热养护UHPC后期水稳定性

热养护能够提高超高性能混凝土(UHPC)的早期力学性能和促使UHPC的水化,但也带来了UHPC后期水稳定性问题.本文通过力学性能、SEM、XRD和孔结构分析研究了20℃标养、90℃蒸汽养护和250℃干热养护三种养护制度下试件接触水和隔绝水时对UHPC长期力学性能和微观结构的影响,结果表明:20℃标养和90℃蒸养下接触水分和隔绝水分对于试件的强度和微观结构影响较小,接触水分能够更好地提高试件的后期强度;250℃干热养护下,接触水分则会显著增加试件的微观孔隙,导致试件在后期出现明显的强度倒缩,引起严重的水稳定性问题.     

橡胶颗粒抑制蒸养混凝土热损伤机制

通过向蒸养混凝土中掺入橡胶颗粒制备蒸养橡胶混凝土来抑制蒸养过程中混凝土产生的热损伤。通过试验测试了蒸养橡胶混凝土的抗压强度；建立了考虑界面过渡区的橡胶混凝土随机骨料模型，基于ABAQUS，模拟研究了橡胶颗粒对降温阶段混凝土温度损伤应力的影响，从细观角度研究橡胶颗粒抑制蒸养混凝土中微裂纹发展规律，并将温度损伤应力作为初始缺陷，模拟了橡胶混凝土的抗压性能，验证了模拟结果的可靠性；通过压汞(Mercury intrusion porosimetry,MIP)测试研究了橡胶颗粒对蒸养混凝土孔结构的影响；通过超景深显微镜研究了橡胶与水泥石之间的结合情况。研究结果表明：橡胶颗粒掺入可以抑制蒸养混凝土的热损伤，减少强度损失。橡胶颗粒可以有效降低蒸养混凝土试件的总孔隙率，蒸养橡胶混凝土试件有害孔径较未掺加橡胶颗粒的普通蒸养混凝土下降了3.1%，同时改善了橡胶和水泥基体的粘结状况。     

蒸养条件下锂渣复合水泥的水化产物与力学性能

利用电感耦合等离子体发射光谱(ICP)、X射线衍射分析(XRD)、扫描电子显微镜与能谱分析(SEM-EDS)及同步热分析(TG-DTG)等手段研究了掺20%锂渣复合水泥在80℃蒸养7 h、7 d和标养28 d条件下的水化产物与力学性能。结果表明:锂渣中SiO_2和Al_2O_3大部分存在于锂辉石中,而少量存在于玻璃体中,且锂渣中存在少量的碳酸盐。与纯水泥不同,锂渣复合水泥在以上三种养护条件下形成的C-S-H凝胶均主要为网状;此外,蒸养7 d时还有水化硫铝酸钙(AFt)和立方体CaCO_3生成,但无水化石榴石形成;蒸养28 d时,还有球形等大颗粒状C-S-H凝胶和立方体CaCO_3生成。蒸养可以促进锂渣和水泥的反应,尤其是锂辉石与水泥水化产物氢氧化钙的反应。在蒸养7 h和7 d条件下,锂渣复合水泥胶砂的抗折强度、抗压强度均明显高于纯水泥胶砂的抗折强度、抗压强度。     

水化硅酸钙晶种对CaO-SiO2-H2O蒸压体系强度的影响及其机理分析

选取石灰与无定形二氧化硅为原料,利用水热合成法在不同热工条件下制备了水化硅酸钙晶种,研究水化硅酸钙晶种对硅酸盐蒸压制品强度的影响。通过化学分析法探讨了不同蒸压时间下水化硅酸钙晶种对粉煤灰反应程度的影响;利用X射线衍射(XRD)、电子扫描电镜(SEM-EDS)和压汞法(MIP)分析了晶种对不同蒸压时间下CaO-SiO_2-H_2O体系水化产物种类及形貌的影响。研究结果表明:采用钙硅物质的量比为1.0、水热合成温度低于150℃时制备的水化硅酸钙晶种提高CaO-SiO_2-H_2O蒸压体系强度最明显,水化硅酸钙晶种的掺入促进了粉煤灰中SiO_2快速溶出以及水石榴石的分解,提高了水化产物含量;水化硅酸钙晶种的加入可以细化孔结构,使孔结构分布均匀,增加50nm以下的无害孔及少害孔数量,减少大于200nm的多害孔数量。     

氯离子渗透对混凝土表层渗水系数及微观结构的影响

使用不同配合比的混凝土试件及颗粒标准养护28 d后,浸泡在超纯水和5%的NaCl溶液中,采用表面渗透性测试仪(Autoclam)和氮气吸附法定期检测混凝土的表层渗水系数及微观孔结构,研究氯离子对混凝土表层渗水性能及水泥水化浆体微观结构的影响。结果表明,NaCl溶液浸泡会显著提高混凝土表层的抗渗能力,对PC1混凝土,浸泡90 d后,表层渗水系数为超纯水浸泡试件的0.91,150 d后仅为超纯水试件的0.76;氯离子浸入混凝土后,会使混凝土的孔结构细化,显著降低100 nm以下的小孔,实验中,PC1混凝土在NaCl溶液浸泡后,小于100 nm的孔与超纯水浸泡相比减少了32.43%;PC2混凝土在NaCl溶液浸泡后,小于100 nm的孔相比减少了57.24%;NaCl溶液浸泡下,水泥水化良好,结构较致密,氯离子对水泥浆体的水化过程有一定的促进作用。     

