Modeling Elastic Modulus of Concrete Containing Recycled Aggregates Based on Composite Material Models

There is an increasing tendency toward using construction waste in concrete production, including old buildings' recycled concrete. This article examines the effect of the quantity and quality of old concrete recycled aggregate on the mechanical properties of concrete. Thus, we used concrete with water-cement ratios of 0.37, 0.45, and 0.55 to produce strong, medium and weak concrete recycled aggregates. Then, we crushed and granulated recycled aggregates to produce new concrete according to natural aggregate grading. Therefore, we used the recycled aggregates to substitute coarse aggregate (gravel) in 50% and 100%. Furthermore, some concrete experiments were conducted, including slump, density, water absorption, porosity, compressive strength, and modulus of elasticity tests. Then, we evaluated relations derived from the composite material theory (series and parallel model) to calculate the mechanical properties of recycled aggregate concrete. The results show the decreased modulus of elasticity and compressive strength in concrete containing 100% recycled aggregate by 8% and 33%, respectively. Besides, like normal concrete compressive strength and modulus of elasticity decreased in the recycled aggregate concrete, with the increase in porosity. In addition, considering composite material theory relations, series relations show more accuracy than parallel relations in estimating the recycled aggregate concrete modulus of elasticity. Furthermore, we evaluated the modulus of elasticity estimation equations of valid regulations and found that the ACI 363-R93 proposed equation was the most accurate. Finally, we presented a model for estimating the recycled aggregate concrete modulus of elasticity using software modeling and with the help of experimental data, with an estimation accuracy of 95%.