Search Results (66)

High-strength concretes (HSCs) are becoming increasingly important in modern construction, due to their ability to withstand high loads and reduce the size of structural elements. This study focuses on designing HSC mixes using materials readily available in the Colombian Caribbean region. The research involved preparing mixes with varying water–cement ratios (0.21 to 0.28) and incorporating a superplasticizer additive to maintain workability. The study evaluated the compressive strength gain of these mixes at different ages (14, 21, and 28 days). The results demonstrate that the materials available in the region, including the coarse aggregates and cement type, are suitable for producing HSC mixes with compressive strengths ranging from 55 to 84 MPa. Notably, the marble granite aggregate exhibited the best performance, achieving the highest compressive strength (84 MPa) with a water–cement ratio of 0.23. This mix also displayed favorable mechanical properties, with a modulus of elasticity of 36,000 MPa and a Poisson’s ratio of 0.26. These findings provide valuable insights for the development and application of HSC in the Colombian Caribbean region. Full article

Currently, millions of tires are consumed annually, which necessitates the efficient disposal of these quantities of spent tires and the development of means to convert them into useful materials. This research deals with the effect of adding the steel fibers extracted from used car tires (RSFs) to incorporate them as concrete components to obtain high-strength concrete (HSC). The HSC was used in this paper to strengthen the pre-damaged beams by jacking. In the first phase, twelve beams were subjected to an overload equal to 80% of their total expected bearing capacity to obtain damaged RC beams, while one beam was loaded to failure (reference beam, RB0). In the second phase, the damaged beams were strengthened with HSC jacketing integrating RSFs with three contents (0, 0.25, and 0.5%) or by HSC jacking and bonded CFRP laminates to the bottom surface of the jacket. Moreover, the Abaqus finite element (FE) program was implemented to simulate the upgraded damaged beams. The result ensured enhanced HSC compressive and tensile strengths by 11.6–14.4% and 11.6–20.9% as the RSF % increased from 0 to 0.25 and 0.5%, respectively. Using the HSC jacket with 0, 0.25, and 0.5% RSF to strengthen the RC-damaged beams increased the load capacity by 8.8, 14.5, and 20.1%, respectively compared to RB0. Furthermore, strengthening the damaged RC beams with both HSC jacket and CFRP laminates enhanced their load capacity by 41.9, 45.5, and 50.3% as the HSC integrated 0, 0.25, and 0.5% RSF, respectively, compared to RB0. Finally, the FE model could reveal several aspects related to the behavior of the damaged beams strengthened with jackets and CFRP laminates and the interaction between the different beam components. Full article

This study was aimed at determining the hardened and fresh properties as well as the high-temperature resistance of high-strength concrete (HSC) produced by incorporating diatomaceous earth, polypropylene, and glass fibers. CDE (calcined diatomaceous earth) was employed as a 10% cement replacement, while polypropylene and glass fibers were added separately to the mixtures at 0.2, 0.4, 0.6, 0.8, and 1.0% volumetric contents. Moreover, the mixtures without using CDE and fibers were used as references. The concrete mixtures were fabricated, followed by the determination of the fresh concrete flow, the absorption capacity, and the flexural, compressive, and splitting tensile strengths of hardened concrete. Furthermore, the specimens fabricated for the hardened concrete were exposed to temperatures of 400 °C, 500 °C, and 600 °C, and the remaining compressive strength was examined. The findings suggested that the incorporation of polypropylene and glass fibers in HSC with CDE enhanced the compressive, flexural, and splitting tensile strengths by 23.4 and 32.6%, 70.0 and 83.5%, and 18.9 and 17.9%, respectively. Moreover, the inclusion of polypropylene and glass fibers reduced the absorption of hardened concrete. Meanwhile, the inclusion of CDE lowered the strengths and increased the absorption. It was further identified that the incorporation of CDE enhanced the resistance of HSC to high temperatures, while polypropylene and glass fibers lowered the resistance. The incorporation of CDE, polypropylene, and glass fibers also lowered the flow of fresh concrete. Full article

