International Journal of Concrete Structures and Materials最新文献

This paper presents an experimental study on the behavior of low-strength concrete columns confined with cold-formed steel under axial compression. The laboratory test specimens consist of four groups of rectangular concrete stub columns in the size of 130 (times ) 200 mm cross section and 300 mm height; the first group composes of the unconfined specimens, while the other three contain the confined specimens under 0%, 25% and 50% sustained axial loads. The jackets are made of two G450-grade channel cold-formed steel sections of 2.4 mm thickness welded together. No bonding material is used between the core concrete and the steel jacket. From the results, it is found that the cold-formed steel jacketing can increase the axial strengths of the unconfined concrete specimens by approximately 40-65%. The strength increase comes mainly from the confinement action, as only small axial deformation is detected in the jacket. Based on the given amount of prescribed preloads in this study, the presence of preload in the column does not have a significant effect on the increase in strength of the confined concrete columns. The measured strength enhancement ratio and the confinement ratio of the tested specimens are compared using five existing strength predictive equations. The performance of the unbonded cold-formed steel jacketing technique adopted in the stub columns is observed to closely conform with the predictive confinement model of the concrete-filled tubes.

Existing concrete creep coefficient prediction models have the limitation of not considering the structural characteristics of CFT. For this reason, these models tend to overestimate the creep deformation of CFT. Therefore, in order to overcome the limitations of existing CFT creep experiments, this study proposes a creep-experiment method involving the use of CFT that passively changes the load applied to a single concrete specimen by calculating the stress redistribution between the concrete and a steel tube in CFT based on a step-by-step method. Furthermore, by actually applying the proposed experimental method, a creep experiment of CFT lasting for approximately 163 days was performed and a superficial creep coefficient model of CFT was proposed based on long-term strain data from the experiment. In order to verify the proposed superficial creep coefficient model, it was compared with two design criteria (CEB-FIP and ACI) based on the experimental results of this study and references. As a result, compared to the existing design criteria, the value predicted by the proposed superficial creep coefficient model showed good agreement with the experimental results of this study and the references, proving that the proposed creep-experiment method of CFT and superficial creep coefficient model are reasonable.

This study investigated the effect of rubber content on the mechanical characteristics of ultra-high-performance rubberised concrete (UHPRuC). The results revealed a distinctive non-linear decrease in the dry density of UHPRuC as the rubber content increased. Notably, lower rubber content led to a columnar failure mode, while higher content (≥ 20%) exhibited a mixed failure mode with vertical cracking and diagonal fracture. Importantly, the compressive strength showed minimal reduction compared to conventional concrete, presenting a remarkable 50% mitigation of strength reduction compared to previous studies. Utilising reference concrete with robust bond strength proved highly effective in preserving strength in rubberized concrete. Despite its effectiveness in mitigating compressive strength reduction, UHPC could not effectively offset flexural strength loss, which ranged from 1.5 to 3 times that of compressive strength loss. The addition of rubber aggregate in UHPC reduced the peak flexural strength, residual strength, and flexural toughness at a similar rate, while significantly increasing the vibration decaying rate. Incorporating 40% rubber in UHPRuC reduced the eCO₂ up to 37%. Our findings emphasise the importance of reference concrete with good bond strength and shows that the addition of rubber aggregate in UHPC leads to reductions in strength but increases the energy-dissipating capacity.

Fault fracture zones are rock formations commonly encountered in submarine tunnels, and the diffusion mechanism of slurry in fault fracture zones has a crucial impact on submarine tunnel reinforcement. Based on the seepage equation of Bingham fluid, the tortuosity parameter, fractal theory, and variable viscosity equation are introduced to establish a spherical permeation grouting model of Bingham fluid considering the slurry diffusion path and viscosity time variability. The viscosity variation law with time of sulfur aluminate cement slurry under different seawater admixture conditions was tested, and the time-varying equation of viscosity of sulfur aluminate cement slurry was obtained by fitting. A set of fault fracture zone permeation grouting test system was developed, and a fault fracture zone grouting simulation test was carried out. The study shows that the diffusion distance calculated without considering the influence of slurry diffusion path and seawater is 1.63–1.91 times of the test value, which obviously overestimates the diffusion distance; the diffusion distance calculated with considering the influence of diffusion path and seawater is 1.06–1.35 times of the test value, which is in good agreement with the test value. The research results can provide some theoretical support for the design of grouting in seawater environment.

