Strength Of Asphalt Mixture Research Articles

Study on the Influence of Asphalt Content on Fatigue Life of Asphalt Mixture

The fatigue failure form of asphalt pavement is not reflected in the design index of asphalt mixture proportion when determining the optimum asphalt content in the existing asphalt mixture proportion design. In order to solve the problem, the effect of different asphalt content on the fatigue life of three types of asphalt mixtures was studied by indirect tensile fatigue test.The results show that: (1) the splitting strength of asphalt mixture decreases with the increase of asphalt content; (2) the fatigue life of asphalt mixture increases first and then decreases with the increase of asphalt content; (3) the order of sensitivity of fatigue life of three types of asphalt mixture to asphalt content is: AC-5 > STRATA > ATB-25.Some useful suggestions are put forward for the design of asphalt mixture with good fatigue resistance.

Strength and durability of dry-processed stone matrix asphalt containing cement pre-coated scrap tire rubber particles

Abstract Application of rubber particle from the scrap tire through dry-process is a practical and economical efficient way to resolve the recycling problem and environmental concern of the disposed tires. However, the added rubber aggregate reduces both the strength and durability of the rubberized asphalt mixture. This study aims to improve the strength and durability of dry-processed asphalt mixture by using the cement (Portland Type Ⅰ) coating methods and gap-gradation system (Stone Matrix Asphalt (SMA)). The cement coating was applied to enhance the bonding performance between rubber aggregate and asphalt binder, and limits its expansion due to swelling in hot asphalt binder. The SMA mixtures were prepared with different sizes and proportions of mineral aggregates. The samples with conventional aggregate and untreated rubber aggregate both serve as control samples for the sample evaluation. Finally, tests on tensile strength, moisture susceptibility, rutting resistance, anti-stripping resistance, fatigue cracking resistance, and bonding between rubber particles and asphalt binder of SMA mixtures were conducted. The results showed that SMA mixture with pre-coated rubber aggregate owns similar performance comparing to the samples prepared with conventional aggregate and also has higher strength and better performance than that of the mixture with untreated rubber aggregate. Results also clearly indicated that the asphalt mixtures with 50% of No.16 mineral aggregates replaced by pre-coated rubber aggregates performed the best-satisfied performances; while, with a further increase in replaced size or proportion, the satisfied performances of SMA mixtures would be degenerated.

Experimental study on the effect of basalt and glass fibers on behavior of open-graded friction course asphalt modified with nano-silica

• The sample which has the largest permeability, had the minimum value of draindown. • The effect of glass fiber in reducing the permeability is far greater than that of the basalt. • The tensile strength of asphalt mixtures increases by adding fiber. • The effect of nano-silica in reducing abrasion and reduction of sensitivity to oxidation is considerable. Open-graded friction course (OGFC) is a mixture having gap graded aggregate which is used in pavement surfacing. Asphalt mixtures were modified by Nano silica, polymer, basalt fiber and glass fiber. A draindown test, Cantabro test, permeability test and an indirect tensile strength test and moisture susceptibility were used to evaluate the performance of OGFC mixtures. Test results revealed optimum compounds for 0.2% basalt fiber with 2% nano-silica and 4.5% Styrene-Butadiene Styrene (SBS) Polymer. The minimum air voids content of fiber-reinforced OGFC mixtures modified with nanomaterial should be 13% for 6% bitumen. The results showed the effect of nano-silica in reducing abrasion and reduction of sensitivity to oxidation is considerable and the effect of basalt fiber per 0.2% in the asphalt mixture to be greater than that of glass fiber in reducing the draindown phenomenon; and for controlling the level of draindown phenomenon, nano-silica compound should also be used with basalt fiber. It was also found that although the use of basalt fiber is more effective in decreasing draindown in comparison with glass fiber, the effect of glass fiber in reducing the permeability of the asphalt mixture is far greater than basalt fiber.

