied to walls and ceilings containing 0, 10, and 20% dregs-grits as a substitute for river sand. Their evaluation included ultraviolet radiation, salt spray, thermal degradation, and thermogravimetric tests. The way the authors reported the mortar composition suggests that dregs-grits may have been used as a substitute for lime rather than for sand. The Portland cement used was type CPIII. They concluded that incorporating 10 and 20% dregs-grits into the mortar did not affect durability under thermal degradation, thermogravimetric, or ultraviolet radiation tests, except under salt spray exposure. Martinez-Lage et al. (2016) studied the feasibility of using fly ash and dregs in mortars and concretes by analyzing the compressive and flexural strengths after 28 days of curing. Mortars containing 10, 20, and 30% dregs were prepared to replace CEM-I 52.5 N/SR cement. They concluded that both flexural and compressive strengths decrease as the content of dregs and fly ash increases. For contents of 10 and 20%, the strength in strength is less than 10%. Oliveira et al. ( 2023 ) investigated coating mortars without additives by partially replacing 10, 15, 20, and 30% of hydrated lime with dregs, evaluating properties in both fresh and hardened state. CPII-F40 cement was used. They concluded that replacing lime with dregs, regardless of percentage, did not impair the performance of the mortars in terms of rheological, physical, or mechanical characteristics. Falcão et al. ( 2024 ) analyzed the effect of dregs on alkali-silica reaction in mortars. Six types of cement were used: CP II-F40, CP II-Z32, CP III-RS40, CP IV-32, CP V-ARI, and CVP-ARI RS. Dregs were added at proportions of 5, 10, and 15% relative to cement mass. Cement, sand, and water masses were kept constant. The alkali-silica reaction was evaluated by the prism method (NBR 15577-4), and compressive strength was used as a control parameter for the tested mortars. The author´s main conclusions were: (a) in reference mortars, some cements produced expansions above the limit established by Brazilian standards, and in most cases, the addition of dregs increased expansions as the residue content increased; (b) cements with high additive content, such as CP IV and CP III, showed excellent ability to inhibit expansion caused by the alkali-silica reaction; and (c) cements with pozzolanic additive demonstrated lower expansion rates over time because the additive continues reacting with cement constituents. Given the above, further research is needed to ensure the performance, durability, and safety of using cellulose waste in mortars. In this context, our group has recently begun a systematic investigation aimed at providing a sustainable application for dregs in coating and laying mortars. As the first result of this long-term effort, we present information on the characterization of the constituents (CPV-ARI cement, Tietê River sand and dregs) and on the influence of the residue on the physico-chemical and mechanical properties of the prepared mortars. Materials and methods Materials: origin and treatments The Portland cement (CP) used in this study was CPV-ARI, a high-early-strength cement manufactured by Cimento Nacional (Arcos, MG, Brazil), which did not undergo any treatment prior to mortar preparation. This type of cement was chosen because it does not contain additives such as slag or pozzolans in its composition. The dregs used in this study were supplied by Suzano Papel e Celulose S.A. industrial plant in Três Lagoas (MS, Brazil). Before mortar preparation, the material was dried at 100 o C for 24 hours, then ground using a Minutem MLW LM-1 ball mill and sieved through a 53 µm (ASTM 270). The sand used was extracted from the Tietê River by the company Porto de Areia Irmãos Brambilla (Pereira Barreto, SP, Brasil). Before use, the sand was dried at 100 o C for 24 hours and then sieved according to NBR 7214:2015. Consequently, the sand used in this study consists of grains ranging from 0.15 to 2.4 mm. Raw materials characterization The specific mass of the precursors (cement, sand and dregs) was determined according to the procedure recommended by NBR 16605:2017, which uses a Le Chatelier volumetric flask. Deionized water was used in the tests with dregs and sand, while kerosene was used for the cement tests. Three tests were performed for each precursor. The fineness modulus and loss on ignition of the cement were evaluated following the methodology prescribed in NBR 11579:2013 and NM 18:2012, respectively. The structural properties of the dregs were investigated using TGA/DSC, energy dispersive X-ray spectroscopy (EDX), X-ray fluorescence spectroscopy (XRF), and X-ray diffraction (XRD) techniques. Thermal behavior was obtained with a simultaneous thermal analyzer from TA Instruments, model Q600 SDT, operating between room temperature to 1100 o C at a heating rate of 10 o C/min under nitrogen atmosphere. Chemical elements identification in the dregs was performed using an EDX detector coupled to a Zeiss scanning electron microscope (SEM), model EVO-LS15. Diffractograms were obtained with a Shimadzu diffractometer, model XRD-6000, using Cu-Ka radiation, at room temperature, with a Bragg angle between 20 and 70 o . Mortar preparation and characterization Nine different mortar compositions were prepared (Table 1 ): one without dregs (Ref), four with the dregs added to the mixture (A), and four width dregs used as a substitute for CP (S), at concentrations of 5, 10, 20, and 40 wt%. The sand mass was kept constant, and the water-to-fines ratio (cement + dregs) was defined for each composition to obtain the ideal mortar consistency of (260 ± 5) mm, as recommended by NBR 16541:2016. The incorporation of dregs into the mixture slightly altered the water/fines ratio, as shown in the table. In the Addition condition, the required values water/cement ratio required was lower (from 0.48 to 0.5) than that of the sample without dregs (0.55). In contrast, under the partial replacement condition, where CP was substituted by dregs, it was necessary to increase the ratio to 0.58 in two of the four proportions tested (5 and 40%). Table 1 Mixture composition of the mortars. Sample name Cement (g) Dregs (g) Sand (g) Water/fines ratio Ref 900 0 2700 0,55 A05 900 45 2700 0,50 A10 900 90 2700 0,50 A20 900 180 2700 0,48 A40 900 360 2700 0,50 S05 855 45 2700 0,58 S10 810 90 2700 0,55 S20 720 180 2700 0,55 S40 540 360 2700 0,58 Five test specimens were prepared for the compressive strength tests and three for the water absorption tests, according to NBR 7215:2019 and NBR 9778:2005, respectively. Cylindrical metal molds measuring 5 cm in diameter and 10 cm in height were used. Immediately after molding, the specimens were stored in a chamber at 100% relative humidity and a temperature of (23 ± 2) ºC. After 24 hours, they were demolded and kept in the chamber until completing 28 days of curing. Mechanical tests were performed using an EMIC universal testing machine, model DL30000M, equipped with a 300 kN load cell and operating at a rate of (0.25 ± 0.05) MPa/s. Water absorption was determined in accordance with NBR 9778:2005, using an oven (Odontobras – SP, Brazil), model EL1.1, and a digital balance with a precision of 0.1 g. First, the specimens were weighed after drying at (105 ± 5) ºC for 72 h. They were then immersed in water for the same period and weighed again. Water absorption was calculated using the expression below, where m i and m s correspond to the dry mass and water-saturated mass of the specimen, respectively. $$\:{Abs}_{H2O}=\left(\frac{{m}_{s}-{m}_{i}}{{m}_{i}}\right)\times\:100$$ Porosity was evaluated using a mercury intrusion porosimeter (Autopore III - Micromeritics) within a pressure range of 0 to 414 MPa. The minimum detectable pore size was 3 nm, corresponding to the maximum applied pressure. A 1 cm 3 sample of each mortar composition was extracted from the specimens used in the water absorption test. Prior to analysis, all samples were degassed under vacuum at a pressure below 50 µPa. Statistical analysis Statistical analysis was performed using SigmaPlot