n Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese - The performance of unpaved road material using soil stabilisers

Volume 49, Issue 4
  • ISSN : 1021-2019



There are over 500 000 km of unsealed roads in South Africa. Unacceptable levels of dust, poor riding quality and impassability in wet weather are experienced on much of this road network. A potential solution to this ever-increasing problem is the use of soil stabilisers (additives), yet the level of research done on these additives consists mostly of small ad hoc studies.

The aim of this paper is to report on the performance of selected soil stabilisers used on South African unpaved roads with respect to their effect on material strength. The behaviour of the soil stabilisers were tested by determining the effectiveness of the stabilisers in improving the strength of unpaved roads as a function of gravel with different properties for a range of soil stabilisers under wet and dry conditions. The effectiveness was tested over a period of nine months. Four different stabilisers were used on four different wearing-course materials.
The conclusion reached was that there are certain stabilisers that do improve the strength behaviour of pavement material under certain conditions. It was found that the enzyme and sulphonated oil-treated materials had an increase in strength over the test period, and it was concluded that these stabilisers need a curing time of a few dry months to reach their maximum strength. The materials treated with the two polymers gained their maximum strength within two months after construction. It was found that the enzyme-treated material showed an increase in strength when applied to a sandy material with a low PI and the sulphonated oil-treated material performed well when applied to a clayey material containing a reactive clay mineral. The polymers showed no material-specific properties.
Most of the stabilised panels showed an increase in dry strength eight months after construction and this was attributed to the fact that the panels had enough time to dry out and reach their maximum strength over the dry winter months.
The final conclusion was that there are some soil stabilisers available that do improve the strength behaviour of pavement materials. It is, however, important to choose the correct stabiliser for the intended purpose.

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