International Concrete Abstracts Portal

Extrusion-based concrete printing technology allows the fabrication of permanent formwork with intricate shapes, into which fresh concrete is cast to build structural members with complex geometries. This significantly enhances the geometric freedom of concrete structures without the use of expensive temporary formwork. In addition, with proper material choice for the permanent formwork, the load-bearing capacity and durability of the resulting structure can be improved. This paper investigates the concrete printing of permanent formwork for reinforced concrete (RC) beam construction. A three-dimensional (3-D)-printable engineered geopolymer composite or strain-hardening geopolymer composite (3DP-EGC or 3DP-SHGC), recently developed by the authors, was used to fabricate the permanent formwork. The 3DP-EGC exhibits strainhardening behavior under direct tension. Two different printing patterns were used for the soffit of the permanent formwork to investigate the effect of this parameter on the flexural performance of RC beams. A conventionally mold-cast RC beam was also prepared as the control beam for comparison purposes. The results showed that the RC beams constructed using the 3DP-EGC permanent formwork exhibited superior flexural performance to the control beam. Such beams yielded significantly higher cracking load (up to 43%), deflection at ultimate load (up to 60%), ductility index (50%), and absorbed energy (up to 107%) than those of the control beam. The ultimate load was comparable with or slightly higher than that of the control beam. Furthermore, the printing pattern at the soffit of the permanent formwork was found to significantly influence the flexural performance of the RC beams.

Integrating glass fiber-reinforced polymer (GFRP) bars into lightweight self-consolidating concrete (LWSCC) would effectively contribute to producing lighter and more durable reinforced concrete (RC) structures. Nonetheless, the shear behavior of GFRP RC structures cast with LWSCC has not yet been fully defined. This paper reports experimental results on the behavior and shear strength of LWSCC beams reinforced with GFRP bars. The beams measured 3100 mm (122.05 in.) long, 200 mm (7.87 in.) wide, and 400 mm (15.75 in.) deep. The test program included six beams reinforced with GFRP bars and one control beam reinforced with conventional steel bars for comparison purposes. The test variables were the reinforcement type and ratio and concrete density. The experimental results indicate that using LWSCC allowed for decreasing the self-weight of the RC beams (density of 1800 kg/m3 [112.4 lb/ft3]) compared to normalweight concrete (NWC). All beams failed as a result of diagonal tension cracking. Increasing the axial stiffness of the longitudinal GFRP reinforcing bars improved the concrete shear capacity of the LWSCC beams. The test results of this study and the results for 42 specimens in the literature were compared to the current fiber-reinforced polymer (FRP) shear design equations in the design guidelines, codes, and literature. Applying concrete density reduction factors of 0.8 and 0.75 in the ACI 440.1R-15 and CSA S806-12 shear design equations, respectively, to consider the influence of concrete density achieved an appropriate degree of conservatism equal to that of the equations for NWC beams.

In this paper, the flexural behavior of four reinforced concrete (RC) beam specimens strengthened with near-surface-mounted (NSM) prestressing screw-threaded steel bars (PSBs) were investigated with four-point bending experiments, where the failure mode, load-deflection relationships, ductility, and cracking behavior were examined as key properties. The digital image correlation (DIC) technique was used to perform full-field measurement and provide information on the deformation and failure process of concrete members. The test results indicated that the beams strengthened with NSM PSBs exhibited improved load-bearing capacity and enhanced ductility performance. It was also observed that prestressing the strengthening bar and increasing the NSM reinforcement ratio can significantly enhance the strengthening effect on the beams while controlling the development and propagation of cracks; however, the deformability of the specimen would reduce accordingly. In addition, the emerging optical technique proved to be effective in measuring the full-field deformation and monitoring the cracking evolution of concrete structures.

With the purpose of solving construction difficulties in composite steel-reinforced concrete (CSRC) structures, the reinforcing bar cage is replaced with steel fiber to form a steel and steel fiber-reinforced concrete (SSFRC) composite structure. By conducting a four-point bending test on 18 specimens, the failure mechanism of SSFRC composite beams without reinforcing bar cages was studied, and load-deflection curves were obtained. The impact of the ratio of steel fiber, the ratio of H-shape steel, and the shear span ratio on failure mode and bonding behavior was analyzed. The bridging effect of the steel fibers can effectively enhance the tensile capacity of concrete after cracking, and debonding failure can be delayed or even avoided. For specimens with a small shear span ratio λ, it can be deemed that the limit of steel fiber ratio ρsf for shearing failure and bending failure was approximately between 1 and 2%. For specimens with a large λ, it was found that the ρsf affected both the debonding failure and the bending failure. The larger the λ, the more steel fibers are needed to transform the failure mode from debonding failure to bending failure. Using the combination of H-shape steel and steel fiber, the damage on SSFRC composite beams can be effectively controlled so that better mechanical behavior can be achieved.

Past research on the effects of alkali-silica reaction (ASR) on the behavior of shear-critical concrete structures have yielded contradictory results, whether they have come from full-scale tests on specimens extracted from existing ASR-affected structures or from laboratory specimens conditioned to accelerate the rate of the reaction. Both increases and decreases in the shear capacity of ASR-affected specimens were reported, when compared with either corresponding control specimens or theoretical strength. Experiments were performed to better characterize the response of ASR-affected reinforced concrete. Ten panels were constructed and tested under in-plane pure shear loading conditions. The panels, containing varying amounts of in-plane and out-of-plane reinforcement, were cast with either non-reactive aggregate, reactive fine aggregate (Jobe-Newman), or reactive coarse aggregate (Spratt). To accelerate the rate of the reaction, the specimens were conditioned under elevated humidity and temperature. Test results indicated that the load capacity of the panels was not adversely affected by ASR strains ranging between 1.2 × 10–3 and 2.5 × 10–3, as measured on corresponding standard expansion prisms, and that the shear stress at first cracking was in fact elevated. The panels’ deformation capacity, however, was reduced by approximately 30% for the reactive specimens compared to similar non-reactive ones.