数字图像系统水泥水化计算机模拟（Ⅰ）

基于数字图像处理为基础的水泥水化模型—CEMHYD3D代表了当今世界水泥水化的计算机模拟的最先进的技术之一。本文以CEMHYD3D为背景，从二维图像的相关水泥参数的获取和水泥微结构的三维重建阐述水泥水化的计算机的模拟技术。     

数字图像系统水泥水化计算机模拟(Ⅱ)

以CEMHYD3D为背景,阐述在完成水泥颗粒的三维重构后,根据元胞自动机理论,水泥水化的反应规则运用到水泥浆体的三维结构中。模拟水泥水化演变过程中水泥主要物相之间的化学反应,以实现水泥水化的水泥浆体的微结构的演变,并对水泥水化计算机模拟问题进行讨论。     

水泥浆体液相离子浓度模拟

提出了一种基于三维水泥水化过程计算机模型的水泥基材料液相(孔溶液)离子浓度预测新方法。综合考虑了环境温度、湿度、材料配合比等因素,基于水泥化学和溶液化学理论,采用固-液相动态平衡分析方法,利用三维计算机模型CEMHYD3D来预测水泥浆体中孔溶液、水化产物的数量,通过溶液平衡方法模拟孔溶液中各主要离子浓度的变化规律。模型预测结果与实验结果对比分析表明,该方法可以成功地预测水泥基材料孔溶液组分的变化规律。     

矿渣微粉活性预测及水化模拟技术

提出了根据矿渣成分和激发环境碱度预测磨细粒化高炉矿渣微粉活性的方法,并且建立了三维矿渣硅酸盐水泥水化过程及微结构发展计算机模型.模型重建含磨细矿渣微粉的水泥浆体的三维微观结构,并且提出模拟矿渣微粉和硅酸盐水泥熟料各矿物组分之间相互作用的算法.模拟结果和实际实验结果的比较表明,新建的三维计算机模型能够成功地模拟矿渣硅酸盐水泥的水化过程及其微结构发展.     

水泥粒径分布对混凝土绝热温升影响的模拟

为了模拟水泥粒径分布对混凝土绝热温升过程的影响,建立了一个基于水化深度的水化模型．该模型假定混凝土中水泥水化过程由水化深度控制,且水化深度随时间的发展与颗粒粒径无关;通过水泥等温放热曲线试验推导得出最大水化深度的存在;假定温度对水化过程的影响满足Arrhenius公式．通过混凝土绝热温升仪测定了3种不同初始温度下的绝热温升曲线,以此得到水化模型所需的基准水化速率曲线．最后将建立的水化模型用于模拟混凝土的绝热温升曲线,结果表明:基于水化深度的水化模型能够准确模拟水泥粒径分布和初始温度对混凝土绝热温升的影响．     

水泥石水渗透系数预测的数值方法

基于水泥石结构的计算机模拟,提出了水渗透系数估计的随机行走算法。在该算法中,将水泥颗粒模拟成各种尺寸的球体,应用水化反应原理,在微观水平上重构水泥石结构,并进一步计算水化度和毛细孔隙率。与实测值和经验公式对比,验证了水泥水化模型的有效性。基于微观水平上重构的水泥石结构,应用随机行走算法计算水渗透系数。与有效介质方法相比,初步证实了该算法的有效性,也详细分析了该算法的局限性。     

煤矸石-水泥二元胶凝材料水化动力学研究

为揭示煤矸石对水泥水化过程的影响,采用等温量热仪研究了煅烧煤矸石-水泥复合胶凝体系的水化动力学。煤矸石-水泥二元胶凝材料水化放热规律与纯水泥基本一致;复合盐(CaCl2—K2SO4,CaCO3—K2SO4)能够促进煤矸石-水泥胶凝材料的水化,缩短煤矸石-水泥胶凝材料的水化诱导期,提高煤矸石-水泥的水化放热量;从加速期水化反应速率常数和水化放热量来看,氯盐-硫酸盐比碳酸盐-硫酸盐对煤矸石-水泥二元胶凝材料激发效果更好。     

从水化反应动力学到水泥浆体微结构

本文通过对水泥水化研究中采用的主要方法的比较,介绍了国内外水泥浆体微结构模拟方面的最新进展,叙述了该方法的主要步骤,展示了数值模拟和图像处理技术在该领城的广阔应用前景。     

高含硼废液对硫铝酸盐水泥水化过程影响机理

研究了高含硼模拟液条件下硫铝酸盐水泥的水化反应特征、缓凝机理和使用氢氧化钙作为促凝剂的可行性。通过采用XRD、TG-DTG、微量热仪、SEM-EDS、EPMA等微观测试分析手段,表征了氢氧化钙对含硼模拟液条件下硫铝酸盐水泥水化过程和反应产物的影响。结果表明,在含硼模拟液中,硫铝酸盐水泥颗粒的表面会生成具有层状特征的硼化物,包裹水泥颗粒,阻碍其进一步溶解,延缓硫铝酸盐水泥水化。氢氧化钙的掺入能诱导硫铝酸盐水泥在含硼模拟液中优先生成含硼钙矾石,缓解硼酸根离子的缓凝效果,有效促进水泥水化反应;随着水化反应进行,含硼钙矾石会逐渐转变为钙矾石。     

