Lightweight concrete production with low Portland cement consumption

The building industry has widespread social, economic and environmental impacts. Considering the materials used, such impacts depend on the production of concrete, since it is the most consumed material and its properties are associated with the consumption of Portland cement, which represents a significant part of CO2 emissions from this sector. This project studied the utility of recycled tire rubber for lightweight concrete with added metakaolin, with the dual purpose of reducing cement consumption while achieving satisfactory strength. Metakaolin was produced in the laboratory, assessing the minimum temperature for formation from kaolin. The lightweight concrete (in which rubber was substituted for sand) was evaluated using compressive strength, calorimetry and thermal conductivity tests of mortar. The results showed that the metakaolin produced at 800 °C exhibits more efficient silica fume replacement and that producing mortar with 40% rubber yields a compressive strength of 20 MPa. Achieving this strength in lightweight concrete permits the production of materials with low cement consumption, 486 kg/m3 for mortar (22.9 kg of cement per m3 per MPa) and 260 kg/m3 for concrete (13 kg of cement per m3 per MPa). The concrete-rubber results showed the best thermal conductivity indices, thus permitting the design of building systems with improved energy efficiency, which reduces their operating costs.