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Highlights • This paper presents a new meso-damage model for freeze-thaw deterioration. • The model was combined with micromechanics and fracture mechanics. • The new model can help compensate for crack development mechanism. Abstract The cracking behaviour of cement-based materials subjected to freeze-thaw cycles significantly affects the engineering properties of the concrete materials and structures. The expansion of the crack width depends on the characteristics of the meso-structure of cement-based materials at different temperatures. In this paper, a new mesoscopic model is presented to describe the macro crack width of cement-based materials subjected to different freeze-thaw cycles. To calculate the surface crack width, the new model deduces the mesoscopic viscoelastic strain equation of the exposed specimen based on the viscoelastic strain of the pore structure of specimens. The surface crack widths predicted from the present mesoscopic model are compared with those from Gong's model and experimental results in the exposed environment, and the average errors are 4.5% and 5.5% in 0- and 90-degree angles, respectively, and 13.8% in a 45-degree angle. [ABSTRACT FROM AUTHOR]

Frost deterioration of concrete is one of the most significant durability problems in low temperature regions. Macro-damage parameter studies have been performed to investigate the variations of the mechanical characteristics in concrete materials. However, the macro-damage parameter often underestimates the pores and overestimates the macroscopic properties of concrete because of its intrinsic limitations. In this paper, an innovative mesoscopic damage parameter is developed by following a unique calculation procedure in which the damage parameter is cumulatively computed from the minimum to the maximum by iterative cycles instead of using a direct calculation method. This research was based on the mercury intrusion porosimetry (MIP) and differential scanning calorimetry (DSC) testing sequence, for determining the volumes and diameters of the pores and the corresponding feature pore size subjected to each rapid freeze-thaw testing. Additionally, the determination of mechanical properties of concrete was tested by conventional mechanical experimental instrument. Finally, a new freeze-thaw damage constitutive relationship is proposed based on the mesoscopic damage parameter. [ABSTRACT FROM AUTHOR]

This paper presents a new mesoscopic transport model for describing the diffusion of chloride in cement-based materials simultaneously subjected to freeze-thaw (FT) conditions and incorporated with chloride ions (Ch-I). The model uses the concept of freeze-thaw stress (FT-S) to reflect the effect of freezing and thawing cycles on the transport of ionic concentrations in porous materials and the concentration gradient of chloride for calculating the effect of different concentrations of chloride ions. In addition to determining the effect of FT-S, the model also considers the interactional effects between environmental exchanges, namely the effects of different temperatures, Cl − concentrations (10.5 g/L, 21.0 g/L and 42.0 g/L), and pore size distributions. The mesoscopic model is validated using experimental data obtained from coupling tests of chloride corrosion and freeze-thaw cycles. Compared with the typical Fick’s results, advantageous agreement between the calculated and measured chloride concentration profiles is demonstrated. The new mesoscopic diffusion model can help compensate for the lack of research on the effect of freeze-thaw cycles on chloride diffusion. [ABSTRACT FROM AUTHOR]

This work investigated the inhibition of ions transporting into and out of the mortar by Pseudoalteromonas (strain B18) and Paracoccus marcusii (strain B23). Mortar samples were immersed for 154 days in sterilized seawater, 2216E liquid medium, and 2216E liquid medium containing one of the above strains. Two strains positively decelerated chloride (Cl − ) ions and magnesium (Mg 2+ ) ions in the solutions permeating into the mortar and OH − ions leaching out from the mortar. And strain B23 is stronger than strain B18 in reducing the permeation of Cl − ions and Mg 2+ ions into and the leakage of OH − ions out of the mortar. Micro structural observation revealed that the biofilm with rod-shaped bacteria covered the mortar surface. Some fibrous and colloidal substances were observed between cells. Thus, biofilm formation can lower the ion permeability of mortar samples. And it can enhance the durability of reinforced concrete (RC) structures located in tidal zones. [ABSTRACT FROM AUTHOR]

