Abstract ：

Ferroaluminate cement is widely used in marine engineering applications owing to the remarkable durability and strength of its main hydrate, Al(Fe)-ettringite. The structure and performance of Al(Fe)-ettringite still require extensive exploration. An Al(Fe)-ettringite molecular model containing different Fe contents (0%, 25%, 50%, and 75%) was developed via Materials Studio. Radial distribution functions, time-correlated functions, and mean square displacement were used to analyze the structure of Al(Fe)-ettringite, after which Al(Fe)- ettringite was prepared using a coprecipitation method. The hydration of Al(Fe)-ye'elimite, the nanoindentation testing, and compressive strength of four ettringite types were assessed to facilitate a comparison with the simulation results. Increasing the Fe content resulted in increased lattice size and density. Fe atoms mainly reacted with Ohs atoms to form Fe-Ohs bonds, resulting in an increased Fe-Ohs bond length, with the Fe atom density resulting in volume expansion and increased density in Al(Fe)-ettringite. At 25% Fe content, the number of Hw-Ow hydrogen bonds in Al(Fe)-ettringite was 1166.14, the MSD value was 1.53 & Aring;2, and the water molecules diffused the fastest. The improved macromechanical properties obtained by adding Fe atoms demonstrate that Fe atom substitution can enhance the ettringite structure. The experimental results validated the simulation results.

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Abstract ：

External wall composite insulation materials have shown great potential for energy saving and emission reduction in the construction industry, but cement-based material as one of the external wall composite insulation materials has the problem of high thermal conductivity. Herein, a composite insulation material was prepared using the press method by expanded polystyrene (EPS) and cement of different calcium silicate content. The addition of porous calcium silicate provides nucleation sites for cement hydration to promote hydration reaction and increase the porosity of the inorganic cementitious phase from 75 % to 85 % and refine the average pore size from 2826.09 nm to 421.31 nm. The cement-based composite insulation material which the calcium silicate content is 20 % has 0.0423 W/(m center dot K) in the thermal conductivity, which is 23.1 % lower than the noncalcium silicate content of cement-based composite insulation material (0.055 W/(m center dot K)). The simulation analysis proves that the improved insulating properties are attributed to the increased interface between solid-phase and gas phase, thinner heat transfer walls, and longer heat transfer paths due to the pore structure changes in the inorganic cementitious phase. This proposed composite insulation material provides a new choice for external wall insulation.

Keyword ：

Thermal conductivity Finite element analysis Composite insulation material Porous calcium silicate

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Abstract ：

Selective extraction of Li+ from high Mg2+/Li+ ratio brines with ionic liquid (IL) based collaborative extractants was investigated by experiments, thermodynamic analyses, and quantum chemical (QC) calculations. Effects of different IL cationic structures and organophosphorus ligands on extraction performances were studied. The results demonstrated that the system 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl) imide + trioctyl phosphate ([HOEMIM][Tf2N] + TOP) was considered as the best extractant, with the very high extraction efficiency of Li+ (83.16 %) and separation selectivity of Li+/Mg2+ (742.11), which is higher than values reported in literature. The thermodynamic model ePC-SAFT was first extended to quantitatively predict the phase equilibria of the so-called "organic-inorganic complex strong electrolyte system" presented in this work. The molecular-level extraction mechanism was explored by QC calculation, indicating that the strong multi-site intermolecular interactions between Li+ and [HOEMIM][Tf2N] + TOP break the Li+ hydration. This work provides guidance to rationally design novel IL-based extractants for efficient extraction of Li+

Keyword ：

Quantum chemical calculation Molecular mechanism Ionic liquid Extraction of lithium ePC-SAFT

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Abstract ：

As a type of excellent rapid protective material with fast hardening and high early strength characteristics, magnesium phosphate cement (MPC) is used as the cementitious material to fabricate concrete canvas. For a thick MPC canvas, sufficient hydration reaction is crucial in keeping its integrity. Borax is used to adjust the hydration progress of MPC in warp-knitted fabrics. The effects of different borax contents (0 %, 1 %, 2 %, 3 %, 4 %, 5 %, 6 %) on the compactness of reaction products and the mechanical properties of MPC canvas are evaluated. In addition, SEM, XRD, hydration heat, and X-CT are used to systematically analyze the hydration morphology, products, exothermic process, and pore structure of MPC canvas. The results show that borax can effectively delay the setting time of MPC, addressing the issue of incomplete hydration of MPC powder in thick canvas. The 4 % borax content (B4 sample) can ensure the complete reaction in a 20 mm thick MPC canvas, achieving the maximum compressive and flexural strengths of 26.37 MPa and 4.9 MPa at 7 d, respectively. Borax effectively optimizes the pore structure of MPC canvas and achieves a dense bond at the interface between MPC and the canvas fabric with the minimum porosity of 11 % in the B4 sample. Therefore, borax is crucial for the structural of MPC canvas.

