In 1996, a steering committee comprising representatives from industry, lime manufacturers, and Queensland Main Roads began to review literature and conduct research into lime stabilisation, especially developing long-term strength of the subgrade. Traditional methods of the design of lime stabilised subgrades initially involved adding sufficient lime to improve the plastic properties, and more recently sufficient to achieve a target pH. In 1997 members of the steering committee reviewed a design procedure based on research work by Little (USA) who recommends that the percentage of lime to be incorporated in the subgrade should be based on the peak 28-day UCS achieved at different percentages of lime. Little believes that design based on the previous pH method may not always be conservative. At the higher lime concentrations he recommends, the pH is raised sufficiently high to allow the silicon and the aluminium in the clay to be dissolved, and these can then form stable compounds in a pozzolanic reaction similar to that which occurs with portland cement (based on long term US data that the resultant strength gains are permanent and ongoing). Queensland Main Roads has now constructed two projects with lime stabilised subgrades near Warwick in South East Queensland. These were based on extensive laboratory testing. The performance of these pavements is being monitored and the results to date are exceeding expectations. (A)
Abstract