Thermal Stress Restrained Specimen Test Research Articles

Research on material selection and low-temperature anti-cracking mechanism of hydraulic asphalt concrete panels in the alpine region

To solve the problem of asphalt concrete panel cracking at low temperatures, this study proposes to use crumb rubber as a modified material for asphalt in the impermeable layer of asphalt concrete panels and to investigate the anti-cracking performance of crumb rubber modified asphalt concrete (CRMAC) in water conservancy projects in different low-temperature environments. Taking matrix asphalt concrete (MAC), CRMAC, and SBS modified asphalt concrete (SBSMAC) as the research objects, the cracking resistance performance of the three kinds of asphalt concrete under different low-temperature conditions were comparatively analyzed by using ultra-low-temperature (−35°C) small beam bending test, which reveals the damage mechanism of asphalt concrete's low-temperature cracking and damage process; the failure temperatures of the three kinds of asphalt concrete were accurately quantified by the thermal stress restrained specimen test (TSRST), and combined with the Pearson correlation coefficient method to determine the evaluation criteria of asphalt concrete low-temperature performance. The results show that the low-temperature crack resistance of CRMAC is better than the other two asphalt concretes under the same temperature conditions. Its failure temperature reaches −43°C, which meets the low-temperature demand for asphalt concrete panels in alpine regions. This study aims to improve the low-temperature cracking resistance of asphalt concrete impermeable panels, provide new ideas for the selection of asphalt concrete panels, and lay the foundation for the application of CRMA in water conservancy projects, and open up new ways to solve the problem of waste tire accumulation.

Evaluation of Low- and Intermediate-Temperature Cracking Performance of Fiber-Reinforced Asphalt Mixtures

This study was conducted to assess the impact of aramid fiber reinforcement on the fatigue and thermal cracking performance of asphalt mixtures at intermediate and low temperatures, respectively. The study also involved evaluating the experimental consistency and ranking fiber-reinforced asphalt mixtures (FRAMs) based on their performance. One aggregate (diabase stone), one binder type (PG 76-22), and two combinations of aramid fibers, added at different dosages, were used to produce three FRAMs. These fibers included polyolefin/aramid (PFA) fibers at 0.05% dosage by mix weight and Sasobit-coated aramid (SCA) fibers at 0.01% and 0.02% dosages. An unreinforced (control) mix was also produced without any reinforcement. All mixtures were produced at a batch plant by keeping their binder content constant (at 5.5%). The manufacturer recommended dry and wet mixing times were used for better fiber distribution and represent actual mixing conditions. The laboratory performance of plant-produced FRAMs was assessed to characterize the low- and intermediate-temperature cracking performance. The indirect tension asphalt cracking test, semi-circular bend test, three-point bending beam tests, and uniaxial fatigue tests were performed at intermediate temperature; the disk shape compact tension test and thermal stress restrained specimen test tests were performed at low temperature. Fibers were successful at improving the fatigue cracking of asphalt mixtures based on intermediate-temperature testing results. In addition, fiber reinforcement, regardless of dosage and combination, showed improvements in low-temperature (thermal) cracking performance. Furthermore, based on ranking analysis for selected performance indicators from each experiment, the SCA 0.02% reinforced mix on average showed the highest cracking resistance.

A novel approach to warm mix asphalt additive production from polypropylene waste plastic via pyrolysis

