Evaluating the durability of recycled concrete made of coarse recycled aggregate concrete containing silica-fume and natural zeolite

Although the mechanical properties of recycled aggregates concrete (RAC's) are well known, the durability properties of these concretes are less agreed upon by researchers. The main objective of this paper is to evaluate the durability of RAC's made of recycled concrete coarse aggregate (RCCA) containing silica-fume (SF) and natural zeolite (NZ). Four series of mixtures were made using four levels of RCCA as 0%, 25%, 50%, and 100% with natural coarse aggregates (NCA's). SF with 5%, 10%, and 15% and NZ with 10%, 20%, and 30% were replaced with cement. To evaluate the durability properties of RAC's, 28 mixed design were made and compressive strength (CS), water absorption by immersion (WAI), water absorption by capillary (WAC), electrical resistance (ER), electrical conductivity (EC), and rapid chloride ion penetration test (RCPT) were measured. The results showed that WAI and WAC of RAC increased with enhancing the RCCA level. By increasing the replacement level of RCCA, and usage of 10% SF replacement showed a greater impact on improving CS. Concretes containing NZ had higher WAI than that of SF. The increasing level of NZ by more than 10%, increases the space of cavities between silicate gels and therefore increases WAC in concretes. With increasing in the RCA level, so did the EC of RAC; however, EC in pozzolanic concretes showed a lower growth rate by increasing the RCCA level. Using 25% of RCCA, and 10% of SF, it was possible to make concrete with very low chloride ion penetration.