Foamed Bitumen Mixtures Research Articles

Expansion process of foamed bitumen considering surface energy

Bitumen, sourced from different crude oils, exhibits distinct foaming properties that significantly influence the performance of foamed bitumen mixtures. This research investigates the relationship between the expansion ratio of foamed bitumen and its surface energy. A theoretical analysis was conducted on a single bitumen bubble to explore the equilibrium between internal steam work and surface energy during expansion. This led to a unique formula linking the bitumen bubble's expansion ratio to its surface energy. The validity of this formula was confirmed through empirical measurements of four different bitumens. Results reveal a significant exponential relationship between the expansion ratio of a single bituminous bubble and the bitumen surface energy. This correlation, supported by experimental data from four bitumen samples, suggests that bitumens with lower surface energy enhance foaming performance.

Stiffness Evaluation of Laboratory and Plant Produced Foamed Bitumen Warm Asphalt Mixtures with Fiber Reinforcement and Bio-Flux Additive

The present paper investigates the viscoelastic stress-strain responses of laboratory and plant produced warm mix asphalt mixtures containing basalt fiber dispersed reinforcement. The investigated processes and mixture components were evaluated for their efficacy in producing highly performing asphalt mixtures with decreased mixing and compaction temperatures. Surface course asphalt concrete (AC-S 11 mm) and high modulus asphalt concrete (HMAC 22 mm) conventionally and using a warm mix asphalt technique with foamed bitumen and a bio-derived fluxing additive. The warm mixtures included lowered production temperature (by 10 °C) and lowered compaction temperatures (by 15 °C and 30 °C). The complex stiffness moduli of the mixtures were assessed under cyclic loading tests at combinations of four temperatures and five loading frequencies. It was found that the warm produced mixtures were characterized by lower dynamic moduli than the reference mixtures in the whole spectrum of loading conditions, however, the mixtures compacted at the 30 °C lower temperature performed better than the mixtures compacted at 15 °C lower temperature, specifically when highest testing temperatures are considered. The differences in the performance of plant and laboratory produced mixtures were ascertained to be nonsignificant. It was concluded that the differences in stiffness of hot mix and warm mixtures can be attributed to the inherent properties of foamed bitumen mixtures and that these differences should shrink in time.

Foamed Bitumen Mixtures for Road Construction Made with 100% Waste Materials: A Laboratory Study

Nowadays, budget restrictions for road construction, management, and maintenance require innovative solutions to guarantee the user acceptable service levels respecting environmental requirements. Such goals can be achieved by the re-use of various waste materials at the end of their service life in the pavement structure, therefore avoiding their disposal in landfill. At the same time, significant savings are achieved on natural aggregate by replacing it with such waste materials, improving the economic and environmental sustainability of road constructions. The purpose of this study is to discuss a laboratory investigation about foamed bitumen-stabilized mixtures for road foundation layers, in which the aggregate structure was entirely made up of industrial by-products and civil wastes, namely metallurgical slags such as electric arc furnace (EAF) and ladle furnace (LF) slags, coal fly (CF) ash, bottom ash from municipal solid waste incineration (MSWI), glass waste (GW) and reclaimed asphalt pavement (RAP). Combining these recycled aggregates in different proportions, six foamed bitumen mixtures were produced and investigated in terms of indirect tensile strength, stiffness modulus, and fatigue resistance. The leaching test carried out on the waste materials considered did not show any toxicological issue and the best foamed bitumen mixture’s composition was characterized by 20% of EAF slags, 10% of LF slags, 20% of MSWI ash, 10% of CF ash, 20% of GW, and 20% of RAP. Its mechanical characterization presented a dry indirect tensile strength at 25 °C of 0.62 MPa (well above the Italian technical acceptance limits), a stiffness modulus at 25 °C equal to 6171 MPa, and a number of cycles to failure at 20 °C equal to 6989 for a stress level of 300 kPa.

