Influence of CaO-based expansive agent,superabsorbent polymers and curing temperature on pore structure evolution of early-age cement paste

Cracks easily generate in concrete at early age owing to the shrinkage deformation.CaO-based expansion agent(CEA)and superabsorbent polymers(SAP)have been extensively used for the mitigation of concrete shrinkage.The macroscopic properties of concrete are highly determined by the microstructure.In this study,the influence of CEA and SAP addition on the pore structure evolution of cement paste under different curing temperatures was evaluated via low-field nuclear magnetic resonance spectroscopy.Test results indicated that,in cement paste,a higher CEA content led to a higher porosity and a larger most probable pore diameter(MPPD).Meanwhile,SAP addition increased the porosity and MPPD of CEA cement paste at early age but decreased them after 7 d,and a higher SAP content always brought a higher porosity and MPPD.Furthermore,the addition of SAP led to a lower porosity and MPPD of CEA cement paste than that of plain cement paste after 14 d.Moreover,the porosity and MPPD of CEA cement paste decreased first and subsequently increased as the curing temperature raised.

Dynamical Properties of Additive Cellular Automata over Finite Abelian Groups

Some dynamical properties were discussed for additive cellular automata(CA)over finite abelian groups.These properties include surjection,ergodicity,sensitivity to initial conditions and positive expansivity.Some necessary and sufficient conditions of determining ergodicity and sensitivity of the above additive CA were presented,respectively.A necessary condition for the positive expansivity of the above additive CA was given.The positive expansivity was proved to be preserved under the shift mappings for the general CA.The discussion was mainly based on the structure theorem of the finite abelian groups and the matrix associated with the global rule of the additive CA over the finite abelian p-groups.

Mechanics Model to Determine Swelling Potential of Expansive Soils

The factors influencing on soil expansion are reviewed in the paper. A mechanics model to determine swelling potential of expansive soils is presented. The mechanics model is based on the softening of expansive soil following absorption of water. The constitutive relationships of the mechanics model include the relationship among swelling under free load, swelling under load, and vertical pressure, and the relationship of swelling under free loading and swelling pressure. A concept of additional compression modulus is introduced and the method determining the modulus is proposed. Finally, the predicted results of swelling potential using the mechanics model compare well with the measured data.

单排弹性实心桩对SH波的散射求解问题

采用波函数展开法结合格拉夫加法定理分析单排实心弹性桩的SH波散射问题,通过改变单一变量,分析桩土剪切模量之比、桩体个数等因素对排桩隔振的影响效果,得到如下结论:当无量纲频率为低频和中频时,排桩后无量纲位移曲线在无限远处趋于0,随着桩体根数的增加隔振效果逐渐提高;在排桩后0~70 a(a为桩径)范围内无量纲位移之比变化幅度较大,且不稳定,隔振效果较差;当桩土剪切模量之比小于500时,在250a~380a范围内减隔振效果较好;当桩土剪切模量之比大于或等于500时,隔振效果并不会随着其增加而大幅增加,即此时可将桩体认为是刚性桩体。当无量纲频率为中频时,在100a~120a范围内隔振效果较好,之后此范围内无量纲位移之比先骤升后逐渐下降,但当无量纲频率上升为高频时,各桩体根数下排桩隔振效果相差不大,且会在距离排桩更近处就已经达到很好的隔振效果。

流变助剂对膨胀型钢结构防火涂料性能的影响

以溶剂型丙烯酸树脂及氯化石蜡为基料,多聚磷酸铵、季戊四醇和三聚氰胺为膨胀体系,通过不同温度下炭层质量保持率、炭层强度、膨胀倍数、炭层形貌、耐火时间等考察了不同类型的流变助剂对防火涂料性能的影响。结果表明:流变助剂对膨胀型钢结构防火涂料性能的影响非常大。聚酰胺蜡、水合硅酸镁类流变助剂对体系的炭层强度、膨胀倍数、耐火性能等基本无影响;改性水合硅酸镁可以提高防火涂料的耐火时间和炭层强度;亲水气相二氧化硅会导致炭层膨胀倍数和耐火时间增加,同时会降低炭层强度,导致炭层易脱落;疏水二氧化硅、改性蒙脱石类流变助剂会抑制膨胀发泡、提高炭层强度,同时会大幅度降低耐火时间。分析探讨了不同类型流变助剂对防火涂料的性能影响的机理。不同流变助剂在高温膨胀发泡过程中主要影响体系的熔融黏度和膨胀倍数,从而影响防火涂料的综合性能。

