Clay brick is one of the oldest and commonly used clay products in construction industry in Khyber Pakhtunkhwa (KP) Pakistan. In spite of its widespread use, studies regarding the manufacturing standards and quality of locally made bricks are much less in comparison to those of technologically advanced countries. The aim of the present study was to investigate the chemistry and phase constitution of the raw materials used in local brick kilns. Phase and microstructural analyses of fired bricks from local kilns were performed and compared with those of the laboratory made bricks. X-ray diffraction of raw materials revealed the presence of illite, quartz, clinochlore and albite while calcite was identified as a minor phase in all the investigated samples. Diopside, anorthite and quartz were observed as major phases in the kiln-fired samples, and only diopside and quartz in the laboratory-fired samples. The presence of albite and clinochlore, although in small concentrations, in the kiln-fired samples indicated that the employed temperature was too low to completely dissolve the initial ingredients. Consistent with X-ray diffraction results, semi-quantitative energy dispersive spectroscopy revealed the presence of silicon, aluminum, calcium, magnesium, iron and potassium along with a small amount of sodium in these samples. An increase in firing temperature decreased porosity which resulted in substantial increase in compressive strength and decrease in water absorption. The optimum mechanical properties were achieved at 1000 oC.

Keywords: Clay bricks, Phase constitution, Microstructure, Diopside, Kiln.