Performance and viscoelastic assessment of high-recycle rate cold foamed bitumen mixtures produced with different penetration binders for rehabilitation of deteriorated pavements

The paper investigates the influence of the binder penetration grade on the volumetric, mechanical and viscoelastic properties of cold recycled mixes with foamed bitumen. Cold recycled mixtures produced with foamed bitumen differ significantly from other bituminous paving materials (e.g. hot mix asphalt) in terms of aggregate coating and bonding with the bituminous binder. What is more, hydraulic binders usually contribute to the strength of those mixtures. These factors result in a decreased viscoelastic response of cold recycled mixtures, which may impact the sensitivity of these mixtures to the type of binder used, which has not been thoroughly studied yet. The main body of the conducted experiments included complex stiffness moduli measurements under cyclic uniaxial compressive loading, supplemented by assessment of air void content, indirect tensile strength, resistance to moisture damage, indirect tensile stiffness and static creep modulus. The composition of investigated mixtures with high rate of recycled materials was designed to reflect a common scenario in rehabilitation of deteriorated pavements subjected to low and medium traffic loads. The three utilized binders were graded as 35/50, 50/70 and 70/100 penetration road paving bitumen, and were added as foamed bitumen in 2.5% amounts to the cold mix. The recycled mixes contained 50% of reclaimed asphalt pavement material, 30% of reclaimed crushed stone base and 20% of virgin aggregates. A hydraulic binder in form of Portland cement was used as a binding agent in amounts of 2%. Each of the investigated mixtures exhibited significantly distinct results in terms of air void content, indirect tensile strength and creep stiffness modulus. The performance of mixtures with 50/70 and 70/100 binders was similar in indirect tensile stiffness moduli and complex stiffness moduli. It was found, that the binder type had significant effects on the compactability of investigated mixtures, which resulted in different mechanical performance. At the same time the influence of the binder type on the viscoelastic properties of the cold mixtures was attenuated. It was concluded that the limited influence of the binder used was caused by the significant amount of reclaimed asphalt material in the evaluated mixtures and the effects of cementitious binding of the Portland cement. The results showed that a wide range of penetration grade bitumen can be used for producing cold recycled mixtures with foamed bitumen with only minor effects on their performance and viscoelastic properties.

Environmental effects on the rheological properties of fine warm RAP-foamed bitumen mixtures using SATS conditioning protocol

ABSTRACT This paper uses the Saturation Ageing Tensile Stiffness (SATS) conditioning to evaluate the combined effects of moisture and oxidative ageing on the rheological characteristics of the Fine Aggregate Matrix (FAM) portion of various Foamed Bitumen Mixtures (FBMs) in combination with Reclaimed Asphalt Pavement (RAP) material produced at 90, 120 and 160°C (i.e. half-warm, warm and hot processes, respectively). A reference fine Hot Mix Asphalt (HMA) with RAP – no foamed bitumen – was also manufactured. Their rheological properties were determined through Dynamic Mechanical Analysis (DMA) tests on specimens tested in their unconditioned and after SATS conditioning states. Rheology of the recovered binders of all FAM mixes before and after SATS conditioning was also studied, and rheological parameters were used to link their long-term performance in terms of cracking susceptibility. The results showed an overall increase in the stiffness of the fine mixtures after the conditioning process, mainly due to oxidation of the bitumen. Although the half-warm and warm fine RAP-FBMs exhibited the highest increase in their complex shear modulus after SATS conditioning, rheological analysis of their corresponding binders indicated that their long-term performance in terms of cracking susceptibility might be superior to those of the hot RAP-FBM, and the HMA-RAP fine mixtures.

Effect of foaming technique and mixing temperature on the rheological characteristics of fine RAP-foamed bitumen mixtures

This paper evaluates and compares the differences in the rheological characteristics of the fine aggregate matrix (FAM) portion of plant produced Foamed Bitumen Mixtures (FBMs) by means of a mechanical foaming process, and by the incorporation of zeolites in combination with Reclaimed Asphalt Pavement (RAP) material. This evaluation explores, for the first time, the impact of plant production variations for half-warm, warm and hot processes (i.e. mixing temperatures around 90°C, 120°C and 160°C, respectively) on their rheological response. A fine Virgin-HMA, a fine HMA-RAP – no foaming technique -, and a 100% fine RAP mixture were also produced for comparison purposes. Dynamic Mechanical Analysis (DMA) tests were conducted on all evaluated FAM mixtures to determine their linear viscoelastic properties. Results indicate that the rheological response of the fine RAP-FBMs is influenced primarily by the contribution of the RAP binder in the total bitumen blend, and ageing of the fine RAP material, which were a function of the foaming technology and the production temperature of the materials.

