Asphalt Stabilization Research Articles

Green environmental protection and sustainable utilization of straw: Investigation for molecular dynamics of highland barley straw fiber to enhancing road performance of asphalt

This study explores the impact of highland barley straw (HBS) fiber, an environmentally friendly material, on the molecular dynamics and performance of asphalt. Despite the widespread use of fibers in enhancing asphalt performance, molecular-scale investigations are lacking. In this study, molecular dynamics software was employed to model matrix asphalt and three types of HBS fiber-modified asphalt with varying cellulose contents (8.62 wt%, 15.88 wt%, 22.06 wt%). Thermodynamic parameters mean squared displacements (MSD), radial distribution function (RDF), free volume fraction (FFV), and mechanical parameters were analyzed through simulation to understand the diffusion behavior of HBS cellulose molecules in asphalt and study the modification mechanism. The findings revealed that the 8.62 wt% cellulose-modified asphalt had the slowest diffusion rate, with the most favorable temperature for asphalt diffusion being 298.15 K. Integration of HBS cellulose molecules facilitated the self-aggregation process of asphaltene-asphaltene and improved the compatibility between asphaltene-resin, resulting in asphalt stabilization. However, the study found that moisture damage weakened the water resistance of HBS cellulose-modified asphalt binder. Specifically, modifying asphalt with 8.62 wt% cellulose increased the Young modulus by 28.37%, bulk modulus by 39.77%, and shear modulus by 26.45%, demonstrating the overall improvement achieved with the combined effect of 8.62 wt% HBS cellulose-modified asphalt. These findings have significant implications for repurposing HBS as a solid waste material and enhancing the low-temperature crack resistance of asphalt binders.

Effect of Emulsified Asphalt on Expansive Soil Strength and Swelling

Some clay soils classified as extended soils threaten the structures resting on them. Many additives are available to improve the properties of expanded soils. This study tries to investigate the consequences of wetting-drying cycles on the swelling behavior of modified expansive clayey soils under laboratory conditions by modifying expansive clayey soil samples using emulsified asphalt. Five different percentages of emulsified asphalt were used: (2, 4, 6, 8, and 10) %. The natural and treatment soils were tested for classification, specific gravity, compaction characteristics, free swell and swell pressure, consolidation, and compressive strength. The liquid limit and plasticity index have been lowered by adding Emulsified Asphalt. After that, the effects of Emulsified Asphalt on undrained shear strength characteristics (cohesion and friction angle) have been studied. The results revealed that when the emulsified asphalt content was increased to 10%, the swelling pressure and swelling potential decreased by 58 and 78 %, respectively. The swell and shrink improvement factor for the 10% emulsified asphalt addition is always larger than 75%. As the duration of wetting-drying cycles increased, the swelling pressure and swelling potential values were also reduced. The plastic limit, on the other hand, increased as the Emulsified Asphalt content increased. Increasing the amount of Emulsified Asphalt increased the maximum dry unit weight values, whereas the optimum water contents increased. It was concluded that emulsified asphalt stabilization may be useful for expansive clay as it improves compressive shear strength.

Evaluating the Potential Environmental Benefits of Cold Recycling-Based Methods for Flexible Pavement Rehabilitation in Virginia

This paper describes a study conducted to quantify the potential environmental benefits of recycled asphalt pavement projects completed in Virginia. Three restorative maintenance projects were evaluated: (i) a 5-in. hot-mix asphalt (HMA) over 5-in. cold in-place recycling (CIR) with foamed asphalt stabilization; (ii) a 3.5-in. HMA over 5-in. CIR with emulsion stabilization; and (iii) one non-recycling structural overlay (5-in. HMA over an existing pavement). In addition, the following reconstruction projects—the first three constructed on primary roads and the last two constructed on interstates—were assessed: (i) a 2.5-in. HMA over 9.6-in. full depth reclamation (FDR) with asphalt stabilization; (ii) a 3.5-in. HMA over 9.0-in. cement stabilized FDR; (iii) a non-recycling reconstruction project (7-in. HMA over 12-in. aggregate base and subbase); (iv) a 6-in. HMA over 6-in. asphalt-stabilized cold central plant recycled layer over a 12-in. lime-stabilized FDR base; and (v) a non-recycling reconstruction project (8-in. HMA over 18-in. aggregate base and subbase). When considering exclusively cradle-to-laid system boundaries, the results show that pavement recycling projects used for interstate reconstruction and primary route restorative maintenance yielded lower global warming (GW) than non-recycling approaches. When considering the entire life cycle, the study found that approximately 98% of the total GW came from pavement–vehicle interaction that takes place during the use stage. Finally, to reduce GW, the Virginia Department of Transportation could encourage (or even incentivize) practices that improve the initial pavement smoothness for recycling projects and use structural designs that are expected to have a low annual deterioration rate.

