Asphalt Mortar Research Articles

Comprehensive Performance Evaluation of Asphalt Mortar Based on Multi-Index Weighted Decision Model

Abstract Aggregate is the key factor to ensure the performance of asphalt mixture. In order to analyze the impact of limestone, basalt, diabase, and steel slag on the road performance of asphalt mortar, with the ratio of mineral powder to asphalt in asphalt mortar being the same as the asphalt concrete (AC)-13 Styrene Butadiene Styrene (SBS) polymer–modified asphalt mixture, the four types of asphalt mortar specimens with different aggregates were designed and molded. The high-temperature performance, low-temperature performance, water stability, and fatigue performance tests were carried out to obtain the performance parameters of asphalt mortar. The multi-index weighted decision model was used to quantitatively evaluate the influence of the four types of aggregate on the comprehensive pavement performance of asphalt mortar. Results indicated that basalt asphalt mortar had the best high-temperature performance, steel slag asphalt mortar had the best low-temperature crack resistance and fatigue performance, and limestone asphalt mortar had the best water stability. Moreover, basalt asphalt mortar had the best comprehensive pavement performance. Finally, the optimized basalt asphalt mortar and steel slag asphalt mortar were applied to the engineering field, and both met the requirement.

Editorial: Special Issue on Smart and Green Infrastructures with Optimum Life Cycle Solutions

Editorial: Special Issue on Smart and Green Infrastructures with Optimum Life Cycle Solutions

Experimental and statistical exploring for mixed-mode (I&II) fracture behavior of cement emulsified asphalt mortar under freeze–thaw cycles and aging condition

This study has been investigated the effect of freeze–thaw cycles and aging condition on the pure mode I, pure mode II and mixed-mode I/II fracture resistance of Cement Emulsified Asphalt Mortar (CEAM). The experiments were conducted on SCB specimens designed with 16 randomized mix designs with different cement contents (C), asphalt-to-cement ratios (A/C), and water-to-cement ratios (W/C) using the d-optimal response surface methodology. The specimens were divided into three groups: control specimens (n = 144), aged specimens (n = 144), and specimens subjected to 1, 3, 5, and 10 freeze–thaw cycles (n = 576). The experiments were performed in three modes of loading: pure tensile (I), pure shear (II), and mixed-mode tensile-shear (I/II). To assess the impact of freeze–thaw and aging damage on fracture properties, the Fracture Energy Ratio (FER) was defined as the ratio of fracture energy of the damaged/conditioned specimen to that of the corresponding control specimen. Then, a number of statistical models were developed for the relationship between FER and mix design variables (A/C, W/C, and C). The results showed that the application of freeze–thaw cycles reduced the fracture energy of CEAM in all three modes. The independent variable with the greatest impact on fracture energy changes was A/C for the pure tensile mode, and C for the pure shear mode and the mixed-mode tensile-shear. The initial freeze–thaw cycles were found to have a greater impact on fracture energy than later cycles. Also, freeze–thaw cycles are more detrimental in reducing mode II fracture energy than mode I and mixed-mode I/II fracture energies and therefore have a more damaging impact on the pure shear fracture properties of CEAM. Aging also reduced the fracture energy of CEAM in all three modes; an effect that was most greatly influenced by the amount of asphalt in the mortar composition. Aging had a greater impact on mode I fracture energy than mode II and mixed-mode I/II fracture energies.

Understanding the influence of filler type and asphalt binder content on the moisture and fatigue resistance of asphalt mortars

An adequate moisture resistance is a key element to guarantee the durability of asphalt materials. This paper identifies the influence of filler typology and bitumen content on the mechanical response of asphalt mortars before and after water action. Two fillers were evaluated: Portland cement and Calcium carbonate, along with different contents of a penetration bitumen (B35/50). Stiffness, ductility, and fatigue were evaluated through a new protocol for asphalt mortar samples using a 3-point-bending test on DMA (Dynamic Mechanical Analyzer). The use of Portland cement presents higher stiffness, lower ductility, and improved fatigue and water resistance compared to Calcium carbonate. It is also possible to optimize bitumen content based on fatigue results. Content beyond the optimal reduce variations after water action but compromise fatigue resistance. Lower content leads to a poorer performance in both terms. This methodology enables asphalt mortar characterisation as a tool to optimise the design of asphalt materials.

Creep model of cement and asphalt (CA) mortar based on micro-meso structure

Creep model of cement and asphalt (CA) mortar based on micro-meso structure

A Novel Evaluation Method of Construction Homogeneity for Asphalt Pavement Based on the Characteristic of Component Distribution.

