International Concrete Abstracts Portal

Fiber-reinforced polymer (FRP) materials provide an excellent alternative for shear, flexure, and confinement retrofitting of deteriorated infrastructure. Despite the advanced technology employed in fabricating FRP materials, the monitoring and quality control of the FRP installation still present a challenge. For externally bonded FRP-rehabilitated structures, the existence of undesirable defects, including surface voids and debonding, on the concrete surface should be evaluated, as these defects would adversely affect the durability and capacity of the FRP-rehabilitated structures. Nondestructive testing has the potential to provide a fast and precise means to assess these FRP rehabilitated structures. This paper presents an experimental and theoretical investigation of the use of ground-penetrating radar (GPR) and infrared tomography (IRT) methods to evaluate reinforced-concrete (RC) slabs externally bonded with glass fiber-reinforced polymer (GFRP). Four externally bonded GFRP RC slab specimens were fabricated. Surface voids, interfacial debonding, and vertical cracks were artificially created on the concrete surface of the RC slabs. Test variables include the location and size of surface voids, interfacial debonding, and diameter of steel reinforcement. Improved two-dimensional and three-dimensional image reconstruction method, using the synthetic aperture focusing technique (SAFT), was established to effectively interpret the GPR test data. The results showed that an in-house developed software, that employed the enhanced image reconstruction technique, provided sharp and high-resolution images of the GFRP-retrofitted RC slabs in comparison to those images obtained from the device’s original software. The data suggests that the GPR testing could effectively be employed to accurately determine the size and location of the artificial voids as well as the spacing of the steel reinforcement. The GPR, however, could not well predict the debonding and concrete cracking, as the GPR signals were corrupted because of the direct wave and coupling effect of the antennae and background noise. Results obtained from the IRT testing showed that this technique can detect and locate near-surface defects including surface voids, interfacial debonding, and cracking with acceptable accuracy. The study suggests the combined use of the GPR and IRT imaging to accurately detect possible internal defects of FRP-rehabilitated concrete structures.

Load testing and structural monitoring facilitated the passage of several super-heavy permit loads at the Burns Harbor access bridge near Portage, IN. Twenty super-heavy permit loads, with gross vehicle weights reaching 848 kips (3770 kN), were required to cross the bridge, which was the only feasible route out of the port. Preliminary load ratings were acceptable due to three factors; the specialized transport’s large footprint effectively distributed load, the bridge was designed for Michigan Truck Trains, and the bridge was assumed to be in good condition. The last condition came into question due to significant cracks throughout the prestressed concrete girders caused by delayed ettringite formation (DEF). While DEF cracks were a function of improper curing and not related to live-load effects, the Indiana Department of Transportation (INDOT) was concerned that repeated heavy loads would negatively influence cracks and the bridge’s overall long-term performance. Due to the cargo’s importance to the local community and lack of an alternate route, INDOT allowed use of the bridge after load tests proved that the transports would not cause damage or reduce the bridge’s service life. Structural monitoring performed during the entire transport period verified structural performance was not diminished during the numerous crossings.

Concrete cracks can occur because of shrinkage, external effects, or internal expansion. Contractors are frequently faced with the question of whether cracking of concrete is considered a defect or whether it falls within the realm of normal behavior of concrete. The end use of the concrete application and the terms of the contract between the parties will determine the extent to which cracking is acceptable or unacceptable.

Inverted “T” bent caps are used extensively in concrete highway bridges because they are aesthetically pleasing and offer a practical means to increase vertical clearance. The problem is that at service load unacceptable diagonal cracks frequently occur at the re-entrant corners between the cantilever ledges and the web. In order to control the diagonal cracks, an extensive three-phase investigation was carried out. The first phase was to predict the diagonal crack widths at the interior portions of the bent caps. A 2-D analytical model, called Compatibility-Aided Strut-and-Tie Model (CASTM), was developed. This model was calibrated by testing seven full-size 2-D test specimens. The second phase was to predict the diagonal crack widths at the end faces of the exterior portions of bent caps. In this phase the CASTM was extended to 3-D analysis, which was calibrated by testing ten 3-D specimens. In the third phase, two whole-wholebent-cap specimens were tested to determine the effective distribution width in the vicinity of an interior applied load on the ledge. Crack control methods for the interior spans and the exterior end faces were recommended.

Presents the results of exploratory experiments using AFBC ash to produce a new kind of expansive cement. The principles for design of the compositions and theoretical consideration are discussed. The tests were carried out to examine the XRD pattern and the pozzolanic activity of the AFBC ash used. The expansive properties of this cement and its effects on porosity, pore structure, heat evolution, setting time, resistance to chemical attack, leaching effect, and strength of hardened cement paste are analyzed in detail. A kind of warm-pressed AFBC ash expansive cement product is also presented. The present results indicate that the sulfoaluminate of AFBC ash can be used as an expansive component. This kind of expansive cement could be used to chemically induce compressive stress in the mortar and thereby reduce the size and amount of shrinkage cracks that frequently occur in portland cement concrete during drying. The results suggest an economically and environmentally acceptable approach.