This review examines the impact of recycled aggregates (RAs) on the fresh and mechanical properties of high-strength concrete (HSC). The results revealed that incorporating RAs can reduce the compressive strength of HSC by up to 25%, with strength values ranging from 40 to 70 MPa depending on the RA content. The addition of supplementary materials like silica fume, fly ash, and polycarboxylate ether significantly mitigated these negative effects, enhancing the compressive strength by approximately 15–20% compared with the control mixes without additives. Furthermore, the tensile strength was observed to decrease by up to 18% with increasing RA content, but fiber reinforcement improved this by 10%, demonstrating the potential of additives to offset mechanical weaknesses. The modulus of elasticity also declined by up to 30% with higher RA dosages, highlighting the critical impact of the adhered mortar quality on the overall stiffness of the concrete. According to the literature, it was noticed that, when the dosage of RCAs is increased, there is a drop in the strength activity index (SAI). When the substitute dosage exceeded 50%, the SAI decreased. These findings underscore the importance of using optimized additive combinations to improve the mechanical performance of RA concrete, making it a viable option for sustainable construction. Overall, the findings suggest that, although RAs may negatively affect certain physical traits of HSC, the use of appropriate additives can optimize its performance, making it a viable option for sustainable construction practices. Full article

Machine learning and response surface methods for predicting the compressive strength of high-strength concrete have not been adequately compared. Therefore, this research aimed to predict the compressive strength of high-strength concrete (HSC) using different methods. To achieve this purpose, neuro-fuzzy inference systems (ANFISs), artificial neural networks (ANNs), and response surface methodology (RSM) were used as ensemble methods. Using an ANN and ANFIS, high-strength concrete (HSC) output was modeled and optimized as a function of five independent variables. The RSM was designed with three input variables: cement, and fine and coarse aggregate. To facilitate data entry into Design Expert, the RSM model was divided into six groups, with p-values of responses 1 to 6 of 0.027, 0.010, 0.003, 0.023, 0.002, and 0.026. The following metrics were used to evaluate model compressive strength projection: R, R², and MSE for ANN and ANFIS modeling; R², Adj. R², and Pred. R² for RSM modeling. Based on the data, it can be concluded that the ANN model (R = 0.999, R² = 0.998, and MSE = 0.417), RSM model (R = 0.981 and R² = 0.963), and ANFIS model (R = 0.962, R² = 0.926, and MSE = 0.655) have a good chance of accurately predicting the compressive strength of high-strength concrete (HSC). Furthermore, there is a strong correlation between the ANN, RSM, and ANFIS models and the experimental data. Nevertheless, the artificial neural network model demonstrates exceptional accuracy. The sensitivity analysis of the ANN model shows that cement and fine aggregate have the most significant effect on predicting compressive strength (45.29% and 35.87%, respectively), while superplasticizer has the least effect (0.227%). RSME values for cement and fine aggregate in the ANFIS model were 0.313 and 0.453 during the test process and 0.733 and 0.563 during the training process. Thus, it was found that both ANN and RSM models presented better results with higher accuracy and can be used for predicting the compressive strength of construction materials. Full article

In this study, an experimental program was conducted to investigate the shear behavior of beams made of high-strength and lightweight cementitious composites (HS-LWCCs) containing hollow glass microspheres and carbon nanotubes. The compressive strength and dry density of the HS-LWCCs were 87.8 MPa and1.52 t/m³, respectively. To investigate their shear behavior, HS-LWCC beams with longitudinal rebars were fabricated. In this test program, the longitudinal and shear reinforcement ratios were considered as the test variables. The HS-LWCC beams were compared with ordinary high-strength concrete (HSC) beams with a compressive strength of 89.3 MPa to determine their differences; the beams had the same reinforcement configuration. The test results indicated that the initial stiffness and shear capacity of the HS-LWCC beams were lower than those of the HSC beams. These results suggested that the low shear resistance of the HS-LWCC beams led to brittle failure. This was attributed to the beams’ low elastic modulus under compression and the absence of a coarse aggregate. Furthermore, the difference in the shear capacity of the HSC and HS-LWCC beams slightly decreased as the shear reinforcement ratio increased. The diagonal compression strut angle and diagonal crack angle of the HS-LWCC beams with shear reinforcement were more inclined than those of the HSC beams. This indicated that the lower shear resistance of the HS-LWCCs could be more effectively compensated for when shear reinforcement is provided and the diagonal crack angle is more inclined. The ultimate shear capacities measured in the tests were compared with various shear design provisions, including those of ACI-318, EC2, and CSA A23.3. This comparison showed that the current shear design provisions considerably overestimate the contribution of concrete to the shear capacity of HS-LWCC beams. Full article