To effectively evaluate the construction homogeneity of asphalt pavement, the tomography image of a core sample of asphalt pavement was obtained via industrial computed tomography (CT) equipment. According to the characteristics of CT images, an improved separation algorithm based on annular partition and Nobuyuki Otsu (OTSU) threshold segmentation was proposed. Based on the distribution of aggregates, voids and asphalt mortar, and the area ratio of each part in the CT images inside the pavement, a novel evaluation method for the distribution homogeneity of asphalt pavement components was put forward, and the validity of the evaluation index was also verified. The results show that the aggregates, voids and asphalt mortar in CT images can be effectively segmented by annular partition combined with the OTSU threshold separation algorithm. By superimposing the segmented image on the original image, the segmentation and identification effects of aggregates, voids and asphalt mortar in the CT image are confirmed. Compared with a non-segregated specimen, the average values of the horizontal heterogeneity coefficients of high, medium, light and fine-aggregate-segregated mixtures increased by 72.0%, 48.3%, 34.7% and 16.1%, respectively, where the change range is in accordance with the segregation degrees of several mixtures. The indirect tensile strength of fine-aggregate-, light-, medium- and high-segregated asphalt mixtures decreased by 8.3%, 16.7%, 25.0% and 45.8%, respectively, when compared with the non-segregated asphalt mixture. The index of the vertical heterogeneity coefficient has good correlation with the indirect tensile strength of segregated asphalt mixtures. The construction quality homogeneity of asphalt pavement in different regions can be reliably evaluated by the horizontal heterogeneity coefficient and vertical heterogeneity coefficient.

Influence of fiber dispersion and distribution on flexural tensile properties of asphalt mixture Based on finite element simulation

• Basalt fibers can improve the low temperature crack resistance of asphalt mixture. • The Weibull distribution can approximately describe the fiber distribution in basalt fiber asphalt mortar. • Better reinforcement can be achieved by well dispersed basalt fibers. • The spatial distribution of fibers truly influence the flexural tensile properties of asphalt mixture. This study aims to reveal the relationship between the uneven distribution characteristics of basalt fibers and the flexural tensile performance of asphalt mixture. Nano Computed Tomography(nano-CT) was used to explore the realistic distribution features of basalt fibers in asphalt mortar. In addition, the distribution fitting and goodness of fit tests were carried out to find out the distribution form that can well describe the distribution of basalt fibers. The three-dimensional fiber models with different distribution forms were established in finite element software ABAQUS. Then the three-point bending test was simulated to analyze the influence of fiber dispersion and distribution on the flexural tensile properties of the asphalt mixture. Simulation results show that the asphalt mixture beam model shows better tensile resistance when the fibers are better dispersed. Moreover, when more basalt fibers are at the bottom of the middle span, it is more conducive to reducing the peak stress at the bottom of the beam and delaying the cracking of the asphalt mixture.

Mixed mode-I/II fatigue performance of Cement Emulsified Asphalt Mortar: Experimental and statistical analysis at intermediate temperature

This study has investigated fatigue life of Cement Emulsified Asphalt Mortar (CEAM) under mixed-mode I/II loadings at the intermediate temperature. For this investigation, SCB specimens of 16 randomized mixture designs with different cement contents (C), asphalt-to-cement ratios (A/C), and water-to-cement ratios (W/C) were prepared and subjected to the cyclic mixed tensile-shear loading with Me = 0, 0.5, 1.0 at three frequencies of 2, 4 and 8 Hz. The results were analyzed using the d-optimal response surface method and revealed that for all three loading modes, the fatigue life increased with increasing C and A/C. The CEAM also showed a longer fatigue life in the pure shear mode than in the pure tensile mode. The difference between the fatigue life of mode I and II was found to be increasing with the increase in cement content and loading frequency. Increasing the loading frequency increased the fatigue life of the mortar in all three modes.

DEM-based stress transmission in asphalt mixture skeleton filling system

• Stress transmission of skeleton filling system are obtained. • Skeleton aggregate is the main stress transmission medium. • Localization of contact force is affected by the modulus of asphalt mortar. Asphalt mixture is a skeleton filling system consisting of aggregate, asphalt, and mineral powder. High performance asphalt mixture design is directly affected by internal stress transmission of skeleton filling system. In this paper, the discrete element method based on digital image was employed to study the stress transmission. By analyzing the effect of skeleton structure on the contact force between aggregate and mortar, it is concluded that the skeleton aggregate in the asphalt mixture is the main stress transmission medium. The lower the degree of disruption, the higher the contact force of skeleton aggregate. At the same time, the variation coefficient of contact force of asphalt mortar with low filling coefficient is larger and the localization phenomenon is more serious. By analyzing the effect of mortar properties on the contact force between aggregate and mortar, it is concluded that the lower the modulus of asphalt mortar, the higher the degree of localization of contact force and the more likely to have local damage.

