Weathering at high latitudes on the Carboniferous Old Red Sandstone, petrographic and geotechnical investigations, Jedburgh Abbey Church, Scotland, a case study

Weathering processes and intensity vary according to the predominant environmental conditions as well as the rocks physical and geotechnical properties in a given area. Jedburgh Abbey Church has been taken as a representative historical building constructed from Carboniferous Old Red Sandstone at humid pre-glacial region. The research aims to examine weathering processes and intensity under the environmental conditions of high relative humidity and low temperature, and to determine the output of weathering through an examination of the rocks petrological and geotechnical properties.Thin section study, scanning electron microscope and X-ray fluorescence techniques have been used to examine the rocks petrography and mineralogy on one hand and to determine weathering products on a microscale on the other hand. It is noted that the Carboniferous Old Red Sandstone has a quartz arenite texture with iron oxide and dolomite within its texture, authigenic clays are also detected. Pitting of quartz grains, exfoliation of silica overgrowth and fragmentation of the rocks feldspar can be noted on a microscale resulting in recession of the rocks components cohesion.The geotechnical results indicated variation in the physical nature of the construction rock from inside to outside the church with recession from the former to the latter due to weathering. The great reduction in mortar and the rocks calcium oxide and high content of both sulphur and chlorine from inside to outside the church is a result of weathering and deposition of air pollutants on the stones surface on the outdoor surfaces. Chemical weathering, e.g. salt hydration and chemical alteration of the rocks carbonate content to sulphate and chloride salts is expected to dominate in the study area at such conditions of low temperature and high relative humidity accompanied with air pollutants.