Development of a masonry mortar freeze-thaw laboratory test method and the performance of CEM II mortar masonry panels

The durability (frost resistance) of masonry mortars has historically been assumed rather than tested, not least as there has been no standard test method available. Since the development of the CEM II cements, and the widespread use of these "blended" cement based binders in mortars, it has been observed that the masonry mortars have not been performing in the UK in the same way the historic CEM I (OPC) based mortars have in the past. In the Construction Products Regulation (CPR), there is a perceived need to have a harmonised standard test method available to assess properties and performance characteristics, not least for durability, including frost resistance. Lucideon (formerly CERAM Research) in the mid 2000's developed a masonry panel durability test for the laboratory assessment of mortar frost resistance, based on the TS 772-22 freeze-thaw test method used for assessing the frost resistance of clay masonry units. This paper presents both the outline of the methodology developed and the assessment of 11 pairs of clay brick based masonry panels built with 2 brick types and 11 different masonry mortars, made from CEM II cements as the primary binders, tested both in the laboratory and over 9 years in Lucideon's Field Exposure site, in Buxton Derbyshire. Whilst there is some correlation between the laboratory test method and the field exposure results for the same panels, there are interesting observations to be made in relation to the "mode of failure" through frost action, specifically relating to the brick type and their characteristics.