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This paper probed deep into a high-temperature resistant inorganic matrix: alkali-activated slag cement (AASC), which is a kind of cementitious material prepared by alkali-activator and pozzolanic or latent hydraulic material. Firstly, the mix ratio of the AASC was optimized to improve the wettability and mechanical properties. Then, the effects of the adhesive matrix and the type of fiber-reinforced polymer (FRP) were observed through FRP-to-concrete bond tests on 93 specimens. The test results, coupled with anchorage analysis, indicate that the AASC has comparable reinforcing effects as those of organic epoxy matrix; the anchorage length of FRP sheets has a significant influence on the failure behavior and failure mode of FRP-enhanced concrete structures. In addition, our tests prove that the AASC has favorable high-temperature resistance and bonding effects. The research results provide a good reference for the design and application of inorganic matrix for FRP-enhancement of concrete structures. [ABSTRACT FROM AUTHOR]

A portable seismic property analyzer (PSPA) was used to simultaneously acquire both ultrasonic surface wave (PSPA-USW) and impact-echo (PSPA-IE) data at predetermined locations along a section of multi-layered pavement. The pavement consisted of a basal concrete layer (~220 mm), an intervening layer of hot-mix asphalt (~60 mm), and a concrete overlay (~220 mm). The section of multi-layered pavement was cored at multiple PSPA test locations for verification purposes. The conditions of the extracted cores were assessed visually, and the static elastic modulus, as well as the compressional wave velocity of each concrete overlay core, were measured in the laboratory. Results from this study demonstrated that the PSPA-USW tool can be used to evaluate the conditions of concrete overlay, the interlayer (hot-mix asphalt), and their bonding conditions from a qualitative perspective. A good correlation between the static and laboratory dynamic modulus from core specimens of concrete overlay were confirmed based on laboratory testing results. However, the field dynamic modulus of core specimens, based on PSPA-USW tests, was lower than both the static modulus and laboratory dynamic modulus. Furthermore, the PSPAIE tool was not able to estimate the depth of the entire pavement and to various pavement layer interfaces due to the interference of flexural mode vibration. Fortunately, the difference between intact and deteriorated pavement can be qualitatively identified from the amplitude spectrum. More core specimens are needed for further studies in order to verify the performance of both PSPAUSW and PSPA-IE techniques for multi-layered pavement condition assessment. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and analytical investigation on the compressive performance of concrete cylinders internally reinforced with steel-fiber-reinforced composite bars (SFCBs) and externally confined with fiber-reinforced polymer (FRP) sheets, termed herein as S-F-RC cylinders. Eleven concrete cylinders, with different confinement conditions and with (or without) longitudinal SFCBs, were tested under monotonic compression. Two distinguishable failure mechanisms, global buckling and local buckling, were discovered for SFCBs in S-F-RC cylinders, under weak and strong confinement conditions, respectively. The S-F-RC cylinders exhibited a marked increase in failure strain of the confinement, directly translating to an enhanced compressive failure strain for the longitudinal SFCBs under strong confinement conditions. Existing models for FRP-reinforced concrete cylinders were found to underestimate the load-carrying capacity of S-F-RC cylinders. An existing compressive stress-strain model for SFCB was extended to the case of S-F-RC cylinders. The proposed method offers accurate predictions, effectively mitigating the discrepancies caused by varying confinement and material properties across different SFCBs. • Compressive performance of FRP-confined SFCB-reinforced concrete is presented. • Different buckling failure mode observed for SFCB under weak or strong confinement. • Model is developed for axial compressive strength of SFCB in FRP-confined concrete. [ABSTRACT FROM AUTHOR]

This paper addresses some open issues of the bond behavior of fiber-reinforced cementitious matrix (FRCM) composites applied to a concrete substrate. The study is focused on the effect of the number of fiber layers on the peak load, the effect of the loading rate on the load response, the relationship between peak load and bonded length (considering also bonded lengths substantially longer than the effective bond length), and the information that can be gained by measuring the slip at the free end of the bonded composite. The FRCM composite investigated is comprised of polyparaphenylene benzobisoxazole (PBO) fibers and a polymer-modified cementitious mortar. The experimental results are compared with results from the literature. The results indicate that the peak load must be carefully interpreted considering the effect of friction (interlocking), which is observed to occur between fibers and matrix and the fibers themselves. In addition, the effect of the loading rate requires additional investigation. Finally, the peak load of specimens with two layers of PBO fiber mesh is approximately double the peak load of tests with one layer of fiber mesh if the bonded length is longer than the effective bond length determined from tests with one layer of fiber mesh. [ABSTRACT FROM AUTHOR]

A ground-coupled ground penetrating radar (GPR) system was used to assess the condition of two reinforced concrete bridge decks. After each GPR assessment was completed, the bridge deck was rehabilitated using a hydrodemolition process to remove deteriorated concrete from upper surface of the deck. LiDAR technology was used to create maps depicting the deck surface before and after the concrete removal. The objective of this work was to corroborate the GPR condition assessments by comparing the spatial distribution of the GPR and LiDAR mappings. This work illustrates that GPR data have the potential to predict concrete repair estimates. [ABSTRACT FROM AUTHOR]