This study aimed to address the critical issue of age deterioration in prestressed concrete (PSC) structures by investigating the strengthening of aged PSC structures using a near-surface mounted (NSM) post-tensioned carbon fiber-reinforced polymer (CFRP). A total of nine PSC beams, each with a length of 6.5 m, were fabricated for a four-point bending test. Various experimental parameters were taken into account, including the strengthening method, compressive strength of concrete in the PSC beam, and the prestressing force of the PSC beam. The results indicated that the NSM post-tensioned CFRP strengthening system proved more efficient when compared to the NSM non-post-tensioned CFRP strengthening system. The flexural capacity of the NSM post-tensioned CFRP strengthening system, under the deteriorated low-strength PSC beam, increased by up to 30.9% compared to the PSC reference beam. Additionally, the experimental results were compared to a finite-element analysis, and a parametric study was conducted to examine the material properties of the PSC beam. Consequently, the NSM post-tensioned CFRP strengthening system is expected to be an effective solution for addressing the issue of deteriorated low-strength PSC structures.

Wash water, municipal solid waste incineration (MSWI) fly ash, and propylene (PP) fibers were employed simultaneously to produce self-compacting repair mortar (SCRM). Different SCRM mixtures were utilized, incorporating 35, 70, and 140 kg/m³ of MSWI fly ash, along with 0.1% of PP fibers. The research focused on investigating the workability, mechanical properties, and global warming potential (GWP) of SCRM. The incorporation of MSWI fly ash and wash water in SCRM resulted in reduced workability, necessitating an increase in the use of superplasticizer. Adding MSWI fly ash decreases compressive strength. The minimum compressive strength was observed when employing 140 kg/m³ of MSWI fly ash and wash water instead of tap water simultaneously. By increasing the proportion of MSWI fly ash content and correspondingly reducing the cement content in SCRM samples, there was a decrease in flexural strength. The ultrasonic pulse velocity (UPV) of all SCRM samples falls within acceptable range. Adding MSWI fly ash to SCRM reduces fracture toughness, and the concurrent use of wash water and MSWI fly ash significantly decreases fracture toughness. Incorporating PP fibers into SCRM resulted in increased compressive strength. Utilizing wash water and MSWI fly ash in SCRM significantly reduces GWP. The avoidance of wash water consumption mitigates the environmental impact of SCRM.

Amidst the global pursuit of sustainable alternatives in concrete production, this study explores the viability of incorporating by-products or waste materials as aggregates to support the concrete construction industry, with a specific emphasis on steel slag. The objective of this study is to evaluate the effectiveness of steel slag as a partial replacement for fine and coarse aggregates in concrete production. The experiment involved casting 30 cubes and 10 beams, replacing fine aggregate from 0 to 60%. Flexural and compressive strength tests at 7 and 28 days followed the ACI method. Results revealed that a 30% replacement of fine aggregate with steel slag led to higher compressive strength at both 7 and 28 days, while a 45% replacement showed superior flexural strength at 28 days. Further chemical analysis and optimization are recommended for deeper insights. The study concludes with marginal improvements in compressive and flexural strength with steel slag partial replacement, identifying 30% for fine aggregate and 45% for coarse aggregate as optimal replacements. In addition, the mineral composition of steel slag exhibits significant variability, with compounds, including silicon dioxide (SiO₂), iron oxide (Fe₂O₃), manganese oxide (MnO), aluminum oxide (Al₂O₃), and calcium oxide (CaO). Chemical analysis indicates high silicate content and minimal alkali content, contributing to enhanced strength during concreting. Higher steel slag replacement reduces workability, confirmed by slump tests. However, all mixes maintain a true slump, and unit weight increases with steel slag aggregate replacement. Compressive strength improves incrementally with higher steel slag content, echoing prior research. In addition, flexural strength rises with steel slag replacing both coarse and fine aggregates, suggesting enhanced performance in reinforced concrete structures. These findings highlight steel slag’s potential as a sustainable alternative in concrete production, aiming to advance its application in the construction industry, promoting environmental sustainability and economic viability.