Steel fiber reinforced high-strength concrete (SFRHSC) is a composite material composed of cement, coarse aggregate, and randomly distributed short steel fibers. The excellent tensile strength of steel fiber can significantly improve the crack resistance and ductility of high-strength concrete (HSC). In this study, experimental and numerical investigations were performed to study the cyclic behavior of the HSC beam-column joint. Three SFRHSC and one HSC beam-column joint were prepared and tested under cyclic load. Two different volume ratios of steel fibers and three stirrups ratios in the joint core area were experimentally studied. After verification of the experimental results, numerical simulations were further carried out to investigate the influence of steel fibers volume ratio and stirrups ratio in the joint core area on the seismic performance. Evaluation of the hysteretic response, ductility, energy dissipation, stiffness, and strength degradation were the main aims of this study. Results indicate that the optimal volume fraction of steel fibers is 1.5%, and the optimal stirrups ratio in the joint core area is 0.9% in terms of the enhancement of the seismic performance of the SFRHSC beam-column joint. Full article

High-strength concrete (HSC) boasts excellent compressive strength and durability, making it a popular choice in various engineering applications. However, under the impact of high temperatures, HSC tends to crack easily, so it is combined with polyvinyl alcohol fiber (PVA fiber) to explore its engineering application prospect. This paper investigated the physical and mechanical characteristics of HSC reinforced with PVA fibers subjected to different heating temperatures and cooling techniques. The experimental results reveal a correlation between rising temperatures and observable changes in the specimens: a progressively lighter surface hue, an augmented frequency of cracking, and a considerable escalation in the mass loss rate, particularly after the temperature exceeds 400 °C. Regarding mechanical properties, the dynamic elastic modulus and compressive and flexural strength all decrease as the heating temperature increases. As the amount of PVA fiber rises while maintaining a steady temperature, these measurements initially show an increase followed by a decrease. The fiber contents yielding the best compressive and flexural strength are 0.2% and 0.3%, in that order. Considering the influence of cooling methods, water spray cooling has a greater impact on physical and mechanical properties than natural cooling. Furthermore, SEM was employed to scrutinize the microstructure of HSC, enhancing comprehension of the alterations in its physical and mechanical characteristics. The findings of this research offer significant information regarding the high-temperature behavior of HSC, serving as a valuable resource for guiding the design, building, and upkeep of structures that incorporate HSC. Additionally, this study will aid in advancing the progress and utilization of HSC technology. Full article

This paper significantly extends investigations into internal damping ratios in both undamaged and damaged conditions for normal-strength concretes (NSCs) and high-strength concretes (HSCs). This study examines concretes with compressive strengths ranging from 42 to 83 MPa. Cyclic loads were applied using a servo-controlled hydraulic testing machine, and for each cyclic step, the dynamic elastic modulus ($E_d$) and internal damping ratio ($\xi$) were determined through acoustic tests. The results show that the normal-strength concretes ($f_c=42$ MPa) exhibited an undamaged internal damping ratio of $\xi =0.5\%$, reaching a maximum of $\xi =2.5\%$ at a damage index of 0.8. Conversely, the high-strength concrete mixtures ($f_c=83$ MPa) showed an undamaged internal damping ratio of $\xi =0.29\%$, with a peak value of $\xi =0.93\%$ at a damage index of 0.32. The initial internal damping values are influenced by porosity and transition zones, which affect the material behavior under cyclic loads. Progressive damage leads to increased Coulomb damping due the cracking process. Few studies have quantified and comprehended the internal damping ratio under cyclic loading-induced damage, and this research advances our understanding of NSC and HSC behavior under dynamic excitation and damage evolution, especially in impact scenarios. Full article