Experimental study on interfacial damage characteristics of CRTS II slab track and CA mortar with AE and DIC techniques

Since the interface is often regarded as the weakest part of the ballastless track structure, there is a great need to investigate the interlayer bonding performance to ensure the safety of train operations for high-speed railways. In this study, the damage characteristics of the interface between China Railway Track System II (CRTS II) slab track and cement emulsified asphalt (CA) mortar (T-CA interface) under shear loading were thoroughly investigated. The interfacial deformation and damage development process during the direct shear experiments were recorded by a combination of acoustic emission (AE) and digital image correlation (DIC) techniques. Consequently, a bilinear cohesive zone model (CZM) of the T-CA interface was proposed. The results show that the AE activities are rare in the initial stage of loading, while they increase sharply when the shear loading approaches the interface bonding strength. The AE parameters can well characterize the entire process of interfacial failure. Through the DIC technique, the macroscopic deformation process was well captured and the shear stress versus relative displacement curves were derived. Subsequently, the relationship between the shear stress and relative displacement of the interface was well fitted by a bilinear CZM, of which parameters are calibrated through the experimental data. The effectiveness of the proposed bilinear CZM is validated by using a three-dimensional finite element model. This work provides a better understanding for the damage mechanism of the bond performance between CRTS II track slab and CA mortar.

Feasibility analysis of resource application of waste incineration fly ash in asphalt pavement materials.

To confirm the feasibility of waste incineration fly ash applied in asphalt pavement materials, the waste fly ash from the waste incineration station in Dongguan (DG-FA) and Guangzhou (GZ-FA) were selected as mineral filler replacing limestone powder (LF) to prepare asphalt mortar. The physical properties, chemical composition, and thermal characteristics of FA were analyzed. The effect of FA on the physical properties and rheological properties of asphalt binder was investigated systematically. The micromorphology of FA asphalt mortar was characterized. Finally, the blocking effect of asphalt binder on the leaching of toxic elements from FA was evaluated through XRF test. The results showed that the granular composition of FA particles was similar to that of LF. Furthermore, compared to LF, the specific surface area and the pore structure of FA were more developed, and the high active amorphous material was higher. Adding FA to asphalt mortar and increasing replacing amount improved its high-temperature rutting resistance as well as its ability to adhere to asphalt, while the low-temperature crack resistance was decreased. Further, the asphalt binder provided the good shielding effect against the migration of heavy metals in FA. While the leaching concentration of Pb element slightly exceeded the hazardous waste leaching standard (GB5085.3-2007), the remaining elements met the standard requirements. Overall, FA improved asphalt mortar performance, and the asphalt had a good curing and stabilizing effect on the toxic elements in fly ash, indicating that FA could be used as a filler in asphalt pavements.

Variable speed mixing test and mixing flowability of asphalt mixtures

ABSTRACT To know the mixing flowability in theory and quantitatively evaluate the mixing workability of the asphalt mixture, a variable speed mixing (VSM) test device was developed in our laboratory. Different asphalt mixtures are tested by recording the mixing power under different mixing speeds (20∼50 r·min-1) and different mixing temperatures (130∼180 °C) to analyze the mixing flowability. Afterwards, the mixing workability index was defined from rheological parameters by establishing the mixing flow model. The experimental results indicate that the mixing flowability of asphalt mixtures obeys the linear Bingham’s visco-plastic model, which conducts two mixing rheological parameters including the mixing plastic limit and the mixing viscosity by the intercept and slope of the flow straight respectively. When the mixing temperature increases, the mixing viscosity decreases and the workability index increases, but the mixing plastic limit is not affected. With the increase of the nominal maximum particle size of asphalt mixtures, the mixing plastic limit increases and the workability index decreases, but the mixing viscosity is not affected. The asphalt becomes more viscous as the asphalt content increase, which leads to worse workability. The composition of aggregate determines the mixing plastic limit, and the viscosity of asphalt mortar determines the mixing viscosity.

