ASTM C719-22 Standard Test Method for Adhesion and Cohesion of Elastomeric Sealants under Cyclic Action (Hockman Cycle)

The standard “ASTM C719-22 Standard test method for adhesion and cohesion of elastomeric grouts under cyclic action (Hockman cycle)” published by the American Society for Testing and Materials (ASTM) describes an accelerated laboratory test method to evaluate the performance of a structural sealant in a test configuration subjected to water immersion, cyclic action, and temperature change.

For the purposes of this standard, the definitions of terms used are based on the ASTM C717-24 Building sealants and standard terminology for sealants.

The test method described consists of subjecting standard joint samples to a series of treatments as follows:

Immersion in water for seven days
Exposure in an oven for seven days under compression
Automatic compression and extension cycle at room temperature with a specified rate and amount of compounding motion
Alternately compressing and extending the joint at high and low temperatures, respectively, under the specified conditions described herein.

The effects of the test are evaluated by visual inspection for cohesive and adhesive failures, sealant deformation, and bubble formation within the sealant.

This test method can be applied to any joint movement. The cyclic movement classes available, together with their associated extension and compression dimensions, are shown in the table provided in the standard.

Failure of a building sealant in an active joint is usually manifested by cohesive failure of the sealant or adhesive failure between the sealant and the substrate, or both. The method described in this test method relates only to the performance of the sealant when properly installed with recommended primers and does not evaluate sealant failures resulting from improper joint design, excessive joint movement, improper application practices, and other factors known to cause sealant failure in buildings and building sites.

The main equipment used in these tests includes:

Compression-expansion machine: Designed to automatically compress the joint width of the test specimen from 12,7 mm to the desired minimum size and to extend the specimen from 12,7 mm to the desired maximum extension at a constant rate of 3,2 mm/h. The machine is equipped with grips of sufficient strength to withstand the resistance of high tensile strength sealants without bending.
Cold box or room: kept at 26,1 degrees plus/minus 1,7 degrees.
Forced draft furnace: controlled at a temperature of 70 degrees plus/minus 2 degrees.
C-clamps or other devices used to hold the sample under pressure.
Cast spacers.
A room or compartment maintained under standard conditions as specified in ASTM C717-24.

The standard substrate used in the test shall be Portland cement mortar, float glass and aluminum alloy. If desired, only one or two of the standard materials may be tested with a sample. Similarly, instead of or in addition to the standard substrate, other substrates such as brick, marble, wood may be specified by the interested party for testing with a sealing sample.

Prior to testing, samples made with multi-component sealants are cured for 14 days under standard conditions. During the second week of the curing period, an attempt is made to separate the sealant from the cast spacers without damaging the sealant bead. If the sealant is damaged, reassemble new samples and repeat, allowing a longer curing period before attempting to remove the cast spacer again. The sealant must not be damaged when the cast spacers are removed.

Samples made with single component sealants are cured for a total of 21 days as follows:

Seven days under standard conditions
Seven days in a temperature of 37,8 degrees plus/minus 2 degrees and 95 percent relative humidity environment
Seven days under standard conditions

Remove the casting spacers from the specimen as soon as possible during the curing period without damaging the sealant. If the sealant is damaged, reassemble new specimens and repeat the process, allowing a longer curing period before attempting to remove the casting spacers again. The sealant should not be damaged when the casting spacers are removed.

Immediately after the curing period, if higher temperature curing conditions were used, the samples are allowed to cool to standard temperature. The samples are then immersed in distilled or deionized water for seven days. After immersion, each sample is bent by hand twice, at an angle of approximately 60 degrees, to check the bond. If the bond is still intact, the samples are compressed to the minimum required size given in the table for the particular sealing class being tested. A C-clamp and spacers or other adequate device may be used for compression.

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