Development of an Improved Test Setup for Measuring the Resilient Modulus of Stabilized Pavement Materials

In a recent study to develop mechanistic empirical relationships for full depth reclamation (FDR) in California, it was determined that the commonly used triaxial testing setup detailed in American Association of State Highway and Transportation Officials (AASHTO) T 307 was not suitable for testing stabilized materials. This paper investigates different testing setups, based on a comprehensive literature review, to determine an appropriate approach for measuring strains on both laboratory-compacted and field-cored specimens. Five different test setups were evaluated, ranging from measurements on the top cap of the triaxial cell, to third-point measurements on the specimen. This study also investigated methods of mounting transducer gauge points on the specimen in a repeatable and accurate manner, and for preparing the specimen ends to mitigate point loads. Two field cores, one sampled from an FDR project with cement stabilization (FDR-PC) and the other from an FDR project with foamed asphalt stabilization (FDR-FA), were subjected to unconfined, low stress cyclic triaxial testing using different deviatoric and seating stresses using each of the five test setups. The effects of non-linear strain distribution on the cyclic stress strain curves were compared. Based on these results, the recommended test setup for determining the resilient modulus of the stabilized material is the third point on-specimen setup for measuring strain. This approach was minimally influenced by the non-linear strain distribution, and provided resilient moduli that closely correlated with stiffnesses back calculated from the falling weight deflectometer deflections measured close to the core locations.

Assessing the Structural Properties of Asphalt Stabilized Subgrade Soil

Studies on the structural properties of asphalt stabilized soil are scares and scattered. In this work, the impact of asphalt stabilization on the deformation under repeated loading, compressive and tensile strength, rutting resistance, and resilient modulus were investigated. The subgrade soil usually used for roadway embankment construction was stabilized with optimum cutback asphalt and with additional 1% of asphalt above and below the optimum. Cylindrical Specimens of 100 mm diameter and 200 mm in height have been constructed and subjected to repeated compressive stress under controlled conditions at 20 ° C using the pneumatic repeated load System (PRLS). The resilient modulus, and plastic parameters were detected. The Wheel tracking test was implemented on asphalt stabilized soil specimens of 150 mm diameter and 50 mm thickness to detect the rutting resistance, while the repeated punching shear test was implemented on asphalt stabilized soil specimens of 150 mm diameter and 120 mm height to detect the resistance to permanent strain accumulation and resilient modulus under the test condition. It was concluded that the Compressive Strength increased up to the optimum Asphalt content of 6%, then decreased, while the Indirect tensile Strength (ITS) decreased up to optimum Asphalt content 6% then increased. The addition of Cut- Back Asphalt decreases the strain (% ϵ) of asphalt stabilized Soil by (65%) at 7% Asphalt content, while it increases the Resilient Modules (Mr) of stabilized Soil by (300%) at 7% Asphalt content. The resilient modulus varies with testing technique and condition.

