Carbonation of Dicalcium Silicate Enhanced by Ammonia Bicarbonate and Its Mechanism

The strength development law of γ-type dicalcium silicate (γ-C_(2)S) under different carbonation processes was investigated,and the carbonation mechanism of γ-C_(2)S under the action of NH_(4)HCO_(3) was clarified by using a wide range of test methods,including XRD and SEM.A method of saturated NH_(4)HCO_(3) solution as a curing agent was identified to improve the carbonation efficiency and enhance the carbonation degree of γ-C_(2)S,and then a high-strength carbonated specimen was obtained.Microhardness analysis and SEM morphology analysis were conducted on the carbonised specimens obtained under atmospheric pressure carbonisation conditions using the curing agent.It was found that γ-C_(2)S could perform carbonisation well under atmospheric pressure,which promoted the carbonisation efficiency and decreased the carbonisation cost simultaneously.Therefore,a new carbonisation process solution was proposed for the rapid carbonisation of γ-C_(2)S.

Preparation, Crystallization and Mechanical Properties of Potassium Aluminosilicate Glass-ceramics

In this study,transparent K_(2)O-Al_(2)O_(3)-SiO_(2)(KAS)glass-ceramics with leucite as the main crystalline phase were prepared by melting-quench method and two-step heat treatment.The effects of SiO_(2)/Al_(2)O_(3) ratio and heat treatment on crystallization and mechanical properties were studied.The crystallization kinetics and X-Ray Diffraction(XRD)results showed that SiO_(2)/Al_(2)O_(3) ratio and heat treatment system had a direct impact on the crystallization behavior of potassium aluminosilicate glass-ceramics.When heat-treated at 680℃/2 h and 780℃/1 h,cracks generated on the surface of the sample with the addition of SiO_(2)/Al_(2)O_(3)=4.8(in mol)due to the huge difference in the coefficient of thermal expansion between glass matrix and surface.When the addition of SiO_(2)/Al_(2)O_(3)(in mol)was 4,the sample with leucite as the main crystalline phase showed an excellent fracture toughness(1.46 MPa·m^(0.5))after the heat treatment of 680℃/2 h and 780℃/5 h.And there was a phase transformation from kaliophilite to leucite.The crystalline phases of the sample heat-treated at 680℃/8 h and 780℃/1 h were leucite and kaliophilite,which resulted in the visible light transmittance of 63%and the fracture toughness of 0.91 MPa·m^(0.5).Furthermore,after the heat treatment of 680℃/2 h and 780℃/5 h,the main crystalline phase of the sample with SiO_(2)/Al_(2)O_(3)=3.2(in mol)was still kaliophilite.Because leucite only grows on the surface of the sample and is hard to grow inward,it is hard to achieve the bulk crystallization of leucite in the sample with SiO_(2)/Al_(2)O_(3)=3.2(in mol).

The Fabrication and Detection Performance of High Sensitivity Au-Ag Alloy Nanostar/Paper Flexible Surface Enhanced Raman Spectroscopy Sensors

Au-Ag alloy nanostars based flexible paper surface enhanced Raman spectroscopy sensors were fabricated through simple nanostar coating on regular office paper,and the surface enhanced Raman spectroscopy detection performances were investigated using crystal violet dye analyte.Au-Ag nanostars with sharp tips were synthesized via metal ions reduction method.Transmission electron microscope images,X-Ray diffraction pattern and energy dispersive spectroscopy elemental mapping confirmed the nanostar geometry and Au/Ag components of the nanostructure.UV-Vis-NIR absorption spectrum shows wide local surface plasmon resonance induced optical extinction.In addition,finite-difference time-domain simulation shows much stronger electromagnetic field from nanostars than from sphere nanoparticle.The effect of coating layer on Raman signal intensities was discussed,and optimized 5-layer coating with best Raman signal was obtained.The Au-Ag nanostatrs homogeneously distribute on paper fiber surface.The detection limit is 10-10 M,and the relationship between analyte concentrations and Raman signal intensities shows well linear,for potential quantitative analysis.The calculated enhancement factor is 4.795×10^(6).The flexible paper surface enhanced Raman spectroscopy sensors could be applied for trace chemical and biology molecule detection.

