The influence of load intensity on structural response of airport pavements assessed by nondestructive evaluation methods

Abstract

The structural condition of pavements can be assessed by applying two distinct methodologies: destructive and nondestructive tests (NDT). There are many options of NDT available for use to structurally evaluate airfield pavements, but the most used and recommended are the Falling Weight Deflectometer (FWD) and the Heavy Weight Deflectometer (HWD). The two techniques apply impulse loads to generate deflection basins on the pavement and their main difference is that FWD imparts lighter loads while HWD applies heavier loads. This difference leads to a discussion about the suitability of converting the results obtained by using the lower loads of the FWD to the heavier loads the HWD can apply because of the structural response of the pavement. Misevaluations of the structure could happen if this response is not linear, and in extreme cases the landing and take-off operations can be exposed to risks. Aiming to support the conclusion about the suitability of this conversion, the research’s objective was to evaluate the influence of the load intensity on the structural response of airport pavements. To investigate the influence of the load, the flexible pavement of three runways from distinct regions of Brazil were evaluated using different FWD and HWD loads. Indexes/parameters obtained from these evaluations were studied: raw and normalized deflections, the Radius of Curvature (RC), the Impulse Stiffness Modulus (ISM), and the back-calculated Resilient Modulus (RM). Each of these indexes, obtained by applying distinct loads, were compared to verify the hypothesis the load variation leads to significant variation in the indexes. Statistical tests were performed to support the reliability of the study. The results showed that raw deflections presented differences whose percentual values are similar to the percentual of difference between the loads, and that the normalized deflections (which would be equal if the structural response was linear) presented influence of the applied load. RC values decreased when the load increased, instead of presenting the expected behavior of decreasing under a heavier solicitation. ISM presented decrease when the load wasincreased. RM decreased when the applied load increased. The subgrade was identified as the most affected by the load variation in comparison to the other structural layers. It was concluded that the structural response of the pavement is not linear, and that the differences are not large enough to prejudice the structural analysis of the airport pavements. However, if the results would be used in processes sensitive to the layers’ modulus variations, the use of loads suitable to the traffic demanding the pavement is recommended.