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Abstract
The increase in construction work has made a lot of construction and demolition waste that causes environmental and disposal problems. One way to deal with the growing amount of demolition concrete waste in a sustainable way is to use it again as aggregate in new concrete, but this is usually limited due to lower workability and damage to mechanical properties. Solving these problems is important to encourage environmentally friendly and structurally sound manufacturing of concrete. The main goal of the study is to use demolition concrete waste as coarse aggregate in concrete after studying the possibility and to check how well the PC-200 superplasticizer will work to improve the mechanical and fresh properties of concrete made using it. To achieve this goal, concrete samples were made with different amounts of replacement of natural coarse aggregate with demolition waste concrete, the replacement levels being 0, 25, 50, 75, and 100%. Two categories of mixes were included in this study: ordinary concrete with a 0.42 water–cement ratio and modified concrete containing PC-200 superplasticizer with low water–cement ratio of 0.28. The tests included the slump test, compressive strength, splitting tensile and flexural strength, and modulus of elasticity after 28 days of curing. The test results showed reduced workability and mechanical strength of ordinary concrete mixes with the introduction of demolition waste aggregates. High levels of modification with PC-200 superplasticizer showed significant improvement in the fresh and hardened properties. Compressive strength increase from 43.1 MPa for the reference modified mix to 52.5 MPa for the 100% waste aggregate. Similar improvements were also observed in the tensile and flexural strength as well as modulus of elasticity. The results indicate that demolition waste aggregates can be successfully used to produce high performance sustainable concrete for structural applications, given the right level of modification.