Study on Fracture Characteristics of Panel Asphalt Concrete Under Different Loading Rates

Study on Fracture Characteristics of Panel Asphalt Concrete Under Different Loading Rates | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Study on Fracture Characteristics of Panel Asphalt Concrete Under Different Loading Rates Hanbing Yang, Jianxin He, Wu Yang, Xinyu Ding, Peng-peng Chen, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4539941/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The development of internal cracks in asphalt concrete can be seen as a sign of macro crack development. To explore the influence of different loading rates on the crack resistance of panel asphalt concrete, based on the theory of fracture mechanics, DIC digital image correlation technology was used as a test method for crack propagation of specimens. SCB (Semi-circular bending)tests were carried out on panel asphalt concrete with different loading rates (0.05, 0.2, 1, 3, 5,1 0 mm/min). The effects of different loading rates on the fracture index and full-field strain of asphalt concrete were analyzed. the results showed that when the loading rate increases from 0.05 mm/min to 10mm/min, the stress intensity factor ( K IC ) and fracture energy ( G f ) increase, and the crack resistance index ( CRI ) shows the opposite law; With the increase of loading rate, the strain (Exx, Eyy) corresponding to the peak load gradually decreases. After reaching the peak strength, with the increase of load displacement, the crack of the sample gradually expands along the edge of the coarse aggregate at a low loading rate, and the crack penetrates the coarse aggregate at a high loading rate; There are obvious differences in crack morphology of asphalt concrete specimens under different loading rates, When the loading rate is 0.05-1 mm/min, the crack morphology is tortuously rising. When the loading rate is 3-10mm/min, the crack morphology develops almost vertically upward along the pre-crack. The results of the study can provide a reference for the development of cracks and fracture behavior of panel asphalt concrete under different loading rates. Panel asphalt concrete loading rate SCB specimen fracture mechanics index DIC Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Highlights The fracture properties of asphalt concrete under various variable water level loading rates were evaluated based on the SCB test. Digital image correlation (DIC) technique can be used to accurately characterize the crack propagation path of asphalt concrete. The K IC and G f of asphalt concrete increased with the increase in loading rate, and the opposite was true for CRI results 1. Introduction Asphalt concrete is widely used in the construction of pumped storage power plant reservoirs due to its excellent impermeability properties [ 1 – 3 ]. The day and night rise and fall of the upper and lower reservoirs of the pumped storage power station cause the water level to fluctuate periodically and frequently [ 4 ], The variable rate water level has caused a certain load change to the asphalt concrete panel, resulting in the initial defect development of the asphalt concrete panel under the coupling of the water load and the environmental action, the strength attenuation, and the cracks [ 5 , 6 ]. Finally, it causes anti-seepage failure and endangers the safety of the state and people's property [ 7 ]. Therefore, it is of great practical significance to study the fracture characteristics of asphalt concrete panels under different loading rates. At present, the fracture performance of asphalt concrete under different loading rates is mainly carried out from two aspects: test conditions and test methods. For example, starting from the test conditions, Yang et al.[ 8 ] Yang used the R curve to study the effects of two loading rates ( 0.03,1 mm/min) on the fracture properties of asphalt concrete. The results show that the loading rate only affects the energy rate. He et al.[ 9 ] studied the effect of loading rate on the mode I fracture toughness of hot mix asphalt ( HMA ) concrete by repeated tests, and analyzed the obtained data by using 2 and 3-parameter Weibull statistical models. The results show that the two-parameter and three-parameter Weibull models can successfully predict the mode I fracture behavior of the tested asphalt material within the consideration range of the loading rate, which provides a new idea for the fracture of asphalt concrete from the perspective of mathematical statistics. Motamedi et al.[ 10 ] conducted fracture toughness experiments at three low temperatures, three loading rates ( 0.5,1,5 mm/min), and different fiber percentages. They found that by decreasing the test temperature and increasing the loading rate, the fracture toughness values of type I and type III increased. Wei et al. [ 11 ] conducted uniaxial compression tests on asphalt mixtures with six loading rates to investigate the damage characteristics and damage modes of asphalt mixtures. The whole failure process was monitored by combining acoustic emission technique (AE) technology, in contrast, the loading rate of 0.05mm/min has fewer frequency bands than other loading rates, and there are fewer AE signals in the high-frequency band. Qing et al. [ 12 ]studied the test method of concrete damage scale under different loading rates. Starting from the test methods, the test methods for evaluating the deformation and crack resistance of hydraulic asphalt concrete in China mainly include the trabecular bending test and splitting test [ 13 ], however, the difficulty of specimen preparation for these methods [ 14 ], the low correlation between the test data and the actual workability of asphalt concrete [ 15 ], and the presence of permanent deformation in the specimens lead to their limitations in evaluating the fracture behavior of asphalt concrete. Given the shortcomings of the above test methods, in recent years, researchers [ 16 ] have proposed the semi-circular bending test (SCB) and obtained the key indicators to characterize the fracture behavior through the SCB test. The fracture behavior of asphalt concrete [ 17 – 21 ], rock [ 22 , 23 ], ceramics [ 24 , 25 ], glass [ 26 ], and other materials under different conditions was studied. Then Huang et al. [ 27 ] and Mull et al. [ 28 ] analyzed the SCB specimens of asphalt concrete based on the theory of fracture mechanics. Bui et al. [ 29 ] investigated the effect of different loading rates on the fracture properties of asphalt concrete based on SCB tests and recommended a loading rate of 1 mm/min for highway asphalt concrete. Based on the SCB test, Mirsayar et al. [ 30 ] evaluated the strength of the bonding layer between asphalt concrete and cement concrete and gave the fracture criteria between the bonding joints under different mixing modes. To further describe the micro-crack extension trajectory of asphalt concrete, Seo et al. [ 31 ] used digital image correlation (DIC) to describe the formation of micro-damage in asphalt concrete. Yuan et al. [ 32 ] studied the full-field displacement field and strain field of asphalt concrete SCB specimens by DIC technology and verified the rationality of the speckle pattern. Comprehensive domestic and international scholars' research, in the field of asphalt cracking, most of them are through the design of larger span load rates to simulate the loading rate on the asphalt concrete cracking behavior of the research did not take into account the stage of the water level, cyclical changes in the asphalt concrete panels brought about by the impact, which is not reasonable. Therefore, based on the SCB test method and the theory of fracture mechanics, the fracture toughness test of panel asphalt concrete at different loading rates ( 0.05,0.2,1,3,5,10 mm/min) was carried out in this paper. The DIC was used to analyze the strain field characteristics of asphalt concrete from crack initiation to instability failure at different loading rates. From the perspective of crack propagation, the whole process analysis and cracking mechanism of low-temperature cracking of asphalt concrete were studied. The research results can provide further theoretical support for understanding the crack development law of panel asphalt concrete and its panel crack-resistant design. 2. Raw materials and mixing ratios The test was conducted using a project-selected lithology of medium-thick layered/thick bedded grey/grey-white fine crystal limestone, and a jaw crusher was to crush the rock to produce coarse and fine aggregates and some fillers, and then a disc crusher was to prepare the filler separately. Asphalt using 70 # road petroleum asphalt produced by PetroChina Karamay Petrochemical Co., Ltd, the asphalt of the various performance indexes of the test, the test results are shown in Table 1 ; mineral grading particle size grading and dosage as shown in Table 2 . Table 1 Asphalt performance index Test Item Units SL 501–2010 Specimen Test Results Needle penetration (25 ◦C,100 g, 5 s) 0.1mm 60 ~ 80 66.5 Ductility (5 cm/min, 10 ◦C) cm ≥ 20 55 Ductility (5 cm/min, 15 ◦C) cm - >150 Softening point (Globe method) ℃ ≥ 45 53.0 Flash point ℃ ≥ 260 320 Mass change after heating in a film oven % - -0.06 Residual needle entry ratio (25 ◦C) % ≥ 61 83.3 Residual ductility (5 cm/min, 10 ◦C) cm ≥ 6 15.1 Table 2 Mineral aggregate gradation Types of raw materials Sieve Size (mm) asphalt 19 − 16 16-13.2 13.2–9.5 9.5–4.75 4.75–2.36 2.36 − 0.075 < 0.075 Dosage (%) 6.6 6.8 10.5 18.2 15.9 30.0 12.0 7.5 3. Test programs and methods 3.1 specimen preparation When the thickness of the SCB specimen is 50 mm, its mechanical properties tend to be stable [ 33 – 35 ].To reduce the shear deformation at the support point, the bearing spacing is 0.8 times the diameter of the specimen [ 36 ]. According to the above research results, the hot mix asphalt mixture was poured into a three-layer compacted Φ150 × 300mm triaxial mold, and the mold was removed after cooling for 24 hours. The triaxial specimen was cut with a cutting machine, and 15 mm was removed at each end to reduce the influence of density inhomogeneity. And cut into 10 SCB specimens with a diameter of 150 mm and a thickness of 50 mm, Using a very thin diamond saw blade with a thickness of 1 mm, a pre-crack with a depth of 15 mm was cut into the bottom center of the SCB specimen, and the specimen preparation process is shown in Fig. 1 . The cut SCB specimens were placed in a 10°C constant temperature chamber for more than 48 hours. To analyze the whole process of dynamic fracture of panel asphalt concrete, after the preparation of pre-cracked SCB specimens, the surface of the specimens was cleaned first. After the surface was completely dried, speckles were randomly spotted on the surface of the specimens with a marker pen [ 37 ]. 