ASTM C42/C42M-20 PDF Download

ASTM C42/C42M-20 is a standard test method that provides procedures for obtaining and testing drilled cores and sawed beams of concrete. The purpose of this standard is to determine the compressive, splitting tensile, and flexural strength of in-place concrete. It is commonly used in situations where doubts exist about the quality of the concrete or when assessing the strength of older structures.

The standard recognizes that concrete strength can vary depending on its location within a structural element, with the concrete at the bottom usually being stronger than the concrete at the top. It also acknowledges that the orientation of the core relative to the horizontal plane of the concrete can affect its strength. These factors should be considered when planning the locations for obtaining concrete samples and when comparing strength test results.

Moisture content is an important factor that affects the strength of concrete cores. The standard acknowledges that there is no standard procedure to ensure that a specimen is in the same moisture condition as the concrete in the structure at the time of testing. However, it provides moisture conditioning procedures to minimize variations and the effects of moisture introduced during specimen preparation.

The standard also notes that the measured compressive strength of a core is generally lower than that of a properly molded and cured standard cylinder tested at the same age. The relationship between the strengths of these two types of specimens is affected by various factors. However, there is a procedure available to estimate the equivalent cylinder strength from a measured core strength.

In terms of acceptance criteria, the standard suggests that the specifier of tests should establish the criteria in the project specifications if there are no core strength requirements in building codes or other contractual or legal documents. It provides an example from ACI 318, which states that the concrete is considered structurally adequate if the average strength of three cores is at least 85% of the specified strength and no single core strength is less than 75% of the specified strength.