Abstract
<jats:p>Special types of fiber-reinforced concretes known as Slurry Infiltrated Fiber Concrete (SIFCON) exhibit outstanding performance characteristics, achieved through a fine-grained matrix and a high volume fraction of steel fibers (5 % – 30 % by volume). The cementitious binder content in such materials can reach up to 900 kg/m³. The present study aims to investigate the feasibility of replacing up to 25 % of the cement in the SIFCON matrix with a fine recycled concrete fraction (particle size below 0,25 mm) obtained from construction and demolition waste. Comparative tests were conducted on two types of mixtures – a control mixture containing 800 kg of cement and a second mixture in which 25 % of the Portland cement was replaced with fine recycled concrete powder. The influence of different water-to-cement ratios and two types of superplasticizers was examined, as the inclusion of the fine recycled fraction tends to reduce the workability of the mixes. The flexural tensile strength and compressive strength were determined for all compositions. The results demonstrate that a substantial portion of Portland cement can be effectively replaced with fine recycled concrete powder. To overcome the reduced workability of mixes containing recycled fines, it is necessary to adjust other parameters of the mixture, such as the water-to-cement ratio and/or the type and dosage of superplasticizer. The mechanical strengths achieved meet the requirements for SIFCON matrices and, at equivalent water-to-cement ratios, are comparable to those of the control mixture. Therefore, the fine fraction derived from recycled concrete represents a viable alternative to conventional fine fillers (such as stone powder), while simultaneously contributing to the reduction of the environmental footprint of SIFCON.</jats:p>