3.2 Test programme To study the influence of different loading rates on the fracture characteristics of asphalt concrete, the loading rate was used as the test variable. Under the conditions of six loading rates (0.05, 0.2, 1, 3, 5, 10 mm/min) and test temperature 10 ± 0.5°C, 20 SCB parallel tests were carried out respectively. The test instrument automatically collects the vertical load and displacement values from the beginning of the test to the complete failure of the specimen [ 38 ].To simplify the loading mode, according to the AASHTO TP124 [ 39 ], the load-displacement curve is obtained. Through the load-displacement curve, the critical stress intensity factor K IC , fracture energy G f , and crack resistance index CRI of the panel asphalt concrete under six different loading rates are calculated, and the results are averaged. The specific test program is shown in Table 3 . Three sets of specimens were taken at each rate and scattered spots were randomly dotted with a marker pen to analyze the whole process of dynamic fracture of asphalt concrete SCB specimens. Table 3 SCB test programme serial number loading rate mm/min fracture index number of specimens Temperature(℃) 1 0.05 K IC G f CRI 20 10 2 0.2 20 3 1 20 4 3 20 5 5 20 6 10 20 3.3 DIC Test Method The tests were conducted using a high-speed industrial camera to acquire digital images of the test process. The industrial camera is placed in front of the test piece and its height is adjusted to the same level as the test piece. The data acquisition system controls the camera to collect the image of the test piece during the test. The surface of the test piece should be flat and speckled. Through testing, the resolution of the captured image is determined to be 3024 pixels, and the interval between each image is 10 s. The digital image correlation technology test system is shown in Fig. 2 . 3.4 Fracture Index Calculation 3.4.1 Stress Intensity Factor The fracture mechanics test is mainly aimed at the crack propagation of the reserved crack specimen under the action of external force and describes the crack propagation ability of the material when the structural defect occurs. In the study of fracture mechanics, the critical stress intensity factor K IC , as a fracture toughness index, can well reflect the stress-strain field strength in the crack tip area, and reflect the ability of the material to prevent the instability and expansion of the crack. It is an important parameter to reflect the performance of the material. The calculation formula is shown in Eq. 1 . $${K_{IC}}=\frac{P}{{2rt}} \times \sqrt {\pi a} \times (4.782 - 1.219\frac{a}{r}+0.063{e^{_{{^{{_{{7.045}}}}}}\frac{a}{r}}})$$ 1 In this equation, K Ic is the critical stress intensity factor (or fracture toughness value) of each specimen at the onset of fracture; P is the critical load; r is the radius of the specimen; t is the thickness of the specimen; and a is the notch length. 3.4.2 Fracture energy Fracture energy is the energy released by the crack extension unit area system, expressed by G f ; the larger the fracture energy is, the stronger the fracture resistance on behalf of asphalt concrete in a certain environment, the energy release rate can be a better description of the fracture performance of the material is a very important parameter in the fracture mechanics, the calculation formula is shown in Eq. 2 . $${G_f}=\frac{{{W_f}}}{{{A_{lig}}}}=\frac{{\int {pdu} }}{{{A_{lig}}}}$$ 2 In this equation, G f is fracture energy or energy release rate; W f is fracture work ; p is the axial load; u is the vertical displacement; A lig = (r-a)*t is the area of the fault zone; r is the radius of the specimen; a represents the length of the incision; t is the thickness of the sample. 3.4.3 Crack resistance index The flexibility index can reflect the crack propagation rate of asphalt concrete [ 40 , 41 ], but it has limitations in evaluating the low-temperature performance of asphalt concrete. For example, there is no post-peak data to calculate the flexibility index at low temperatures, or the post-peak curve is difficult to fit, which makes it impossible to determine the inflection point of the curve. Therefore, KASEER et al. [ 42 ] proposed a fracture index to replace the flexibility index: the crack resistance index. The crack resistance index refers to the strain capacity of asphalt concrete when the first crack occurs under tensile load, which can distinguish asphalt concrete with similar fracture energy but different peak loads. The calculation formula is shown in Eq. 3 . $$CRI=\frac{{{G_f}}}{{{p_{\hbox{max} }}}}$$ 3 In this equation, GRI is the crack resistance index, G f is the fracture energy, and p max is the maximum axial load. 4. Effect of loading rate on fracture properties of asphalt concrete 4.1 Load-displacement curves of asphalt concrete under different loading rates In this paper, different loading rates are used to simulate the effects of diurnal changes in reservoir water level on asphalt concrete panels in actual projects, and the load-displacement curves of the specimens under different loading rates are shown in Fig. 3 . It can be seen from Fig. 3 that the load-displacement curve fluctuates greatly at the same loading rate, indicating that the data is very discrete, and the load-displacement curve shows an unstable and unsmooth trend. This is because there are voids or defects in the specimen, which leads to the fracture of the specimen when the fissures begin to penetrate holes and create cracks, the cracks and holes are connected, or there is a large strength of coarse aggregate at the front edge of the pre-crack, test curve is unstable. The fracture behavior of asphalt concrete and fracture load and loading rate shows a positive correlation trend, the larger the rate of asphalt concrete bearing capacity is stronger, before reaching the peak load Pmax, the damage behavior of the specimen is mainly manifested as linear elastic fracture, with the increase of loading rate, the initial section of the curve slope is gradually steeper, the larger the curve encloses the larger the area of the curve, and the whole is elevated by a progressive relationship. 4.2 Stress intensity factor of asphalt concrete under different loading rates To eliminate the problems caused by the uneven distribution of coarse and fine aggregate particle sizes between samples and the uncertainty of the number of coarse aggregates at the leading edge of the pre-crack of the sample, six loading rates (0.05, 0.2, 1, 3, 5, 10mm/min) were selected to carry out 20 groups of parallel tests to obtain the mean value of K IC under six loading rates, and the change rule of the mean value of K IC under different loading rates was plotted as shown in Fig. 4 , and to further discuss the discrete nature of K IC , the variance of the K IC was discussed, and the results are shown in Fig. 5 . It can be seen from the diagram that with the increase in loading rate, the final strength of the cracked specimen increases, and the fracture resistance of asphalt concrete increases. This is because, under high-speed loading conditions, the internal structure of asphalt concrete will be quickly adjusted to resist deformation, thereby improving the final deformation capacity. Under low-speed loading conditions, asphalt has enough time to flow and deform, resulting in a decrease in material strength. In Fig. 4 , the average values of K IC from low to high for different loading rates are 0.1206, 0.1945, 0.3533, 0.5528, 0.6929, 0.8479 MPa-m 0.5 , respectively, and compared with the results of 0.05 mm/min, the critical stress-intensity factor of 10 mm/min is increased by about 7.03 times, which means that the loading rate has a significant influence on the stress This means that the loading rate has a significant effect on the stress intensity factor K IC , and the slope of the curve tends to flatten and decrease with the increase of the loading rate, and the overall growth is a power function law. It can be seen from Fig. 5 that when the loading rate is less than 3mm/min, the variance of the data is not much different, and the degree of dispersion is similar. When the loading rate is greater than 3mm/min, the variance increases rapidly and the dispersion becomes larger. 4.3 Fracture energy of asphalt concrete under different loading rates Figure 6 shows the variation rule of asphalt concrete fracture energy under different loading rates, it can be seen that the change of fracture energy with the loading rate shows a logarithmic distribution law, with the increase of the loading rate, the upper and lower limits of the fracture energy increase, this is because the loading rate is too fast to make the specimen from the initiation of cracking to the destruction of the time used for a shorter period, the crack is not developed sufficiently to cause the data to a greater degree of dispersion. When the loading rate is 3mm/min, the curve begins to flatten, indicating that when the loading rate exceeds 3mm/min, the effect of the loading rate on fracture energy decreases, and G f is not sensitive to the change in loading rate. Therefore, if the influence of loading rate on the fracture energy of asphalt concrete is considered, the change in loading rate of less than 3mm/min can be studied. 4.4 crack resistance index of asphalt concrete under different loading rates crack resistance index test results are shown in Fig. 7 , with the increase in loading rate, the asphalt concrete cracking resistance index gradually decreases, when the loading rate is greater than 5mm/min, the gradual change curve of its cracking resistance index appears inflection point, and gradually tends to flatten out, this is contrary to the K IC and G f law, cracking resistance index with the increase in loading rate of the law of change is negatively correlated with the trend of change, indicating that when the loading rate is less than 5mm/min, the change of cracking resistance index of asphalt concrete is significantly affected by its impact, and the upper limit value and lower limit value fluctuation amplitude of the test data obtained from the calculation of the different loading rate is not much difference between the test data of the degree of uniformity of the test data, the reliability of the strong discrete degree. 