Concept Paper: Developing Pavement Structural Deterioration Curves

An SN (structural number) can be calculated for a road pavement from the properties and thicknesses of the surface,basecourse, sub-base and subgrade. Historically, the cost of collecting structural data has been very high. Data were initially collectedusing Benkelman Beams and now by FWD (falling weight deflectometer). The structural strength of pavements weakens over timedue to environmental and traffic loading factors but due to a lack of data, no structural deterioration curve for pavements has beenimplemented in a PMS (pavement management system). IRI (international roughness index) is a measure of the road longitudinalprofile and has been used as a proxy for a pavement’s structural integrity. This paper offers two conceptual methods to developPSDC (pavement structural deterioration curves). Firstly, structural data are grouped in sets by design ESA (equivalent standardaxles). An ISN (“initial” SN), SNI (intermediate SN) and a TSN (terminal SN), are used to develop the curves. Using FWD data, theISN is the SN after the pavement is rehabilitated (Financial Accounting “Modern Equivalent”). Intermediate SNIs, are SNs other thanthe ISN and TSN. The TSN was defined as the SN of the pavement when it was approved for pavement rehabilitation. The secondmethod is to use TSD (traffic speed deflectometer) data. The road network already divided into road blocks, is grouped by trafficloading. For each traffic loading group, road blocks that have had a recent pavement rehabilitation, are used to calculate the ISN andthose planned for pavement rehabilitation to calculate the TSN. The remaining SNs are used to complete the age-based or if available,historical traffic loading-based SNIs.