Research on Water Stability for a Porous Asphalt Mixture with a Hemispherical Penetration Test

This study investigates the applicability of a hemisphere penetration test for assessing the water stability of porous asphalt mixtures. Three distinct grades of porous asphalt mixtures were selected for analysis. The optimal asphalt–aggregate ratios for these gradations were determined through a comprehensive analysis of the relationship curves for the asphalt–aggregate ratio and both the draindown loss and the Cantabro loss. Experimental investigations were conducted on PA-13 porous asphalt mixture specimens using four hemispheres with varying diameters. Through systematic immersion and freeze–thaw hemisphere penetration tests, an 80-mm-diameter hemisphere was established as the standard size for the evaluation of water stability in porous asphalt mixtures. Subsequent experiments employing the 80-mm-diameter hemisphere in both immersion and freeze–thaw conditions explored the influence of three critical factors on the PA-13’s water stability: gradation, asphalt–aggregate ratio, and aging duration. The results revealed that coarser gradations significantly compromised the water stability, while the asphalt–aggregate ratio played a pivotal role in determining the mixture performance. Notably, the water stability exhibited a complex temporal pattern during aging that was characterized by initial deterioration, subsequent improvement, and eventual further deterioration. Additionally, the study demonstrated that the conditioning methods (immersion versus freeze–thaw) substantially affected the water stability assessments. The findings conclusively demonstrate the feasibility of utilizing an 80-mm-diameter hemisphere penetration test combined with penetration work ratio analysis for the evaluation of water stability in porous asphalt mixtures. Furthermore, this research provides valuable insights and methodological references for assessing water stability in dense-graded asphalt mixtures, potentially advancing quality control and performance evaluation in asphalt pavement engineering.