Pavement geotechnical properties of polymer modified weathered semi-arid shale subgrade

The use of non-traditional stabilizers with limited water demand for strength development provide significant cost benefit in geotechnical and pavement engineering applications in arid and semi-arid regions. Series of tests were conducted on weathered clay shales of the Witwatersrand super group from Johannesburg East Rand. The specimens were stabilized with different percentages of acrylic based water borne polymer and cured for between 3 and 56 days at 20°C and 50°C respectively. Atterberg limit, Dry and Soaked UCS, Permeability tests and Mercury intrusion porosimetry (MIP) tests were conducted. The results revealed that the strength and durability of the stabilized shale was very sensitive to the curing temperature, increase of curing temperature from 20°C and 50°C resulted in 150% increase in mobilized strength and 200% increase in soaked strength. The curing period at which the maximum strength was developed was dependent on curing temperature. The optimum properties at high temperature are associated with distribution and abundance of very fine pores < 0.002mm. Modified materials with % binder content greater than 8% and cured for more than 14 days at 50°C, were adequate for pavement subgrade and subbase according to local specification TRH 4 (2008).