Foamed Bitumen Research Articles

The Impact of Long-Time Chemical Bonds in Mineral-Cement-Emulsion Mixtures on Stiffness Modulus

Deep cold in-place recycling is the most popular method of reuse of existing old and deteriorated asphalt layers of road pavements. In Poland, in most cases, the Mineral-Cement-Emulsion mixture technology is used, but there are also applications combining foamed bitumen and cement. Mineral-Cement-Emulsion mixtures contain two different binding agents – cement as well as asphalt from the asphalt emulsion. Asphalt creates asphalt bonding (responsible for flexible behaviour), whereas cement generates hydraulic bonds (responsible for stiffness of the layer). Final properties of Mineral- Cement-Emulsion mixtures are a result of a combination of both binding agents. While the stiffness of the material is unaffected by asphalt bonding, an increase in stiffness with time is visible for materials treated with hydraulic binders. This publication presents the change in stiffness modulus of Mineral-Cement-Emulsion mixtures by Simple Performance Test. For the analysis, two batches of specimens were used: the first was tested 28 days after compaction (period stated in Polish recommendations) and the second was tested 1.5 years after compaction. Analysis showed that after 1.5 years the stiffness modulus increased by about 10% in comparison to the 28 days after compaction. The change is minor but still significant. Unexpectedly, the level of the increase was unaffected by the combination of the binding agents (asphalt emulsion, cement).

Impact of low viscosity grade bitumen on foaming characteristics

The construction of highway infrastructure requires large quantities of construction materials and is an energy-intensive activity. Issues like scarcity of construction materials, increasing cost of materials, increasing cost of construction processes, and the emphasis on less polluting construction procedures have led to advancements in pavement construction practices. One such example is foamed bitumen technology. In this process, cold water is injected into a hot bitumen medium, which leads to drastic expansion of bitumen, forming a fine mist or foam. The performance of foam bitumen mixtures is influenced by the bitumen properties, as well as by the foaming process. This paper deals with research on the rheology of three different types of binders having low viscosity (in the range of 500 to 3 000 Poise at 60°C) on foaming characteristics. The water content and temperature also have significant effects on foam decay and the expansion ratio of foam. Results show that a low viscosity bitumen consumes less energy during the foam process compared to high viscosity bitumen. The conclusion drawn from this study is that the expansion ratio and half-life of foam bitumen depend on the rheology of the bitumen, as well as on the chemical composition of the bitumen. It was concluded that, with an increase in carbonyl and sulphoxide compound, the expansion ratio decreases and the half-life increases.

Laboratory Methods for Identification of Geologic Origins of Natural Asphalts with Special Emphasis on their Potential Uses: The Case of Trinidad Pitch and Utah Bitumen

It is widely acknowledged that the physicochemical properties of asphalt binders primarily dictate their performance and their end-use applications. However, limited data on the subject exists. This research investigates the physicochemical characterization of two natural bitumens: Trinidad pitch (TP) and Utah foam bitumen (UFB), using elemental analysis, Fourier transform-infrared spectroscopy (FT-IR), thin-layer chromatography with flame ionization detection (TLC-FID), proton-nuclear magnetic resonance spectroscopy (1H-NMR), and penetration, softening point, and viscosity tests. The results showed that TP differed significantly from UFB, mainly in the hydrocarbon, heteroatomic, vanadium, and clay-mineral contents. In terms of the SARA (i.e., saturates, aromatics, resins, and asphaltenes) fractions, the most striking compositional difference was that UFB contained more saturates than TP. Physical tests demonstrated that TP was characterized by lower penetration and higher softening points than UFB. These findings suggest that UFB is a potential candidate for the production of petroleum, and TP is a suitable construction material for road pavement.

Laboratory testing of low temperature asphalt concrete produced in foamed bitumen technology with fiber reinforcement

Abstract The paper presents the design process and test results of warm mix asphalt concrete produced with modified foamed bitumen and recycled synthetic fiber reinforcement. Recycling and low-temperature asphalt production techniques are now seen as the possibilities to increase the sustainability and energy effectiveness of road construction. Although low processing temperatures permit increased use of reclaimed and recycled materials in new asphalt mixes, they sometimes result in impaired service performance. The aim of this article was to present a possibility of producing a better performing asphalt concrete (in comparison to a control hot-mix) at lower temperatures. For this purpose two road paving bitumens modified with a surface active agent and a Fischer-Tropsch wax thoroughly tested for their basic, rheological characteristics and foaming performance. Selected binders were used for producing two control mixes (hot-mix and foamed warm mix with 35/50 bitumen) as well as the experimental mix with the modified 50/70 bitumen and an addition of synthetic fiber material from recycling of automotive tires. Basic properties of the mixes were tested (air void content, moisture susceptibility with one freeze-thaw cycle, wheel tracking) along with stiffness moduli and fatigue resistance. It was concluded that the control foamed warm-mix performed significantly worse than the hot-mix, while the experimental warm-mix with modified bitumen and fiber additive exhibited increased performance and resistance to fatigue and moisture.

