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.

This study uses neutron radiography (NR) and visual inspection to quantify water penetration in concrete samples exposed to water pressure on one face. It provides experimental data regarding the impact of mixture proportions on the hydraulic permeability of concrete. Specifically, it illustrates the influence of water-cement ratio (w/c), curing duration, entrained air content, and coarse aggregate (CA) size and volume on water transport. In addition, this paper quantifies the impact of permeability-reducing admixtures (PRAs) on water transport in concrete. It was observed that decreasing the w/c and/or increasing the curing duration reduced the fluid transport. Liquid and powder PRAs efficiently reduced fluid transport in concrete without impacting the compressive strength. The liquid PRA showed more consistent results, likely due to better dispersion than the powder PRA. Fluid ingress in concrete samples appears to increase with entrained air content due to a lower degree of saturation (DOS) at the start of the test. Increasing the CA volume fraction or decreasing the CA size will increase the fluid transport in concrete due to an increase in the connectivity of the interfacial transition zone. The influence of entrained air content, curing duration, CA volume fraction, and CA size was less noticeable on mixtures with PRAs due to the higher density and low permeability of these samples compared to control samples.

This paper presents a case study on the evaluation of bridge decks using various nondestructive test methods. In consultation with a local transportation agency, five representative bridges are selected and assessed by qualitative/empirical (visual inspection and chain drag) and quantitative (ground-penetrating radar [GPR] and rebound hammer) approaches. The primary interest lies in quantifying delaminated areas in deck concrete, which has been a major problem in the bridge engineering community because conventional GPR contours provide a wide range of deterioration that differs from the amount of actual repair. A consistent condition rating of 7 has been assigned to all decks over a decade old, aligning with the outcomes of chain drag: delamination of less than 3.31% of the entire deck area. The variable scanning rates of GPR (4 to 20 scans/ft [13 to 66 scans/m]) influence contour mapping, whereas mutual correlations associated with these rates are insignificant. A tolerable range of ±20% is suggested for interpreting GPR contour maps at a 95% confidence interval. The performance threshold limit of 20% used to identify degraded concrete in rebound hammering exhibits a coefficient of correlation of 0.967 against GPR-based deterioration; however, the results of these methods deviate from the areas of actual repair. For practical implementation, analytical and computational models are formulated to decompose the intensity of GPR scales into two categories: initiation and progression of corrosion (0 to 39%) and delamination of deck concrete (40 to 100%), which show good agreement with the repaired areas. Parametric investigations emphasize the significance of reinforcing bar spacing and concrete cover in determining the extent of delamination in the concrete decks.

The improvement of durability and service life of reinforced concrete structures in the marine environment with the incorporation of corrosion inhibitors has attracted significant attention in recent years. The present study aims to evaluate the performance of a commercially available organic corrosion inhibitor in protecting the steel reinforcement of concrete structures in marine conditions. The study was performed on a control mixture and a test mixture with water-cement ratios (w/c) of 0.4 and 0.6, providing aggressive laboratory and field environments following the recommendation of international standards for corrosion inhibitors assessments. Corrosion monitoring methods and visual inspection of reinforcing bars confirmed the effectiveness of migrating corrosion inhibitor in mitigating chloride-induced corrosion. The migratory properties of the corrosion inhibitor and its ability to densify the matrix microstructure were confirmed through scanning electron microscopy and X-ray photoelectron spectroscopy analyses.

Corrosion-resistant stainless steel strands are an alternative to carbon steel strands in prestressed concrete structures, particularly in extremely aggressive environments. The benefits of using stainless steel strands include prolonged service life and fewer inspections of the structure. The flexural behavior of stainless steel prestressed concrete girders was experimentally studied. Seven full-scale 42 ft (12.8 m) long AASHTO Type II girders were designed, cast, and tested in flexure. Two of the seven girders had carbon steel strands and served as control girders. Experimental results showed that the overall flexural behavior of the girders prestressed with stainless steel strands is different than those prestressed with carbon steel strands. The capacity of all stainless steel girders increased up to failure, which reflects the stress-strain shape of the stainless steel strands. When the girders had the same initial prestressing force, the ultimate capacity of the stainless steel non-composite and composite girders was approximately 11.7% and 23.7% higher than that of the control girders, respectively. Experimental results revealed that regardless of failure mode, the girders prestressed with stainless steel strands can achieve ultimate capacity and deformability as high as those prestressed with carbon steel strands. Although the composite stainless steel girders failed due to rupturing of strands, they failed at a noticeable deflection with many flexural cracks in the midspan. Rupture of strands failure mode is particularly important because it demonstrates the importance of the ultimate strand strain in design. The guaranteed ultimate strain of stainless steel strands is 1.4%. Stainless steel prestressed concrete I-girders are recommended to be designed to fail by rupturing the strands. The analytical load-deflection curves showed good agreement with experimental ones. A simple numerical design procedure was developed to predict the nominal flexural resistance of stainless steel pretensioned girders designed to fail by rupture of strands.