Mechanical mechanism analysis of differences in tension and compression within semi-flexible pavement materials at micro and macro scales

To investigate the mechanism behind tensile–compressive strength differences in pavement materials and to improve material design, this study conducted relevant experiments. The compressive and tensile strengths and moduli of semi-flexible pavement material (SFPM-16) were tested at different curing ages. X-ray diffraction (XRD) and thermogravimetric–differential scanning calorimetry (TG-DSC) were used to examine how the types and contents of binder hydration products influenced these mechanical parameters. In addition, CT scanning and image processing techniques were applied to analyze the relationship between two- and three-dimensional pore distributions in the mixture and its tensile and compressive properties. The results indicate that the mechanical parameters of SFPM-16 after 3 days of curing exceed 70 % of those at 28 days. The compressive-to-tensile mechanical parameters ratio increases exponentially with curing age and CH content, and approached 6.2. The C-S-H gel generated during the hydration process fills the skeletal structure of the mixture, but the increase in Ca(OH)2 crystals (CH) makes the material more prone to brittle failure, thereby making the different mechanical characteristics in tension and compression more significant. The larger the indicator values characterizing the two-dimensional and three-dimensional distribution of pores, the more pronounced the different mechanical characteristics in tension and compression of SFPM-16. As the variance of surface porosity increases, the direct tensile mechanical parameters exhibit the most significant reduction (approximately 18 %). The compressive and tensile mechanical parameters of SFPM-16 decrease linearly with increasing overall porosity and increase linearly with increasing the proportion of pores below 1 mm³ , with R t rising by about 22 %. Based on these findings, a relationship model was established between the ratio of compressive to tensile mechanical parameters and microstructural indicators. The research outcomes reveal the formation mechanism of the different mechanical characteristics in tension and compression of semi-flexible pavement materials at micro- and macro-scales, quantify the correlations between macroscopic mechanical parameters and microscopic indicators, and hold significant theoretical value and engineering implications. ● Revealed the mechanism of the mechanical characteristics in tension and compression of SFPM at micro- and macro-scales. ● Proposed microstructural indicators to characterize the mechanical characteristics in tension and compression in SFPM. ● Established a relationship model between the macroscopic mechanical parameters and microstructural indicators for SFPM.