Abstract
Recycled materials are now widely used in various industrial sectors to enhance sustainability and reduce environmental charges. Using recycled aggregates in concrete production significantly lowers demand for natural aggregates and the amount of solid waste sent to landfills. This paper summarizes the main results of a study undertaken to design low and normal strength concrete with various replacement ratios of coarse recycled concrete aggregates (RCA). To persuade the concrete industry to use recycled materials as one of the main components of concrete produced, the overall mechanical and durability performances of the RCA-concrete should be close or even similar to the concrete made with natural ingredients. The present research adopted an approach that consists of designing a series of low and normal strength with RCA having an equal target 28-day design strength to the corresponding natural aggregates concrete but while varying the water–cement ratios (w/c). Coarse recycled concrete aggregates, obtained by crushing waste concrete debris collected from different construction and demolition waste sources, were used in three different proportions of 30%, 50% and 100% (by weight) to produce new concrete with various w/c ratios and different compressive strength grades. Concrete mixes produced with general use Portland cement and various RCA contents were investigated in terms of their key mechanical and durability performances. The mechanical properties (crushing value) of the used RCA were visibly lower than the natural coarse aggregates (NCA). Thus, RCA-concrete showed lower performance than the NCA-concrete. It was found that by using up to 30% coarse RCA, the mechanical properties of concrete were not significantly affected. Beyond 30% of partial replacement of NCA by the coarse RCA, a continuing decrease in the mechanical performance with an increase in RCA amount was found. However, reducing the w/c ratio of concrete designed with the coarse RCA resulted in a compressive strength improvement, a better resistance to sulphate attack, carbonation, and chloride ion penetrations. Additionally, a proper design of Portland cement concrete produced with various proportions of RCA could also contribute to promoting sustainability in the construction industry and lowering its environmental impact.
Highlights
In the construction industry, ordinary Portland cement is used extensively and it is one of the major contributors to CO2 emissions and contributes to environmental damage
Permeability characteristics including air permeability, water permeability and surface permeability of recycled concrete aggregates (RCA)-concrete compared with natural coarse aggregates (NCA)-concrete were performed by Zaharieva et al [24] and showed that the permeability and diffusion properties were dependent on the physical characteristics of the RCA, mix proportions, and curing conditions of the concrete mix
RCA added at different contents as a partial substitution of NCA did not have any negative impact on the workability of concrete but even improved the initial slump
Summary
Ordinary Portland cement is used extensively and it is one of the major contributors to CO2 emissions and contributes to environmental damage. Permeability characteristics including air permeability, water permeability and surface permeability of RCA-concrete compared with NCA-concrete were performed by Zaharieva et al [24] and showed that the permeability and diffusion properties were dependent on the physical characteristics of the RCA, mix proportions, and curing conditions of the concrete mix The authors attributed this to the lower density and mechanical properties, and higher porosity of the RCA, which has a fraction of old mortar bonded on the original aggregate compared to the NCA. They assume that based on the criteria used for normal concrete made with natural aggregates, concrete designed with RCA could be classified as concrete of moderate quality rather than low quality. This ensures a more representative and practical RCA product used that contains concrete debris from different sources and with different physical properties and strength classes
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
