Coloured concrete produced from low-carbon cements: Mechanical properties, chromatic stability and sustainability

The global construction industry is responsible for 39% of CO2 emissions and for more than 50% of the extracted natural resources. Dematerialization and the use of low-carbon materials would be mitigating actions in the current scenario. In developing countries, where the housing deficit is high, a short-term and novel solution could come from the construction of social housing using multipurpose coloured concrete casings, which have no rendering of mortars and paints and are produced from low-carbon cements. In the Amazon, the wide availability of light and kaolinite-rich waste would enable the production of low-carbon cements (LCC) from ternary mixtures of clinker, calcined kaolin waste and limestone. The objective was evaluated the performance of coloured concretes from LCC against the weathering of the rainy equatorial climate of the Amazon, environment which favours the formation of biofilm films, impairing the aesthetic quality of the facades. The LCC provided coloured concretes with good pigmentation capacity and a significant reduction in CO2 emissions. On the other hand, its use compromised the surface quality of concrete due to the low chromatic stability. The climate conditions of the Amazon and low alkalinity of the LCC favoured the growth of microorganisms, leading the concrete surfaces to become prematurely blackened, decreasing their albedo and, consequently, raising the surface temperature of the substrate, which compromises the thermos-energetic performance of the building. Nevertheless, the results are promising and justify the continuity of research using new compositions of limestone calcined clay cement associated with the use of more efficient surface protection systems.