Introduction to ASTM C 1736

ATM C 1736 can be broken down into the following sequence of events: force is introduced to a sealant bead via a rolling probe; this in turn induces a depres­sive strain in the sealant bead (i. e., creates an elongation of the bead), which in turn stresses the adhesive bond-line of the joint seal at the sealant-to-joint sub­strate interface.

The primary purpose of the method is to reveal sealant adhesion anomalies not discernible via visual examination of the unstrained seal at the time of the evaluation that might affect the air and/or water infiltration resistance of the sealed joint. Sealant adhesion anomalies might be a pre-existing lack of adhe­sion or nominal (borderline) adhesion. A pre-existing lack of adhesion might not be detected in an inspection of unstrained sealed joints due to the “elastic recovery" of sealants. Elastic recovery is a desirable sealant quality that inciden­tally tends to hide adhesive bond loss in cursory inspections, because the bead “recovers" or “snaps back" into its original position at the bond-line, giving the joint a “sealed" appearance.

Borderline sealant adhesion can be exposed when the rolling device proce­dure induces a non-pre-existing failure. Repairs of identified adhesive failures can restore the seal, which is why progressive applicators have started to use the procedure as an internal quality assurance program. In addition, inappro­priate geometry, under which the sealant is too thick and the movement

FIG. 1—Upper portion depicts an uncontrolled “screen roller" type device used in proce­dural section 7.3, lower portion is the controlled force device per section 7.4.

capability of the joint might be inhibited, can be identified, examined, and, if need be, repaired.

A variety of fixed roller devices can be used to satisfy the requirements of the standard in a “depression inducement procedure," listed in Section 7.3 of ASTM C 1736, including “window screen insertion devices" (screen rollers), “backer rod insertion devices," or any other device(s) meeting the criteria. These devices are manually controlled by the user.

The “force control procedure" (Section 7.4 of ASTM C 1736) uses a patented test system [8]. In this system, the roller force load is accurately maintained (using air pressure) on the active test area. Changing the air pressure in the de­vice also changes the force delivered to the bead. The force is monitored with a

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gauge and is adjustable. A simple calculation provides the force load delivered to the bead under test.[33]