Chemical Stabilisation Alternatives for Marginal Materials Found Within the Cobar Region

The Cobar region is home to a wide range of soil types where the material properties of the soil can vary significantly depending on the area within the Shire. Typically however naturally occurring Cobar soils are not suitable for use as road pavement materials without treatment. This can be seen from the undesirable material behaviour exhibited on the 1,600km of natural surface roads found within the area, particularly during and following rainfall events. With gravel resheeting not a feasible option at present for the Council, the aim of this project was to investigate the effectiveness of alternative and traditional binders in regards to the treatment of Cobar soils on unsealed roads, with a focus on reducing moisture sensitivity and increasing stability and durability. The investigation conducted involved obtaining soil samples from two particular areas of interest within the region and undertaking soil classification testing on the materials, namely Shire Road 3 (SR3) and Regional Road 7518 (RR7518). A variety of binders, including application rates, were then identified for trial on the two soils with binder testing conducted to investigate the effectiveness of the selected binding agents. The binders chosen were quicklime, lignosulfonate, bitumen emulsion, sodium silicate and 70/30 blend cement/fly ash. From unconfined compressive strength, Atterberg limit, linear shrinkage, abrasion, capillary rise and erosion testing undertaken on the samples the most suitable binding agents from those tested were determined for the two soils. Results obtained indicate that 1.5% quicklime in combination with 3% bitumen emulsion is most suitable in the treatment of the soil sampled from SR3. For the soil sampled from RR7518, results obtained indicate that the addition of 1.5% 70/30 blend cement/fly ash with 3% bitumen emulsion is most suitable in improving the material properties of the soil. Practical and economic implications of the selected binders were investigated with no practical field application issues identified for the products as part of on site pavement stabilisation works. Further cost benefit analysis is required to be undertaken however as initial calculations suggest that the price per square meter for use of bitumen emulsion as a binding agent may not be feasible. From the investigation undertaken for this study, the project aims were achieved with effective binders identified for the treatment of Cobar soils sampled from SR3 and RR7518. Results obtained showed a significant increase in the strength and durability characteristics of both materials due to the addition of the selected binders