Main Road Rn7 Between La Pacaudière and Changy (Loire, France) A High Performance Treated Capping Layer at the Limit of the Specifications

A new section of main road Route Nationale 7 (RN7) has been under construction since 2007 between La Pacaudiere and Changy (Loire, France). The capping layer had to be treated with 1% lime and 5.5% cement. At the beginning of the working, the building company proposed another solution to build the capping layer : using a hydraulic road binder instead of cement and increase the mechanical performances of the subgrade formation, to reduce the thickness of the capping layer. A building trial was made in 2008 to compare both solutions. After treatment and compaction, the measurements by gamma densitometer with two probes showed that the compaction rate objectives had only been reached by the building company solution. Unfortunately, the laboratory study showed that the soil treated with the hydraulic road binder had bad mechanical performances in case of less compaction or binder content. So, an efficient monitoring plan was set up to guaranty optimal building conditions. Moreover, the building company has made the layer with high performance working machines such as an in-situ moistening machine and a pulvimixer. Results of daily moisture content, gamma densitometer, diametral compression and deflexion tests showed that the realisation objectives had been reached.