Towards a new method to estimate liquid redistribution coefficients in small fragments of mortar

Institute for Environmental Design and Engineering, University College London, United Kingdom

^* Corresponding author: toby.cambray.20@ucl.ac.uk

Abstract

Inappropriate replacement mortars in historic buildings often lead to irreparable damage to historic masonry; the influence of the mortar on drying dynamics is crucial to these risks. The chemical and compositional analysis of historic mortar is widely practised for the purposes of formulation of replacement mortars but the compatibility, hygrothermal behaviour and moisture safety mainly depend on the physical properties. The chemistry and composition alone do not give a complete understanding of these functional properties, so physical measurements are necessary. However, it is often the case that only small fragments are available from existing walls due to the thickness of mortar joints, friability of the material and conservation constraints on removing material. While some physical properties lend themselves to measurement with small specimens (pore size distribution, sorption curves), liquid transport is harder to measure accurately for small (<25mm) irregular specimens. A new approach was proposed, combining several established techniques, allowing liquid redistribution to be estimated in such specimens. Specimens were subjected to drying experiments, without the usual constraints to approximate 1D flux (sealing the sides and bottom of a strictly prismatic specimen). The experiment was duplicated in 3D hygrothermal simulation, in which the liquid transport properties were adjusted until the simulation results closely approximated the experimental results. The method was demonstrated on cast cylinders of control materials, and will be developed to cover smaller, irregular pieces in subsequent work.