The paper aims to investigate the influence of basalt fiber (BF) on the crack resistance of the asphalt mixture and conduct a mechanical analysis. First, two typical asphalt mixtures, namely AC-13 and SMA-13, were designed. The impact of BF on the mixture design results was analyzed. Then, several macroscopic tests, namely the four-point bending test, indirect tensile test, and semicircular bending test (SCB), were conducted to assess the effect of BF on the cracking resistance of asphalt mixtures. Finally, the influence of BF on the cracking resistance of asphalt mixtures was analyzed based on an environmental scanning electron microscope (ESEM) observation. The results show that: (1) BF increases the optimal asphalt content of AC13 and decreases the optimal asphalt content of SMA-13, which is caused by the different asphalt-absorption capacity of BF and lignin fiber (LF). (2) BF enhances both the fatigue crack resistance and temperature crack resistance of asphalt mixtures. The enhancement on the SMA-13 is more significant, indicating that the enhancement of BF on asphalt mixtures is related to the type of aggregate gradation. (3) BFs in the asphalt mixture lap each other to form a spatial network structure. Such structure can effectively improve the crack resistance of the mixture by dispersing the load stress and preventing the flow of asphalt mastic. The study results provide an effective method to design crack-resistant asphalt mixtures.

It is now more popular to use basalt fibers in the engineering programs to reinforce the crack resistance of asphalt mixtures. However, research concerning the impact of the basalt fiber diameter on the macro performance of AC-13 mixtures is very limited. Therefore, in this paper, basalt fibers with three diameters, including 7, 13 and 25 μm, were selected to research the influences of fiber diameter on the crack resistance of asphalt mixtures. Different types of crack tests, such as the low temperature trabecular bending test (LTTB), the indirect tensile asphalt cracking test (IDEAL-CT), and the semi-circular bend test (SCB), were conducted to reveal the crack resistance of AC-13 mixtures. The entire cracking process was recorded through the digital image correlation (DIC) technique, and the displacement cloud pictures, strain, average crack propagation rate (V) and fracture toughness (FT) indicators were used to evaluate the crack inhibition action of the fiber diameter on the mixture. The results showed that the incorporation of basalt fiber substantially improved the crack resistance, slowed down the increase of the displacement, and delayed the fracture time. Basalt fiber with a diameter of 7 μm presented the best enhancement capability on the crack resistance of the AC-13 mixture. The flexibility index (FI) of the SCB test showed a good correlation with V and FT values of DIC test results, respectively. These findings provide theoretical advice for the popularization and engineering application of basalt fibers in asphalt pavement.

To clarify the influence of fiber type on the long-term performance of stone mastic asphalt (SMA), this paper used basalt fiber (BF) and lignin fiber (LF) to modify SMA-13 (SMA with aggregate nominal maximum particle size of 13.2 mm) asphalt mixture. The pavement performances (high-temperature performance, cracking resistance at low and medium temperature, and water stability) of the two kinds of fiber-reinforced SMA-13 were checked under different aging degrees (unaged, short-term aged and long-term aged), scanning electron microscope (SEM) test was conducted to explain the strengthening mechanism of the fibers. Fourier transform infrared spectrometry (FTIR) was used to analyze the changes in the chemical composition of asphalt after aging. The results of the wheel tracking test and uniaxial penetration test showed that the high-temperature performance of the BFSMA-13 (defined as the SMA-13 containing BF) is better than that of the LFSMA-13 (defined as the SMA-13 containing LF) at different aging degrees. The high-temperature performance of BFSMA-13 increases with the increase of the aging degree, while the aging process decreases the high-temperature property of LFSMA-13. The results of the three-point bending test and semi-circular bending (SCB) proved that BFSMA-13 is more capable of deformation and less prone to cracking at low and medium temperatures. The results of the immersion Marshal test indicated that BF can better improve the strength and the water stability of the SMA-13 mixture than LF. The SEM images showed that basalt fibers form a solid three-dimensional network structure in the mixture which could contribute to the strengthening of the mixture. The results of infrared spectroscopy analysis showed that styrene–butadiene–styrene (SBS) degrades during asphalt mixture aging, and that the chemical composition of asphalt changes more after aging in LFSMA-13 than in BFSMA-13. The conclusions of this study help toward further understanding of the performance changes of the SMA-13 mixture during its service life and to guide the selection of fiber additives for SMA-13 mixtures.

