Study of permeability characteristics of open graded friction courses used in wearing courses

Abstract

Open graded friction course (OGFC) has been used by several countries since 1950. While many countries report good performance, some countries have stopped using OGFC due to unacceptable performance and/or lack of adequate durability. High permeability is one of the important characteristics of the OGFC mixtures. There is a high possibility of fail the ordinary OGFC mixtures in tropical countries due to heavy dust content in the environment. In the absence of proper, maintenance standard of roads, there is high potential of clogging of dust in OGFC layers. So, there is a need of an improved mix design procedure to help highway agencies in successful use of OGFC. The primary objectives of this study were to evaluate the permeability characteristics of OGFC in the laboratory with various gradations and recommend a proper testing method to evaluate the performance of the OGFC mixes. Typical permeability measures (void ratio, porosity) do not indicate the pore sizes and pore distribution and pore connectivity of the mixtures. An experimental procedure has been proposed to measure the permeability under both laminar and turbulent flow conditions. Three gradations used in a previous study were analysed in the experimental setup proposed in the study. Analysis of the test results of the mixtures showed a comparison of the mixture designs with respect to the pore size and the number of pores which can be used as OGFC mixture design parameter in future.