水泥混凝土浆体-集料界面过渡区结构与性能试验技术

水泥混凝土浆体—集料界面过渡区结构与性能影响混凝土的整体性能,其试验技术的合理采用关系到对其结构与性能的正确测试与评价.针对水泥混凝土浆体—集料界面过渡区结构与性能特点及其对混凝土整体性能影响,论述了当前国内外有关其研究的试验技术.界面过渡区结构试验技术包括宏观技术、微观技术和模拟技术;性能试验技术集中于力学性能和耐久性能两方面;而界面过渡区力学性能和耐久性能试验技术亦是当前界面过渡区对混凝土性能影响试验技术的焦点;最后指出当前试验技术存在的问题,提出新试验技术发展的重点.     

再生集料混凝土的微观结构特征

研究了两种不同类型的再生混凝土集料(RC集料)和一种花岗岩集料配制的混凝土的微观结构特征，尤其是集料和水泥浆体之间的界面过渡区的某些结构细节。结果表明，界面过渡区的微观结构特征与集料的密实程度有关，过于密实(天然集料)和过于疏松(低标号混凝土)的集料可引起界面区的多孔性或聚集粗大颗粒的水化产物，而适中密实程度的集料可形成较为密实的界面区。     

抛填骨料路面混凝土的研究

通过在路面混凝土中抛填一定量的粗集料,制成粗集料嵌锁型路面混凝土,并对其力学性能以及界面过渡区的显微硬度分布进行了研究。结果表明:抛填粗集料后,路面混凝土的7 d和28 d抗折强度有所提高,7 d和28 d抗压强度有显著提高,粗集料抛填量为8%～10%时强度达到最大值;掺粉煤灰的混凝土抛填骨料后强度有明显增加;抛填骨料路面混凝土的收缩率显著降低,弹性模量有所提高,显微硬度测试表明抛填骨料表面的界面过渡区比普通集料窄,且显微硬度更高。由此可见抛填干燥的骨料会吸收浆体水分,增强界面过渡区,有利于提高混凝土的性能。     

硅灰裹石对水泥混凝土抗硫酸盐侵蚀性能的影响

使用测长法研究了硅灰裹石对混凝土试样抗硫酸盐侵蚀性能的影响,揭示了渗透性在混凝土硫酸盐侵蚀中的作用。研究结果表明：混凝土中水泥浆体与集料之间的界面过渡区是硫酸盐侵蚀的薄弱区域;集料含量增加,即界面区含量愈多,试样的抗硫酸盐侵蚀性能愈差。采用硅灰裹石处理集料可以大幅度地提高混凝土试样的抗硫酸盐侵蚀能力。     

负载纳米TiO2石英砂功能集料-水泥石的界面粘结性能

光催化水泥基材料是先进建筑功能材料的研究热点之一,但传统内掺法制备的TiO₂-水泥基复合材料中TiO₂有效利用率低、经济效益差。针对此问题,采用负载法制备纳米TiO₂功能集料（QST）,并将QST集料负载于普通水泥砂浆表面。研究QST集料对水泥砂浆干缩性能的影响,通过拉拔法测试QST集料与水泥石的界面粘结力;采用SEM、EDS、MIP等微观测试方法,研究纳米TiO₂对集料-水泥石界面过渡区水化产物、孔结构的影响。结果表明：与普通石英砂集料相比,表面负载纳米TiO₂的石英砂功能集料可减少水泥砂浆的干缩,提高集料-水泥石的界面粘结力。在QST集料-水泥石的界面过渡区,纳米TiO₂促进了水泥浆体的水化,减少了界面过渡区Ca(OH)₂的富集,细化并改善了界面过渡区的孔结构。     

考虑界面过渡区及集料因素的水泥基材料碳化模型

集料和界面过渡区对水泥基材料抗碳化性能有显著影响。基于Fick第二定律，提出一种考虑集料和界面过渡区影响的CO₂扩散模型，模型中首次引入界面过渡区的扩散系数并给出相应参数的计算方法，并基于质量守恒定律给出CO₂反应模型，利用该模型研究荷载作用下C30和C50混凝土中CO₂的浓度分布。结果表明，考虑集料和界面过渡区影响能更准确地计算CO₂在水泥基材料中的扩散系数及碳化深度值。通过与文献中的试验数据进行比较，进一步验证了理论模型的可靠性。模型将集料和界面过渡区作为评价混凝土耐久性的重要因素，为钢筋混凝土结构的设计和寿命预测提供依据。     