IMPACT OF RECYCLED ASPHALT PAVEMENT ON PROPERTIES OF FOAMED BITUMINOUS MIXTURES

In recent years, the use of foamed bitumen technology along with Reclaimed Asphalt Pavement is gaining popularity across the world. The mechanical response of foamed bitumen mixtures containing reclaimed asphalt pavement is significantly influenced by constituent material properties and aggregate gradation. This article presents results from a study where foamed bitumen mixtures conforming to Indian specifications were evaluated. For this purpose, foamed bitumen mixtures using a different percentage of reclaimed asphalt pavement and bitumens were prepared. Initially, the foaming characteristics of virgin bitumens were evaluated to optimize for optimum water content and foaming temperature. In the second stage, mixture design was conducted to optimize for foamed bitumen content in foamed bitumen mixtures containing a different percentage of reclaimed asphalt pavement. Finally, these foamed bitumen mixtures were evaluated for their mechanical properties. The results from this laboratory study indicated properties of foamed bitumen and foamed mixtures are significantly influenced by properties of bitumen, the quantity of bitumen, and reclaimed asphalt pavement. Among the different mixtures, a mixture containing 50% reclaimed asphalt pavement exhibited best results in resilient modulus and resistance to moisture damage tests. A mixture containing 80% reclaimed asphalt pavement also shows acceptable strength and resistance to water susceptibility. Thus, it is possible to design high-quality bituminous mixes using higher reclaimed asphalt pavement percentages, which meet the required volumetric and desired performance criteria.

Impact of binder on properties of foamed bituminous mixtures

Foamed bitumen technology is gaining acceptance across the world as an approach towards sustainable road construction. This technology offers advantages in terms of reduced energy consumption, materials recycling and reduced bitumen requirement. The properties of foamed bitumen mixtures depend on various factors, including the properties of the constituent materials and production conditions. This paper concentrates on the influence of the properties of the binder on the foaming characteristics of bitumen and the properties of foamed bitumen mixtures. Initially, four binders of different grades were evaluated for physical properties and foaming characteristics. The optimum foam content was then used to prepare foamed bituminous mixtures containing recycled asphalt pavement. These mixtures were evaluated for their mechanical properties, including indirect tensile strength, retained tensile strength and resilient modulus. The results from this laboratory study indicate that the properties of foamed bitumen and foamed mixtures are significantly influenced by the physical properties of the binder used, the quantity of binder and the recycled asphalt content. For a particular binder content in the mixture, use of a higher viscosity grade binder resulted in higher indirect tensile strength. A higher recycled asphalt pavement content in the mixture also resulted in higher indirect tensile strength. For all binder grades, a larger resilient modulus was observed for binder content the range of 2·3–2·5%.

Structural design of pavements incorporating foamed bitumen mixtures

This paper presents a rational structural design methodology termed the ‘cumulative damage approach’ for road, port and airport pavements incorporating cold bituminous mixtures with foamed bitumen. This has been developed along with a laboratory test, the uniaxial indirect tensile test, to evaluate the fatigue characteristics of these mixtures. The test was developed with a view to addressing the limitations of conventional fatigue tests for foamed bitumen mixtures. The new design approach takes account of the actual stiffness evolution of the mixtures obtained from the fatigue test. It is compared with a traditional approach for conventional flexible pavements, which is based on pavement life as a function of computed tensile strain in the material and interpretation of fatigue data in a conventional way. The results show that the traditional design approach yields conservative outcomes for pavements with foamed bitumen mixtures if the same transfer function or shift factor used for hot mix asphalt is applied. The results also show that if all factors other than induced load influence are the same, the shift factor for foamed bitumen mixtures could be 25–35% higher than for hot mix asphalt.

Development of a tool to assess in-situ curing of Foamed Bitumen Mixtures

This paper discusses the simplest yet crucial mix design consideration of Foamed Bitumen Mixtures (FBMs); curing. The objective of the present study is to attain better understanding of the curing mechanism of FBMs and lessen the gap between laboratory curing and field evolution of these mixtures. This was achieved by carrying out a laboratory curing study in two phases. The first phase aimed to understand the curing mechanism and to interpret the level of impact of factors such as temperature and time on the curing of FBMs. The effect of these factors on curing was evaluated with reference to stiffness gain and water loss of FBM specimens. The second phase was intended to develop a tool to assess in-situ curing of FBMs. With a view to assessing in-situ strength (or stiffness) the applicability of the maturity method, which is commonly used to estimate in-situ compressive strength of concrete before removal of formwork, to FBMs was evaluated. A strong correlation was found between maturity and the stiffness values obtained from the laboratory tests which resulted in development of maturity-stiffness relationships. The application of the method to assess the in-situ stiffness was presented using three hypothetical pavement sections. The results illustrate the influence of ambient temperature and the importance of cement addition to FBMs.