Basic Performance of Fibre Reinforced Asphalt Concrete with Reclaimed Asphalt Pavement Produced In Low Temperatures with Foamed Bitumen

During the reconstruction of road pavements, the reclaimed asphalt pavement (RAP), which is obtained through milling of the worn out existing asphalt, is commonly used for producing new base courses in cold recycling processes. Two of these techniques are most popular: one using mineral-cement-emulsion mixes and one utilizing mineral cement mixes with foamed bitumen. Additionally, some amounts of RAP can be incorporated into traditional hot mix asphalt. The demand for energy efficient and environmentally friendly solutions however, results in a need for development of new techniques that would result in cheaper and more reliable solutions with smaller carbon footprint. The reduction of processing temperatures with simultaneous incorporation of reclaimed material is the most efficient way of obtaining these objectives, but it often results in the overall decrease of bituminous mix quality. The paper presents the possibility of using RAP for producing asphalt concrete in warm mix asphalt (WMA) production process by the use of foamed bitumen modified with Fischer-Tropsch synthetic wax and polymer-basalt fibers. Additionally, a series of reference mixtures were produced to investigate the effects of the additives and of the warm process. The carried out analyses and tests shown that the experimental warm mix asphalt produced with RAP and foamed bitumen returned satisfactory performance. The introduction of synthetic F-T wax in the warm foam bitumen mixes resulted in a significantly improved compaction levels and moisture and frost resistance and the addition of polymer-basalt fibers has further improved the permanent deformation resistance of the mixes. All of the designed and tested mixes have fulfilled the requirements for binding course asphalt concrete with medium traffic loads.

Evaluation of Foaming Performance of Bitumen Modified with the Addition of Surface Active Agent

The article presents the analysis of the performance of foamed bitumen modified using surface active agents. Although, bitumen foaming permits production of asphalt concrete and other asphalt mix types without using chemical additives in significantly reduced temperatures, the decrease in processing temperatures still impacts the adhesion performance and bitumen coating of aggregates in final mixes. Therefore, in some cases it may be feasible to incorporate adhesion promoters and surface active agents into warm and half-warm mixes with foamed bitumen to increase their service life and resilience. Because of the various nature of the available surface active agents, varying bitumen compatibility and their possible impact on the rheological properties of bitumen, the introduction of surface active agents may significantly alter the bitumen foaming performance. The tests included basic performance tests of bitumen before and after foaming. The two tested bitumen were designated as 35/50 and 50/70 penetration grade binders, which were modified with a surface active agent widely used for improving mixture workability, compactibility and adhesion in a wide range of asphalt mixes and techniques, specifically Warm Mix Asphalt. Alongside to the reference unmodified bitumen, binders with 0.2%, 0.4% and 0.6% surface active agent concentration were tested. The analysis has shown a positive influence of the modifier on the foaming performance of both of the base bitumen increasing their maximum expansion ratio and bitumen foam halflife. In the investigations, it was found that the improvement was dependent on the bitumen type and modifier content. The improved expansion ratio and foam half-life has a positive impact on the aggregate coating and adhesion, which together with the adhesion promoting action of the modifier will have a combined positive effect on the quality of produced final asphalt mixes.

Inactive Mineral Filler as a Stiffness Modulus Regulator in Foamed Bitumen-Modified Recycled Base Layers