掺P2O5水泥基材料水化动力学研究

基于水化动力学模型,采用SEM、XRD和C-80Ⅱ型导热式微量热仪研究了硅酸盐水泥和掺P2O5硅酸盐水泥胶凝体系的水化特性和水化动力学,分析了P2O5对硅酸盐水泥水化机制的影响规律。研究结果表明,掺入P2O5后硅酸盐水泥的水化产物数量和尺寸显著减小。P2O5掺量为3．5％时,硅酸盐水泥熟料水化热总量降低32．6%,硅酸盐水泥的初凝和终凝分别被延缓1．10h和12．54h。掺入P2O5复合体系的水化机制与硅酸盐水泥类似,加速期由自动催化反应控制,减速期由自动催化和扩散反应双重反应控制,稳定期扩散反应占据主导。P2O5会增加硅酸盐水泥在加速期和减速期的水化反应阻力,减小稳定期的水化反应阻力。掺入P2O5后,水泥在加速期和减速期的表观活化能增加,稳定期表观活化能略有降低P2O5溶液环境有利于水泥熟料C3A的水化,延缓C3S和C2S的水化。     

Influence of New Compound Admixture on Shotcrete Performance

To analyze the influence of new compound admixture on shotcrete performance, the ordinary Portland cement pr425 was used as matrix components. The optimum proportion of admixture was obtained by analyzing the influence of content on cement setting time and compressive strength. The microstructure of cement test block and the mechanism of reducing dust of composite macromolecule admixture were analyzed by scanning electron microscopy and infrared spectroscopy. It was shown that the ratio of polyacrylic acid was 0.02%. The ratio of J85 accelerator was 5%. The ratio of bentonite was 4.5% in composite admixture. The most optimal content of admixture in the slurry was 7%. The compound coagulant formed by additive together with C_3 A, C_4 AF which provided nucleation for hydration and crystallization of C_3S and C_3S, and played an active role to promote the activity of the mineral admixture in cement, and increased the elastic modulus of C-S-H gel and accelerated the hydration process of portland cement. Bentonite and polyacrylic acid promote the wettability, cohesiveness and workability of cement paste in the process of hydration. The formation of cement test block gel was even. The interface between the matrix phase and the aggregate phase was not obvious which ensured the matching between the matrix and the aggregate phase. The addition of bentonite formed hydrogen bonds in cement paste and improved the cohesiveness of the system. The J-85 accelerator promoted the combination of aluminate and gypsum which hindered the formation of calcium carbide around the cement particles which made cement rapid condensation. Polyacrylic acid mainly changed the strength of hydroxyl absorption peak in cement paste to improve the initial strength of cement test block. The addition of new admixtures promoted the process of cement hydration to be more thorough and affected the later strength development of concrete by affecting the formation of calcium carbonate stone.     

A binder of phosphogypsum-ground granulated blast furnace slag-ordinary portland cement

A new hydraulic cementitious binder was developed by mainly utilizing industrial byproducts phosphogypsum(PG)and ground granulated blast furnace slag(GGBFS)with small addition of ordinary portland cement(OPC).The hydration process and microstructure were studied by X-ray diffraction(XRD) and scanning electronic microscopy(SEM).OPC hydrated first at early age to form primarily C-S-H gel,ettringite and calcium hydroxide(CH).GGBFS activated by CH and sulfate ions hydrated continuously at later age,producing mo...     

集料与硅酸盐水泥石界面区的若干研究

利用XRD层析法和SEM研究了集料与硅酸盐水泥石界面区的组成、CH晶体取向指数等。实验结果表明,界面区中水化产物主要是C-S-H凝胶、CH晶体、AFt、孔隙以及未水化的熟料矿物;界面区中CH晶体发育良好,取向作用较强,界面处它以(001)面平行于集料表面生长;水化龄期增长或水灰比提高时,CH晶体取向作用增强,而且水灰比高时,界面区中孔洞、裂纹增多,降低界面粘结强度;水泥中掺入5.0%wt硅灰后,CH晶体取向作用下降;水泥中掺入5.0wt%FDN减水剂,由于水泥早期水化程度低,对水泥石-集料早期粘结强度不利,但28d后其粘结强度就能赶上并超过其它试样。     

现浇大体积混凝土的裂缝控制技术

高层建筑基础大体积混凝土施工,一般使用低水化热的矿渣水泥,而本工程因混凝土设计标号高,必须使用高水化热的普通硅酸盐水泥．在本文,合理选用原材料,用ＵＥＡ外加剂代替相应水泥用量并调整配合比,对混凝土温度进行了估算,根据工程实际合理设置后浇带,不仅实现了温度控制的目标,也解决了高标号大体积混凝土使用普通硅酸盐水泥的裂缝控制技术问题．     

