Mechanism, prevention and remedy of alkali-pumping in new constructed asphalt pavement

The issue of alkali-pumping has emerged in recent years raising concerns on the quality of the newly constructed asphalt pavement. To understand alkali-pumping and its effects, we conducted two-year on-site inspection of a pavement and analysed the mineral composition of alkali-pumping. The water permeability, void characteristics, and water stability of the asphalt pavement with and without alkali-pumping were tested and compared. Then, we preliminary analysed the mechanisms. Furthermore, the probability of the alkali-pumping and its control method. Lastly, 3D ground-penetrating radar was utilised for analysing the relationship between the dielectric constant and the distribution of alkali-pumping. Subsequently, dielectric constant thresholds corresponding to alkali-pumping were established. The results showed that alkali-pumping is caused by the segregation of the pavement and the leakage of alkali elements. Furthermore, the dielectric constants with and without alkali-pumping were significantly different, and their spatial distribution was well correlated with the occurrence of alkali-pumping. Finally, it was determined that asphalt pavements with a dielectric constant smaller than 3.5 are likely to experience alkali-pumping, while those with a dielectric constant between 3.5 and 6.5 are unlikely to experience alkali-pumping, and in those with a dielectric constant greater than 6.5, the probability of alkali-pumping is negligibly small.