Tuning Structural and Electronic Configuration of FeN_(4) via External S for Enhanced Oxygen Reduction Reaction

The Fe-N-C material represents an attractive oxygen reduction reaction electrocatalyst,and the FeN_(4)moiety has been identified as a very competitive catalytic active site.Fine tuning of the coordination structure of FeN_(4)has an essential impact on the catalytic performance.Herein,we construct a sulfur-modified Fe-N-C catalyst with controllable local coordination environment,where the Fe is coordinated with four in-plane N and an axial external S.The external S atom affects not only the electron distribution but also the spin state of Fe in the FeN_(4)active site.The appearance of higher valence states and spin states for Fe demonstrates the increase in unpaired electrons.With the above characteristics,the adsorption and desorption of the reactants at FeN_(4)active sites are optimized,thus promoting the oxygen reduction reaction activity.This work explores the key point in electronic configuration and coordination environment tuning of FeN_(4)through S doping and provides new insight into the construction of M-N-C-based oxygen reduction reaction catalysts.

Towards green asphalt materials with lower emission of volatile organic compounds: A review on the release characteristics and its emission reduction additives

Recently, researchers in the road field are focusing on the development of green asphalt materials with loweremission of volatile organic compounds (VOCs). The characterization methodology of asphalt VOCs and theinfluencing factors on VOCs release have always been the basic issue of asphalt VOCs emission reduction research.Researchers have proposed a variety of asphalt VOCs characterization methodologies, which also have mutuallyirreplaceable characteristics. Asphalt VOCs volatilization is affected by many factors. In this study, asphalt VOCscharacterization methodologies were summarized, including their advantages, disadvantages, characteristics andapplicable requirements. Subsequently, the influencing factors of VOCs release, such as asphalt types and environment conditions, are summarized to provide theoretical support for the emission reduction research. Theclassification and mechanism of newly-development asphalt VOCs emission reduction materials are reviewed. Thereduction efficiencies are also compared to select better materials and put forward the improvement objective ofnew materials and new processes. In addition, the prospects about development of VOCs release mechanism ofasphalt materials during the full life cycle and feasibility research of high-efficiency composite emission reductionmaterials in the future were put forward.

Research on the Low-carbon Cementitious Materials:Effect of Triisopropanolamine on the Hydration of Phosphorous Slag and Steel Slag

Cement,phosphorous slag(PS),and steel slag(SS)were used to prepare low-carbon cementitious materials,and triisopropanolamine(TIPA)was used to improve the mechanical properties by controlling the hydration process.The experimental results show that,by using 0.06%TIPA,the compressive strength of cement containing 60%PS or 60%SS could be enhanced by 12%or 18%at 28 d.The presence of TIPA significantly affected the hydration process of PS and SS in cement.In the early stage,TIPA accelerated the dissolution of Al in PS,and the formation of carboaluminate hydrate was facilitated,which could induce the hydration;TIPA promoted the dissolution of Fe in SS,and the formation of Fe-monocarbonate,which was precipitated on the surface of SS,resulting in the postponement of hydration,especially for the high SS content.In the later stage,under the continuous solubilization effect of TIPA,the hydration of PS and SS could refine the pore structure.It was noted that compared with portland cement,the carbon emissions of cement-PS-TIPA and cement-SS-TIPA was reduced by 52%and 49%,respectively.

