Laboratory Testing

To complement the exterior and accelerated exposures described above, three key ASTM C920-05 tests were run. These included adhesion, joint movement testing, and hardness. Adhesion to concrete mortar was tested according to ASTM C794-06 [8], with dry adhesion being tested after the initial 3 weeks of cure and wet adhesion after additional 1 week of water soak. Joint movement to concrete mortar, at ±25 %, was tested according to ASTM C719-93 (2005). Hardness was tested as per ASTM C661-06 [9].

Tensile properties were also measured as a general indicator of sealant performance. Samples for tensile testing were laid up as 1/8 in. (3.2 mm) thick wet plaques on PTFE foil covered aluminum panels and cured as below. Dumb­bell shaped specimens, with a gauge length of 0.725 in. (18.4 mm), were cut from the dried plaques and tested on a model H10K-S Tinius Olsen[28] tensile tester. Tensile testing was done at 2 in. (51 mm)/min and at 23±2 ° C and 50±5 % relative humidity. Elongation to break, maximum stress, and stress at 25 % elongation were measured and reported as the mean± standard deviation of three measurements. The stress at 25 % elongation was also measured at 0.2 in. (5.1 mm)/min and 0.02 in. (0.51 mm)/min to assess the strain rate sensitivity of the two sealants.

In the four laboratory tests described above, the acrylic specimens were cured for 1 week at 23±2 ° C and 50±5 % relative humidity, followed by 2 weeks at 50 ° C. The polyurethane specimens were cured for 3 weeks at 23±2 ° C and 50 ±5 % relative humidity.