International Concrete Abstracts Portal

Noncorrosive fiber-reinforced polymer (FRP) reinforcement presents an attractive alternative to conventional steel reinforcement, which is prone to corrosion, especially in harsh environments exposed to deicing salt or seawater. However, FRP reinforcing bars’ lower axial stiffness leads to greater crack widths when FRP reinforcing bars elongate, resulting in significantly lower flexural stiffness for FRP bar-reinforced concrete members. The deeper cracks and larger crack widths also reduce the depth of the compression zone. Consequently, both the aggregate interlock and the compression zone for shear resistance are significantly reduced. Additionally, due to their limited tensile ductility, FRP reinforcing bars can rupture before the concrete crushes, potentially resulting in sudden and catastrophic member failure. Therefore, ACI Committee 440 states that through a compression-controlled design, FRP reinforced concrete members can be intentionally designed to fail by allowing the concrete to crush before the FRP reinforcing bars rupture. However, this design approach does not yield an equivalent ductile behavior when compared to steel-reinforced concrete members, resulting in a lower strength reduction, ϕ, value of 0.65. In this regard, using FRP-reinforced ultra-high-performance concrete (UHPC) members offer a novel solution, providing high strength, stiffness, ductility, and corrosion-resistant characteristics. UHPC has a very low water-cementitious materials ratio (0.18 to 0.25), which results in dense particle packing. This very dense microstructure and low water ratio not only improves compressive strength but delays liquid ingress. UHPC can be tailored to achieve exceptional compressive ductility, with a maximum usable compressive strain greater than 0.015. Unlike conventional designs where ductility is provided by steel reinforcing bars, UHPC can be used to achieve the required ductility for a flexural member, allowing FRP reinforcing bars to be designed to stay elastic. The high member ductility also justifies the use of a higher strength reduction factor, ϕ, of 0.9. This research, validated through large-scale experiments, explores this design concept by leveraging UHPC’s high compressive ductility, cracking resistance, and shear strength, along with a high quantity of noncorrosive FRP reinforcing bars. The increased amount of longitudinal reinforcement helps maintain the flexural stiffness (controlling deflection under service loads), bond strength, and shear strength of the members. Furthermore, the damage resistant capability of UHPC and the elasticity of FRP reinforcing bars provide a structural member with a restoring force, leading to reduced residual deflection and enhanced resilience.

Coastal reinforced concrete (RC) bridges are critical infrastructures, yet they face significant threats from corrosion due to saline environments and extreme loads such as wave-induced forces and seismic events. This state-of-the-art review examines the resilience of corrosion-damaged RC bridges under such conditions. It compiles advanced methodologies and technological innovations to assess and enhance durability and safety. Key highlights include synthesizing loss estimation models with advanced reliability methods for a robust resilience assessment framework. Analyzing catastrophic bridge failures and environmental deterioration, the review underscores the urgent need for innovative materials and protective technologies. It emphasizes advanced analytical models including performance-based earthquake engineering (PBEE) and incremental dynamic analysis (IDA) to evaluate combined impacts. The findings advocate for engineered cementitious composites (ECCs) and advanced sensor systems for improved realtime monitoring and resilience. Future research should focus on developing comprehensive resilience models accounting for corrosion, seismic, and wave-induced loads to enhance infrastructure safety and sustainability.

This research investigates the impact of using washed waste fines (WWF), a byproduct from ready-mixed concrete (RMC) plants, as a partial replacement for natural sand in concrete. Cylindrical (100mm x 200mm) and cubic mortar specimens (50mm x 50mm x 50mm) were created with 20% WWF substitution. Hardened properties such as compressive strength, tensile strength, UPV, and durability parameters such as chloride migration coefficient and carbonation coefficient were evaluated. The study also examined the microstructure of concrete using a Scanning Electron Microscope (SEM). Results showed that incorporating WWF enhanced both the hardened and durability properties of concrete, increasing compressive strength by 25% compared to the control case. Additionally, WWF decreased the non-steady-state chloride migration and carbonation coefficients, indicating improved durability. SEM analysis revealed a denser microstructure, and WWF incorporation reduced the permeable porosity and absorption capacity of concrete.

Corrosion of prestressing steel can threaten the durability of prestressed concrete. To ensure the durability of unbonded post-tensioning (PT) systems, it is crucial to investigate the effects of construction defects such as grease leakage and high-density polyethylene (HDPE) sheath damage. This study quantified the thickness of grease coating (PT-coating) and HDPE sheath damage as experimental variables. An accelerated corrosion test was conducted in two environments: 1) chloride ions only (Cl-) and 2) both chloride ions and dissolved oxygen (Cl- + DO). The corrosion current density and weight loss of prestressing strands and the suspended concentration density of corrosion cell solution were measured to quantify the corrosion performance. Increasing the grease coating thickness over 0.3 mm (0.012 in.) did not significantly enhance corrosion resistance. Realistic levels of HDPE sheath damage had no significant detrimental effects on durability; however, excessive HDPE sheath area loss must be avoided for long-term durability. It was examined to quantify the interrelationship between three data: electrochemical measurement, weight loss, and suspended concentration density as quantitative corrosion data. The findings of this study can serve as a basis for developing durability-related provisions, as well as controlling the construction defects of unbonded PT systems in field applications.

Engineered cementitious composites (ECC), a prominent innovation in the realm of concrete materials in recent years, contain a substantial amount of cement in their composition, thereby resulting in a significant environmental impact. To enhance the environmental sustainability of ECC, it is plausible to substitute a large portion of cement in the composition with fly ash, a by-product of coal-fired power plants. In recent years, there has been increased research in ECC containing high-volume fly ash (HVFA) binders and its wider application in construction practices. In this particular context, it becomes imperative to review the role of the HVFA binder in ECC. This review first examines the effects of incorporating an HVFA binder in ECC on fiber dispersion and fiber/matrix interface behavior. Additionally, mechanical properties, including the compressive strength, tensile behavior, and cracking behavior under loading, as well as durability performances of HVFA-based ECC under various exposure conditions, are explored. At last, the review summarizes the research needs pertaining to HVFA-based ECC, providing valuable guidance for future endeavors in this field.