This report details the progress made in tests in Oklahoma, USA ,and Christchurch, New Zealand, during the period August 2004 to June 2005, exploring digital imaging technology to measure chipseal surface texture. It details the research methodology to develop a technology to replace the sand circle test as a means to measure chipseal surface texture more accurately and safely.
The project used digital imagery and exploited ‘information theory’ to develop a quantitative relationship between texture measured by the sand circle test and the fast Fourier transform of a digital image of the surface taken at the same spot as the test. The preliminary correlation achieved and reported in the interim report has been confirmed by a larger group of data collected after the interim report was written.
A reliable statistical correlation using linear regression analysis with a coefficient of determination of 80% between digital image processing output and sand circle measurements taken at the same spot was found. Thus, both concept and scientific principle were conclusively proven.
A key finding was that separate regression models would have to be developed for each chipseal design type and possibly for each aggregate nominal size or chip grade.
Keywords: chipseal, digital image processing, macrotexture, information theory, road, road surface, sand circle test, surface texture, texture measurement