MODELING OF LIFE-CYCLE COSTS OF PAVEMENT REHABILITATION

The rehabilitation of pavements can be regarded as a cycle of gradual depreciation and subsequent replacement of the capital invested in the pavement layers of roads. The capital recovery cost is functionally related to the strength of the pavement and the life-cycle length between rehabilitation measures, which is the basis for annual-worth cost analysis of any rehabilitation measure. Whereas the cost of such measures is composed of a fixed term and a term that varies with overlay thickness, the life-cycle length is dependent on the acceptable minimum performance or serviceability level and the strength of the rehabilitated pavement structure. These relationships and a financial equation for annualized costs are the basic modules of the proposed modeling. The problem of salvage value is illustrated but can be avoided by applying the repeatability assumption of financial analysis. This means, with regard to pavements, that the same measure of rehabilitation must be used at the same trigger point of acceptable minimum performance. Based on the author's earlier modeling of the AASHTO Road Test and Brampton Road Test data, and on inventory data collected and modeled in Ontario, a form for the life-cycle length function has been derived and discussed. Ontario 1984 cost data were used to give an example of calculation of annualized costs. If user costs are not included in the analysis, more frequent single overlays would appear to be economical compared with multicourse overlays and less frequent rehabilitations.