Correlation Between Asphalt Mixture Stiffness Determined Through Static and Dynamic Indirect Tensile Tests

At present, Italian technical specifications only provide stiffness measurements in few cases, whereas they require the execution of the static indirect tensile strength test, both in mix design and in quality control phases. Despite this test is typically carried out only to determine the material strength, it is, however, possible to obtain a measure of the specimen stiffness properties from the stress–strain curve. The present paper deals with the correlation between asphalt concrete stiffness measurements obtained through dynamic indirect tensile tests, according to EN 12697-26, and static indirect tensile strength tests, according to EN 12697-23. In particular, data from static tests have been processed to obtain stiffness measurements through the application of Hondros’ theory or graphically from the stress–strain curve. Although based on empirical derivation, this relationship would enable the laboratories that are not equipped with a proper machine for dynamic modulus tests to estimate the stiffness properties of the bituminous material, by exclusively performing simple static tests. The experimental program included static and dynamic indirect tensile tests at 10, 20 and 30 ∘C on three asphalt concretes, different for binder type and compacted to two air voids contents. Results proved that good correlations (R2 values higher than 0.92) can be established between dynamic modulus and static moduli, independently from test conditions and mixture composition.