The article presents the results of a cold recycled mix test with a foam bitumen including the addition of the inactive mineral filler as a dust of basalt. Basalt dust was derived from dedusting system by extraction of aggregates in the mine. Assessment of the impact of a basalt dust on the properties of a recycled base layer was carried out in terms of the amount of mineral filler (basalt) in the composition of the mineral mixture. This experiment involved a dosing of mineral filler in range from 5 to 20% with steps of 7.5% in the mineral mixture composition. The foamed bitumen was performed at optimum foaming process settings (ie. bitumen temperature, air pressure) and at 2.5% of the water content. The amount of a hydraulic binder as a Portland cement was 2.0%. The evaluation of rheological properties allowed to determine whether the addition of inactive mineral fillers can act as a stiffness modulus controller in the recycled base layer. The analysis of the rheological properties of a recycled base layer in terms of the amount of inactive fillers was performed in accordance with given standard EN 12697-26 Annex D. The study was carried out according to the direct tension-compression test methodology on cylindrical samples. The sample was subjected to the oscillatory sinusoidal strain ε0 < 25με. Studies carried out at a specific temperature set-points: - 7°C, 5°C, 13°C, 25°C and 40°C and at the frequency 0.1 Hz, 0.3 Hz, 1 Hz, 3 Hz, 10 Hz and 20 Hz. The obtained results allow to conclude that the use of an inactive filler can reduce the stiffness of an appropriate designed mixes of the cold recycled foundation. In addition, the analysis of the relation E′-E″ showed a similar behaviour of a recycled base, regardless of the amount of inactive fillers in the mix composition, at high temperatures/high frequency of induced load.

Suitability of different foamed bitumens for warm mix asphalts with increasing recycling rates

Due to the current need for more sustainable production processes and construction materials, foamed bitumen has become one of the most interesting solutions for asphalt paving works, both for new (warm mix) and recycled asphalt mixtures (warm recycled mix). However, significant work still needs to be carried out in order to fully understand the performance of foamed bitumens, and their adequacy for incorporation into asphalt mixtures with different amounts of reclaimed materials, which is the main objective of this work. Three types of bitumen, with increasing penetration grades were selected in order to evaluate their foaming properties, namely their expansion ratio and half-life, as well as the foam index assessed using the foam decay curves obtained through a semi-automated process. After determining the most suitable composition of each foamed bitumen (water content, temperature, foam stabilizing additive content), these were incorporated into asphalt mixtures with 0%, 30% and 50% reclaimed asphalt material. As the amount of reclaimed material increased, the penetration grade of the new bitumen added was also increased, in order to compensate the lost properties of the aged binder. The suitability of these solutions was assessed through water sensitivity tests, and it was concluded that the proposed approach is adequate to obtain long-lasting solutions. Moreover, it became evident that foamed bitumens perform better when incorporated into recycled asphalt mixtures.

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.

Comparative Evaluation and Modification of Laboratory Compaction Methods of Road Base Mixtures Manufactured in Low-emission CIR Technology with Foamed Bitumen and Bitumen Emulsion

The paper evaluates the influence of laboratory compaction methods on the properties of recycled mixtures with foamed bitumen (Foam-Mix) and bitumen emulsion (Emulsion-Mix). In Poland, the requirements concerning the design of recycled mixtures and quality control of the cold in-place recycled base course layers specify two laboratory methods of sample preparation: static compaction in a hydraulic press and impact compaction with the use of Marshall hammer. The statistical analysis (Student t-test) indicates that the compaction method has a significant effect on physical and mechanical characteristics of the recycled mixtures. The method of sample preparation has been found to affect the arrangement of aggregate grains in the compacted material. The hydraulic press method over-compacted the samples from both mixtures, crushing the grains. The samples compacted in the hydraulic press had better strength parameters and resistance to water, which was undoubtedly related to the lower air void content, regardless of the asphalt binder used. Static compaction, which according to the Polish guidelines is conducted under pressure of 100kN maintained for 5minutes, in many cases (depending on the grading of the recycled mixture or amount of binding materials) produces mixtures with excessive bulk density being inadequate to real conditions and difficult to attain in the field. This paper proposes the technique for the calibration of compaction methodology for foamed and emulsion mixture samples in the hydraulic press against the Marshall method.

Analysis of IT-CY Stiffness Modulus of Foamed Bitumen Asphalt Concrete Compacted at 95 °C

This study is to compare the results of temperature sensitivity tests of foamed bitumen asphalt concrete (AC 8) compacted at 95°C with that of the reference mixture compacted at the conventional temperature of 140°C. The tests and subsequent analysis confirm the advantageous effects the modification of bitumen 50/70 with 2.5% Fischer-Tropsch (FT) synthetic wax has on the characteristics of asphalt concrete. The characteristics investigated in this study included the air void content and moisture resistance of the specimens in one freezing cycle test (ITSR). Additionally, the relationships between air void content and stiffness moduli were investigated. The analysis of temperature sensitivity was conducted based on the measured indirect tensile stiffness modulus, Sm, (IT-CY) at -10°C, 0°C, 10°C and 25°C. The parameters of the asphalt concrete compacted at 95°C made with FT wax modified foamed bitumen (FT=2.5%) are comparable to those of the reference mixture compacted at 45°C.