To evaluate the long-term performances of different polymer-modified asphalt mixtures, three modifiers were chosen to modify AC-13 (defined as the asphalt concrete with the aggregate nominal maximum particle size of 13.2 mm); namely, high viscosity modifier (HVM), high modulus modifier (HMM), and anti-rutting agent (ARA). The deformation and cracking resistance of different polymer-modified mixtures were checked at different aging conditions (unaged, short-term aged, and long-term aged for 5, 10, and 15 days respectively). The results of the Hamburg wheel-track test and uniaxial penetration test (UPT) showed that the rutting resistance of all asphalt mixtures changed in a V-shape as the aging progressed. From the unaged stage to the long-term aging stage (5 days), the rutting resistance decreases gradually. While after the long-term aging stage (5 days), the rutting resistance increases gradually. Results from the semicircular bending test (SCB) and the indirect tensile asphalt cracking test (IDEAL-CT) indicated that the cracking resistance of all the mixtures gradually decline with the deepening of the aging degree, indicating that aging weakens the crack resistance of asphalt mixtures. Additionally, test results showed that the rutting resistance of ARA AC-13 (defined as AC-13 containing ARA) is the best, the cracking resistances of ARA AC-13, HMM AC-13 (defined as AC-13 containing HMM) and HVM AC-13 (defined as AC-13 containing HVM) have no significant difference, and different polymer modifiers had different sensitivities to aging due to the polymer content and the type of modifier. The conclusions of this study help to further understand the long-term performance of polymer-modified asphalt mixtures during service life and to help guide the selection of modifiers for mixtures.

Steel slag has been used as an aggregate for asphalt mixtures for many years, but its excessive volume expansion has limited its wide applicability. With the development of steel-making technology, a considerable amount of steel slag powder (SSP) was produced in Shanghai. The objective of this article is to evaluate the feasibility of using SSP as a filler in hot-mix asphalt mixtures (HMAs), with the aim to eliminate the volume expansion of steel slag asphalt mixture while retaining good pavement performance. First, a common AC-13 mixture was designed with limestone aggregate and mineral filler. Then, 25, 50, 75, and 100 % of the limestone mineral filler in the AC-13 was replaced by SSP, according to the volume ratio, respectively. The asphalt content was kept constant in this process. Then the volume expansion property, rutting resistance property, low temperature property, moisture property, and failure property of the asphalt mixtures were checked. According to the test results, the AC-13 that used SSP exhibited negligible volume expansion, while other properties were better than those of the common AC-13, especially the rutting resistance and moisture properties. The test results also showed that the higher the replacement ratio of SSP, the greater the effect on the properties of the asphalt mixtures. Finally, it was concluded that SSP could replace mineral filler in asphalt concrete (AC) with better pavement performances and acceptable volume expansion.

A wide variety of polymer additives have been widely used in recent years. However, the effect of different polymer additives on the durability of asphalt binders has not been investigated thoroughly. To evaluate the aging property of styrene-butadiene-styrene (SBS) asphalt binder with different polymer additives, three polymer modifiers, namely high modulus modifier (HMM), anti-rutting agent (ARA), and high viscosity modifier (HVM), were added to it. First, the Thin Film Over Test (TFOT) and Pressure Aging Vessel (PAV) was performed on the asphalt binders. The rheological properties of the four asphalt binders before and after aging were then checked by the Dynamic Shear Rheometer Test (DSR). The chemical compositions of the asphalt binders were determined by the Fourier Transform Infrared Spectrometer (FTIR) test. Several aging indicators were adopted to reflect the aging degree of the asphalt binders. The results show that when polymer additives are added to the SBS asphalt binder, the complex modulus, storage modulus, loss modulus, and rutting factor substantially increase and the phase angle decreases. All the test parameters become higher after aging. The phase angle of the SBS asphalt binder is the highest at both unaged and aged states, while its other parameters values are the smallest. Moreover, the Carbonyl Aging Indicator (CAI) of SBS with polymer additives becomes lower under both TFOT and PAV conditions, indicating that polymer additives can improve the aging resistance of SBS asphalt, of which HVM modifies the aging resistance best. Complex Modulus Aging Indicator (CMAI) and Storage Modulus Aging Indicator (SMAI) have the best correlation coefficients with CAI, and the two aging indicators can be used to predict the aging degree of polymer modified asphalt binders.