software (Systat Inc, San Jose, CA, USA), version 12.0. The significance level was set at p < 0.05. Water absorption and compressive strength data showed a normal (Shapiro-Wilk) and homogeneous (Levene's test) distribution and were subjected to one-way analysis of variance, followed by Fisher LSD test. Results and discussion Raw material characterization The densities (mean ± SD) obtained for the cement, dregs, and sand were (3.13 ± 0.02), (2.58 ± 0.01), and (2.62 ± 0.01) g/cm 3 , respectively. The CPV-ARI cement exhibited a fineness modulus of 5.9 and a loss on ignition of 5.7%, both in accordance with the limits established by standards NBR 11579 and NM18, respectively. Figure 1 shows the TGA/DSC thermograms obtained for the dry dregs. In the TGA curve (red), three mass-loss events can be observed: from 50 to 200 o C, from 200 to 550 o C, and from 550 to 1000 o C. The first event corresponds to a slight mass loss (1%), attributed to the evaporation of residual water. The second event, corresponding to a 4,5% mass loss, may be due to the decomposition of sulfur-containing compound resulting from the chemical recovery stage of the kraft process, and is associated with the endothermic peak at 353 o C in the DSC curve. This endothermic event was also reported by Andesanya et al. (2025), who attributed it to the dehydroxylation of brucite; however, as shown below, this phase is not observed in our XRD data. Martins et al. ( 2007 ) and Torres et al. ( 2020 ) associated this endothermic peak with gypsum dehydration; however, complete gypsum dehydration generally occurs below 200°C. Elemental analysis by EDX shows the presence of small amounts of sulfur and sodium in the dregs (Table 2 ), indicating that, despite the high efficiency of the kraft chemical recovery process, it is not fully complete. Among the possible sulfur compounds formed in this process is sodium thiosulfate. Despite its greater solubility compared to sulfides, sulfates, and sulfites, sodium thiosulfate can precipitate in highly alkaline media, and its decomposition occurs between 300 and 400°C (Padamurthy et al. 2019 ; McAmish et al. 1976). The last mass-loss event (34,4%) results from the decomposition of calcium carbonate, which releases CO 2 and forms calcium oxide (Santos et al. 2019 ). This decomposition corresponds to the endothermic peak observed at 734 o C in the DSC curve. A decrease in the mass percentage of C and O can also be observed in the EDX analysis (Table 2 ), as expected given that calcium carbonate is known to be the main constituent of the dregs. The SEM image of the dry dregs in Fig. 2 shows crystalline structures of various sizes. The analysis performed in the highlighted area reveals predominantly the presence of C, O, and Ca, confirming that the Ca in these crystalline structures is present in the form of carbonate. Table 2 Main chemical elements detected in the dregs by EDX spectroscopy. Chemical element Treated to 100 o C (atom%) Treated to 750 o C (atom%) O 51.3 38.8 C 8.4 3.3 Ca 20.7 33.9 Mg 10.3 12.6 Mn 2.7 3.1 Si 2.2 2.7 Na 1.9 1.7 S 1.6 2.1 Al 0.9 1.1 Fe 0.7 0.8 To observe the phase transformations, the dried dregs powder (treated at 100 o C for 24 h) was subjected to two additional heat treatments: 500 o C for one hour (a temperature between the two endothermic transitions observed in Fig. 1 ) and 750 o C for two hours (above the endothermic transition centered at 734 o C). Figure 3 shows the diffractograms of dregs powders treated at three different temperatures. In the first two diffractograms, corresponding to treatments at 100 and 500 o C, only the calcium carbonate phase (ICSD #73446) was observed. In contrast, the powder treated at 750 o C, exhibited the CaO (ICSD #51409) and MgO (ICSD #61325) phases. The absence of the crystalline magnesium phase in the dregs powders treated at 100 and 500 o C suggest that Mg may be partially substituting Ca in the calcium carbonate structure. Therefore, the diffractograms presented in Fig. 3 were analyzed using the Rietveld refinement method using the GSAS-II software package. For the diffractograms corresponding to 100 and 500 o C, a standard crystalline phase of calcium-magnesium carbonate was used (ICSD card #40108). During refinement, the occupancy parameter of the Ca and Mg atoms were set at 0.87 and 0.13, respectively. These values were estimated from XRF data, using a calibration curve constructed with standard mixtures of CaO (Sigma-Aldrich, 99+%) and MgO (Sigma-Aldrich, ≥ 99%) in different proportions. Figure 4 shows the Rietveld output for the analyzed dregs powders, and the structural parameters extracted from the refinement are summarized in Table 3 . Table 3 Lattice parameters obtained from the Rietveld refinement of the dregs powder heat-treated at three different temperatures. T ( o C) Lattice parameters (Ǻ) Weigth fraction (%) Ca 0.87 Mg 0.13 (CO 3 ) 2 CaO MgO Ca 0.87 Mg 0.13 (CO 3 ) 2 CaO MgO 100 a = b = 4.98904 c = 17.0616 α = β = 90 γ = 120 1 0 0 500 a = b = 4.98839 c = 17.07828 α = β = 90 γ = 120 1 0 0 750 a = b = c = 4.81512 α = β = γ = 90 a = b = c = 4.21342 α = β = γ = 90 0 0.864 0.136 Mortar in the hardened state The influence of dregs on the composition of mortars was evaluated based on their physical and mechanical properties in the hardened state. Figure 5 shows the results of the compressive strength tests for the mortars without dregs (Reference) and with dregs under addition and replacement conditions. Overall, compressive strength decreased as the dregs content increased, regardless of the incorporation method. This trend is more pronounced in the replacement condition, suggesting that dregs do not participate in the hydration process. In this condition, the reduction in cement limits the formation of binding phases such as calcium silicate hydrate (C–S–H), which is essential for strength development. In the addition condition, although the cement content has been maintained, the dregs may act as an inert material, diluting the matrix without contributing reactivity. Statistically, no significant difference were observed between Ref and S05, A5 and S5, A5 and A10, A10 and A20, A20 and S10, and A40 and S20. In contrast, Falcão et al. ( 2024 ) observed no significant difference in compressive strength when incorporating 5–15 wt% dregs into the mortar. This difference in behavior may be attributed to the richer composition used by authors (cement/sand = 1:2.25), the fixed water/cement ratio at 0.47, and the difference in dreg granulometry. Opposite to the behavior observed for compressive strength, the water absorption results (Fig. 6 a) show an increase in absorption as the dregs content increases, with a more pronounced effect in the addition condition. Statistically, only A05 did not differ significantly from the control composition (Ref). Similar behavior was observed in porosity measurements (Fig. 6 b), with pore volume increasing as the dregs content increased. The evolution of pore distribution as a function of dregs content after 28 days of curing is shown in Figs. 7a and 7c (replacement condition) and 7b and 7d (addition condition). In general, regardless of the method of incorporation, the pore size distribution in Ref shown a narrow peak between 0.02 and 0.61 µm, centered at 0.09 µm (Figs. 7c and 7d), corresponding to C-S-H gel pores. Increasing the dregs content shifted this peak toward larger pores, likely due to the weakening of the interfacial transition zone (ITZ) between the cementitious matrix and the sand grains (Chen et al. 2024 ; Scrivener et al. 2004 ). Structurally, the ITZ is less dense and more porous compared with surrounding cement matrix. The peak shift indicates that the powder does not contain a sufficiently fine particle size for the dregs to act as a filler, as their particle size was not controlled for this purpose. Figure 7 Evolution in pore-size distribution in hardened mortars prepared under the replacement (a, c) and addition (b,d) conditions. Unlike the other compositions, two distinct pore distributions were observed in A40 and S40: one corresponding to smaller pores within the cement matrix, and