Performance of Soil Embankment Model under Static and Cyclic Loading

The sandy soil with high gypsum content, (usually referred to as gypseous soil), possesses a type of cohesive forces when mixed with optimum amount of water and then compacted, but losses its strength when flooded with water again. The gypseous soil obtained from Al-Fallujah was subjected to laboratory investigation. The physical and chemical properties and then optimum liquid asphalt (emulsion) requirement were determined. A laboratory soil embankment-model of 50x50x30 cm was implemented to study the impact of absorption by capillary rise on the stability of embankment. Load repetitions test was carried out on four gypseous soil models, two of them were pure soil at dry and absorbed conditions, and the other two were stabilized with emulsion at dry and absorbed condition. Another set of four gypseous soil models of the same condition were tested under static load. The impact of changing the hydraulic conductivity of soil due to asphalt stabilization was investigated and the vertical deformation was determined using LVDT. For the pure soil in dry condition the vertical deformation was 7.45 mm at 157 load repetitions, while for pure soil model under absorbed condition, the vertical deformation was 12.5 mm at 29 load cycles. The stabilized soil at dry condition exhibits vertical deformation of 9.75 mm at 911 load cycles, and shows 10.47 mm deformation at 897 load cycles under absorption. When tested under static load, the ultimate sustained pressure was 0.8 MPa with vertical settlement 0.03 mm for pure soil at dry condition, and reduced to 0.3 MPa with vertical settlement 12 mm at absorbed condition.

Impact of Asphalt Stabilization on Deformation Behavior of Reinforced Soil Embankment Model under Cyclic Loading

Gypseous soil, which covers vast area in west, middle, east and south west regions of Iraq exhibit acceptable strength properties when dry, but it is weak and collapsible when it comes in touch with moisture from rain or other sources. When such weak soil is adopted for earth reinforced embankment construction, it may exhibit hazardous situation. Gypseous soil was in- vestigated for the optimum liquid asphalt requirements of both cutback and emulsion using the one-dimensional unconfined compression strength test. The optimum fluid content was 13% (7% of cutback with 6% water content), and 17% (9% of emulsion with 8% water content). A laboratory model box of 50x50x25 cm was used as a representative of embankment; soil or asphalt stabilized soil have been compacted in five layers at maximum dry density (modified compaction) and an aluminum reinforcement strips were introduced between layers and connected to the facing strips. The model was subjected to cyclic loading and the lateral deformation of facing strips and the vertical deformation were detected at different stages of loading cycles and different height of the facing strips using LVDT. The reference embankment model was that of reinforced pure soil under absorbed condition. For asphalt-stabilized soil, the cutback asphalt stabilized- soil model exhibit improvement in load carrying capacity by nine folds. It shows a reduction of 23% in vertical displacement under sustained load of 436 repetitions. For emulsion-stabilized soil, the reduction in vertical displacement was 38.5% under a sustained load of 950 cycles. The load carrying capacity was improved by twenty folds. The lateral displacement at the upper first and third layers were lower by 0.55% and 1.9% respectively when compared to cutback asphalt stabilized model.

Ten-Year Performance of Full-Depth Reclamation with Expanded Asphalt Stabilization on Trans-Canada Highway, Ontario, Canada

In 2001, the Ministry of Transportation Ontario, Canada, constructed its first stabilization project involving full-depth reclamation with expanded (foamed) asphalt on the Trans-Canada Highway, south of Wawa, Ontario. The project involved three mix designs, two with corrective aggregate and one without corrective aggregate. A control section of full-depth reclamation with the same thickness of hot-mix overlay (without expanded asphalt stabilization) was placed in the middle of the project. The project has been monitored annually for the past 10 years. Analysis of roughness data and pavement distress data indicated a significant difference between the test sections with expanded asphalt stabilized base and the control section. The expanded asphalt stabilization has delivered superior performance compared with the conventional full-depth reclamation with hot-mix overlay. Performance curves for the treatments on this project were compared with the ministry's average performance curve for full-depth reclamation (reconstruction) projects and with the performance of treatments on two adjacent projects. This project demonstrated the exceptional performance of the expanded asphalt mixes through 10 years of proven superior pavement condition and ride.

The effects of asphalt binder and granular material characteristics on foamed asphalt mix strength

This paper systematically studies the effects of asphalt foam characteristics and pulverized asphalt pavement (PAP) material attributes on foamed asphalt mix strength. A fracture face image analysis procedure was employed to quantify asphalt dispersion, which was key to establishing the relationships between material microstructural features and measured strengths. Foamability of asphalts was found to be one of the primary factors determining foamed asphalt mix quality. Foams with higher expansion ratios and longer half-life have better dispersion through granular materials, resulting in greater strength improvement. High fines contents in the PAP materials negatively affect mix strength by producing a continuous and weak unbonded mineral filler phase. The microstructural analysis found that typically unquantified physical, chemical and/or mineralogical characteristics of the PAP materials significantly affect asphalt dispersion quality and mastic strength. Therefore, the suitability of PAP materials and available binders for foamed asphalt stabilization should be evaluated for each individual project.

