Report on Methods for Estimating In-Place Concrete Strength
|Publication Date:||1 January 2019|
In-place tests are performed typically on concrete within a structure, in contrast to tests performed on molded specimens made from the concrete to be used in the structure. Historically, they have been called nondestructive tests because some of the early tests, such as rebound number and ultrasonic pulse velocity, were noninvasive and did not damage the concrete. Over the years, however, new methods have developed that result in superficial local damage. Therefore the terminology "in-place tests" is used as a general name for these test methods, which includes those that do not damage the concrete and those that result in some near-surface damage. In this report, the principal application of in-place tests is to estimate the compressive strength of the concrete. The pull-off test can be used to estimate the tensile strength of concrete or evaluate bond strength between layers. The significant characteristic of most of these tests is that they do not directly measure the compressive strength of the concrete in a structure. Instead, they measure some other property that can be correlated to compressive strength (Popovics 1998). The strength is then estimated from a previously established relationship between the measured property and concrete strength. The uncertainty of the estimated compressive strength depends on the variability of in-place test results and the uncertainty of the relationship between these two parameters. These sources of uncertainty are discussed in this report. An alternative approach for correlation between tests results and concrete strength is presented in EN 13791 (2007) and BS 6089 (2010).
In-place tests can be used to estimate concrete strength during construction so that operations requiring a specific strength can be performed safely or curing procedures terminated. They can also be used to estimate concrete strength during the evaluation of existing structures. These two applications require slightly different approaches, so parts of this report are separated into sections dealing with new and existing construction.
A variety of techniques are available for estimating the in-place strength of concrete (Malhotra 1976; Bungey et al. 2006; Malhotra and Carino 2004). No attempt is made to review all methods in this report; only those methods that have been standardized by ASTM International are discussed. Examples of methods not covered include internal fracture tests (Chabowski and Bryden-Smith 1980; Domone and Castro 1987) and torque tests (Stoll 1985).