Transverse cracking is a serious problem for semi-rigid base asphalt pavement. The shrinkage of the base course and the surface course, as well as reflective cracks, are key factors for transverse cracking in asphalt pavement. Crack spacing can directly reflect the degree of transverse cracking in pavements. Therefore, this study aims to calculate the transverse crack spacing and discuss its affecting factors. To this end, a calculation model of transverse crack spacing for the semi-rigid base asphalt pavement was first established. Then, the transverse crack spacings of different composite structures were calculated, and the influences of the shrinkage coefficient, the structural layer thickness, and the pavement tensile strength on transverse crack spacing were expounded. Finally, the transverse crack spacing of the pavement after the appearance of the reflective was calculated. The results show that the lower lime and fly ash content and skeleton gap gradation can be adopted during the design of the base course. Meanwhile, the lower lime and fly ash content in the macadam base, the skeleton gap gradation and asphalt concrete with a larger particle size in the surface layer can be used during the design of surface layer. In addition, the transverse crack spacing of the semi-rigid base asphalt pavement could be increased by reducing the shrinkage coefficient, increasing the thicknesses of the surface course and the base course, and improving the tensile strength of the pavement. After the appearance of reflective cracks, the transverse crack spacing of the surface layer ranged between 32.8 m and 66.5 m. 15fp-AC25, 15fp-AC20, 15df-AC25, and 17fp-AC25 were found to be the best semi-rigid base asphalt pavement structures to reduce transverse cracking. Finally, transverse cracking in pavement composite structures under different bonding conditions needs to be analyzed in the follow-up work.
Styrene-butadiene-styrene (SBS) is currently the most widely used asphalt modifier. However, high-SBS-concentration high-viscosity modified asphalts (HVMA) are characterized by poor flow and storage instability. To make up for the lack of performance of traditional SBS-HVMA, a nano-based high-viscosity composite modified asphalt with excellent performance was developed. Since carbon nanotubes (CNTs) are nanomaterials, they are prone to agglomeration when added to the modified asphalt, and the dispersion effect is poor, which affects the modifier’s contribution rate. To better disperse CNTs in the modified asphalt, the nanomaterials were modified, and two new CNT additives were prepared by combining two polymers with CNTs. The appropriate ratio of these two new additives was selected to be further combined with SBS to obtain CNTs/SBS-HVMA. The flow characteristics and anti-aging properties of the three kinds of bitumen in different temperature ranges were studied by taking the common SBS-HVMA and Tafpack super (TPS) high-viscosity modified asphalts (TPS/SBS-HVMA) as comparison samples and by evaluating the road performance of a stone mastic asphalt (SMA-13) mixture. The storage stability, workable performance, rheological characteristics, and aging resistance of three high-viscosity asphalts were analyzed through a segregation test, dynamic viscosity analysis, Brookfield viscosity measurements, bending beam rheometer (BBR) tests, dynamic shear rheometer (DSR), and multiple stress creep recovery (MSCR) before and after short-term aging. The experimental results showed that CNT/SBS-HVMA exhibited good storage stability and workability. DSR measurements and other rheological tests revealed that TPS/SBS-HVMA had higher low-temperature flexibility than the other modified asphalts, while CNT/SBS-HVMA exhibited good high-temperature resistance, aging resistance, and deformation resistance. Through the verification of asphalt mixture performance, it was found that the high-temperature rutting resistance of CNTs/SBS-HVMA prepared by new CNT additives was 7% and 28% higher than those of SBS-HVMA and TPS/SBS-HVMA, respectively, but the low-temperature performance of CNT/SBS-HVMA was 5% lower than that of SBS-HVMA. This showed that CNT/SBS addition improved the high-temperature performance of the asphalt without a significant negative impact on the low-temperature performance of the asphalt.
