Mechanical and microstructural properties of recycled concretes mixed with ceramic recycled cement and secondary recycled aggregates. A viable option for future concrete

The concept of construction and demolition waste (CDW) embodies a vast amount of residues, among which the ceramic materials (mainly, bricks and tiles) are an important part as, in many countries of the European Union, they represent more than 50% of the total. Therefore, the reutilization of this type of waste is one of the most important challenges faced by the construction sector within the circular economy paradigm. This research work deals with a dual reutilization of the CDW ceramic fraction: firstly, as coarse recycled aggregates and, secondly, through the use of clay brick powder as a pozzolanic addition to the cement. Thus, two different recycled concrete mixtures were produced: (1) with a 50% partial substitution of the natural coarse aggregates (RC-RA) and (2) with a 50% substitution of the natural coarse aggregates and a 25% substitution of the ordinary Portland cement (RC-RAC). The mechanical performance (consistency, density and compressive strength) and microstructural properties such as porosity, elemental mapping analysis, hydration products and interfacial transition zones (ITZ) were assessed and compared with a control concrete (CC). It was revealed that the recycled concretes incorporating ceramic as secondary materials have a comparable performance level to the one exhibited by the conventional concrete at 28 days, in part due to their pozzolanic characteristics but also due to a lower effective w/c ratio, which demonstrates their potential for reuse and possible contribution to the circular economy.