Fatigue equation for asphalt mixture under low temperature and low loading frequency conditions

Abstract In order to reveal the thermal fatigue behavior of asphalt mixtures under low temperature conditions, the four-point bending beam tests of strength and fatigue were carried out. The asphalt mixtures are typical viscoelastic materials whose fatigue properties are significantly influenced by low loading frequency. Thus, the fatigue tests under low loading frequency were used to simulate the thermal fatigue of asphalt mixtures. Based on the nominal stress ratio (not considering the effect of loading rate on the strength value) and the real stress ratio (the strength value corresponding to the loading rate of fatigue test), the fatigue equations of asphalt mixtures under low temperature and low frequency conditions were established. The flexural strengths of the four-point bending beam tests at different loading rates at 0 °C, −10 °C and −20 °C were studied. The results show that the flexural strength of asphalt mixtures expresses a power function on the pattern of variation with the loading rates. The intersection of fatigue curve characterized by the nominal stress ratio and the abscissa axis is much larger than 1. The fatigue curve based on the nominal stress ratio cannot be extended to fatigue failure point (1,1). But the fatigue curve characterized by the real stress ratio can be extended to the strength failure point, whose fatigue life is 1. So, the behavior of strength failure and fatigue failure was integrated. The uniform characterization model of fatigue equations for asphalt mixture under low temperature and low loading frequency conditions was realized, which means that the fatigue equations and curves under different loading frequencies could be characterized by one equation and one curve. The results can provide a theoretical basis for predicting the thermal fatigue performance of asphalt mixtures under low temperature conditions more accurately.

Unified Strength Model of Asphalt Mixture under Various Loading Modes.

Although the rutting resistance, fatigue cracking, and the resistance to water and frost are important for the asphalt pavement, the strength of asphalt mixture is also an important factor for the asphalt mixture design. The strength of asphalt mixture is directly associated with the overall performance of asphalt mixture. As a top layer material of asphalt pavement, the strength of asphalt mixture plays an indispensable role in the top structural bearing layer. In the present design system, the strength of asphalt pavement is usually achieved via the laboratory tests. The stress states are usually different for the different laboratory approaches. Even at the same stress level, the laboratory strengths of asphalt mixture obtained are significantly different, which leads to misunderstanding of the asphalt mixtures used in asphalt pavement structure design. The arbitrariness of strength determinations affects the effectiveness of the asphalt pavement structure design in civil engineering. Therefore, in order to overcome the design deviation caused by the randomness of the laboratory strength of asphalt mixtures, in this study, the direct tension, indirect tension, and unconfined compression tests were implemented on the specimens under different loading rates. The strength model of asphalt mixture under different loading modes was established. The relationship between the strength ratio and loading rate of direct tension, indirect tension, and unconfined compression tests was adopted separately. Then, one unified strength model of asphalt mixture with different loading modes was established. The preliminary results show that the proposed unified strength model could be applied to improve the accurate degree of laboratory strength. The effectiveness of laboratory-based asphalt pavement structure design can therefore be promoted.

Performance evaluation of fatigue resistance of asphalt mixtures modified by SBR/PP polymer blends and SBS

Abstract Using durable asphalt mixtures to increase the quality of pavement, improving the safety and comfort of drivers and reduce pavement damage and maintenance cost is inevitable. Major damage to asphalt pavement is fatigue, which happens due to everyday increase in traffic and the passing load. One way to improve the quality, strength and fatigue resistance of asphalt mixtures is to use high quality or modified, asphalt binder. This study aimed to use a polymer blend (a combination of two polymers) made of efficient and inexpensive polymers to modify the properties of asphalt binder and asphalt mixtures against fatigue. For this purpose, SBR and PP polymers with ratios of 70/30, 50/50 and 30/70, at 3, 4 and 5 wt% of asphalt binder were used, and the fatigue performance of asphalt mixtures containing these polymer blends was compared with that of asphalt mixtures containing 4% and 5% SBS polymer. Nanoclay CLOSITE 15A was used at 1.5 wt% of asphalt binder to increase the stability of polymers in asphalt binder. The results of bending beam fatigue, indirect tensile fatigue, indirect tensile strength, and resilient modulus tests performed on asphalt specimens showed that the use of polymer blends improves the fatigue performance of asphalt mixtures so that in samples containing 5% of polymer blends containing 50% and 70% SBR, fatigue life is increased by more than 50% compared to that of 5% SBS samples. Accordingly, it can be said that polymer blends can be used as an efficient and economical additive in asphalt mixtures.

