International Concrete Abstracts Portal

This study presents a comprehensive review of eco-friendly materials and advanced repair techniques for rehabilitating reinforced-concrete (RC) structures, emphasizing their role in promoting sustainability and enhancing performance. By evaluating fifty-five research programs conducted between 2001 and 2024, the study focuses on emerging materials such as geopolymers, natural fibers, and fiber-reinforced composites, highlighting their mechanical properties, environmental benefits, and potential for integration into traditional RC systems. The review is thematically organized into four areas: (1) Sustainability and Environmental Impacts, (2) Material Innovation and Properties, (3) Repair Techniques and Efficiency, and (4) Structural Performance. Key findings reveal that these materials not only reduce the carbon footprint of construction but also significantly improve structural durability, corrosion resistance, and long-term performance under varying environmental conditions. Specifically, geopolymer concretes exhibit low CO₂ emissions and superior bond strength; bamboo and flax fibers offer strong tensile capacity with renewable sourcing; and MICP techniques deliver self-healing functionality that reduces dependency on chemical-based crack sealants. Additionally, the use of recycled and bio-based materials further contributes to cost-efficiency and environmental resilience, fostering circular economy principles. By synthesizing findings across these domains, this study provides practical insights into how eco-friendly materials can simultaneously address environmental, structural, and economic challenges in RC repair. The study underscores the importance of adopting innovative repair methods that incorporate these sustainable materials to address modern civil engineering challenges, balancing infrastructure longevity, sustainability, and reduced environmental impact.

This paper presents an experimental study on the residual bond of glass fiber-reinforced polymer (GFRP) rebars embedded in ultra-high-performance concrete (UHPC) subjected to elevated temperatures, including a comparison with ordinary concrete. Based on the range of thermal loading from 25°C (77°F) to 300o°C (572o°F), material and push-out tests are conducted to examine the temperature-dependent properties of the constituents and the behavior of the interface. Also performed are chemical and radiometric analyses. The average specific heat and thermal conductivity of UHPC are 12.1% and 6.1% higher than those of ordinary concrete, respectively. The temperature-induced reduction of density in these mixtures ranges between 5.4% and 6.2% at 300o°C (572o°F). Thermal damage to GFRP, in the context of microcracking, is observed after exposure to 150°C (302°F). Fourier transform infrared spectroscopy reveals prominent wavenumbers at 668 cm^-1 (263 in.^-1) and 2,360 cm^-1 (929 in.^-1), related to the bond between the fibers and resin in the rebars, while spectroradiometry characterizes the thermal degradation of GFRP through diminished reflectivity in conjunction with the peak wavelength positions of 584 nm (2,299×10^-8 in.) and 1,871 nm (7,366×10^-8 in.). The linearly ascending bond-slip response of the interface alters after reaching the maximum shear stresses, leading to gradual and abrupt declines for the ordinary concrete and UHPC, respectively. The failure mode of the ordinary concrete interface is temperature-sensitive; however, spalling in the bonded region is consistently noticed in the UHPC interface. The fracture energy of the interface with UHPC exceeds that of the interface with the ordinary concrete beyond 150o°C (302o°F). Design recommendations are provided for estimating reductions in the residual bond of the GFRP system exposed to elevated temperatures.

The deformability of reinforced concrete walls with staggered lap splices was studied through tests of six cantilevered walls under constant axial load and cyclic reversals of lateral displacement. The height-to-length aspect ratios of the walls were approximately 3.2. Four walls had staggered laps, one wall had non-staggered laps, and one wall had mechanical couplers. Laps were detailed to yield the spliced reinforcement. Test walls with staggered laps lost lateral-load resistance at smaller drift ratios (1.0% to 2.1%) than both the test wall with non-staggered laps (2.3%) and the test wall with mechanical couplers (3.5%). Staggered lap splices resulted in larger strain concentrations than non-staggered lap splices. It was concluded that both staggered and non-staggered lap splices a) can have reduced strain capacity relative to continuous bars (leading to bond failure before or after yield) and b) alter inelastic strain distributions, causing large reductions in effective plastic hinge length.

Eleven large-scale reinforced concrete beams were tested to failure under four-point bending to investigate tension lap splices of No. 14 and 18 (43 and 57 mm) bars. Additional variables included transverse reinforcement, concrete compressive strength (nominally 5 or 10 ksi (34 or 69 MPa)), and target bar stress at splice failure (60 or 100 ksi (420 or 690 MPa)). Results show that both the ACI 408R-03 and ACI 318-19 [2] bond length equations become less conservative as bar diameter increases, so a bar size factor is proposed for modifying bond length equations to obtain similar conservatism across all diameters. A minimum clear cover of one bar diameter is also recommended for large-bar lap splices. Increasing the limit on ((c_b+K_tr ))⁄d_b in the ACI 318-19 development length equation from 2.5 to 4.0 was shown to produce similar mean ratios of test-to-calculated bar stresses across different amounts of transverse reinforcement. Finally, results suggest that development length should be limited to 50d_b when designing lap splices without transverse reinforcement.

Inner surface reinforcement is one of the most widely adopted techniques for upgrading or strengthening shield tunnels. An important failure mode in this method is the debonding of the thin plates from the segments, resulting in less reinforcement effect than expected. A shield tunnel lining is a discontinuous curved structure formed by connecting segments with bolts, and its structural form and internal force state are essentially different from reinforced concrete beams. However, there are few reports on the evolution process of debonding failure of similar structures. Therefore, to develop a thorough understanding of the debonding failure, a three-dimensional refined numerical model for a shield tunnel strengthened by a thin plate at the inner surface based on the mixed-mode cohesive method was proposed. The validity and rationality of the model were corroborated by a full-scale experiment. Then, the model was applied to other inner surface reinforcement schemes commonly used in practice to explore the debonding mechanism of the adhesive layer. Finally, anti-debonding measures were proposed, and their effectiveness was elucidated by numerical analysis. The results show that the proposed numerical model can accurately predict the failure process of the adhesive interface of the shield tunnel strengthened by a thin plate. There are obvious interfacial stress concentrations at the joints and the plate ends, which are the essential reasons for the debonding failure initiating from those places. Anchoring the thin plate only at the plate ends and joints can significantly and sufficiently increase the debonding load. Therefore, it is not necessary to add anchoring measures elsewhere.