建筑加减法——华南师范大学附属小学教学楼扩建设计

建筑是人活动的容器,教学楼是学生学习及活动的容器。校园的扩建不是对原有学习环境的简单复制,而是应该面对未来的多种教学方式,挑战单一地块的多样性使用的可能性。华南师范大学附属小学教学楼扩建项目,根据场地限制条件,结合功能要求,通过对建筑体块进行加减整合,给简单无趣的场地带来蓬勃生机。

莫来石晶须加入量对莫来石制品性能的影响

以莫来石、黏土和α-氧化铝微粉为主要原料,分别添加0、1%、2%莫来石晶须,1600℃烧结3 h后制得莫来石制品,研究莫来石晶须加入量对莫来石制品物相组成、显微结构和性能的影响。结果表明:随着莫来石晶须加入量的增加,细小的二次莫来石穿过晶界向莫来石晶须跃迁的几率增加,使莫来石晶须快速长大呈长柱状并交错互锁,提高试样的致密程度和强度,降低试样的热膨胀性和高温蠕变性;确定出莫来石晶须加入量为2%时莫来石制品的各项性能最佳。

大跨度钢梁桥区段接触网附加导线架设方案探讨

对大跨度钢梁桥区段附加导线架设问题进行研究,提出了该区段附加导线架设与悬挂安装方案,旨在消除梁体伸缩对附加导线的影响。方案通过在实际线路中应用,有效解决了大跨度钢梁桥上附加导线断线的问题,提高了接触网系统的稳定性和可靠性,可为大跨度钢梁桥区段附加导线架设提供参考。

A new design of dual-constituent triangular lattice metamaterial with unbounded thermal expansion

Triangular lattice metamaterials composed of bi-layer curved rib elements (called the Lehman-Lakes lattice) possess unbounded thermal expansion, high stiffness and impossibility of thermal buckling, which are highly desirable in many engineering structural applications subjected to large fluctuations in temperature. However, the requirement of such lattice metamaterial is that it must be a hinged joint in order to achieve the bending deformation upon heating freely, which directly leads to poor manufacturability, especially in small dimensions. In this study, a new design of dual-constituent triangular lattice metamaterial (DTLM) with good manufacturability is proposed to achieve the identical unbounded thermal expansion. In this lattice, a special bi-layer curved rib element where layer one is partially covered by layer two is presented, where the hinge joints are not necessary because the flexural rigidity in the single-layer part is much smaller than that in the bi-layer part, and the desirable thermal bending deformation can be achieved. A sample fabricated by additive manufacturing is given in order to show the good manufacturability;simultaneously, the multifunctional performance of the tailored DTLM with zero, large positive or negative coefficient of thermal expansion (CTE) can remain excellent, as well as the Lehman-Lakes lattice. Examples illustrate that the DTLM with zero CTE has about 34.2% improvement in stiffness and meanwhile has 17% reduction in weight compared with the Lehman-Lakes lattice. The stiffness of the DTLM has a moderate reduction when achieving the same large positive or negative CTE. In addition, the thermomechanical properties of the DTLM are given by the closed-form analytical solution and their effectiveness is verified by the detailed numerical simulation.

储能系统锂离子电池附加受控电压源等效电路模型研究

该文在少温度和少放电电流样本测试条件下,基于二阶RC等效电路模型提出一种模型改进的方法,构建反向传播(BP)神经网络来预测宽范围温度和电流倍率下的模型端电压误差,实现对模型的动态补偿。该方法可避免对锂离子电池重复进行充、放电实验而造成循环寿命折损。仿真和实验结果表明,所提小样本数据扩展的方法具有一定的可行性;附加受控电压源的电池模型在不同温度和电流倍率下的适应性更好,模型精度得到提升。该方法通过模型分析实现电池筛选组成梯次利用储能系统,并结合电池模型实现荷电状态(SOC)预测及发热预警,在新能源发电电池储能系统应用中具有一定的实际工程意义。