To address the environmental issues arising from the growing scarcity of natural fine aggregates (NFA) and landfilling of waste glass, research is being conducted globally to utilize waste glass as a sustainable fine aggregate. However, contradictory results have been obtained regarding the effect of the type of waste glass and the physical properties of waste glass fine aggregate (GFA) on concrete, making it challenging to promote the use of GFA in concrete. Therefore, to promote the use of GFA in concrete, it is necessary to examine it under field conditions, such as mass-production processes or real-scale concrete applications. This study introduced a mass-production process for GFA, and the effect of mass-produced GFA on mortar was evaluated. The fine aggregate properties (particle aspect ratio, crushing rate, and solubility) of the GFA and the effects of color, content, and particle size on the mortar properties (compressive strength, flexural strength, and ASR expansion behavior) were analyzed, along with the results reported in previous studies. Consequently, the high aspect ratio and microcracks in the particles of mass-produced GFA led to an increase in the strength reduction and ASR expansion of the mortar. These effects appear to be particularly severe for transparent GFA. Overall, this study proposed the content of GFA within 20% or the replacement of fine particles (< 500 μm) in NFA as a condition for sustainable fine aggregate.

In this study, concrete specimens were fabricated based on domestically manufactured materials, and long-term exposure tests were conducted in a domestic coastal environment. This study analyzes the long-term compressive strength characteristics of concrete mixed with admixtures. The mixed materials used were divided into blast furnace slag and fly ash. The blast furnace slag and fly ash were, respectively, produced by replacing ~ 30% and ~ 15% of the cement. The compressive strength was measured at 28 day, 1 year, and 10 years of age and compared with that of ordinary concrete. In addition, the long-term compressive strength results obtained in this study were compared with those of concrete mixed with admixtures reported in the literature. The strengths of the ordinary specimen at 1 year and 10 years of age increased by ~ 10 MPa and ~ 22 MPa compared with those at 28 day of age. However, concrete mixed with admixtures yielded compressive strength increases of ~ 5 MPa and ~ 26 MPa at 1 year and 10 years of age, respectively, compared with those at 28 day of age. A comparison of the compressive strengths of concrete mixed with admixtures reported in the literature (based on age) and those obtained in this study showed that there was an initial strength difference in the range of 10–25%. However, the compressive strength at 10 years of age was almost similar to those reported in the literature with differences of less than 5%. These findings confirmed that when using pozzolanic admixtures, the development rate of the initial strength may vary owing to various factors; however, the long-term strength converges within a certain range.

Although concrete materials generally exhibit outstanding mechanical properties, it is susceptible against crack formation. It has been reported that narrow cracks (≤ 150 µm) could be naturally sealed in the cement matrix by externally supplied water-induced hydration. However, the crack width of larger than 150 µm is difficult to be sealed without using additional self-healing admixture. In this study, the self-healing cementitious mortar was successfully developed by using a combination of polyvinyl alcohol (PVA) fiber and superabsorbent polymer (SAP), aiming to heal the wide cracks. Although the mechanical properties were slightly reduced, it shows outstanding self-healing performance by using the dual admixtures. A self-healing rate of 60% was observed in the control sample with an initial crack width of 300 µm, while a self-healing rate of nearly 100% was confirmed with suitable SAP and PVA. In addition, it was confirmed that lower hydration degree of self-healing mortar in early stage contributes to the enhanced self-healing performance of developed composite system by internally supplied water from SAP.