Mix design considerations of foamed bitumen mixtures with reclaimed asphalt pavement material

In the present work, a mix design parametric study was carried out with the aim of proposing a practical and consistent mix design procedure for foamed bitumen mixtures (FBMs). The mix design parameters that were adopted in the study are mixing and compaction water content (MWC), compaction effort using a gyratory compactor and aggregate temperature. This parametric study was initially carried out on FBMs with virgin limestone aggregate without reclaimed asphalt pavement (RAP) material and a mix design procedure was proposed. This proposed methodology was also found to apply to FBMs with RAP. A detailed consideration was also given to characterising the RAP material so as to understand its contribution to the mechanical properties of FBMs. Optimum MWC was achieved by optimising mechanical properties such as indirect tensile stiffness modulus and indirect tensile strength (ITS-dry and ITS-wet). A rational range of 75–85% of optimum water content obtained by the modified Proctor test was found to be the optimum range of MWC that gives optimum mechanical properties for FBMs. It was also found that the presence of RAP influenced the design foamed bitumen content, which means that treating RAP as black rock in FBM mix design is not appropriate. To study the influence of bitumen and water during compaction, modified Proctor compaction and gyratory compaction were employed on mixes with varying amounts of water and bitumen. By this, the work also evaluated the validity of the total fluid (water + bitumen) concept that is widely used in bitumen–emulsion-treated mixes, and found it not to be applicable.

Investigation on the Combined Effect of Fibers and Cement on the Mechanical Performance of Foamed Bitumen Mixtures Containing 100% RAP

Concerns about virgin aggregate sources and increasing demands for construction materials of transport infrastructures as the key parameters in development are the most important reasons, which convinced pavement engineers to develop new methods in order to use higher amount of recycled asphalt pavement (RAP). One of the common methodologies to produce mixtures containing RAP is foamed bitumen mix (FBM). In addition, according to previous research studies, incorporating various types of fibers and hydraulic binders such as cement could significantly improve the mechanical performance of mixtures. The present research study evaluated FBM containing 100% RAP and two types of fiber and Portland cement. Dynamic modulus, unconfined dynamic creep compression, and indirect tensile strength were evaluated in the laboratory at optimum moisture content, which was investigated in this research. Both types of fiber and cement proved to enhance specific properties of mixtures.

New experiences with foamed bitumen asphalts in hungarian road building

Abstract The use of low temperature (LT) asphalt products can result in a significant decrease of temperature required for asphalt production. This reduces energy costs and consumption. Moreover, safety during asphalt production and laying improves because the amount of potentially harmful vapours and aerosols decreases. Temperature decrease, in addition to the above, reduces the short-term ageing of bitumen in the asphalt production process, and ultimately has a positive impact on the durability of pavements. COLAS Group in Hungary considers propagating the use of low temperature sorts of asphalt in road construction in Hungary as a high priority innovation task Between 2012 and 2014, COLAS Group equipped its asphalt mixers with units from different manufacturers, capable of producing foamed bitumen, at four COLAS Group mixing plants in Hungary. This was followed by several test production runs and course laying with asphalt mixes containing foamed bitumen. Some of the foam asphalt mixes were produced and laid at low temperatures. The other part of the mixes were produced at conventional temperature and were layed after 2 - 2.5 hours of transport. The test asphalt mixtures were made with 50/70 and 10/40-65 modified bitumen also containing 10-20% RA. We compared the compactability of foamed bitumen mixtures produced with four different foaming kits. We produced Marshall specimens at various compaction temperatures, tested the bulk densities of the specimens, then represented the bulk densities subject to the compaction temperature. We established the following: the Marshall bulk density (better compactability) of foamed bitumen asphalt mixes is higher for all asphalt types compared to the normal bitumen mixtures, higher Marshall bulk density of foamed bitumen asphalt mixes can be achieved both in normal (50/70) and modified bitumen mixtures (25/55-65,10/40-65), better compactability of foamed bitumen asphalt mixes is independent of the type of the foaming kit. It works for all types of foaming kits.