In this study, comprehensive investigation of the shrinkage compensation mechanisms of calcium-based expansive agents (CEAs), their effects on the properties of (ultra) high-strength concrete (HSC/UHSC), and the existing problems in applying this methodology was conducted. Analyses showed that the rational use of CEAs under certain conditions could greatly or completely inhibit the development of autogenous shrinkage of HSC/UHSC and significantly reduce the risk of associated cracking. However, it was found that the hydration of the CEAs affected the hydration process of other binders, thereby altering the microstructure of concrete. This, in turn, led to a reduction in mechanical properties such as compressive strength, flexural strength, and elastic modulus, with the rate of reduction increasing as the amount of CEA used increased. Moreover, when attempting to improve the shrinkage compensation effects, increasing the amount of CEA presented a risk of delayed expansion cracking of the HSC/UHSC. Neither the expansion mechanism, expansion conditions, nor the inhibition methods have yet been fully clarified in the current stage. Lastly, newly proposed Ca–Mg composite EAs were outlined, and the research prospects of Ca–Mg composite EAs in HSC/UHSC were explored. Full article

This review explores the mechanical behavior of high-strength concrete-filled steel tubes (CFSTs), focusing on their structural integrity and failure mechanisms. This study highlights the crucial role of the steel tube in providing passive confinement, which limits crack progression and enhances the ductility of the concrete. The concept of concrete as a structural system composed of micro- and mini-pillars, derived from rock mechanics, can be a useful approach to understanding CFST behavior. The review identifies that the strength index (SI) can, in some cases, decrease with an increase in the confinement factor (ξ), particularly in high-strength and ultrahigh-strength concrete (HSC and UHSC), which seems to be different to the common understanding of confinement. The experimental results show that different crack patterns and concrete compositions significantly impact the CFST performance. For example, silica fume in concrete mixtures can reduce the strength enhancement despite increasing the unconfined compressive strength. This work advocates for a mechanistic approach to better comprehend the interaction between concrete and steel tubes, emphasizing the need for optimized concrete mixtures and improved mechanical interaction. Future research should focus on the potential of HSC and UHSC in CFST, addressing factors such as crack progression, confinement effects, and concrete–steel interaction. Full article

High-strength concrete (HSC) has a high compressive strength, high density, excellent durability, and seepage resistance, but its deformation ability is weak. Adding fibers can improve the physical and mechanical properties of HSC. Additionally, the HSC structure may face the threat of fire. In the process of fire extinguishing, the damage mechanism of high-temperature-resistant concrete is complicated due to the different contact conditions with water at different locations. Hence, it is essential to conduct pertinent research on the behavior of fiber-reinforced HSC with different cooling methods after high-temperature action. In this paper, polyvinyl alcohol fiber (PVA fiber) was selected to be added into the HSC to carry out high-temperature experimental research, so as to explore the apparent changes, failure pattern, and mass loss rate of the fiber-reinforced HSC using different cooling methods and analyze the influence of its residual compressive strength and flexural strength. The test results suggest that, with the increase in heating temperature, the color of the specimen’s surface transitions from dark blue-gray to white, and the quantity of surface cracks on the specimen gradually rises. The mechanical strength gradually decreases as the heating temperature increases. At a consistent heating temperature, the mechanical strength initially rises, and then falls with an increase in fiber content. The maximum compressive strength and flexural strength were achieved at PVA fiber contents of 0.2% and 0.3%, respectively. For different temperatures and fiber contents, the mechanical strength after natural cooling is generally higher than that after immersion cooling. In addition, X-ray polycrystalline diffractometry (XRD) and scanning electron microscopy (SEM) tests were conducted to analyze the compositional alterations and microstructure of the fiber-reinforced HSC following high-temperature exposure, accompanied by an explanation of the factors influencing the alterations in the physical and mechanical properties. Therefore, the findings of this study can serve as a valuable reference for the utilization of HSC in engineering structures and contribute to the advancement of HSC technology. Full article

