Research on Fracture Behavior of Fiber-Asphalt Mixtures Using Digital Image Correlation Technology.

Many researchers use fiber to improve the cracking resistance of asphalt mixtures, but research concerning the effects of fiber on fracture behavior is limited. The fracture behavior of asphalt mixtures with various fiber types (basalt fiber, glass fiber, and polyester fiber) and contents (0.1%, 0.2%, 0.3%, 0.4%, and 0.5%) has been studied using the indirect tensile asphalt cracking test (IDEAL-CT) in conjunction with digital image correlation (DIC) technology. The evaluation indexes used in the test included crack initiation energy (Gif), crack energy (Gf), splitting tensile strength (RT), cracking tolerance index (CTindex), and the real-time tensile strain (Exx) obtained using digital image correlation technology. The results showed that despite the fiber type, the increase of fiber content resulted in first, an increase, and then, a decrease of the cracking resistance of asphalt mixtures, indicating the presence of optimum fiber content-specifically, 0.4%, 0.3%, and 0.3% for basalt fiber, glass fiber, and polyester fiber, respectively. The development of real-time tensile strain, obtained based on digital image correlation technology, could be divided into two stages: slow-growth stage and rapid-expansion stage. In addition, asphalt mixture with basalt fiber presented the best cracking resistance at both the slow-growth and rapid-expansion stages. This research is helpful in understanding the effects of fiber type and content on the fracture behavior of asphalt mixtures and has certain reference significance for the application of fiber in asphalt mixtures.

Evaluation of the Interfacial Interaction Ability between Basalt Fibers and the Asphalt Mastic.

The interfacial properties between the asphalt mastic and fibers plays an essential role in the fiber-enhanced asphalt mixture properties. However, there is a lack of comprehensive studies on the indicators to evaluate the interfacial interaction ability of fibers with the asphalt mastic. Therefore, this paper selected three types of basalt fibers (denoted as A-BF, B-BF and C-BF) coated with different impregnating agents to prepare the fiber asphalt mastic. The Dynamic Shear Rheometer (DSR) test-based indicators, pull-out strength, and adhesion work were used to access the fiber asphalt mastic interfacial interaction ability. The differences between different indicators were compared and analyzed. The results show that all the selected indicators in this paper can effectively reflect the different fiber asphalt mastic interfacial properties. The evaluation results with different indicators are consistent. The interfacial interaction between fibers and the asphalt mastic increases with increasing temperature. The evaluation result with adhesion work is the most accurate. However, the pull-out strength test is simple, and the test result correlates well with adhesion work, which can be adopted daily to evaluate the fiber asphalt mastic interfacial properties.

Effects of Fiber Diameter on Crack Resistance of Asphalt Mixtures Reinforced by Basalt Fibers Based on Digital Image Correlation Technology.

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.

Investigation on Fatigue Performance of Asphalt Mixture Reinforced by Basalt Fiber.

Basalt fiber has been widely used in asphalt mixture due to its excellent mechanical properties and good combination with asphalt. In order to systematically evaluate the enhancement effect of basalt fiber on the fatigue performance of the mixtures, gradations of Stone Mastic Asphalt and Superpave with different nominal maximum aggregate sizes, namely SMA-13, SUP-20 and SUP-25, were prepared, and a four-point bending beam fatigue test was adopted under the strain control mode. The fatigue damage mode was assessed based on the phenomenology theory, energy dissipation theory and change rate of dissipated energy. The results showed that basalt fiber could well increase the fatigue life of the mixtures. Basalt fiber could also increase the cumulative dissipated energy of the mixtures, and it was linearly correlated with the fatigue life in double logarithmic coordinates. In the meantime, adding basalt fiber could increase the change rate of dissipated energy of the mixtures. Furthermore, it is not appropriate to take the stiffness modulus declined to 50% of the original as the fatigue failure criterion of the mixture; this paper suggested that it is reasonable when the stiffness modulus was 15-25% that of the initial. These findings provide a theoretical basis for exploring the fatigue failure of asphalt pavements.