The utilization of waste plastics as an additive in warm mix asphalt (WMA), which is an environmentally friendly technology, by pyrolysis method is an emerging concept. In this study, WMA additive was synthesized from char (C) and wax (W) products obtained from the pyrolysis of polypropylene (PP) type waste plastics. Seven different pyrolysis modified bitumen were prepared as PP 6%C, PP 6%C-3%W, PP 6%C-6%W, PP 6%C-10%W, PP 3%C-6%W, PP 1%C-6%W and PP 6%W. Base bitumen and Sasobit® 3% (by weight of bitumen) modified bitumen were used as control groups. The rheological properties of the binders were investigated by Rolling Thin Film Oven, Pressure Aging Vessel, Rotational Viscometer, Dynamic Shear Rheometer and Bending Beam Rheometer tests, and the morphological properties were analyzed by Scanning Electron Microscope, Fourier Transformed Infrared Spectroscopy and Zeta Potential analysis. Asphalt mixture performance characteristics were evaluated by Marshall Design, Hamburg Wheel Tracking and Thermal Stress Restrained Specimen Tests. Binder test results demonstrated that with the addition of PP 6%C-6%W and Sasobit® 3%, the viscosity of bitumen decreased significantly and accordingly the plant temperature reduced by 14ºC and 9ºC. Besides, PP 6%C-6%W modified bitumen performed better than base bitumen at low, medium and high temperatures. Sasobit® 3% improved the high temperature performance of the bitumen. The additive-bitumen modification mechanism involved physical process. Furthermore, the additives were well distributed in bitumen and no agglomeration was observed. WMA-1 (PP 6%C-6%W) and WMA-2 (Sasobit® 3%) have 5% and 9% higher Marshall stability than hot mix asphalt (HMA), respectively. Moreover, the addition of PP 6%C-6%W and Sasobit® 3% increased the rutting resistance of the mixture by 9% and 21%, respectively. Moreover, PP 6%C-6%W improved the low temperature performance of the mixture by decreasing fracture temperature by 3ºC and increasing the fracture strength by 15%. All in all, PP pyrolysis products have strong indicators to become a WMA additive.

Influence of bitumen grade and air voids on low-temperature cracking of asphalt

Low-temperature cracking is one of the main causes of pavement distress in colder areas with below-freezing temperatures. Resistance of asphalt to this cracking depends on a number of factors. A complex knowledge about this phenomena is a key factor during the design process, the building and the use stage of roads. Among the leading drivers are the type of bitumen and air voids in the bituminous mixture. In this research project, both the bituminous binders and mixtures were tested to determine the influence of these components on the low-temperature performance of asphalt pavements. A wide range of bituminous binders were tested, including 20/30, 35/50, 50/70, 70/100 and 100/150 grades. This approach allowed for an in-depth evaluation of the impact of bitumen type and air voids on the low-thermal susceptibility of asphalt mixture. The basic tests for bitumen were performed such as the penetration value at 25 °C (EN 1426), the softening point with the Ring & Ball method (EN 1427) and the group composition with SARA analysis using the Thin Layer Chromatography with Flame Ionization Detector (TLC/FID) method. Both neat bitumen and bitumen after Rotating Thin Film Oven Test (RTFOT) short-term simulated ageing (EN 12607–1) were tested. Next, bituminous mixtures based on mentioned bitumen with 2.2%, 3.5% and 6.5% air voids were prepared and subjected to uniaxial tension in Thermal Stress Restrained Specimen Test (TSRST) to determine their low-temperature performance. The test results point to the binder type as the key determinant of the low-temperature performance of asphalt. Softer bitumens of a higher penetration have a better low-temperature performance and the group composition is the determinant of the TSRST failure temperature. The effect of air voids were of secondary importance in this respect.

Effects of the ductility and brittle point of modified asphalt on the freeze-break behavior of asphalt concrete: A 3D-mesoscopic damage FE model

Hydraulic asphalt concrete is widely used in pumped storage power stations and other anti-seepage engineering. The low-temperature freeze-break of asphalt mixtures is a rather complex phenomenon significantly affected by the ductility (at 5℃) and the brittle point of asphalt binder. In order to achieve better crack resistance at low temperatures, the influence of ductility and brittle point on low-temperature fracture becomes a major problem. This paper firstly proposes an effective modulus equation of asphalt mortar, which accounts for ductility and brittle point of modified asphalts as dominant factors. Then, a three-dimensional (3D) mesoscale finite element (FE) model, which considers this equation and the damage evolution of the asphalt mixture from linear viscoelastic (LVE) to elastic-brittle due to cooling, is established through an aggregate random placement procedure to simulate the freeze-break behavior of asphalt concrete samples in the thermal stress restrained specimen test (TSRST). The numerical simulation results of thermal stress are in good agreement with the previously published TSRST thermal stress data, and this verifies that our model is effective. Furthermore, the proposed model can predict the freeze-break temperature of asphalt mixture with good accuracy, and well describe the mesoscale thermal stress, strain, and damage distributions.

