The water ingress characteristics of stressed masonry

• Main Author: Tait, Colin J.
• Other Authors: Khalaf, Fouad
• Published: Edinburgh Napier University 1999
• Subjects: 624; TH Building construction
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.300349

Water ingress, usually by wind-driven rain, is the main cause of premature deterioration in masonry structures. Water acts as a transport mechanism for aggressive chemicals and can also undergo freeze/thaw cycles leading to bursting of the masonry microstructure. Factors such as the absorption rates of brick, water/cement ratio of the mortar, workmanship of the mason and poor design detail have all been identified as influencing the amount of water likely to penetrate a structure. It is also recognized that the majority of water ingress occurs at the brick unit/mortar joint interface, where interstices are present that allow access to the masonry interior. The size, extent and influence that the brick/mortar interface has in governing water ingress is likely to be controlled by both the applied stress level and bed orientation of the main mortar beds relative to the direction of loading. Very little research has investigated these parameters in detail. By using a new ingress measurement technique, the effect of the applied stress level and bed orientation was quantified. The main mortar beds of concentrically loaded masonry panels were found to deteriorate in their resistance to water ingress as they were orientated from perpendicular to parallel relative to the direction of loading. Poisson's ratio effects, which generated differential expansion between brick and mortar were believed to control water ingress at mortarjoints orthogonal to the main beds. Water ingress at these mortarjoints was also found greatly influenced by both applied stress level and bed orientation. Factors such as the applied pressure head of water impinging onto the panel, the variability of the brick type used, eccentricity of applied loads and the pre-wetting of panels were also found to have some controlling influence on the water ingress characteristics of masonry. Empirical modelling of water ingress dependent upon time, stress level, bed orientation and pressure head of water, was also undertaken. This enabled the volume of water ingress to be mathematically generated, with these models exhibiting good agreement with experimental data. Suggestions for future work include assessing the effect of higher applied stress levels on water ingress, verification of the laboratory work with on-site tests and the introduction of freeze/thaw testing on loaded panels to simulate an abrasive external environment. Numerical analysis using finite element modelling was also identified.