another associated with larger pores from the IZT and dregs particles. This confirms that dregs act as inert particles, generating larger voids after the evaporation of retained water. Furthermore, the relative proportion of these two pore populations is greater in A40 than in S40, indicating that in the replacement condition the population of smaller pores is reduced due to the lower cement content, corroborating the interpretation that these smaller pores are associated with the cementitious matrix. Finally, in addition to these factors, the lower density of dregs (2.58 g/cm 3 ) compared with cement (3.13 g/cm 3 ) contributed to changes in packing density and pore structure, resulting in the observed compressive strength behavior as the residue content increased. Conclusion In this study, the influence of dregs on the physical and mechanical properties of mortars was evaluated. Dregs was incorporated into the mortar composition in two different ways: by direct adding them to the mixture and by partial replacing cement. Two endothermic events were observed in the thermogravimetric curve: the first was probably associated with sodium thiosulfate, and the second with the decomposition of calcium and magnesium carbonate, releasing CO 2 and forming CaO e MgO. No significant change was observed in the lattice parameters of the Ca 0.87 Mg 0.13 (CO 3 ) 2 phase in the dregs powders treated at 100 and 500 o C. In the diffractogram of the powder treated at 750 o C for 2 h, only the CaO and MgO phases were observed, with weight fractions of 86.4% and 13.6%, respectively. Increasing the dregs content in the mortar composition, regardless of the incorporation method (addition or replacement), increases the pore volume and alters the particle-size distribution, resulting in a decrease in compressive strength. Despite the significant reduction in strength for dregs contents of 20 and 40%, this does not preclude the use of the residue in mortar for certain civil construction applications in civil, such as laying and coating. Declarations Acknowledgements This work was supported by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (Finance Code 001) and Fundação de Amparo à Pesquisa do Estado de São Paulo (Finance Code 17/13769-1). The authors are grateful to Suzano Papel e Celulose S.A. and Porto de Areia Irmãos Brambilla for donating the dregs and sand, respectively; to technicians Elton José de Souza and Gilson Campos Ferreira, for technical assistance with scanning electron microscopy and compressive strength measurements, respectively; and to Dr. Celso Valentim Santilli, from the Chemistry Institute of Unesp - Araraquara, for the porosity measurements. Funding Author Luis Felipe Moreira Cesar received a scholarship from the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (Finance Code 001). Author João Carlos Silos Moraes received funding from the Fundação de Amparo à Pesquisa do Estado de São Paulo (Grant No. 23/13769-1) for the repair of the SEM EVO LS15 equipment. Authors contributions Luis Felipe Moreira Cesar, João Carlos Silos Moraes, and Jorge Luis Akasaki contributed to the conception and planning of the study. Luis Felipe Moreira Cesar and João Carlos Silos Moraes contributed to the preparation, collection, and analysis of the data. Agda Eunice de Souza Albas contributed to the collection and analysis of the XRF data. Nelson Batista de Lima contributed to the analysis and refinement of the XRD data. The first draft of the manuscript was written by Luis Felipe Moreira Cesar, and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript. Ethical Approval This is not applicable Consent to Participate This is not applicable Consent to Publish This is not applicable Competing interests The authors declare that they have no relevant financial or non-financial interests to disclose. Data Availability Statement The authors declare that the data supporting the findings of this study are available within the paper and its Supplementary Information files. 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Am J Environ Sci 10:44-47. https://doi.org/10.3844/ajessp.2014.44.47 Cite Share Download PDF Status: Under Review Version 1 posted Reviewers agreed at journal 26 Feb, 2026 Reviewers invited by journal 26 Feb, 2026 Editor assigned by journal 17 Feb, 2026 First submitted to journal 16 Feb, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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Cesar","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA5UlEQVRIiWNgGAWjYLCCBDirAkIxk6DlDLFa4ICxjQgtuu29Dx883GPHwN/e/vBz5bzDefz8Zw8wF+7BrcXszHFjg4RnyQwSZ84YS57ddrhYckZeAvOMZ3i03Ehjk0g4wMxgIJHDINm47XDihhs8Bsw8B/BqYf+RcKCewUD++eOfjXMOJ+4/f4agFjaGhAOHgbYwmEk2NgBtYcghoOXMMWagw47zSJzJMbNsOJaeOONGXsLhGfi0HG9j/PjjQLUcf/vxxzcbaqwT+/vPHnxcgEcLDPCgsInQgFv7KBgFo2AUjAIGBgBTYlOIFuMQ0wAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0002-5595-1159","institution":"Sao Paulo State University Julio de Mesquita Filho Ilha Solteira Campus Faculty of Engineering: Universidade Estadual Paulista Julio de Mesquita Filho Faculdade de Engenharia","correspondingAuthor":true,"prefix":"","firstName":"Luis","middleName":"Felipe Moreira","lastName":"Cesar","suffix":""},{"id":597715678,"identity":"205edd94-6d62-412e-a096-c4f37279694c","order_by":1,"name":"Agda Eunice de Souza Albas","email":"","orcid":"","institution":"Sao Paulo State University Julio de Mesquita Filho: Universidade Estadual Paulista Julio de Mesquita Filho","correspondingAuthor":false,"prefix":"","firstName":"Agda","middleName":"Eunice de Souza","lastName":"Albas","suffix":""},{"id":597715679,"identity":"8a3af9a8-5328-4055-a194-50839382b256","order_by":2,"name":"Nelson Batista de Lima","email":"","orcid":"","institution":"IPEN: Instituto de Pesquisas Energeticas e Nucleares","correspondingAuthor":false,"prefix":"","firstName":"Nelson","middleName":"Batista","lastName":"de Lima","suffix":""},{"id":597715680,"identity":"b60df208-b50a-48f9-9a1b-bb82342c385b","order_by":3,"name":"Jorge Luis Akasaki","email":"","orcid":"","institution":"Sao Paulo State University Julio de Mesquita Filho: Universidade Estadual Paulista Julio de Mesquita Filho","correspondingAuthor":false,"prefix":"","firstName":"Jorge","middleName":"Luis","lastName":"Akasaki","suffix":""},{"id":597715681,"identity":"22adb379-eaa6-4da9-94da-182b64d79303","order_by":4,"name":"João Carlos Silos Moraes","email":"","orcid":"","institution":"UNESP: Universidade Estadual Paulista Julio de Mesquita Filho","correspondingAuthor":false,"prefix":"","firstName":"João","middleName":"Carlos Silos","lastName":"Moraes","suffix":""}],"badges":[],"createdAt":"2026-02-06 12:43:42","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8807219/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8807219/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":104401034,"identity":"b1fd94e8-2aca-431f-89fb-015852f481fd","added_by":"auto","created_at":"2026-03-11 12:11:43","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":79002,"visible":true,"origin":"","legend":"\u003cp\u003eDSC (heat flow) and TGA (mass-loss) curves of dry dregs powder.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8807219/v1/09f8c21e577c33e2964f371d.png"},{"id":103852181,"identity":"38d0da88-36b0-4489-b7f3-a5c68d9b1e0d","added_by":"auto","created_at":"2026-03-03 17:05:10","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":535991,"visible":true,"origin":"","legend":"\u003cp\u003eSEM image of dry dregs powder at 10,000´magnification, highlighting an area over a crystalline structure.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-8807219/v1/65da61a216c722010b8ee56e.png"},{"id":103852183,"identity":"70d01aa8-4d76-4607-9055-c9c7bac4a2fe","added_by":"auto","created_at":"2026-03-03 17:05:10","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":105328,"visible":true,"origin":"","legend":"\u003cp\u003eXRD patterns of dregs subjected to three different heat-treatment conditions: 100 \u003csup\u003eo\u003c/sup\u003eC for 24 h, 500 \u003csup\u003eo\u003c/sup\u003eC for 1 h, and 750 \u003csup\u003eo\u003c/sup\u003eC for 2 h.