Evaluation of mechanical, physical and chemical properties of ecological modular soil-alkali activated bricks without Portland cement

Abstract

With the growth of civil construction materials to mitigate environmental impacts and meet technical demands, modular soil-cement bricks have emerged as an alternative construction material in Brazil due to economic, social, and environmental reasons. However, the composition of Portland cement still generates environmental impacts due to CO2 emissions. Thus, this study aimed to produce modular bricks through alkali activation in real scale using a mixture of clay soil and sand, metakaolin (M) or blast furnace slag (BFS) as precursors, NaOH solution as a simple activator, or compound with hydrated lime. Thermal curing effects were analyzed. Water absorption, compressive strength, XRF, XRD, SEM and EDS analysis were performed, as well as Life Cycle Analysis (LCA). All bricks presented suitable water absorption values according to Brazilian standards. Groups with metakaolin and simple activator presented the lowest compressive strength since an incomplete geopolymerization was verified; however, when a compound activator was used, the compressive strength was highly increased. The BFS group presented the best overall performance under water absorption and compressive strength with mean values of 3.6 MPa and 13.4%, respectively. Microstructural analyses confirmed the development of microstructures such as Zeolite, Calcite and Hydrated Calcium Silicate from the alkali activation reactions. Alkali activated bricks presented at least 35% less CO2 emissions compared to ceramic bricks in LCA. Modular bricks made with MK or BFS and compound activator met all the requirements for their use, showing that these mixtures can be an alternative for sustainable brick production, with the reuse of industrial waste instead of Portland cement incorporation.