Despite the successful use of cement-stabilised minestone (CSM) in road construction, some CSM pavements have suffered deformation attributed to the expansion of the CSM layer. Three sites where deformation has occurred are described, and evidence from field samples is presented. Chemical analyses of the retrieved samples showed that the materials had reduced iron sulfide and increased sulfate contents when compared with reported values for the raw minestones. Examination of thin sections suggested that much of the distress within the CSMs was associated with deteriorating pyritic minestone particles.In addition, sulfate minerals were frequently found in close association with both the pyritic minestone and the products of cement hydration. X-ray diffraction analysis and scanning electron microscopy produced further evidence of sulfate minerals in the cracks of the CSMs. It is concluded that the long-term expansion of CSM is due to the oxidation of pyrite, a component of the raw minestone, to form sulfate minerals. Not only does the ongoing sulfate production increase the potential for sulfate attack on the products of cement hydration, but the reduced mineral density of the sulfate products generates crystallisation pressures within the CSM.
Abstract