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Opening holes in construction structures is used often to allocate electrical or ventilating lines. However, it may result in stress concentration and hence the reduction in mechanical properties. In order to manage these problems, an approach of preparing full-field aligned steel fiber–reinforced cementitious composites (FASFRC) around the hole is proposed to maximize the effect of reinforcement of steel fibers around the hole by aligning the steel fibers according to the direction of local tensile stress. Thus, the approach of preparing an open-hole plate using FASFRC is developed. The advantage of FASFRC in improving the uniaxial tensile performance of the open-hole is investigated by comparing the performance with that of specimens using ordinary steel fiber–reinforced cementitious composites (SFRC) and aligned steel fiber–reinforced cementitious composites (ASFRC). The evolution of the failure process of the specimens subjected to uniaxial tension is monitored using the digital image correlation (DIC) method, and numerical simulation is carried out to calculate the optimal fiber volume dosage around the hole and the stress concentration factor. The experimental results show that in the FASFRC specimens, the fibers are effectively aligned- the direction of tensile stress and more steel fibers are allocated in the area around the hole. The uniaxial tensile strength of FASFRC is 43% to 49% higher than that of SFRC and ASFRC with various fiber volume dosages. The tensile work and uniaxial tensile toughness ratio of FASFRC are 35%–52% and 7%–21% higher than that of SFRC and ASFRC. The full-field deformation obtained from DIC shows that FASFRC tends to exhibit multicracking and strain-hardening behavior, which are different from SFRC and ASFRC. The modeling results have good agreement with the tests for various types of specimens; hence, the numerical simulation on the uniaxial tensile test of FASFRC is reliable. The numerical results show that the optimal fiber volume dosage in the area around the hole for FASFRC is 2.0% (the corresponding fiber volume dosage in other area is 1.0%). This investigation provides an option for improving the mechanical properties and alleviating the stress concentration of open-hole structures without increasing total steel fiber dosage. [ABSTRACT FROM AUTHOR]

Incorporation of microcapsules with encapsulated repair agents in asphalt can effectively improve the self-healing performance of asphalt and extend the service life of pavements. Microcapsules should be kept intact during the construction of asphalt concrete in order to play a self-healing role at a later stage, and the added microcapsules do not affect the basic performances of asphalt. The dispersion of microcapsules in asphalt and their survivability during heating, mixing and construction of asphalt concrete were analyzed by fluorescence microscopy tests, thermogravimetric analysis, and simulated pavement construction pressure. The effect of microcapsules on the basic properties of asphalt before excitation was analyzed by comparing the needle penetration, softening point and 10 °C ductility of asphalt with different microcapsule admixtures. The effect of microcapsules on the performance of RTFOT aged asphalt after excitation was analyzed by rolling and excitation of microcapsules in asphalt specimens under low temperature conditions, and then testing the basic properties. The tests compared the self-healing performance of asphalt with different microcapsule dosing. The results show that the microcapsules have good survival ability in the mixing and compaction process of asphalt concrete. The microcapsules have no significant effect on the needle penetration and softening point of asphalt, and to a certain extent will reduce the ductility of asphalt. The excitation of microcapsules can restore the asphalt properties after releasing the repair agent, and significantly improve the self-healing performance of asphalt. [ABSTRACT FROM AUTHOR]

An experimental method, based on the modified two‐parameter model and digital image correlation technique, was proposed for determining the mixed mode fracture toughness (KI+II) of concrete. Three‐point bending tests on notched concrete beam specimens of different sizes, maximum aggregate sizes, and aggregate volume contents were conducted, and the values of KI+II were evaluated considering the crack deflection. The values of KI+II and KI under mode I loading were compared. The results show that KI+II increases with the specimen size and gradually stabilizes. In addition, KI+II decreases with the maximum aggregate size, but the aggregate volume content has little effect on KI+II. Higher values of KI+II are presented after considering the effect of crack deflection. Only a monotonic loading process is required for the proposed method to determine KI+II. [ABSTRACT FROM AUTHOR]

In recent years, in-situ polymerization has emerged as a promising technique for enhancing cementitious composites. This review examines the progress and advancements in in-situ polymerization modified cementitious composites (iPMCC), including the in-situ polymerization system, manufacturing, workability, mechanical properties, durability, microstructure, mechanism, application scenarios, and challenges. Incorporating monomers into ordinary cement-based composites (OCC) has significantly improved flexural strength (up to 203 %) while maintaining compressive strength with slight increases or minor decreases. The continuous polymer network forms strong crosslinks with cement hydrates, resulting in a more resilient polymer-cement system that effectively inhibits crack initiation and propagation under external loading conditions. iPMCC also demonstrate reduced porosity, contributing to improved durability. Lastly, this review illuminates the potential applications of iPMCC and identifies future research and challenges. It is essential for cement-based materials to demonstrate improved longevity and mechanical performance while integrating versatile applications. Overall, this review provides valuable insights into in-situ polymerization techniques for developing robust and functional cementitious materials, while also paving the way for future design, development, and utilization of organic/inorganic composite systems. [Display omitted] • The in-situ polymerization-modified cementitious composites (iPMCCs) are reviewed. • The enhancement of organic-inorganic bonding via in-situ polymerization. • The effects and mechanisms of improved flexural performance in iPMCCs. • Potential of in-situ polymerization for durable and functional concrete. • The major challenges for iPMCCs research and applications. [ABSTRACT FROM AUTHOR]

• UHPC specimens with aligned steel fibers (ASF-UHPC) were successfully prepared by using magnetic field treatment. • The model of uniaxial tensile, flexural and compressive strength of UHPC is proposed with consideration of the orientation of steel fibers. • The mechanical properties of the UHPC specimens with aligned steel fiber distribution were significantly improved. Copper-plated microwire steel fiber is generally added to ultra-high-performance concrete (UHPC) to reduce its brittleness. In the UHPC, the steel fibers are randomly dispersed. When subjected to a specific load, the steel fibers that have an orientation consistent with or close to the direction of tensile stress can take full effect of reinforcement on the matrix, while the reinforcing effect of those steel fibers perpendicular to the tensile is relatively weak. From this point of view, the influence of steel fiber orientation on the strength of UHPC was modeled and analyzed in this investigation. During modeling, the tensile, flexural, and compressive strength of the UHPC were correlated with the orientation efficiency factor of steel fiber. In the tests, aligned steel fiber reinforced ultra-high-performance concrete (ASF-UHPC) specimens were prepared by using electromagnetic field treatment to align the steel fibers in the specimens, and the tensile, flexural, and compressive properties of ASF-UHPC specimens were tested and compared with the modeling results. The reinforcement mechanism of aligned steel fiber on the properties of UHPC was analyzed. The results showed that the mechanical properties of ASF-UHPC specimens are significantly higher than those of UHPC with randomly distributed steel fibers (RSF-UHPC) specimens, and the model can well predict the mechanical properties of UHPC. [ABSTRACT FROM AUTHOR]