ABSTRACT

This paper correlates the durability of bricks in various environments to their physical and microstructural characteristics. Micro-analytical and physical characterisation techniques were employed to find the raw materials and firing temperature of the historic bricks. Mercury Intrusion Porosimetry (MIP) and Scanning Electron Microscopy (SEM) helped in finding the effects at microstructure level with the variation of raw materials/firing temperature. The results showed that historic bricks fired at high temperature and made with non-calcium clays possessed superior physical characteristics and survived several centuries without any significant weathering. Also, differences in the state of conservation of the bricks were examined in cases where similar bricks were exposed to different conditions. The calcium-rich bricks fired at low temperature had a poorer degree of vitrification, but the weathering resistance again varied with respect to exposure conditions. Such bricks were found severely deteriorated when exposed to salt, and the extent of damage and damage patterns were also dependent on the kind of salt. Poorly fired bricks, which were not exposed to much salt, were found with minor external weathering traces such as powdering of edges. MIP results showed that the cores of bricks remained unaffected in spite of the external powdering. It could be generalised that poorly vitrified structure with a large number of small pores is more susceptible to salt crystallisation. Understanding the micro-characteristics of historic bricks helps in tracing back the manufacturing factors, which are indeed important in deciding on efficient replacement/protective treatments for the structure.

摘要

本文将砖在各种环境中的耐久性与其物理和微观结构特征相关联。采用微观分析和物理表征技术来确定历史砖的原材料和烧制温度。压汞法 (MIP) 和扫描电子显微镜 (SEM) 有助于发现微观结构水平随原材料/烧制温度变化的影响。结果表明，历史悠久的砖在高温下烧制并由非钙粘土制成，具有优越的物理特性，并且在没有任何明显风化的情况下存活了几个世纪。此外，在类似砖块暴露在不同条件下的情况下，研究了砖块保存状态的差异。低温烧制的富钙砖的玻璃化程度较差，但耐候性再次随暴露条件而变化。这种砖在暴露于盐时会严重损坏，损坏程度和损坏模式也取决于盐的种类。未暴露于太多盐的烧制不良的砖被发现有轻微的外部风化痕迹，例如边缘粉末化。MIP 结果表明，尽管外部粉化，砖的核心仍然不受影响。可以概括，具有大量小孔的不良玻璃化结构更容易受到盐结晶的影响。了解历史砖的微观特征有助于追溯制造因素，