Research on the Fracture Characteristics of Asphalt Mixtures in High Altitude and Cold Regions with Large Temperature Differences

Due to the harsh climatic conditions in high altitude and cold regions with large temperature differences, asphalt pavement is generally prone to cracking, and the cracks propagate rapidly, which reduces the service life and service level of the road. The factors influencing the fracture characteristics of asphalt mixtures were analyzed in this paper, and the mixtures with different aggregate gradations from various types of asphalt were prepared. The fracture characteristics were explored using the thermal stress restrained specimen test (TSRST) and low-temperature bending test, and the good consistency of the low-temperature fracture performance was identified according to the results of frost-break temperature, flexural strength, and fracture toughness. The frost-break temperature was confirmed as the best indicator of the material crack resistance and could be used as the index to evaluate the performance of asphalt mixtures at low temperatures. The frost-break temperature of matrix asphalt mixture is 8–10 °C higher than that of modified asphalt mixture, and AC asphalt mixture is 2–4 °C higher than that of SMA asphalt mixture. The excellent asphalt performance has a more important influence on the fracture characteristics of asphalt mixture. The asphalt mixture of the same type had similar fracture toughness at varying notch depths, the most deviation is 3.78% which shows that the initial crack depth has little effect on the fracture toughness of asphalt mixture at low temperature. The results of the study can provide a basis for the selection of asphalt pavement surface materials and the optimization of mixtures in high altitude and cold regions with large temperature differences.

Assessment of the low-temperature performance of asphalt mixtures for bridge pavement

The alternative Stone Mastic Asphalt containing an increased amount of bituminous mastic bituminous mixtures (SMA-MA) have been successfully used for additional protective layers on steel and concrete deck bridges. In this application, the mixtures must feature the desired behaviour at both high and low (i.e. below freezing) temperatures. The SMA-MA mixtures owe their improved low-temperature resistance to the bituminous binder used in them, softer than the binders used in mastic asphalts (MA). This article reports a study comparing the selected low-temperature parameters of the SMA-MA and MA mixtures to the parameters of the bituminous binders used in them. The performance of HMA was evaluated by subjecting the specimens to UTST (Uniaxial Tension Stress Test) and TSRST (Thermal Stress Restrained Specimen Test) tests at the test temperatures from −25°C to −10°C. The low-temperature performance of bituminous binders was, in turn, assessed with the BBR test.

Thermal fatigue and cracking behaviors of asphalt mixtures under different temperature variations

Thermal cracking is one of the most annoying distresses in asphalt pavements. The cracking of asphalt pavements caused by extremely low temperature and the damage of thermal fatigue caused by repeated temperature variations are particularly pronounced. The service condition of asphalt pavements has been affected significantly. Laboratory experiments with cyclic loads simulating the actions caused by repeated temperature variations on pavements have been conducted in many previous studies to investigate the thermal fatigue characteristics of asphalt mixtures. In those studies, an equivalent cyclic mechanical stress that can be applied by an actuator was mostly used to replace the cyclic thermal stress induced by a temperature variation. It could simplify the experimental process but could not consider the performances of asphalt mixtures varying as a function of temperature. In the present study, the thermal fatigue properties and cracking behaviors of asphalt mixtures were comprehensively investigated through a modified thermal stress restrained specimen test (TSRST) and the numerical analysis. Various temperature ranges (-20 to −10 °C, −10 to 0 °C), cyclic cooling rates (10 °C/h, 20 °C/h), low-temperature performance cooling rates (10 °C/h, 8 °C/h, 6 °C/h, 4 °C/h, 2 °C/h) and pre-crack dimensions were considered for the study to address the influences of those parameters on the analysis results. Based on the testing and simulation results, it was found that the effects of thermal fatigue on asphalt mixtures under different temperature variations and cooling rates were quantified, and the damage characteristics of the asphalt mixtures were also explored. The results showed that under the low-temperature performance state, the thermal stress of asphalt mixtures increases with a uniform cooling rate and it could be obtained that the faster the cooling rate, the larger the thermal stress generated. In the cyclic thermal stress test, due to the viscoelastic properties of asphalt mixtures, the thermal stress showed significant stress relaxation phenomena under the temperature variations. The magnitude of thermal stress decreased gradually within each cycle. It demonstrates that under the same temperature variation, the thermal stress decreases continuously with the increasing thermal cycles. Through the numerical simulation, it was clear that under different temperature ranges and cooling rates, the magnitude of thermal stress increased with the temperature range decreased, whereas the magnitude of thermal stress increased with an acceleration of the cooling rate. The lower temperature range induced a larger stress intensity factor (KI), which implies a faster cracking evolution. Analyzing the effects of different pre-crack dimensions on the number of temperature cycles, the height of pre-crack showed significant effects on the number of temperature cycles than width.

