International Concrete Abstracts Portal

This paper examines the pre-application of a waterproofing slurry overlay on the performance of bonded CFRP strengthening systems. Overall, the waterproofed specimens experienced an undesirable bond failure between the adhesive and waterproofing coating and/or concrete substrate and less flexural capacity compared to the control specimen with only the CFRP composite. The control performed at a higher strength and resulted with concrete substrate failure. Due to the influence of moisture during the waterproofing slurry system application, further experimentation was performed to isolate the effect of moisture in the concrete specimens and its effects on the adhesive component as a performance factor. The moisture tests resulted in bond failures and lower strength capacities. The waterproofing application was altered relative to the manufacturer’s recommendations to accommodate an on-site construction protocol. Future research will vary curing time, active waterproofing compound, and on-site construction prior to applying the CFRP composite system to further improve performance.

The external confinement of reinforced concrete (RC) columns by means of externally bonded fiber reinforced polymer (FRP) laminates is a well established technique for strengthening and retrofitting purposes. This paper presents a pilot research that includes laboratory testing of full-scale square and rectangular (with side-aspect ratio smaller than 1.5) RC columns externally confined with glass and basalt-glass FRP laminates and subjected to pure axial load. Specimens that are representative of full-scale building columns were designed according to a dated ACI 318 code (i.e., prior to 1970) for gravity loads only. The study was conducted to investigate how the external confinement affects peak axial strength and deformation of a prismatic RC column. The results showed that the FRP confinement increases concrete axial strength, but it is more effective in enhancing concrete strain capacity.

This paper describes an experimental program undertaken to study the behavior and effectiveness of using Carbon Fiber Reinforced Polymer (CFRP) Grid, as an alternative for steel spirals to confine precast concrete piles. The research focuses on the effectiveness of the confinement of the specified C-Grid on the concrete core of piles. The experimental program consists of a total of seven short piles including one without confinement, two with steel spiral and four with C-Grid. The parameters included in the study were the number of grid layers, the overlap length, and the spacing between the circumferential wires of C-Grid. All the specimens were subjected to concentric axial compression up to failure. Results indicate that the specified C-Grid can provide equivalent performance or more than typical spiral steel reinforcement for precast prestressed concrete piles. The paper also presents an analytical model to predict the performance of piles reinforced with C-Grid as spiral reinforcement. The analytical model yields results that match well with the experimental results.

Seismic retrofitting of RC columns by external bonding of FRPs has been proven to be a cost-effective and simple technique in recent years. In this study, the ultimate drift capacity of FRP retrofitted columns were predicted by selecting design parameters as the ratios of confinement, axial load, longitudinal reinforcement and plastic damage with a database consisting flexure dominated RC columns with and without damage. The database consisted of 28 strengthened and 6 repaired specimens, representing typical deficient building columns with poor transverse reinforcement detailing, that were tested under cyclic displacement excursions and constant axial load. For the strengthened columns, a drift based design equation was proposed and this equation was modified regarding the damage amount and axial load level for the repaired columns. The deformation capacities were predicted with a good accuracy and the simplified design equations gave reliable results considering safe design regulations.

The onset and evolution of bar buckling at the plastic hinge of old-type reinforced concrete (RC) columns confined with composite material [textile-reinforced mortar (TRM) and fiber-reinforced polymer (FRP)] jackets was investigated experimentally and analytically in this study. The interaction between composite jacket (or concrete cover, for unconfined concrete) and embedded longitudinal compression reinforcement at the onset and evolution of bar buckling was achieved through strain measurements of the compression reinforcement. Moreover, the implementation of a stress-strain confinement model, which relates lateral with axial strains, allowed the description and monitoring of the axial-lateral strain relationship at the base of the columns throughout the evolution of bar buckling. Finally, based on the aforementioned confinement model and on the experimental measurements, the post-buckling behaviour of columns was related with the stiffness of the jacket.