International Concrete Abstracts Portal

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.

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.

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.

Chloride diffusivity and steel corrosion are two major factors in the durability characteristics of concrete structures. It is possible to use the electrical resistivity (ER) of concrete as a measure of concrete’s ability to resist the movement of ions within the material. In this study, surface electrical resistivity (SR) and bulk electrical resistivity (BR) of concrete cylinders were measured from 3 to 161 days for concrete mixtures with four varying water-cement ratios (w/c) (0.45 to 0.60) and three distinct cement types. The study investigated the influence of important durability parameters such as cement type, long-term curing period, and w/c on concrete electrical resistivity. In addition, the impact of cylinder size on SR of concrete was observed. The findings show that both SR and BR of concrete decrease with increasing w/c, except for concrete with cement Type-I/II, which showed a minor increase in resistivity with a w/c of 0.55. Concrete with Type-V cement showed the highest electrical resistance. Moreover, a strong linear relationship between the two types of resistivity was established, and a new equation was introduced in terms of cement type, w/c, and long-term curing period. The correlation between SR and BR was validated by determining the mean absolute error (MAE) of the proposed equation for the three types of cement, which were 0.41 (Type-I/II), 0.65 (Type-III), and 0.35 (Type-V). For all three cement types, the mean absolute percentage error (MAPE) and coefficient of variation (COV) were within acceptable limits, and the 95% confidence interval (CI) indicated a small error margin for the proposed equation when estimating BR from SR using experimental data. Statistical analysis showed that the new equation was less reliable for Type-III cement than the other two types, possibly due to its rapid strength increase property.

The objective of this paper is to investigate the microscopic pore characteristics and macroscopic mechanical properties of concrete under different curing conditions. Ultrasonic nondestructive testing technology was used to measure the ultrasonic sound velocity of specimens of different ages, and the compressive strength and splitting tensile strength were obtained through indoor mechanical performance tests. The pore-size distribution characteristics and internal microstructure were observed using nuclear magnetic resonance (NMR) technology and scanning electron microscopy (SEM) testing, respectively. The results revealed that, compared with standard curing conditions, the decrease of the curing temperature and humidity can result in the volume and proportion of macropores and microcracks being larger, which results in the deceleration of the ultrasonic wave speed inside the concrete and the decrease of the mechanical properties. Under the same curing condition, a lower water-binder ratio (w/b) enables the internal pore surface area of the material to increase, and the mechanical properties are improved. With the decrease of the curing temperature and relative humidity, the stress-strain curve appeared delayed in the initial compaction stage and presents more obvious brittleness characteristics in the failure stage. By fitting the relationship between the concrete strength and the porosity under different curing conditions, an extended model that can be applied to cement-based materials was obtained. Additionally, it was found that the porosity is negatively correlated with the ratio of the compressive strength to splitting tensile strength of the concrete.