Hielscher Ultrasound Technology

Ultrasonic Mixing of Asphalt Rejuvenators

  • Asphalt rehabilitators and rejuvenators enable to recycle existing asphalt pavements by applying rejuvenating agents to the construction material.
  • Ultrasonic dispersers are a powerful technique to mix nano-particles and nano-droplets into asphalt and bitumen emulsions.
  • Power ultrasound is used to manufacture high-performance additives for long-term durable pavements.

Asphalt Rehabilitation

Ultrasonic mixing of asphalt additivesWeathered, dried, aged and cracked asphalt has lost its original tar oils and is damaged by oxidation, so that cracks, potholes and rutting in the wheel path occur on the surface. In regards to the huge amount of asphalt used in construction, the rehabilitation and rejuvenation of pavements and other asphalt structures is an important sector, which helps to save resources and expenditures.
Existing asphalt structures, damaged by weather, age and traffic load, can be rehabilitated and rejuvenated by the application of fog seals, slurry seals, chip seals, scrub seals, cape seals and other asphalt rejuvenators. Those seal formulations consist in a mixture of water, asphalt emulsion, aggregate (small gravel, also called chips), polymers, and nano-additives
Modified asphalt pavements that contain certain reinforcing nanoparticles exhibit desirable thermal, electrical and mechanical properties and have thereby improved functionalities. In order to reduce cost of asphalt binder and road maintenance and to increase their environmental-friendliness, alternative technologies such as ultrasonically blended and functionalized additives and new asphalt composite formulations, which have the capability of self-repair, are essential to preserve and renew existing pavements in the future.

Ultrasonic Production of Additives for Asphalt Emulsions

An asphalt emulsion consists of three main components: asphalt, water and an emulsifying surfactant. Being a stable dispersion of asphalt cement droplets in water, an asphalt emulsion can be pumped, stored and mixed with aggregates. An emulsion should “break” quickly upon contact with aggregate when mixed or after being sprayed. Breaking is the separation of the water from the asphalt. When the water has evaporated, the emulsion is “set”. After breaking, curing and setting, the asphalt residue has the adhesion, durability and water-resistance properties of the original base asphalt.
Ultrasonic emulsification allows to formulate high-quality asphalt emulsions
The ultrasonic emulsifying technique is compatible with multiple emulsifier and surfactant formulations. The choice of emulsifier impacts the setting characteristics of asphalt emulsions, making them slow setting, medium setting and quick setting. Additives, modifiers, fillers, fibers, rubbers and other formulation ingredients can be added during various stages of the sonication process – depending on the formulation and the mixing requirements of the specific compounds.

Ultrasonic disperser UIP4000hdT (4kW ultrasound power)

UIP4000hdT – 4000 watts ultrasonic inline mixer

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Emulsion Grade

The emulsion grade of an asphalt emulsion and asphalt rejuvenator is an important factor, that determines the breakup velocity (fast, medium or slow setting). The type (ionic / non-ionic) and concentration of the emulsifying agents as well as the formulation specifics such as emulsions/solids ratio, porosity, particles size and gradation influence the setting behaviour. Since ultrasonic emulsification parameters can be precisely controlled, the sonication impact on the emulsion can be adjusted to the targeted asphalt quality. Weather micron-, submicron or nano-emulsions are targeted, ultrasonic processing gives you the full control over the process parameters.

Rheology

Asphalt emulsions exhibit viscosities of approx. 50–1000 cP at 60°C, which is considerably lower than the viscosity of asphalt itself (10,000–400,000 cP). Due to their lower viscosity, asphalt emulsions can be applied using lower temperature techniques, which reduce emissions and energy consumption, avoid asphalt oxidation, and are considerably less hazardous than hot asphalt techniques. Furthermore, the application of asphalt emulsions is more economical and environmental-friendly than cold techniques using cutback asphalts. Viscosity and rheology of an asphalt emulsion emulsions can be influenced and adjusted by the emulsifier concentration and the energy input during ultrasonic emulsification.