Development of a new modified TSRST test to measure the thermal stress of asphalt supporting layer in the slab track system

The unique thermal stress environment of asphalt supporting layer (ASL) in the slab track system is critical to its service safety. The extra thermal load is responsible for causing large thermal stress in ASL. A new modified thermal stress restrained specimen test (TSRST) method was developed to measure the thermal stress development of ASL during the cooling process. The high density polyethylene (HDPE) blocks were assembled onto the asphalt mixture beam to provide extra thermal load automatically during the cooling process, the modified TSRST test were conducted on two types of asphalt mixture types comparing to the standard TSRST test. The tests results show that the extra thermal load accelerates the development of thermal stress in asphalt concrete and elevates the fracture temperature and transition temperature. The modified TSRST test was proved to characterize the effect of the extra thermal load effectively, and the test results have good repeatability.

Thermal cracking in cold regions’ asphalt mixtures prepared using high polymer modified binders and softening agents

ABSTRACT This study was conducted to assess high polymer modified asphalt binders including a corn oil-based softening agent (SA) and their impact on the cracking performance of mixtures in cold regions. Styrene–Butadiene-Styrene (SBS) polymer modifier, corn-oil-based softening agent, and Performance Grade 52–34 binder were proportioned at various dosages to prepare modified binders. The mixtures were aged according to three loose mix aging procedures (short-term, long-term, and extended long-term). It was found that the SBS and corn-oil combination improved both the high and low continuous grade along with percent recovery, and reduced fatigue cracking potentiality based on a reduced negative ΔTc at the binder level. In addition, at the mixture level, an increase in the Disc-shaped Compact Test (DCT) fracture energy was observed at low temperatures; also an increase in cracking temperature due to thermal stress from Thermal Stress Restrained Specimen Test (TSRST) was observed, indicating better cracking resistance. Regardless of aging, the flexural stress from the beam fatigue test also decreased, indicating higher resistance to fatigue cracking at intermediate temperatures. The study suggests that the balanced application of SBS and corn-oil can lead to the optimum improvement in low temperature cracking performance of the evaluated asphalt mixtures.

Influence of low-temperature polyurethane solid-solid PCMs particles on the pavement performance of asphalt mixtures

In order to slow down the cooling rate of the mixture and reduce the low temperature cracking of asphalt pavement in large temperature difference areas, low-temperature polyurethane solid-solid phase change materials (LPSPCMs) were prepared by prepolymer method. The researches show that LPSPCMs have good phase change heat storage performance and thermal stability performance, and can be applied to hot mix asphalt mixtures. The LPSPCMs particles were incorporated into the asphalt mixture, and the road performance of the LPSPCMs particulate asphalt mixture was tested and analyzed and found: as LPSPCMs particles change the abrasion resistance and embedded effect between asphalt mixes, with the increase of LPSPCMs particles, the high-temperature performance of asphalt mixes first increased and then decreased. The water stability of asphalt mixtures gradually decreases with the increase of LPSPCMs particles content because relative to limestone aggregates, LPSPCMs particles adhere poorly to asphalt. The thermal stress restrained specimen test (TSRST) showed that the cracking temperature of the asphalt mixture gradually decreased with the increase of LPSPCMs particles contents because of the phase change temperature control effect of LPSPCMs particles indicated that LPSPCMs particles improve the low-temperature performance of asphalt mixtures. On this basis, the correlation between the evaluation index of the phase change temperature adjustment effect and the improvement effect of the low-temperature performance of the mixture was established.

