Q.: We build residential basements and tried to work later in the season this year, but were concerned about the concrete coming up to strength in cold weather. Is there a field test that we can use to measure in-place strength?
A.: Several field tests for determining in-place strength are standardized by ASTM and are done with equipment available commercially. These tests are described briefly in the Portland Cement Association's Design and Control of Concrete Mixtures, 13th edition, and in more detail in "In-place Methods for Determination of Strength of Concrete," ACI 228.1R-89. The ASTM C 900 pullout test is used for this purpose. It involves casting an insert in the concrete, then pulling it to failure with a calibrated device. This test measures stresses on a cone-like surface around the insert and provides a result that can be correlated with compressive strength. In some cases, the cone doesn't pull out and little or no patching is required.
The pullout device is fairly expensive--$3,000 to $4,000. Also, there are costs for testing to calibrate pullout and compressive tests for typical winter concrete mixes in your area. We know of two companies that sell pullout testing devices in the United States:
- Germann Instruments Inc. 8845 Forest View Rd. Evanston, IL 60203 (708-329-9999)
- James Instruments Inc. 3727 N. Kedzie Chicago, IL 60618 (800-426-6500; in IL: 312-463-6565)