Cold spray additive manufacturing of Invar 36 alloy:microstructure,thermal expansion and mechanical properties

In this work,the Invar 36 alloys were manufactured using cold spray(CS)additive manufacturing technique.The systematic investigations were made on the microstructural evolution,thermal expansion and mechanical properties under as-sprayed(AS)and heat-treated(HT)conditions.XRD(X-ray diffraction)and ICP-AES(inductively coupled plasma atomic emission spectroscopy)analyses show that no phase transformation,oxidation,nor element content change have occurred.The X-ray computed tomography(XCT)exhibited a near fully dense structure with a porosity of 0.025%in the helium-produced sample under as-sprayed condition,whereas the nitrogen-produced samples produced at 5 MPa and 800℃show more irregular pore defects.He-AS sample shows a more prominent grain refinement than that of nitrogen samples due to the more extensive plastic deformation.The post heat-treatment exhibited a promoted grain growth,inter-particle diffusion,as well as the formation of annealing twins.Between25℃and 200℃,the nitrogen samples possessed lower CTE(coefficient of thermal expansion)values(1.53×10^(-6)/℃)compared with those produced by casting and laser additive manufacturing.The He-AS samples exhibited a noticeable negative CTE value between 25℃and 200℃,which may due to the significant compressive residual stress(-272 MPa)compensating its displacement with temperature increase during CTE test.The N2-HT and He-HT Invar 36 samples present a notable balance between strength and ductility.In conclusion,the CS technique can be considered as a potential method to produce the Invar36 component with high thermal and mechanical performance.

隐性教育视角下英汉翻译课程教学探讨——以张培基主编的《英汉翻译教程》为例

本文以张培基主编的《英汉翻译教程》为研究素材,以隐性教育为视角,从素材挖掘和实施路径两方面分析探讨了如何在以该《教程》为指导的英汉翻译教学中开展“隐性教育”活动,以期达到育人功效。该研究表明,在以该《教程》为参考的翻译教学中,可根据其内容的设计与安排,有目的地扩充译史知识与本土翻译理论的讲解,并有选择性地布置翻译练习材料,采用线上线下结合的混合教学模式及多种教学方法,如此方可有效发挥英汉翻译教学中的育人功能。

地基软弱下卧层验算探讨

通过对规范软弱下卧层计算不同方法的比较,复核1≤E_(s1)/E_(s2)<3时软弱下卧层计算时地基压力扩散角取值。对于高层建筑筏板基础,由于主楼所处的位置不同,筏板基础周边的压力不同导致自重压力值pc不同,利用公式计算软弱下卧层顶面处的附加压力值p_(z)和软弱下卧层顶面处土的自重压力值p_(cz)如何取值规范未明确,通过与附加应力系数法和有限元计算结果进行计算比较,给出设计建议。

A state-of-the-art review on delayed expansion of cemented paste backfill materials

Utilizing delayed expansion cemented paste backfill materials(DECPB) in mine backfill operations offers an effective solution to the challenge of achieving proper contact between the in-situ cemented backfill mass and the roof in mined-out areas(backfill-roof contact).This article presents recent progress in both theoretical and experimental research concerning DECPB.The types and mechanisms of expansive additives,including expansive agents,foaming agents,and expansive mineral materials relevant to DECPB,are explained,along with their impact on the expansive properties and mechanical characteristics of DECPB.The composition,material characteristics,preparation methods,and controlled release mechanisms of microcapsules are analyzed.Two methods for measuring the volume change rate of paste backfill slurries are discussed.Research indicates that an appropriate content of expansive additives not only enhances the expansive properties of cemented paste backfill materials but also contributes to improving their mechanical properties.Chemical foaming agents and bentonite are found to be more suitable for preparing DECPB compared to expansive agents.The delayed expansion of cemented paste backfill material is influenced by microcapsules,with their wall materials,preparation parameters,and the alkaline slurry environment affecting their controlled release mechanism.Developing and optimizing precise measurement devices and methods forfor the volume change rate of cemented paste backfill materials is essential requirement for studying the performance of DECPB.Combining delayed expansion technology with retarding techniques in cemented paste backfill materials can provide a reliable solution for achieving proper backfill-roof contact in the future.