The integration of steel fibers into high-strength concrete (HSC) offers a solution to address the brittleness and limited ductility typically associated with conventional HSC structures. To investigate the bonding properties between shaped steel and high-strength concrete with steel fiber (SFRC), thirteen tests of the shaped steel/SFRC specimens are conducted to explore the effects of various factors such as steel fiber volume ratio, concrete strength grade, reinforcement ratio, steel embedment depth, and cover thickness on bond–slip behavior. Three distinct failure modes, such as pushout failure, bond splitting, and yielding failure of steel, are identified during the pushout tests. Three different types of bond strength, such as the initial bond strength, the ultimate bond strength, and the residual bond strength, are observed from the load–slip curves between the shaped steel and concrete. By incorporating nonlinear spring elements, a numerical model for accurately simulating the bond performance between the shaped steel and SFRC specimens is developed. The bond strength between the shaped steel and concrete increase as the concrete strength, cover thickness, steel fiber volume ratio, and stirrup ratio increase, while it decreases as the steel embedment depth increases. A model for the bond strength between shaped steel and SFRC is developed, and it agrees well with the test data. Full article

Modern concrete mix design is a complex process involving superplasticisers, fine powders, and fibres, requiring time and energy due to the high number of trial tests needed to achieve rheological properties in the fresh state. Concrete batching involves the extensive use of materials, time, and the testing of chemical admixtures, with various methodologies proposed. Therefore, in some instances, the required design properties (physical and mechanical) are not achieved, leading to the loss of resources. The concrete equivalent mortar (CEM) method was introduced to anticipate concrete behaviour at fresh and hardened states. Moreover, the CEM method saves time and costs by replacing coarse aggregates with an equivalent sand mass, resulting in an equivalent specific surface area at the mortar scale. This study aims to evaluate the performance of fibre in CEM and concrete and determine the relationships between the CEM and the concrete in fresh and hardened states. Steel and polypropylene fibres were used to design three series of mixtures (CEM and concrete): normal-strength concrete (NSC), high-strength concrete (HSC), high-strength concrete with fly ash (HSCFA), and equivalent normal-strength mortar (NSM), high-strength mortar (HSM), and high-strength mortar with fly ash (HSMFA). This study used three-point bending tests and digital image correlation to evaluate load and crack mouth opening displacement (CMOD) curves. An analytical mode I crack propagation model was developed using a tri-linear stress–crack opening relationship. Post-cracking parameters were optimised using inverse analysis and compared to actual MC2010 characteristic values. The concrete slump is approximately half of the CEM flow; its compressive strength ranges between 78% and 82% of CEM strength, while its flexural strength is 60% of CEM strength. The post-cracking behaviour showed a significant difference attributed to the presence of aggregates in concrete. The fracture energy of concrete is 28.6% of the CEM fracture energy, while the critical crack opening of the concrete is 60% of that of the CEM. Full article

This study employed a rapid freezing method to investigate the impact of individual additions of expansion agent, steel fibers, and High Elasticity Module Polyethylene Fiber (HEMPF), as well as their combinations, on the freeze-thaw resistance of High-Strength Concrete (HSC). The findings reveal that the non-air-entrained HSC of C80 exhibits excellent freeze-thaw resistance. However, this resistance is sensitive to the curing environment’s humidity. The expansion agent has a negative impact on the freeze-thaw resistance of HSC, while steel fibers and HEMPF fibers have positive effects. Combining HSC with an expansion agent and high elasticity modulus fibers ensures not only high freeze-thaw resistance but also a total alteration of humidity sensitivity, leading to an extended freeze-thaw life of HSC under dry curing conditions. Full article