Preparation and Thermal Shock Resistance of Mullite Ceramics for High Temperature Solar Thermal Storage

Mullite thermal storage ceramics were prepared by low-cost calcined bauxite and kaolin.The phase composition,microstructure,high temperature resistance and thermophysical properties were characterized by modern testing techniques.The experimental results indicate that sample A3(bauxite/kaolin ratio of 5:5)sintered at 1620℃has the optimum comprehensive properties,with bulk density of 2.83 g·cm^(-3)and bending strength of 155.44 MPa.After 30 thermal shocks(1000℃-room temperature,air cooling),the bending strength of sample A3 increases to 166.15 MPa with an enhancement rate of 6.89%,the corresponding thermal conductivity and specific heat capacity are 3.54 W·(m·K)^(-1)and 1.39 kJ·(kg·K)^(-1)at 800℃,and the thermal storage density is 1096 kJ·kg^(-1)(25-800 mullite ceramics;sintering properties;high-temperature thermal storage;thermal shock resistance).Mullite forms a dense and continuous interlaced network microstructure,which endows the samples high thermal storage density and high bending strength,but the decrease of bauxite/kaolin ratio leads to the decrease of mullite content,which reduces the properties of the samples.

Review of advanced road materials, structures, equipment, and detection technologies

As a vital and integral component of transportation infrastructure,pavement has a direct and tangible impact on socio-economic sustainability.In recent years,an influx of groundbreaking and state-of-the-art materials,structures,equipment,and detection technologies related to road engineering have continually and progressively emerged,reshaping the landscape of pavement systems.There is a pressing and growing need for a timely summarization of the current research status and a clear identification of future research directions in these advanced and evolving technologies.Therefore,Journal of Road Engineering has undertaken the significant initiative of introducing a comprehensive review paper with the overarching theme of“advanced road materials,structures,equipment,and detection technologies”.This extensive and insightful review meticulously gathers and synthesizes research findings from 39 distinguished scholars,all of whom are affiliated with 19 renowned universities or research institutions specializing in the diverse and multidimensional field of highway engineering.It covers the current state and anticipates future development directions in the four major and interconnected domains of road engineering:advanced road materials,advanced road structures and performance evaluation,advanced road construction equipment and technology,and advanced road detection and assessment technologies.

Effects of Co_(2)O_(3)Addition on Microstructure and Properties of SiC Composite Ceramics for Solar Absorber and Storage

SiC composite ceramics for solar absorber and storage integration are new concentrating solar power materials.SiC composite ceramics for solar absorber and storage integration were fabricated using SiC,black corundum and kaolin as the raw materials,Co_(2)O_(3)as the additive via pressureless graphite-buried sintering method in this study.Influences of Co_(2)O_(3)on the microstructure and properties of SiC composite ceramics for solar absorber and storage integration were studied.The results indicate that sample D2(5wt%Co_(2)O_(3))sintered at 1480℃exhibits optimal performances for 119.91 MPa bending strength,93%solar absorption,981.5 kJ/kg(25-800℃)thermal storage density.The weight gain ratio is 12.58 mg/cm2after 100 h oxidation at 1000℃.The Co_(2)O_(3)can decrease the liquid phase formation temperature and reduce the viscosity of liquid phase during sintering.The liquid with low viscosity not only promotes the elimination of pores to achieve densification,but also increases bending strength,solar absorption,thermal storage density and oxidation resistance.A dense SiO_(2) layer was formed on the surface of SiC after 100 h oxidation at 1000℃,which protects the sample from further oxidation.However,excessive Co_(2)O_(3)will make the microstructure loose,which is disadvantageous to the performances of samples.

Ferro-vanadium Slag in Improving Inner Chloride Solidification Rate of Cement Materials

We investigated the effects of ferro-vanadium slag(FVS)as a supplemental cementing material which can dissolve a large amount of active aluminum phases without excessive pretreatment or excitation to enhance the inner chloride solidified rate(CSR)of cement-based materials.Cement-FVS pastes with 0-30%content of FVS was designed,and the CSR was examined.Hydrates at different curing ages were studied by X-ray diffraction(XRD)and thermo-gravimetric analysis(TGA);hydration heat and^(29)Si nuclear magnetic resonance(^(29)Si-NMR)were tested to analyze the hydration degree of the system;mechanical properties in cement-FVS system were evaluated by compressive strength test,pore structure and the fractal regression.Results revealed that the incorporation of FVS could greatly promote the CSR of cement-FVS system.Compared with the control groups,30%dosage of FVS could increase the CSR by 69%at 3 d,47%at 7d,36%at 28 d and 34%at 60 d.It was demonstrated that the incorporation of FVS could enhance the chemical solidifying ability of chloride,and the main reason was the promoted generation of Kuzel’s salt and the Friedel’s salt in hydrate products,and the enhanced chloride migration resistance capacity by increasing the volume of gel pores in the cement-FVS system.Considering the influence of FVS on strength performance,this paper suggested that the suitable dosage of FVS as a supplemental cementing material was around 10%.The study in this paper might provide one efficient path to promote the chloride solidifying capacity of cement-based material and meanwhile the comprehensive utilization of FVS.