养护温度对长江下游疏浚超细砂浆特性影响机制

为了实现长江下游疏浚砂的综合利用，拓展细骨料来源，研究不同养护温度对不同疏浚砂掺量砂浆特性的影响。以疏浚砂为原料，设计了3种不同疏浚砂掺量的砂浆配合比，研究了40、60、80、90℃4种养护温度对不同龄期抗压、抗折强度的影响，并结合X射线衍射、热重-差示扫描量热、扫描电镜、压汞测试，分析了不同养护温度及不同疏浚砂掺量砂浆的微观结构。研究结果表明：随着养护温度升高，砂浆内部水化产物分布不均匀，阻碍了后续的水化反应，砂浆的抗压、抗折强度总体上先增大后减小，养护温度越高，蒸养损伤越大；疏浚砂颗粒粒径极小，具有良好的填充效果，适量掺入疏浚砂能提高体系的密实度，同时还能减少有害孔和多害孔的数量，进而提高砂浆的力学性能；蒸养条件下，砂浆孔结构缺陷增多，疏浚砂的优化作用被放大，一定程度上可以抵消蒸养带来的部分不利影响，随养护温度的升高，疏浚砂对抗压强度的提升率逐渐降低，最大能提升31.35%，对抗折强度的提升率先增大后减小，最大能提升14.29%。     

基于碟片法的溶蚀作用下水泥净浆微观结构演变研究

溶蚀作用下水泥基材料的微结构变化导致混凝土材料服役性能退化。为了克服传统试验因试样厚度影响而产生的脱钙不均匀现象,以NH4NO3溶液对约1mm的碟片状水泥净浆试件进行加速脱钙,通过控制质量损失来控制溶蚀程度。然后把质量损失作为衡量溶蚀程度的参数,结合压汞法(MIP)、环境扫描电子显微镜(ESEM)及能谱分析(EDS),研究不同溶蚀程度下水泥净浆的微观形貌、化学组成和孔隙结构变化规律。试验结果表明:试件钙硅比(Ca/Si)与质量损失大致呈两段线性关系。在第一阶段,水泥浆体试件Ca/Si逐渐降低,氢氧化钙(CH)分解,质量损失10%试件中CH已被严重溶蚀;水化硅酸钙(C-S-H)凝胶的Ca/Si随着溶蚀程度增加而降低,证明C-S-H凝胶第一阶段已开始分解。在第二阶段,主要表现为C-S-H凝胶继续分解。试验还发现,溶蚀后水泥净浆试件内部孔径小于50nm的孔略微增加,50~200nm的孔含量有部分减少;孔径大于200nm的多害孔大量增加。     

干湿循环作用对混凝土抗氯离子渗透侵蚀性能的影响

为了加速模拟海洋潮差区环境对混凝土耐久性能的影响,掺入矿粉和纳米改性矿物掺合料,研究了氯盐干湿循环作用对混凝土抗氯离子侵蚀性能及微观结构的影响,并将干湿循环试验与常规浸泡试验进行了对比。结果发现,干湿循环作用粗化了混凝土试件表层孔结构,增大了孔径>50 nm的孔隙含量,显著提高了自由及总氯离子浓度;掺入纳米改性矿物掺合料能降低混凝土内部孔隙率,减少有害孔含量,提高混凝土内部氯离子结合能力;干湿循环60天后混凝土表层Ca（OH）₂逐渐被消耗,生成了Friedel盐和CaCO₃。      

0～20℃硅酸盐水泥的水化性能

采用X射线衍射仪(XRD)及环境扫描电子显微镜(ESEM)研究0℃、5℃、10℃及20℃时硅酸盐水泥的水化过程,并进行凝结时间及力学强度测试。结果表明,温度越低,硅酸盐水泥的初凝和终凝时间越长,水泥早期的水化程度和力学强度也越低;但水化后期,水泥水化产物C-S-H凝胶明显细长,水化产物间距较小,大孔减少且孔隙分布更均匀,水化程度和后期强度较高。     

内掺Ca(OH)_2对碱矿渣混凝土强度发展的影响

通过水化热、孔隙率及吸水率测试、XRD等分析手段,研究了内掺Ca(OH)_2对碱矿渣混凝土性能发展规律的影响。测试结果表明,加入Ca(OH)_2后,碱矿渣水泥水化速率提高,可进一步加快其早期强度发展;碱矿渣混凝土试件28d的毛细孔率及吸水率均有所下降,说明混凝土孔结构得到了优化;XRD分析表明,碱矿渣混凝土中富钙水化产物增多并生成了水化铝酸四钙。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

From Industry 4.0 to Research 4.0. Development of High Performance Fibers in the Light of Digitization

We associate a variety of innovations with the term ＂Industry 4.0＂. The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di...     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Roman iron and steel: A review

ABSTRACT

The production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them.     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...