Page 37 - תקצירי תזות הנדסה ירוקה 2025

The effects of using recycled concrete aggregates on crack development and bending capacity in reinforced concrete beams
Agnessa Nir; Agneskush@gmail.com Dr. Orit Leibovich
SCE - Shamoon College of Engineering, Be’er-Sheva
The recycling of construction waste offers a sustainable solution to two critical environmental issues: minimizing landfill waste from building materials and reducing the reliance on environmentally damaging quarries. While recycled materials are commonly used as lower-grade fillers, the potential for utilizing recycled concrete aggregates )RCA( in structural concrete warrants further investigation. This research examines the viability of RCA in reinforced concrete beams, particularly focusing on global bending behavior and crack formation under loads.
A comparison of their performances should be conducted between concrete made with RCA and conventional natural aggregate )NA( concrete. For RCA to be a viable alternative in structural elements, its behavior under bending, shear, axial force, and torsion must be assessed. Current international codes regulating the use of RCA typically permit aggregate replacement solely from recycled concrete. However, Israel’s older buildings, slated for demolition and recycling, often contain lower-quality concrete due to their outdated type of cement, poorer mix components, lower quality assurance standard, and the lower construction quality common in early 20th century Israel. Thus, assessing the impact of such local RCA on concrete properties is essential to check whether it meets the international requirements or if specific local adjustments are necessary.
This study tests RCA bending behavior by comparing RCA and NA beams by means of 4 full-scale, reinforced concrete beam tests. Each beam was loaded in a 4-point bending test after 28 days. The results enabled detailed comparisons between RCA and NA beams of deflections, strain development, strain distribution across the height of the section, moment-curvature responses, and crack development. To understand the practical implications, beam behavior was divided into two conditions: the serviceability limit state, representing daily use, and the ultimate limit state, representing extreme conditions )e.g., during earthquakes(. In the serviceability limit state, crack formation significantly impacts structural performance. Extensive cracking can degrade the durability and functionality of a structure. The analysis showed that RCA exhibited lower tensile strength than NA concrete, which led to earlier crack development. This tendency towards increased cracking in RCA-based elements may diminish their service life quality over time.
Under ultimate load conditions, differences emerged in strain levels, crack quantity, and deflection between the RCA and NA beams. Moment-curvature curves revealed that the main difference between the two materials occurred in the initial cracking stage, influenced by the type of aggregate used. This suggests that RCA’s increased deflection and cracking affect its performance in the serviceability limit state.
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