再生混凝土单轴受压下多重界面过渡区的破坏机理研究

为研究再生粗骨料混凝土在单轴受压荷载下的破坏特性,使用数字图像相关技术记录混凝土立方体在破坏过程中的应变变化规律,并结合显微硬度测试、背散射电子成像技术等观测手段对界面过渡区的宽度和孔隙率进行定量表征。试验结果表明,分别经骨料强化和砂浆强化后,再生混凝土的抗压强度较未处理试样提升了17.86%和35.55%,说明砂浆强化更有利于提升再生混凝土的抗压强度。骨料强化可以提升老砂浆显微硬度值,降低老骨料-老砂浆界面过渡区孔隙率;砂浆强化可以提升新砂浆显微硬度值,降低老骨料-新砂浆界面过渡区以及新-老砂浆界面过渡区的孔隙率。经强化处理后的特定界面产生贯通裂缝的概率降低。     

基于粒形分析的再生细骨料颗粒特性和制备砂浆性能研究

运用数字图像技术分析再生细骨料的颗粒形貌参数,以此为基础对再生细骨料的堆积密度、吸水率、压碎值等颗粒特性开展研究,并对再生细骨料制备水泥砂浆的工作性能和力学性能进行了分析。实验结果表明,再生细骨料与同级配的标准砂和天然河砂相比,钝度、长宽比、坚固度和球度等指标均相对较低,压碎值和吸水率显著增加;使用再生细骨料制备水泥砂浆时,质量替代量达到30%时流动度明显下降,质量替代量达到40%时抗压强度和峰值应力显著下降。     

Assessment of recycling process induced damage sensitivity of recycled concrete aggregates

This paper evaluates the complex nature of recycled concrete aggregates that are susceptible to damage due to recycling. The study was carried out by microstructural assessment techniques beyond the standard testing methods normally specified for aggregates. The laboratory produced recycled concrete aggregates were investigated using fluorescent microscopy and image analysis. Contrary to common opinion, microstructural studies showed that adhered mortar (AM) is not always the primary parameter determining the quality of the recycled coarse aggregate. Sandstone coarse aggregate originally had defects in the form of voids and cracks. Further processing of the recycled coarse aggregate changed the microstructural profile of the material and enhanced their properties. The unusual results of the performance tests carried out on the recycled aggregate concretes could be explained with the findings of microscopic level investigations.     

Use of limestone obtained from waste of the mussel cannery industry for the production of mortars

Various types of cement−SiO₂−CaCO₃ mortar were prepared by replacing quarry limestone aggregate with limestone obtained as a by-product from waste of the mussel cannery industry. The CaCO₃ aggregate consists mainly of elongated prismatic particles less than 4 μm long rather than of the rounded particles of smaller size (2-6 μm) obtained with quarry limestone. The mechanical and structural properties of the mortars were found to be influenced by aggregate morphology. Setting of the different types of mortar after variable curing times was evaluated by scanning electron microscopy (SEM), thermogravimetric analysis (TG) and mercury intrusion porosimetry (MIP) techniques. Mortars with a high content in mussel shell limestone exhibited a more packed microstructure, which facilitates setting of cement and results in improved mortar strength. The enhanced mechanical properties of the new mortars allow the cement content in the final mortar composition to be decreased and production costs to be reduced as a result.     

基于单纯重心型设计法的再生骨料砂浆 配合比设计

再生骨料干拌砂浆是一种绿色新型建筑材料，既解决建筑垃圾的利用问题，又减轻了建筑原材料的过度开采，降低碳排放，是材料工业可持续发展的必然趋势。本文采用单纯重心型设计法对再生骨料掺量、水灰比和水泥用量三个因素进行研究以优化再生骨料干拌砂浆的配合比，以稠度、2 h稠度损失率和抗压强度作为关键的性能评价指标。结果表明，单纯重心型设计法可用于优化再生骨料砂浆的配合比。在优化的配合比下，再生骨料砂浆的稠度、2 h稠度损失率和强度之间可以达到很好的平衡。     

