环氧胶砂修补混凝土公路局部缺陷的试验

通过对环氧树脂胶砂和环氧树脂砼及其成份的试验，取得了相关配方和粘结力等数据，提出了修补公路砼路面局部缺陷的用料及其配方和操作实践与工艺。     

A Rheological Model for Evaluating the Behavior of Shear Thickening of Highly Flowable Mortar

Neither the modified Bingham model nor the Herschel–Bulkley model can be used to characterize and calculate the performance of shear thickening of highly flowable mortar because of their incalculability of the rheological parameters. A new exponential rheological model was established to solve the characterization and calculation of shear thickening of the lubrication layer (highly flowable mortar) during the pumping of concrete in this paper. This new exponential rheological model has three rheological parameters, namely, yield stress, consistency coefficient, and consistency exponent. They can quantitatively describe the yield stress, differential viscosity, and shear thickening degree of highly flowable mortar. The calculating results of the rheological parameters of the newly established model for the mortars with different compositions showed that the consistency exponent of mortar decreased with the increase of its sand-binder ratio or the dosage of fly ash in the binder. This indicates that the shear thickening degree of mortar decreases. The consistency exponent of mortar initially decreases and subsequently increases with the increase in silica fume content or the dosage of the superplasticizer. It illustrates that the degree of the shear thickening of mortar initially decreased and subsequently increased. These varying patterns were confirmed by the rheological experiment of mortars.     

Mortar Element Method for Flow Problems in Primitive Variables Form

Parallel implementation of the finite element method for the Helmholtz equation and the Stokes equations is discussed in the environment of a distributed-memory massively parallel computer where data is shared among the processors by communication procedures called message-passing. For implementation of the finite element methods based on domain decomposition, “pre-assembly type” and “restriction type” are introduced for data on nodal points. They simplify the implementation and reduce the amount of message-passing between subdomains. In order to reduce this further, the mortar element method is applied to the primitive variables of the Stokes equations. It maintains natural treatment of stress boundary conditions, which is an advantage of the finite element method. Its implementation can be described concisely by the idea of the two data types.     

THEORETICAL ANALYSIS ON THE NUCLEATION OF MICRO-DAMAGE IN CEMENT MORTAR UNDER COMPRESSIVE LOADING AND SULFATE ATTACK

Effect of uniaxial compression on the nucleation of micro-damage in cement mortar under sulfate attack is investigated.Shape and size of micro-voids in cement mortar is detected using Micro Computed Tomography techniques.The formation of delayed ettringite crystal is analyzed using scanning electron microscope and energy disperse spectrum methods.Deformation of micro-voids and the distribution of stress at the surface of a micro-void are calculated.It is found that the nucleation of micro-cracks is caused by the tensile stress at the voids’ surface,and such damage nucleation will be speeded up by the remote uniaxial compressive load.     

Altered Volcanic Tuffs from Los Frailes Caldera. A Study of Their Pozzolanic Properties

This work presents the results of the study of the physical, chemical, mineralogical and pozzolanic properties of the altered volcanic tuffs (AVT) that lie in the Los Frailes caldera, south of the Iberian Peninsula, and demonstrates their qualities as pozzolans for the manufacturing of mortars and pozzolanic cements of high mechanical strength. The main objective of this research is to show to what extent the AVTs can replace portland cement (PC) in mortars, with standardised proportions of 75:25% and 70:30% (PC-AVT). To achieve these objectives, three AVT samples were studied by a petrographic analysis of thin section (PATS), DRX, FRX and MEB. The pozzolanic properties were determined by three methods: electrical conductivity (ECT), chemical pozzolanicity tests (CPT) at 8 and 15 days and mechanical strength tests (MS) of the specimens at 2, 7, 28 and 90 days. Studies of a PATS, DRX, FRX and MEB showed that the AVT samples’ constitutions are complex where smectite (montmorillonite), mordenite, quartz, halloysite, illite, kaolinite, volcanic glass and lithic fragments coexist. The results of the ECT and CPT tests confirmed the pozzolanic properties of the samples analysed and proved an increase in mechanical strength from 2 to 90 days of testing.     