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-8807219/v1/0bd5774b24d93b3d9df7966d.png"},{"id":103852187,"identity":"b17f95cc-5538-4c9b-a431-97570d97ebc5","added_by":"auto","created_at":"2026-03-03 17:05:10","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":572862,"visible":true,"origin":"","legend":"\u003cp\u003eRietveld refinement plot of the dregs treated at different temperatures, showing the observed (black) and calculated (red) diffractograms, as well as their difference (blue).\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-8807219/v1/fb571bbca1b488bb451b91eb.png"},{"id":104401233,"identity":"9a64d58a-a77b-4c86-ad2d-6c3e30074cb4","added_by":"auto","created_at":"2026-03-11 12:12:10","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":102128,"visible":true,"origin":"","legend":"\u003cp\u003eCompressive strength of hardened mortars without dregs (blue triangle), with dregs added to the mixture (black squares), and with dregs partially replacing Portland cement (red circles).\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-8807219/v1/c690c2e5a8480d12f8e306ec.png"},{"id":104400796,"identity":"4f9ce6e6-1345-40a8-96f6-9b0f3ad27fae","added_by":"auto","created_at":"2026-03-11 12:11:05","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":362419,"visible":true,"origin":"","legend":"\u003cp\u003e(a)\u003cstrong\u003e \u003c/strong\u003eWater absorption and (b) porosity of hardened mortars without dregs (blue triangle), with dregs added to the mixture (black squares), and with dregs partially replacing Portland cement (red circles).\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-8807219/v1/21d2ea17e54468568b3530ae.png"},{"id":103852184,"identity":"dced47aa-9e26-48ca-8a00-3fe01c932b8d","added_by":"auto","created_at":"2026-03-03 17:05:10","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":510280,"visible":true,"origin":"","legend":"\u003cp\u003eSee image above for figure legend\u0026nbsp;\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-8807219/v1/a7932a2a529a288a0361a910.png"},{"id":104408336,"identity":"12d37454-9497-42bb-8407-4949b0e761da","added_by":"auto","created_at":"2026-03-11 12:42:09","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3016215,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8807219/v1/bd6d36ba-b60c-4720-8bac-bbbf68024c77.pdf"}],"financialInterests":"","formattedTitle":"Influence of pulp industry dregs on the physical and mechanical properties of mortar","fulltext":[{"header":"Introduction","content":"\u003cp\u003eBrazil is the second-largest producer of cellulose in the world, with an annual production of over 20\u0026nbsp;million tons (IB\u0026Aacute; 2025). As a consequence, the Brazilian pulp industry generates large amounts of solid waste, mostly lime mud, dregs, grits, and biomass ash. In modern industries, lime mud is essentially recovered through advanced calcination systems, making dregs the most abundant residue resulting from cellulose production. This waste corresponds to approximately 15 kg per ton of cellulose pulp produced (Torres et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2020\u003c/span\u003e), resulting in nearly 300 thousand tons of dregs annually from Brazilian industries, most of which is disposed of in landfills. Finding sustainable solutions for this waste is a major challenge to reduce damage to the environment and, consequently, impact on the food chain and human health.\u003c/p\u003e \u003cp\u003eDifferent investigations have been carried out using paper pulp residues, such as: (a) the use of dregs as a filler in the production of geopolymeric mortars based on biomass fly ash, which is also generated during cellulose production (Novais et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Novais et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2019\u003c/span\u003e); (b) the use of dregs as filler to replace commercial calcium oxide in natural rubber composites (Bittencourt et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2020\u003c/span\u003e); (c) use of dregs-grits in mortar for wall and ceiling coating (Zanella et al. \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2014\u003c/span\u003e); (d) the use of dregs-grits as a permeable reactive barrier for the removal of copper and sulfate in mine drainage (Farage et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2020\u003c/span\u003e); (e) the replacement of clinker with dregs-grits in the manufacture of Portland cement (Buruberri et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Sim\u0026atilde;o et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2019\u003c/span\u003e); and (f) use of dregs-grits for the correction of acidic soils (Medeiros et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Cabral et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2008\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn the literature, few studies have investigated the replacement of Portland cement with dregs in mortars. Gemelli et al. (\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2001\u003c/span\u003e) examined mortars containing waste from the pulp and paper industry. They used four different materials: bottom ash, grit, dregs, and fibers. Only one sample was prepared using dregs as a replacement (2.62% relative to the dregs-free composition) for CP I-S32 cement. The incorporation of dregs into the mortar as a cement replacement reduced compressive strength by 20.4%.\u003c/p\u003e \u003cp\u003eZanella et al. (\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) evaluated the durability of mortars applied to walls and ceilings containing 0, 10, and 20% dregs-grits as a substitute for river sand. Their evaluation included ultraviolet radiation, salt spray, thermal degradation, and thermogravimetric tests. The way the authors reported the mortar composition suggests that dregs-grits may have been used as a substitute for lime rather than for sand. The Portland cement used was type CPIII. They concluded that incorporating 10 and 20% dregs-grits into the mortar did not affect durability under thermal degradation, thermogravimetric, or ultraviolet radiation tests, except under salt spray exposure.\u003c/p\u003e \u003cp\u003eMartinez-Lage et al. (2016) studied the feasibility of using fly ash and dregs in mortars and concretes by analyzing the compressive and flexural strengths after 28 days of curing. Mortars containing 10, 20, and 30% dregs were prepared to replace CEM-I 52.5 N/SR cement. They concluded that both flexural and compressive strengths decrease as the content of dregs and fly ash increases. For contents of 10 and 20%, the strength in strength is less than 10%.\u003c/p\u003e \u003cp\u003eOliveira et al. (\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) investigated coating mortars without additives by partially replacing 10, 15, 20, and 30% of hydrated lime with dregs, evaluating properties in both fresh and hardened state. CPII-F40 cement was used. They concluded that replacing lime with dregs, regardless of percentage, did not impair the performance of the mortars in terms of rheological, physical, or mechanical characteristics.\u003c/p\u003e \u003cp\u003eFalc\u0026atilde;o et al. (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) analyzed the effect of dregs on alkali-silica reaction in mortars. Six types of cement were used: CP II-F40, CP II-Z32, CP III-RS40, CP IV-32, CP V-ARI, and CVP-ARI RS. Dregs were added at proportions of 5, 10, and 15% relative to cement mass. Cement, sand, and water masses were kept constant. The alkali-silica reaction was evaluated by the prism method (NBR 15577-4), and compressive strength was used as a control parameter for the tested mortars. The author\u0026acute;s main conclusions were: (a) in reference mortars, some cements produced expansions above the limit established by Brazilian standards, and in most cases, the addition of dregs increased expansions as the residue content increased; (b) cements with high additive content, such as CP IV and CP III, showed excellent ability to inhibit expansion caused by the alkali-silica reaction; and (c) cements with pozzolanic additive demonstrated lower expansion rates over time because the additive continues reacting with cement constituents.