Influence Mechanism of Curing Regimes on Interfacial Transition Zone of Lightweight Ultra-High Performance Concrete

This study aims to clarify the effects of curing regimes and lightweight aggregate(LWA)on the morphology, width and mechanical properties of the interfacial transition zone(ITZ) of ultra-high performance concrete(UHPC), and provide reference for the selection of lightweight ultra-high performance concrete(L-UHPC) curing regimes and the pre-wetting degree LWA. The results show that, under the three curing regimes(standard curing, steam curing and autoclaved curing), LWA is tightly bound to the matrix without obvious boundaries. ITZ width increases with the water absorption of LWA and decreases with increasing curing temperature. The ITZ microhardness is the highest when water absorption is 3%, and the microhardness value is more stable with the distance from LWA. Steam and autoclaved curing increase ITZ microhardness compared to standard curing. As LWA pre-wetting and curing temperatures increase, the degree of hydration at the ITZ increases, generating high-density CSH(HD CSH) and ultra-high-density CSH(UHD CSH), and reducing unhydrated particles in ITZ. ITZ micro-mechanical properties are optimized due to hydration products being denser.

The Fabrication and SERS Performance of Multi-layer Hollow Au-Ag Alloy Nano Urchins Structure-based SERS Fiber Probe

Novel hollow Au Ag alloy nano urchins were synthesized via Ag seeds growth method,and self-assembly coated on the wall and end-tip of silica fiber for fiber probe fabrication.The nano urchins homogeneously distributed on fiber surface because of fiber silanization.The sizes and tip sharpness of the nano-urchins could be controlled by Ag seeds.The elements distribution analysis indicated there was high Ag content in tip-top for better surface enhance Raman scattering performance.The detectable concentration could be as low as 10-8 M using crystal violet molecules as analyte.Moreover,the fiber probes were stable in air,due to Au in the alloy.This fiber probe could be used for low content single molecular analysis.

Numerical Simulation of a Viscoelastic Thinning Process for Preparing Flexible Glasses by Redrawing Method

The forming process of the flexible ultrathin glasses(UTG)prepared by the redrawing method was numerically simulated using ANSYS Polyflow software.In the forming process by the redrawing method,temperature,viscosity,transverse and longitudinal velocity distribution of the glasses with different compositions were studied.Furthermore,the influence of these factors on the width and thickness of the flexible glass plate was investigated.It is found that the internal and external heat exchange of glass has a dominant influence on the viscosity variation during the UTG forming process,which is inconsistent with the general viscosity-temperature dependence.The glass that first reaches the lower limit of forming viscosity can significantly resist the shrinking effect caused by surface tension,making the glass wider during the forming.If the original glass width remains unchanged,the glass thickness or feeding speed is reduced,wider and thinner flexible glasses can be produced.

Effect of High Content Limestone Powder on Microstructure and Mechanical Properties of Cement-based Materials

Compared with the control sample without limestone powder(LP), the mechanical properties of the sample with 30% LP can be significantly improved by using a small amount of water reducer to reduce the water-cement ratio, without significantly affecting the fluidity of the fresh mixture and increasing the economic cost. In addition, compared with the sole addition of limestone powder, dual addition of metakaolin and limestone powder can effectively improve the strengths. The reason of this phenomenon was investigated by means of XRD, TG-DTG, SEM, LF-NMR and isothermal calorimetry, etc. The reactive aluminum-rich phases in metakaolin react with limestone powder in the hydration process, and the formed calcium carboaluminate reduces the porosity and makes the hardened paste denser. The addition of ground granulated blast furnace slag can also improve the strength of the specimen added with limestone powder, whereas, the effect is inferior to that of metakaolin, for the ground granulated blast furnace slag contains less reactive aluminate phases, and accordingly, the amount of calcium carboaluminate generated is lower than that of metakaolin.