超低离子渗透性水泥基材料的性能与微观结构

采用显微硬度、MIP、SEM—EDXA研究了超低离子渗透性水泥基材料（Ultra Low Ion Permeability Cementitious Materials,简称ULIPCM）的微观结构,同时研究了UI。IPCM的宏观性能。结果表明：ULIPCM的28d抗压强度≥80MPa,抗折强度≥11．0MPa,弹性模量在38．0～42．0GPa之间;Cl^-扩散系数≤0．8×10^-13m^2·s^-1,6h导电量≤300C;抗硫酸盐侵蚀性能较好;28d收缩值可控制在400×10“以内。UI．IPCM的集料与水泥石界面过渡区的微观结构和性能得到了显著改善,有利于提高其力学性能和抗渗性能。ULIPCM的集料与水泥石界面过渡区由普通混凝土的60～100μm细化为30μm以下,有效阻断了侵蚀性介质的渗入通道;ULIPCM的孔隙率、最可几孔径等孔结构参数均得到了优化,显著改善了其孔结构;ULIPCM的集料与水泥石界面过渡区中的CH晶体较少,且CH晶体的取向性差。     

再生细骨料及其混凝土的微观结构特征

采用扫描电镜、能谱分析、X射线衍射、显微硬度和氮吸附等微观测试方法研究了再生细骨料及其混凝土的微观结构特征.研究结果表明:再生细骨料是一种组成复杂的、具有一定水化活性的和高渗透性的人造骨料,其主要矿物相为SiO2、CaCO3以及少量的C2S.再生细骨料混凝土内部水泥石孔隙较多,结构密实性较差,同时其与再生细骨料间存在较为明显的界面过渡区,该界面过渡区宽度较大,且界面过渡区两侧的骨料和水泥石的显微硬度均较低.再生细骨料的多孔结构,以及再生细骨料混凝土内部水泥石和界面过渡区微观结构缺陷是导致其大孔增多的主要原因,大孔的增多会对混凝土抗渗性产生不利影响.     

地下工程混凝土的梯度功能设计与性能研究

为了解决地下工程混凝土的耐久性技术难题,在地下工程混凝土的结构设计中引入梯度功能设计思路．采用Cl-离子扩散法检测功能梯度混凝土的抗渗性能,采用收缩试验评价其收缩变形一致性,采用显微硬度计、SEM测试其微观性能．结果表明,与单一的高性能混凝土相比,功能梯度混凝土的抗渗性能明显提高,特别是其抗离子渗透性,Cl-扩散系数DNEL下降了1～2个数量级,表观Cl^-扩散系数Da下降了50％左右;功能梯度混凝土的收缩变形匹配良好;适用于地下工程结构混凝土保护层的无细观界面过渡区水泥基材料的集料与水泥石界面过渡区由传统混凝土的60～100pm细化为30pm以下,从而有效地阻断了侵蚀性介质的渗入通道．     

水泥混凝土浆体 集料界面区结构与性能

混凝土浆体-集料界面区结构与性能影响混凝土的整体性能,是混凝土材料研究的热点之一。针对水泥混凝土浆体-集料界面区结构与性能特点,从混凝土界面区结构、性能、研究手段、改善方法及其对水泥混凝土性能影响等方面,综述了国内外水泥混凝土浆体-集料界面区结构与性能研究进展。总结了界面区结构特征与性能影响因素及微观和宏观两种界面区研究手段,分析界面区结构与性能差异原因及对混凝土整体性能影响程度,概括了矿渣粉和偶联剂等无机和有机两类界面区结构与性能改善方法,最后,提出混凝土界面区结构与性能研究重点和方向。     

Quantitative characterization and elastic properties of interfacial transition zone around coarse aggregate in concrete

