Minero-petrographical, physical, and mechanical properties of moderately welded ignimbrite as a traditional building stone from Uşak Region (SW Turkey)

Abstract

Ignimbrites are commonly used building stone since the ancient times because of its lightweight, soft, and insulating properties. However, they are prone to deteriorate due to their weak structure. The moderately welded Usak ignimbrite has a wide range of exposure in the Usak region of the inner western part of Anatolia. It is mainly composed of plagioclase (oligoclase, andesine), biotite, Fe-Ti oxides (magnetite, hematite), and low amount of amphibole (brown hornblende), quartz mineral composition having hypocrystalline and eutaxitic texture. Geochemical data reveal that the ignimbrite is characterized by trachyandesite composition, calc-alkaline and peraluminous in character. According to the calculated weathering index values, the ignimbrite shows slight to moderate weathering. Apparent dry and partially saturated unit weights are 10.49 and 13.90 kN/m3, respectively. Open porosity is 35.4%. This high value results in high water absorption capacity and low uniaxial compressive strength. Capillary water absorption capacity was determined as 51.84 g/m2 s0.5; with this value, the ignimbrite is in “high” water absorption rock class. Dry and partially saturated uniaxial compressive strength values were determined as 6.89 MPa and 3.45 MPa respectively. Tested ignimbrite specimens are in “weak rock class” according to UCS values both in dry and partially saturated conditions. Therefore, the stone loses about 50% of its strength in partially saturated condition. Longitudinal and shear wave velocities of the specimens were determined as 2.4 and 1.32 km/s respectively. Based on these values, dynamic shear modulus, Poisson’s ratio, and Young’s modulus were calculated as 1.91 GPa, 0.27 GPa, and 4.87 GPa, respectively. Slake durability tests were carried out on ignimbrite specimens after the second cycle 91.33%; Usak ignimbrite is characterized by “medium-high” durability. Specimens were exposed to 25 freeze and thaw cycles and the average of the weight lost values were determined as 0.89%. Thermal conductivity properties were investigated by the thermal conductivity coefficient which was ranged between 0.352 and 0.449 W/mK. Minero-petrographic investigations and geochemical and physico-mechanical test results indicate that the structure of Usak ignimbrite is weak and sensitive to environmental and utilization condition. Therefore, it is necessary to pay attention to this feature in the areas of utilization.