Investigation of the matric suction role on the curing mechanism of foamed asphalt stabilised mixtures

Moisture content is of great importance for foamed asphalt stabilised mixtures, since it influences mixing, compaction, curing process and the structural performance. The curing process, in which water evaporates, is responsible for the increase of the bearing capacity of foamed mixtures. Although different loading resistance mechanisms contribute simultaneously to the layer stiffness, the aim of this research is to evaluate the influence of matric suction in the stiffness of two foamed asphalt mixtures that have been used as base course materials in experimental test sections. Filter paper, X-ray microcomputed tomography and triaxial resilient modulus tests were conducted at four moisture conditions. The filter paper test indicated an increase in the matric suction when water evaporated from the specimen, which was validated by the reduction of the air voids measured with microcomputed tomography. From triaxial resilient modulus and matric suction results, it was observed that although other mechanisms might be dominating the loading resistance of foamed mixtures, the matric suction influences the stiffness of these materials.