在盐湖环境中高强与高性能混凝土的抗冻性

用快冻法研究了高强与高性能混凝土在水中和在西藏、内蒙古、新疆和青海盐湖卤水中的冻融耐久性,探讨了其冻融破坏机理。结果表明:在水中冻融时,活性掺合料严重降低了非引气高强混凝土的抗冻性,目前的非引气高性能混凝土不具备高抗冻性的特征,并非真正意义上的"高性能",其冻融破坏起因于单硫型水化硫铝酸钙向钙矾石转化时的膨胀压,不含活性掺合料的普通与高强混凝土的冻融破坏源于水冻胀压;在盐湖卤水中冻融时,引起混凝土冻融破坏的主导因素是盐结晶压,混凝土的抗卤水冻蚀性主要取决于盐结晶压的损伤负效应和卤水冰点降低的损伤正效应,而且与盐湖卤水的成分密切相关。高强与高性能混凝土具有很高的抗卤水冻蚀性,在盐湖地区属于高耐久性的混凝土,适用于不同类型的盐湖环境。

不同添加剂对钛酸铝热膨胀系数影响的研究

钛酸铝是一种优异的高熔点、低膨胀无机非金属材料．为提高其强度、抑制其热分解，往往在钛酸铝中引入添加剂．本文研究了单一添加剂和复合添加剂对钛酸铝膨胀系数的影响．结果表明：引入少量的稀土元素氧化物能显著降低钛酸铝的热膨胀系数．引入1～4mol％CeO2或2mol％La2O3可使钛酸铝的膨胀系数降至接近于零．这就为开发零膨胀材料提供了新的方法．在钛酸铝中引入1～4mol％Fe2O3，其膨胀系数保持不变．在含有4mol％Fe2O3的钛酸铝中再引入SiO2，钛酸铝的膨胀系数增大，而加入另一种稀土元素氧化物则能降低其膨胀系数．三种添加剂的适当配比能将钛酸铝的膨胀系数调整至最小．这对于引入复合添加剂对钛酸铝的改性是很有意义的．

钛酸铝陶瓷及其研究进展

钛酸铝陶瓷以其独特的低膨胀和耐高温性能而倍受青睐 ,但其较低的强度及一定温度范围内的不稳定性制约了该材料的实际应用。本文简要阐述了钛酸铝的微观结构特征 ,并从添加剂的选择、材料合成工艺、材料烧结工艺等方面 ,系统介绍了前人在该领域所做的研究工作。最后在总结前人工作的基础上 。

偏高岭土及其在高性能混凝土中的应用

介绍了偏高岭石结构、火山灰性及其在高性能混凝土中应用研究现状。有关研究结果表明:偏高岭土可有效提高水泥砂浆和混凝土的强度,改善混凝土的抗渗性和耐蚀性,有效地抑制碱集料反应等,是一种很有开发应用价值的混凝土功能性掺合料。

膨胀剂对混凝土早期基本徐变的影响

研究了自制CaO和MgO膨胀剂的掺加对C60自密实混凝土力学、变形性能及基本徐变的影响,并将徐变测试结果与fib 2010模型计算结果进行了对比.结果表明:6%CaO膨胀剂、6%(CaO+MgO)膨胀剂和10%(CaO+MgO)膨胀剂的掺加对C60自密实混凝土的抗压强度和弹性模量影响较小,但会显著降低混凝土自收缩,并增大其基本徐变变形;混凝土的徐变度和徐变系数基本随着膨胀剂总掺量或CaO膨胀组分掺量的提高而增大;当CaO膨胀剂掺量较低时,混凝土徐变度实测结果与fib 2010模型计算结果吻合度较好,CaO膨胀剂掺量较高时,混凝土徐变发展趋势明显高于模型计算结果,复合掺加MgO膨胀剂后,随着持荷时间的延长,混凝土徐变进一步增加.对于CaO膨胀剂掺量较高以及复合掺加MgO膨胀剂的混凝土,有必要研究膨胀对徐变随时间发展系数的影响,进而对模型进行修正.

混凝土膨胀剂应用的若干问题

介绍混凝土膨胀剂在国内应用情况以及存在的若干问题 ,提出相应的解决对策 ,为我国膨胀混凝土应用的科学性和可靠性提供理论和实践依据。