Foamed bitumen: an alternative way of producing asphalt mixtures

With the constant need to improve and make the production of asphalt mixtures more sustainable, new production techniques have been developed, the implementation of which implies the correct knowledge of their performance. One of the most promising asphalt production techniques is the use of foamed bitumen. However, it is essential to understand how this binder will behave when subjected to the expansion process. The loss of volume of the foamed bitumen could be translated by a decay curve, which allows to determine the ideal temperature and water content added to the bitumen in order to assure adequate conditions to the mix the bitumen with the aggregates. On the present study, a conventional 160/220 pen grade bitumen was tested by using different temperatures and water contents, and it was concluded that the optimum temperature for the production of foamed bitumen (with the studied bitumen) is 150°C, which corresponds to a viscosity of 0.1Pa.s. The water content mostly influence the half-life of the bitumen foam, resulting in quicker volume reductions for higher water contents.

The use of gabbro dust in the cold recycling of asphalt paving mixes with foamed bitumen

Abstract Mineral fines are a waste product of aggregate production in quarries and asphalt mixing plants. The incorporation of mineral gabbro dust into foam bitumen causes developing of a mesh reinforcement in the recycled base mixture. This mesh reinforcement, observed in a recycled base structure, induces an increase in stiffness modulus, where its elastic part of complex modulus dominates over the imaginary part. Therefore, it is possible to create a recycled mixture with a lower susceptibility to loading time/temperature. In result, the presence of gabbro dust in recycled mixture limits the magnitude of strains induced by the traffic load. This paper presents the results of the tests carried out on the mineral dusts derived from gabbro rock. Structural and functional properties of the fines were determined to prepare their characteristics. Then, the cold recycled mixtures for the road base were designed with the 5–20% mineral fines content. The mixtures were prepared in cold recycling technology with foamed bitumen. Further tests involved determining mechanical and physical properties of the recycled mixes, including air voids content, Marshall stability, Marshall quotient (stiffness), indirect tensile strength and stiffness modulus at 20°C). The results indicated a positive influence of the gabbro dusts on the investigated parameters. With the use of ANOVA tests, the significance of the influence of the gabbro dust and foamed bitumen on these properties was evaluated. Harrington’s multicriteria method was employed to establish gabbro dust and foamed bitumen amounts, the addition of which would guarantee optimal properties of the recycled base mixture.

Relation Degree Analysis of Controllable Factors in the Bitumen Foaming Process

Relation Degree Analysis of Controllable Factors in the Bitumen Foaming Process

A closer scientific look at foam bitumen

In the asphalt industry, a substantial interest is observed to find possibilities to reduce the production temperature of asphalt mixtures. In the context of this research, new methods for the visualisation of unstable bitumen foam, such as dynamic X-ray radiography, computed tomography (CT) and high-speed camera investigations, have been developed. Moreover, characterisation with empirical methods such as expansion ratio and half-life was determined accurately using ultrasonic measurements. This opens new possibilities to characterise bitumen foam (foaming process) for practical applications. Examination of the foam bitumen stream using a high-speed camera revealed that the foam bitumen contains fragmented pieces of bitumen, which resemble more a liquid than foam. This indicates that the foam is formed afterwards and not, as assumed, within the expansion chamber of the foam generator. In situ thermal imagery of the surface, during the hot foaming process, showed that the temperature distribution depends on the foaming water content (W.C.) and bubble size distribution. Higher W.C. results in more inhomogeneous temperature distribution as compared to lower W.C. (<2 wt%). The dynamic X-radiography results indicated that as the foam decays, the bubble size distribution becomes progressively larger with time for 160°C bitumen temperature. Furthermore, at the beginning of the foam formation, majority of the bubbles is small in cross-section size (0.2–10 mm2). At a later stage, the bubbles become polydisperse. Moreover, theoretical investigations based on the 3D X-ray CT scan data set of bubble merging show that the disjoining pressure increases as the foam film gets thinner with time and finally undergoes rupture. The speed of the bubbles also increases with time when the bubbles are getting closer to each other.

