Document Type : Research Article
Department of Civil and Mechanical Engineering, Khatam Ol Anbia University, Tehran, Iran.
Civil and Environmental Engineering Faculty, Khaje Nasir Toosi University of Technology, Tehran, Iran.
Recycling is introduced as one of the most significant approaches in waste management practices. Various studies have concentrated on the influence of recycled concrete aggregate in concrete; however, no specific model has been suggested to predict the behavior of parent concrete. In this paper, response surface methodology coupled with the central composite design was used to design tests and model characteristics of recycled concrete. Effective factors in experimental work included compressive strength (fc) of parent concrete, and substitution rate of parent concrete while compressive strength (fc), tensile strength (ft), and water absorption of recycled concrete were objective responses. Statistical analysis suggested that models were adequate with an acceptable correlation coefficient (above 0.80). Perturbation and response surface plots revealed that fc and ft of recycled concrete heavily depended on the fc of parent concrete. For parent concretes with fc of 19 MPa and 85% substitution rate, the fc and ft values of recycled concrete were 31.6 MPa and 2.89 MPa while these values for parent concrete with fc of 36 MPa and 85% substitution rate were 42.1 and 3.7 MPa. In fact, as the fc of parent concrete enhanced, fc and ft of produced concretes increased. However, in case the fc of parent concretes increased, water absorption of recycled concrete decreased. The lowest water absorption of recycled concrete was 3.2%, which belonged to fc of 36 MPa and 15% substitution whereas the highest water absorption was observed for the parent concrete with fc of 19 and 85% substation rate.