International Concrete Abstracts Portal

This study reviewed, synthesized, and extended the service life prediction models for conventional reinforced concrete (RC) structures to those with advanced concrete materials (that is, high-performance- concrete [HPC] and ultra-high-performance concrete [UHPC]), and corrosion-resistant steel reinforcements (that is, epoxy-coated [EC] steel, high chromium [HC] steel, and stainless- steel [SS]) subjected to chloride attack. The developed corrosion initiation and propagation models were validated using field and experimental data from literature. A case study was performed to compare the corrosion initiation and propagation times, and service life of RC structures with different concretes and reinforcements in various environments. It was found that UHPC structures surpassed 100 years of service life in all studied environments. HPC enhanced the service life of conventional normal-strength concrete (NC) structures by over three times. In addition, the use of corrosion-resistant reinforcement prolonged the service life of RC structures. The use of HC steel or epoxy-coated steel doubled the service life in both NC and HPC. SS reinforcement yielded service lives exceeding 100 years in all concrete types, except for NC structures in marine tidal zones, which showed an 88-year service life.

Despite improvements in nondestructive testing (NDT) technologies, the quality assurance of concrete reinforcing bar placement is still primarily conducted with conventional methodologies, which can be time-consuming, ineffective, and damaging to the concrete components. This study investigated the performance of two commercially available cover meters and one groundpenetrating radar (GPR) device. A cover meter was found to have the greatest accuracy for depths smaller than 3.19 in. (81.0 mm), while the GPR performed better for greater depths. The effect of reinforcing bar depth, diameter, and type; neighboring reinforcing bars; and concrete conditioning on the performance of the devices was quantified. The use of epoxy-coated reinforcing bar, galvanized reinforcing bar, and stainless-steel reinforcing bar were found to have a negligible effect on cover meter accuracy. A model was developed to predict the precision of the GPR post-measurement analysis given a depth and concrete dielectric constant.

Pour-backs and overlays are utilized commonly in bridge elements and repairs; it is crucial to corrosion protection that the bond between grout and concrete in these regions is carefully constructed. The integrity of the bond is crucial to ensure a barrier against water, chloride ions, moisture, and contaminants; bond failure can compromise the durability of concrete structures' long-term performance. This study examines the influence of surface preparation methods on the bond durability and chloride permeability between concrete substrate and grouts, including both "non-shrink" cementitious and epoxy grouts. A microstructural analysis of scanning electron microscopic (SEM) images was conducted to characterize the porosity of specimen interfaces. Pull-off testing was performed to quantify tensile strength. Results show that a water-blasted surface preparation technique improved the tensile bond strength for cementitious grout interfaces and reduced porosity at the interface. In contrast, epoxy grout interfaces were less affected by surface preparation. The study establishes a relationship between chloride ion permeability, porosity, and bond strength. The findings highlight the importance of surface preparation in ensuring the durability of concrete-grout interfaces.

This paper presents the findings of an experimental study on the corrosion performance of both conventional and corrosionresistant steel reinforcements in normal-strength concrete (NC), high-performance concrete (HPC), and ultra-high-performance concrete (UHPC) columns in an accelerated corrosion-inducing environment for up to 24 months. Half-cell potential (HCP), linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS) methods were used to assess the corrosion activities and corrosion rates. The reinforcement mass losses were directly measured from the specimens and compared to the results from electrochemical corrosion rate measurements. It was concluded that UHPC completely prevents corrosion of reinforcement embedded inside, while HPC offers higher protection than NC in the experimental period. Based on electrochemical measurements, the average corrosion rate of mild steel and high-chromium steel reinforcement in NC in 24 months were, respectively, 6.6 and 2.8 times that of the same reinforcements in HPC. In addition, corrosion-resistant steel reinforcements including epoxycoated reinforcing bar, high-chromium steel reinforcing bar, and stainless-steel reinforcing bar showed excellent resistance to corrosion compared to conventional mild steel reinforcement. There was no active corrosion observed for epoxy-coated and stainless steel reinforcements during the 24 months of the accelerated aging; the average corrosion rateS of high-chromium steel was 50% of that of mild steel in NC based on the electrochemical corrosion measurements; and the average mass loss of high-chromium steel was 47% and 75% of that of mild steel in NC and HPC, respectively. The results also showed that the LPR method might slightly overestimate the corrosion rate. Finally, pitting corrosion was found to be the dominant type of corrosion in both mild and high-chromium steel reinforcements in NC and HPC columns.

Although the bond strength between reinforcing bars and pre-damaged concrete affects the seismic performance of repaired concrete structures, few studies have focused on the bond performance between the reinforcing bar and pre-damaged concrete. In the present study, to evaluate the effect of retrofitting with carbon fiber-reinforced polymer (CFRP) or ultra-high-performance concrete (UHPC) on the bar bond strength, lap-splice tests were performed on 20 beam specimens. The beam specimens were pre-damaged until bond failure or reinforcing bar yielding, and then the retrofitted beam specimens were reloaded to evaluate the bond strength recovery. Specimens were divided into five groups according to the reinforcing bar diameter, use of stirrups along the splice length, and type of preloading. Four retrofitting methods— CFRP sheet (C), a combination of CFRP sheet and crack injection epoxy (CE), UHPC (U), and a combination of CFRP sheet and UHPC (CU)—were applied to each group after preloading. The test results showed that the bar bond strength was improved by the used retrofitting methods, particularly by the retrofitting method of CU. In the specimens with a 20 mm reinforcing bar diameter and slight pre-damage, the retrofitting methods of C and CE were appropriate to restore the bar bond strength. For the specimens with a 28 mm reinforcing bar diameter and serious pre-damage, the bar bond strength was improved by retrofitting with U and CU. To consider the effects of pre-damage and retrofitting with CFRP sheet and/or UHPC on the bar bond strength, a modification of the existing methods for bar bond strength was proposed. The proposed method predicted the test results well.