An investigation into the potential use of TDR measurement systems to accurately assess the moisture content at the centre of completed earth walls

Abstract

When conserving or extending historic buildings, the ability to improve fabric thermal performance is often limited by the traditional nature of the original material. This limits the ability for historic buildings to adapt to our changing climate. Following greater awareness of the climate emergency, there is a growing argument that traditional building materials and methods should evolve to become more climate resilient. Whilst traditional cob has inherent thermal qualities, it’s inability to meet stringent thermal insulation standards is the rationale behind this study. The CobBauge walling system is one iteration of the traditional cob building technique to allow cob and other historic earthen building methods to conform to many country’s thermal building regulations. The moisture content of earth walls has a well-known impact upon the development of wall strength and corresponding rates of shrinkage when repairing and extending historic earthen buildings. There is a known relationship between the density and thermal conductivity of earthen walls (Volhard, 2016, Minke, 2000), yet the ability to safely construct an earth wall system that incorporates two layers of different densities to improve the thermal performance of historic earth buildings raises questions concerning differential shrinkage. To assess the shrinkage this research develops a methodology that can be used to investigate moisture distribution and shrinkage movement within an innovative composite cob walling system (CobBauge) that can be used to repair or extend historic earthen structures. Objectives • To design a moisture measurement system that uses TDR probes and can be placed within existing, upgraded and extended composite earth walls. • To analyse the impact upon accuracy of positioning of TDR sensors in an earth wall. • To compare the shrinkage of small-scale samples with a full-scale CobBauge wall throughout the build process in relation to the moisture readings provided by the TDR moisture measurement system.