Multi-scale finite element simulation of asphalt mixture anti-cracking performance

This study investigates the anti-cracking performance and cracking mechanisms of asphalt mixtures. The results of experimental tests were compared with simulated tests of asphalt mixtures based on the multi-scale finite element method (FEM). The FEM considered the mesostructure of the asphalt mixtures, the internal viscoelasticity of asphalt mortar, and the asphalt mastic-aggregate interface. Coarse aggregates were generated based on the polygonal random aggregate generation and placement method. Numerical cracking models of the asphalt mixtures were established by the multi-scale FEM and fracture tests were simulated according to the experimental test conditions. The reliability of the simulations was verified by comparison with the experimental test results. The influences on cracking behavior were investigated, with an energy-saving and economical alternative mixture—cold recycled mixture (CRM)—used for comparison. The simulations were highly accurate and could effectively simulate the asphalt mixtures’ cracking processes and mechanisms. The cracking behavior was directly related to notch length, test temperature, void content, and mixture type. A significant difference in the macroscopic anti-cracking performance of hot mixture asphalt and CRM was found. According to the simulations of crack development, there is a 'critical point' of crack propagation from the interface to the interior of the mortar. The mesoscale influences on the cracking behavior of asphalt mixtures are discussed and ranked in terms of importance.

Effect of Asphalt Mortar Viscoelasticity on Microstructural Fracture Behavior of Asphalt Mixture Based on Cohesive Zone Model

Effect of Asphalt Mortar Viscoelasticity on Microstructural Fracture Behavior of Asphalt Mixture Based on Cohesive Zone Model

Effects of High Temperature on Creep Properties of Cement and Emulsified Asphalt Mortar

Effects of High Temperature on Creep Properties of Cement and Emulsified Asphalt Mortar

Effect of fiber characteristic parameters on the high and low temperature rheological properties of basalt fiber modified asphalt mortar

Fiber has an important influence on the performance of asphalt materials. However, the effect of fiber characteristic parameters (length, type, etc.) on the function of asphalt mortar is still lack of understanding. Therefore, a systematical experimental plan was conducted to evaluate the effects of the selected parameters of filler-binder ratio, fiber type, fiber content and fiber length on the rheological properties of asphalt mortar, including five filler-binder ratios (0.6, 0.8, 1.0, 1.2 and 1.4), four fiber types (three chopped basalt fibers with different coating agents named A, B and C and one flocculent basalt fiber), five fiber contents (1%, 2%, 3%, 4% and 5%) and three fiber lengths (6 mm, 9 mm, 15 mm). Then, Dynamic Shear Rheological (DSR) tests and Bending Beam Rheological (BBR) tests were employed to evaluate the rheological behavior of each asphalt mortar. The corresponding reinforcing mechanism was subsequently analyzed by Environmental Scanning Electron Microscope (ESEM) test. The results show that basalt fiber can obviously enhance the high-temperature rheological properties of asphalt mortars, while strengthen the stress dissipating ability at low temperatures to some extent. Besides, the fiber type, fiber content and fiber length all impact the rheological properties of asphalt mortars. The asphalt mortars with type A basalt fiber present the superior rheological performance at both high and low temperature, with the optimum fiber content of 2% and fiber length of 9 mm, respectively. The test results of ESEM reveals that basalt fiber shows spatial distribution in asphalt mortar, presenting the function of stabilization and reinforcement.

Fine aggregate sizes effects on the creep behavior of asphalt mortar

Asphalt mortar consists of fine aggregates dispersed in an asphalt mastic (a matrix of asphalt binder and filler) and can have a significant influence on the high-temperature performance of asphalt mixtures. However, the fine aggregate sizes (FAS) governing the creep performance of asphalt mortar is not well understood. The effect of different FAS on the creep properties of asphalt mortar was investigated through experimental and numerical methods. A static compressive yield test and a dynamic triaxial creep test were performed on various asphalt mortar samples to determine their creep response under different conditions of temperature and stress level. It was found that the maximum strain in the asphalt mortar gradually reduces with an increase in FAS under the conditions of constant temperature – constant stress level, different temperature – constant stress level, and constant temperature – different stress level. Further, the modified Burgers model was proposed as a viscoelastic prediction model of asphalt mortar. A viscoelastic fitting analysis was carried out to validate the proposed model and the results indicated its adequacy for predicting the asphalt mortar’s creep response. At the end of the study, a grey relation entropy (GRE) analysis was done to quantify the degree of influence of the various FAS on the viscoelastic behavior of asphalt mortar. From the GRE analysis, FAS between 0.15 mm and 0.3 mm was found to be the most crucial. Below 0.15 mm FAS, asphalt mortar is mostly viscous. It begins to show elastic properties when the maximum FAS is between 0.15 mm and 0.3 mm, while above 0.3 mm and towards 2.36 mm the asphalt mortar increasingly becomes more elastic. The findings from this study can be useful to pavement engineers and other pertinent stakeholders seeking to optimize the aggregate gradation design of asphalt mixtures through the fine aggregate portion in order to enhance rutting resistance performance.

