FOAMED BITUMEN: AN EXCELLENT ADDITIVE IN RECYCLING

FOAMED BITUMEN OVERVIEW - A GLOBALLY RECOGNIZED ADDITIVE

A Binding Agent with Great Potential

Cold recycling with foamed bitumen has become a globally utilized technology and is now gaining attention from road authorities and construction companies for its application in road rehabilitation and new construction.

Cold recycling with foamed bitumen creates a highly stable and flexible base layer. As part of the pavement structure, it forms an ideal foundation for the asphalt surface layer while reducing the required asphalt thickness. The foamed bitumen used is produced at 175°C from hot bitumen using an advanced technology. The microprocessor-controlled injection system, installed in Wirtgen's recyclers, generates foamed bitumen and injects it into the material for binding with precisely metered quantities.

Foamed bitumen is injected into the mixing chamber with precisely metered quantities thanks to a special injection system. Microprocessors control this process across the entire working width, adhering to the working speed and depth of the recycler.

Producing foamed bitumen

Foamed bitumen is produced in accordance with standards for road construction bitumen. In this process, a small amount of water and air is injected into hot bitumen under high pressure. This results in the bitumen foaming and expanding to approximately 20 to 80 times its original volume. The foamed bitumen is then injected into the mixing chamber through nozzles. It is ideally suited for moist and cold materials.

New material is frequently produced using reclaimed asphalt pavement (RAP). This is referred to as BSM (bitumen-stabilized material).

A perfectly engineered process:

- Durable layers

- Economical

- Resource-saving

- Reduced CO2 emissions

- Reduced construction time

Projects around the world

Foamed bitumen technology is a reliable solution for road rehabilitation, even in desert environments. A continuous train of transport vehicles operates in Saudi Arabia on a total stretch of more than 380 km.

At this job site, cement is pre-spread on the road surface before the WR 2500 begins its work. The machine's appropriately sized engine allows it to easily push and pull the truck carrying the hot bitumen and water during the recycling process.

The WR 2500 is also used in the New World: customers in the USA are among those benefiting from Wirtgen's foamed bitumen technology.

WHAT IS BITUMEN? HOW IS FOAMED BITUMEN PRODUCED?

Bitumen is a highly viscous, black, sticky organic liquid primarily used in road construction. It can be classified into three main types: petroleum bitumen, shale oil bitumen, and natural bitumen.

Foamed bitumen is produced by adding a small amount of water (~2-3% by weight of bitumen) to hot bitumen. The waterproofing bitumen grades used are B60 to B200, typically employed in hot mix asphalt for construction applications. Therefore, bitumen and asphalt are closely related.

In WIRTGEN's plants, when water is injected into hot bitumen, it vaporizes abruptly, causing the bitumen to foam and expand. This expansion is 15 to 20 times the original volume, and the foamed bitumen is then immediately mixed with the materials to be treated.

The small amount of water triggers a reaction with the hot bitumen, leading to a sudden expansion in the bitumen's volume.

The intensity and effectiveness of the foaming process can be optimally controlled by managing the operating process based on fundamental physical conditions, such as pressure and temperature. In Wirtgen machines, this process takes place in separate expansion chambers where water is injected into the hot bitumen (at a temperature of approximately 180°C and a pressure of approximately 5 bar). The foamed bitumen is thus produced on site, exiting the expansion chamber through nozzles and immediately mixed with the mineral aggregate to be treated.

Taking pressure and temperature into account, foamed bitumen of the highest quality is produced in the expansion chamber..

Properties of Foamed Bitumen

The key parameters for determining the properties of the final foamed bitumen product are "expansion" and "half-life."

"Expansion" is defined as the ratio between the maximum volume reached by the foamed bitumen and the initial volume of the unfoamed bitumen. As a rule, the expansion of foamed bitumen is approximately 15 to 20 times the original volume.

"Half-life" is defined as the time it takes for the foamed bitumen to reduce in size from its maximum to 50%, or half of the expansion. After a certain time, the foamed bitumen will contract. The half-life is measured in seconds and typically ranges from 10 to 15 seconds.

As a general rule: the greater the expansion and the longer the half-life, the better the quality of the foamed bitumen.

Important for assessing the quality of foamed bitumen: When the percentage of added water increases, the parameters "half-life" and "expansion" develop in opposite directions.

Producing Foamed Bitumen in Wirtgen Recyclers

Another important parameter for the quality of the bitumen binder is the use of injection bar technology. Particular importance has been placed on certain application-specific features when designing the high-quality injection bars in Wirtgen machines.

