Correlation of Asphalt Concrete Layer Moduli Determined from Laboratory and Nondestructive Field Tests

The falling weight deflectometer (FWD) is widely used for in situ nondestructive assessment of pavement layer moduli. For this purpose, FWD deflections are used with a number of back-calculation methodologies to come up with layer moduli. Back-calculating layer moduli from FWD deflections collected on thin asphalt concrete (AC) pavements is a challenge because the predicted deflection basin is not sensitive to the AC modulus. This study utilizes the portable seismic pavement analyzer (PSPA) to improve the reliability of back-calculated thin AC layer moduli. Compared with the FWD, the PSPA provides a direct measurement of seismic modulus at a higher load frequency level relative to the frequencies associated with typical truck traffic. Thus, the seismic modulus determined from PSPA tests needs to be corrected with the load frequencies typically used for pavement design. This paper compares AC moduli determined from laboratory dynamic modulus tests with corresponding values determined from FWD and PSPA measurements. The results exhibited favorable correlation between the AC moduli determined from laboratory and field tests at corresponding load frequencies and temperatures. The paper also proposes a methodology to obtain a composite modulus from mixture properties determined from laboratory tests of individual AC lifts for the purpose of comparing the composite modulus with corresponding values determined from field tests. The authors generated master curves of individual AC lifts on the basis of corresponding binder temperature–viscosity relationships and volumetric properties obtained from laboratory tests. A procedure was proposed for correcting PSPA AC seismic modulus at corresponding load frequencies and temperatures by using the master curves with Odemark’s assumption. This evaluation showed a promising correlation between the corrected PSPA modulus and FWD back-calculated AC modulus. From this, the authors provide a simple equation as an alternative method for correcting PSPA modulus when the material properties of individual layer are not readily available to employ the proposed methodology.