International Journal of Concrete Structures and Materials最新文献

Recycling of abandoned waste bottom ash has been a key issue in Republic of Korea in terms of environmental protection as well as economic concern. In this work, a method for recycling of abandoned bottom ash has been discussed based on the results from laboratory and industrial-scale experiments. Abandoned bottom ash was magnetically separated and properties of magnetically separated bottom ash samples as well as properties of mortar and masonry cement brick made of bottom ash were investigated. According to the experimental results, bulk and skeletal densities were ranked in the order of strongly magnetic > weakly magnetic > as-received > non-magnetic (from heavier to lighter) bottom ash. From laboratory-scale experiments, compressive strengths of mortars made of bottom ash samples (measured by ASTM C 109) were lower than that of mortar made of standard sand. Among bottom ash samples, mortar made of non-magnetic bottom ash (after removal of unburnt carbon) showed higher compressive strength with lower thermal conductivity (measured by ASTM C 1113) and weight than others. Masonry cement brick made of magnetic bottom ash showed lower weight and thermal conductivity than those made of standard sand, while meeting the KS strength guideline as a masonry cement brick. The results suggest the applicability of bottom ash as lightweight aggregate for production of masonry cement brick. However, considering the lower strength obtained from masonry cement brick made of as-received bottom ash (without removal of unburnt carbon), unburnt carbon content should be removed prior to its utilization as lightweight aggregate.

Basically, the interface shear strength between two concrete layers of varying ages must be sufficient to withstand the applied actions on the structure, specifically fire attack, which may cause the complete collapse of the composite structure. Thus, interfacial shear behavior was investigated and analyzed in this paper under the influence of a set of parameters, including temperature (25, 200, 400, and 600 °C), time exposure (30, 60, 90, 120, and 180 min), concrete type, and fibers type (polypropylene fiber (PPF), steel fiber (SF), and hybrid fiber) by employing a Z-shape push-off test. The test consists of two parts with different ages: normal strength concrete (NCS) and high-performance concrete (HPC). HPC includes high-strength concrete (HSC) and fly ash concrete (FAC). Initially, twenty-five Z-shaped push-off tests were made, four of which were cast as one unit (NSC/or concrete with hybrid (FSP)), and the rest were composite specimens. Furthermore, a 3D finite element model of a composite push-off specimen was developed to simulate and analyze the impact of various time and temperature exposures on the interfacial shear strength of composite specimen N-FSP. The results indicated that temperature degree and exposure time adversely affected the interfacial shear strength. Also, interfacial shear strength is significantly influenced by fiber types. Including combined fiber (SF + PPF) improved the interfacial shear strength by 114% compared to the composite specimen NSC-NSC after exposure to a temperature of 600 °C. In contrast, using PPF negatively affected the interfacial shear strength, recording only 84% of the composite specimen NSC-NSC. In addition, the inclusion of supplementary cementitious material enhanced the interfacial shear strength by 60.5% in the NSC-FAC composite specimen with 30% FA, compared to the NSC-NSC specimen. Finally, a finite element (FE) model was proposed with a satisfactory level of accuracy (0.95 to 1.03) in predicting the maximum shear strength. Additionally, the difference between the FE and experimental stiffness was between 0.92 and 1.07.

Ultra-high performance concrete (UHPC) with excellent mechanical properties and durability is a promising material for reinforcement of existing normal concrete (NC) structures. In this paper, the shear failure behavior of the NC–UHPC interface was studied by the slant shear test and the SEM (scanning electron microscope) visualization test, considering influence of the substrate strength and the interface roughed treatment. As the NC substrate and the UHPC overlay are tightly combined at the interface transition zone (ITZ), the interface exhibits good slant shear performance, and the measured interfacial shear strength could reach 19.4 MPa with C40 substrate and 21.8 MPa with C50 substrate. In addition, the microstructure and composition of the ITZ, the possible interfacial failure modes, and the load-carrying mechanism of the interface under compression–shear force are revealed. The high interface roughness and the substrate strength have positive influence on the shear strength, and greatly affect the prone failure mode and the load-slip characteristic.

This study investigates the strain softening behavior of high-performance fiber-reinforced cementitious composites (HPFRCCs) under uniaxial compression. HPFRCC mixtures with different compressive strengths ranged from 120 to 170 MPa were prepared. The measurement method of feedback control on loading rate based transverse displacement was applied. Stress–strain and stress−inelastic displacement curves were plotted and analyzed with the results in the literature. It was found that the post-peak energy absorption of HPFRCC considering inelastic deformation was about 3–7 times higher than conventional concrete. Based on the experimental results in the present work, fitting models on post-peak stress–strain/−displacement curves were considering for different aspect ratios proposed.

