International Concrete Abstracts Portal

Extensive experimental verification has shown that the use of fiber-reinforced polymer (FRP) anchors in combination with externally bonded fiber-reinforced polymer composites increases the flexural capacity of existing Reinforced Concrete (RC) structures. Thus, a rational prediction model is introduced in this study so that the fiber splay anchors may be accurately designed for practical strengthening applications. Simplified structural mechanics principles are used to build this model for capacity prediction of a group of fiber splay anchors used for FRP flexural strengthening. Three existing test series utilizing fiber splay anchors to secure FRP-strengthened T-beams, block-scale, and one-way slabs were used to calibrate and verify the accuracy and applicability of the present model. The present model is shown to yield very accurate predictions when compared to the results of the block-scale specimen and eight different one-way slabs. The proposed model is also compared with the predictions of a design equation adapted from the case of channel shear connectors in composite concrete-steel construction. Results show a very promising correlation.

This study addressed a critical knowledge gap by examining the influence of staggering on the bond strength of lapped glass fiber-reinforced polymer (GFRP) bars in concrete members. It involved a comprehensive investigation of new-generation GFRP bars with varying staggering configurations in nine large-scale GFRP-RC beams with a rectangular cross-section of 300 mm × 450 mm and a length of 5,200 mm. The tests investigated splice strength with three staggering distances: 0, 1.0, and 1.3 times the splice length (l_s) from the center-to-center of two adjacent splices, and three splice lengths of 28, 38, and 45 times the bar diameter (d_b). Results revealed a slight improvement in ultimate load-carrying capacity (less than 10%) for partially and fully staggered splices compared to non-staggered ones, with the latter exhibiting a more ductile failure mode. The effect of staggering was consistent across different splice lengths, demonstrating that splice length was not a factor. Although staggering reduced flexural crack width, it increased the total number of cracks due to expanded splice regions. Bond strength improved with staggering, with gains of 4.0% and 8.0% for partially and fully staggered splices, respectively. ACI 440.11-22 provides more accurate predictions of the bond strength of lap-spliced GFRP bars than the other design codes showing an average test-to-prediction ratio of 1.03 for non-staggered splices. Nevertheless, it requires some reconsideration when it comes to staggered splices. To address this, a proposed modification factor was introduced to account for staggering conditions when calculating bond strength and splice length in ACI 440.11-22.

This study examined how tendon configuration affects the temperature behavior of post-tensioned concrete structures during fire exposure using finite element analysis. The thermal behavior of various tendon configurations was modeled, showing good agreement with experimental data. Parametric studies found that unbonded single-strand tendon (S) and prestressing (pre-tensioned) strand (R) had lower thermal resistance compared to bonded post-tensioned tendon (B), unbonded post-tensioned tendon (U), and grouted extruded-strand tendon (G). The S and R specimens stayed at or below the critical temperature for one-way slabs, validating current safety codes. The B, U, and G specimens remained well below critical temperatures, indicating thinner concrete cover might suffice. These findings highlight the need to consider tendon configuration in structural fire resistance evaluation and incorporate heat resistance assessment to ensure the safety and efficiency of prestressed concrete structures during fires.

Pourbacks and overlays are commonly used in bridge elements and repairs, as it is crucial to corrosion protection that the bond between grout and concrete in these regions is carefully constructed. The integrity of the bond is crucial to ensure a barrier against water, chloride ions, moisture, and contaminants; bond failure can compromise the durability of concrete structures’ long-term performance. This study examines the influence of surface preparation methods on the bond durability and chloride permeability between concrete substrate and grouts, including both non-shrink cementitious and epoxy grouts. A microstructural analysis of scanning electron microscopic (SEM) images was conducted to characterize the porosity of specimen interfaces. Pulloff testing was performed to quantify tensile strength. Results show that a water-blasted surface preparation technique improved the tensile bond strength for cementitious grout interfaces and reduced porosity at the interface. In contrast, epoxy grout interfaces were less affected by surface preparation. The study establishes a relationship between chloride ion permeability, porosity, and bond strength. The findings highlight the importance of surface preparation in ensuring the durability of concrete-grout interfaces.

This paper presents the behavior of unreinforced cylindrical concrete elements confined with a hybrid system, consisting of an ultra-high-performance concrete (UHPC) jacket and basalt fiber-reinforced polymer (BFRP) grids. For exploring the feasibility of the proposed strengthening scheme, a series of tests are conducted to evaluate material properties and to obtain results related to interfacial bond, load-bearing capacity, axial responses, and failure modes. To understand the function of the individual components, a total of 57 cylinders are loaded under augmented confining conditions, including plain cores with ordinary concrete (CONT), plain cores with UHPC jackets (Type A), and plain cores with UHPC jackets plus BFRP grids (Type B). By preloading the cores at up to 60% of the control capacity (60%fc′) before applying the confinement system, the repercussions of inherent damage that can take place in vertical members on site are simulated. The compressive strength of UHPC rapidly develops within 7 days, whereas its splitting strength noticeably ascends after 14 days. The adhesion between the ordinary concrete and UHPC increases over time. While the Type B specimens outperform their Type A counterparts in terms of axial capacity by more than 18%, reliance on the BFRP grids is reduced with the growth of UHPC’s strength and adhesion because of the interaction between the hardened UHPC and the core concrete. The adverse effects of the preloading are noteworthy for both types, especially when exceeding a level of 30%fc′. The BFRP grid-wrapping alleviates the occurrence of a catastrophic collapse in the jacketed cylinders, resulting from a combination of the axial distress and lateral expansion of the core. Analytical models explain the load-carrying mechanism of the strengthened concrete, including confinement pressure and BFRP stress. Through parametric investigations, the significance of the constituents is clarified, and design recommendations are suggested.