Foamed Asphalt Mixes Research Articles

Effect of Temperature and Asphalt Binder Type on the Properties of Foamed Asphalt Mix

In this study, an effect of temperature on both indirect tensile strength (ITS) test and Marshall Stability Test of foam asphalt mixture using Shell #70 A asphalt is firstly investigated. A detailed investigation of the mechanical properties of foam asphalt mixture was then carried out using two different asphalt binders. The experimental work compares the mechanical properties of foam asphalt mixes including water stability test, indirect tensile strength (ITS) test, and freeze-thaw splitting test. The test results indicate that the foam asphalt mixture is temperature dependent and also temperature sensitive material. The foaming properties of asphalt have an important effect on the properties of the foam asphalt mixture for the strength and water stability of the foam asphalt mixture.

Evaluation of foamed sulfur asphalt stabilized soils for road applications

This paper summarizes the research carried out to evaluate and compare the performance of marginal soils, namely marl, sabkha and dune sand treated with foamed sulfur asphalt (FSA) with the mixes of the same soils treated with conventional foamed asphalt (FA) for the construction of road bases. FSA and FA mixes were designed for the three soils utilizing low percentage of Portland cement (2%) and were optimized to meet dry and wet indirect tensile strength (ITS) requirements. Designed mixes were evaluated for Marshall stability, static triaxial (shear strength) and dynamic resilient modulus at 22°C.Results indicate that properly designed FSA mixes displayed a significant improvement in ITS (17% for marl and 9.4% for sand soils), Marshall stability (14% for marl and sand soils) and shear strength (135%, 76% and 250% for marl, sabkha and sand soils, respectively) as compared with those of conventional FA mixes. Resilient modulus testing indicated that FSA has marginally reduced the resilient modulus of soils compared with FA. Foamed sulfur asphalt technology can be used successfully to construct road bases from available marginal soils.

Investigating physical and rheological properties of foamed bitumen

Foamed asphalt mixes are gaining ground as effective alternatives to asphalt base and sub-base standard layers in Europe and in other countries worldwide. As a significant amount of research is being conducted to advance sustainable practices for road pavements, foaming asphalt mixes have become a valid option to common asphalt paving technologies. Several advantages and the environmental benefits of foamed asphalt mixes have been debated and assessed.The present study aimed to evaluate: (1) the foaming characteristics of several bitumens sourced from different refineries with the same classification grade; (2) the physical, rheological, and chemical properties of bitumens before and after foaming; and (3) the effectiveness of a foaming additive in the enhancement of final product performance.Results showed that the same penetration-grade bitumen can provide very different results in terms of foaming properties (expansion ratio and half-life) depending on its chemical composition (differential scanning calorimetry and optical microscope analysis). The experimental program also assessed how the foaming process affected the physical and rheological behavior of bitumens (penetration, Ring and Ball test, dynamic viscosity, complex modulus, and phase angle).

The influence of material related parameters on the mechanical properties of foamed asphalt mix

By indirect tensile strength (ITS) test and unconfined compressive strength (UCS) test, the influence of various material related parameters, including asphalt foamability, aggregate temperature, mixing moisture content (MMC) and foamed asphalt (FA) content, on the mechanical properties of FA mixes was studied. The results indicated that both asphalt foamability and aggregate temperature greatly affected ITS of FA mixes. Too low aggregate temperature was unfavorable for mechanical properties of FA mixes. Foamed index alone was unfit for the evaluation of asphalt foamability. Compared with half-life, expansion ratio had more prominent influence on ITS of FA mixes. MMC had significant impact on the mechanical properties of FA mixes and should be optimized by trial and test in FA mix design. The mechanical properties of FA mix were sensitive to the change of FA content. Compared with the ITS determined with standard Marshall specimens, both the ITS and UCS determined with static compressed specimens by 15 cm diameter were more effective in terms of choosing the optimal asphalt content for FA mixes.

Effects of reclaimed asphalt pavement on indirect tensile strength test of foamed asphalt mix tested in dry condition

Indirect tensile strength (ITS) test was conducted to analyse strength of the foamed asphalt mixes incorporating reclaimed asphalt pavement. Samples were tested for ITS after cured in the oven at 40°C for 72 hours. This testing condition known as dry condition or unconditioned. Laboratory results show that reclaimed asphalt pavement (RAP) contents insignificantly affect the ITS results. ITS results significantly affected by foamed bitumen contents.

Effects of reclaimed asphalt pavement on indirect tensile strength test of conditioned foamed asphalt mix

This paper presents the results of Indirect Tensile Strength (ITS) Test for samples prepared with reclaimed asphalt pavement (RAP). Samples were conditioned in water at 25°C for 24 hours prior to testing. Results show that recycled aggregate from reclaimed asphalt pavement performs as well as virgin aggregate.