Evaluation of the Low-Temperature Cracking Performance of Recycled Asphalt Mixture: A Development of Equivalent Fracture Temperature

This study aims to develop a new index to evaluate the low-temperature cracking performance (LTCP) of recycled asphalt mixtures. To achieve this, the assumption that fracture energy has limitation in evaluating the LTCP of mixtures was put forward firstly. To reveal this limitation theoretically, a concept of energy absorption rate that characterized the fracture energy of the mixtures was then given. Thirdly, an equivalent fracture temperature (EFT) corresponding to the critical cracking temperature in a thermal stress restrained specimen test (TSRST) was proposed to evaluate the LTCP of mixtures based on a three-point bending beam (3PBB) test. Finally, some data derived from previous work were collected to verify the proposed assumption, and the 3PBB test and TSRST were conducted to investigate the LTCP of five recycled mixtures with different reclaimed asphalt pavement (RAP) material contents and to verify the rationality of the proposed EFT. The results confirmed that fracture energy had some limitations in predicting the LTCP of mixtures. The EFT was as accurate as the critical cracking temperature in evaluating the LTCP of mixtures. Compared to fracture energy and critical cracking temperature, EFT had bigger absolute change and relative change between different mixtures, meaning it was better to differentiate the LTCP of mixtures. Compared to failure strain, EFT was also more definite and less variable when processed by different data analysts, meaning it was more objective.

Investigation on low-temperature cracking characteristics of asphalt mixtures: A virtual thermal stress restrained specimen test approach

In order to characterize the effects of aggregate characteristics on the low-temperature cracking characteristics of asphalt mixtures, a virtual approach for the thermal stress restrained specimen test (TSRST) was established based on the discrete element method (DEM) and the simulation software particle flow code in two-dimension (PFC2D). A two-dimensional (2D) virtual specimen was established according to the random generation algorithm. The meso contact parameters between each phase in materials at different temperatures were determined through laboratory tests. The internal thermal stress curve of the specimen and the meso mechanism of crack propagation were analyzed during the virtual test, and the reliability of the virtual test was confirmed by the results of laboratory tests. Finally, the effects of aggregate properties on the low-temperature crack resistance of asphalt mixtures were analyzed. The results of the virtual test and the laboratory test are highly consistent, which proves that the virtual TSRST can be used as a reliable method to evaluate the low-temperature crack resistance of asphalt mixtures. The damage of the specimen can be divided into three stages: crack initiation, stable propagation, and unstable propagation. The asphalt mixture with less aggregate content, coarser gradation and smaller flat ratio has better low-temperature crack resistance.

Effect of Freeze–Thaw cycles on the pavement performance of SBS modified and composite crumb rubber modified asphalt mixtures

The effect of freeze–thaw cycles on the pavement performance of SBS modified asphalt mixture (SBSMA) and SBS/crumb rubber composite modified asphalt mixture (CCRMA) was studied using a triaxial repeated creep test, semicircular bending fatigue test based on digital image correlation (DIC), and thermal stress restrained specimen test. The mechanical model of the residual strain (RS) of the asphalt mixtures is established, and the residual viscous flow strain (εRvf,N) and residual viscoelastic strain (εRve,N) are separated. Based on the horizontal strain (Exx) of DIC, a new mesofatigue damage variable (D) is proposed. According to the characteristic curve of D, the antifatigue damage parameter (AFDP) is established and the correlation between AFDP and fatigue life (Nf) is analyzed. Simultaneously, a calculation model of the relaxation temperature stress (σRts(T)) of the asphalt mixture at different cooling rates (v) is established based on the finite element method. Results showed that the growth rates of RS, εRvf,N, and D of both asphalt mixtures accelerate, AFDP decreases, and freeze–break temperature (TD) rises with increasing freeze–thaw cycles. However, the growth rates of RS, εRvf,N, and D of CCRMA are always slower than SBSMA, the AFDP is larger than SBSMA, TD is lower than SBSMA, εRve,N is a fixed value under specific conditions, and a good correlation exists between the AFDP and Nf. The pavement performance of the asphalt mixtures worsens after the freeze–thaw cycles, and the influence of a salt freeze–thaw cycles is greater than that of a water freeze–thaw cycles. Moreover, CCRMA has better high-temperature deformation resistance, fatigue damage resistance, and low-temperature cracking resistance than SBSMA. The conversion point temperature (TZ) increases with the acceleration of v, and the σRts(T) calculation model can accurately reflect the σRts(T) of the asphalt mixture at different v.

