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.

Semi-flexible pavement (SFP) is widely used in recent years because of its good rutting resistance, but it is easy to crack under traffic loads. A large number of studies are aimed at improving its crack resistance. However, the understanding of its fatigue resistance and fatigue-cracking mechanism is limited. Therefore, the semi-circular bending (SCB) fatigue test is used to evaluate the fatigue resistance of the SFP mixture. SCB fatigue tests under different temperature values and stress ratio were used to characterize the fatigue life of the SFP mixture, and its laboratory fatigue prediction model was established. The distribution of various phases of the SFP mixture in the fracture surface was analyzed by digital image processing technology, and its fatigue cracking mechanism was analyzed. The results show that the SFP mixture has better fatigue resistance under low temperature and low stress ratio, while its fatigue resistance under other environmental and load conditions is worse than that of asphalt mixture. The main reason for the poor fatigue resistance of the SFP mixture is the poor deformation capacity and low strength of grouting materials. Furthermore, the performance difference between grouting material and the asphalt binder is large, which leads to the difference of fatigue cracking mechanism of the SFP mixture under different conditions. Under the fatigue load, the weak position of the SFP mixture at a low temperature is asphalt binder and its interface with other materials, while at medium and high temperatures, the weak position of the SFP mixture is inside the grouting material. The research provides a basis for the calculation of the service life of the SFP structure, provides a reference for the improvement direction of the SFP mixture composition and internal structure.

To determine the mechanical properties of cement asphalt mortar (CAM) in the field, this contribution first presents a model to elaborate the relationship of strength to ultrasonic pulse velocity (UPV). Next, a mechanical test (compressive, flexural strength, and static modulus) and a UPV test are conducted on CAM at different ages to calibrate the proposed model. Finally, three fitted formulas are established based on the proposed model and verified with additional test results. Results suggest that a UPV test is a helpful method for estimating the mechanical properties of CAM in the field and can reach a high precision.

This paper aims to investigate the fatigue cracking evolution of cold recycled asphalt mixtures with asphalt emulsion (CRME) under different curing times. The fatigue cracking model of CRME based on damage mechanics and fracture mechanics was analyzed according to the fatigue loading curve. Firstly, the fatigue cracking evolution of CRME was studied through an SCB strength test and SCB fatigue test. Then, the fatigue damage mechanics were used to establish a nonlinear fatigue cracking model, and the damage degree of CRME at the initial cracking point was determined. The Paris formula was used to characterize the law of fatigue crack propagation. Finally, the microstructure of CRME was observed by scanning electron microscopy (SEM) with the backscattering method. The results indicate that the initial cracking point appears at around 60% of the fatigue life according to the SCB fatigue test by means of image analysis. The damage variable was obtained through the cracking model, and the value of the damage variable was determined as 0.06–0.17 at the initial cracking point. In addition, the Paris formula showed that the crack growth of CRME can be reflected by the stress intensity factor and correlative parameters. Moreover, cement hydration products were mixed with the asphalt membrane to form a denser spatial structure during the curing process, which may provide higher fatigue performance of CRME. This research may provide a theoretical reference for studying the fatigue cracking behavior of CRME.