Performance of fiber reinforced asphalt concrete under environmental temperature and water effects

This paper studies the reinforcing effects and mechanisms of fibers for asphalt concrete (AC) mixtures under the environment temperature and water effects. Four typical fiber types – polyester, polyacrylonitrile, lignin and asbestos – are studied. Laboratory tests were conduct on the fiber reinforced AC (FRAC) to measure its strength, strain and fatigue behavior. Results show that fibers have significantly improved AC’s rutting resistance, fatigue life, and toughness. The flexural strength and ultimate flexural strain, and the split indirect tensile strength (SITS) at low temperature have also improved. The polymer fibers (polyester and polyacrylonitrile) have improved rutting resistance, fatigue life, and SITS more significantly than lignin and asbestos fibers, which may be primarily due to their greater networking function; while lignin and asbestos fibers result in greater flexural strength and ultimate flexural strain, which may be primarily due to their greater asphalt stabilization effect. However, fiber’s effect under the water freezing–thaw effect does not seem promising, and the SITS of FRAC with lignin and asbestos fibers even reduces to some extent under this effect. It is also found that a fiber content of 0.35% by mass of mixture achieves the optimum performance outputs of rutting resistance and SITS for polyester fiber.

Effects of Palm Kernel Shells in Lateritic Soil for Asphalt Stabilization

Effects of Palm Kernel Shells in Lateritic Soil for Asphalt Stabilization

Understanding Internal Structure Characteristics of Foamed Asphalt Mixes with Fracture Face Image Analyses

The rate of use of full-depth reclamation with foamed asphalt to rehabilitate cracked pavements is increasing worldwide. However, the state-of-the-art understanding of foamed asphalt mixes and the state-of-the-practice engineering application are largely empirical because of the lack of in-depth knowledge of this material's internal structure characteristics. A fracture face image analysis framework for quantification of the asphalt mastic phase distribution in foamed asphalt mixes, which is a key microscopic structure characteristic, is described. Fracture face asphalt coverage is a quantitative indicator of asphalt spot distribution on fractured faces and is primarily a function of the asphalt dispersion in the mix, the relative strengths of the asphalt mastic and mineral filler phases, and the boundary conditions of specimen compaction and testing. Fracture face image analyses combined with laboratory testing results are presented. It was found that (a) the strength of the asphalt mastic phase is much less susceptible to moisture conditioning than the strength of the mineral filler phase, (b) filler contents that are too low or too high both negatively influence the effectiveness of asphalt stabilization, and (c) the image analyses show that the impact of asphalt grade on the asphalt distribution in the mix dominates the effectiveness of asphalt stabilization but not the strength of the asphalt cement itself. Additionally, engineers can perform a qualitative fracture face asphalt distribution check at the project level of mix design to diagnose mix problems, for which an interim guideline is proposed.

Early-Life Performance of Cold-in-Place Pavement Recycling with Foamed Asphalt Technique

The cold-in-place recycling technique with foamed asphalt stabilization was used to rehabilitate a severely damaged, heavily trafficked highway, part of the Trans European Network. Lack of experience, at least as far as the performance of the aforementioned technique for heavy-duty pavements was concerned, was the main reason for the Greek Ministry of Public Works to undertake a field experiment incorporating semirigid and flexible pavements. To achieve this goal, a comprehensive monitoring and data analysis research study was performed; it concentrated on the falling weight deflectometer as a major tool for the in situ evaluation of early-life performance of the recycled pavement. In addition, as-built roughness and ground-penetrating radar measurements, accomplished with in situ material coring and related laboratory tests, were performed. The roughness data analysis raised several issues concerning the construction of the recycled layer. According to the deflection analysis, an improvement in the recycled pavement structural condition was observed during the early life. The foamed asphalt material of the semirigid pavement proved to be stiffer than that of the flexible pavement. Furthermore, significant differences between pavement design parameters and related in situ characteristics were obtained through the strain response analysis.