\u003c/p\u003e \u003cp\u003eGiven the above, further research is needed to ensure the performance, durability, and safety of using cellulose waste in mortars. In this context, our group has recently begun a systematic investigation aimed at providing a sustainable application for dregs in coating and laying mortars. As the first result of this long-term effort, we present information on the characterization of the constituents (CPV-ARI cement, Tiet\u0026ecirc; River sand and dregs) and on the influence of the residue on the physico-chemical and mechanical properties of the prepared mortars.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eMaterials: origin and treatments\u003c/h2\u003e \u003cp\u003eThe Portland cement (CP) used in this study was CPV-ARI, a high-early-strength cement manufactured by Cimento Nacional (Arcos, MG, Brazil), which did not undergo any treatment prior to mortar preparation. This type of cement was chosen because it does not contain additives such as slag or pozzolans in its composition.\u003c/p\u003e \u003cp\u003eThe dregs used in this study were supplied by Suzano Papel e Celulose S.A. industrial plant in Tr\u0026ecirc;s Lagoas (MS, Brazil). Before mortar preparation, the material was dried at 100 \u003csup\u003eo\u003c/sup\u003eC for 24 hours, then ground using a Minutem MLW LM-1 ball mill and sieved through a 53 \u0026micro;m (ASTM 270).\u003c/p\u003e \u003cp\u003eThe sand used was extracted from the Tiet\u0026ecirc; River by the company Porto de Areia Irm\u0026atilde;os Brambilla (Pereira Barreto, SP, Brasil). Before use, the sand was dried at 100 \u003csup\u003eo\u003c/sup\u003eC for 24 hours and then sieved according to NBR 7214:2015. Consequently, the sand used in this study consists of grains ranging from 0.15 to 2.4 mm.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eRaw materials characterization\u003c/h3\u003e\n\u003cp\u003eThe specific mass of the precursors (cement, sand and dregs) was determined according to the procedure recommended by NBR 16605:2017, which uses a Le Chatelier volumetric flask. Deionized water was used in the tests with dregs and sand, while kerosene was used for the cement tests. Three tests were performed for each precursor. The fineness modulus and loss on ignition of the cement were evaluated following the methodology prescribed in NBR 11579:2013 and NM 18:2012, respectively.\u003c/p\u003e \u003cp\u003eThe structural properties of the dregs were investigated using TGA/DSC, energy dispersive X-ray spectroscopy (EDX), X-ray fluorescence spectroscopy (XRF), and X-ray diffraction (XRD) techniques. Thermal behavior was obtained with a simultaneous thermal analyzer from TA Instruments, model Q600 SDT, operating between room temperature to 1100 \u003csup\u003eo\u003c/sup\u003eC at a heating rate of 10 \u003csup\u003eo\u003c/sup\u003eC/min under nitrogen atmosphere. Chemical elements identification in the dregs was performed using an EDX detector coupled to a Zeiss scanning electron microscope (SEM), model EVO-LS15. Diffractograms were obtained with a Shimadzu diffractometer, model XRD-6000, using Cu-Ka radiation, at room temperature, with a Bragg angle between 20 and 70\u003csup\u003eo\u003c/sup\u003e.\u003c/p\u003e\n\u003ch3\u003eMortar preparation and characterization\u003c/h3\u003e\n\u003cp\u003eNine different mortar compositions were prepared (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e): one without dregs (Ref), four with the dregs added to the mixture (A), and four width dregs used as a substitute for CP (S), at concentrations of 5, 10, 20, and 40 wt%. The sand mass was kept constant, and the water-to-fines ratio (cement\u0026thinsp;+\u0026thinsp;dregs) was defined for each composition to obtain the ideal mortar consistency of (260\u0026thinsp;\u0026plusmn;\u0026thinsp;5) mm, as recommended by NBR 16541:2016.\u003c/p\u003e \u003cp\u003eThe incorporation of dregs into the mixture slightly altered the water/fines ratio, as shown in the table. In the Addition condition, the required values water/cement ratio required was lower (from 0.48 to 0.5) than that of the sample without dregs (0.55). In contrast, under the partial replacement condition, where CP was substituted by dregs, it was necessary to increase the ratio to 0.58 in two of the four proportions tested (5 and 40%).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMixture composition of the mortars.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample name\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCement\u003c/p\u003e \u003cp\u003e(g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eDregs\u003c/p\u003e \u003cp\u003e(g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSand\u003c/p\u003e \u003cp\u003e(g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eWater/fines ratio\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRef\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e900\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2700\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0,55\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eA05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e900\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2700\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0,50\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eA10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e900\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2700\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0,50\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eA20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e900\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e180\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2700\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0,48\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eA40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e900\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e360\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2700\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0,50\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e855\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2700\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0,58\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e810\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2700\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0,55\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e720\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e180\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2700\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0,55\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e540\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e360\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2700\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0,58\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eFive test specimens were prepared for the compressive strength tests and three for the water absorption tests, according to NBR 7215:2019 and NBR 9778:2005, respectively. Cylindrical metal molds measuring 5 cm in diameter and 10 cm in height were used. Immediately after molding, the specimens were stored in a chamber at 100% relative humidity and a temperature of (23\u0026thinsp;\u0026plusmn;\u0026thinsp;2) \u0026ordm;C. After 24 hours, they were demolded and kept in the chamber until completing 28 days of curing.\u003c/p\u003e \u003cp\u003eMechanical tests were performed using an EMIC universal testing machine, model DL30000M, equipped with a 300 kN load cell and operating at a rate of (0.25\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05) MPa/s. Water absorption was determined in accordance with NBR 9778:2005, using an oven (Odontobras \u0026ndash; SP, Brazil), model EL1.1, and a digital balance with a precision of 0.1 g. First, the specimens were weighed after drying at (105\u0026thinsp;\u0026plusmn;\u0026thinsp;5) \u0026ordm;C for 72 h. They were then immersed in water for the same period and weighed again. Water absorption was calculated using the expression below, where \u003cem\u003em\u003c/em\u003e\u003csub\u003e\u003cem\u003ei\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003em\u003c/em\u003e\u003csub\u003e\u003cem\u003es\u003c/em\u003e\u003c/sub\u003e correspond to the dry mass and water-saturated mass of the specimen, respectively.