Effect of Fine Steel Slag Powder on the Early Hydration Process of Portland Cement

1 IntroductionSteel slag is the waste residue of fluxing mineralsused in the process of steel producing. Its dischargeamount is about 10 % of the production of steel . Steelslag hasn’t been utilized widely and effectively in a longperiod of time[1]. Hundreds of million tons of steel slagare deposited,andthe amount is still increasing withtensof milliontons every year .The deposited steel slag occu-pies great amounts of farmlands and induces serious en-vironment problems . The main chemical c…     

Pozzolanic Activity of Burned Coal Gangue and Its Effects on Structure of Cement Mortar

The pozzolanic activity of coal gangue burned at different burning temperatures was investigated. The burned coal gangue was mixed with portland cement in different proportions （ 20% - 60% ）. The pozzolanic activity of coal gangue burned and the hydration products were examined, the compressive strengths of the pastes of the mixtures were tested, and the mechanism of the reaction was discussed. The experimental results slum, that the coal gangue burned at 750 ℃ has the optimum pozzolanic activity, and the burned coal ganguc with SiO2 and Al2 O3 is in an active form. When the coal gangue burned at 750℃ is mixed into portland cement, the content of calcium hydroxide in paste is significantly reduced, while the contents of hydrated calcium silk.ate and hydrated calcium aluminate are increased accordingly, hence resulting in the improvement of the microstructure of mortar. The compressive strength of cement paste decreases with increasing the content of burncd coal gangue. The decease in strength is small in the range of 20% - 30% coal gangue substitution and significant in 30%- 60% substitution.     

Durability of alite-calcium barium sulphoaluminate cement

The durability of the cement was mainly studied. Under 1.0 MPa of hydraulic pressure for 8 hours, water could penetrate completely through the sample made by portland cement, but could not penetrate through that by alite-barium sulphoaluminate cement. Under the condition of freezing and thawing cycle, the loss ratio of compressive strength of the cement was only about 17.3% at curing 28 d ages, but the loss of portland cement was as high as 29.5%. Alite-calcium barium sulphoaluminate cement also has an excellent resistance to sulfate attack. The coefficients of resistance to sulfate attack of the cement exceeded 1.0. Meanwhile, the composition and microstructure of the hardened paste of alite-calcium barium sulphoaluminate cement were analyzed by XRD and SEM.     

Properties of supersulphated phosphogysumslag cement (SSC) concrete

Supersulphated phosphogysum-slag cement （SSC） is a newly developed non-burned cementitious material mainly composed of phosphogysum （PG） and ground granulated blast furnace slag （GGBFS）, with small amount of steel slag （SS） and clinker （CL）. SSC is a kind of environmentally-friendly cementitious material due to its energy-saving, low-carbon emission, and waste-utilization. We prepared concretes with supersulphated phosphogysum-slag cement, and studied the mechanical properties, micro- properties and resistance to chloride penetration of concrete in comparison with those of portland slag cement （PSC） and ordinary portland cement （OPC） concrete. The test results show that the compressive strength of SSC concrete can reach 38.6 MPa after 28 d, close to PSC concrete and OPC concrete. Microanalyses indicate that large quantities of ettringite and C-S-H, and little amount of Ca（OH）2 are generated during the hydration of SSC. The dense cement paste structure of SSC is formed by ettringite and C-S-H, surrounded unreacted phosphogysum. The property of resistance to chloride penetration of SSC concrete is better than PSC and OPC concrete due to the fact that SSC can form much more ettringite to solidify more Cl^-.     

Application of X-ray computed tomography in characterization microstructure changes of cement pastes in carbonation process

The microstructure characteristics and meso-defect volume changes of hardened cement paste before and after carbonation were investigated by three-dimensional(3D)X-ray computed tomography(XCT),where three types water-to-cement ratio of 0.53,0.35 and 0.23 were considered.The high-resolution 3D images of microstructure and filtered defects were reconstructed by an XCT VG Studio MAX 2.0 software.The meso-defect volume fractions and size distribution were analyzed based on 3D images through add-on modules of 3D defect analysis.The 3D meso-defects volume fractions before carbonation were 0.79%,0.38% and 0.05% corresponding to w/c ratio=0.53,0.35 and 0.23,respectively.The 3D meso-defects volume fractions after carbonation were 2.44%,0.91% and 0.14% corresponding to w/c ratio=0.53,0.35 and 0.23,respectively.The experimental results suggest that 3D meso-defects volume fractions after carbonation for above three w/c ratio increased significantly.At the same time,meso-cracks distribution of the carbonation shrinkage and gray values changes of the different w/c ratio and carbonation reactions were also investigated.