The effect of high temperature minerals and microstructure on the compressive strength of bricks

Abstract

The widely distributed Adıyaman region clay sources were long conceived to be of utmost importance as potential appropriate sources for the immense brick and tile demand of the rapid urbanisation in southeast Anatolia enhanced by the State Irrigation Project initiated in the 1980s. This project seeks to improve the social structure of the region as well as the equity in income distribution. In this respect, the long neglected study of the brick production properties of these soil/clay raw material resources in Adıyaman were determined via mineralogical (X-ray diffractometry), chemical, sub-microscopic analyses (scanning electron microscopy, energy dispersive spectroscopy). Compressive strength tests for experimental fired and unfired-dried tablet specimens were also carried out. The analyses were conducted for 3 widespread raw material sources and their natural admixtures collected from selected clay (montmorillonite) and carbonate (calcite) rich sediments located in the Adıyaman-Center (Rezip-Rzp), Kahta (Kht) and Besni (Bsn) areas. The presence of high-temperature minerals (HTM) such as bredigite (1040 °C), akermanite (1040 °C), hematite (900 °C and 1040 °C) and diopside (900 °C) in the specimen Rzp were most probably responsible for the enhanced specimen compressive strength. In contrast, the lower specimen strengths of the fired tablet specimens Bsn and Kht were related to the microstructures/pore-HTM networks developed after firing. The pores-with the welded high temperature mineral (bredigite) infills was the responsible microstructure for the slight increase in Bsn at 900 °C compared to the specimen tablet of 1040 °C. Although this microstructure caused a slight increase in the compressive strength of the fired specimens of Bsn, it is incomparable to the increases in the Rezip. This makes the Rzp material source appropriate for the brick industry besides its feasible accessibility in the field. The study revealed that the clay mineral contents of the raw materials and their natural admixtures were responsible for the quality and especially the compressive strength of the specimens.