Interfacial and Vacancies Engineering of Copper Nickel Sulfide for Enhanced Oxygen Reduction and Alcohols Oxidation Activity

Rational design and construction of highly efficient nonprecious electrocatalysts for oxygen reduction and alcohols oxidation reactions(ORR,AOR)are extremely vital for the development of direct oxidation alkaline fuel cells,metal-air batteries,and water electrolysis system involving hydrogen and value-added organic products generation,but they remain a great challenge.Herein,a bifunctional electrocatalyst is prepared by anchoring CuS/NiS_(2)nanoparticles with abundant heterointerfaces and sulfur vacancies on graphene(Cu_(1)Ni_(2)-S/G)for ORR and AOR.Benefiting from the synergistic effects between strong interfacial coupling and regulation of the sulfur vacancies,Cu_(1)Ni_(2)-S/G achieves dramatically enhanced ORR activity with long term stability.Meanwhile,when ethanol is utilized as an oxidant for AOR,an ultralow potential(1.37 V)at a current density of 10 mA cm-2 is achieved,simultaneously delivering a high Faradaic efficiency of 96%for ethyl acetate production.Cu_(1)Ni_(2)-S/G also exhibits catalytic activity for other alcohols electrooxidation process,indicating its multifunctionality.This work not only highlights a viable strategy for tailoring catalytic activity through the synergetic combination of interfacial and vacancies engineering,but also opens up new avenues for the construction of a self-driven biomass electrocatalysis system for the generation of value-added organic products and hydrogen under ambient conditions.

Hydration Characteristics and Mechanical Properties of Cement-Based Materials Modified by Calcined Zeolite and Montmorillonite

Montmorillonite and clinoptilolite zeolite were used as representative materials to prepare calcined clay-cement binary cementitious materials in order to study the effect of calcination treatment on the activation of clay minerals and the activity difference between layered and framed clays in this research.The influence of different calcined clay content(2%,4%,6%,8%,10%)on the fluidity,compressive strength,microstructure,phase change,and hydration heat of cement-based materials were analyzed.The calcined clay improves the fluidity of cement-based materials as compared with the uncalcined group.The addition of calcined montmorillonite(CMT)improves the development of mechanical strength,and the optimal compressive strength reaches 85 MPa at 28 days with 8%CMT.However,the activity of calcined clinoptilolite zeolite(CZL)is weak with few reaction sites,which slightly reduced the mechanical strength as compared to the blank sample.The addition of CMT changes the microscopic morphology of hydration products such as C-S-H and C-A-H,leading to the formation and transformation of ettringite in the early stage.It promotes the gradual polymerization of Si-O bonds into Si-O-Si bonds simultaneously,which accelerates the early hydration process.However,CZL acts mainly as a filling function in the cementitious system.In brief,CMT as an admixture can improve the mechanical properties of cement,but CZL has little effect.This work provides a guideline for the applications of calcined clay in cement,considering the influence of clay type on workability and mechanical strength.

Versatile Surface Modification of Ceramsite Via Honeycomb Calcium-aluminum-silicate-hydrate and Its Functionalization by 3-thiocyanatopropyltriethoxysilane for Enhanced Cadmium(Ⅱ) Removal