Laboratory Mix Design Procedure for Foamed Bitumen Mixtures

The primary objective of this study was to propose a practical and consistent mix design procedure for foamed bitumen mixture (FBM). The main focus of the proposed methodology was the use of the gyratory compaction method. The study maximized the mix design parameters, such as mixing water content (MWC) and compaction effort. The study was initially carried out on FBMs with virgin limestone aggregate without reclaimed asphalt pavement (RAP) material, and a mix design procedure was proposed. The proposed methodology was validated on FBMs with 50% RAP and 75% RAP. Efforts were also made to optimize the foamed bitumen (FB) content in FBMs with and without RAP. Optimum MWC was achieved by optimizing mechanical properties such as indirect tensile stiffness modulus and indirect tensile strength (ITS-dry and ITS-wet). A rational range of 75% to 85% optimum water content was obtained by the modified Proctor test and found to be the optimum range of MWC that gave optimum mechanical properties for FBMs. The study used a gyratory compactor for FBM compaction and found that a unique, mixture-specific number of gyrations that was independent of the FB content could be established. The study also found that the presence of RAP influenced the design's FB content: treating RAP as black rock in FBM mix design was not appropriate.

Laboratory Study on Mechanical Parameters of Foamed Bitumen Mixtures in the Cold Recycling Technology

The paper presents the results of laboratory testing of the physical and mechanical parameters of the recycled material using the foamed bitumen and resistance to the action of water. The tests were performed on the mineral recycled base mixes with foamed bitumen, in which the material from the existing pavement layers was used. The effect of two kind of binding agents (foamed bitumen and Portland cement) was evaluated. The bitumen binder was added to the recycled material in the amount of 2.0% to 3.5%, and hydraulic binder of 1.0% to 2.5% with steps every 0.5%. The effects of different binder materials contents on the air void content, Marshall stability and resilient modulus at temperature 25°C of the recycled mixes were investigated. Moreover, the detrimental effect of water was measured by comparing indirect tensile strength (soaked and unsoaked) and determine tensile strength retained of foamed bitumen mixtures. The results were subject to the optimization process. This allowed to state that if 2.5% foamed bitumen and 2.0% of Portland cement are used, the recycled base course has the required physical and mechanical properties and moisture resistance.

New developments with half-warm foamed bitumen asphalt mixtures for sustainable and durable pavement solutions

Internationally, a growing health, safety and environmental awareness of the public can be observed. In this context, significant efforts are underway to develop advanced technologies to reduce the use of non-renewable fossil fuels, in order to reduce emissions and human exposure. Also, in the road industry, the search for new sustainable solutions is eminent. The introduction of asphalt mixtures that can be produced at lower temperatures is an important development in this direction. Lower temperature means in general that lower than 140°C. In this article, developments with the so-called half-warm foamed bitumen mixtures produced at temperatures below 100°C and even as low as 90°C are discussed. Mixtures used in binder and base layers are considered. The role of life-cycle assessment as used in the Netherlands is described for half-warm foamed bitumen mixtures. The performance properties according to the CE marking are also discussed at the same time. Finally, the workability of these mixtures is studied, showing how compaction of this type of mixtures can be managed. In all cases, a reference hot base course mixture is used for comparison.

Effects of Active Filler Selection on Foamed Bitumen Mixture in Western Australia

This study investigated the effects of different active filler types and contents on the mechanical properties of foamed bitumen treated materials under laboratory conditions. Four different active fillers were tested namely Portland cement, hydrated lime, quicklime and fly ash, at varying concentration of 0%, 1%, 3% and 5%. To evaluate the effects of the additional active fillers, samples were prepared under laboratory conditions and tested using indirect tensile strength, indirect tensile resilient modulus and unconfined compressive strength tests. Based upon our findings, all active filler types except fly ash contributed in improving the strength of foamed bitumen mixtures at different levels. Cement, regardless of adding contents, always provided the highest mechanical performance compared with the other two counterparts: hydrated lime and quicklime. Fly ash was deliberated to be precluded because fly ash on its own did not affect any mechanical strength of foamed bitumen mixes instead it acted as a mineral filler to modify aggregate gradation. The addition of active filler content should be limited within 3% in terms of strength gain and potential cracking prevent when mixing with 4% foamed bitumen content and locally sourced raw materials for base course.