Study on the optimization design of mixing moisture content in foamed asphalt mix

This research discussed the rational mixing moisture content (MMC) in foamed asphalt (FA) mix design. Sieve analysis was firstly used to study the bitumen dispersion and bitumen-aggregate coating and bonding action in FA mixes with three levels of MMC. Then, through variance analysis, the impacts of MMC, bitumen content and their interaction effect on the mechanical properties of FA mixes were studied. Indirect tensile strength test and dry density determination were carried out on FA mixes consisting of different gradings and material types to explore the rational MMC. On base of that, monotonic triaxial test was performed on two types FA mixes with various filler contents to further investigate the rational MMC for FA mix. The research results indicated that improper MMC led to bitumen clots and affected cohesion of FA mix. MMC and bitumen content had important impacts on mechanical properties of FA mix, while their interaction effect could be ignored in mix design. Optimal MMC increased to a certain extent with the increase of fine aggregates content, especially filler content in the grading. 70–80% of the optimum moisture content (OMC) was recommended as rational range of MMC for FA mix with 5–15% filler content and 75–85% of OMC for mix with 15–20% filler content, which offered a reference for easy and simplified MMC design for FA mix.

Study of road bases construction in Saudi Arabia using foam asphalt

This paper summarizes the research carried out to compare the performance of foamed asphalt pavement mixes with conventional crushed aggregate for the construction of road bases. The research work focused on the investigation and evaluation of the feasible use of foamed asphalt technology for Saudi roads using marginal quality construction materials, marl, and reclaimed asphalt pavement (RAP) materials for local applications. Materials included the Ministry of Transport (MOT) granular base class A and B, subbase material class B, and reclaimed asphalt pavement (RAP) material. Foamed asphalt mixes were designed for subbase class B (foamed SB) and RAP (foamed RAP) material utilizing low percentage of Portland cement. Foamed asphalt mixes were optimized to meet dry and wet indirect tensile strength (ITS) requirements. Designed mixes in addition to granular base class A and B were evaluated for CBR, dynamic resilient modulus at 25 °C and wheel tracking test dry at 50 °C and soaked at 22 °C. Results indicate that base class A has the lowest rutting followed by base class B then foamed SB and finally foamed RAP for dry condition at 50 °C, while foamed RAP has the lowest rutting followed by foamed SB then base class B and finally class A for soaked condition at 22 °C. Portland cement was effective in reducing ITS loss of foamed asphalt mixes. Resilient modulus testing indicated that SB mix has behavior comparable to base class A. Foamed RAP mix has shown the best behavior. Saturation has reduced resilient modulus of all mixes significantly. Foamed asphalt technology can be used successfully to construct road bases from locally available marginal or recycled materials.

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.

Micromechanics of the Effects of Mixing Moisture on Foamed Asphalt Mix Properties

The mixing moisture content (MMC) is an important mix design variable in pavement full-depth reclamation (FDR) with foamed asphalt. It has been known for many decades that MMC in the granular material subjected to foamed asphalt treatment can affect asphalt dispersion. This paper investigates the micromechanics of this phenomenon by combining direct microstructure observations and conventional laboratory testing. It was found that for a typical loose moist granular material with a considerable amount of fine particles, the agglomeration state evolves through a series of states as the MMC increases. If the MMC is high, the fine particles become saturated and form a pastelike substance that coats larger aggregate particles, creating large agglomerations with low surface area to volume ratios. Inferior asphalt dispersion is resulted for mixes in this state. Theories for wet agglomeration processes are used to explain the observations on the basis of thermodynamic equilibrium. Fracture face image analysis for tested indirect tensile strength specimens confirmed this observation. Laboratory tests also found that mixes with inferior asphalt dispersion due to suboptimal MMC yield low strength and low stiffness. These effects are particularly significant for granular materials with higher fines content. The main practical implication of the findings is that relatively dry loose granular mixes are preferred for foamed asphalt dispersion, and a balance should be sought between asphalt dispersion and mix compactability. The existing postulation that high MMC aids foamed asphalt dispersion is therefore dismissed.