Penetration Capability

The penetrating capabilities of asphalt rejuvenators are crucial, since a high-performance rejuvenating agent penetrates the pavement structure and seals the surface. A high-performance asphalt rejuvenator, which is able to penetrate deep into the asphalt binder (bitumen), increases the flexibility and restores from the inside so that a self-healing of the pavement achieved. Prepare highly functionalized asphalt emulsions formulating submicron- and nano-sized droplets with power-ultrasound!

Additives

Polymers, rubber, fillers, oils and rejuvenating agents are added to asphalt emulsions in order to improve the key properties of native asphalt, such as high and low temperature performance grading (PG), viscosity, low temperature cracking, ductility and stress relaxation, softening point and penetration, affinity for and stability with polymers and rejuvenation of aged asphalt in RAP/RAS mixes (reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS)). Ultrasonic dispersers mix solids and droplets as monodisperse particles into the asphalt emulsion. Ultrasonic mixing and blending technology produces high-performance asphalt mixtures!

Master Batch

Ultrasonic emulsification and dispersion is ideal to prepare master batches of highly concentrated asphalt emulsions. Ultrasonically prepared emulsions with high asphalt content (up to 90%) are diluted later to reach 70% or 60% concentration in order to reach the desired water/oil phase ration according for the final application.

UIP16000 (16kW) is Hielscher's most powerful ultrasonic extraction equipment.

UIP16000 – 16kW ultrasound power per ultrasonic mixing unit

Advantages of Ultrasonic Asphalt Emulsions

The ultrasonic mixing technology allows to develop and produce asphalt rejuvenating formulations which are easy to handle, cost-effective and environmental-friendly. Powerful ultrasonic cavitation creates sub-micron and nano dispersions and emulsions, which exhibit excellent penetrability, high-performance, and long-term endurance.
Mix your paving emulsions and dispersions for asphalt mixtures by high-power ultrasonication!

High-Power Ultrasonic Disperser for Asphalt Emulsions

UIP4000hdT flow cell for inline sonication on industrial scaleHielscher Ultrasonics manufactures and supplies high-power ultrasonic mixers for asphalt and bitumen emulsions. Industrial ultrasonic dispersers for inline emulsification offer opens the possibility to process a wide range of asphalt and bitumen emulsions. Sonication allows for the facile testing of new formulations, which are uniformly emulsified for excellent emulsion stability and performance. Various ultrasonic reactor geometries and inserts such as the MultiPhaseCavitator allow for the easy adaption of the ultrasonic processor to your specific asphalt or bitumen formulation.
A coarse premix of liquid and solids is fed into the ultrasonic disperser, where the both phases (water + asphalt or bitumen + optional additives) are wet-milled and grinded uniformly into a highly stable colloidal suspension. Ultrasonic milling and dispersing is capable to process high volumes in a rapid process.

The table below gives you an indication of the approximate processing capacity of our ultrasonicators:

Batch Volume Flow Rate Recommended Devices
10 to 2000mL 20 to 400mL/min UP200Ht, UP400St
0.1 to 20L 0.2 to 4L/min UIP2000hdT
10 to 100L 2 to 10L/min UIP4000hdT
n.a. 10 to 100L/min UIP16000
n.a. larger cluster of UIP16000

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Hielscher Ultrasonics manufactures high-performance ultrasonicators for sonochemical applications.

High-power ultrasonic processors from lab to pilot and industrial scale.

Literature/References

  • Wang, H.; Yang, J.; Gong, M. (2016): Rheological Characterization of Asphalt Binders and Mixtures Modified with Carbon Nanotubes. RILEM Conference Papers 2016.
  • Ronald, M.; Pumarejo Luis, F. (2016): Asphalt emulsions formulation: State-of-the-art and dependency of formulation on emulsions properties. Construction and Building Materials 123, 2016. 162–173.


Facts Worth Knowing

What is an Asphalt Emulsion?

