Laboratory Seismic Testing of Asphalt Concrete

Sammanfattning: Nondestructive laboratory seismic testing to characterize the complex modulus and Poisson’s ratio of asphalt concrete is presented in this thesis. These material properties are directly related to pavement quality and the dynamic Young’s modulus is used in thickness design of pavements. Existing standard laboratory methods to measure the complex modulus are expensive, time consuming, not truly nondestructive and cannot be directly linked to nondestructive field measurements. This link is important to enable future quality control and quality assurance of pavements based on the dynamic modulus.Therefore, there is a need for a more detailed and accurate laboratory test method that is faster, more economic and can increase the understanding and knowledge of the behavior of asphalt concrete. Furthermore, it should be able to be linked to nondestructive field measurements for improved quality control and quality assurance of pavements. Seismic testing can be performed by using ultrasonic measurements, where the speed of sound propagating through a material with known dimensions is measured. Seismic testing can also be used to measure the resonance frequencies of an object. Due to any excitation, a solid resonates when the frequency of the applied force matches the natural frequencies of the object. In this thesis, resonance frequency measurements have been performed at several different temperatures by applying a load impulse to a specimen while measuring its dynamic response. The measured resonance frequencies and the measured frequency response functions have been used to evaluate the complex modulus and Poisson’s ratio of asphalt concrete specimens. Master curves describing the complex modulus as a function of temperature and loading frequency have been determined through these measurements.The proposed seismic method includes measurements that are significantly faster, easier to perform, less expensive and more repeatable than the conventional test methods. However, the material properties are characterized at a higher frequency range compared to the standard laboratory methods, and for lower strain levels (~10-7) compared to the strain levels caused by the traffic in the pavement materials. Importantly, the laboratory seismic test method can be linked together with nondestructive field measurements of pavements due to that the material is subjected to approximately the same loading frequency and strain level in both the field and laboratory measurements. This allows for a future nondestructive quality control and quality assurance of new and old pavement constructions.