Evaluation of Repeatability of Kansas Test Method KT-73, “Density, Absorption and Voids in Hardened Concrete,” Boil Test

For years, the Kansas Department of Transportation (KDOT) and concrete producers in the state have used a Rapid Chloride Test for concrete cylinders, American Association of State Highway and Transportation Officials (AASHTO) T277. This test has been thought of as an appropriate quality control test to evaluate permeability in concrete. Unfortunately, it has a low repeatability—a 51% difference in the mean between two laboratories/operators as percent of the mean (AASHTO T277, 2011). This could mean the difference between reliable permeability results and questionable results. This has a direct impact on KDOT’s ability to judge the quality of the concrete mixture, and whether it will be a long-term durable concrete or a concrete that fails early. KDOT has also used the Kansas Test Method KT-73 (2012), Density, Absorption and Voids in Hardened Concrete, a permeability test commonly referred to as the Boil Test, to evaluate concrete durability in the state of Kansas. It covers the determinations of density, percent absorption, and percent permeable voids in hardened concrete. KT-73 reflects testing procedures found in ASTM C642 (2013). KDOT has relied on this test to evaluate concrete permeability, but some concrete producers in the state have objected to its accuracy, preferring the Rapid Chloride Test which has a low repeatability. In 2009, with the help of several ready mix producers and private laboratories, KDOT conducted a round robin evaluation of KT-73. The results of this round robin showed that the KT-73 Boil Test could be repeated with a fairly high degree of precision. This study demonstrates that the expected range between two properly conducted tests at different laboratories should not be more than 8% of the average. The repeatability of the Boil Test is significantly better than the repeatability of the Rapid Chloride Test for concrete cylinders, AASHTO T277 (2011), which many concrete producers have relied on to verify their concrete’s durability. The Boil Test and the Rapid Chloride Test take about equal amounts of time to perform, but the equipment required for the Boil Test is significantly less expensive. Thus, the Boil Test is not only less expensive to perform, but is a better indicator with respect to reliability of the permeability and durability of concrete used in the state of Kansas.