An asphalt emulsion is a mixture of water and asphalt. Since asphalt is an oily, hydrophobic compound, it cannot be mixed with water. By adding a surface active agent also known as emulsifier, surfactant, emulsifying agent, stabilizer) to the water before or during adding the asphalt, the asphalt and water become mixable. The addition of surfactant facilitates the dispersion of asphalt particles in the aqueous phase (water) and keeps it dispersed in suspension. To mix the asphalt as small particles into the suspension, mechanical shear mixing equipment (e.g ultrasonicatior, high-shear mixer, colloidal mill etc.) are used. A high-quality asphalt emulsion gives the pavement rutting resistance, moisture susceptibility, cracking resistance and fatigue performance.
Definition of Emulsion
“An emulsion is a heterogeneous system thermodynamically unstable formed by at least two immiscible liquid phases, where one is dispersed in the other in form of little droplets (beads) whose diameter is generally higher than 0.1µm. Such a system has a minimum stability which could be improved by addition of appropriate agents, such us surfactants, or finely solid divided”. (Becher, P. Emulsion. Theory and Practice. 1961.)

What is Bitumen?

Bitumen is a cementitious material used in construction as asphalt binder, that hold the asphalt together. It has a melting point of 180ºC. Bitumen emulsions are a dark brown liquid, which can be either cationic, where emulsions have droplets which carry a positive charge, or anionic, where emulsions have negatively charged droplets.

What are Slurry Seals?

Slurry seals are a formulation of water, asphalt emulsion, aggregate, and additives to an existing asphalt pavement surface. A slurry seal is similar to a fog seal except the slurry seal has aggregates as part of the mixture. Polymer is common additive that improves the asphalt emulsion’s properties. This combined mixture of the emulsion and aggregates is the so-called slurry in order to protect the underlying pavement structure and to provide a new roadway surface.

What are Fog Seals?

Fog sealing refers to the application of a special formulated asphalt emulsion to an existing asphalt pavement surface. A fog seal emulsion consists in a water-oil mixture, which can be easily sprayed onto an existing pavement, also known as “fogging.”

What are Chip Seals?

The application of a chip seal involves an asphalt emulsion that contains globules of paving asphalt, water, an emulsifying agent or surfactant, polymer, and often a rejuvenator additive. CHip seals are applied in a two-step process which includes first the distribution of the asphalt emulsion and subsequently a layer of small crushed rock to an existing asphalt pavement surface. The small crushed rock is also called “chips”, which gives the chip sealing method its name.

What are Scrub Seals?

A scrub seal treatment is very similar to the chip sealing, where an asphalt emulsion and crushed gravel are used to rehabilitate a damaged asphalt pavement. The only difference is the application method: For the application of a scrub seal , the asphalt emulsion is applied by so-called scrub brooms, which ensure that the asphalt emulsion penetrates the pavement crackings.

What are Cape Seals?

Cape sealing refers to the application of a chip or scrub seal with a subsequent application of slurry seal or microsurfacing at a later date. Whilst chip or scrub seals seal and bond the cracks in the existing pavement, the subsequent slurry seal or microsurfacing improves the chip retention and smoothness of the roadway surface. Cape seals a re mostly used as an intermittent workaround, used for asphalt structures which exhibit only moderate distress, slight or no ruts, moderate crack widths. Cape sealing is mostly used as remedy to extend the pavement life until rehabilitation or reconstruction is performed.

What is Microsurfacing?

Microsurfacing is treatment comparable to a slurry seal. For microsurfacing, a formulation consisting in water, asphalt emulsion, aggregate, and chemical additives is applied to the surface of an asphalt concrete pavement. Polymer additives are used to improve the mixture properties of the asphalt emulsion. The major difference between slurry seal and microsurfacing is in how they “break” or harden. Whilst the slurry sealing requires that the water evaporates from the asphalt emulsion after its distribution, the asphalt emulsion in a microsurfacing coating contains chemical additives which allow it to break without relying on the sun or heat for evaporation to occur. This makes microsurfacing the preferred treatment for heavily used roads (short time to break) or colder climate.

What is Causing Pavement Deterioration?

As pavement ages it starts to deteriorate. How quickly it breaks down is influenced by many factors. The primary factors are the environment and traffic loadings. Sunlight over time oxidizes the surface layer and causes it to become brittle. If the pavement is too brittle cracks start to form as a result from high repetitions of traffic loading on the pavement. If the pavement is not sealed properly, rainwater or irrigation water can infiltrate the cracks into the base layer and damage the structural integrity of the pavement. Water can erode or wash away the underlying base layers and cause the pavement to fail from lack of support.