Approximate migration coefficient of interfacial transition zone and the effect of aggregate content on the migration coefficient of mortar

In this study, the electrochemical technique is applied to accelerate chloride ion migration in mortar to estimate its transport properties. In order to investigate the effect of aggregate content on the chloride migration coefficient of mortar, specimens with different fine aggregate volume fractions were cast and tested. The chloride migration coefficient of mortar was determined experimentally as a function of the volume fraction of aggregate. The chloride migration coefficient of mortar is used to assess the dilution, tortuosity and interfacial transition zone (ITZ) effects of aggregate in the cement-based composites. A model modified from the Bruggeman theory for the migration coefficient of mortar is used, and the regression analysis is used to determine the approximate chloride migration coefficient of ITZ. Based on the experimental and regression analytical results, the approximate ITZ migration coefficient is 2.83, 1.76 and 1.55 times of the matrix migration coefficient for the ITZ with the thickness of 20, 40 and 50 μm, respectively.     

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.     

细骨料品种对外掺MgO砂浆膨胀性能的影响研究

 为了阐明骨料岩性对MgO混凝土膨胀特性的影响规律及作用机理,研究了20,38,60℃水养护温度下不同骨料砂浆的膨胀率,并结合能谱、元素聚类及相分布等微观测试手段深入分析了水泥基体区与细骨料界面过渡区的微结构及元素富集特性。研究结果表明：养护温度从20℃提高至60℃时,砂浆膨胀率增大,且天然砂与辉石闪长岩砂浆的膨胀率最高,其次为灰岩砂浆,玄武岩砂浆最小。38℃水养条件下,辉石闪长岩砂浆和玄武岩砂浆界面区的Ca,Mg元素富集程度高于灰岩与天然砂砂浆,天然砂较高的表面孔隙率和表面含水率有助于吸引更多的MgO迁移至界面区,快速水化形成晶粒尺寸较大、结构较疏松的“外部膨胀水化产物”水镁石;骨料颗粒通过影响界面过渡区的元素富集特性、水化物相类型和形态来影响MgO砂浆的膨胀特性,含有细粉的人工细骨料可以通过改变外掺MgO水泥水化程度和MgO含量来改变MgO砂浆的特性。     

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。     

骨料种类对混凝土孔结构及微观界面的影响

基于RapidAir和MAP-BEI测试技术,对比研究了分别以玄武岩、砂岩和灰岩为人工骨料的大坝混凝土内部孔结构及界面特征.结果表明:配合比一定时,灰岩混凝土气泡数量最多,间距系数和平均孔径最小;砂岩混凝土气泡数量最少,间距系数和平均孔径最大,工程中应予以足够重视.界面Ca(OH)2的富集程度受骨料化学属性及物理性能(如长期吸水率)影响.上述3种骨料-浆体界面Ca(OH)2的富集程度为砂岩玄武岩灰岩,界面过渡区厚度为砂岩灰岩玄武岩,砂岩界面性能最薄弱.     

筛余砂浆气孔结构对其28d抗压强度的影响

为便于高性能混凝土引气剂的开发和应用,采用定量体视学图像分析法测定掺有11种引气剂的混凝土筛余砂浆气孔结构参数,运用灰色关联分析方法研究不同范围孔径对筛余砂浆28d抗压强度的影响,并采用显微硬度仪对筛余砂浆界面过渡区显微硬度进行了测试分析.结果表明：筛余砂浆28d抗压强度与各范围孔径的灰色关联度均为负值,但不同范围孔径对筛余砂浆28d抗压强度的影响有所不同.在筛余砂浆总孔隙率相近条件下,增加10~200μm孔径的孔隙率,降低200~1600μm孔径的孔隙率,可使砂浆气孔的平均孔径减小,砂浆界面过渡区宽度缩短、显微硬度提高,最终减小因引气而造成的砂浆28d抗压强度损失.     

考虑骨料形状效应时混凝土界面面积率的计算

提出了考虑骨料形状效应时混凝土界面面积率的数值算法.通过引入辅助椭圆,构造出八边形骨料.根据模拟所得的骨料分布,应用蒙特卡洛数值方法计算界面面积率.通过数值算法的有效性得到圆形骨料混凝土界面面积率解析解的证实后,定量评价了影响界面面积率的关键因素,发现界面面积率随着界面厚度的增大而增大,但随着最大骨料直径和骨科形状系数的增大而减小,也发现骨料级配对界面面积率有重要影响.     

Microstructural characteristics,porosity and strength development in ceramic-laterized concrete

Interfacial bonding between constituent materials and pore sizes in a concrete matrix are major contributors to enhancing the strength of concrete. In a bid to examine how this phenomenon affects a laterized concrete, this study explored the relationship between the morphological changes, porosity, phase change, compressive, and split tensile strength development in a ceramic-laterized concrete. Varying proportions of ceramic aggregates, sorted from construction and demolition wastes, and lateritic soil were used as substitutes for natural aggregates. Strength properties of the concrete specimens were evaluated after 7, 14, 28 and 91 days curing, but morphological features, using secondary electron mode, were examined only at 7 and 28 days on cured specimens, using Scanning electron microscope (SEM). From all the mixes, selected samples with higher 28 day crushing strength, and the reference mix, were further characterized with more advanced analysis techniques, using the mercury intrusion porosimetry (MIP), thermogravimetric analysis (TGA), X-ray Diffractometer, and SEM (backscatter electron mode-for assessment of the interfacial transition properties between aggregates and paste).The reference mix yielded higher mechanical properties than the concrete containing secondary aggregates, this was traced to be as a result of higher peaks of hydration minerals of the concrete, coupled with its low tortuosity and compactness. However, a laterized concrete mix containing both 90% of ceramic fine and 10% of laterite as fine aggregate provided the optimal strength out of all the modified mixes. Although, the strength reduction was about 9% when compared with the reference case, however, this reduction in strength is acceptable, and does not compromise the use of these alternative aggregates in structural concrete.     

Combined use of waste glass powder and cullet in architectural mortar

The use of 100% waste glass cullet (WGC) as fine aggregates in architectural cement-based mortar had been proven to be feasible in previous works. This paper reports a further study on investigating the influence of using waste glass powder (WGP) as a supplementary cementitious material on the properties of glass-based architectural cement mortars. The experimental results showed a good linear relationship between the particle size of WGP and the flow values of the fresh mortar, revealing that the particle size of WGP played an important role in controlling the workability. For the hydration of white cement, the inclusion of WGP not only affected the second exothermic peak of hydration but also changed the third peak. In particular, the result indicated that the use of finer WGP had an advantage in increasing the flexural strength of the cement mortar when compared with the corresponding compressive strength, which was attributed to the morphological and pozzolanic effect of WGP. In addition, the very fine WGP could act as micro-fibers and micro-aggregates in filling the microstructure of the mortar. At 90 days of curing, the mortar prepared with finer WGP showed a distinct improvement in strength due to the improved interfacial transition zone and the pore-size refinement.     

干燥大温差条件下混凝土界面过渡区的研究

采用显微硬度仪和扫描电镜,对比研究了干燥大温差气候条件和标准养护条件下混凝土界面过渡区的结构和形态.研究表明:干燥大温差环境使混凝土界面过渡区的宽度增加,显微硬度降低,过渡区水化产物结构疏松,孔隙率高,与骨料的粘结减弱,有明显的微裂缝产生.界面过渡区的劣化是造成混凝土宏观,性能下降的内在原因之一.因此,又分析了界面过渡区劣化的原因.