Structural Assessment of Cracked Flexible Pavement

Abstract

Highway authorities in various countries have been using different tools to determine the structural capacity of pavement for their rehabilitation programs, pavement design, research and management for more than 50 years. The earlier common tools were Benkleman beams and Deflectographs, which have been gradually phased out after the introduction of Falling Weight Deflectometer (FWD) since the 1980s. FWD is able to record pavement surface deflections in relation to a dynamic load, simulative to a moving wheel. Back-analysing surface deflection measurements enables estimation of in-situ moduli of materials in different pavement layers. Cracked or poor materials give relatively low in-situ layer moduli.

In Hong Kong, although FWD and the associated back-analysis and forwardanalysis, have been in use for a number of years, the results of a recent review on FWD residual life show doubts on the correlation between the estimated residual life from FWD survey and the actual in-situ pavement performance in practice. Hence, a new method, simply making use of FWD’s surface deflection measurements, to estimate the residue structural capacity is developed.

This paper presents the research on studying the use of FWD center deflection for crack identification of flexible pavement. Detailed observation of cracks on cores from 31 pavement sections were used to define the condition code. Backanalysed stiffness levels related to the center deflection were used to develop Structual Condition Index. The findings lead to the development of a simplified non-destructive structual assessment technique to determine the probability of crack existence within flexible pavement.