A heater controlled by a thermostat ensures optimal operating temperature of the system before and during the foaming of the bitumen. This minimizes the need for cleaning the system during production interruptions or after completion of work.

Technology for the foaming process: The tank is electrically heated with thick insulation, keeping the bitumen at the optimum processing temperature throughout.

Bitumen is foamed in separate expansion chambers, with bitumen injection nozzles across the entire working width. A microprocessor controls the foaming process and the addition rate across the working width, working depth, pre-set mixing ratio, and material density. Water and air are injected through separate nozzles.

The microprocessor controlling the foamed bitumen production process in Wirtgen machines precisely meters and injects water, bitumen, and air.

The injection bars located directly above the milling and mixing chamber of the Wirtgen WR 2500 recycler consist of 16 injection nozzles with expansion chambers where the hot bitumen is foamed and then evenly sprayed across the entire working width.

Activated by compressed air, a control circuit with pistons cleans each nozzle regularly during the injection process, preventing clogging due to contamination. At the same time, the nozzles can be individually shut off to reduce the injection quantity and the mixing width.

Safe operation is ensured at all times indirectly via pneumatically controlled pistons. The control circuit guarantees that the hot bitumen flow is not affected.

The bitumen injection nozzles can be shut off from the operator's cabin to quickly and automatically reduce the spraying width. This is a necessary requirement for overlapping purposes. Note that the injection rings are deactivated by the microprocessor in a targeted manner to reduce the amount of binder added, ensuring that the percentage of binder added remains constant.

During the foaming process, foam samples can be taken from an external inspection nozzle to check and optimize the foam properties (expansion and half-life).

Testing the foam properties in Wirtgen's laboratory

To optimize the foam properties, tests can be carried out to check the suitability of the bitumen using the Wirtgen WLB 10 laboratory foamer before starting work on the job site.

To determine the optimum conditions during the foaming process, test runs are carried out with varying bitumen temperatures and quantities of added water. After the properties of the foamed bitumen have been optimized, the foamed bitumen can be injected directly into the aggregate placed in the laboratory mixer. This foamed bitumen-treated material is used to produce test specimens for verification of suitability.

With the WLB 10 mobile foamed bitumen laboratory manufactured by Wirtgen, the properties of the foamed bitumen can be tested before the project begins.

USING FOAMED BITUMEN AS A BINDER FOR COLD RECYCLED MATERIALS

Types of Applications

Foamed bitumen is a versatile binder that can be used for a variety of materials of different origins and types. Milled asphalt, RAP, contaminated road material, or natural gravel can be treated with foamed bitumen and used for road construction or rehabilitation. Roads with unbound gravel surfaces, experiencing reduced trafficability due to dust or becoming soggy after rain, can be successfully treated with foamed bitumen.

Cold in-place recycling with foamed bitumen is a cost-effective alternative to new construction. Cold recyclers mix the foamed bitumen into unbound layers of gravel. This not only improves the load-bearing capacity of the road but also increases its service life. The recycled pavement layer should be sealed with a surface treatment or a thin asphalt layer.

A large variety of mineral aggregates are suitable. Thanks to the addition of foamed bitumen, aggregates of different types can be transformed into high-quality base course material.

Suitability of aggregates used in the process

Well-graded aggregates with a satisfactory gradation from fines to coarse particles are required for treatment with foamed bitumen. A sieve analysis will help determine whether additional aggregate needs to be added. For example, if the mineral aggregate lacks fines (at least 5% passing the 0.075 mm sieve), 0/2 crushed aggregate with a high fines content may need to be added. When using foamed bitumen as a binder, the fines content in the aggregate is crucial.

The foaming process leads to an increase in the surface area of the bitumen and a simultaneous reduction in viscosity. The dispersion properties are thus improved, ensuring that the fines in the aggregate are completely coated. The fines and the foamed bitumen form a rigid bond with the coarse aggregate.

Example of a sieve analysis of a suitable aggregate to be used with foamed bitumen as a binder.

Properties of Cold Recycled Material

The suitability of cold recycled materials bound with foamed bitumen is usually checked by means of the indirect tensile strength test on Marshall specimens. The specimens are dried and then tested in a dry and a soaked condition.

Typical values resulting from the indirect tensile strength test usually lie within the following ranges (with the addition of approximately 1.5 - 4.5% foamed bitumen and 1 - 2% cement):

Typical values for the modulus of elasticity of materials stabilized with foamed bitumen and cement:

HISTORY OF FOAMED BITUMEN TECHNOLOGY

Wirtgen - A Pioneer in Foamed Bitumen Technology

In 1956, Professor Ladis Csanyi of Iowa State College first recognized the suitability of foamed bitumen as a binding agent. The technology was later refined by Mobil Oil, which developed the first expansion chamber where bitumen was mixed with water to create foamed bitumen.

