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Go to Editorial ManagerThe accumulation of large amounts of construction and demolition waste in Iraq, especially after the 2014 conflicts, has created a serious environmental problem. To achieve sustainable goals, recycling these materials in the construction sector supports the principles of the circular economy and reduces the demand for natural aggregates, as recycling represents one aspect of crisis recovery. This study investigates the mechanical performance and bond strength of Self-Compacting Concrete (SCC) containing demolition brick aggregate (DBA) and discarded brick aggregate (CBA) at 100% replacement ratios for fine and coarse aggregates, with and without 10% crumb rubber (CR) as a volumetric replacement for fine aggregate. Ten SCC mixes were designed and experimentally evaluated after 28 days. The results showed that adding 10% rubber to the reference mix resulted in a 13.5% decrease in compressive strength and a 16.8% decrease in bond strength. Complete replacement of natural aggregate with recycled brick aggregate resulted in significant decreases in compressive and bond strengths of up to 60% and 50%, respectively. Furthermore, incorporating crushed rubber into the recycled brick aggregate further decreased the compressive and bond strengths. The predominant failure patterns observed in the bond strength test were splitting and sliding failure. The combination of these two types of waste aggregate could promote the use of sustainable SCC in practical applications
This study investigates the influence of nano silica on the mechanical performance and interfacial behavior of fiber-reinforced cementitious composites (FRCCs) incorporating steel, glass, polypropylene, and raffia fibers. The objective is to evaluate the impact of nano-silica content (0%, 1.5%, 2.5%, and 3.5%) on workability, compressive strength, fiber–matrix bond strength, and tensile response under uniaxial loading. The addition of nano-silica reduced flowability due to its high surface area and water demand but enhanced compressive strength, reaching a maximum value of 77.14 MPa at 3.5 percent nano-silica. Field Emission Scanning Electron Microscopy (FESEM) confirmed matrix densification and refinement of the interfacial transition zone (ITZ) in nano silica modified mixtures, supporting the observed strength gains. Single-fiber pull-out tests revealed that nano silica significantly improved average and equivalent interfacial bond strengths. Steel fibers exhibited the most consistent bond improvement, while raffia fibers demonstrated the weakest performance. Longer fiber embedment enhanced bond strength and energy absorption for high-modulus fibers. Equivalent bond strength trends indicated a strong dependency on fiber type and embedment length. Direct tensile tests demonstrated that nano-silica significantly enhanced the tensile strength and ductility of composites. The most substantial improvement was observed in steel fiber-reinforced composites, with cracking strength increasing by 166.7% and ductility by 143.3% at 2.5% NS. Correction factors were proposed to align theoretical tensile predictions with experimental results. Overall, nano silica proved highly effective in improving FRCCs by densifying the matrix, strengthening the fiber matrix interface, and enhancing mechanical performance under tensile loading.