Mechanistic Comparison of Cement- and Bituminous-Stabilized Granular Base Systems

The Saskatchewan, Canada, Department of Highways and Transportation is investigating alternative recycling and strengthening systems for inservice thin granular pavements. This research is being performed to improve the granular pavement structural integrity and to reduce the dependence on new source aggregates. A pilot project investigated the mechanistic-climatic laboratory characterization of materials used to construct test sections on Control Section Highway 15-11 (C.S. 15-11). This research demonstrated the use of ground-penetrating radar and falling weight deflection measurements to select uniform field test section locations. In situ recycled granular base was sampled and found to be a typical thin granular pavement requiring strengthening because it is relatively high in fine sand fraction and has a high portion of intermediate plastic clay fines. These two properties are known to cause marginal performance of granular bases in the field. This research showed that cement and bitu-minous stabilization significantly improved the mechanistic primary response and climatic durability properties of marginal granular base materials. However, it was found that the asphalt emulsion with cement stabilization showed the highest performance improvement. It also was found that the addition of cement to emulsified and foamed asphalt stabilization systems significantly improved the mechanistic-climatic durability of the marginal granular base aggregate. This study demonstrated the rapid triaxial tester to be a pragmatic and cost-efficient methodology to characterize the mechanistic constitutive relations of granular base materials for performing mechanistic road structural modeling.

Evaluation of Foamed Asphalt Cold In-Place Pavement Recycling Using Nondestructive Techniques

In light of the increasing cost of hot-mixed asphalt mixtures and the limited availability of good materials, cold in-place recycling using foamed asphalt stabilization offers an attractive alternative for rehabilitating pavements. The lack of experience—at least as far as the performance of the aforementioned technique for heavy duty pavements is concerned—led the Greek Ministry of Public Works to undertake a field experiment with the purpose of the rehabilitation of a severely damaged heavy trafficked semirigid pavement, part of the Trans European Network. In order to achieve this goal, a comprehensive monitoring and data analysis research study was performed, concentrating on the falling weight deflectometer nondestructive technique (NDT) as a major tool for the in situ evaluation (mainly in terms of deflection and layer moduli) of the recycled pavement's early life performance. Regarding layer thickness estimation, two different approaches are used, analyzed, and thoroughly discussed, reflecting cases often encountered in practical international experience, such as the use of conventional means like coring or advanced NDT, and using the ground penetrating radar.

EXAMINATION OF CAUSES OF RUNWAY PAVEMENT FAILURE AND MEASURES AT NEW CHITOSE AIRPORT

Blistering of the runway surface course was found during a runway inspection at New Chitose Airport in June 2001. A more detailed survey revealed that water penetration has reduced the bearing capacity of both the surface course and the binder course below the joint, as well as the asphalt stabilization layer. Because of a working time restriction on the runway, the thick lift method, whereby asphalt is placed in a short time, was applied in combination with a large-grain asphalt mixture that can be placed at lower temperatures than usual. The study reports the causes of pavement failure and the results of measures against such failure.

Engineering and environmental aspects of cutback asphalt (MC-70) stabilization of swelling and collapsible soils: A. S. Al-Homoud, T. Khedaywi & A. M. Al-Ajlouni, Environmental & Engineering Geoscience, 1(4), 1995, pp 497–506