Investigation on high-temperature stability of recycled aggregate asphalt mixture based on microstructural characteristics

Construction and demolition wastes (CDW) are a complex mixture containing cement mortar and mineral aggregate. Recycled aggregate (RA) is a production of CDW after the crushing process. The presented study efforts mainly focus on the influence of RA content on the high-temperature stability of RAAM, but the analysis of the RA morphology effect is still lacking. Giving microstructural insight into the impacts of RA on the high-temperature failure of RAAM is beneficial in promoting the utilization of CDW in pavement engineering. In this paper, RAAM with different RA contents was firstly designed by the Marshall method, and the mechanical properties of RAAM at high temperatures were investigated using a uniaxial penetration test (UPT). Then, high-precision spatial models of RA particles were reconstructed based on CT images, and four indicators were introduced to quantify the RA macro shape and micro-morphology through spatial model data. Furthermore, the relationships between shear resistance of RAAM and RA morphology were established according to UPT test results and spatial model indicators. Finally, an X-ray CT saner was employed to track the evolution of microstructure damage before and after compressive deformation. Results show that the attached cement mortar is the primary resource of pores in RA particles, and pores volume and number in RA particles are random. Compared with natural aggregate, RA particle has more complicated morphological characteristics due to its porous cement mortar. The complex morphology and attached porous cement mortar of RA particles significantly affect the asphalt mixture high-temperature stability. Using RA particles causes more structural failures in RAAM during high-temperature deformation, and the damage inside cement mortar and interface with asphalt mortar are the primary resources of failure. This study shows that RA with content less than 50% can be an effective alternative for natural aggregate when considering the high-temperature stability of RAAM.

Optimization of Asphalt-Mortar-Aging-Resistance-Modifier Dosage Based on Second-Generation Non-Inferior Sorting Genetic Algorithm.

The use of steel slag powder instead of filler to prepare asphalt mortar was beneficial to realize the effective utilization of steel slag and improve the performance of asphalt concrete. Nevertheless, the anti-aging properties of steel-slag powder–asphalt mortar need to be further enhanced. This study used antioxidants and UV absorbers in steel-slag powder–asphalt mortar to simultaneously improve its thermal-oxidation and UV-aging properties. The dosage of modifier was optimized by second-generation non-inferior sorting genetic algorithm. Fourier-Transform Infrared Spectroscopy, a dynamic shear rheometer and the heavy-metal-ion-leaching test were used to evaluate the characteristic functional groups, rheological properties and heavy-metal-toxicity characteristics of the steel-slag-powder-modified asphalt mortar, respectively. The results showed that there was a significant correlation between the amount of modifier and G*, δ, and the softening point. When the first peak appeared for G*, δ, and the softening point, the corresponding dosages of x1 were 2.15%, 1.0%, and 1.1%, respectively, while the corresponding dosage of x2 were 0.25%, 0.76%, and 0.38%, respectively. The optimal value of the modifier dosage x1 was 1.2% and x2 was 0.5% after weighing by the NSGA-II algorithm. The asphalt had a certain physical solid-sealing effect on the release of heavy-metal ions in the steel-slag powder. In addition, the asphalt structure was changed under the synergistic effect of oxygen and ultraviolet rays. Therefore, the risk of leaching heavy-metal ions was increased with the inferior asphalt-coating performance on the steel-slag powder.

Evaluation of the High- and Low-Temperature Performance of Asphalt Mortar Based on the DMA Method

Asphalt mortar is a typical temperature-sensitive material that plays a crucial role in the performance of asphalt mixture. This study evaluates the high- and low-temperature performance of asphalt mortar based on the dynamic mechanical analysis (DMA) method. Temperature-sweep tests of asphalt mortars were conducted using the DMA method under fixed strain level, frequency, and heating rate conditions. The dynamic mechanical response curves, characteristic temperature, and other indices were obtained and used to investigate the high- and low-temperature performance of asphalt mortar. The results showed that the phase transition temperatures T1, T0, and Tg can be used to evaluate the low-temperature performance of asphalt mortar. Additionally, they had a good linear relationship, and the evaluation results were consistent. Meanwhile, T2, E60, and tan(δ)max indicators can effectively evaluate the high-temperature performance of asphalt mortar. Asphalt plays a key role in the performance of asphalt mortar. Mortars with neat asphalt A70 and modified asphalt AR had the worst and best high- and low-temperature performances, respectively. Furthermore, the finer gradation improved the low-temperature performance of asphalt mortar, while the coarser gradation improved the high-temperature properties of modified asphalt mortars but had the opposite effect on neat asphalt A70.