5. Strain field cloud analysis of asphalt concrete under different loading rates Related studies have shown [ 43 , 44 ] that DIC can describe the fracture behavior of asphalt concrete in the loading process in a more reasonable way, therefore, in this study, digital image correlation technology is used as a means of monitoring the crack extension of the specimen, and semicircular bending is performed on the panel asphalt concrete specimens under the conditions of different loading rates (0.05, 0.2, 1, 3, 5, 10 mm/min) tests to investigate the correlation of the strain of the specimens with time. 5.1 Cloud map analysis of horizontal strain field characteristics 5.1.1 Analysis of cracking stages corresponding to peak loads at different loading rates Figure 8 shows the characteristic cloud diagram of horizontal strain (Exx) of asphalt concrete pre-cracked SCB specimens reaching peak strength at different loading rates, in which the red area in the horizontal direction represents the tensile strain region and the purple area represents the compressive strain region, and different colors represent different values of horizontal strain. As shown in Fig. 8 , as the loading rate increases, the horizontal strain on the surface of the sample gradually increases, and cracking usually occurs in the concentrated area of the normal strain of the sample. Under the action of tensile stress, the stress concentration will occur at the tip of the pre-crack of the asphalt concrete, resulting in the relative displacement of the mortar inside the specimen, which will destroy its spatial structure and cause the specimen to crack. Calculations by the DIC showed that the horizontal strains on the surface of asphalt concrete specimens at different loading rates were 0.2459, 0.2424, 0.2102, 0.1447, 0.1355, and 0.1275, respectively. By observing the cloud pattern of the horizontal strain corresponding to the peak load at different loading rates, it can be found that the horizontal strain on the surface of the Tarmac specimen decreases gradually with the increase in loading rate. This means that the faster the loading rate is, the more likely the specimen is to be damaged, which is also the starting point of the horizontal strain value of the specimen cracking. 5.1.2 Crack propagation analysis of asphalt concrete under different loading rates Different loading rates will affect the transfer of concentrated stress in asphalt concrete, and then affect its deformation and crack propagation. To compare the difference in crack propagation of asphalt concrete under different loading rates, the samples with a low loading rate of 0.2 mm/min and a high loading rate of 10 mm/min were selected as the research objects. The evolution cloud diagram of surface horizontal strain (Exx) during the loading process was obtained by DIC. As shown in Fig. 9, in the crack development stage, the total strain field begins to increase, and small cracks appear in the local concentration area of Exx near the pre-crack, meanwhile, with the increase of vertical displacement, the cracks show an upward trend. This is due to the generation of micro-cracks in the loading process, which gradually expand to cause the specimen to be destabilized and eventually damaged. By comparing the specimen evolution cloud diagrams under different loading rates, it can be concluded that the surface horizontal strain of the specimen under a high loading rate evolves faster, the crack extension is faster, and the specimen is more prone to instability damage. The strain evolution cloud diagram of the specimen with a loading rate of 0.2 mm/min is shown in Fig. 9(a). When P = 0.045kN, u = 0.280mm, the specimen is in the early stage of loading, the local cracks in the initial defects inside the specimen are compacted, and it can be seen that the strain distribution is relatively decentralized. When P = 0.800kN and u = 2.224mm, the specimen undergoes a slight plastic deformation, the strain field starts to localize and concentrate, and the crack as well as the edge of the specimen produces a regional stress concentration phenomenon; When P = 1.401 kN, u = 5.263 mm, the specimen reaches the peak strength, and the top of the pre-crack produces small cracks, which is the starting point of the specimen cracking. After the peak point, the force decreases with the increase of load displacement. When P decreases to 1.263 kN and u = 7.321 mm, the crack begins to expand along the edge of coarse aggregate ( red box area in the figure ), which is the stage of crack development. When P is reduced to 0.185kN and u = 11.69mm, the specimen produces obvious macroscopic cracks and the load-carrying capacity fails. The strain evolution of the specimen with a loading rate of 10 mm/min is shown in Fig. 9(b). The strain field at the surface of the specimen during the compaction and elasticity phases of cracking approximates the variation of the low loading rate, When P = 6.273 kN, u = 3.995 mm, the specimen reaches the peak strength, and there is stress concentration and small cracks at the tip of the pre-crack. After the peak point the specimen is damaged, with the increase of vertical displacement, when P is reduced to 4.230kN, u = 6.991mm, the crack starts to expand upward through the coarse aggregate (the red box area in the figure); when P is reduced to 2.667kN, u = 7.665mm, the crack develops vertically upward again through the coarse aggregate approximating to the loading direction, and at this time, an obvious macroscopic cracks; When P decreases to 0.204 kN and u = 10.330 mm, the load carrying capacity fails. 5.1.3 Cracking analysis corresponding to the end of loading at different loading rates From Fig. 10 , it can be seen that the crack pattern of panel asphalt concrete specimens under different loading rates varies significantly, and the crack pattern of asphalt concrete under low loading rate is not developed vertically upward along the prefabricated crack but is a zigzagging upward tendency, and the formation of this crack pattern may be because asphalt concrete follows the "concept of the weakest link" when subjected to concentrated loading. " The failure of the specimen is mainly due to the generation of internal voids or defects, and the cracks begin to penetrate the hole and form a connection between the cracks and holes. In addition, due to the existence of coarse aggregate with higher strength at the leading edge of the precast cracks in asphalt concrete, the cracks will break along the cemented surface and take on a curved shape during the loading process as the loading rate is small and the aggregate cemented surface is more likely to be broken compared to the aggregate itself. In addition, due to the existence of coarse aggregate with higher strength at the leading edge of the precast cracks in asphalt concrete, the cracks will break along the cemented surface and take on a curved shape during the loading process as the loading rate is small and the aggregate cemented surface is more likely to be broken compared to the aggregate itself. so the cracks will be caused by the presence of coarse aggregate with higher strength at the leading edge of the cracks in the precast cracks in asphalt concrete, this phenomenon is particularly evident at loading rates of 0.05-1 mm/min, and a small strain difference between the specimen crack and the surrounding area can be observed. At the loading rate of 3-10mm/min, the cracks developed almost vertically upwards. This is due to the larger loading rate, which resulted in the cracked specimen being subjected to a larger concentrated load internally, which could not follow the weakest principle, and in the case of a larger concentration of stresses, the cracks went directly through the aggregate, and the breakage surfaces were smoother, which indicated that the cracks did not develop sufficiently, resulting in a more severe strain concentration. By comparing the crack morphology at different loading rates, it is clear that at lower loading rates, the crack development is more zigzag and the strain difference with the surrounding area is smaller. In contrast, at higher loading rates, the crack pattern develops almost directly upward and the breaking surface of the crack is smoother. 5.2 Characteristic cloud analysis of the vertical strain field Figure 11 shows the characteristic cloud diagrams of vertical strains corresponding to the peak load during loading of pre-cracked semicircular bending specimens at different loading rates, and the horizontal strains on the surface of the asphalt concrete specimens gradually decrease with the increase of loading rate, through calculation, the vertical strains on the surface of the asphalt concrete specimen under different loading rates are 0.0198,0.0147,0.0091,0.0060,0.0052, and 0.0043, respectively. As the loading rate increases, it shows a decreasing trend, indicating that the stiffness of the specimen increases and the anti-deformation ability increases, which is also the initial vertical strain value of the specimen cracking. 6. Conclusions The K IC and G f of asphalt concrete increased with increasing loading rate, and the CRI results were the opposite; the dispersion of K IC and G f increased with increasing loading rate, but the calculated CRI data were more uniformly dispersed. These results show that the higher loading rate can improve the resistance of asphalt concrete, but also increase the difference between the performance of the specimens, however, the results of CRI show that the crack propagation index of asphalt concrete changes more evenly under different loading rates. The evolution law of the strain concentration area can well reflect the crack extension characteristics, with the increase of the loading rate, the strain evolution characteristics of the specimen surface changed significantly, and the tensile stress concentration area was extended to the loading direction. With the loading rate decreases, the strain corresponding to the peak load (Exx, Eyy) gradually increases, and after reaching the peak strength with the increase of load displacement, the cracks of the specimens expand step by step along the edge of the coarse aggregate at low loading rates, and the cracks expand upward through the coarse aggregate at high loading rates. Due to the change of loading rate leads to the different stress distribution within the asphalt concrete, the stress transfer path of asphalt concrete is more complicated when the loading rate is 0.05-1mm/min, which leads to the crack development along the zigzagging path and zigzagging up of the crack pattern. While at the loading rate of 3–10 mm/min, the specimen was subjected to a larger concentrated load and the direction of crack development was more direct, almost coinciding with that of the pre-cracks, with the crack morphology almost vertically upward along the pre-cracks. 