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1.1 This test method covers the determination of the bonding strength of air-setting refractory mortar by determining the flexural strength (modulus of rupture) at room temperature of oven-dried brick-mortar joints.

1.2 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

3.1 The data developed by this test method show the bonding strength and intrinsic strength of different qualities of air-setting mortar. The procedures described in this test method measure the bonding strength and intrinsic strength of air-setting mortars when used with specific brands or lots of refractory brick.

3.2 Note that it is possible to obtain results with these methods for brick and mortar combinations which are incompatible for use at high operating temperatures. The user must determine this compatibility. Only brick and mortar combinations known or intended to be compatible for a particular use should be tested.

3.3 Properties of the brick, including its strength, apparent porosity, and pore size distribution, can affect the measurement of both the bonding strength of the brick-mortar composite and the intrinsic strength of the mortar. The average modulus of rupture of the test brick, as determined by Test Methods C133, should exceed that expected for the mortar being tested. The testing of specific brands or lots of brick and mortar is preferred.

3.4 Three modes of failure are available: the break may occur within the brick itself, at the brick-mortar interface, or within the mortar itself. The latter provides a practical measurement of the strength of the mortar itself and is the predominant mode of failure with the four-point flexure test described. The three-point flexure test measures the failure strength of the brick-mortar composite. Failure within the brick itself suggests that either the particular brick contained a serious flaw, or that the mortar joint strength is of the same magnitude or greater than that of the refractory brick. The mode of failure should always be reported in the final report.

3.5 A ruggedness test for this test method3 performed in 1985 found the following variables to be rugged: specimen size (2.5 to 3.0 in.), mortared surface (cut versus uncut), joint thickness (¹/₁₆ to ¹/₈ in.), pulling of rods (fast versus slow), the loading rate (500 to 1000 lbf/min), the method of load application (three- versus four-point), and the operator.

3.6 The cold bonding strengths of refractory mortars obtained by this test method are suitable for use in research and development, quality control, and for establishing and evaluating compliance with specifications between producers and consumers.