The search for alternative materials to replace ordinary Portland cement has been the object of work that enhances the investigation of the use of pozzolanic materials and the reduction of the carbon footprint with supplementary cementitious materials. However, not all materials are available to meet the large-scale demand for cement replacement. A relevant exception is the calcined clay, a material found worldwide that, when subjected to appropriate heat treatment, presents pozzolanic reactivity and can be used as a supplementary material to cement. This review presents, through a systematic search, methods for measuring the pozzolanic reactivity of calcined clays, namely, direct, indirect, qualitative, quantitative, chemical and physical methods such as electrical conductivity (Lùxan), the force activity index, the modified Chapelle, R³, Frattini test, thermal analysis, X-ray diffraction and X-ray fluorescence spectrometry. The most usual methods to assess the pozzolanic reactivity of calcined clays were exposed and analyzed. It should be pointed out that there is greater use of the Frattini and modified Chapelle methods as well as the analysis of the mechanical strength behavior of the material in cementitious matrices. X-ray diffraction and thermal analysis were exposed as the most used correlation methods but it was also concluded that different tests are needed to generate accurate results.

Global warming is intensified by substantial greenhouse gas emissions, with the cement industry contributing significantly by releasing around 0.8 tons of CO₂ per ton of cement produced. To mitigate these impacts, in this study, we investigated the pozzolanic potential of calcined clays, assessing their influence on the properties of Portland cement as sustainable alternatives for partial replacement. Three clays from Campos dos Goytacazes, RJ, were analyzed. After drying and calcining at 600 °C, they underwent physical and chemical analysis. The samples were characterized in terms of grain size, moisture content, grain density and plasticity limit. Chemical analysis by X-ray fluorescence identified the elemental composition of the clays, while X-ray diffraction determined the presence of crystalline and amorphous phases. A mineralogical characterization confirmed the amorphization process and classified the clay as kaolinitic. Scanning electron microscopy provided detailed images of the morphology of the particles. The surface area was measured using the Blaine method, which is essential for understanding the reactivity of calcined clays. A preliminary analysis showed that the calcination at 600 °C led to greater pozzolanic reactivity in the clay samples. A thermal analysis showed a loss of mass, suggesting the dihydroxylation of the kaolinite. The pozzolanic reactivity was extensively evaluated by isothermal calorimetry, which monitored the release of heat during hydration reactions through compressive strength tests on the mortars that showed higher strength than the reference. In addition, modified Chapelle and R³ tests were carried out, which showed a direct correlation with the compressive strength, also indicating significant pozzolanic reactivity in the material. The results showed that the clays, when calcined, had a highly reactive amorphous structure, resulting from their transformation through the process of dihydroxylation and amorphization. Calorimetry identified the acceleration of the cement hydration reactions, stimulating the formation of calcium silicate hydrates and aluminum compounds, which are essential for mechanical strength. The partial replacement of Portland cement with calcined clays helps to reduce CO₂ emissions without compromising strength and durability, representing a promising strategy for reducing greenhouse gas emissions, with a view to greater environmental sustainability and the efficiency of building materials.

Sustentabilidade do futuro: livro de memórias do Sustentare & WIPIS (978-65-272-0451-0) - Determinação Da Absorção De Água Por Capilaridade Em Argamassa Com Substituição Parcial De Areia Natural Por Pet-Pcr

The variability of the properties of commercial hydrated limes compromises the technological performance of multi-purpose mortars, especially due to differences in the degree of hydration, chemical composition, specific surface area, and particle size distribution. Given this context, this study investigated the influence of these physicochemical characteristics on the behavior of multi-purpose mortars produced with a 1:1:6 mix ratio (cement:lime:sand). Four commercial limes used in the northern region of Rio de Janeiro state were analyzed. The samples were subjected to physicochemical characterization techniques, including thermogravimetric analysis, X-ray diffraction, energy dispersive spectroscopy, determination of specific surface area by the BET and Blaine methods, laser particle size analysis, helium pycnometry, and scanning electron microscopy. The mortars were evaluated in their fresh state and in their hardened state after 28 days, considering parameters of water demand and retention, capillary absorption, and mechanical strength. The results showed significant variation among the limes analyzed, with degrees of hydration between 65 and 90%, BET surface areas from 1.21 to 4.15 m²/g, Blaine values between 1,682 and 13,571 cm²/g, and median diameters ranging from 9.46 to 99.67 μm. Analysis of the results indicated that the degree of hydration, although relevant, did not show a consistent correlation when considered in isolation in relation to the performance of the mortars. The physical characteristics, particularly the specific surface area and particle size distribution, were associated with the observed behavior, influencing water demand, water retention, and capillary absorption. Increases in the flexural and compressive strengths of mortars with added lime were also observed. Microstructural analysis indicated denser and more homogeneous matrices, associated with refinement of the porous structure. The results reinforce the importance of the physical-chemical characterization of commercial limes as a tool for understanding and controlling the technological performance of mortars, contributing to a more careful selection of the materials used.

Sustentabilidade do futuro: livro de memórias do Sustentare & WIPIS (978-65-272-0451-0) - Determinação Da Resistência À Compressão Em Argamassa Com Substituição Parcial De Areia Natural Por Pet-Pcr