Pyrite, and organic matter do not fit with soil treatment on Highway A28

Characterization of Palynofacies is commonly practiced on organic petrology especially by petroleum industry as it allows the identification of organic matter present in the samples of petroleum source rocks. This practice is not usual in the typical geotechnical studies for infrastructures of work road floor. An expert report on a case of pathology appeared on marl treated with hydraulic binders has shown the interest of this methodology for detecting materials that could produce swelling problems after the precipitation of secondary ettringite. This study was conducted after building capping layer of the A28 highway (between Le Mans and Rennes - France), where significant swelling have deteriorated the layer performed with cuts of the project. The presentation will focus on this technique that allows detecting disruptive material (organic matter, pyrite and gypsum), otherwise than by chemical soil analysis, that can perform secondary ettringites causing such swelling-type pathology.