Dynamic Modulus and Repeated Load Tests of Cold In-Place Recycling Mixtures Using Foamed Asphalt

As part of the validation effort to evaluate the consistency of a new cold in-place recycling using foamed asphalt (CIR — foam) mix design process for the Iowa Department of Transportation, the dynamic modulus and repeated load tests were conducted to evaluate the performance characteristics of CIR — foam mixtures over a wide range of loading and temperature conditions. The main objective of this research is to study the impacts of the foamed asphalt contents and reclaimed asphalt pavement (RAP) material characteristics on dynamic modulus and flow number. Dynamic modulus and repeated load tests were conducted on CIR — foam mixtures with RAP materials collected from seven different CIR project sites located throughout Iowa. Dynamic modulus values of the RAP materials varied depending on the sources and foamed asphalt contents. Coarse RAP materials with a small amount of residual asphalt content exhibited a higher modulus value at 4.4°C but exhibited a lower dynamic modulus value at 37.8°C than fine RAP materials with a large amount of residual asphalt content. Flow numbers were varied significantly depending on their RAP sources and foamed asphalt contents. Fine RAP materials with a hard residual asphalt binder exhibited a higher flow number than coarse RAP materials with a soft residual binder. The relative rankings of RAP materials in terms of the flow number did not change when the foamed asphalt was increased from 1.0 to 3.0%, which supports the repeated load test being consistent in evaluating a rutting potential of RAP materials.

Investigation of the Curing Mechanism of Foamed Asphalt Mixes Based on Micromechanics Principles

This study investigated the curing mechanism of foamed asphalt mixes. Various laboratory strength and stiffness tests were performed on mixes with various asphalt and portland cement contents, and the specimens were subjected to two relatively extreme curing conditions. It was found that portland cement enhances certain properties of foamed asphalt mixes by strengthening the mineral filler phase, with the curing mechanism similar to that of typical cement treated materials. The curing mechanism of foamed asphalt mastic is primarily related to water evaporation. The bonding between asphalt mastic and aggregate particles cannot fully develop until most of the water retained at the interface evaporates. This bonding, once formed, is only partially damaged by reintroduced water. This proposed mechanism was supported by observations of fracture faces on tested specimens. A long-term curing study confirmed the validity of this mechanism regardless of the curing duration. Standard curing procedures are proposed for use in project level mix design and evaluation based on the findings.

Degree of Influence of Active Fillers on Properties of Recycled Mixes with Foamed Asphalt

Active fillers in foamed asphalt mixes are added to modify the fine fraction of aggregate gradation or to reduce the moisture sensitivity of the mix. Some countries use cement as an active filler, and other countries use lime or fly ash, among other ingredients. However, limited information is available concerning the influence of different types of active fillers on the mechanical properties of foamed asphalt mixes. This paper presents the results of a project carried out to study the relative influence of active fillers on the mechanical properties of recycled mixes with foamed asphalt. Four active fillers were studied: portland cement concrete, cement kiln dust, hydrated lime, and fly ash Class C. Indirect tensile strength, triaxial resilient modulus, and triaxial permanent deformation tests were carried out to quantify the influence of these active fillers on the properties of one particular full-depth reclamation material. Different curing methods and moisture conditioning were used to evaluate the role of active fillers after the mix production process. As a result of this study, it was concluded that, for the full-depth reclamation material tested, whereas some active fillers have an important influence on the mechanical properties and long-term performance of foamed asphalt mixes, others act only as mineral fillers of the aggregate gradation. Also, because foamed asphalt takes a long time to cure, some active fillers play an important role in contributing to the early strength of foam recycled mixes.

Laboratory Test Methods for Foamed Asphalt Mix Resilient Modulus

ABSTRACT This paper investigates laboratory test methods for resilient modulus of foamed asphalt mixes. By comparing test results from different laboratory test methods, the effects of various stress states are identified. The indirect tensile resilient modulus test and the free-free resonant column test were found to yield stress states irrelevant to pavement structures, and to greatly overestimate resilient modulus. Triaxial resilient modulus test results showed that the role of foamed asphalt treatment is to transform the material behavior from that of typical unbound granular materials to that of partially asphalt-bound materials. Flexural beam tests indicated that when subjected to tension, the resilient modulus of soaked foamed asphalt mixes can be very low. Since triaxial and flexural beam tests each characterize one of the two most important stress states relevant to pavement design, test results from these two methods need to be combined to be used in design.

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.

Temperature sensitivity of foamed asphalt mix stiffness: field and lab study

Knowledge of the temperature sensitivity of foamed asphalt stiffness is very important in mix and structural design, field non-destructive testing and advanced research. However, this subject has not been studied extensively, especially the effects of the stress state on the temperature sensitivity, which is essential to understand the behavior of weakly bonded granular materials. This paper first presents triaxial resilient modulus testing results of foamed asphalt treated materials with various asphalt contents at various temperatures. General observations are made in terms of the effects of the bulk stress, deviator stress, temperature and their interactions. Based on these observations, the temperature sensitivity coefficient of foamed asphalt stiffness is defined and a simplified model to predict foamed asphalt mix stiffness at any triaxial stress state and temperature is proposed and validated. A procedure to normalize back-calculated resilient modulus to a standard temperature is also presented. The essential step of this procedure is to estimate the temperature sensitivity coefficient based on the field test results at various temperatures. Finally, an example is presented comparing the stiffness of a foamed asphalt material over two years. It was found that the stiffness did not change significantly over the two years period, despite the accumulation of traffic loading.