The study discussed the effects of different mineral incorporations and the curing time on the strength of modified magnesium phosphate cement (MPC) mortars through mechanical tests, mathematical model analysis and microstructure characterization. Fly ash (FA), silica fume (SF), and metakaolin (MK), which exhibit excellent durability and bonding properties, were used to modify the MPC. A quantitative relationship was established between the strength of modified MPC mortars and the mineral incorporation and curing time. First, the strength of each mineral-modified MPC mortar cured in air with different mineral incorporations and curing durations was evaluated. The strengths of MPC mortars containing 10% fly ash, 15% silica fume, and 10% metakaolin—which perform best in their incorporations—were compared to analyze the function of the three minerals. To establish the relationship between strength and mineral incorporation and curing time, three mathematical models, linear model, general nonlinear model, and data distribution shape nonlinear model (DDSNM), are commonly used for material property analysis based on statistics. DDSNM best describes the trend of strength change among the three models and the error is small for three minerals. Based on DDSNM, the influence of various minerals on the strength of MPC mortar was quantitatively evaluated by calculating the variable partial derivatives, and verified by scanning electron microscopy and X-ray diffraction. MK performs the best in improving the flexural strength performance of MPC, while SF performs the best in the compressive strength. FA-MPC has low sensitivity to dosage fluctuations and is easy to prepare.

Abstract

This study investigated the effectiveness and limitations of newly developed biological mortars regarding chloride ion diffusion resistance. Through several tests on the glycocalyx production capacity and growth potentials of bacteria cells under marine environments, Bacillus licheniformis was isolated and immobilized in the expanded vermiculites together with a bacterial culture medium for producing biological mortars. The chloride ion diffusion coefficient of the mortars up to 91 days was determined through natural diffusion cell tests. Subsequently, the service life of RC structure repaired with biological mortars under chloride attack was evaluated considering multilayer theory and time-dependent diffusion. The addition of expanded vermiculites immobilizing Bacillus licheniformis significantly reduced the chloride ion diffusion coefficient. When its addition increased from 10 to 30%, the chloride ion diffusion coefficient decreased by 50–90% compared to that of mortars without bacteria. The service life of reinforced concrete structures repaired with biological mortars containing 30% expanded vermiculite concentration and thickness of 50 mm was evaluated to be six times longer than that of repaired with conventional mortar. Overall, this novel approach holds significant potential in addressing the salt-induced deterioration challenges faced by RC structures.

Abstract

This detailed review looks at how carbon fiber-reinforced polymer (CFRP) may be used to improve the flexural capacity of reinforced concrete (RC) beams. It investigates the history, characteristics, and research trends of FRP composites, assesses various flexural strengthening methods utilizing FRP, and addresses the predictive power of finite-element (FE) modeling. The assessment highlights the importance of enhanced design codes, failure mode mitigation, and improved predictive modeling methodologies. It emphasizes the advantages of improving FRP reinforcement levels to meet code expectations and covers issues, such as FRP laminate delamination and debonding. The findings highlight the need of balancing load capacity and structural ductility, as well as the importance of material behavior and failure processes in accurate prediction. Overall, this review offers valuable insights for future research and engineering practice to optimize flexural strengthening with CFRP in RC beams.

Beam-like members sustaining the combined action of transverse load and membrane force exhibit a special load response to progressive deflection. A theoretical model is therefore developed to depict the resistance behaviours of clamped reinforced concrete (RC) beams observed in tests. The support-induced membrane effects are simulated by a longitudinal spring and a rotational spring. The load responses to progressive deflection are obtained using the membrane approach, and the prediction accuracies of proposed method are validated by a series of four-point bending tests on hybrid fibre reinforced-lightweight aggregate concrete (HFR-LWC) beam. It is illustrated that the bearing capacities of clamped HFR-LWC beam are significantly enhanced by the membrane effect. Ultimate load of the clamped beam ranges from 64.0 to 184.0 kN, and the larger bearing capacity compared with simply supported beam is obtained. An ultimate load of 1.85 to 5.31 times the yield line value is achieved, and thereby, the ultimate resistance of the clamped beam might be seriously underestimated using yield line approach. A strong support constraint is beneficial for increasing the load-carrying capacity of clamped HFR-LWC beam, although the large longitudinal restraint stiffness would inevitably gives rise to brittle failure. The relative errors between predicted load and measured value are less than 7.23%, indicating that the presented model is a promising tool to estimate the ultimate load of clamped beam-like member.