Use of coarse recycled aggregates in designated concrete mixes
This thesis is a detailed investigation on the suitability of secondary aggregates for use in concrete production. The aggregates under investigation, originated from construction and demolition sites of the Greater London area and were mainly from reinforced concrete structures dating back to the 60's-70's. The study investigated three sources of recycled concrete aggregate (RCA I, RCA II and RCA III). The first step in the investigation involved the characterisation of the aggregates through an extensive testing regime including physical, mechanical and chemical-mineralogical assessments. Aggregates where then classified based on the requirements of BS 8500 and BSEN 12620 which provide the main guidance for aggregates for concrete. All sources conformed to the relevant standard requirements and RCA I was selected for the next step of this investigation. Following the establishment of conformity of these aggregates for concrete production a further in depth investigation involved the production of designated concrete mixes conforming to BS 8500 and BSEN 206 using coarse RCA I at various proportions up to 100%, totally replacing coarse natural aggregate. The investigation included assessment of equivalent strength concrete in the fresh (workability, stability, air entrainement etc.) and hardened states (engineering properties and durability performance). Concrete performed satisfactorily in most of its performance aspects. In order to demonstrate the performance of RCA concrete and compare with conventional concrete containing natural aggregates, a full scale demonstration programme was devised. It involved the construction of industrial pavements in real construction sites, using conventional concrete and concrete containing up to 100% coarse RCA. Site visits and site inspections at 3 and 6 months into service revealed concrete performing satisfactorily regardless of the RCA content. These findings were in line with those of the scientific investigation carried out in the laboratory.