Valorisation of dune sand-tuff for Saharan pavement design

The current experimental research aims to valorise two Saharan soils (dune sand and tuff) for pavement purposes in arid zones. A mixture of 65 % tuff and 35 % dune sand (named TDSopt) was previously studied and exhibited optimum geotechnical characteristics that were suitable for low-traffic pavements. However, the rise of groundwater level with aggressive sulphate in the Ouargla region, Algeria, weakened the mechanical properties of this TDSopt. Further treatment with sulphate-resistant binders was therefore proposed to remedy this defect. In this research, laboratory testing was performed to define the optimum treatment for the TDSopt, followed by the hydromechanical characterisation of the treated TDSopt. Experimental results validated the following observations. First, the treatment of TDSopt with cement and/or lime resulted in decreased dry density, but an increased California Bearing Ratio (CBR) index. Also notably improved were unconfined compressive strength (UCS), secant modulus (E50) and resistance to immersion (Rimm). More specifically, the defined optimum recipe – TDSopt plus 1.33 % cement and 2.66 % lime – increased the CBR index by 75 % and 35 % for the soaked and unsoaked specimens, respectively. UCS, E50 and Rimm increased by 65 %, 75 % and 65 %, respectively. The optimum treatment also increases the shrinkage limit void ratio of compacted TDSopt from 0.39 to 0.46. Finally, the strength parameters (UCS, cohesion and friction angle) of optimum treated specimens were larger than those of untreated material regardless of water content. At Modified Proctor Optimum, the UCS, cohesion and friction angle increase from 0.54 to 2.46 MPa, 167 to 800 kPa and 23° to 40°, respectively.