Performance deterioration mechanism and improvement techniques of asphalt mixture in salty and humid environment

To prolong the service life of asphalt pavement in coastal areas, firstly, the continuous immersion, dry-wet cycle and freeze-thaw cycle in 0% (pure water), 5% and 10% NaCl solution were selected to speed up the corrosion of salty and humid environment on asphalt mixture. The changing law of mechanical property of asphalt mixture was studied by splitting test. Then the deterioration of microstructure and road performance of asphalt mixture in salty and humid environment was tested by laboratory tests. Finally, the effects of additives such as anti-stripping agent, fiber and hydrated lime on water stability and mechanical property of asphalt mixture were studied. The test results show that the splitting strength of asphalt mixture gradually decreases with the increase of action number after treated by different ways. The method of dry-wet cycle reflects the adverse effect of salty and humid environment on the performance of asphalt mixture better. Dry-wet cycle in 10% NaCl solution for twelve times is recommended to simulate the corrosion effect of salty and humid environment. After treated by dry-wet cycle in 10% NaCl solution, the high temperature performance, low temperature crack resistance and water stability of asphalt mixture all decrease by various degrees. Especially the water stability declines seriously, which residual stability and freeze-thaw splitting strength ratio cannot meet the requirement of specification. The void ratio of asphalt mixture increases first and then stabilizes with the increase of dry-wet cycles. The chloride crystal precipitates and continues to expand in the mixture, which eventually leads to the performance deterioration of asphalt mixture. Among different additives, basalt fiber achieves best effect in combating the deterioration of asphalt mixture in salty and humid environment.

Study on the feasibility of desulfurized-high-calcium-fly-ash (DHCFA) used in asphalt mixture as mineral powder

Harmless treatment and resource utilization of wastes like fly ash have always been a social difficulty and a research hot spot in the field of pavement. In this paper, samples of fly ash generated from a coal-fired power plant in Yan’an City, Shaanxi Province were collected; and a desulfurized-high-calcium-fly-ash (DHCFA) was selected as the representative to be used for the alternative of traditional limestone fine powder (LFP) in asphalt mixture. Specifically, the chemical and physical characteristics of DHCFA and LFP were studied and compared firstly. Then the performance of asphalt mortar and asphalt mixture containing different amounts of DHCFA were further investigated. XRF and XRD results show that DHCFA and LFP both have significant alkalinity, and DHCFA has relatively richer chemical composition and phase distribution. TG-DSC results show DHCFA and LFP both satisfy the construction requirements on thermal stability. Asphalt mortar results showed DHCFA had the similar effect as LFP (control sample) on the whole. Asphalt mixture results revealed that the characteristics of DHCFA such as density, composition and compaction influence the performance of asphalt mixture. DHCFA could improve the low temperature performance and water stability of asphalt mixture, while reducing the high temperature performance and strength. Above results indicates that DHCFA could be used for mineral powder in asphalt mixture, however, its dosage should be carefully verified since it has adverse impact on the high temperature performance and strength of asphalt mixture.

Comparing the Effect of Nanomaterial and Traditional Fillers on the Asphalt Mixture Properties

Several parameters affect asphalt mix performance against loading and environmental conditions. Minor changes in the filler amount or type can cause obvious changes in the asphalt mixture properties. Accordingly, in this research attempts have been made to optimally make asphalt mixture strong against loading and environmental conditions by changing the type, size and percentage of filler used in asphalt mixture. In this line, the effect of two types of cement and nano-silica fillers in two different percentages was investigated and compared as an alternative for part of the main filler in asphalt mixture samples made by two types of limestone and granite aggregate. Cement filler by 2% and 4% of the aggregate mass as the alternative for part of the main filler is added to stone materials before mixing with binder, but nano-silica filler by 2% and4 % of weight of the binder as the alternative for part of the main filler is added to binder and a modified and homogeneous binder is produced using a high speed mixer. In the following, considering the optimum binder content for each mixture, resilient modulus tests were conducted to determine the strength performance against loading and indirect tensile strength ratio was used to determine moisture sensitivity of asphalt mixtures. Results obtained from resilient modulus tests show that the use of nano-silica and cement has been capable of favorably improving the resilient modulus of samples containing these two types of fillers. The improvement of the resilient modulus of samples containing nano-silica is very significant. Additionally, the studies conducted based on the indirect tensile strength ratio show that both types of alternative fillers, especially cement has been capable of desirably improve the strength of asphalt mixtures against moisture damage.

