Evaluation of an HMA Stiffness Modulus Based on Indirect Tensile Testing

In the structural pavement design based on mechanistic principles and in quality control evaluations, stiffness of the hot mix asphalt (HMA) is one of the most important input parameters. The ASTM D4123 and EN 12697-26 (Annex C) standards describe procedures for characterizing the reference modulus using the indirect tensile test (ITT) applicable to cylindrical specimens. The objectives of this paper are the: (1) to evaluate the repeatability and reproducibility of ITT performed according to Annex C of the EN 12697-26 standard through an interlaboratory comparison using two different testing devices; and (2) to validate and calibrate a model based on ITT to predict stiffness modulus for local implementation under Portuguese conditions. An extensive testing program was performed involving two types of testing equipment (NAT and MATTA), and using specimens compacted in laboratory. ISO 5725-2 standard practice was followed to determine the precision of ITT. In addition, other tests conducted on specimens drilled in existing road pavements have shown that the stiffness modulus is more sensitive to temperature and air voids. Based on the results, a model for prediction stiffness modulus was validated and calibrated for the tested materials and a good adjustment was achieved.