In Situ Measurement of Compression Set in Building Sealants During Outdoor Aging

The durability of sealants is dictated by many factors such as joint design, surface preparation, application, formulation, joint movement, and weather. Among these factors the link between formulation (material behavior) and weathering durability is difficult to assess in short term tests. We attempt to address this challenge by monitoring changes in apparent modulus during exposure to outdoor weathering and cyclic strain. This is accomplished via custom built systems that apply cyclic strain to 16 samples simultaneously via programs that simulate wood (cold compression) and concrete=metal (hot compression) construction materials. A key finding of the research presented here is that changes in apparent modulus are primarily driven by underlying changes in the compression set, a potentially critical contributor to stress in structures during rapid temperature changes. Detection of the compression set is made possible by the in situ material property assessments used in this research. Aging tests that rely on offline evaluation of property changes may miss or underestimate this effect on the sealant's stiffness due to time delay and=or losing track of the original zero stress-zero strain state.