Correlation between Physical-mineralogical Properties and Weathering Resistance Using Characterisation Case Studies in Historic Indian Bricks

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.