تقوية العوارض الخرسانية المطاطية المسلحة بواسطة تقنية NSM-CFRP التي تتعرض لأحمال متكررة

Strengthening Rubberized Reinforced Concrete beams subjected to repeated loads by NSM-CFRP Bars

ABstract

This study examines the behavior of rubberized reinforced concrete beams subjected to repeated loading, strengthened using Near-Surface Mounted (NSM) Carbon Fiber Reinforced Polymer (CFRP) bars and strips. The research addresses the growing environmental issue of waste from discarded vehicle tires, which are challenging to dispose of due to their non-biodegradable nature. By recycling tire rubber and incorporating it as a partial replacement for coarse and fine aggregates in concrete, the study aims to mitigate tire waste and evaluate its impact on concrete properties and structural performance.
The experimental program involved volumetric replacement of fine and coarse aggregates with rubber particles at ratios of 10% and 20%, individually and in combination. Fourteen beam specimens (250 × 150 × 1600 mm) were prepared, including two control beams (one tested under monotonic loading and the other under repeated loading) and twelve strengthened beams. These were divided into two groups: six beams strengthened with NSM-CFRP bars and six with NSM-CFRP strips. Repeated loading tests followed a protocol of 30 cycles, starting with 30%, 60%, and 80% of the ultimate load, followed by loading to failure.
Results indicated that replacing aggregates with rubber significantly reduced mechanical properties, including compressive strength, tensile strength, and flexural strength by 51.66%, 22.59%, and 38%, respectively, at a 20% replacement ratio. The ultimate load capacity of rubberized concrete was lower, especially at higher replacement levels of aggregates. Strengthening with NSM-CFRP strips enhanced ultimate load capacity under repeated loading more than NSM-CFRP bars. Numerical modeling using ABAQUS demonstrated good agreement with experimental results, with minor deviations. The analysis revealed that increasing CFRP bar diameters from 6 mm to 8 mm improved ultimate load by 2.25%, while increasing strip thickness from 1.2 mm to 2 mm resulted in a marginal improvement of 0.74%, suggesting limited cost-efficiency for thicker strips.
This research highlights the potential of rubberized concrete as a sustainable material and the effectiveness of NSM-CFRP strengthening systems in improving the performance of concrete beams under repeated loading conditions.