Prediction of Crack Resistance of LFSMA-13 with and without Anti-Rut Agent Using Parameters of FTIR Spectrum under Different Aging Degrees.

This paper aims to better analyze the crack resistance of lignin fiber reinforced SMA-13 (LFSMA-13) asphalt mixtures, with and without polymer anti-rut agent (ARA), under different aging degrees. IDEAL-CT test and Fourier transform infrared (FTIR) spectroscopy were utilized to analyze the relationships between the crack resistance of LFSMA-13, with and without ARA, and the parameters of the FTIR spectrum of the asphalt extracted from the test samples. A convenient testing method to predict the anti-crack ability of the mixtures in a road was also derived in this study. The test samples were prepared using the specifications listed by AASHTO. The fracture formation work (Winitial) and cracking index (CTIndex) in the IDEAL-CT test were adopted to reflect the cracking ability of the asphalt mixtures in both the crack formation stage and the crack propagation stage. The peak areas of the FTIR spectrum were utilized to reveal the chemical properties of the asphalt material inside the SMA-13 asphalt mixtures, with and without ARA under different aging degrees. Grey correlation analysis was adopted to choose the most suitable FTIR spectrum parameters to derive the prediction models of Winitial and CTIndex under different aging degrees. After conducting a series of tests, the results showed that the aging process could well affect the crack resistance of the test samples and the peak areas of the asphalt extracted from the mixtures. The FTIR parameters selected from the grey correlation analysis could be used to well predict the anti-crack ability of the asphalt mixtures.

Genome-Wide Identification and Expression Analysis of the Dof Gene Family in Medicago sativa L. Under Various Abiotic Stresses.

The Dof transcription factor is a plant-specific transcriptional regulator that plays important roles in plant development and acts as a mediator in plant external stress responses. However, Dofs have previously been identified in several plants but not in alfalfa (Medicago sativa L.), one of the most widely cultivated forage legumes. In the present study, a total of 40 MsDof genes were identified, and the phylogenetic reconstruction, classification, conserved motifs, and expression patterns under abscisic acid (ABA), cold, heat, drought and salt stresses of these Dof genes were comprehensively analyzed. The Dof genes family in alfalfa could be classified into eight classes. Gene ontology (GO) and tissue-specific analysis indicated that most MsDof genes may be involved in biological functions during plant growth. Moreover, the expression profiles and quantitative real-time PCR analysis indicated that eight candidate abiotic tolerance genes were induced in response to four abiotic stresses. This study identified the possibility of abiotic tolerance candidate genes playing various roles in stress resistance at the whole genome level, which would provide new information on the Dof family in alfalfa.

Suitability of Fiber Lengths for Hot Mix Asphalt with Different Nominal Maximum Aggregate Size: A Pilot Experimental Investigation.

Fiber length is a key parameter for the mixture design of basalt fiber-reinforced hot mix asphalt (HMA), which significantly affects the mix performance. To evaluate the suitability of fiber lengths for HMA with different nominal maximum aggregate size (NMAS), basalt fiber with the lengths of 3, 6, 9, 12, and 15 mm were selected for dense graded gradations with different NMASs (namely, SUP-13, SUP-20, and SUP-25), so as to prepare the fiber-reinforced HMA mixtures. Then, the mix performance was evaluated by an indirect tensile asphalt cracking test (IDEAL-CT), a four-point bending beam fatigue test, a wheel tracking test, a uniaxial penetration test, a low temperature bending beam test, and a freeze-thaw splitting test. Based on the performance results, the optimum fiber length for each mix gradation was proposed by the normalization method. The results showed that adding basalt fiber can enhance the comprehensive performance of all three types of HMA to a great extent. Furthermore, fiber length presented remarkable impact on the crack resistance, the fatigue resistance of the HMA, and the low temperature crack resistance, but it had limited influence on the high temperature deformation resistance, and water stability. The optimum fiber length for SUP-13, SUP-20, and SUP-25 was 6, 9, and 12 mm, respectively.