Backscattered electron images (BSE) obtained by scanning electron microscope was used to quantitatively characterize the microstructure of interfacial transition zone (ITZ) in concrete. Influences of aggregate size (5, 10, 20, and 30 mm), water to cement ratio (0.23, 0.35 and 0.53) and curing time (from 3d to 90d) on the microstructure of interfacial transition zone between coarse aggregate and bulk cement matrix were investigated. The volume percentage of detectable porosity and unhydrated cement in ITZ was quantitatively analyzed and compared with that in the matrix of various concretes. Nanoindentation technology was applied to obtain the elastic properties of ITZ and matrix, and the elastic modulus of concrete was then calculated based on the Lu & Torquato model and self-consistence scheme by using the ITZ thickness and elastic modulus obtained from this investigation. The experimental results demonstrated that the microstructure and thickness of ITZ in concrete vary with a variety of factors, like aggregate size, water to cement ratio and curing time. The relative low elastic properties of ITZ should be paid attention to, especially for early age concrete.     

Mechanical Properties and ITZ Microstructure of Recycled Aggregate Concrete Using Carbonated Recycled Coarse Aggregate

The effect of carbonation treatment and mixing method on the mechanical properties and interfacial transition zone (ITZ) properties of recycled aggregate concrete (RAC) was investigated. Properties of recycled concrete aggregate (RCA) were tested firstly. Then, five types of concretes were made and slump of fresh concrete was measured immediately after mixing. Compressive strength and splitting tensile strength of hardened concrete were measured at 28 d. Meanwhile, the microstructure of RAC was analyzed by backscattered electron (BSE) image. It was found that the water absorption ratio of carbonated recycled concrete aggregate (CRCA) was much lower when compared to the untreated RCA. Comparatively, the apparent density of CRCA was not significantly modified. The concrete strength results indicate that the mix CRAC-2 prepared with CRCA by adopting two-stage mixing approach shows the highest compressive strength value compared to the other mixes. The microstructural analysis demonstrate that the mix CRAC-2 has a much denser old ITZ than the untreated RAC because of the chemical reaction between CO₂ and the hydration products of RCA. This study confirms that the ITZ microstructure of RAC can be efficiently modified by carbonation treatment of RCA and encourages broadening the application of construction and demolition wastes.     

Test method to simulate the influence of the interface on the concrete carbonation process

A trial test method is introduced to form and magnify regular interface. Through researching on the carbonation of the magnifying interfacial transition zone (ITZ), the practical carbonation of the concrete can be simulated. Because the diffusion rate of CO₂ in the ITZ is several times greater than that in the bulk paste, the diffusion rate and direction of CO₂ will change and form a new carbonation front line. An interfacial effect zone caused by the ITZ will change the distribution of the complete carbonation zone and the partial carbonation zone. One of the important reasons for the formation of the partial carbonation zone was the existence of the interfacial effect zone. Consequently, the method mentioned in this paper provides a new way for researching on the microstructure of the cement based materials during the carbonation process.     

Investigation of the Interfacial Transition Zone between Aggregate-Cement Paste by AC Impedance Spectroscopy

Three different types and sizes of coarse aggregate were chosen,and the alternating current(AC) impedance of cement paste samples with and without aggregate was measured at different curing ages.Based on Song's equivalent circuit model,the electrical properties from the AC impedance results were obtained,and the resistance of connected pores RCCP was used to characterize the microstructure of the interfacial transition zone(ITZ).The results show that the RCCP of concrete sample with aggregate is lower than that of cement paste sample,which indicates that the introduction of aggregate in cement paste makes the ITZ porous.Furthermore,for the same type of aggregate,an increase in particle size leads to a more porous ITZ,which accounts for the "water effect" and a larger aggregate would accumulate a thicker water film around it.In addition,for the same size of aggregate,the physical interaction between aggregate and cement paste is dominant in early age,and the microstructure of the ITZ around limestone aggregate is denser,which mainly depends on its rough surface and high water absorption.However,the microstructures of the ITZ around granite and basalt aggregates are denser in later age,which may be due to their higher chemical activity,and the chemical interaction between them and cement paste resulting in the generation of more hydrates.AC impedance spectroscopy thus proves to be powerful for evaluation of the microstructure of the ITZ.     

