Effect of Positive Drainage on Flexible Pavement Life-Cycle Cost

Drainage characteristics have a significant effect on pavement performance. Pavements with poor subsurface drainage properties prematurely exhibit distress and have higher life-cycle cost. Shorter service life and higher maintenance cost are some of the reasons for the higher lifecycle cost. It has been proved in the last 20 years that subsurface drainage increases the pavement service life and reduces its life-cycle cost. A case study demonstrates and quantifies the benefits of providing subsurface drainage through reduction of moisture in daylighted base layers of flexible pavements. The effect of higher base course moisture content on the pavement in situ structural capacity was assessed through the analysis of deflection tests performed with the falling weight deflectometer. In this analysis, a structural adequacy index was used to assess the pavement structural service life. This information was then fed into a life-cycle analysis module to determine the effect of the higher moisture content on the pavement life-cycle cost. An increase in base course moisture content from 16% to 45% resulted in the reduction of pavement service life from 13 to 7 years. For a 40-year period, this translates to a three-fold increase in life-cycle cost for a 250-ft-long pavement section. Reducing moisture retention through various means, thereby improving the subsurface drainage quality of flexible pavement systems, can achieve substantial long-term savings.