Laboratory study on permanent deformation of foamed asphalt mix incorporating reclaimed asphalt pavement materials

For the purpose of investigating the effects of bitumen grade, content of reclaimed asphalt pavement (RAP) material and ageing of RAP, this paper presents the evaluation of permanent deformation of foamed asphalt (FA) mixes by using the dynamic creep test. The mix design of WC-20 was conducted based on the gradation requirement of FA mix and RAP aggregate size. Three parameters, creep strain slope (CSS), Intercept and secant creep stiffness modulus (SCSM), were used to analyze the test results. Mean comparison and multiple analysis of variance (MANOVA) reveal that bitumen grade significantly affects CSS, whilst content and ageing of RAP would have insignificant effect on CSS. High bitumen grade may help FA mixes on the reduction of susceptibility to permanent deformation. Test results reflect that variances of CSS, Intercept, and SCSM are large. There is a good exponential relationship between CSS and SCSM, however no correlation between CSS and air void is found. Comparison of test results between FA mixes and hot asphalt mixes exhibits that susceptibility and creep strength of FA mixes are better than those of selected hot asphalt mixes.

Effects of moisture on strength and permanent deformation of foamed asphalt mix incorporating RAP materials

Based on literature review on moisture susceptibility of hot-mixed asphalt and foamed asphalt (FA) mixes, a 24-h-soaking preconditioning method was selected to evaluate moisture effects on the strength and permanent deformation of FA mixes incorporating RAP materials in this study. Two grades of bitumen and two types of aged RAP materials were considered. Indirect tensile strength (ITS) test and dynamic creep test of FA mixes incorporating different RAP contents and stabilized by the two bitumens were tested under dry and soaked conditions. As well as ultimate strain, creep strain slope and secant creep stiffness modulus under two conditions were analyzed to evaluate moisture susceptibility of FA mixes in permanent deformation. Retained ITS results were evaluated to investigate moisture effect on property of indirect tensile strength of FA mixes. Bitumen grade and RAP content significantly affect ITS result of FA mixes, ITS will decrease with an increase of RAP content under both dry and soaked conditions. Bitumen grade and ageing of RAP material significantly affect moisture susceptibility of FA mixes in permanent deformation. Lower-grade bitumen and less aged RAP material help FA mixes to improve their moisture susceptibility in permanent deformation.

A Study on Properties of Foamed-Asphalt-Treated Mixes

Abstract From both economical and ecological points of view, cold recycling is much more beneficial than hot recycling. However, due to not only the intrinsic properties of binding mechanisms but also the difficulties of process control, cold recycling did not gain common acceptance in Taiwanese paving industries. For the further development of environment-friendly paving materials and construction processes, this particular study investigated the engineering properties of foamed-asphalt-treated bases in Taiwan. Using a laboratory foaming plant, work was performed on local materials to produce foamed-asphalt-treated cold mixtures. The engineering properties of foamed-asphalt-treated mixes were tested and compared with those of hot recycled mixes. Test results show the benefits of utilizing high percentages (80%) of milled asphalt in foamed asphalt mixes. The optimum asphalt content of foamed asphalt mixes can be reduced from 3.5 to 2.0%, which is less than the mixes consisting of all new aggregate, and the moisture resistance of the mixture is enhanced. Resilience modulus and fatigue data show that foamed-asphalt-treated mixes perform as well as hot recycled mixes.

Stabilization of Dune Sand Using Foamed Asphalt

Abstract Foamed asphalt technology has increasingly gained acceptance as an effective and economical soil improvement and stabilization technique, mainly because of its improved aggregate penetration, coating capabilities, and handling and compaction characteristics. This laboratory research program was carried out to investigate the feasible use of foamed asphalt technology in Saudi Arabia to improve the prevalent dune sands for possible use as a base or subbase material. Several variables were investigated to evaluate the relative improvement of dune sand as well as to permit the development of design procedures for the future use of foamed asphalt technology in the harsh climatic conditions of eastern Saudi Arabia. Statistical analysis of the results was employed to verify the effects of emulsified asphalt and foamed asphalt treatment, with and without the addition of Portland cement, on the strength characteristics of the treated mixes. The results displayed significant improvement in the performance of dune sand foamed asphalt mixes, as compared to that of the emulsified asphalt mixes.