The leaching behavior of R7T7 borosilicate glasses with different waste loading amounts was evaluated via hanging the static immersion method at different temperatures and two leaching systems (i.e., deionized water and simulated North Mountain groundwater) for 365 days. The changes of etched layer phases, morphology, and composition with leaching time were also analyzed by X-ray diffractometry, scanning electron microscopy-X-ray energy spectrometry, and inductively coupled plasma mass spectrometry. The results show that the glass starts to appear in heterogeneous phases when the loading amount of waste exceeds 20%, and its composition is mainly molybdenum-rich materials and noble metals. The results of leaching experiments reveal a positive correlation between the mass loss rate of the glass and the leaching temperature. In the initial leaching phase, the three elements Na, Si, and B were leached at a higher rate in deionized water rather than in simulated Beishan groundwater, while after equilibration the three elements were leached at comparable rates in both leaching agents. The surface of the glass has a variety of crystalline phases generated after 365 days of leaching, mainly in spherical, floral, and prismatic and honeycomb morphologies, consisting mainly of components such as Mg-Si-O and Si-Nd-Gd-O. Based on the analysis above, the leaching process of glass solid is controlled due to the ion diffusion mechanism and glass network dissolution mechanism. The results of these studies can provide the data to support the future safety evaluation of high-level radioactive glass waste in geological disposal processes.

The development of cohesionless cracks can be regarded as a sign of macroscopic crack development. An identification model of cohesionless cracks was adpoted with results of crack development by digital image correlation (DIC) method. Three-point bending tests were carried out on fully-graded concrete specimens with different loading rates (0.000 1 mm/s, 0.001 0 mm/s, 0.010 0 mm/s), considering the rate correlation of crack propagation of fully-graded concrete. The results show that for the fully-graded concrete specimens with different loading time intervals, cohesionless cracks will occur throughout the peak load, indicating that the prefabricated cracks have cracked when the peak load is reached. The cracks of the specimen is mainly concentrated after the load is loaded to 50% of the peak load. Under the same conditions, the slower the loading rate is, the earlier the unbonded cracks appear. With the increase of the loading rate, the cracks are thin and long.

The feed-to-glass conversion within the cold cap and the mathematical modeling of the process are of great concern for the accurate simulation of the melter for vitrification of high-level liquid waste (HLLW). To figure out the feed-to-glass conversion during the HLLW vitrification, the phase transitions and structural features within the cold cap were investigated. The results show that the cold cap consists of the upper reaction layer (at 100-700 ℃) and the lower foam layer (at 700-1 000 ℃). The dehydration and nitrate decomposition occur in the reaction layer, while the continuous melt as well as the formation and dissolution of intermediate phases appear in the foam layer. The reaction layer can be simplified into a one-dimensional mass transfer model based on the mass conservation equation and experimental results. Subsequently, the kinetic equation of feed-to-glass conversion is proposed to quantitatively describe the three reaction rates of dehydration (at 100-400 ℃), and melting (at 200-300 ℃) and decomposition (at 400-700 ℃) of nitrates as functions of temperature in the reaction layer, providing some crucial parameters for melter simulation.

To study the promotion process of cement hydration by polycarboxylate superplasticizers modified calcium silicate hydrate (C-S-H/PCE) and understand the mechanism of C-S-H/PCE seeds promotion of cement hydration. Acrylic acid-based polycarboxylate superplasticizer (PCE-1) and silane-based polycarboxylate superplasticizer (PCE-2) were used to surface modify the hydrothermal synthesized calcium silicate hydrate (C-S-H/Unmodified) seeds, resulting in the polycarboxylate superplasticizer modified C-S-H seeds (C-S-H/PCE-1 and C-S-H/PCE-2). Subsequently, these three C-S-H seeds were added to the cement paste. The compressive strength, phase composition, and heat release curve of cement paste and the surface tension of C-S-H seeds were tested. The results showed that the surface modification of PCE-1 and PCE-2 resulted in an increase in the surface contact angle of C-S-H seeds from 36.9° to 41.1° and 42.9°, resulting in lattice mismatch of the sedimentary phase (hydration product) on the surface of the substrate material (C-S-H seeds) and inhibiting the epitaxial growth of cement hydration products on the surface of C-S-H seeds. PCE modification reduced the promoting effect of C-S-H seeds on the hydration process of Portland cement. Moreover, the degree of reduction in the hydration promoting effect of C-S-H/PCE-2 on Portland cement is significantly greater than that of C-S-H/PCE-1 crystal nucleus. Tests of the adsorption equilibrium of PCE in the pore solution indicated that the C-S-H/PCE seeds did not directly introduce new crystal nucleation sites but exposed new C-S-H surfaces through the desorption of PCE on the surface of C-S-H/PCE seeds. The desorption degree of PCE on the surface of C-S-H/PCE seeds determined the promoting effect of C-S-H/PCE seeds on cement hydration.