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Theoretical and Applied Fracture Mechanics, p 104314 Fan S, Wang H, Zhu H et al (2018) Evaluation of self-healing performance of asphalt concrete for low-temperature fracture using semicircular bending test[J]. J Mater Civ Eng 30(9):04018218 Pirmohammad S, Ayatollahi MR (2014) Fracture resistance of asphalt concrete under different loading modes and temperature conditions[J]. Constr Build Mater 53:235–242 Li X, Braham AF, Marasteanu MO et al (2008) Effect of factors affecting fracture energy of asphalt concrete at low temperature[J]. Road Mater pavement Des 9(sup1):397–416 Ji W, Xiao L, Lin Q (2023) Experimental study of pure shear fracture in rock-type materials[J]. Theoret Appl Fract Mech 125:103899 Baldassari M, Monaco A, Sapora A et al (2023) Size effect on flexural strength of notched and un-notched concrete and rock specimens by Finite Fracture Mechanics[J], vol 125. Theoretical and Applied Fracture Mechanics, p 103787 Elghazel A, Taktak R, Bouaziz J (2016) Combined numerical and experimental mechanical characterization of a calcium phosphate ceramic using modified Brazilian disc and SCB specimen[J]. Mater Sci Engineering: A 670:240–251 Barkallah R, Taktak R, Guermazi N et al (2021) Mechanical properties and wear behaviour of alumina/tricalcium phosphate/titania ceramics as coating for orthopedic implant[J]. Eng Fract Mech 241:107399 Dong S, Xia K, Huang S et al (2011) Rate dependence of the tensile and flexural strengths of glass–ceramic Macor[J]. J Mater Sci 46:394–399 Huang B, Shu X, Tang Y (2005) Comparison of semi-circular bending and indirect tensile strength tests for HMA mixtures[M]//Advances in Pavement Engineering. : 1–12 Mull MA, Othman A, Mohammad L (2005) Fatigue crack propagation analysis of chemically modified crumb rubber–asphalt mixtures[J]. J Elastomers Plast 37(1):73–87 Bui HH, Saleh M (2021) Effects of specimen size and loading conditions on the fracture behaviour of asphalt concretes in the SCB test[J]. Eng Fract Mech 242:107452 Mirsayar M, Shi X, Zollinger D (2017) Evaluation of interfacial bond strength between Portland cement concrete and asphalt concrete layers using bi-material SCB test specimen[J]. Eng Solid Mech 5(4):293–306 Seo Y, Kim YR, Schapery RA et al (2004) A study of crack-tip deformation and crack growth in asphalt concrete using fracture mechanics[J]. J Assoc Asphalt Paving Technol, 73 Yuan F, Cheng L, Shao X et al (2020) Full-field measurement and fracture and fatigue characterizations of asphalt concrete based on the SCB test and stereo-DIC[J]. Eng Fract Mech 235:107127 Jiang Xinlong Y, Shu, Li Tingyu (2022) Research on low temperature performance index of asphalt concrete based on semi-circular bending test [ J ], vol 19. JOURNAL OF RAILWAY SCIENCE AND ENGINEERING, pp 428–434. 02 Fu Xin L, Qiu C (2012) Parameter analysis of semi-circular bending test with notch based on NSYS [ J ]. Highway Traffic Technol 29(02):13–17 Liu Yu (2009) Dynamic response and fracture performance of asphalt mixture based on semi-circular bending test [ D ]. Harbin Institute of Technology Rope Peak (2017) Research on the fracture test method and evaluation index of asphalt mixture based on semi-circular bending test [. D ].Chang 'an University Blaber J, Adair B, Antoniou A, Ncorr Open-Source 2D Digital Image Correlation Matlab Software. Experimental Mech 2015, 55(6):1105–1122 AL Q (2015) IMAD L. et al. Testing protocols to ensure performance of high asphalt binder replacement mixes using RAP and RAS[R]. Civil Engineering Studies, Illinois Center for Transportation Series AASHTO TP 124 – 20 Standard method of test for determining the fracture potential of asphalt mixtures using the illinois flexibility index test (I-FIT)[S] Ozer H, Al-Qadi IL, Lambros J et al (2016) Development of the fracture-based flexibility index for asphalt concrete cracking potential using modified semi-circle bending test parameters[J]. Constr Build Mater 115:390–401 Sreedhar S, Coleri E, Haddadi SS (2018) Selection of a performance test to assess the cracking resistance of asphalt concrete materials[J]. Constr Build Mater 179:285–293 Kaseer F, Yin F, Arámbula-Mercado E et al (2018) Development of an index to evaluate the cracking potential of asphalt mixtures using the semi-circular bending test[J]. Constr Build Mater 167:286–298 Stewart CM, Garcia E (2019) Fatigue crack growth of a hot mix asphalt using digital image correlation[J]. Int J Fatigue 120:254–266 Xing C, Tan Y, Liu X et al (2017) Research on local deformation property of asphalt mixture using digital image correlation[J]. Constr Build Mater 140:416–423 Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4539941","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":319647051,"identity":"9ef99892-429a-448e-9044-1936db1a79f6","order_by":0,"name":"Hanbing Yang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAy0lEQVRIiWNgGAWjYBAC++P9jx8kVEjI8bM3EKvnzBk2gwdnbIwlew4Qq+VGDoPkw7a0xA0zEojUwdiQe8Agge1w4gbJxxtvMNTYRBPUwsxwLuFBAs9h4+3SacUWDMfSchsIaWFjbDAwSJA4LLtzdo6ZBGPDYcJaeJgZDCQSDA4zbrh5hkgtEmw8QC0JaYobbvAQqcWAhy3NIOEAKJCBfkkgxi8G8o8PP/z5DxSVhzfe+FBjQ1gLinaJBFKUQ7SQqmMUjIJRMApGBgAAGlZC5isx5ToAAAAASUVORK5CYII=","orcid":"","institution":"Xinjiang Agricultural University","correspondingAuthor":true,"prefix":"","firstName":"Hanbing","middleName":"","lastName":"Yang","suffix":""},{"id":319647052,"identity":"0b4c2f48-570f-4f67-879f-3491c4f0614b","order_by":1,"name":"Jianxin He","email":"","orcid":"","institution":"Xinjiang Agricultural University","correspondingAuthor":false,"prefix":"","firstName":"Jianxin","middleName":"","lastName":"He","suffix":""},{"id":319647053,"identity":"9d06fb7b-2ac5-4e51-9e89-1e633b2bbd20","order_by":2,"name":"Wu Yang","email":"","orcid":"","institution":"Xinjiang Agricultural University","correspondingAuthor":false,"prefix":"","firstName":"Wu","middleName":"","lastName":"Yang","suffix":""},{"id":319647054,"identity":"4bb60264-dd32-48dc-a54a-88c656252ce2","order_by":3,"name":"Xinyu Ding","email":"","orcid":"","institution":"Xinjiang Agricultural University","correspondingAuthor":false,"prefix":"","firstName":"Xinyu","middleName":"","lastName":"Ding","suffix":""},{"id":319647055,"identity":"2e22e8bf-e270-41f4-8da3-81ce24458113","order_by":4,"name":"Peng-peng Chen","email":"","orcid":"","institution":"Xinjiang Agricultural University","correspondingAuthor":false,"prefix":"","firstName":"Peng-peng","middleName":"","lastName":"Chen","suffix":""},{"id":319647056,"identity":"93971eda-07e6-4e1d-91ed-3933f8d8552e","order_by":5,"name":"Liang Liu","email":"","orcid":"","institution":"Xinjiang Agricultural University","correspondingAuthor":false,"prefix":"","firstName":"Liang","middleName":"","lastName":"Liu","suffix":""}],"badges":[],"createdAt":"2024-06-06 11:14:20","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4539941/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4539941/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":60707295,"identity":"febe7ee0-2740-4f34-87a1-c5c06f92798f","added_by":"auto","created_at":"2024-07-19 19:32:20","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":49873,"visible":true,"origin":"","legend":"\u003cp\u003eSpecimen preparation process\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4539941/v1/86a608af8251f9e31203d687.png"},{"id":60707293,"identity":"5c812430-9ace-4f8b-93be-5b80dcba5814","added_by":"auto","created_at":"2024-07-19 19:32:20","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":160134,"visible":true,"origin":"","legend":"\u003cp\u003eDIC Technical Measurement System\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4539941/v1/65815d3f8e6861adb854e6b7.png"},{"id":60707291,"identity":"ead8ddc7-6d65-494c-8f97-df17c2c36029","added_by":"auto","created_at":"2024-07-19 19:32:19","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":57065,"visible":true,"origin":"","legend":"\u003cp\u003eLoad-displacement curves of asphalt concrete under different loading rates\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4539941/v1/8d7b70b80d13f7e92068459d.png"},{"id":60708074,"identity":"513b285c-6aa6-46aa-90b4-a646ceefa4a5","added_by":"auto","created_at":"2024-07-19 19:40:19","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":24695,"visible":true,"origin":"","legend":"\u003cp\u003eChanging law of \u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003eIC\u003c/em\u003e\u003c/sub\u003e mean value with loading rate\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4539941/v1/ff428b58ce0ce4a59fec71a2.png"},{"id":60708075,"identity":"a875e50b-5b54-4d93-bdc2-c8ca350f6bc3","added_by":"auto","created_at":"2024-07-19 19:40:20","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":49068,"visible":true,"origin":"","legend":"\u003cp\u003eVariance variation curves of \u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003eIC\u003c/em\u003e\u003c/sub\u003e values at different loading rates\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4539941/v1/bbe79b00bed294a8fecc93c5.png"},{"id":60707298,"identity":"b0f98133-85d2-4f75-b097-816de85f3b50","added_by":"auto","created_at":"2024-07-19 19:32:20","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":30192,"visible":true,"origin":"","legend":"\u003cp\u003eLaw of variation of the mean value of \u003cem\u003eG\u003c/em\u003e\u003csub\u003e\u003cem\u003ef\u003c/em\u003e\u003c/sub\u003e with loading rate\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-4539941/v1/680950ef7b54c0c922f6d74b.png"},{"id":60707300,"identity":"507f5541-ca9a-4e46-86c5-32cfab9d167d","added_by":"auto","created_at":"2024-07-19 19:32:20","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":28850,"visible":true,"origin":"","legend":"\u003cp\u003eChanging law of \u003cem\u003eCRI\u003c/em\u003e mean value with loading rate\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-4539941/v1/2fe2ce99859bdf7e75ba587c.png"},{"id":60707299,"identity":"ddfd56a7-7e76-46ed-9577-137c903dcc32","added_by":"auto","created_at":"2024-07-19 19:32:20","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":947573,"visible":true,"origin":"","legend":"\u003cp\u003eHorizontal strain clouds corresponding to peak loads of asphalt concrete at different loading rates\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-4539941/v1/b6359f20f40d44a1d7d1501f.png"},{"id":60707297,"identity":"64fa50ba-778d-44ba-8656-93988d8d017a","added_by":"auto","created_at":"2024-07-19 19:32:20","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":1187381,"visible":true,"origin":"","legend":"\u003cp\u003eCloud view of the crack extension of the specimen under different loading rates\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-4539941/v1/aebda365f711343b3534fb1f.png"},{"id":60708076,"identity":"7fd668de-d3b8-4174-8a5f-e2f76a21e0ba","added_by":"auto","created_at":"2024-07-19 19:40:20","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":921944,"visible":true,"origin":"","legend":"\u003cp\u003eCorresponding horizontal strain cloud at the end of loading\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-4539941/v1/10f6c43df71ba3c8d24300ed.png"},{"id":60707303,"identity":"f130b96f-fad3-422e-a4da-9fb79afc78af","added_by":"auto","created_at":"2024-07-19 19:32:20","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":982192,"visible":true,"origin":"","legend":"\u003cp\u003eVertical strain cloud corresponding to the peak load of the specimen at different loading rates\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-4539941/v1/fa96080fcda1365afce7929a.png"},{"id":68192572,"identity":"ff263ebb-1ba4-4797-b772-dc32df1dad99","added_by":"auto","created_at":"2024-11-04 14:03:46","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4842541,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4539941/v1/3dd5d53d-40ec-46a9-8528-b51e093177ae.pdf"}],"financialInterests":"","formattedTitle":"\u003cp\u003eStudy on Fracture Characteristics of Panel Asphalt Concrete Under Different Loading Rates\u003c/p\u003e","fulltext":[{"header":"Highlights","content":"\u003cul start=\"12\"\u003e\n \u003cli\u003eThe fracture properties of asphalt concrete under various variable water level loading rates were evaluated based on the SCB test.\u003c/li\u003e\n \u003cli\u003eDigital image correlation (DIC) technique can be used to accurately characterize the crack propagation path of asphalt concrete.