Investigation of the Reusability of a Polyurethane-Bound Noise-Absorbing Pavement in Terms of Reclaimed Asphalt Pavement.

A key aspect of sustainable pavement construction is the use of environmentally-friendly designed pavement materials. These materials are characterized by the fact that they are renewable raw materials, require a low amount of energy during production and in the best case, are made from a high proportion of recyclable materials in order to reduce waste. A number of recent studies have demonstrated the recyclability of waste materials that can be very well utilized in road construction. This study describes the recycling of a new and innovative topcoat system that already contains recycled materials. However, the focus is on guaranteeing the mechanical performance of the innovative absorption layer where different portions of used material are added. Therefore, low-temperature behaviour, durability, fatigue and noise absorption are investigated in detail and it is concluded that their function is preserved. In order to investigate these characteristics, the impedance measuring tube, the uniaxial cyclic compression test (UCCT), the three point bending test (3PB), the uniaxial tension stress test (UTST) and the thermal stress restrained specimen test (TSRST) are used. However, the examined absorption material can be reused to build innovative roads.

Evaluation on the Performance of Hydraulic Bitumen Binders under High and Low Temperatures for Pumped Storage Power Station Projects.

The high and low-temperature performance of five hydraulic bitumen binders was evaluated using the dynamic shear rheometer (DSR) test, infrared spectrum test and direct tensile (DT) test. These hydraulic bitumen binders were respectively applied for several pumped storage power stations (PSPS) projects that were constructed or under construction. In order to relate the bitumen performance to the mixture performance, the slope flow test, three-point bending test and thermal stress restrained specimen test were carried out on hydraulic asphalt mixtures. The test results indicated the DSR rheological master curves can well distinguish the difference of each bitumen binder as well as the effect of polymer modification. Phase angle master curves, black diagrams and infrared spectra all indicated that several penetration-grade hydraulic bitumen binders were not virgin bitumen binders but were modified with relatively lower SBS polymer content when compared with traditional SBS-modified bitumen. When selecting the commonly used Karamay SG70 hydraulic bitumen as a reference, the normal SBS-modified bitumen was superior to other bitumen in terms of low- and high-temperature performance. Several slightly SBS-modified bitumen binders did not always show consistent results, which indicated that slightly modified bitumen may not really have the desired performance as expected. Therefore, SBS-modified bitumen will be more promising when dealing with extremely low or high temperatures. Bitumen performance was well compared with the mixture performance by using the bitumen creep, relaxation and tensile failure strain corresponding to the asphalt concrete slope flow, the maximum bending strain and the failure temperature, respectively. Compared with the traditional penetration, softening point and ductility test, it indicated that the DSR rheological test, creep test, direct tensile test and stress relaxation test can be used as more powerful tools for the characterization and optimization of hydraulic bitumen binders.

Field Evaluation of High Modulus Asphalt Concrete Resistance to Low-Temperature Cracking

High-modulus asphalt concrete has numerous advantages in comparison to conventional asphalt concrete, including increased resistance to permanent deformations and increased pavement fatigue life. However, previous studies have shown that the construction of road pavements with High Modulus Asphalt Concrete (HMAC) may significantly increase the risk of low-temperature cracking. Those observations were the motivation for the research presented in this paper. Four test sections with HMAC used in base and binder courses were evaluated in the study. Field investigations of the number of low-temperature cracks were performed over several years. It was established that the number of new low-temperature cracks is susceptible to many random factors, and the statistical term “reversion to the mean” should be considered. A new factor named Increase in Cracking Index was developed to analyze the resistance of pavement to low-temperature cracking. For all the considered field sections, samples were cut from each asphalt layer, and Thermal Stress Restrained Specimen Tests were performed in the laboratory. Correlations of temperature at failure and cryogenic stresses with the cracking intensity observed in the field were analyzed. The paper provides practical suggestions for pavement designers. When the use of high modulus asphalt concrete is planned for binder course and asphalt base, which may result in lower resistance to low-temperature cracking of pavement than in the case of conventional asphalt concrete, it is advisable to apply a wearing course with improved resistance to low-temperature cracking. Such an approach may compensate for the adverse effects of usage of high modulus asphalt concrete.

