Argamassa autonivelante com incorporação de resíduos como agregado leve: otimização de dosagem da matriz cimentícia e avaliação das propriedades nos estados fresco e endurecido

Abstract

The construction industry has increasingly sought materials that combine efficiency, sustainability, and enhanced productivity. In this context, self-leveling mortar (SLM) has gained prominence due to its high flowability and workability. However, its mix design still lacks consolidated standard specifications, and its formulation generally requires a high content of fines, particularly Portland cement (PC), as well as significant variability in admixture dosage. At the same time, the use of lightweight screeds has emerged as an important strategy for reducing the self-weight of buildings while improving acoustic insulation, thereby highlighting the potential of incorporating lightweight aggregates into SLM. In this context, the present study aimed to optimize the mix design of SLM using the Taguchi method and to assess the feasibility of incorporating Expanded Polystyrene (EPS) and Ethylene-Vinyl Acetate (EVA) waste as lightweight aggregates. For this purpose, the materials were characterized in terms of their physical, chemical, mineralogical, and thermal properties. During the mix design stage, five independent variables were investigated, namely cement, limestone filler, sand, water, and superplasticizer admixture, with spread flow adopted as the response variable. This approach enabled the development of a predictive equation and the definition of a reference mixture. The model showed good agreement between predicted and experimental results, with the reference mixture presenting a predicted spread flow of 25.81 cm and an experimental value of 25.20 cm. Based on this reference composition, sand was partially replaced by EVA or EPS, separately and by volume, at replacement levels ranging from 30% to 80%. In the fresh state, all mortars were evaluated in terms of spread flow, V-funnel flow time, fresh bulk density, flow retention, and regeneration time. In the hardened state, compressive strength, flexural tensile strength, density, substrate bond strength, and microstructure were assessed. The results showed that flowability was mainly influenced by the superplasticizer admixture, followed by water and limestone filler. In the fresh state, all SLM mixtures containing EVA and EPS exhibited spread flow values between 25.0 cm and 25.6 cm and V-funnel times between 7.0 s and 8.1 s, confirming behavior compatible with SLM applications and meeting the criteria established by the European Federation for Specialist Construction Chemicals and Concrete Systems, EFNARC (2002). Mixtures containing EPS achieved this spread flow range with lower superplasticizer contents, from 0.84% to 0.86%, whereas mixtures containing EVA required higher dosages, ranging from 1.03% to 1.12%. In the hardened state, density decreased as the EVA and EPS contents increased. Compared with the reference mixture, which exhibited a density of 2.16 g/cm³, the 80EVA and 80EPS mixtures reached 1.74 g/cm³ and 1.71 g/cm³, respectively, corresponding to reductions of approximately 19.6% and 20.6% in apparent density. Regarding compressive strength at 28 days, the reference mixture reached 27.58 MPa, whereas the 30EVA, 40EVA, and 30EPS mixtures achieved 20.18 MPa, 19.83 MPa, and 24.28 MPa, respectively. Even at the highest replacement levels, the results remained compatible with flooring applications, with compressive strengths ranging from 12.68 MPa to 12.92 MPa for the mixtures with the highest EVA contents and 16.6 MPa for the 80EPS mixture, all of which exceeded the 5 MPa typically required for screed mortars. In the substrate bond strength test, the 80EVA and 80EPS mixtures achieved values of 0.95 MPa and 0.66 MPa, respectively, both higher than that of the reference mixture, which reached 0.37 MPa. Overall, the SLM mixtures investigated in this study exhibited characteristics and performance that demonstrate the technical feasibility of their application in screeds incorporating lightweight waste-derived aggregates, while also aligning with Sustainable Development Goals (SDGs) 9, 12, and 13.