\u003c/li\u003e\n \u003cli\u003eThe \u003cem\u003eK\u003csub\u003eIC\u003c/sub\u003e\u003c/em\u003e and \u003cem\u003eG\u003csub\u003ef\u003c/sub\u003e\u003c/em\u003e of asphalt concrete increased with the increase in loading rate, and the opposite was true for \u003cem\u003eCRI\u003c/em\u003e results\u003c/li\u003e\n\u003c/ul\u003e"},{"header":"1. Introduction","content":"\u003cp\u003eAsphalt concrete is widely used in the construction of pumped storage power plant reservoirs due to its excellent impermeability properties [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. The day and night rise and fall of the upper and lower reservoirs of the pumped storage power station cause the water level to fluctuate periodically and frequently [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], The variable rate water level has caused a certain load change to the asphalt concrete panel, resulting in the initial defect development of the asphalt concrete panel under the coupling of the water load and the environmental action, the strength attenuation, and the cracks [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Finally, it causes anti-seepage failure and endangers the safety of the state and people's property [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Therefore, it is of great practical significance to study the fracture characteristics of asphalt concrete panels under different loading rates. At present, the fracture performance of asphalt concrete under different loading rates is mainly carried out from two aspects: test conditions and test methods. For example, starting from the test conditions, Yang et al.[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] Yang used the R curve to study the effects of two loading rates ( 0.03,1 mm/min) on the fracture properties of asphalt concrete. The results show that the loading rate only affects the energy rate. He et al.[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] studied the effect of loading rate on the mode I fracture toughness of hot mix asphalt ( HMA ) concrete by repeated tests, and analyzed the obtained data by using 2 and 3-parameter Weibull statistical models. The results show that the two-parameter and three-parameter Weibull models can successfully predict the mode I fracture behavior of the tested asphalt material within the consideration range of the loading rate, which provides a new idea for the fracture of asphalt concrete from the perspective of mathematical statistics. Motamedi et al.[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] conducted fracture toughness experiments at three low temperatures, three loading rates ( 0.5,1,5 mm/min), and different fiber percentages. They found that by decreasing the test temperature and increasing the loading rate, the fracture toughness values of type I and type III increased. Wei et al. [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] conducted uniaxial compression tests on asphalt mixtures with six loading rates to investigate the damage characteristics and damage modes of asphalt mixtures. The whole failure process was monitored by combining acoustic emission technique (AE) technology, in contrast, the loading rate of 0.05mm/min has fewer frequency bands than other loading rates, and there are fewer AE signals in the high-frequency band. Qing et al. [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]studied the test method of concrete damage scale under different loading rates. Starting from the test methods, the test methods for evaluating the deformation and crack resistance of hydraulic asphalt concrete in China mainly include the trabecular bending test and splitting test [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], however, the difficulty of specimen preparation for these methods [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], the low correlation between the test data and the actual workability of asphalt concrete [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], and the presence of permanent deformation in the specimens lead to their limitations in evaluating the fracture behavior of asphalt concrete. Given the shortcomings of the above test methods, in recent years, researchers [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] have proposed the semi-circular bending test (SCB) and obtained the key indicators to characterize the fracture behavior through the SCB test. The fracture behavior of asphalt concrete [\u003cspan additionalcitationids=\"CR18 CR19 CR20\" citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], rock [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e], ceramics [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e], glass [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e], and other materials under different conditions was studied. Then Huang et al. [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] and Mull et al. [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e] analyzed the SCB specimens of asphalt concrete based on the theory of fracture mechanics. Bui et al. [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e] investigated the effect of different loading rates on the fracture properties of asphalt concrete based on SCB tests and recommended a loading rate of 1 mm/min for highway asphalt concrete. Based on the SCB test, Mirsayar et al. [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e] evaluated the strength of the bonding layer between asphalt concrete and cement concrete and gave the fracture criteria between the bonding joints under different mixing modes. To further describe the micro-crack extension trajectory of asphalt concrete, Seo et al. [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e] used digital image correlation (DIC) to describe the formation of micro-damage in asphalt concrete. Yuan et al. [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e] studied the full-field displacement field and strain field of asphalt concrete SCB specimens by DIC technology and verified the rationality of the speckle pattern.\u003c/p\u003e \u003cp\u003eComprehensive domestic and international scholars' research, in the field of asphalt cracking, most of them are through the design of larger span load rates to simulate the loading rate on the asphalt concrete cracking behavior of the research did not take into account the stage of the water level, cyclical changes in the asphalt concrete panels brought about by the impact, which is not reasonable. Therefore, based on the SCB test method and the theory of fracture mechanics, the fracture toughness test of panel asphalt concrete at different loading rates ( 0.05,0.2,1,3,5,10 mm/min) was carried out in this paper. The DIC was used to analyze the strain field characteristics of asphalt concrete from crack initiation to instability failure at different loading rates. From the perspective of crack propagation, the whole process analysis and cracking mechanism of low-temperature cracking of asphalt concrete were studied. The research results can provide further theoretical support for understanding the crack development law of panel asphalt concrete and its panel crack-resistant design.\u003c/p\u003e"},{"header":"2. Raw materials and mixing ratios","content":"\u003cp\u003eThe test was conducted using a project-selected lithology of medium-thick layered/thick bedded grey/grey-white fine crystal limestone, and a jaw crusher was to crush the rock to produce coarse and fine aggregates and some fillers, and then a disc crusher was to prepare the filler separately. Asphalt using 70 # road petroleum asphalt produced by PetroChina Karamay Petrochemical Co., Ltd, the asphalt of the various performance indexes of the test, the test results are shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e; mineral grading particle size grading and dosage as shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eAsphalt performance index\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTest Item\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eUnits\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSL 501\u0026ndash;2010\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSpecimen Test Results\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNeedle penetration (25 ◦C,100 g, 5 s)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.1mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e60\u0026thinsp;~\u0026thinsp;80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e66.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDuctility (5 cm/min, 10 ◦C)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ecm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026ge;\u0026thinsp;20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e55\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDuctility (5 cm/min, 15 ◦C)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ecm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026gt;150\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSoftening point (Globe method)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e℃\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026ge;\u0026thinsp;45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e53.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFlash point\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e℃\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026ge;\u0026thinsp;260\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e320\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMass change after heating in a film oven\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-0.06\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eResidual needle entry ratio (25 ◦C)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026ge;\u0026thinsp;61\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e83.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eResidual ductility (5 cm/min, 10 ◦C)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ecm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026ge;\u0026thinsp;6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMineral aggregate gradation\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eTypes of raw materials\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"7\" nameend=\"c8\" namest=\"c2\"\u003e \u003cp\u003eSieve Size (mm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003easphalt\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e19\u0026thinsp;\u0026minus;\u0026thinsp;16\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e16-13.2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e13.2\u0026ndash;9.5\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e9.5\u0026ndash;4.75\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e4.75\u0026ndash;2.36\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2.36\u0026thinsp;\u0026minus;\u0026thinsp;0.075\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.075\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDosage (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e6.