\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:{Abs}_{H2O}=\\left(\\frac{{m}_{s}-{m}_{i}}{{m}_{i}}\\right)\\times\\:100$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ePorosity was evaluated using a mercury intrusion porosimeter (Autopore III - Micromeritics) within a pressure range of 0 to 414 MPa. The minimum detectable pore size was 3 nm, corresponding to the maximum applied pressure. A 1 cm\u003csup\u003e3\u003c/sup\u003e sample of each mortar composition was extracted from the specimens used in the water absorption test. Prior to analysis, all samples were degassed under vacuum at a pressure below 50 \u0026micro;Pa.\u003c/p\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eStatistical analysis was performed using SigmaPlot software (Systat Inc, San Jose, CA, USA), version 12.0. The significance level was set at p\u0026thinsp;\u0026lt;\u0026thinsp;0.05. Water absorption and compressive strength data showed a normal (Shapiro-Wilk) and homogeneous (Levene's test) distribution and were subjected to one-way analysis of variance, followed by Fisher LSD test.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results and discussion","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eRaw material characterization\u003c/h2\u003e \u003cp\u003eThe densities (mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD) obtained for the cement, dregs, and sand were (3.13\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02), (2.58\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01), and (2.62\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01) g/cm\u003csup\u003e3\u003c/sup\u003e, respectively. The CPV-ARI cement exhibited a fineness modulus of 5.9 and a loss on ignition of 5.7%, both in accordance with the limits established by standards NBR 11579 and NM18, respectively.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows the TGA/DSC thermograms obtained for the dry dregs. In the TGA curve (red), three mass-loss events can be observed: from 50 to 200 \u003csup\u003eo\u003c/sup\u003eC, from 200 to 550 \u003csup\u003eo\u003c/sup\u003eC, and from 550 to 1000 \u003csup\u003eo\u003c/sup\u003eC. The first event corresponds to a slight mass loss (1%), attributed to the evaporation of residual water. The second event, corresponding to a 4,5% mass loss, may be due to the decomposition of sulfur-containing compound resulting from the chemical recovery stage of the kraft process, and is associated with the endothermic peak at 353 \u003csup\u003eo\u003c/sup\u003eC in the DSC curve. This endothermic event was also reported by Andesanya et al. (2025), who attributed it to the dehydroxylation of brucite; however, as shown below, this phase is not observed in our XRD data. Martins et al. (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2007\u003c/span\u003e) and Torres et al. (\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) associated this endothermic peak with gypsum dehydration; however, complete gypsum dehydration generally occurs below 200\u0026deg;C.\u003c/p\u003e \u003cp\u003eElemental analysis by EDX shows the presence of small amounts of sulfur and sodium in the dregs (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), indicating that, despite the high efficiency of the kraft chemical recovery process, it is not fully complete. Among the possible sulfur compounds formed in this process is sodium thiosulfate. Despite its greater solubility compared to sulfides, sulfates, and sulfites, sodium thiosulfate can precipitate in highly alkaline media, and its decomposition occurs between 300 and 400\u0026deg;C (Padamurthy et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; McAmish et al. 1976).\u003c/p\u003e \u003cp\u003eThe last mass-loss event (34,4%) results from the decomposition of calcium carbonate, which releases CO\u003csub\u003e2\u003c/sub\u003e and forms calcium oxide (Santos et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). This decomposition corresponds to the endothermic peak observed at 734 \u003csup\u003eo\u003c/sup\u003eC in the DSC curve. A decrease in the mass percentage of C and O can also be observed in the EDX analysis (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), as expected given that calcium carbonate is known to be the main constituent of the dregs. The SEM image of the dry dregs in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows crystalline structures of various sizes. The analysis performed in the highlighted area reveals predominantly the presence of C, O, and Ca, confirming that the Ca in these crystalline structures is present in the form of carbonate.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMain chemical elements detected in the dregs by EDX spectroscopy.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eChemical element\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTreated to 100 \u003csup\u003eo\u003c/sup\u003eC\u003c/p\u003e \u003cp\u003e(atom%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTreated to 750 \u003csup\u003eo\u003c/sup\u003eC\u003c/p\u003e \u003cp\u003e(atom%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e51.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e38.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e8.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e20.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e33.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMg\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e10.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e12.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMn\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSi\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAl\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFe\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo observe the phase transformations, the dried dregs powder (treated at 100 \u003csup\u003eo\u003c/sup\u003eC for 24 h) was subjected to two additional heat treatments: 500 \u003csup\u003eo\u003c/sup\u003eC for one hour (a temperature between the two endothermic transitions observed in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) and 750 \u003csup\u003eo\u003c/sup\u003eC for two hours (above the endothermic transition centered at 734 \u003csup\u003eo\u003c/sup\u003eC). Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the diffractograms of dregs powders treated at three different temperatures. In the first two diffractograms, corresponding to treatments at 100 and 500 \u003csup\u003eo\u003c/sup\u003eC, only the calcium carbonate phase (ICSD #73446) was observed. In contrast, the powder treated at 750 \u003csup\u003eo\u003c/sup\u003eC, exhibited the CaO (ICSD #51409) and MgO (ICSD #61325) phases.\u003c/p\u003e \u003cp\u003eThe absence of the crystalline magnesium phase in the dregs powders treated at 100 and 500 \u003csup\u003eo\u003c/sup\u003eC suggest that Mg may be partially substituting Ca in the calcium carbonate structure. Therefore, the diffractograms presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e were analyzed using the Rietveld refinement method using the GSAS-II software package. For the diffractograms corresponding to 100 and 500 \u003csup\u003eo\u003c/sup\u003eC, a standard crystalline phase of calcium-magnesium carbonate was used (ICSD card #40108). During refinement, the occupancy parameter of the Ca and Mg atoms were set at 0.87 and 0.13, respectively. These values were estimated from XRF data, using a calibration curve constructed with standard mixtures of CaO (Sigma-Aldrich, 99+%) and MgO (Sigma-Aldrich, \u0026ge;\u0026thinsp;99%) in different proportions. