Influence of Fine Fraction of Thermally Treated Concrete Waste on the Hydration and Hardening Processes of Portland Cement

The main components of construction and demolition waste are concrete and masonry rubble and can be re-used in different applications such as road works, filling material in quarries or concrete manufacturing. The use of recycled concrete aggregate (RCA) as a substitute of natural aggregates in concrete production is limited to low amounts due to the decrease of mechanical properties and durability of concretes. This negative effect is mainly due to the lower strength and higher porosity specific for RCA as compared with natural aggregate, determined by the presence of adhered mortar/cement paste on the surface of natural aggregate. In this paper concrete rubble is thermally and mechanically treated in order to reduce the amount of adhered mortar/cement paste on the surface of natural aggregate and the separated fine material, called thermally treated fine fraction (TTFF), is used as supplementary cementitious material for portland cement preparation. The compressive strengths developed after 28 days of hardening by the mortars specimens in which portland cement was substituted with 10% and 25% TTFF are comparable with the one developed by portland cement. The data obtained by thermal analysis (TG/DTG), suggests a possible intensification of portland cement hydration process at early ages (2 days) in the presence of small amounts of TTFF (10-25%).