International Concrete Abstracts Portal

This study characterized pitting corrosion in prestressed piles, links it to stress concentration factors via ultimate strength tests, and finally incorporates the findings into a simple predictive damage assessment model. Six 1/3 scale Class V concrete prestressed piles were exposed for 38 months to outdoor tidal cycles simulating a marine environment. At exposure end, 24 strands were extracted from the piles, and the corrosion loss along the strands was quantified using a new Pascal’s law-based strand profiler. This identified regions of locally higher steel loss caused by pitting corrosion. The same data set was used to confirm gravimetric loss measurements by summing localized section losses over the specimen length. Profiler data was complemented by microscopic imaging to further define pitting geometry. Ultimate load tests were conducted to examine the effect of pitting on residual tensile strength and ductility. Similitude principles were used to show how the results can be used to predict the state of in-service pile strands where only inspection report crack widths are required.

Titanium alloy bars (TiABs) have recently been accepted as a structural material for near-surface mounted retrofit (NSMR) of reinforced concrete structural elements. This paper shows that TiABs in NSMR applications can be used simultaneously as anodes in impressed current cathodic protection (ICCP) to prevent corrosion of the existing reinforcement. Following a successful proof-of-concept study performed for small-scale prisms, dual-purpose TiABs were used as longitudinal and shear reinforcements to retrofit large-size structural beams. Prior to structural tests, the specimens were investigated to characterize the TiAB functionality within the ICCP system. During ICCP, cathodic potentials were in the expected linear region of the cathodic polarization curve of the steel rebars, and the 100-mV potential shift (decay) criterion following shut-off was satisfied upon the interruption of the protection current. The applied current and potential to achieve the required cathodic potentials were stable and were satisfactorily maintained while achieving the structural retrofit requirements.

Pourbacks and overlays are commonly used in bridge elements and repairs, as 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. Pulloff 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.

Chloride threshold values for steel reinforcing bars in reinforced concrete under the effect of varying temperatures and extended long-term conditions in hot climate are investigated. This investigation covers a gap in the current codes, including ACI 318, where the effect of temperature on the chloride threshold is not addressed. A total of 96 concrete specimens reinforced with carbon steel reinforcing bars sourced from two manufacturers were cast with different chloride contents and exposed to four temperatures of 20, 35, 50, and 65°C (68, 95, 122, and 149°F) for a period of more than 2 years. The chloride threshold values were determined based on corrosion potential, corrosion rate, and mass loss at the end of the exposure period. The results of the three techniques showed a consistent trend of significant dependency of the chloride threshold value on temperature. The average water-soluble chloride threshold values based on mass loss were found to be 0.77%, 0.72%, 0.47%, and 0.12% by weight of cement for temperatures of 20, 35, 50, and 65°C (68, 95, 122, and 149°F), respectively. These findings are significant as they showed a dramatic drop in the chloride threshold values at high temperature. This research highlights the need for reassessment of ACI Code limits considering hot climate.

This paper proposes a series of empirical modifications to an existing three-step analytical model used to derive the cyclic shear capacity of circular RC columns considering corrosive conditions. The results of sixteen shear-critical RC columns, artificially corroded to various degrees and tested under quasi-static reversed cyclic loading, are used for model verification. The final model is proposed in a stepwise damage-state format relative to the measured damage of the steel reinforcement. New empirical decay coefficients are derived to determine the degraded material properties based on an extensive database of over 1,380 corroded tensile tests. An additional database of 44 corroded RC circular piers is collected to assist in the modification of ductility-based parameters. Compared to the shear-critical test specimens, the model results indicate that the peak shear capacity can be predicted well across a range of deterioration severities (0 to 58.5% average transverse mass loss), with a mean predictive ratio of ± 8.60 %. As damage increases, the distribution of the corrosion relative to the location of the shear plane becomes a critical performance consideration, increasing predictive variance.