ASTM C451-19 PDF Download

ASTM C451-19 is a standard test method that determines the early stiffening of hydraulic cement paste. The purpose of this test is to measure the degree to which a cement paste develops early stiffening or whether it complies with the specified limit on early stiffening. The standard provides information on how to establish compliance with a specification limit, which is typically stated in terms of the minimum allowable final penetration calculated according to the Calculation Section.

The test method also includes a remix procedure, described in the Procedure Section, which can be used to estimate the relative tendency of a cement to manifest early stiffening. By comparing the behavior in the initial test and the remix procedure, it is possible to differentiate between a relatively less serious and less persistent tendency to early stiffening (false set) and one that is more serious and persistent (flash set).

Severe false setting in a cement can cause difficulties in handling and placing, especially when used in stationary mixers or non-agitating equipment. It is less likely to be noticeable in transit mixing or when concrete is remixed before placing or transporting. Cements with severe false setting typically require slightly more water, resulting in slightly lower strengths and increased drying shrinkage.

Early stiffening resulting from false set is not likely to cause a cement to fail the applicable time of setting requirement. However, early stiffening resulting from flash set, depending on its severity, can cause a cement to fail the time of setting requirement.

The standard also includes warnings about the caustic nature of fresh hydraulic-cementitious mixtures, which can cause chemical burns upon prolonged exposure. It is important to follow safety precautions when conducting the test. The standard references notes and footnotes for explanatory purposes, but they are not considered requirements of the standard.