Assessment of mortar properties in vintage clay brick unreinforced masonry buildings

Mortar is a principal structural component of unreinforced masonry (URM) buildings, with mortar mechanical properties having an important influence on the behaviour of URM buildings when subjected to earthquake induced shaking. However, the mechanical properties of in situ mortar have long been known to be difficult to obtain. Recommendations on mortar properties for preliminary assessment of URM buildings, as well as details of field assessment procedures for in situ mortar characterisation have been previously suggested in national standards and guidelines in the USA, New Zealand and seismically active countries in Europe. An experimental study was implemented in order to investigate an improved characterisation procedure for vintage mortars, to be used by structural engineering practitioners with the aim to improve the accuracy of building seismic assessments, computer modelling and subsequent seismic retrofit designs. The tested mortar samples were extracted from 60 different vintage URM buildings throughout New Zealand. A non-standard mortar compression test procedure was developed, and an alternative in situ assessment technique to estimate mortar compressive strength was investigated. Supplementary tests to estimate the mortar aggregate/binder ratio and to predict the presence of cement in the mortar are also discussed.