The impact of bitumen roofing production waste (BTw) on physical mechanical properties of concrete

Abstract

This article presents how concrete properties would change if part of a coarse aggregate (granite crushed stone) were replaced with bitumen roofing production waste (BTw). BTw is a huge ecological problem because these wastes are generated in large quantities when replacing old bitumen-based roof tiles. Wastes are also produced during the production of bituminous roof coatings. Usually BTw are stored in landfills or it is attempted to use/dispose them in the production of asphalt concrete. There are very few works which analyse the impact of BTw on the properties of cement materials, although the impact of these wastes on the properties of cement materials could be beneficial because BTw consist of aggregate, granules, bitumen and fibers. In order to use BTw, standard concrete samples were first formed, then 5/16 granite fraction was replaced with BTw in amounts of 2%, 4% and 6% by weight The amounts of limestone Portland cement, fine aggregate (sand), water and superplasticizer in the concrete mixtures were constant. The new generation of superplasticizer based on polycarboxylates was used in mixtures. The following concrete properties were identified and analyzed: density of the mixture, flowability, density of concrete samples, water absorption, compressive strength, forecasted frost resistance, and microstructure studies were conducted as well. The results of the studies showed that BTw can be used in small amounts, i. e. up to 6%, then the density of the samples slightly decreased (by 2.4%) and water absorption increased (by 0.7%). Compressive strength, after replacing 2% granite crushed stone, decreased by 2.4%. However, gradual addition of the amount of BTw resulted in more closed pores that improved the frost resistance of the concrete. When 6% of bulk filler was replaced with BTw, closed porosity, compared to control samples, increased by 54% and forecasted frost resistance - by 26%. Microstructure analysis showed that with 6% BTw a dense cement stone structure was formed, showing the hydrates of portlandite and CSH.