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e shows the Rietveld output for the analyzed dregs powders, and the structural parameters extracted from the refinement are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eLattice parameters obtained from the Rietveld refinement of the dregs powder heat-treated at three different temperatures.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eT (\u003csup\u003eo\u003c/sup\u003eC)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e \u003cp\u003eLattice parameters (Ǻ)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e \u003cp\u003eWeigth fraction (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCa\u003csub\u003e0.87\u003c/sub\u003eMg\u003csub\u003e0.13\u003c/sub\u003e(CO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCaO\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMgO\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCa\u003csub\u003e0.87\u003c/sub\u003eMg\u003csub\u003e0.13\u003c/sub\u003e(CO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCaO\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eMgO\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ea\u0026thinsp;=\u0026thinsp;b = 4.98904\u003c/p\u003e \u003cp\u003ec\u0026thinsp;=\u0026thinsp;17.0616\u003c/p\u003e \u003cp\u003eα\u0026thinsp;=\u0026thinsp;β\u0026thinsp;=\u0026thinsp;90 γ\u0026thinsp;=\u0026thinsp;120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ea\u0026thinsp;=\u0026thinsp;b = 4.98839\u003c/p\u003e \u003cp\u003ec\u0026thinsp;=\u0026thinsp;17.07828\u003c/p\u003e \u003cp\u003eα\u0026thinsp;=\u0026thinsp;β\u0026thinsp;=\u0026thinsp;90 γ\u0026thinsp;=\u0026thinsp;120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e750\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ea\u0026thinsp;=\u0026thinsp;b = c\u0026thinsp;=\u0026thinsp;4.81512\u003c/p\u003e \u003cp\u003eα\u0026thinsp;=\u0026thinsp;β\u0026thinsp;=\u0026thinsp;γ\u0026thinsp;=\u0026thinsp;90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ea\u0026thinsp;=\u0026thinsp;b = c\u0026thinsp;=\u0026thinsp;4.21342\u003c/p\u003e \u003cp\u003eα\u0026thinsp;=\u0026thinsp;β\u0026thinsp;=\u0026thinsp;γ\u0026thinsp;=\u0026thinsp;90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.864\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.136\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eMortar in the hardened state\u003c/h3\u003e\n\u003cp\u003eThe influence of dregs on the composition of mortars was evaluated based on their physical and mechanical properties in the hardened state. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e shows the results of the compressive strength tests for the mortars without dregs (Reference) and with dregs under addition and replacement conditions. Overall, compressive strength decreased as the dregs content increased, regardless of the incorporation method. This trend is more pronounced in the replacement condition, suggesting that dregs do not participate in the hydration process. In this condition, the reduction in cement limits the formation of binding phases such as calcium silicate hydrate (C\u0026ndash;S\u0026ndash;H), which is essential for strength development. In the addition condition, although the cement content has been maintained, the dregs may act as an inert material, diluting the matrix without contributing reactivity. Statistically, no significant difference were observed between Ref and S05, A5 and S5, A5 and A10, A10 and A20, A20 and S10, and A40 and S20.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn contrast, Falc\u0026atilde;o et al. (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) observed no significant difference in compressive strength when incorporating 5\u0026ndash;15 wt% dregs into the mortar. This difference in behavior may be attributed to the richer composition used by authors (cement/sand\u0026thinsp;=\u0026thinsp;1:2.25), the fixed water/cement ratio at 0.47, and the difference in dreg granulometry.\u003c/p\u003e \u003cp\u003eOpposite to the behavior observed for compressive strength, the water absorption results (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea) show an increase in absorption as the dregs content increases, with a more pronounced effect in the addition condition. Statistically, only A05 did not differ significantly from the control composition (Ref). Similar behavior was observed in porosity measurements (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb), with pore volume increasing as the dregs content increased.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe evolution of pore distribution as a function of dregs content after 28 days of curing is shown in Figs.\u0026nbsp;7a and 7c (replacement condition) and 7b and 7d (addition condition). In general, regardless of the method of incorporation, the pore size distribution in Ref shown a narrow peak between 0.02 and 0.61 \u0026micro;m, centered at 0.09 \u0026micro;m (Figs.\u0026nbsp;7c and 7d), corresponding to C-S-H gel pores. Increasing the dregs content shifted this peak toward larger pores, likely due to the weakening of the interfacial transition zone (ITZ) between the cementitious matrix and the sand grains (Chen et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Scrivener et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). Structurally, the ITZ is less dense and more porous compared with surrounding cement matrix. The peak shift indicates that the powder does not contain a sufficiently fine particle size for the dregs to act as a filler, as their particle size was not controlled for this purpose.\u003c/p\u003e \u003cp\u003e\u003cstrong\u003eFigure\u0026nbsp;7\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eEvolution in pore-size distribution in hardened mortars prepared under the replacement (a, c) and addition (b,d) conditions.\u003c/p\u003e\n\u003cp\u003eUnlike the other compositions, two distinct pore distributions were observed in A40 and S40: one corresponding to smaller pores within the cement matrix, and another associated with larger pores from the IZT and dregs particles. This confirms that dregs act as inert particles, generating larger voids after the evaporation of retained water. Furthermore, the relative proportion of these two pore populations is greater in A40 than in S40, indicating that in the replacement condition the population of smaller pores is reduced due to the lower cement content, corroborating the interpretation that these smaller pores are associated with the cementitious matrix.\u003c/p\u003e\n\u003cp\u003eFinally, in addition to these factors, the lower density of dregs (2.58 g/cm\u003csup\u003e3\u003c/sup\u003e) compared with cement (3.13 g/cm\u003csup\u003e3\u003c/sup\u003e) contributed to changes in packing density and pore structure, resulting in the observed compressive strength behavior as the residue content increased.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn this study, the influence of dregs on the physical and mechanical properties of mortars was evaluated. Dregs was incorporated into the mortar composition in two different ways: by direct adding them to the mixture and by partial replacing cement. Two endothermic events were observed in the thermogravimetric curve: the first was probably associated with sodium thiosulfate, and the second with the decomposition of calcium and magnesium carbonate, releasing CO\u003csub\u003e2\u003c/sub\u003e and forming CaO e MgO. No significant change was observed in the lattice parameters of the Ca\u003csub\u003e0.87\u003c/sub\u003eMg\u003csub\u003e0.13\u003c/sub\u003e(CO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e phase in the dregs powders treated at 100 and 500 \u003csup\u003eo\u003c/sup\u003eC. In the diffractogram of the powder treated at 750 \u003csup\u003eo\u003c/sup\u003eC for 2 h, only the CaO and MgO phases were observed, with weight fractions of 86.4% and 13.6%, respectively.\u003c/p\u003e \u003cp\u003eIncreasing the dregs content in the mortar composition, regardless of the incorporation method (addition or replacement), increases the pore volume and alters the particle-size distribution, resulting in a decrease in compressive strength. Despite the significant reduction in strength for dregs contents of 20 and 40%, this does not preclude the use of the residue in mortar for certain civil construction applications in civil, such as laying and coating.