Towards Sustainable Building Materials: An Experimental Investigation into the Effect of Recycled Construction Waste Aggregate on the Properties of High-Performance Concrete

This study presents a comparison of the mechanical properties of selected high-performance concrete mixtures, some of which contained a proportion of recycled concrete aggregate (15% or 30%) as a substitute for natural aggregate. A reference mix-ture without recycled concrete aggregate was used for comparison. Initially, the prop-erties of concrete containing both the natural and recycled aggregate types were char-acterized. This was followed by a series of mechanical tests investigating the compres-sive strength, flexural strength, and chemical resistance (including resistance to de-icing agents and sulfuric acid). The structural performance of reinforced concrete (RC) beams produced from the mixtures was assessed, and surface morphology was evaluated using a digital microscope. The results confirmed that the use of recycled aggregate had a measurable yet limited effect on the properties of hardened concrete. While the com-pressive strength tended to decrease slightly with an increasing degree of replacement, the flexural strength remained stable in all the mixtures. The tested mixtures demon-strated adequate resistance to de-icing agents and sulfuric acid. Interestingly, specimens subjected to a frost-resistance test showed improved flexural strength, potentially due to ongoing hydration or microcrack healing. In addition, the RC beams with partial ag-gregate replacement achieved a higher load-bearing capacity compared to the reference beams. The optical surface evaluation method proved to be a valuable tool, comple-mentary to conventional strength testing. This research enhances the current under-standing of recycled aggregate concrete and supports its potential for structural appli-cations.