Interlaboratory Study on Measuring Coefficient of Thermal Expansion of Concrete

Coefficient of thermal expansion (CTE) is one of the sensitive inputs in the new Mechanistic–Empirical Pavement Design Guide (MEPDG). The most widely used test method to measure CTE of concrete is outlined in AASHTO TP60-00, Coefficient of Thermal Expansion of Hydraulic Cement Concrete. Several state highway agency materials laboratories and university research centers have custom-built manually operated or automated CTE measuring devices based on recommendations from AASHTO TP60. Automated CTE devices are also commercially available. With many states in the process of implementing the MEPDG, it is important that the CTE measurements from the various devices provide accurate and comparable results. Results from a nationwide CTE interlaboratory study conducted by FHWA are presented. Eleven custom-built and seven commercially purchased CTE units were used in the study. The 18 CTE devices were divided into four groups, with each group testing one 410 stainless steel (SS) specimen and two concrete specimens with low and high CTE. Statistical analysis was performed to determine overall variability of the CTE measurements from the various devices. Additionally, variability was determined between custom-built and commercially available CTE units and between two CTE measuring methodologies (AASHTO TP60 and Texas test method). Accuracy of the CTE measurements from the interlaboratory study was determined from the CTE value of a 410 SS specimen measured according to ASTM E228-06, Standard Test Method for Linear Thermal Expansion of Solid Materials with a Push-Rod Dilatometer.