Backcalculation of pavement layer moduli and its application on overlay design

This paper mainly describes the modulus backcalculation program, ELSBACK, which has been developed in both languages, English and Chinese, to determine the structural properties of existing pavements from nondestructive test data. Both static and dynamic loading models are considered in the ELSBACK program. In addition, this program is capable of dealing with the temperature influences on measured deflections by incorporating local temperature-deflection regression equations. A sensitivity analysis of the effect of variations in input values on the backcalculated moduli is also presented. Verification of the ELSBACK program is carried out by comparing the backcalculated moduli from ELSBACK with laboratory testing data and results of other backcalculation programs. The comparison indicates that the ELSBACK program performed very well in comparison to the other available programs. The major application of the program ELSBACK is to evaluate the existing pavement and determine the required thickness, if any. Therefore, the typical cases of applying ELSBACK on the milling and overlay maintenance technique were also presented in this paper.