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e10.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e18.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e15.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e30.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e12.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e7.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e"},{"header":"3. Test programs and methods","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e3.1 specimen preparation\u003c/h2\u003e \u003cp\u003eWhen the thickness of the SCB specimen is 50 mm, its mechanical properties tend to be stable [\u003cspan additionalcitationids=\"CR34\" citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e].To reduce the shear deformation at the support point, the bearing spacing is 0.8 times the diameter of the specimen [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. According to the above research results, the hot mix asphalt mixture was poured into a three-layer compacted Φ150 \u0026times; 300mm triaxial mold, and the mold was removed after cooling for 24 hours. The triaxial specimen was cut with a cutting machine, and 15 mm was removed at each end to reduce the influence of density inhomogeneity. And cut into 10 SCB specimens with a diameter of 150 mm and a thickness of 50 mm, Using a very thin diamond saw blade with a thickness of 1 mm, a pre-crack with a depth of 15 mm was cut into the bottom center of the SCB specimen, and the specimen preparation process is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The cut SCB specimens were placed in a 10\u0026deg;C constant temperature chamber for more than 48 hours. To analyze the whole process of dynamic fracture of panel asphalt concrete, after the preparation of pre-cracked SCB specimens, the surface of the specimens was cleaned first. After the surface was completely dried, speckles were randomly spotted on the surface of the specimens with a marker pen [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Test programme\u003c/h2\u003e \u003cp\u003eTo study the influence of different loading rates on the fracture characteristics of asphalt concrete, the loading rate was used as the test variable. Under the conditions of six loading rates (0.05, 0.2, 1, 3, 5, 10 mm/min) and test temperature 10\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u0026deg;C, 20 SCB parallel tests were carried out respectively. The test instrument automatically collects the vertical load and displacement values from the beginning of the test to the complete failure of the specimen [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e].To simplify the loading mode, according to the AASHTO TP124 [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e], the load-displacement curve is obtained. Through the load-displacement curve, the critical stress intensity factor \u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003eIC\u003c/em\u003e\u003c/sub\u003e, fracture energy \u003cem\u003eG\u003c/em\u003e\u003csub\u003e\u003cem\u003ef\u003c/em\u003e,\u003c/sub\u003e and crack resistance index \u003cem\u003eCRI\u003c/em\u003e of the panel asphalt concrete under six different loading rates are calculated, and the results are averaged. The specific test program is shown in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. Three sets of specimens were taken at each rate and scattered spots were randomly dotted with a marker pen to analyze the whole process of dynamic fracture of asphalt concrete SCB specimens.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSCB test programme\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eserial number\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eloading rate mm/min\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003efracture index\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003enumber of specimens\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eTemperature(℃)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\" morerows=\"5\" rowspan=\"6\"\u003e \u003cp\u003e\u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003eIC\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e\u003cem\u003eG\u003c/em\u003e\u003csub\u003e\u003cem\u003ef\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e\u003cem\u003eCRI\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\" morerows=\"5\" rowspan=\"6\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e3.3 DIC Test Method\u003c/h2\u003e \u003cp\u003eThe tests were conducted using a high-speed industrial camera to acquire digital images of the test process. The industrial camera is placed in front of the test piece and its height is adjusted to the same level as the test piece. The data acquisition system controls the camera to collect the image of the test piece during the test. The surface of the test piece should be flat and speckled. Through testing, the resolution of the captured image is determined to be 3024 pixels, and the interval between each image is 10 s. The digital image correlation technology test system is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Fracture Index Calculation\u003c/h2\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e3.4.1 Stress Intensity Factor\u003c/h2\u003e \u003cp\u003eThe fracture mechanics test is mainly aimed at the crack propagation of the reserved crack specimen under the action of external force and describes the crack propagation ability of the material when the structural defect occurs. In the study of fracture mechanics, the critical stress intensity factor \u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003eIC\u003c/em\u003e\u003c/sub\u003e, as a fracture toughness index, can well reflect the stress-strain field strength in the crack tip area, and reflect the ability of the material to prevent the instability and expansion of the crack. It is an important parameter to reflect the performance of the material. The calculation formula is shown in Eq.\u0026nbsp;\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$${K_{IC}}=\\frac{P}{{2rt}} \\times \\sqrt {\\pi a} \\times (4.782 - 1.219\\frac{a}{r}+0.063{e^{_{{^{{_{{7.045}}}}}}\\frac{a}{r}}})$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eIn this equation, \u003cem\u003eK\u003c/em\u003e\u003csub\u003eIc\u003c/sub\u003e is the critical stress intensity factor (or fracture toughness value) of each specimen at the onset of fracture; \u003cem\u003eP\u003c/em\u003e is the critical load; \u003cem\u003er\u003c/em\u003e is the radius of the specimen; \u003cem\u003et\u003c/em\u003e is the thickness of the specimen; and \u003cem\u003ea\u003c/em\u003e is the notch length.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e3.4.2 Fracture energy\u003c/h2\u003e \u003cp\u003eFracture energy is the energy released by the crack extension unit area system, expressed by \u003cem\u003eG\u003c/em\u003e\u003csub\u003e\u003cem\u003ef\u003c/em\u003e\u003c/sub\u003e; the larger the fracture energy is, the stronger the fracture resistance on behalf of asphalt concrete in a certain environment, the energy release rate can be a better description of the fracture performance of the material is a very important parameter in the fracture mechanics, the calculation formula is shown in Eq.\u0026nbsp;\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$${G_f}=\\frac{{{W_f}}}{{{A_{lig}}}}=\\frac{{\\int {pdu} }}{{{A_{lig}}}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eIn this equation, \u003cem\u003eG\u003c/em\u003e\u003csub\u003e\u003cem\u003ef\u003c/em\u003e\u003c/sub\u003e is fracture energy or energy release rate; \u003cem\u003eW\u003c/em\u003e\u003csub\u003e\u003cem\u003ef\u003c/em\u003e\u003c/sub\u003e is fracture work ; \u003cem\u003ep\u003c/em\u003e is the axial load; \u003cem\u003eu\u003c/em\u003e is the vertical displacement; \u003cem\u003eA\u003c/em\u003e\u003csub\u003e\u003cem\u003elig\u003c/em\u003e\u003c/sub\u003e = (r-a)*t is the area of the fault zone; \u003cem\u003er\u003c/em\u003e is the radius of the specimen; \u003cem\u003ea\u003c/em\u003e represents the length of the incision; \u003cem\u003et\u003c/em\u003e is the thickness of the sample.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e3.4.3 Crack resistance index\u003c/h2\u003e \u003cp\u003eThe flexibility index can reflect the crack propagation rate of asphalt concrete [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e], but it has limitations in evaluating the low-temperature performance of asphalt concrete. For example, there is no post-peak data to calculate the flexibility index at low temperatures, or the post-peak curve is difficult to fit, which makes it impossible to determine the inflection point of the curve. Therefore, KASEER et al. [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e] proposed a fracture index to replace the flexibility index: the crack resistance index. The crack resistance index refers to the strain capacity of asphalt concrete when the first crack occurs under tensile load, which can distinguish asphalt concrete with similar fracture energy but different peak loads. The calculation formula is shown in Eq.\u0026nbsp;\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$$CRI=\\frac{{{G_f}}}{{{p_{\\hbox{max} }}}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eIn this equation, \u003cem\u003eGRI\u003c/em\u003e is the crack resistance index, \u003cem\u003eG\u003c/em\u003e\u003csub\u003e\u003cem\u003ef\u003c/em\u003e\u003c/sub\u003e is the fracture energy, and \u003cem\u003ep\u003c/em\u003e\u003csub\u003e\u003cem\u003emax\u003c/em\u003e\u003c/sub\u003e is the maximum axial load.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"4. Effect of loading rate on fracture properties of asphalt concrete","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Load-displacement curves of asphalt concrete under different loading rates\u003c/h2\u003e \u003cp\u003eIn this paper, different loading rates are used to simulate the effects of diurnal changes in reservoir water level on asphalt concrete panels in actual projects, and the load-displacement curves of the specimens under different loading rates are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. It can be seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e that the load-displacement curve fluctuates greatly at the same loading rate, indicating that the data is very discrete, and the load-displacement curve shows an unstable and unsmooth trend. This is because there are voids or defects in the specimen, which leads to the fracture of the specimen when the fissures begin to penetrate holes and create cracks, the cracks and holes are connected, or there is a large strength of coarse aggregate at the front edge of the pre-crack, test curve is unstable. The fracture behavior of asphalt concrete and fracture load and loading rate shows a positive correlation trend, the larger the rate of asphalt concrete bearing capacity is stronger, before reaching the peak load Pmax, the damage behavior of the specimen is mainly manifested as linear elastic fracture, with the increase of loading rate, the initial section of the curve slope is gradually steeper, the larger the curve encloses the larger the area of the curve, and the whole is elevated by a progressive relationship.