Experimental and numerical investigation of rheological and mechanical properties of self-compacting concretes containing recycled aggregates using Box-Behnken method

Concrete is widely used as a building material all over the world, but it is not considered an environmentally friendly material due to environmental degradation and the use of large amounts of natural resources. Therefore, it is necessary to provide a solution to reduce the effects of recycled aggregate pollution. In the present study, the effect of the strength of recycled aggregates on the rheological and mechanical properties of self-compacting concrete is investigated experimentally and numerically. Hence, two types of recycled aggregates with known and unknown strength origins are utilized for the studied samples. The experimental design in this research is accomplished by the Box Behnken method, which is one of the response surface methods. Input variables in mixtures, including micro silica in the range of 5-15% as a percentage substitute for the weight of cement and recycled coarse and fine grains in the range of 0-50% for both series of recycled materials, are replaced by natural materials. The studied responses are slump flow, funnel V, compressive and tensile strengths. The results indicate that the increase in recycled aggregates reduces the rheological and mechanical properties of the mixtures, while micro silica effectively improves the mechanical properties. In addition, the sensitivity of most of the studied responses is related to recycled fine particles. It should be noted that recycled materials of known strengths are shown better results than recycled materials of unknown strengths. Some mathematical relationships are also provided using analysis of variance for all responses to predict the rheological and mechanical properties of mixtures.