Investigation of Low-Temperature Cracking Characteristics of Asphalt Mixtures: A Virtual Thermal Stress Restrained Specimen Test Approachtang Junyaoa, Ma Taoa*, Zheng Binshuangb, Zhang Yaoc, Huang Xiaominga a School of Transportation, Southeast University, Nanjing 211189, Chinab School of Modern Posts, Nanjing University of Posts and Telecommunications, Nanjing 210003, Chinac College of Architectural Science and Engineering, Yangzhou University, Yangzhou 225127, China

Investigation of Low-Temperature Cracking Characteristics of Asphalt Mixtures: A Virtual Thermal Stress Restrained Specimen Test Approachtang Junyaoa, Ma Taoa*, Zheng Binshuangb, Zhang Yaoc, Huang Xiaominga a School of Transportation, Southeast University, Nanjing 211189, Chinab School of Modern Posts, Nanjing University of Posts and Telecommunications, Nanjing 210003, Chinac College of Architectural Science and Engineering, Yangzhou University, Yangzhou 225127, China

TSRST heterogeneous modelling for investigating failure depending on asphalt mix design and experimental conditions

Thermal Stress Restrained Specimen Test (TSRST) is used to determine low temperature cracking susceptibility of asphalt mixture. In this test, a specimen is subjected to a constant temperature decrease rate. Due to the prohibited thermal shrinkage, cryogenic stress is built up in the sample. The progression of stress causes failure in the specimen. There is a particular experimental limitation to measuring time-dependent stress. This paper aims to overcome this limitation and develop a numerical approach to estimate the specimen's local stress and strain value. It consists of heterogeneous multi-scale modelling of asphalt mixture. The heterogeneous scales are mortar and hot mix asphalt. The asphalt mixture scale is simulated as a triphasic model containing viscoelastic matrix, elastic inclusions, and air voids. Granular skeletons are generated using a random object modeller software or MOA (Modeleur d’Objet Aléatoire). These models correspond to a specific aggregate grading curve. After that, the heterogeneous geometries are imported into ABAQUS finite element code. The coupled thermal and mechanical numerical simulations are realised at different temperatures. Results have shown that the heterogeneous numerical model developed in this study can precisely predict time-dependent stress at different temperatures. Localising the critical zone with maximum stress within the matrix is considered in this study. The intensity of local stress and strain values are determined to specify the zones which are susceptible to damage. It was observed that the local stress is almost four to five times greater than the average failure stress at the global scale.

Investigation Of Comparability Of TSRST And SCB Cracking Tests For Evaluation Of Low-Temperature Properties In Asphalt Mixtures And Use In Quality Control

Mix design procedure for asphalt mixtures in the Baltic region requires to ensure resistance to low temperatures due to climatic conditions. Thermal Stress Restrained Specimen Test (TSRST) has been considered as the most precise direct test method to determine the thermal behaviour of asphalt mixtures. As the TSRST test is time-consuming and the equipment is much more expensive, therefore the possibility to use Semi-Circular Bending (SCB) as a preliminary test was evaluated and the potential threshold was recommended. This study presents the evaluation of low-temperature properties with SCB and TSRST methods and the test suitability assessment for use in quality control. The supplementary rating was made by analysing Fraass breaking point test results of asphalt binders. In total 36 different asphalt samples were tested to investigate fracture test methods and to assess the influence of bitumen type and composition on resistance to low-temperature cracking. The results displayed an acceptable correlation between both test methods that allow using SCB for pre-screening purposes. At the same time, the results indicated that the type of used bitumen has a crucial influence on asphalt mixtures resistance to low-temperature cracking.