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e4.2 Stress intensity factor of asphalt concrete under different loading rates\u003c/h2\u003e \u003cp\u003eTo eliminate the problems caused by the uneven distribution of coarse and fine aggregate particle sizes between samples and the uncertainty of the number of coarse aggregates at the leading edge of the pre-crack of the sample, six loading rates (0.05, 0.2, 1, 3, 5, 10mm/min) were selected to carry out 20 groups of parallel tests to obtain the mean value of \u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003eIC\u003c/em\u003e\u003c/sub\u003e under six loading rates, and the change rule of the mean value of \u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003eIC\u003c/em\u003e\u003c/sub\u003e under different loading rates was plotted as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, and to further discuss the discrete nature of \u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003eIC\u003c/em\u003e\u003c/sub\u003e, the variance of the \u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003eIC\u003c/em\u003e\u003c/sub\u003e was discussed, and the results are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIt can be seen from the diagram that with the increase in loading rate, the final strength of the cracked specimen increases, and the fracture resistance of asphalt concrete increases. This is because, under high-speed loading conditions, the internal structure of asphalt concrete will be quickly adjusted to resist deformation, thereby improving the final deformation capacity. Under low-speed loading conditions, asphalt has enough time to flow and deform, resulting in a decrease in material strength. In Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, the average values of \u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003eIC\u003c/em\u003e\u003c/sub\u003e from low to high for different loading rates are 0.1206, 0.1945, 0.3533, 0.5528, 0.6929, 0.8479 MPa-m\u003csup\u003e0.5\u003c/sup\u003e, respectively, and compared with the results of 0.05 mm/min, the critical stress-intensity factor of 10 mm/min is increased by about 7.03 times, which means that the loading rate has a significant influence on the stress This means that the loading rate has a significant effect on the stress intensity factor \u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003eIC\u003c/em\u003e\u003c/sub\u003e, and the slope of the curve tends to flatten and decrease with the increase of the loading rate, and the overall growth is a power function law. It can be seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e that when the loading rate is less than 3mm/min, the variance of the data is not much different, and the degree of dispersion is similar. When the loading rate is greater than 3mm/min, the variance increases rapidly and the dispersion becomes larger.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e4.3 Fracture energy of asphalt concrete under different loading rates\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e shows the variation rule of asphalt concrete fracture energy under different loading rates, it can be seen that the change of fracture energy with the loading rate shows a logarithmic distribution law, with the increase of the loading rate, the upper and lower limits of the fracture energy increase, this is because the loading rate is too fast to make the specimen from the initiation of cracking to the destruction of the time used for a shorter period, the crack is not developed sufficiently to cause the data to a greater degree of dispersion. When the loading rate is 3mm/min, the curve begins to flatten, indicating that when the loading rate exceeds 3mm/min, the effect of the loading rate on fracture energy decreases, and \u003cem\u003eG\u003c/em\u003e\u003csub\u003e\u003cem\u003ef\u003c/em\u003e\u003c/sub\u003e is not sensitive to the change in loading rate. Therefore, if the influence of loading rate on the fracture energy of asphalt concrete is considered, the change in loading rate of less than 3mm/min can be studied.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e4.4 crack resistance index of asphalt concrete under different loading rates\u003c/h2\u003e \u003cp\u003ecrack resistance index test results are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, with the increase in loading rate, the asphalt concrete cracking resistance index gradually decreases, when the loading rate is greater than 5mm/min, the gradual change curve of its cracking resistance index appears inflection point, and gradually tends to flatten out, this is contrary to the \u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003eIC\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eG\u003c/em\u003e\u003csub\u003e\u003cem\u003ef\u003c/em\u003e\u003c/sub\u003e law, cracking resistance index with the increase in loading rate of the law of change is negatively correlated with the trend of change, indicating that when the loading rate is less than 5mm/min, the change of cracking resistance index of asphalt concrete is significantly affected by its impact, and the upper limit value and lower limit value fluctuation amplitude of the test data obtained from the calculation of the different loading rate is not much difference between the test data of the degree of uniformity of the test data, the reliability of the strong discrete degree.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"5. Strain field cloud analysis of asphalt concrete under different loading rates","content":"\u003cp\u003eRelated studies have shown [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e] that DIC can describe the fracture behavior of asphalt concrete in the loading process in a more reasonable way, therefore, in this study, digital image correlation technology is used as a means of monitoring the crack extension of the specimen, and semicircular bending is performed on the panel asphalt concrete specimens under the conditions of different loading rates (0.05, 0.2, 1, 3, 5, 10 mm/min) tests to investigate the correlation of the strain of the specimens with time.\u003c/p\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e5.1 Cloud map analysis of horizontal strain field characteristics\u003c/h2\u003e \u003cdiv id=\"Sec18\" class=\"Section3\"\u003e \u003ch2\u003e5.1.1 Analysis of cracking stages corresponding to peak loads at different loading rates\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e shows the characteristic cloud diagram of horizontal strain (Exx) of asphalt concrete pre-cracked SCB specimens reaching peak strength at different loading rates, in which the red area in the horizontal direction represents the tensile strain region and the purple area represents the compressive strain region, and different colors represent different values of horizontal strain. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e, as the loading rate increases, the horizontal strain on the surface of the sample gradually increases, and cracking usually occurs in the concentrated area of the normal strain of the sample. Under the action of tensile stress, the stress concentration will occur at the tip of the pre-crack of the asphalt concrete, resulting in the relative displacement of the mortar inside the specimen, which will destroy its spatial structure and cause the specimen to crack. Calculations by the DIC showed that the horizontal strains on the surface of asphalt concrete specimens at different loading rates were 0.2459, 0.2424, 0.2102, 0.1447, 0.1355, and 0.1275, respectively. By observing the cloud pattern of the horizontal strain corresponding to the peak load at different loading rates, it can be found that the horizontal strain on the surface of the Tarmac specimen decreases gradually with the increase in loading rate. This means that the faster the loading rate is, the more likely the specimen is to be damaged, which is also the starting point of the horizontal strain value of the specimen cracking.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section3\"\u003e \u003ch2\u003e5.1.2 Crack propagation analysis of asphalt concrete under different loading rates\u003c/h2\u003e \u003cp\u003eDifferent loading rates will affect the transfer of concentrated stress in asphalt concrete, and then affect its deformation and crack propagation. To compare the difference in crack propagation of asphalt concrete under different loading rates, the samples with a low loading rate of 0.2 mm/min and a high loading rate of 10 mm/min were selected as the research objects. The evolution cloud diagram of surface horizontal strain (Exx) during the loading process was obtained by DIC. As shown in Fig.\u0026nbsp;9, in the crack development stage, the total strain field begins to increase, and small cracks appear in the local concentration area of Exx near the pre-crack, meanwhile, with the increase of vertical displacement, the cracks show an upward trend. This is due to the generation of micro-cracks in the loading process, which gradually expand to cause the specimen to be destabilized and eventually damaged. By comparing the specimen evolution cloud diagrams under different loading rates, it can be concluded that the surface horizontal strain of the specimen under a high loading rate evolves faster, the crack extension is faster, and the specimen is more prone to instability damage.\u003c/p\u003e \u003cp\u003eThe strain evolution cloud diagram of the specimen with a loading rate of 0.2 mm/min is shown in Fig.\u0026nbsp;9(a). When \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.045kN, \u003cem\u003eu\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.280mm, the specimen is in the early stage of loading, the local cracks in the initial defects inside the specimen are compacted, and it can be seen that the strain distribution is relatively decentralized. When \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.800kN and \u003cem\u003eu\u003c/em\u003e\u0026thinsp;=\u0026thinsp;2.224mm, the specimen undergoes a slight plastic deformation, the strain field starts to localize and concentrate, and the crack as well as the edge of the specimen produces a regional stress concentration phenomenon; When \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.401 kN, \u003cem\u003eu\u003c/em\u003e\u0026thinsp;=\u0026thinsp;5.263 mm, the specimen reaches the peak strength, and the top of the pre-crack produces small cracks, which is the starting point of the specimen cracking. After the peak point, the force decreases with the increase of load displacement. When \u003cem\u003eP\u003c/em\u003e decreases to 1.263 kN and \u003cem\u003eu\u003c/em\u003e\u0026thinsp;=\u0026thinsp;7.321 mm, the crack begins to expand along the edge of coarse aggregate ( red box area in the figure ), which is the stage of crack development. When \u003cem\u003eP\u003c/em\u003e is reduced to 0.185kN and \u003cem\u003eu\u003c/em\u003e\u0026thinsp;=\u0026thinsp;11.69mm, the specimen produces obvious macroscopic cracks and the load-carrying capacity fails.