Mechanical and compaction properties of graphite nanoplatelet-modified asphalt binders and mixtures

This paper presents an experimental investigation of the properties of asphalt binders and mixtures modified with graphite nanoplatelets (GNPs). The focus is on studying the effects of GNP addition on low-temperature rheological and fracture properties of asphalt binders and mixtures and on compaction effort of asphalt mixtures. This is the first time that these effects are investigated and significant findings are reported. The study considers three types of GNP materials, including graphite nanoplatelets and sub-microscale graphite flakes. The cost of these materials is reasonably low, which makes them suitable for large-scale applications, unlike other types of graphite and graphene materials. The experimental results indicate that the addition of GNPs leads to considerable improvements of low-temperature strength and fracture properties of asphalt binders and mixtures. While the properties of asphalt binders at intermediate temperatures are minimally affected, for some combinations of binders and GNPs the increase in low-temperature strength is over 100%. A similar effect is observed for some of the asphalt mixtures investigated, in which the low-temperature fracture energy almost doubles. The laboratory compaction experiments show that the number of gyrations required for achieving a target density can be reduced by as much as 20–40% by adding a small percentage of GNPs into asphalt binders. The results of this experimental study indicate that GNP-modified asphalt binders and mixtures have significant potential for increasing the durability of asphalt pavements in cold regions, by reducing the compaction effort and improving the low-temperature strength and fracture properties of asphalt materials.

Three-Dimensional Simulation of Aggregate and Asphalt Mixture Using Parameterized Shape and Size Gradation

Aggregate occupies at least three-quarters of the volume of asphalt mixture and can significantly affect the performance of pavement. The geometrical morphology influences the slippage and interlock among aggregates for resisting and distributing applied loads. In recent years, the discrete-element method (DEM) has been employed for simulation of asphalt mixture structure. This paper introduces an approach for simulation of aggregate and asphalt mixtures using parameterized shape and size gradation. Both the plane geometry factor (PGF) and the section aspect ratio (SAR) were employed to describe the three-dimensional (3D) geometric characteristics of aggregates. A numerical technique of aggregate models was implemented with probabilistic parameters depending on statistical results of PGFs and SARs. The 3D numerical model of asphalt mixtures was assembled with three different components, and was validated by uniaxial compression tests via comparison with the laboratory result. It was found that the PGF and SAR are appropriate to describe the three-dimensional features of aggregate shapes, because a simplified space object can be described by a two-dimensional (2D) graphical projection and a vector scalar corresponding to the space vector. Probability distribution curves of PGFs and SARs between coarse aggregates were in concordance with the Gauss-type function, because their correlation coefficients were all greater than 95%. It was verified that the developed clumping algorithm of aggregates was reasonable in terms of the shape and size gradation. Based on the parallel-bond model and Burger's model, the results of virtual tests were in good agreement with those of laboratory uniaxial tests. The angularity (PGF) of aggregates has a beneficial effect on the strength and stability of asphalt mixtures, whereas the flat-elongated feature (SAR) has a negative effect on the strength and stability of asphalt mixtures.

Using Lightweight Materials to Enhance Thermal Resistance of Asphalt Mixture for Cooling Asphalt Pavement

This study aims to enhance the thermal resistance of asphalt mixture to cool asphalt pavement. Four kinds of asphalt mixtures were prepared by replacing basalt aggregate and limestone mineral powder with shale ceramsite (SC) and fly ash cenosphere (FAC), respectively. A series of experiments, including environment scanning electron microscope test, thermophysical parameter test, indoor irradiation test, shear strength test, and rutting test, were performed to verify the purpose of this study. The results show that using low‐density SC and FAC could produce lightweight asphalt mixtures, which had lower thermal conductivity than control asphalt mixture. The indoor irradiation test shows that the resultant asphalt mixtures had lower temperatures at the depth of lower than 4 cm. The addition of SC had a negative effect on the shear strength and dynamic stability of asphalt mixture. However, the two indicators increased due to the addition of FAC. The results presented in this study indicate that it is feasible to use lightweight aggregate to prepare low‐thermal‐conductivity asphalt mixture and use this kind of asphalt mixture to cool asphalt pavement.

