Evaluation of Strength of Concrete Paving	Print    Inquire    847-972-3050

Description
CTLGroup conducted an investigation to evaluate the strength of the concrete used for a section of highway operated by a Midwest State Highway Agency (MSHA). As part of the contractor's quality control program, the contractor was responsible for the quality of materials and construction, and the MSHA's engineer was responsible for determining the acceptability of such materials and construction..

To measure strength, the project specification allowed the use of compressive strength of field-molded cylinders in lieu of flexural strength of field-molded beams. However, it also required that a correlation equation be developed to relate compressive and flexural strengths. The specification also allowed the use of core compressive strengths, for cases when the cylinder strengths fell below the specified lower critical limit listed in the specifications.

Soon after paving began, the contractor evaluated concrete strength on the basis of compressive strength of field-molded cylinders. At that point, however, no criteria were available for accepting the cylinder compressive strengths. During the course of construction, the contractor obtained cores from each sublot, and also established a correlation equation relating compressive and flexural strengths. The MSHA's engineer established a different procedure to relate core and cylinder compressive strengths to flexural strengths, and used that to compute the pay factor. Because the two procedures for relating cylinder and core compressive strengths to flexural strength were in conflict, the MSHA retained an arbitrator to examine the concrete strength concern.

The arbitrator retained CTLGroup to perform technical evaluations related to the in-place concrete strength for the paving project. CTLGroup tested cores, developed a correlation equation between compressive and flexural strengths using the project materials, analyzed the data, and made recommendations to the arbitrator.