Keyword ：

Magnesium phosphate cement Borax Structural integrity Concrete canvas

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Abstract ：

The properties of magnesium phosphate cement (MPC) are studied by measurements of setting time, flowability, compressive strength and by multiple technique analyses of pH values, calorimetry, XRD, TG, MIP and SEM taking calcium lactate (CL) content as variables. Results show that CL can significantly prolong the setting time and promote the synergetic development of compressive strength of MPC, but the addition of CL leads to a decrease in flowability of MPC. Comprehensive consideration on these properties, the optimal dosage of CL is 5%. In this case, the setting time, flowability and 1 day & 28 days compressive strength of MPC are 84 minutes, 185 mm, 40.8 MPa & 54.2 MPa, respectively. Multiple technique analyses show that the addition of CL can decrease the liquid phase pH value and hydration rate of MPC, resulting in the extension of setting time. A low content of CL (3%) can improve the reaction degree and optimize the matrix pore structure of MPC, and thus promoting the strength development (50.90 MPa increased to 65.93 MPa). However, an excessive addition of CL (7%) will lead to the decrease in reaction products and the increase in matrix porosity of MPC, resulting in a decrease in compressive strength (43.30 MPa reduced to 37.36 MPa).

Keyword ：

Magnesium phosphate cement Mechanical properties Setting time Reaction degree

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Abstract ：

This study first systematically investigated selective Li+ extraction from Mg2+-rich brines with Na+ and K+ using ionic liquid (IL) based synergistic extractant (SE) systems from molecular mechanisms to extraction performances. The ternary combination 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([AMIM] [Tf2N]), tri-iso-butyl phosphate (TIBP) and dichloromethane (DCM), i.e., [AMIM][Tf2N]-TIBP-DCM was selected as a suitable SE from the diverse organic phosphorus ligands, ILs and diluents. The single-stage Li+ extraction efficiency was as high as 96.87%, and selectivities of beta Li+/Mg2+, beta Li+/Na+, and beta Li+/K+were up to 1161.94, 76.74, and 1263.46, respectively. It was found that Li+ is extracted from the aqueous phase to organic phase in Li+-4TIBP[Tf2N] complex. The molecular-level mechanism was identified as the multi-type interaction formed between metal ions and [AMIM][Tf2N]-TIBP to destroy the hydration of metal ions through quantum chemical (QC) calculations. The work proposes valuable theoretical guidance to develop novel IL-related SE systems for the high-efficiency Li+ extraction from salt lake brines.

Keyword ：

Extraction of lithium Quantum chemical calculation Synergistic extractant Ionic liquid Magnesium -rich brine Molecular mechanism

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Abstract ：

The mechanical properties and electromagnetic transmission properties of high alumina cement (HAC) paste with different glass powder (GP) contents were investigated in this paper. The effects of hydration phase, unhydrated phase, GP phase and pore phase on the dielectric properties of HAC paste were quantitatively analyzed. The results show that the strength, fluidity and setting time of HAC paste decrease with the increase of GP replacement rate. The real part, imaginary part and loss angle tangent of dielectric constant decrease. The addition of GP leads to a reduction in reflectivity and absorptivity of electromagnetic waves in the paste, while increasing transmittivity. Furthermore, the real part of the dielectric constant of each phase in the HAC paste follows the order: hydration product phase > unhydrated phase > GP phase > pore phase. With an increase in GP content, the real part of the dielectric constant of the hydration product phase increases. Finally, based on the results of vector network analysis (VNA), mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM), the reasons for the changes of mechanical properties and electromagnetic properties of HAC paste under different GP replacement rates were analyzed from the aspects of phase composition, pore distribution and microstructure.