The scientificity of "recycled aggregate concrete" or "recycled concrete" is discussed. It is suggested that "recycled aggregate concrete" must be used.

The incorporation of tuff powder into cement-based materials as mineral admixtures can reduce cement production and greenhouse gas emissions such as CO₂, as well as utilize industrial solid waste. This review represented the mechanism of tuff powder in cement-based materials, and summarized the influence of tuff powder incorporation on the setting time, workability, mechanical properties and durability of cement-based materials. Some aspects for the preparation and use of tuff powder were given, and some problems for the effect of tuff powder on the properties of cement-based materials were proposed. In addition, some aspects for future studies on the properties of cement-based materials incorporating tuff powder were also discussed.

Solvent exchange method is widely used in the drying and hydration termination of cement-based materials. This review represented the influence of solvent exchange on the microstructure of cement paste. The selection principle of exchange parameters (i.e., sample size, liquid/solid ratio, exchange time and removal method) was described. The physical and chemical reactions between common exchange solvents (i.e., isopropanol, acetone, methanol, and ethanol) and cement hydration products (i.e., calcium hydroxide, calcium silicate hydrate and ettringite) were discussed. The pore structure parameters (i.e., porosity and pore size distribution) of cement-based materials were analyzed under the influence of exchange parameters and solvents. In addition, the existing problems and research prospects of the solvent exchange method were also given.

As a typical porous media material, the diffusivities of concrete are closely related to its pore structure. It is necessary to propose a model for predicting the diffusivities based on the time-varying pore structure since the pore structure can continuously change with the hydration process. In this work, the parameters of the pore structure, the moisture distribution in the unsaturated state, and the prediction and validation of the relative diffusion coefficients of cement paste at different saturation levels were analyzed based on the reconstructed cement paste microstructure. It is indicated that the predicted relative diffusion coefficients are related to the extracted pore parameters (i.e., hydration degree α, porosity ρ and dimensionless peak pore size B^*), and the relationships between α and time t, ρ and α, and B^* and ρ were systematically analyzed, and a diffusivity prediction model containing the time-varying parameters f (α(t), ρ(t), B^*(t)) was proposed. The proposed model can fully consider the time-varying process of concrete pore structure affected at different water-cement ratios and hydration time, thus providing a microscopic perspective approach for analyzing the diffusivities of unsaturated concrete from the perspective of time-varying pore structure.

Ultra-high performance concrete (UHPC) was prepared via mixing water containing different chloride salts (i.e., NaCl, CaCl₂ and MgCl₂). The electrochemical indexes of the internal reinforcement during passivation period were measured by linear polarization, electrochemical impedance spectroscopy and cyclic polarization. The passivation behavior and evolution of steel bars in UHPC under the coupling action of different chloride salts were investigated. The results show that the reinforcement in UHPC is able to be passivated under three different chloride salt systems. The resistances of UHPC matrix, steel passivation film and steel charge transfer increase continuously with the hydration age. At the same concentration of Cl^- ions, the introduction of Ca salts increases the possibility of steel corrosion to a certain extent, while the introduction of Mg salts delays the corrosion process of steel bars to some extent. The pitting corrosion sensitivity of reinforcement increases with the increment of Cl^- ions concentration. At a high Cl^- ions concentration, the pitting sensitivity of steel bars in Na-Ca system is greater than that in Na-Mg system.

Silicic acid was used as a modifier to magnesium oxysulfate (MOS) cement to improve the water resistance of MOS cement. The effect of silicic acid on the mechanical properties, volume stability, and water resistance was investigated. The phase composition, microstructure, and ion leaching concentration were investigated. The co-existence of magnesium silicate hydrate (M-S-H) gel with MOS system was also analyzed. The results show that the addition of silicic acid enhances the mechanical properties and improves the volume stability of MOS cement through promoting the formation of 5Mg(OH)₂·MgSO₄·7H₂O crystals and M-S-H gel. When MOS cement containing silicic acid immerses in water, the residual silicic acid continues to react with free Mg²⁺ and OH^- to form M-S-H gel. Meanwhile, 5Mg(OH)₂·MgSO₄·7H₂O crystals and M-S-H gel coexist in MOS cement, resulting in an improvement in the water resistance of MOS cement.