International Concrete Abstracts Portal

This paper investigates the efficacy of ultra-high-performance concrete (UHPC) jacketing as an option for seismic retrofit (repair or strengthening) of structural components that have been damaged by reinforcement corrosion. Previous work has illustrated that UHPC cover fully mitigates corrosion in the absence of service cracks and significantly reduces the corrosion rate in the case of preexisting cracks. In the present experimental study, cover replacement by UHPC is used to repair and strengthen corroded columns. Six lap-spliced columns designed based on pre-1970s design standards were constructed and subjected to artificial corrosion. Parameters of the investigation were: a) the aspect ratio of the specimens; b) the bar size (to account for the effect of bar diameter loss on bond); and c) the condition of the specimen (repair or strengthening after damage due to application of simulated seismic load to assess the effectiveness of retrofitting corroded components, even after having endured earthquake damage). The results show that thin UHPC jackets replacing conventional concrete cover suffice to impart a significant increase in strength and ductility of the columns. The jackets also endow the corroded and unconfined lap splices with significant force and deformation development capacity, thus alleviating a source of excessive column flexibility in existing construction.

One strategy for the rehabilitation of existing reinforced concrete columns is to target the improvement of specific local vulnerabilities in the columns related to inadequate strength or ductility. Eight full-scale columns were tested to evaluate the performance of a rehabilitation technique for square or rectangular reinforced concrete columns using a system of discrete external steel collars. Unlike other external confinement methods such as steel jacketing and fiber-reinforced polymer (FRP) wrapping, the proposed collar system exploits the benefits of confining elements with significant flexural stiffness. The project investigates the effectiveness of steel collars for rehabilitating columns when they are loaded axially at an eccentricity from the column centroid. Parameters investigated include collar spacing, collar flexural stiffness, active confining pressure, and load eccentricity. The columns were tested under monotonically applied axial loading and exhibited both strengths and ductilities well in excess of what would be expected with conventionally reinforced columns.

This paper presents an analytical method to predict the flexural performance of reinforced concrete (RC) beams strengthened by fiber-reinforced geopolymer composites (FRGC). In addition, a parametric study was performed to determine the effect of the thickness and tensile strength of the strengthening material on the moment, ductility, and energy absorption capacity of the composite beam. The proposed model adopts sectional strip discretization and incorporates the constitutive relationship of each component material. The strengthening configurations considered in the analysis include bottom, two-sided, and three-sided jackets. Four failure conditions were simulated to account for the original failure of the RC beam and are described in terms of the steel reinforcement ratio in the range of 0.87 to 2.29%. The result showed a good agreement between the predicted and experimental values and that the proposed analytical method can be used to predict the momentcurvature response. The parametric study revealed that the change in the moment and ductility value is more sensitive in the variation of FRGC thickness than the tensile strength regardless of the jacketing configurations and failure type of the unstrengthened beam.

The axial behavior of circular reinforced concrete (RC) columns strengthened with a combined ultra-high-performance fiber-reinforced concrete (UHPFRC) and glass fiber-reinforced polymer (GFRP) jacketing technique was experimentally investigated. Thirteen base column specimens were cast, each 120 mm (4.8 in.) in diameter and 500 mm (20 in.) in height, two strengthened with a 15 mm (0.6 in.) thick UHPFRC jacket, four confined by full and intermittent strips of GFRP composites, six strengthened with a novel technique of combined UHPFRC and GFRP jacketing, and one without any external strengthening. Experimental results showed that specimens confined by the combined strengthening technique recorded average increases of 197% and 252% in load-carrying capacity and energy absorption, respectively, compared to the control column. The galvanized midlayer increased load-bearing capacity by roughly 10% on average. It was also observed that specimens confined by seven intermittent GFRP strips recorded a 17% average increase in load-carrying capacity compared to the specimen with three strips of total equal width. Finally, a previous model adopted for specimens confined by concrete jacketing was modified and verified against the results of present and previous studies.

Section enlargement and jacketing using ultra-high-performance concrete (UHPC) have been used to strengthen existing reinforced concrete structures. The structural performance of these strengthened structures is highly dependent on the bond performance at the interface between the UHPC and normal-strength concrete (NSC) substrates. This study investigates the shear strength and ultimate failure mode of the interface in UHPC-NSC composites using an experimental program of slant shear test. The main test parameters include the roughness and inclination angle of the interface and the curing condition of the UHPC. Both the roughness at the interface due to sand-blasting and the inclination angle of the interface control the failure modes showing distinct transitions of the failure modes between concrete crushing and near-interface concrete cracking. The failure criteria for the interface of UHPC-NSC composites can be explained using the theory of plasticity by identifying the failure modes.