Evaluation of performance and moisture sensitivity of glass-containing warm mix asphalt modified with zycothermTM as an anti-stripping additive

The rising repair and maintenance costs of road and airstrip pavements subjected to frequent and repeated traffic loading is a major impetus for researches to delve into the use of additives and admixtures in the asphalt mixture production. The primary goal of these efforts is to improve the durability and load-bearing performance of asphalt mixtures. Due to favorable properties, such as high stiffness, all-around fracture, and high internal friction angle, crushed glass may be used as a high-potential additive for improving asphalt mixtures’ quality. Despite the many advantages of crushed glass, the inadequate adhesion between bitumen and glass particles can lead to stripping and reduced strength of glass-containing asphalt mixtures (glass-asphalt). In this study, glass particles were used, as aggregates in warm mix asphalt (WMA) mixtures. Four different amounts of zycothermTM were used in WMA mixtures to serve as bitumen modifier and anti-stripping agent. The performance properties of the pure bitumen and the zycothermTM-modified bitumen were evaluated through Scanning Electron Microscopy (SEM), Fourier Transform Infrared spectroscopy and bitumen tests. The WMA specimens and control specimens were also subjected to the modified Lottman test, resilient modulus test, and creep test. The results showed that use of zycothermTM as an anti-stripping agent considerably improves the performance properties and moisture sensitivity of glass-asphalt.

Healing process in Mineral asphalt mixtures

The article presents an issue related to the phenomenon of regeneration occurring in mineral-asphalt mixtures. The introduction of the work discusses the problem of decreasing strength and fatigue life of asphalt mixtures expressed by changing the stiffness modulus. Attention is paid to the complexity of this phenomenon, which is associated with microstructural changes. The review of the state of knowledge discusses a phenomenon called "healing" referring directly to the regeneration of mineral-asphalt mixtures. Later on, based on fatigue tests of the four-point bending beam in the controlled deformation mode, this phenomenon was analyzed. Rest periods between load and heating of samples regenerating the tested mixture are taken into account. Based on the analysis of the test results, it was found that the heating process is a more effective factor leading to a greater regeneration gain not only the stiffness of the sample, but also its lifespan expressed in cycles compared to the rest period. At the end of the work, hysteresis changes were shown to analyze energy changes and the essence of regenerative processes in the context of extending the life of mineral asphalt mixes used in the pavement construction layers.

Investigate the effect of using polymeric anti-stripping additives on moisture damage of hot mix asphalt

Moisture damage in asphalt mixtures can be defined as the loss of durability and strength caused by the effect of moisture. In order to improve the strength of asphalt mixtures against this damage, anti-stripping additives are used to increase the aggregate-asphalt binder adhesion and cohesion. In this study, the influence of Polybutylene on the moisture susceptibility of asphalt mixtures is investigated. To evaluate the effects of anti-stripping additives on the specimens made with granite and limestone aggregates, the indirect tensile strength ratio test and the theoretical concepts of surface free energy have been used. The results of the mechanical tests indicated that the PB additive has increased the strength of the asphalt mixtures against moisture damage. The results of the SFE method also indicated that Polybutylene additive improved the adhesion between asphalt binders and acidic aggregates which were susceptible to moisture damage. Also, using Polybutylene increased the cohesion free energy, which increased the asphalt binder film strength against cohesion failure. Moreover, the calculations based on thermodynamic concepts indicated that the asphalt binder modification has reduced the debonding energy, which also represented the reduced tendency of the system to stripping.

Laboratory and field evaluation of sodium stearate organically modified LDHs effect on the anti aging performance of asphalt mixtures