Use of building rubbles as recycled aggregates

The application of building rubble collected from damaged and demolished structures is an important issue in every country. After crushing and screening, this material could serve as recycled aggregate in concrete. A series of experiments using recycled aggregate of various compositions from building rubble was conducted. The test results show that the building rubble could be transformed into useful recycled aggregate through proper processing. Using unwashed recycled aggregate in concrete will affect its strength. The effect will be more obvious at lower water/cement ratios. When the recycled aggregate was washed, these negative effects were greatly improved. This is especially true for the flexural strength of the recycled concrete. The recycled coarse aggregate is the weakest phase at a low water/cement ratio. This effect will dominate the strength of recycled concrete. This mechanism does not occur in recycled mortar. The quantity of recycled fine aggregate will govern the mortar strength.     

再生砖混粗骨料颗粒的形态表征与分析

本文采用图像处理技术对再生砖混粗骨料的颗粒形态进行了表征,计算并分析了各组分的高宽比、圆整度和紧凑系数等特征参数的分布情况。试验结果表明,通过颜色分析可以准确识别骨料材质,基于识别结果求得的骨料颗粒的高宽比、圆整度和紧凑系数具有相似的分布规律。砖、石、木和陶瓷4种组分中,砖和石占比较大,其特征参数也相差较小,针状颗粒少,圆整度好,而木骨料则多为针状颗粒,高宽比较大,陶瓷则由于具有较高的强度,其面积和周长相较于其余骨料最大。此外,砖、石骨料不同等效直径的级配分布基本成正态分布,能够混合形成一种级配良好的骨料。研究成果有助于揭示再生砖混粗骨料的颗粒形态特点,推动再生砖混粗骨料的研究和应用。     

化学溶液预处理再生粗骨料对再生混凝土改性的影响

为研究不同浓度的硅酸钠溶液和硅烷溶液复合改性再生粗骨料对再生混凝土力学与变形性能及微观结构的影响,通过立方体抗压强度试验研究复合改性对再生混凝土力学性能的影响,同时基于数字图像相关(DIC)方法研究复合改性对再生混凝土变形性能的影响,并借助扫描电子显微镜(SEM)和能谱仪(EDS)微观测试方法分析改性再生混凝土内部微观结构。结果表明:质量分数为5%的硅酸钠溶液和质量分数为10%的硅烷溶液改性后的再生粗骨料24 h吸水率降幅最大,由其制成的再生混凝土28 d抗压强度显著提高,较未改性再生混凝土提高了35.80%;硅酸钠溶液和硅烷溶液复合改性再生粗骨料可有效减小再生混凝土的变形,应力较大时,可阻止应力过度集中,使再生混凝土整体变形性能较好;此外,还可以改善再生粗骨料表面疏松结构和粗糙程度,加强骨料与砂浆界面过渡区(ITZ)性能,但对于新、旧砂浆ITZ性能的改善不明显。     

基于图像颜色特征的涂层老化失效检测方法

结合数字图像技术和色度学相关原理,针对腐蚀过程涂层表面出现的色彩变化,建立了基于颜色特征的涂层材料腐蚀性能检测方法。利用建立的腐蚀形貌采集系统,对现场暴露不同时期的涂层试片进行采集。采用HSV颜色空间对腐蚀试样表面的变色程度进行描述,提出颜色特征参数CP,实现对涂层腐蚀试样外观变色的计算机判别,为材料的腐蚀特征检测提供了新的方法。     

Measurements and modeling of cement base materials deformation at early age: The case of sulfo-aluminous cement

Early-age volume variations of self-leveling mortar of sulfo-aluminous cement base are evaluated in an endogenous configuration and during the drying process. Two displacement measuring techniques are used: a classical method using displacement sensors and a more original one using digital 3-D image correlation. The latter technique reveals itself to be very useful in measuring shrinkage and swelling as soon as the screed is poured. An advanced hydromechanical modelization confirms on the one hand the amplitude of the deformations measured by digital 3-D image correlation and underlines on the other the importance of Young's modulus concerning this amplitude.     