Keyword ：

Electromagnetic transmission properties High alumina cement Glass powder Mechanical properties

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Abstract ：

Aiming for an all -solid waste concrete, a quaternary solid waste binder (SWBs) system comprising blast furnace slag, fly ash, desulfurization gypsum, and Bayer red mud was developed and utilized for both binders and preparation of cold bonded artificial aggregates. The first section investigated and discussed the hydration properties and strength gain mechanism of SWBs, revealing that ettringite formation and growth contribute to early age strength development of SWBs, while C -A -S -H formation contributes significantly to the later strength gain. The second section systematically studied the concrete performances, including mechanical properties, shrinkage, chlorides, and seawater resistance. An all -solid waste -based concrete strategy was presented by gradually substituting cement and natural aggregates. It was observed that SWBs-based concrete exhibited significantly lower shrinkage and excellent chloride ion resistance, although slightly lower mechanical properties were observed. The solid waste -based artificial aggregates proved viable alternatives to natural rock aggregates in low -strength concrete classes. Incorporating artificial aggregates endowed the concrete with self -curing properties and reduced its shrinkage and chloride migration, with only a minor effect on its mechanical strength. Lastly, an all -solid waste concrete combining the characteristics of SWBs and cold -bonded artificial aggregates was achieved. The resulting concrete exhibited lower shrinkage and excellent chloride and seawater resistance. This study provides a reference for designing and developing solid waste -based binders and concrete.

Keyword ：

Concrete Shrinkage Artificial aggregate Chloride migration Solid waste -based binders Interfacial microstructures

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Abstract ：

The high geothermal environment causes a temperature gradient inside shotcrete, which affects the development of its mechanical strength. This research investigated the strength evolution of shotcrete in simulated high geothermal environment by applying a unidirectional heat source. The influence of temperature gradient on the pore structure, morphology, phase composition, and hydration degree of shotcrete was also studied. It was found that the early strength of shotcrete was improved but that the later strength was reduced in the high geothermal environment. It was attributed to the increase in harmful porosity and total porosity of the concrete caused by the high-temperature curing. Cracks and pores can be observed in the microstructure near the heat source region. Besides, the ettringite content in shotcrete was lower than that under standard curing environment and presented gradient distribution in the direction of the temperature gradient.

Keyword ：

Porosity Microstructure High geothermal environment Strength Shotcrete

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Abstract ：

The evolution of globalization and rapid industrialization, coupled with intensive human activities, leads to a significant release of acidic gases and particles (e.g., NOX and SO2) is unavoidable. These emissions eventually result in dry and wet acid depositions due to atmospheric circulation. This infiltration of acidic elements alters the chemical properties of water systems, thereby deteriorating ground stability. The economically developed soft clay areas face considerable threats from these acid environmental attacks. This study focused on employing a "one-part" geopolymer (OPG) comprising ground granulated blast furnace slag (GGBFS), fly ash (FA), and solid sodium hydroxide (NH) to stabilize the soft clay. Simultaneously, the deterioration behavior of OPG stabilized soft clay under two different acids (HNO3 and H2SO4) with various pH values (pH of 2, 4, and 6) and varied immersion periods up to 240 days was evaluated including the mass loss, neutralization depth (ND), pH value, and unconfined compressive strength (UCS). Additionally, scanning electron microscopy (SEM) and X-ray energy spectrometry (EDS) characterized the evolution of microstructure and hydrate composition of OPGstabilized soft clay post varied acid immersion. The results highlighted the superior acid resistance of the stabilized soft clay with an 80:20 GGBFS/FA ratio compared to other ratios. The presence of significant hydration products, such as calcium silicate hydrates (C-S-H), calcium aluminate (aluminosilicate) hydrates (C-A-(S)-H), and sodium aluminosilicate hydrates (N-A-S-H), was observed in the OPG stabilized soft clay. In addition, the contents of Si in the OPG played a significant role in enhancing the acid resistance of the OPG stabilized soft clay. Based on these experimental results, two proposed mechanisms detailed the deterioration and acid resistance of the OPG stabilized soft clay under HNO3 and H2SO4 attack. The findings of this study contribute to advancing scientific comprehension concerning the acid resistance of the OPG stabilized soft clay in ground improvement practices.

Keyword ：

Ground granulated blast furnace slag and fly 'One-part " geopolymer Acid resistance ash Soft clay stabilization

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