Wirtgen took on a leading role in this technology in the 1990s with its improved binder. Integrating this system into Wirtgen recyclers in 1995 finally brought the benefits of this technology to the forefront.

The WR 2500 was the first recycler to incorporate this technology. In 1997, Wirtgen developed the WLB 10 - Foamed Bitumen Laboratory - to enable the production of foamed bitumen in the laboratory. Over 300 laboratory units have been sold worldwide, used by contractors, construction material testing laboratories, institutes, universities, and consulting engineers. Today, Wirtgen offers customers state-of-the-art cold recyclers equipped with foamed bitumen technology for both on-site and in-plant applications.

A Globally Established Technology

The success and acceptance of this technology in over 90 countries and in almost all climatic conditions reflect the high degree of acceptance of foamed bitumen as a binder. This technology is suitable wherever pavements are subjected to high traffic loads or where construction requires high load-bearing capacity and cost-effectiveness.

Foamed bitumen technology offers a truly sustainable solution for both rehabilitation and new construction projects.

Mixtures with foamed bitumen are building materials capable of meeting very high demands. The use of this innovative binder has enabled over 2500 Wirtgen recyclers of various types to withstand the challenges of working in all climates and on roads with very high traffic volumes, and they are still in use worldwide today.

FOAMED BITUMEN PRODUCTION IN THE LABORATORY

Pre-determining the properties of foamed bitumen

A small amount of water causes a sudden increase in the volume of hot bitumen (foamed bitumen). The WLM 30 laboratory-scale twin-shaft compulsory mixer is suitable for batches of 25 kg and particularly for high mixing intensity.

Preliminary testing with the WLB 10 S mobile foamed bitumen laboratory allows the quality of the foamed bitumen to be precisely determined in the laboratory before starting work on the construction site. The extremely simple handling procedure makes it possible to vary parameters such as water content, air pressure, and temperature quickly and easily.

The quality of the foamed bitumen is primarily expressed in terms of the expansion ratio and half-life.

With the WLB 10 S mobile foamed bitumen laboratory and the WLM 30 twin-shaft compulsory mixer, we have incorporated many years of practical experience into this state-of-the-art laboratory technology. These machines allow for comprehensive sample testing in a very short time.

The mix that makes all the difference

The WLB 10 S foamed bitumen laboratory is used for:

- General testing of commonly used bitumen types to determine their suitability for the foaming process.

- Optimizing the foaming process by varying the temperature and the amount of water added.

- Producing mixes in the laboratory using different bitumen application rates.

To carry out the mix production process in the laboratory, the WLB 10 S is directly connected to the WLM 30. The foamed bitumen produced by the WLB 10 S is then injected into the aggregate during the mixing process taking place in the WLM 30. The material is mixed homogeneously and without any losses. The mix is produced quickly on the basis of the test specimens.

PROPERTIES OF BITUMEN-STABILIZED MATERIAL (BSM)

Aggregates treated with foamed bitumen are distinguished by their optimum load-bearing capacity and durability.

Material Structure

The cold mix produced with foamed bitumen behaves like a bound building material with constant intergranular friction but significantly increased cohesion (adhesive strength) and stability. This type of material is referred to as BSM (bitumen-stabilized material).

The BSM mix does not coat the aggregate but forms a homogeneous mass of bitumen binder and aggregate. The bitumen content is typically in the range of 1.5% to 2.5% by weight of the mixed material. After final compaction, the material is characterized by its flexible properties and high load-bearing capacity. This technology has gained worldwide recognition.

Using BSM on the job site

Properties of Bitumen-Stabilized Material (BSM)

Easy workability is one of the distinguishing features of the BSM mix. Provided there is sufficient moisture, there are no limits to the number of passes for subsequent compaction. However, another important point is that the BSM layer can be opened to traffic immediately after completion of the rolling operation.

In some cases, the cold recycled layer is overlaid with a thin asphalt layer, which acts as a wearing course. Any intervention to maintain the road is then concentrated mainly on the asphalt surface layer, avoiding any impact on the cold recycled layer. This keeps road maintenance costs low.

USE ON THE CONSTRUCTION SITE OR IN THE PLANT

Versatile binder

Cold recycling with foamed bitumen can be carried out either on the construction site (in-place) or in a plant (in-plant).

In-place cold recycling: The recycler mills the damaged asphalt pavement into small pieces and simultaneously mixes it with foamed bitumen, water, and cement in the required proportions. This method creates a new, homogeneous BSM in a single operation. In-place cold recyclers are equipped with powerful milling and mixing rotors and a high-performance injection system. Some models also feature a paving screed for placing and pre-compacting the new mix.