Characterising aggregate surface geometry in thin-sections of mortar and concrete

Measurement of microstructural gradients at the aggregate/cement paste interfacial transition zone (ITZ) in hardened mortar and concrete is commonly performed via quantitative image analysis of multiple micrographs of specimen surfaces, using a scanning electron microscope. However, due to the random orientation of interfaces sectioned by the specimen surface, measurements of the microstructural gradients at the interface have an unknown angular component, and thus have an unknown error. We present a method for the identification of interfaces that are perpendicular to the specimen surface, and therefore, are more suitable for accurate ITZ analysis. This method employs simple optical and electron imaging techniques on petrographic thin-sections. Use of 3D laser scanning confocal microscopy helped to validate the method. Quantitative 2D image analysis of backscattered electron micrographs, captured over three angular classes of interface gives an indication of this error in the determination of interfacial porosity and anhydrous cement content.     

Influence of lightweight aggregate on the microstructure and durability of mortar

The results of an investigation on the effect of dry and prewetted lightweight aggregates on the microstructure and durability of mortar are presented in this paper. The results are compared with those obtained for normal aggregate mortar. There appears to be only a small difference in the microstructure of the interfacial transition zone (ITZ) between dry and prewetted lightweight aggregate mortars. The porous ITZ surrounding lightweight aggregate appears to extend for about 10 and 15 μm from the aggregate surface for dry and prewetted lightweight aggregates, respectively. The ITZ for dry and prewetted lightweight aggregates seems to be surrounded by dense paste that extends from 10 to about 50 μm from the aggregate surface. This dense paste has lower porosity than that observed in the bulk paste located 50 μm and farther from aggregate surface. The normal aggregate mortar prepared with the same water/cement ratio appears to have porous ITZ that extends beyond 35 μm from the aggregate surface. The dry and prewetted lightweight aggregate mortars seem to have a lower sorptivity and electrical conductivity than does the normal aggregate mortar. Lightweight aggregate mortars also appear to have excellent resistance to sulfate attack as compared with normal aggregate mortar.     

Microscopy of historic mortars—a review

Mortars with mud, gypsum and lime as binder have, since ancient times, been used for very different applications. The characterisation of these historic mortars was until 1970-1980 mostly based on traditional wet chemical analyses but the interpretation of these results is difficult and often impossible without a good knowledge of the nature of the different mortar components. More recently developed mortar characterisation schemes have optical microscopy as a first step in identifying the aggregates, of the various mineral additions (latent hydraulic), binder type, binder-related particles and in describing the pore structure. Optical microscopy is also a valuable aid for damage diagnosis of degraded historic mortars and for the study of the interfacial zone, the bonding and possible reaction rims between aggregates, bricks or stone and the mortar. Automated image analysis techniques or manual point-count/linear traverse methods can be used to determine mix proportions, binder/aggregate ratio, aggregate size distribution and air void system.     

再生粗骨料附着砂浆含量对再生混凝土抗冻耐久性的影响

选取五种不同附着砂浆含量的商用再生粗骨料在全取代天然粗骨料条件下制备C40再生混凝土,探讨了30%极限拉应力水平下,再生粗骨料附着砂浆含量对再生混凝土抗冻耐久性的影响规律,通过数学拟合确定了基于相对动弹性模量和抗冻耐久性指数要求的砂浆界限含量。结果表明:冻融循环后,再生混凝土抗压强度损失率与附着砂浆含量存在较强线性关系;再生混凝土质量损失率、相对动弹性模量、抗冻耐久性指数均与再生粗骨料附着砂浆含量呈二次函数关系;以冻融循环300次后再生混凝土相对动弹性模量降至60%为限值,获得对应的砂浆界限含量为49.52%(质量分数);以不同设计使用年限及不同冻融工况所规定的抗冻耐久性指数作为界定条件,得到了再生混凝土在拉应力条件下满足相应抗冻耐久性指数的砂浆界限含量。最后,通过搜集文献数据验证了本研究结果的合理性。     

高炉干渣的特性及配制水泥干粉砂浆的性能研究

介绍了高炉干渣的基本性能和将其作为细集料用于干粉砂浆的试验结果。实验表明：干渣细集料性能稳定,物理力学指标符合建筑砂的要求,可大掺代砂配制水泥干粉砂浆,在合理的集料级配下．干渣砂浆的工作性与普通砂浆相当。且砂浆强度达到甚至高于普通砂配制的干粉砂浆.     