\u003c/p\u003e \u003cp\u003eThe strain evolution of the specimen with a loading rate of 10 mm/min is shown in Fig.\u0026nbsp;9(b). The strain field at the surface of the specimen during the compaction and elasticity phases of cracking approximates the variation of the low loading rate, When \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;6.273 kN, \u003cem\u003eu\u003c/em\u003e\u0026thinsp;=\u0026thinsp;3.995 mm, the specimen reaches the peak strength, and there is stress concentration and small cracks at the tip of the pre-crack. After the peak point the specimen is damaged, with the increase of vertical displacement, when \u003cem\u003eP\u003c/em\u003e is reduced to 4.230kN, \u003cem\u003eu\u003c/em\u003e\u0026thinsp;=\u0026thinsp;6.991mm, the crack starts to expand upward through the coarse aggregate (the red box area in the figure); when \u003cem\u003eP\u003c/em\u003e is reduced to 2.667kN, \u003cem\u003eu\u003c/em\u003e\u0026thinsp;=\u0026thinsp;7.665mm, the crack develops vertically upward again through the coarse aggregate approximating to the loading direction, and at this time, an obvious macroscopic cracks; When \u003cem\u003eP\u003c/em\u003e decreases to 0.204 kN and \u003cem\u003eu\u003c/em\u003e\u0026thinsp;=\u0026thinsp;10.330 mm, the load carrying capacity fails.\u003c/p\u003e\u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section3\"\u003e \u003ch2\u003e5.1.3 Cracking analysis corresponding to the end of loading at different loading rates\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFrom Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e10\u003c/span\u003e, it can be seen that the crack pattern of panel asphalt concrete specimens under different loading rates varies significantly, and the crack pattern of asphalt concrete under low loading rate is not developed vertically upward along the prefabricated crack but is a zigzagging upward tendency, and the formation of this crack pattern may be because asphalt concrete follows the \"concept of the weakest link\" when subjected to concentrated loading. \" The failure of the specimen is mainly due to the generation of internal voids or defects, and the cracks begin to penetrate the hole and form a connection between the cracks and holes. In addition, due to the existence of coarse aggregate with higher strength at the leading edge of the precast cracks in asphalt concrete, the cracks will break along the cemented surface and take on a curved shape during the loading process as the loading rate is small and the aggregate cemented surface is more likely to be broken compared to the aggregate itself. In addition, due to the existence of coarse aggregate with higher strength at the leading edge of the precast cracks in asphalt concrete, the cracks will break along the cemented surface and take on a curved shape during the loading process as the loading rate is small and the aggregate cemented surface is more likely to be broken compared to the aggregate itself. so the cracks will be caused by the presence of coarse aggregate with higher strength at the leading edge of the cracks in the precast cracks in asphalt concrete, this phenomenon is particularly evident at loading rates of 0.05-1 mm/min, and a small strain difference between the specimen crack and the surrounding area can be observed. At the loading rate of 3-10mm/min, the cracks developed almost vertically upwards. This is due to the larger loading rate, which resulted in the cracked specimen being subjected to a larger concentrated load internally, which could not follow the weakest principle, and in the case of a larger concentration of stresses, the cracks went directly through the aggregate, and the breakage surfaces were smoother, which indicated that the cracks did not develop sufficiently, resulting in a more severe strain concentration. By comparing the crack morphology at different loading rates, it is clear that at lower loading rates, the crack development is more zigzag and the strain difference with the surrounding area is smaller. In contrast, at higher loading rates, the crack pattern develops almost directly upward and the breaking surface of the crack is smoother.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003e5.2 Characteristic cloud analysis of the vertical strain field\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e11\u003c/span\u003e shows the characteristic cloud diagrams of vertical strains corresponding to the peak load during loading of pre-cracked semicircular bending specimens at different loading rates, and the horizontal strains on the surface of the asphalt concrete specimens gradually decrease with the increase of loading rate, through calculation, the vertical strains on the surface of the asphalt concrete specimen under different loading rates are 0.0198,0.0147,0.0091,0.0060,0.0052, and 0.0043, respectively. As the loading rate increases, it shows a decreasing trend, indicating that the stiffness of the specimen increases and the anti-deformation ability increases, which is also the initial vertical strain value of the specimen cracking.\u003c/p\u003e\u003c/div\u003e"},{"header":"6. Conclusions","content":"\u003cp\u003eThe \u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003eIC\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eG\u003c/em\u003e\u003csub\u003e\u003cem\u003ef\u003c/em\u003e\u003c/sub\u003e of asphalt concrete increased with increasing loading rate, and the \u003cem\u003eCRI\u003c/em\u003e results were the opposite; the dispersion of \u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003eIC\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eG\u003c/em\u003e\u003csub\u003e\u003cem\u003ef\u003c/em\u003e\u003c/sub\u003e increased with increasing loading rate, but the calculated \u003cem\u003eCRI\u003c/em\u003e data were more uniformly dispersed. These results show that the higher loading rate can improve the resistance of asphalt concrete, but also increase the difference between the performance of the specimens, however, the results of \u003cem\u003eCRI\u003c/em\u003e show that the crack propagation index of asphalt concrete changes more evenly under different loading rates.\u003c/p\u003e \u003cp\u003eThe evolution law of the strain concentration area can well reflect the crack extension characteristics, with the increase of the loading rate, the strain evolution characteristics of the specimen surface changed significantly, and the tensile stress concentration area was extended to the loading direction. With the loading rate decreases, the strain corresponding to the peak load (Exx, Eyy) gradually increases, and after reaching the peak strength with the increase of load displacement, the cracks of the specimens expand step by step along the edge of the coarse aggregate at low loading rates, and the cracks expand upward through the coarse aggregate at high loading rates.\u003c/p\u003e \u003cp\u003eDue to the change of loading rate leads to the different stress distribution within the asphalt concrete, the stress transfer path of asphalt concrete is more complicated when the loading rate is 0.05-1mm/min, which leads to the crack development along the zigzagging path and zigzagging up of the crack pattern. While at the loading rate of 3\u0026ndash;10 mm/min, the specimen was subjected to a larger concentrated load and the direction of crack development was more direct, almost coinciding with that of the pre-cracks, with the crack morphology almost vertically upward along the pre-cracks.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eFunding Information:\u003c/h2\u003e \u003cp\u003eThe authors are grateful for the support provided by the Sponsored by Natural Science Foundation of Xinjiang Uygur Autonomous Region (2022D01A199) program.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eFu H, Chai J, Xu Z et al (2024) Research on material selection and low-temperature anti-cracking mechanism of hydraulic asphalt concrete panels in the alpine region[J]. 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Constr Build Mater 140:416\u0026ndash;423\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Panel asphalt concrete, loading rate, SCB specimen, fracture mechanics index, DIC","lastPublishedDoi":"10.21203/rs.3.rs-4539941/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4539941/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe development of internal cracks in asphalt concrete can be seen as a sign of macro crack development. To explore the influence of different loading rates on the crack resistance of panel asphalt concrete, based on the theory of fracture mechanics, DIC digital image correlation technology was used as a test method for crack propagation of specimens. SCB (Semi-circular bending)tests were carried out on panel asphalt concrete with different loading rates (0.05, 0.2, 1, 3, 5,1 0 mm/min). The effects of different loading rates on the fracture index and full-field strain of asphalt concrete were analyzed. the results showed that when the loading rate increases from 0.05 mm/min to 10mm/min, the stress intensity factor (\u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003eIC\u003c/em\u003e\u003c/sub\u003e) and fracture energy (\u003cem\u003eG\u003c/em\u003e\u003csub\u003e\u003cem\u003ef\u003c/em\u003e\u003c/sub\u003e) increase, and the crack resistance index (\u003cem\u003eCRI\u003c/em\u003e) shows the opposite law; With the increase of loading rate, the strain (Exx, Eyy) corresponding to the peak load gradually decreases. After reaching the peak strength, with the increase of load displacement, the crack of the sample gradually expands along the edge of the coarse aggregate at a low loading rate, and the crack penetrates the coarse aggregate at a high loading rate; There are obvious differences in crack morphology of asphalt concrete specimens under different loading rates, When the loading rate is 0.05-1 mm/min, the crack morphology is tortuously rising. When the loading rate is 3-10mm/min, the crack morphology develops almost vertically upward along the pre-crack. The results of the study can provide a reference for the development of cracks and fracture behavior of panel asphalt concrete under different loading rates.\u003c/p\u003e","manuscriptTitle":"Study on Fracture Characteristics of Panel Asphalt Concrete Under Different Loading Rates","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-07-19 19:32:15","doi":"10.21203/rs.3.rs-4539941/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"1bbc9ad7-52b9-4517-b566-eea0487ad12f","owner":[],"postedDate":"July 19th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-11-04T13:55:36+00:00","versionOfRecord":[],"versionCreatedAt":"2024-07-19 19:32:15","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4539941","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4539941","identity":"rs-4539941","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}