A low-cost and efficient filter medium for Cd(Ⅱ) removal was prepared by anchoring-SCN functional groups(by 3-thiocyanatopropyltriethoxysilane, TCPS) on ceramsite via the approach of synthesizing a honeycomb calciumaluminum-silicate-hydrate(C-A-S-H) layer as intermediate. The specific surface area of ceramsite was increased enormously by more than 50 times because of the modification of honeycomb layer. Moreover, the abundant Si-OH bonds existing in the structure of CAS-H can serve as active sites for TCPS. The combined effects ensure that the hybrid filter medium(named ceramsite/C-A-S-H/TCPS) demonstrated a high Cd(Ⅱ) adsorption capacity of 18.27 mg·g^-1 for particle size of 0.1-0.6 mm, 12.63 mg·g^-1 for 0.6-1.25 mm and 8.64 mg·g^-1 for 1.25-2.35 mm. The Cd(Ⅱ) adsorption capacity per unit area of ceramsite/C-A-S-H/TCPS(0.1-0.6 mm) is up to 4.07 mg·m^-2, which is much higher than that of many nano-adsorbents. In addition, ceramsite/C-AS-H/TCPS could maintain a high removal efficiency(> 85%) in a wide range of p H 3-11 and showed excellent selectivity in the presence of competing ions. Furthermore, Cd(Ⅱ) could be desorbed from ceramsite/C-A-S-H/TCPS composites with nearly 100%, suggesting the potential application in recycling of heavy metal ions.

Use of Different Barium Salts to Inhibit the Thaumasite Form of Sulfate Attack in Cement-based Materials

We investigated the effects of different barium compounds on the thaumasite form of sulphate attack（TSA）resistance of cement-based materials when they were used as admixtures in mortars.Moreover,we analyzed the inhibition mechanisms within different types of barium salts,namely BaCO_3 and Ba（OH）_2,on the thaumasite formation.The controlcement mortar and mortars with barium salts to cement and limestone weight ratios of 0.5%,1.0%,and 1.5% were immersed in 5%（by weight）MgSO_4 solution at 5 ℃ to mimic TSA.Appearance,mass,and compressive strength of the mortar samples were monitored and measured to assess the generaldegradation extent of these samples.The products of sulphate attack were further analyzed by XRD,FTIR,and SEM,respectively.Experimentalresults show that different degradation extent is evident in allmortars cured in MgSO_4 solution.However,barium salts can greatly inhibit such degradation.Barium in hydroxide form has better effectiveness in protection against TSA than carbonate form,which may be due to their solubility difference in alkaline cement pore solution,and the presence of these barium compounds can reduce the degree of TSA by comparison with the almost completely decomposed controlsamples.

Degradation of Formaldehyde and Benzene by TiO2 Photocatalytic Cement Based Materials

A novel photocatalytic cement based material was prepared. The distribution of TiO2 on the surface of cement was characterized by scanning electron microscope（SEM） and X-ray diffraction（XRD）, which showed the relationship of photocatalysis and presence of TiO2. TiO2 also had an impact on cement hydration, which was studied by thermal analysis. With 300 W UV illuminations, formaldehyde and benzene were degraded efficiently by the prepared photocatalytic cement based materials. 15wt% TiO2/cement showed the highest degradation efficiency and capability. The results show that formaldehyde and benzene can be degraded within 4 and 9 hours, respectively. Besides, inorganic ions can induce TiO2 agglomeration. As a result, the presence of inorganic ions in cement is unfavorable for degradation. The photocatalytic cement based materials were fabricated and the degradation efficiency of formaldehyde was measured on building roof under sunlight illumination. Formaldehyde in glass chamber can be degraded thoroughly within 10 days.

Effect of Silica Fume on the Thaumasite Form of Sulfate Attack on Cement-based Materials

Thaumasite form of sulfate attack（TSA） can be observed in cement containing limestone under sulfate condition at low temperature. Mixing with suitable mineral admixture could be a good choice to improve the TSA resistance performance of cement-based materials. We investigated the durability performance of limestone-cement mortars reinforced with silica fume（SF） in 5% MgSO_4 solution at 5 ℃. The mortars, which were immersed in aggressive condition, were prepared with 2%, 4%, 6%, 8%, and 10% cement replacement by SF at a fixed water-to-binder ratio. Appearance, compressive strength, change of length and mass and corrosion products were investigated to evaluate the TSA resistance performance of SF based specimens. The results showed that specimens in the absence of SF almost disintegrated. Increasing SF dosage can reduce the degree of deterioration of SF mortars in TSA environment. Mortar mixtures with more than 6% SF merely show slight degeneration in relation to macroscopic and microscopic tests and characterizations.