Reconstruction of a Cement-Stabilised Fly-Ash Road-Base

In 1999 - in the province of Noord-Brabant in the Netherlands - an eighteen-year-old asphalt road with a cementstabilised fly-ash road-base, appeared to be in bad condition. Further investigation showed that the base was almost completely disintegrated, probably due to bad drainage and due to a possibly low cement content. The base material was tested in leaching tests according to NEN- 7343. These tests showed that heavy metals – Mo, V and Se - were critical in view of the leaching criteria. The base material was therefore indicated to be no longer suitable for the unbound road-base. Three options were investigated: 1 dump the base material and construct a new base 2 isolate the base in the existing road by applying special conditions in order to reduce the amount of leaching and comply with the environmental regulations. 3 break up the asphalt and the existing base, mix it in situ with cement, and compact it. Thus, a stabilized and solidified layer is created which is in accordance with all existing environmental and civil engineering standards. The third option was chosen in view of environmental benefits and economy, but also to gather experience with the techniques of stabilisation and solidification. In 2000 a project team was formed to work out a research programme. The team consisted of representatives of the local authorities (the province of Noord-Brabant), two research institutes (TNO and KOAC-WMD) and the Dutch cement industry (ENCI). This paper describes the pavement reconstruction design and the laboratory tests performed to determine the required cement content of a mixture, taking into account all criteria (leaching, compressive strength, density, level of compaction etc.). For this purpose, test specimens with varying cement content were produced and were tested. After succesfully finishing the laboratory programme, the actual reconstruction was performed in a demonstration project in August 2001.