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the Coordena\u0026ccedil;\u0026atilde;o de Aperfei\u0026ccedil;oamento de Pessoal de N\u0026iacute;vel Superior (Finance Code 001) and Funda\u0026ccedil;\u0026atilde;o de Amparo \u0026agrave; Pesquisa do Estado de S\u0026atilde;o Paulo (Finance Code 17/13769-1). The authors are grateful to Suzano Papel e Celulose S.A. and Porto de Areia Irm\u0026atilde;os Brambilla for donating the dregs and sand, respectively; to technicians Elton Jos\u0026eacute; de Souza and Gilson Campos Ferreira, for technical assistance with scanning electron microscopy and compressive strength measurements, respectively; and to Dr. Celso Valentim Santilli, from the Chemistry Institute of Unesp - Araraquara, for the porosity measurements.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAuthor Luis Felipe Moreira Cesar received a scholarship from the\u0026nbsp;Coordena\u0026ccedil;\u0026atilde;o de Aperfei\u0026ccedil;oamento de Pessoal de N\u0026iacute;vel Superior\u0026nbsp;(Finance Code 001). Author Jo\u0026atilde;o Carlos Silos Moraes received funding from the\u0026nbsp;Funda\u0026ccedil;\u0026atilde;o de Amparo \u0026agrave; Pesquisa do Estado de S\u0026atilde;o Paulo\u0026nbsp;(Grant No. 23/13769-1) for the repair of the SEM EVO LS15 equipment.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eAuthors contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eLuis Felipe Moreira Cesar, Jo\u0026atilde;o Carlos Silos Moraes, and Jorge Luis Akasaki contributed to the conception and planning of the study. Luis Felipe Moreira Cesar and Jo\u0026atilde;o Carlos Silos Moraes contributed to the preparation, collection, and analysis of the data. Agda Eunice de Souza Albas contributed to the collection and analysis of the XRF data. Nelson Batista de Lima contributed to the analysis and refinement of the XRD data. The first draft of the manuscript was written by Luis Felipe Moreira Cesar, and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eEthical Approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis is not applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eConsent to Participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis is not applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eConsent to Publish\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis is not applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no relevant financial or non-financial interests to disclose.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003cstrong\u003eData Availability Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that the data supporting the findings of this study are available within the paper and its Supplementary Information files. Should any raw data files be needed in another format they are available from the corresponding author upon reasonable request. Source data are provided with this paper.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eAdesanya ED, Marshi ATM, Krishnan S, Yliniemi J, Bernal SA (2025) Co-calcination of kaolinitic clay and green liquor dregs to produce supplementary cementitious materials. Case Stud Constr Mater 22:e04520. https://doi.org/10.1016/j.cscm.2025.e04520\u003c/li\u003e\n \u003cli\u003eBittencourt NL, Bacarin GB, Cabrera FC (2020) Natural rubber composites reinforced with Dregs residue from cellulose kraft industry. Progr Rubber Plast and Recycl Technol 36:102-114. https://doi.org/10.1177/1477760619895004\u003c/li\u003e\n \u003cli\u003eBuruberri LH, Seabra MP, Labrincha JA (2015) Preparation of clinker from paper pulp industry wastes. 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J Compos Sci 7:181. https://doi.org/10.3390/jcs7050181\u003c/li\u003e\n \u003cli\u003ePadamurthy A, Nandanavanam J, Rajagopalan P (2019) Evaluation of reaction characteristics of Na2S2O3.5H2O thermochemical energy storage. Mater Today Proc 17 (2019) 239-245. https://doi.org/10.1016/j.matpr.2019.06.425\u003c/li\u003e\n \u003cli\u003eSantos VR, Cabrelon MD, Triches ES, Quinteiro E (2019) Green liquor dregs and slaker grits residues characterization of a pulp and paper mill for future application on ceramic products. J Clean Prod 240:118220. https://doi.org/10.1016/j.jclepro.2019.118220\u003c/li\u003e\n \u003cli\u003eScrivener KL, Crumbie AK, Laugesen P (2004) The interfacial transition zone (ITZ) between cement paste and aggregate in concrete. Interface Sci 12:411–421. https://doi.org/10.1023/B:INTS.0000042339.92990.4c\u003c/li\u003e\n \u003cli\u003eSimão L, Hotza D, Raupp-Pereira F, Labrincha JA, Montedo ORK (2019) Characterization of pulp and paper mill waste for the productions of waste-based cement. Rev Int Contam Ambie 35:237-246. https://doi.org/0.20937/rica.2019.35.01.17\u003c/li\u003e\n \u003cli\u003eTorres CMME, Silva CM, Pedroti LG, Fernandes WEH, Ballotin FC, Zanuncio AJV (2020) Dregs and grits from kraft pulp mills incorporated to Portland cement clinker. J Mater Cycles Waste Manage 22:851-861. https://doi.org/10.1007/s10163-020-00983-x\u003c/li\u003e\n \u003cli\u003eZanella BP, Sá EB, Acorinti NO, Trannin ICB, Simões SJC (2014) Durability of mixed mortar lining containing Dregs-Grits. Am J Environ Sci 10:44-47. https://doi.org/10.3844/ajessp.2014.44.47\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"environmental-science-and-pollution-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"espr","sideBox":"Learn more about [Environmental Science and Pollution Research](https://www.springer.com/journal/11356)","snPcode":"11356","submissionUrl":"https://submission.nature.com/new-submission/11356/3","title":"Environmental Science and Pollution Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Dregs, waste reuse, mortar, X-ray diffraction, Rietveld refinement, thermal analysis, pore size distribution","lastPublishedDoi":"10.21203/rs.3.rs-8807219/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8807219/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis 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/cm\u0026sup3;, respectively. The main chemical elements detected in the dregs (\u0026gt;\u0026thinsp;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\u003csub\u003e0.87\u003c/sub\u003eMg\u003csub\u003e0.13\u003c/sub\u003e(CO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e phase, observed in the dregs treated at 100 and 500 \u003csup\u003eo\u003c/sup\u003eC, and for the CaO and MgO phases, observed after treatment at 750 \u003csup\u003eo\u003c/sup\u003eC. 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.\u003c/p\u003e","manuscriptTitle":"Influence of pulp industry dregs on the physical and mechanical properties of mortar","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-03 17:05:05","doi":"10.21203/rs.3.rs-8807219/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2026-02-26T18:25:19+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-02-26T17:46:29+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-02-18T04:48:26+00:00","index":"","fulltext":""},{"type":"submitted","content":"Environmental Science and Pollution Research","date":"2026-02-16T06:02:27+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"environmental-science-and-pollution-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"espr","sideBox":"Learn more about [Environmental Science and Pollution Research](https://www.springer.com/journal/11356)","snPcode":"11356","submissionUrl":"https://submission.nature.com/new-submission/11356/3","title":"Environmental Science and Pollution Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"9fecd72d-7056-4f64-97e4-b0c024528f91","owner":[],"postedDate":"March 3rd, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-03T19:36:41+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-03 17:05:05","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8807219","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8807219","identity":"rs-8807219","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}