International Concrete Abstracts Portal

This paper presents the behavior of reinforced concrete beamsretrofitted with carbon fiber-reinforced polymer (CFRP) sheets andultra-high-performance concrete (UHPC) jackets in a multi-hazardenvironment. Following the procedural protocol of a publishedstandard, the beams are cyclically loaded under thermomechanicaldistress at elevated temperatures, varying from 25 to 175°C (77to 347°F), to examine their hysteretic responses alongside ancillarytesting. The thermal conductivity of UHPC is higher than thatof ordinary concrete by more than 62% and, according to a theoretical inference, premature delamination would not occur within the foregoing temperature range. The difference in load-carrying capacities between the strengthened and unstrengthened beams declines with temperature. While the UHPC+CFRP retrofit scheme is beneficial, CFRP plays a major role in upgrading the flexural resistance. The thermomechanical loading deteriorates the hysteretic loops of the beams, thereby lowering the stiffness and capacity. Elevated temperatures are concerned with the pinching, plasticity, characteristic rigidity, stress redistributions, and energy-release patterns of the beams. Due to the retrofit, the configuration of plastic hinges alters, and the localized sectional deformations form a narrow damage zone. The adverse effects of the temperatures on rotational stiffness are pronounced during the early loading stageof the beams.

To investigate the effect of prestressing on the shear strength of nuclear power plant containment structures, five reinforced or post-tensioned semi-cylindrical concrete walls and two planar walls were tested under cyclic lateral loading. The major test parameters were the presence of unbonded post-tensioning, the magnitude of horizontal prestressing force, and the use of crossties. The test results showed that because of the high reinforcement and prestressing ratio, web-crushing failure occurred in all specimens. The shear strengths of reinforced concrete (RC) and prestressed concrete (PSC) walls were greater than the nominal shear strength specified in the current design/evaluation methods. In the case of walls subjected to horizontal prestressing force, early delamination cracking occurred due to radial tensile stress. The delamination cracking was restrained by the use of crossties. Further, the effect of prestressing on the web-crushing strength was not significant. When the diameter of the cylindrical wall was the same as the length of the planar wall, the peak shear strength of the cylindrical wall was equivalent to that of the planar wall despite the different wall shape.

In this study, a procedure for interpreting impact-echo data in an automated, simple manner for detecting defects in concrete bridge decks is presented. Such a procedure is needed because it can be challenging for inexperienced impact-echo users to correctly distinguish between sound and defective concrete. This data interpretation procedure was developed considering the statistical nature of impact-echo data in a manner to allow impact-echo users of all skill levels to understand and implement the procedure. The developed method predominantly relies on conducting segmented linear regression analysis of the cumulative probabilities of an impact-echo data set to identify frequency thresholds distinguishing sound concrete from defective concrete. The accuracy of this method was validated using two case studies of five slab specimens and a full-scale bridge deck, each containing various typical defects. The developed procedure was found to be able to predict the condition of the slab specimens containing shallow delaminations without human assistance within 3.1 percentage points of the maximum attainable accuracy. It was also able to correctly predict the condition of the full-scale bridge deck containing delaminations, voids, corrosion damage, concrete deterioration, and poorly constructed concrete within 3.5 percentage points of the maximum attainable accuracy.

With the development and commercialization of post-tensioned (PT) concrete structures, concerns pertaining to structural safety for disasters and diverse conditions, such as fire and high temperatures, have emerged. To better understand fire-resistance performance, effects associated with cover thickness and tendon configurations for six unbonded PT concrete slabs were evaluated in regardto temperature changes, deflection, tendon tensile forces, and fire endurance/time. In addition, the factors and relationship between the extent of damage caused by concrete cracking/delamination and tendon force at post-tensioning were evaluated. Thermal resistance and deflection rates for materials such as galvanized steel duct or high-density polyethylene (HDPE) sheathing were also examined. It is the authors’ hope that the aforementioned informationidentifying parameters affecting fire-resistance performanceof PT slabs may be helpful to the practitioner when consideringtendon configurations for unbonded PT concrete structures.

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.