To improve the compatibility of layered double hydroxides (LDHs) with asphalt binders, the sodium stearate was used to organically modify the LDHs (SS-LDHs). In order to investigate the improvement effects of LDHs and SS-LDHs on the aging resistance of asphalt mixtures in laboratory and field, two kinds of aging simulating tests were conducted in laboratory and a test road was paved with LDHs and SS-LDHs modified asphalt mixtures, respectively. The chemical structure and viscosity of asphalt binders reclaimed from asphalt mixtures were tested by Fourier transform infrared spectroscopy and Brookfield viscometer respectively to investigate the LDHs and SS-LDHs effects on the anti aging properties of asphalt mixtures. Finally, the semi-circular bending test was conducted by universal testing machine to test the blending strength and fatigue life of asphalt mixture before and after aging. The results show that, at the same aging condition, the carbonyl index and viscosity aging index of reclaimed asphalt binders with LDHs or SS-LDHs are lower than that of reclaimed asphalt binders without LDHs and SS-LDHs, while the styrene-butadienestyrene index is higher, the increment of semi-circle flexural strength and the reduction of fatigue life is less than that of asphalt mixtures without LDHs and SS-LDHs, which indicates that LDHs and SS-LDHs can improve the anti thermo-oxidative aging and anti UV aging performance of the asphalt mixture. In comparison, the improvement effect of SS-LDHs on the anti aging performance of asphalt mixture is much better than that of LDHs.

Micromechanical Analysis of Asphalt-Mixture Shear Strength Using the Three-Dimensional Discrete Element Method

AbstractThis study investigated the shear strength of asphalt mixtures and its influence factors by using a three-dimensional (3D) discrete-element method (DEM). The uniaxial penetration test, a sh...

The prediction of adhesive failure between aggregates and asphalt mastic based on aggregate features

The interface stripping between aggregates and asphalt mastic deteriorates the strength of asphalt mixture, causing disease such as cracks and pits of asphalt pavement. This paper aim to quantify the effect of aggregate on interface, and develop a method to predict the adhesive failure. At first, microstructural models of aggregate particles were reconstructed based on computed tomography (CT) images, then aggregate features and energy consumption of interface during fracture were determined by digital image processing and numerical simulation respectively; dissipation damage energy (DDE) quantified the adhesive failure, and an effective method was established by artificial neural network based on back-propagation (ANN-BP) to present the relationship between DDE and aggregate features. Results show that the influence of aggregate on interface damage can be evaluated by multiple parameters of aggregate features; ANN-BP is an effective tool to synthesize the coupling influences of different aggregate features and determine a prediction model; ANN-BP model presents a prediction for adhesive failure according to the states of aggregates, the prediction results are acceptable to show the damage of asphalt mixture.

Shear-Property-Based Design Approach of Asphalt Mixture in Long and Steep Sections—Taking Togo No. 1 Highway as a Case

Abstract The asphalt pavement in long and steep slope sections is more prone to serious rutting distress than that in common slope sections. Therefore, it should be designed with more consideration of anti-rutting property. Since anti-rutting property of hot-mixed asphalt mixture (HMA) is closely related to its shear property, the objective of this study was, relying on the No. 1 Highway reconstructive project in Togo, to propose a design approach to asphalt mixture in long and steep slope sections based on shear property. In this article, a rutting prediction model developed by Tongji University was used to quantify the critical shear strength of asphalt mixture. First, this model was calibrated using field survey data of the existing road, making the model suitable for the Togo No. 1 Highway reconstructive project. Then, the critical shear strength of asphalt mixture was given according to the allowable rutting depth and the calibrated model. Last, four asphalt mixtures with different gradations of AC13-1, AC13-2, Sup13-1, and Sup13-2 were designed using local raw materials, the shear property of which was determined with the uniaxial penetration test (UPT) and the Wheel Track Test. Finally, Sup13-2 was chosen as the optimum gradation for the No.1 Highway reconstructive project with respect to shear property, and its other engineering properties were determined. The concluded design procedure of shear-property-based design approach was given at the end of this article.

Failure criterion of an asphalt mixture under three-dimensional stress state

A self-developed triaxial test method was adopted to characterize mechanical behavior of the asphalt mixture under three-dimensional stress states in this study. The conventional uniaxial tests and triaxial tests were conducted in the laboratory to verify the triaxial test results obtained using the technique developed. It is shown that the three dimensional stress states affect significantly the ultimate failure strength of AC-13 asphalt mixture and the failure modes are mainly represented both for the tensile failure and shear failure. The nonlinear strength criterions, as well as a linear engineering model of asphalt mixture under three-dimensional stress states in σoct-τoct space, were established based on the triaxial compressive/tensile tests, the plane tensile and compressive/axial tensile tests. In addition, a new method to carry out the strength design of asphalt pavement under the three-dimensional stress state was given to consider the failure effect of each stress component to the asphalt pavements.