Experimental investigation of the permanent deformation and void ratio attenuation of porous asphalt mixtures with hydraulic effects

Abstract To investigate the quantitative influence of the material gradation characteristics, saturation degree and loading frequency on the permanent deformation of porous asphalt (PA) mixtures under temperature, loading, and hydraulic coupling conditions, a hydraulic coupling repeated loading test is conducted for five types of PA mixtures with different nominal maximum aggregate sizes, void ratios, saturation degrees and load frequency inputs. The test results indicate that the PA-20 mixture has better anti-deformation performance than the PA-13 and PA-16 mixtures. A larger void ratio corresponds to weaker anti-permanent deformation performance. When the initial void ratio is 24%, the flow number prominently decreases to approximately less than 11% of the initial void ratio of 16%. The results of the loading test with water storage show that the saturation state has a more significant impact on the permanent deformation of PA-13 mixtures than PA-16 and PA-20. When the frequency increases, the cumulative microstrain of the mixture greatly decreases, and the influence degree of frequency on the deformation becomes increasingly obvious when the void ratio increases due to the effect of hydraulic coupling. To easily evaluate the void ratio attenuation of PA, a uniform expression is proposed to characterize the three-stage strain growth, which shows that the permanent deformation curve exhibits nonlinear growth in the second stage of deformation. Then, the minimum permanent deformation growth rate is presented to quantitatively evaluate the deformation resistance performance. Overall, a higher saturation degree of the lower loading frequency corresponds to a smaller PDGRmin. A formula is presented to analyse the effect of permanent deformation on the change in void ratio: the loading frequency, saturation degree and initial void ratio significantly affect the attenuation of the AV ratio. Specifically, the coupling of frequency and water storage slows the decrease in air void ratio.