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Microstructural study of the interfacial transition zone in concrete using backscatter-mode scanning electron microscopy with image analysis.

机译：混凝土的界面过渡区的微观结构研究，采用反向散射模式扫描电子显微镜和图像分析。

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摘要

In order to understand the behavior and to predict the properties and service performance of concrete, one has to first understand its microstructural features.;A number of concrete models are based on the idea of the existence of an interfacial transitional zone (ITZ) around aggregate grains, constituting a third phase with properties different from the aggregate and bulk cement paste phases. Although the ITZ concept has been accepted in concrete technology for many years, the details of differences between the microstructure of the ITZ and the bulk cement paste have not been adequately established.;In this study, the microstructure of concrete was studied using backscatter mode scanning electron microscope coupled with image analysis on polished surfaces. The specific features quantitatively evaluated included (a) pores greater than 0.25 mum, i.e. those detectable at the magnification used; (b) calcium hydroxide; and (c) unhydrated cement particles. The quantitative image analysis provide area fraction measurement of each of these as a function of the distance away from the aggregate surface. In addition, paste area not specifically identified as pore area, calcium hydroxide, or unhydrated cement was recorded separately as area fraction of 'hydrated cement'.;The presumed basis for the development of the ITZ is a local deficiency in cement grains near the aggregate surface. This microstructural effect is valid and shows up strongly in all the concretes examined. However the supposed development of zones of appreciably higher porosity and uniformly higher calcium hydroxide contents in the ITZ around the aggregate grains are not confirmed. It is found that there is only a small statistical excess of porosity near the interface. The local variations in porosity laterally at any given distance around any given aggregate grain are much greater than this modest statistical excess porosity. Calcium hydroxide contents also shows similar lateral variations around grains and also major differences from grain to grain. Some grains have an appreciable portion of their perimeters covered by calcium hydroxide deposits extending through a significant part of the width of the ITZ; adjacent grains may be mostly or entirely free of calcium hydroxide deposits.;Models postulating that ITZs constitute a "third phase" that has significant and uniform excess porosity compared with bulk cement paste do not appear to be well based. Thus, the percolation concept applied on the concrete seems to be misleading.
机译：为了了解混凝土的行为并预测其性能和使用性能，首先必须了解其微观结构特征。;许多混凝土模型都基于围绕骨料存在界面过渡区（ITZ）的思想颗粒，构成第三相，其性质不同于骨料和散装水泥浆相。尽管ITZ概念已经在混凝土技术中被接受了很多年，但ITZ的微观结构与散装水泥浆之间的差异的细节尚未得到充分的确定。；在本研究中，使用反向散射模式扫描研究了混凝土的微观结构。电子显微镜结合对抛光表面的图像分析。定量评估的特定特征包括（a）大于0.25微米的孔，即在放大倍数下可检测到的孔; （b）氢氧化钙； （c）未水合的水泥颗粒。定量图像分析提供了这些区域中每个区域的面积分数测量值，这些区域分数是距骨料表面距离的函数。此外，未明确标识为孔面积，氢氧化钙或未水合水泥的浆糊面积被单独记录为``水合水泥''的面积分数。; ITZ发展的推测基础是集料附近水泥颗粒的局部缺乏表面。这种微观结构效果是有效的，并且在所有检查的混凝土中都表现出强烈的效果。然而，未证实在聚集体晶粒周围的ITZ中孔隙率明显较高且氢氧化钙含量均较高的区域的发展。发现在界面附近仅有很小的统计孔隙率过剩。在任何给定的聚集晶粒周围任何给定距离处，孔隙度的侧向局部变化远大于这种适度的统计过剩孔隙度。氢氧化钙的含量在晶粒周围也表现出相似的横向变化，并且晶粒之间也存在较大差异。一些晶粒的周边有明显的一部分被氢氧化钙沉积物覆盖，该沉积物延伸穿过ITZ宽度的很大一部分。相邻的晶粒可能大部分或完全没有氢氧化钙沉积物。模型假定ITZ构成了一个“第三相”，与散装水泥浆相比，它具有明显且均匀的过剩孔隙率，但似乎并没有很好的依据。因此，应用于混凝土的渗滤概念似乎具有误导性。

著录项

  • 作者

    Huang, Jingdong.;

  • 作者单位

    Purdue University.;

  • 授予单位 Purdue University.;
  • 学科 Engineering Civil.;Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 1998
  • 页码 317 p.
  • 总页数 317
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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