Variation of micro-topographic and geotechnical limits on weathering progress on the constructional Triassic sandstone, Aachen city, Germany, case study

Abstract

Rock's surface micro-topography and geotechnical properties' limits are expected to be altered on weathering progress to a new form(s) and limits, respectively. The quantification of weathering damage for a given rock is of value e.g. to compute weathering rate, weathering intensity and rock's durability to weathering processes and to take a decision regarding restoration urgency. The current study aims to examine the variation/constancy of micro-topography and geotechnical properties’ limits of the Triassic sandstone constituting well-aged wall, at Aachen city, on weathering progress over short duration (12 years of investigation from 2007 to 2019). The Equotip hardness tester and micro-erosion meter are tools used for micro-topographic and rock's surface hardness investigations on one hand, and the mercury intrusion porosimetry has been used for measuring rock's pore size distribution and salt susceptibility on the other hand. These tools are accurate, numerical, comprehensive, easily applicable and preferable particularly for ancient buildings and archaeological sites where sampling is not recommended or prohibited. The wall side under consideration has been selected as its constructional blocks present a wide spectrum of weathering forms as well as rock's surface micro-topography (over 12 years of investigation) through increasing the weathering forms' dimensions and/or creation of new weathering forms. The net result of the current study indicated a noticeable variation in stone's micro-topography on weathering progress, the rock's stone surface hardness highly controls rock's weathering susceptibility and no clear relation can be noted between stone's surface roughness and its susceptibility. The pore size distribution is the most controlling parameter for rock's weathering susceptibility.