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Despite having a high early mechanical strength and using sulfoaluminate cement as the primary cementitious material, self-compacting repair mortar (SCRM) suffers from rapid hydration rates leading to construction time constraints. This study examined how several forms of calcium sulfate, including hemihydrate gypsum, anhydrite, and dihydrate gypsum, affected SCRM’s workability, hydration process, and microstructure. The outcomes demonstrated that adding hemihydrate gypsum sped up SCRM’s early hydration rate and boosted its expansion rate. For a cement with 8% hemihydrate gypsum, 6 h after adding the water, the flexural strength and compressive strength increased by 39.02% and 34.08%, respectively. The hydration rate of SCRM can be efficiently delayed by dihydrate gypsum, although the result is subpar. The material exhibited the lowest fluidity loss in 20 min, the setting time was extended, and the 28-day flexural and compressive strengths were raised by 26.56% and 28.08%, respectively, after adding 8 percent anhydrite.

Mimicking natural structures has been highly pursued recently in composite structure design to break the bottlenecks in the mechanical properties of the traditional structures. Bone has a remarkable comprehensive performance of strength, stiffness and toughness, due to the intricate hierarchical microstructures and the sacrificial bonds within the organic components. Inspired by the strengthening and toughening mechanisms of cortical bone, a new biomimetic composite structure, with a designed progressive breakable internal construction mimicking the sacrificial bond, is proposed in this paper. Combining the bio-composite staggered plate structure with the sacrificial bond-mimicking construction, our new structure can realize tunable stiffness and superior toughness. We established the constitutive model of the representative unit cell of our new structure, and investigated its mechanical properties through theoretical analysis, as well as finite element modeling (FEM) and simulation. Two theoretical relations, respectively describing the elastic modulus decline ratio and the unit cell toughness promotion, are derived as functions of the geometrical parameters and the material parameters, and validated by simulation. We hope that this work can lay the foundation for the stiffness tunable and high toughness biomimetic composite structure design, and provide new ideas for the development of sacrificial bond-mimicking strategies in bio-inspired composite structures.

The relatively high shrinkage of the alkali-activated slag (AAS) has restricted its application as a widely-used building material. This research attempts to study the effect of a hydrothermally synthesized C-A-S-H gel, which has a similar composition to that of the main AAS product, on the shrinkage performance of the AAS. The C-A-S-H nano-particles were mixed into AAS mortars in a proportion ranging from 1 wt % to 5 wt % using two different methods, and the drying and autogenous shrinkage ratio of modified AAS mortars were measured at various ages. The effect of C-A-S-H on their microstructures was also characterized. Results obtained indicated that the addition of C-A-S-H gel to AAS mortars had reduced their drying and autogenous shrinkage, with the addition of 3 wt % reaching the maximum reduction. However, the added amount was not directly proportional to the decrease of shrinkage; the proportion of early-stage drying shrinkage of AAS mortars was greater than that of autogenous shrinkage; the dispersion method was slightly better than the dry mixing method in both shrinkage reduction. MIP results suggested that the addition of C-A-S-H gel had reduced the total porosity and the average pore size of AAS mortars, optimized their pore structure distribution, and significantly reduced the volume of mesopores (

Boron carbonitrides (BCN) have attracted great interest in superhard or energy storage materials. In this work, thin BCN sheets were synthesized at 250 °C by a facile and green solvothermal method. The structure and morphology were characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Based on the results of electrochemical experiments, the thin BCN sheet exhibited excellent capacitance performance (343.1 F/g at a current density of 0.5 A/g) and cycling stability (90%), which showed high potential applications in supercapacitors.

A series of “ravine-like” boron carbonitrides (abbreviation: BCN) were synthesized by a green precursor pyrolysis method at different temperatures (about 700–1100 °C). The highest electrochemical performance of BCN-800 (Named BCN-temperature) electrode was observed, because the “ravine-like” structure can significantly increase the contact area and improve the wettability between electrode and electrolyte. The BCN electrode exhibited ultrahigh specific capacitance 805.9 F/g (at a current density of 0.2 A/g), excellent rate capability, and good cycling stability (91%) after 3000 cycles at a current density of 8 A/g, showing high potential applications in supercapacitors.

C-A-S-H (CaO-Al2O3-SiO2-H2O) and N-A-S-H (Na2O-Al2O3-SiO2-H2O) have a wide range of chemical compositions and structures and are difficult to separate from alkali-activated materials. Therefore, it is difficult to analyze their microscopic properties directly. This paper reports research on the synthesis of C-A-S-H and N-A-S-H particles with an average particle size smaller than 300 nm by applying the hydrothermal method. The composition and microstructure of the products with different CaO(Na2O)/SiO2 ratios and curing conditions were characterized using XRD, the RIR method, FTIR, SEM, TEM, and laser particle size analysis. The results showed that the C-A-S-H system products with a low CaO/SiO2 ratio were mainly amorphous C-A-S-H gels. With an increase in the CaO/SiO2 ratio, an excess of Ca(OH)2 was observed at room temperature, while in a high-temperature reaction system, katoite, C4AcH11, and other crystallized products were observed. The katoite content was related to the curing temperature and the content of Ca(OH)2 and it tended to form at a high-temperature and high-calcium environment, and an increase in the temperature renders the C-A-S-H gels more compact. The main products of the N-A-S-H system at room temperature were amorphous N-A-S-H gels and a small amount of sodalite. An increase in the curing temperature promoted the formation of the crystalline products faujasite and zeolite-P. The crystallization products consisted of only zeolite-P in the high-temperature N-A-S-H system and its content were stable above 70%. An increase in the Na2O/SiO2 ratio resulted in more non-bridging oxygen and the TO4 was more isolated in the N-A-S-H structure. The composition and microstructure of the C-A-S-H and N-A-S-H system products synthesized by the hydrothermal method were closely related to the ratio of the raw materials and the curing conditions. The results of this study increase our understanding of the hydration products of alkali-activated materials.