老混凝土中骨料-水泥界面过渡区(ITZ)(Ⅰ)——元素与化合物在ITZ的富集现象

利用扫描电子显微镜（SEM）、电子探针（EPXM）和电子能谱（EDXA）对骨料颗粒和水泥浆体界面过渡区（ITZ）进行了研究，研究的重点是老混凝土中骨料－水泥界面过渡区的微观结构特征和成份分布，结果表明，老混凝土由于在成熟度高，其ITZ中水化物十分丰富，密实度高。ITZ内部和外部的水化产物组成存在一定的差别，表现在Ca,K和Fe等元素富集于ITZ，而Si元素在此区域的含量相对较低，对于特定的元素或物质在ITZ中的富集现象的研究，有助于提高对混凝土材料稳定性的认识。     

超细矿粉对混凝土界面区硫酸盐腐蚀的影响

为了研究骨料与水泥石界面区(ITZ)的组成及结构对混凝土抗硫酸盐腐蚀性能的影响,利用紫外分光光度计绘制了硫酸钠溶液浸泡混凝土试样的SO2-4浸入浓度/深度曲线,并辅以扫描电镜(SEM)和电子探针能谱(EDS)等对ITZ进行观测;同时利用XRD定量分析研究了混凝土本体相和界面相的水化产物富集的差异.结果表明:Ca(OH)2、钙矾石(AFt)等晶体富集于硫酸钠溶液浸泡后试样的ITZ,引起AFt二次结晶型的硫酸盐腐蚀破坏.在适量石膏的激发下,掺入超细矿粉(GGBS)可阻止AFt转变成单硫型水化硫铝酸钙(AFm),减少AFt二次结晶的生成,明显提高抗硫酸盐侵蚀能力,试样的同深度硫酸根浓度最低,抗硫酸盐侵蚀性能最好.     

Polymer-modified concrete with improved flexural toughness and mechanism analysis

By selecting different types of polymer mixing into concrete, the toughness of concrete is investigated, and results indicate polymer has obvious effect to improve the toughness of concrete. Microstructure of polymer-modified concrete were studied through environment scanning electron microscope and digital micro-hardness tester, results show that polymer acts as a flexible filler and reinforcement in concrete, and alters the microstructure at mortar and ITZ. By crack path prediction and energy consumption analysis, the crack path of polymer-modified concrete is more tortuous and consumes more energy than that of ordinary concrete.     

水泥基复合材料界面过渡区体积分数的定量计算

为了计算水泥基复合材料的界面过渡区体积分数,采用最邻近表面分布函数和骨料比表面积2种方法,结合实际骨料的筛分曲线,给出了界面过渡区体积分数定量关系式．结果表明：单位体积水泥基复合材料中,当骨料的体积分数〈0．5,界面厚度〈50μm时,2种方法计算的误差约为10％;界面区厚度越小,2种方法计算的误差也越小．     

The chloride permeability of persulphated phosphogypsum-slag cement concrete

The chloride permeability and microstructure of persulphated phosphogypsum-slag cement concrete (PPSCC), the Portland slag cement concrete (PSCC) and ordinary Portland cement concrete (OPCC) were investigated comparatively. Some test methods were used to evaluate the chloride permeability and explain the relationship between the permeability and microstructure of concrete. The results show that the resistance to chloride penetration in PPSCC is significantly better than that in OPCC, the reasons are as follows: 1) the slag in PPSCC is activated by clinker (alkali activation) and phosphogypsum (sulfate activation), forming more low Ca/Si C-S-H gel and gel pores below 10 nm than OPCC, improving the resistance to chloride penetration; 2) the hydration products of PPSCC have a much stronger binding capacity for chloride ions; and 3) in the same mix proportion, PPSCC has a better workability without large crystals calcium hydroxide in the hydration products, the interfacial transition zone (ITZ) is smoother and denser, which can cut off the communicating pores between the pastes and aggregates.