Exploring mechanical properties of a novel sustainable two-stage (preplaced aggregate) concrete using polypropylene, glass fiber and Portland limestone cement

• Use of PLC reduces CO2 emissions in sustainable concrete production. • Tested 63 cylinders and 21 prisms for Polypropylene and glass‑fiber PAFRC. • Evaluated effects of PLC, fiber volume content, and fiber length on PAFRC. • Up to 6% of polypropylene fibers improved PAFRC mechanical performance. • Glass fiber addition enhanced PAFRC flexural strength. This study evaluates a sustainable preplaced aggregate (two-stage) fiber-reinforced concrete (PAFRC) that incorporates Portland limestone cement (PLC) and high dosages of polypropylene (PP) and alkali-resistant glass (GF) fibers. Aggregates and fibers were preplaced in the formwork and subsequently injected with a flowable grout; mechanical performance was assessed at 28 days. The results indicate that 4% PP increased compressive strength, splitting-tensile strength, and elastic modulus by 15.2%, 15.9%, and 18.6%, respectively, whereas 1% and 2% GF improved flexural strength by 10.2% and 10.4%, respectively. The 2% PP mixture exhibited the highest compressive strength (20.3 MPa), and the 4% PP mix attained the greatest splitting-tensile strength (3.6 MPa). Peak flexural performance (4.9 MPa) was observed for both the 6% PP and 2% GF mixes. Incorporating PLC in the PAFRC system reduces clinker demand and embodied CO2, and the preplaced method enables higher fiber contents without severe segregation. These results demonstrate a practical pathway to enhance both the mechanical performance and sustainability of concrete for repair and structural applications.