Complex modulus characterisation of cold-recycled mixtures with foamed bitumen and different contents of reclaimed asphalt

Cold-in place recycling with foamed bitumen (FB) is currently employed for the rehabilitation of road pavements, from local roads to heavy-duty motorways. The mechanical properties of FB mixtures may vary from that of an improved granular material to that of an asphalt concrete, depending on their composition. The objective of the present study was to characterise the linear viscoelastic (LVE) response of FB mixtures with different contents of reclaimed asphalt (50%, 70% and 0%). This objective was tackled by measuring the complex Young's modulus by means of uniaxial cyclic compression tests, in a range of temperatures (from −20°C to 55°C) and frequencies (from 0.03 to 10 Hz). The thermo-rheological behaviour was modelled using the Huet–Sayegh model, commonly used for bituminous mixtures. In order to focus on the influence of reclaimed asphalt content, the same grading and FB content were used for all the mixtures. In addition, an effort was made to produce mixtures with similar volumetric properties. Considering all the tested mixtures, the stiffness modulus ranged between 171 and 4075 MPa, whereas the phase angle ranged between 4° and 18°. Though these values are well below those normally measured on asphalt mixtures, the frequency and temperature variations clearly highlight a typical asphalt-like behaviour. In addition, the time–temperature superposition principle can be considered valid, regardless of the reclaimed asphalt content. Overall the experimental results showed that it is possible to characterise the LVE response of cold-recycled FB mixtures using the same experimental and analytical approach adopted for asphalt mixtures.

Rehabilitation by In-situ Cold Recycling Technique Using Reclaimed Asphalt Pavement Material and Foam Bitumen at Vadodara Halol Road Project (SH 87) – A Case Study

Cold Recycling Technology (CRT) of worn out bituminous pavement is a relatively new technology which has important application in the road surface treatment and paving towards green highway. Due to economic and environmental constraints like reduction in construction cost, preservation of aggregate and binder, etc, more attention is turning towards recycling of bituminous surface as an alternative to conventional pavement rehabilitation. The objective of this paper is to analyze flexible pavement with insitu cold recycling technique using Reclaimed Asphalt Pavement Material (RAP) and Foam Bitumen. As a case study, pilot project consisting of segregated stretches having major distresses and totaling 10 km length were selected on Vadodara Halol Road Project (SH 87) where cold recycling technique using reclaimed material and foam bitumen was used as a part of rehabilitation of flexible pavement instead of conventional overlay in order to achieve economy and executing within limited time period. Various field as well as laboratory tests are conducted and representative cores were extracted to investigate the pavement characteristics. The results of tests conducted on the cold recycling surface are very encouraging and adopted CRT is found to be economically viable also.

Evaluation of Additional Laboratory Tests for Design of Full-Depth Reclamation Mixtures Using Foamed Bitumen

The mix proportion design methods for full-depth reclamation mixtures using foamed bitumen normally fix a constant active filler content, and an indirect tensile strength (ITS) test is used to determine the optimum bitumen content. However, it has been reported in the literature that for some materials the ITS test is not sufficiently sensitive to bitumen content. This lack of sensitivity is a problem for the practitioner engineer who has to validate the bitumen content adopted in the mixture design. The main objective of this work is to examine the sensitivity to bitumen content of additional laboratory tests that could complement current design methods based on ITS. The mixtures used in the study were prepared by using three recycled blends of reclaimed asphalt pavement and aggregate that were mixed with bitumen foam contents of 1.25%, 2.5%, and 3.75%. Test results confirmed the low sensitivity of the ITS test, and it was found that the indirect tensile fatigue (ITF) test was the most sensitive among all tests. To explain the higher sensitivity of the ITF test compared with the ITS test, a stress–strain diagram and a simple unidirectional mechanical model were developed. In addition, an S-N fatigue diagram was used to illustrate that at a larger number of load cycles, the effect of the foamed bitumen content is clear, as shown in the experimental work. Overall, the laboratory program and material behavior analysis indicate that when the ITS test does not provide conclusive results, the laboratory program should be complemented with ITF tests to determine the optimum foamed bitumen content with more reliability.

Significance of RAP Content and Foamed Binder Content on Mechanistic Characteristics of Recycled Foamed Bituminous Mixes

To reduce the energy consumption and CO2 emissions during asphalt production, several environmentally friendly technologies have been developed during the last years. One of these technologies is the cold recycling by using foamed bitumen. Foaming the bitumen reduces the binder viscosity temporarily and increases the volume as well. Homogenous foams are produced by injection of cold water into hot bitumen. The paper presents the results of laboratory testing of the physical and mechanical parameters of the recycled mixes using the foamed bitumen and resistance to the action of water. The aim of the tests was to evaluate the properties of the mixes in terms of the RAP Content and Foam Binder Content. To evaluate the significance of impact of both factors i.e., Foam Binder Content and RAP Content on the distribution of the analyzed parameters, two-way Analysis of Variance (ANOVA) was performed. ANOVA Analysis results suggest that the RAP in cold mixes is not completely acting as black rock implying that some portion of the residual aged binder is possibly rejuvenated or softened by adding new binders.

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.