化学腐蚀对混凝土材料力学特性影响的试验研究

对不同水化学环境腐蚀过程中砂浆试样物理力学性质进行了试验研究,分析了溶液pH值、浓度及水化学成分对砂浆的腐蚀程度,探讨了砂浆试样的化学腐蚀机制。试验结果表明:在相对封闭的环境条件下,无论是哪种水化学溶液,随着化学侵蚀时间的加长,溶液的pH值均趋于碱性;同时,溶出的Ca2+、Mg2+离子具有累积性特点。在其他条件相同的情况下,水化学溶液的离子成分对砂浆试样的腐蚀程度各不相同。酸性条件下,Na2SO4溶液砂浆试样物理化学性质的影响要比NaHCO3溶液大;中性条件下,与纯净的蒸馏水相比,Na2SO4溶液对砂浆试样的腐蚀作用要强一些。     

缓凝砂浆在单螺杆挤出机中的流动分析

在预应力钢筋上连续包裹一层缓凝砂浆是新型缓粘结预应力混凝土体系得以工程应用的关键。为了弄清包覆过程,了解物料性能、加工条件和螺杆参数等输入变量对包覆输出结果的影响,基于缓凝预应力筋包覆试验,运用Polyflow软件,对宾汉姆体的缓凝砂浆在螺旋槽内流动和变形情况进行CFD(computational fluid dynamics)模拟。得到了可视化的速度场和剪切速率场,模拟了分析螺杆转速、螺杆几何参数对物料流变特性的影响。模拟结果可视,且直观地验证了包覆试验现象,揭示了包覆机理,为包覆装置可靠作业和结构优化提供了理论依据。     

中国古建筑石灰灰浆的光谱分析技术

石灰是中国古代最早使用的重要胶凝材料,广泛应用于房屋、墓葬、城墙、堤坝等古代建筑工程中。古人还在石灰灰浆中添加糯米浆、动物血液、植物汁液、红糖、桐油、纸筋、秸草等有机材料以增进其性能。此外,中国古代还使用石灰、粘土和砂石组成现在称为"三合土"的混合石灰材料以构筑墓葬、城墙和水利工程等建筑墙体。在古建筑遗址的修复和保护工作中,本着"修旧如旧"的原则,必须对古建筑修建所采用的原材料和施工工艺进行分析研究,从而为修复工作提供科学可靠的依据。本文综述了在对中国古代建筑石灰灰浆的分析中所采用的光谱分析技术,包括拉曼光谱、红外光谱、X射线衍射和X射线荧光光谱,以及扫描电子显微镜、热重分析等其它一些分析技术,讨论了各种分析技术的用途、优势和劣势。     

水溶剂法合成聚丙烯酸系混凝土减缩剂的研究

根据减缩剂的作用机理及分子结构设计原理,用水溶剂法合成了聚丙烯酸系混凝土减缩剂(SRA-PA),对影响酯化反应和聚合反应的因素进行了探讨,并用红外光谱表征了其分子结构。通过实验得到SRA-PA的最佳合成条件:酯化反应催化剂用量为聚乙二醇单甲醚1200(MPEG)用量的5%,反应温度100℃,反应时间4h,丙烯酸(AA):MPEG=3:1;聚合反应聚乙二醇单甲醚丙烯酸酯(PEA):甲基丙烯酸甲酯(MMA)=2:3,过硫酸铵(APS)用量为单体总质量的2.5%。通过砂浆的收缩与强度测试等方法研究SRA-PA的主要性能,研究表明掺SRA-PA的砂浆减缩率3d达到50%~60%、28d达到20%~30%,同时不降低砂浆的强度。     

预拌湿混砂浆及其专用改性剂

预拌砂浆由于其具有节能、环保以及使用方便等优势,市场发展空间巨大。然而,传统湿拌砂浆仅有4～6 h的可操作时间,这成为制约其快速发展的技术瓶颈。文章系统介绍了具有24 h可操作时间的新型预拌湿混砂浆及其改性剂的技术优势、研究重点及发展趋势。