In-Place Methods to Estimate Concrete Strength

Description

In-place tests are performed typically on concrete within astructure, in contrast to tests performed on molded specimensmade from the concrete to be used in the structure. Histori-cally, they have been called nondestructive tests becausesome of the early tests did not damage the concrete. Over theyears, however, new methods have developed that result insuperficial local damage.

Therefore, the terminology in-place tests is used as a general category that includes thosethat do not alter the concrete and those that result in minorsurface damage. In this Report, the principal application ofin-place tests is to estimate the compressive strength of theconcrete. The significant characteristic of most of these testsis that they do not directly measure the compressive strengthof the concrete in a structure. Instead, they measure someother property that can be correlated to compressive strength(Popovics 1998).

The strength is then estimated from apreviously established relationship between the measuredproperty and concrete strength. The uncertainty of the estimatedcompressive strength depends on the variability of the in-placetest results and the uncertainty of the relationship betweenthese two parameters. These sources of uncertainty arediscussed in this Report.In-place tests can be used to estimate concrete strengthduring construction so that operations that require a specificstrength can be performed safely or curing procedures can beterminated.

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 thein-place strength of concrete (Malhotra 1976; Bungey1989; Malhotra and Carino 1991). No attempt is made to review all of these methods in this report; only those methods that have been standardized by ASTM are discussed. Teodoru (1989) prepared a compilation of national standards on in-place test methods.