The temperature shrinkage of materials primarily causes transverse cracking. Current research mainly focuses on the temperature shrinkage of single materials. This work aims to analyze the effect of the structural combination on temperature shrinkage. To this end, the temperature rise method was first discussed to measure the shrinkage coefficient to replace the traditional temperature drop method. Then, the temperature shrinkage coefficients of the lime–fly ash-stabilized macadam, and ATB and AC asphalt mixtures were measured. The effect of gradation types, lime–fly ash content, and nominal maximum aggregate size on the temperature shrinkage was studied. Finally, the temperature shrinkage of composite structural characteristics was analyzed. The results show that the difference between the temperature shrinkage coefficients obtained by temperature rise and drop methods was relatively small. Thus, the temperature rise method can be used to measure the temperature shrinkage coefficient. In addition, the lime–fly ash-stabilized macadam with the suspended dense gradation or a higher lime–fly ash content has the largest temperature shrinkage strain. The suspended dense gradation should be avoided, and the content of lime–fly ash should be approximately reduced to control the temperature shrinkage strain of the semi-rigid base course. As for the asphalt mixture, the temperature shrinkage strain increased with the decrease in the nominal maximum aggregate size. The asphalt mixture with a larger nominal maximum aggregate size should be given priority to control the temperature shrinkage. Finally, when combined with the base course or surface layer, the temperature shrinkage of the base course was promoted by the surface layer, while the base course inhibited the surface layer. Meanwhile, the mutual influence between the semi-rigid base course and the surface layer was more substantial than that of the mutual influence between the flexible base course and surface layer.
In order to investigate the feasibility of warm mix technology in high-viscosity asphalt mixes, in the current experiment, Shell 70 Grade A asphalt (base asphalt) was modified by AR-HVA (a high-viscosity modifier), and the high-viscosity modified asphalt was further incorporated with two surface-active warm mixes (Evotherm M1 and Retherm). The physical properties of the high-viscosity warm mix-modified asphalts were analyzed by dynamic and Brinell viscosity tests. The compatibility of the warm mixes with the high-viscosity modified and the base asphalt was analyzed by fluorescence microscopy. The modification mechanism of the high-viscosity warm mix-modified asphalts was revealed by Fourier-transform infrared spectroscopy. The high-viscosity modifier significantly reduced the penetration of the matrix asphalt and increased its softening point and 5°C ductility, whereas the two warm mixes increased the penetration and ductility of the high-viscosity modified asphalt and reduced its softening point. The surface-active warm mixes reduced the 60°C viscosity of the asphalt, and the viscosity reduction effect of M1 was better than that of Retherm. The high-viscosity modifier AR-HVA was well dispersed in the asphalt; however, its continuity was not good. The addition of the surface-active warm mixes effectively enhanced the continuity of the high-viscosity AR-HVA-modified asphalt. Infrared spectroscopy revealed little difference between the main components of the matrix asphalt and the high-viscosity asphalt. The addition of the surface-active warm mixes altered the amounts of four components in bitumen and increased its aromatic content.
The high-temperature rheological properties of rubberized asphalt and mixture were evaluated by frequency scanning, repeated creep recovery (RCR) test, temperature sweep test, Hamburg wheel tracking test (HWTT). Based on the Pearson correlation coefficient, the correlation of the mixture gradation and asphalt characteristics with the high-temperature stability of the mixture was analyzed. Finally, the gray correlation theory was applied to analyze the evaluation indexes of the high-temperature rheological properties of rubberized asphalt and mixture. The results show that the asphalt-stone ratio and the fractal dimension (Dc) of coarse aggregate have a significant correlation with the high-temperature performance of the mixture, and the mixture with a smaller asphalt-stone ratio and a higher percentage of coarse aggregate has a better high-temperature performance. The correlation degree of softening point, viscous stiffness modulus and permanent deformation with rubber-asphalt mixture is higher than 0.7, and are significantly higher than those of rotational viscosity at 180°C. Therefore, we recommend the use of permanent deformation, softening point, and viscous stiffness modulus to evaluate the high-temperature performance of rubberized asphalt mixture.
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