Impurities of recycled concrete aggregate - types, origin and influence on the concrete strength parameters

Current development megatrends are aimed at finding a balance between the economy, social and environmental aspects. It is also required that the economic processes that are undertaken should be highly effective in these three dimensions. Both the finite amount of the natural resources and the need to manage the construction and demolition waste, while the constant demand for the concrete mix, makes it necessary to develop knowledge and practice in the field of concrete recycling. One of the main issues in the recovery of concrete aggregate is the presence of impurities. Aggregate treatment is a possible solution, but these are energy consuming and costly processes. Therefore, there is a need to estimate their impact on concrete parameters. Such knowledge is necessary for assessing the need for additional aggregate treatment processes. Harmful aggregate impurities are materials that hinder the curing of the concrete, reduce its strength and tightness, cause splinters, violate the anti-corrosion protection of reinforcement. The paper analyses the type of impurities in RCA, as well as its sources and their influence on the technical parameters of the concrete. Six concrete mixes with the same content of coarse aggregate and water-cement ratio were prepared for the research. The first mix contained only natural aggregates, while the second mix was replaced in half by recycled aggregates. In subsequent samples, the recycled aggregate in 5% by volume was successively replaced with: glass, brick, foamed polystyrene and a mixture of these impurities. Both impurities and the recycled aggregate were prepared in 2/8mm fractions. The obtained results were compared to the results presented in the literature.