Energy piles—A fairly new renewable energy concept—Use a ground heat exchanger (GHE) in the foundation piles to supply heating and cooling loads to the supported building. Applying phase change materials (PCMs) to piles can help in maintaining a stable temperature within the piles and can then influence the axial load acting on the piles. In this study, two kinds of carbon-based composite PCMs (expanded graphite-based PCM and graphite nanoplatelet-based PCM) were prepared by vacuum impregnation for potential application in energy piles. Thereafter, a systematic study was performed and different characterization tests were carried out on two composite PCMs. The composite PCMs retained up to 93.1% of paraffin and were chemically compatible, thermally stable and reliable. The latent heat of the composite PCM was up to 152.8 J/g while the compressive strength of cement paste containing 10 wt % GNP-PCM was found to be 37 MPa. Hence, the developed composite PCM has potential for thermal energy storage applications.

Although nondestructive ultrasonic technologies have been applied in laboratory and field tests in the field of heritage conservation, few studies have quantified the relationship among the real microstructures, micromechanical properties, and macroscopic acoustic responses of earthen-site soils. This paper develops a micromechanics-based multiscale model for quantitatively exploring the ultrasonic propagation characteristics of elastic waves in untreated and consolidated earthen-site soils. Scanning electron microscope images and image processing technology are integrated into the finite-element simulation. The effects of microstructure and wave features on the acoustic characteristics of soils are quantitatively investigated under pulsive loading. The simulation results of untreated and consolidated soils are efficiently compared to ultrasonic test data. It is demonstrated that the integration of microstructure image processing and multiscale modeling can predict the ultrasonic pulse velocity well, which improves the accuracy of laboratory testing and field monitoring and better serves the evaluation and implementation of engineering practice in the field of heritage conservation.

Using waste clay brick powder (RBP) to partially replace cement in the preparation of concrete, is one way to recycle construction waste. In order to investigate the physical and mechanical properties and volume stability of recycled micropowder ultra-high-performance concrete (UHPC), the basic mechanical and shrinkage properties of recycled micropowder UHPC were studied at replacement rates of 10%, 20%, 30%, 40% and 50%. The results show that: (1) When the activated recycled brick powder is used to replace the cement, the compressive strength, flexural strength and splitting tensile strength of the UHPC initially increase and then decrease with the increase in the substitution rate. When the substitution rate is 10%, the 28 d compressive strength, flexural strength and splitting tensile strength of the UHPC are the highest; (2) Replacing cement with recycled brick powder can reduce the autogenous shrinkage of the UHPC, and the autogenous shrinkage rate of the UHPC decreases with the increase in the brick powder replacement rate. The drying shrinkage of the UHPC can be reduced by replacing cement with recycled brick powder. The drying shrinkage of the UHPC initially decreases, and then increases, with the increase in the replacement rate of brick powder. When the replacement rate of the brick powder was 30%, the drying shrinkage of the UHPC was the least, and this was 49.7% lower than that in the benchmark group. The prediction models of autogenous shrinkage and drying shrinkage are in good agreement with the experimental results, which can be used to predict the shrinkage development of recycled brick powder UHPC.

Mechanical properties of glass fiber reinforced polymer (GFRP) composites degrade under the combined effects of mechanical load and alkaline solution, affecting the service ability and safety of GFRP reinforced structures. In this study, GFRP bars were loaded with cyclic tension at different stress levels and immersed in alkaline solution for days to investigate the tensile properties and degradation law of GFRP bars. The degradation mechanisms were studied at micro-, meso- and macro-scales with scanning electron microscopy (SEM) and three-dimensional X-ray microscopy, respectively. The results show that tensile strength and degradation rate of GFRP bars are mainly dependent on the different stress levels and alkaline solution. When stress level is higher, the tensile strength degrades more quickly, especially in the early stages of soaking. With the loading and immersion time, the elastic modulus and Poisson’s ratio increase at first and then decrease. The ultimate tensile strain is relatively stable, whereas the ultimate elongation is significantly reduced. A strength-degradation model was proposed and fit well with experimental data, demonstrating that the model can be applied to predict tensile strength degradation under combined effects of the load and alkaline solution.

Graphene aerogels have many advantages, such as low density, high elasticity and strong adsorption. They are considered to be widely applicable in many fields. At present, the most valuable research area aims to find a convenient and effective way to prepare graphene aerogels with excellent properties. In this work graphene/carbon nanotube aerogels are prepared through hydrothermal reduction, freeze-drying and high temperature heat treatment with the blending of graphene oxide and carbon nanotubes. A new reducing agent-ascorbic acid is selected to explore the best preparation process. The prepared aerogels have compression and resilience and oil absorption properties due to the addition of carbon nanotubes as designed.