Light brightened aggregates extracted from by-products of kaolin raw material classification processes, used to reduce urban heat islands.

The process of urbanisation is resulting in increasingly dense urban areas. It is documented that cities and urban areas have significantly higher temperatures than the surrounding non-urbanised areas. Such a phenomenon has been well known for many years and is referred to as the urban heat island (UHI). The magnitude of this phenomenon varies according to specific local and geographical characteristics. It depends largely on factors such as vegetation (e.g. woodland, flower meadows) but also on land use and land cover conditions. The thermal properties of the materials used in the built environment, the proportion of evaporative surfaces, natural or artificial shading and the city's air corridors are also significant. Development not only affects urban heat points, but also reduces the natural retention capacity. The amount and intensity of precipitation in heavily built-up areas is increased by which the time of rainwater run-off into the catchment is shortened. Surfaces in the city are generally of low retention and do not provide effective opportunities to respond to locally occurring water deficits and do not reduce the effects of excess water in storm rainfall. Drainage systems, especially in old towns, do not always show the required capacity to receive large amounts of water after intense and heavy rainfall or snowmelt. In addition, the water that runs off is already irretrievably lost. The purpose of the study was to determine the possibility of obtaining aggregates with a grain size of 2-8 mm from clay-sand fractions formed by enrichment of kaolin clays, which were also modified with additives. The results obtained will allow further research into the development of technology concepts for the production of lightweight aggregates used, for example, in cool roofs of buildings. Special attention was paid to the microstructure of the aggregate, since the idea of the study was to obtain a material with adequate porosity on the meso-scale, so detailed microscopic analyses were carried out. Brightened materials were obtained with high absorbability above 30%wt and low apparent density of 1.5 g/cm and bulk density of 0.9 g/cm. A promising material for the substrate layer of a green roof has been obtained using post-processing raw materials. The aggregate granules are bright, reflect solar radiation and do not heat up. Through suitable sintering, the granules are lightweight and have a high open porosity, which is beneficial for rainwater management.