Critical Freeze/Thaw Saturation Measurement of In-Service Masonry

When planning an insulation retrofit for an existing masonry building, it is important to analyze the freeze/thaw durability of the masonry units. The critical freeze/thaw saturation value is an important measure of durability, and frost dilatometry is an effective method of determining this value. This study reports developments in the field sampling of masonry units and critical saturation testing of in-service masonry.

The challenge when sampling masonry is to ensure that selected units are representative of the entire building or capture the range of material properties of units on the building. Two approaches to sampling are explored. Bulk sampling involves the removal of a large number of samples with the goal of randomly capturing the range of units of interest. Alternatively, field testing of a relevant material property can be performed to identify units that capture the range of material on the façade. A nondestructive field drying rate measurement technique is presented along with pilot study results suggesting it could completely replace the need for bulk sampling.

Significant variation in the permanent strain resulting from the frost dilatometry method has been found in previous testing. It is thought that this variation is due to lack of material homogeneity within the brick, resulting in variations between sample slices. It appears from the current study that use of the mean strain for as little as four samples at each saturation level will allow accurate determination of critical saturation. It further appears that use of a 95th percentile strain value for each saturation level could alternatively be used as a conservative method. Overall, the proposed new methodology was found to have a high level of reproducibility for critical saturation measurement.

Note: This article was published in Proceedings of Buildings XIII, 2016. Copyright 2016 ASHRAE. Reprinted by permission at rdh.com. This article may not be copied and/or distributed electronically or in paper form without permission of ASHRAE. For more information about the Buildings XIII Conference Proceedings, visit http://web.ornl.gov/sci/buildings/2016/proceedings/.