The basic objective of this research was to investigate the effectiveness of Cutback Asphalt (MC-70) as a soil stabilizing agent. For this purpose, four different soils from Northern Jordan, which exhibit certain engineering problems, such as swelling and collapsibility, were selected. The collapsible soil samples were obtained from sites in Mafraq (Soil A) and within the Jordan University of Science and Technology Campus (Soil B). The swelling soil samples were obtained from Irbid (Soil C) and Ramtha (Soil D). To conduct this work, soil-Cutback Asphalt (MC-70) mixtures were prepared at 3 percent, 5 percent, 7 percent and 10 percent Cutback Asphalt (MC-70) by dry weight of soil. Both natural and Cutback Asphalt (MC-70) treated soils were subjected to similar laboratory tests to observe the influence of Cutback Asphalt (MC-70) on swelling and collapse potential. The test results showed that Cutback Asphalt (MC-70) is effective in stabilizing the tested soils. Upon mixing with soils, bituminous materials act as a binding agent between soil particles. Additionally, test results showed that Cutback Asphalt (MC-70) percentages in excess of 7 percent do not show a substantial reduction in swelling and collapsibility potentials. A general comparison of the effectiveness and economic feasibility of Cutback Asphalt (MC-70) to lime and cement, as stabilizing agents for reduction of swell potential of soils containing a high percentage of fines (e.g., Irbid Soil), showed that Cutback Asphalt (MC-70) causes higher reduction in swell potential than cement and a lower reduction than lime. However, Cutback Asphalt (MC-70) was found to be the least economical agent. On other hand, there are cases where lime or cement can have problems which can be resolved by the use of Cutback Asphalt (MC-70), e.g., the case where complex reactions occur between the lime and salts in the soils where cation exchange, agglomeration and carbonation were unaffected by the addition of lime, and the case of the treatment of sulfate-bearing soils especially in the abundance of water.

Engineering and Environmental Aspects of Cutback Asphalt (MC-70) Stabilization of Swelling and Collapsible Soils

The basic objective of this research was to investigate the effectiveness of Cutback Asphalt (MC-70) as a soil stabilizing agent. For this purpose, four different soils from Northern Jordan, which exhibit certain engineering problems, such as swelling and collapsibility, were selected. The collapsible soil samples were obtained from sites in Mafraq (Soil A) and within the Jordan University of Science and Technology Campus (Soil B). The swelling soil samples were obtained from Irbid (Soil C) and Ramtha (Soil D). To conduct this work, soil-Cutback Asphalt (MC-70) mixtures were prepared at 3 percent, 5 percent, 7 percent and 10 percent Cutback Asphalt (MC-70) by dry weight of soil. Both natural and Cutback Asphalt (MC-70) treated soils were subjected to similar laboratory tests to observe the influence of Cutback Asphalt (MC-70) on swelling and collapse potential. The test results showed that Cutback Asphalt (MC-70) is effective in stabilizing the tested soils. Upon mixing with soils, bituminous materials act as a binding agent between soil particles. Additionally, test results showed that Cutback Asphalt (MC-70) percentages in excess of 7 percent do not show a substantial reduction in swelling and collapsibility potentials. A general comparison of the effectiveness and economic feasibility of Cutback Asphalt (MC-70) to lime and cement, as stabilizing agents for reduction of swell potential of soils containing a high percentage of fines (e.g., Irbid Soil), showed that Cutback Asphalt (MC-70) causes higher reduction in swell potential than cement and a lower reduction than lime. However, Cutback Asphalt (MC-70) was found to be the least economical agent. On other hand, there are cases where lime or cement can have problems which can be resolved by the use of Cutback Asphalt (MC-70), e.g., the case where complex reactions occur between the lime and salts in the soils where cation exchange, agglomeration and carbonation were unaffected by the addition of lime, and the case of the treatment of sulfate-bearing soils especially in the abundance of water.

Studies on the Control of Swell and Collapse Potential of Selected Jordanian Soils Using Asphalt Stabilization

The basic objective of this research was to investigate the effectiveness of “bitumen” as a soil stabilizing agent. For this purpose, four different soils from Northern Jordan, which exhibit certain engineering problems, such as swelling and collapsibility, were selected. Two of these soils are swelling soils (Irbid and Ramtha), while the other two are collapsible (JUST and Mafraq). To conduct this work, soil-bitumen mixtures were prepared at 3%, 5%, 7% and 10% bitumen by dry weight of soil. Both natural and bitumen treated soils were subjected to similar laboratory tests to observe the influence of bitumen on swelling and collapse potential. The test results showed that bitumen is effective in stabilizing the tested soils. Upon mixing with soils, bituminous materials act as a binding agent between soil particles. Additionally, test results showed that cutback bitumen percentages in excess of 7% do not show a substantial reduction in swelling and collapsibility potentials.