Comparison of experimental techniques used in lipid crystallization studies

Four methods were used to monitor the crystallization behavior of anhydrous milk fat (AMF), milk fat triacylglycerols (MF-TAG), and MF-TAG plus diacylglycerols (MF-DAG). The crystallization process was monitored by measuring the solid fat content, turbidity, and scattering intensity of the crystallizing material, as well as by imaging using polarized light microscopy combined with digital image processing. In general, induction times followed the order MF-DAG>AMF>MF-TAG for all techniques. However, the absolute value for the induction times differed substantially; on average 3 min by microscopy, 7 min by light-scattering spectroscopy, 13 min by turbidimetry, and 25 min by pulsed nuclear magnetic resonance. Microscopic imaging coupled to image processing proved to be the most sensitive method, suitable for the study of early events in the crystallization of fats.     

Effects of externally supplied lithium on the suppression of ASR expansion in mortars

Lithium salts are being externally supplied for mitigating the progress of deterioration of ASR-affected concrete structures. However, it is not clear whether the sodium or potassium in the ASR gel in concrete is replaced by the lithium supplied from the outside. In this article, we examine changes in the composition of the ASR gel, previously formed in mortar specimens, after they are immersed in LiOH solution, using backscattered electron (BSE) imaging and energy-dispersive X-ray (EDX) analysis, associated with length change measurement of the mortar prisms. The intrusion of lithium ions into mortar specimens containing a reactive aggregate could arrest their further expansion within a relatively short time after immersion in 0.50 N LiOH solution. The alkali ions incorporated in most ASR gels, located not far away from interfaces between the cement paste and reactive aggregate particles, appear to be replaced by the lithium ions supplied from the solution. However, the ASR gel within the reacted aggregate particles did not appear to have been affected by the lithium ions.     

煤炭港航交重智能计量系统研究

根据现代化港口管理对煤炭交重智能化计量的需要,设计实现了一套以船舶水尺图像采集和识别为核心的港航交重计量系统,给出了系统的设计思想和软硬件构成,且针对关键技术问题进行了详细研究。该计量系统以数码单反相机代替传统人眼观察进行水尺图像采集,并结合使用电子水平尺获取船舶的姿态信息,进而通过融合形态学及BP神经网络的图像识别算法对吃水深度进行判别,并求取多幅图像分析结果平均值来降低风浪造成的影响。同时系统中还利用构建于远程服务器端的数据库管理程序对全部测量和分析过程进行记录,使得事后对测量结果进行追溯成为可能。     

Assessment of the elastic moduli of cement paste and mortar phases in concrete from pulse velocity tests

This paper describes a method for estimating the elastic moduli of the cement paste, mortar and ‘coarse aggregate-paste mixture’ phases in concrete. It is concluded that the elastic moduli of these phases can be predicted without recourse to tests on neat mortar and cement paste mixes. The elastic modulus of a mortar phase in concrete can be significantly different from that of a ‘neat mortar’ having the same mix proportions. Factors such as age, mix proportions and aggregate types, influence the elastic moduli of the different phases.     

基于细观尺度的再生混凝土性能研究综述

基于当前国内外学者对再生混凝土性能试验的结果,研究骨料、砂浆、界面过渡区等细观参数对再生混凝土宏观性能影响.在骨料方面,骨料分布的均匀程度高、颗粒级配较好、大中型骨料颗粒数越多的再生混凝土在抗拉、抗压、抗折强度及弹性模量等方面都会有所提高;在砂浆方面,随着新、老砂浆的强度提高,再生混凝土力学性能更好,老砂浆厚度越高,再生混凝土内部氯离子浓度越大;在界面过渡区方面,随着新、老界面过渡区弹性模量的提高,再生混凝土的性能表现地越好,界面过渡区厚度越大,氯离子扩散系数越大.