The disposal of graphite tailings, a byproduct of graphite mining, poses significant recycling challenges. This study explores eco-friendly cement mortar by partially replacing sand with activated graphite tailings, focusing on waste utilization. Activating the pozzolanic properties of graphite tailings at various thermal activation temperatures converts them into high-quality binder materials. Quantitative assessments of graphite tailings' activity, conducted through ion leaching tests and raw material diffraction analysis, produce an activity index Ka, evaluating their performance under different thermal activation temperatures. Variable testing of substitution rates and activation temperatures examines changes in mechanical properties, microstructure, and pore distribution of the graphite tailings mortar. Optimum results reveal a 30 % substitution rate and a 750°C activation temperature. Graphite tailings, as pozzolanic binder materials, enhance mortar strength by improving particle size distribution, reducing "micro-area bleeding" and "boundary effects". After thermal activation, reactive minerals on the tailings' surface undergo secondary hydration reactions with cementitious products, modifying chemical structures and micro-morphology at the interface. Semi-quantitative XRD analysis and FT-IR spectroscopy characterize the ensuing chemical reactions, unveiling molecular bond and functional group changes. The superior performance of thermally activated graphite tailings primarily stems from increased active SiO 2 and Al 2 O 3 post-activation. The active SiO 2 and Al 2 O 3 reacts with cementitious products to form C-(A)-S-H gels, filling micro-pores at the tailings-mortar interface, which is the key characteristic that enables graphite tailings to serve as high-quality pozzolanic binder aggregates. A predictive model for compressive strength, utilizing reference models from solid waste mortar concrete, quantifies the positive impact of chemical activation. The theoretical results obtained from this predictive model closely align with the experimental findings. [Display omitted] • An activity evaluation system for thermally activated graphite tailings is established. • Graphite tailings are high quality filler aggregates as a substitute for natural aggregates. • Thermally activated graphite tailings can be used as pozzolanic binder aggregates. [ABSTRACT FROM AUTHOR]

Highlights • Post-modern pavement as a new concept for next pavement generation is introduced. • High structural performance, sustainability and social requirements are main criteria. • Performance of interlocking concrete block pavements as post-modern pavement was evaluated. • Block pavements showed high structural performance, eco-friendly characteristics, and social acceptance in Japan. • Block pavement can be considered as postmodern pavement and resilient infrastructure in the world. Abstract Researchers dealing with pavements and experts on materials have been increasingly focused on the structural strength of the pavement materials without paying sufficient attention to the environment and cultural norms. In the 21st century, the concept of pavement design and rehabilitation needs to be modified owing to new requirements such as the additional structural loads derived from the climate change, environmental challenges, social requirements, and aging population. Therefore, the concept of post-modern pavement (PMP) was proposed to address the structural, sustainability, and socio-psychological requirements. In this review of the state-of-the-art, the potential of the interlocking concrete block pavement (ICBP) was evaluated based on its laboratory and field structural performance, sustainability, and social acceptance as a PMP in Japan. Therefore, the relevant literature in English and Japanese, including journals, conference proceedings, technical reports, books, and theses, over a span of 47 years (1971–2018), were studied. It was found that the structural and functional performances of the ICBP in different facilities were satisfying. Furthermore, owing to its waste material use, less noise emission, air purifying characteristics, and heat island reduction, the environmental performance of ICBP was in harmony with sustainable practices. In addition, pavements users, both able and differently abled, rated the ICBP as a more appropriate pavement system owing to its physical appearance, serviceability, aesthetic features, lower heat island effect, rapid maintenance, and positive psychologic effects after earthquake and tsunami events. As a result, the ICBP can be recommended as a PMP for the design and development of resilient transportation infrastructure assets in Japan. [ABSTRACT FROM AUTHOR]

• Pull-out test of steel fiber in UHPC matrix with different nanosilica content was carried out. • The effect mechanism of nanosilica on bond-slip behavior of steel fiber in UHPC matrix was revealed. • The synergistic action of steel fiber and nanosilica can impart strain hardening characteristics to UHPC. • Tensile behavior of nanosilica reinforced strain hardening UHPC were investigated. The bond properties between the fiber and matrix are a critical factor that affects the tensile properties and toughness of fiber-reinforced cementitious composites. This research aims to provide an effective method to improve the tensile properties of ultra-high performance concrete (UHPC) with strain hardening characteristics. The compressive, flexural, and tensile behavior was measured on UHPC with two geometric configurations of steel fibers and four nanosilica (nano-SiO 2) mass fractions (0/1/3/5 wt% substitution rate of cement mass). The pull-out load-slip responses of steel fibers were also captured. In particular, determined the effect of fiber slip response on tensile properties of UHPC, then calculate elastic, strain hardening, and softening tensile parameters. Furthermore, the SEM, EDS, MIP, and XRD tests were used to reveal the enhancement mechanism of interfacial bonding performance and mechanical properties. The results show that the compressive and flexural strength peaks at 3 wt% of nanosilica, owing to nanosilica effectively ameliorating the pore structure and promoting the hydration process of the matrix. While the fiber pullout behavior and tensile properties show better performance at 5 wt% associated with increased hydration products attached to the fiber surface and more severe scratches after being pulled out. Notably, the addition of nanosilica endows strain hardening properties to UHPC containing straight fibers as well as increases the tensile toughness of UHPC containing hooked fibers due to the reinforcement of the matrix tunnel surrounding the steel fibers. [ABSTRACT FROM AUTHOR]