Investigation into the freeze–thaw durability of semi-flexible pavement mixtures

Semi-flexible pavement (SFP) is made of a composite material that consists of porous asphalt concrete (PA) filled with highly flowable grouting material. At present, most researches on SFP focuses on the materials design and pavement performance characterisation, and very limit effort has been made on evaluating its freeze–thaw durability, which limits the application of SFP in cold regions. The present paper was to fill this gap. In the study, two SFP mixes made with a given PA but two different grouting materials (early-strength (ES) and high-strength (HS) grouting materials) were evaluated. ASTM C666 freeze–thaw durability tests were performed not only on the SFP mixes but also on each of SFP component (PA, ES and HS grouting materials), where relative dynamic modulus and mass loss of the tested samples were measured. In addition, indirect tensile strength of the samples was also tested, and the stiffness and strain–stress behaviour of the samples were evaluated. The results indicate that the order of the freeze–thaw resistance of the individual components was the PA matrix < ES grouting material (4.9 MPa at 3 h and 25.4 MPa at 28 days) ≪ HS grouting material (82.4 MPa at 28 days). The relative dynamic elastic modulus and strain–stress behaviours of SFP-ES samples were very similarly to those of PA, indicating the loss of integrity of the composite during freeze–thaw cycling. Differently, relative dynamic elastic modulus and strain–stress behaviours of SFP-HS samples were close to those of HS grouting material, indicating that enhanced freeze–thaw resistance of a SFP mix can be achieved by incorporating a high strength grouting material into a PA matrix.