In-plant cold recycling: The pavement material is removed and transported to a mobile cold mixing plant located near the construction site. The milled material is then processed with foamed bitumen, water, and cement in the required quantities to create a new and homogeneous BSM cold mix. This reclaimed material can be immediately placed in the correct lane and layer thickness or stored for later use.

The powerful twin-shaft continuous mixer installed in the KMA 220 mixes the milled material and foamed bitumen injected into the process.

The KMA 220 cold mixing plant upgrades the different materials to produce a high-quality cold mix (BSM).

Advanced Injection System

Absolute quality is ensured by the thermostatically controlled heating system, which maintains the set operating temperature of the entire injection system at all times, including before and during the production of foamed bitumen. This ensures balanced distribution to the systems after operational breaks or at the end of the working day.

The application rate or foaming process is controlled by a microprocessor controller.

COLD MIXES CONTAINING FOAMED BITUMEN

Construction site building material

In general, all granular building materials and RAP are suitable for recycling with foamed bitumen. Wirtgen recyclers mill both the asphalt layer and the underlying base course into small pieces and mix them with foamed bitumen on site in a single operation. After compaction, a high-quality bitumen granulate is produced which is notable for its very high load-bearing capacity.

RAP in the plant

RAP reclaimed by cold milling machines can be processed immediately after milling or stored in stockpiles for an extended period.

The Wirtgen KMA 220 mobile cold mixing plant uses this material to produce cold mix in the plant for reuse by Vögele pavers.

New and reclaimed materials

Materials reclaimed from existing pavements, recycled materials, and new materials can be processed using appropriate crushing and screening technology to obtain a mix that is then mixed with foamed bitumen in the KMA 220 cold mixing plant. All road construction materials with a suitable mix composition can be recycled with foamed bitumen.

Laboratory Testing

The performance of laboratory-produced specimens from the previously created mix is checked by means of design specimen testing.

The optimum mix formula usually consists of 1.5% to 2.5% by weight of bitumen and 1% by weight of cement. The application rates of foamed bitumen and cement must be optimally matched.

EXAMPLES OF BSM LAYERS IN PAVEMENT STRUCTURES

Low overall costs

The CR 3800 cold recycler is recycling an asphalt layer with bitumen emulsion, transferring the recycled mix to a Vögele paver. The homogeneous asphalt mix is processed by the WR 240 cold recycler.

The pavement structures shown in the diagrams are examples of three different types of construction projects. These construction methods are particularly economical from the point of view of construction costs due to the low binder requirement, the use of RAP, and the rapid completion times. The reduced thickness of the asphalt pavement leads to significant cost savings.

In addition, maintenance costs are also low. Unlike conventional asphalt layers, the BSM layer is not susceptible to cracking. Maintenance requirements are limited to the upper, thin asphalt surface layer, which only needs to be replaced at certain intervals. Costly replacement of the asphalt pavement over its entire depth is not necessary. Due to the advantages offered by this construction method and its exceptional material properties, bitumen-stabilized materials are widely used in Public Private Partnership (PPP) projects.

FOAMED BITUMEN - DIVERSE APPLICATIONS FROM ONE MATERIAL

Cold recycling is a fast and efficient road construction method. It offers short construction times, the ability to recycle existing layers, and rapid return to service. Simultaneous injection of foamed bitumen and cement slurry is performed by the WR 240 cold recycler.

Bitumen is available worldwide and is added to the mixing process after being foamed at a temperature of approximately 175°C. In-place cold recycling is carried out using the CR 2200 cold recycler and the WM 1000 slurry mixer.

100% Reusability

Because foamed bitumen offers numerous advantages, it plays a prominent role among binding agents. Adding foamed bitumen to granulated asphalt makes it possible to recycle the material almost 100%, even in cold conditions. Processing without heating the material results in minimized CO2 emissions.

Low application rates of only 1.5% to 2.5% by total weight reduce costs. Road construction bitumen is available worldwide and is suitable for immediate use without further processing. Paving material mixed with foamed bitumen can be placed, compacted, and immediately opened to traffic. This minimizes construction time and traffic disruption.

PERSPECTIVES ON FOAMED BITUMEN TECHNOLOGY FOR THE VIETNAMESE CONSTRUCTION INDUSTRY

Eco-friendly road rehabilitation

Protecting the environment and ensuring profitability are not mutually exclusive goals. This is confirmed by the efficient foamed bitumen technology applied in conjunction with environmentally friendly Wirtgen machine technology.

The process utilizes recycled material with the addition of binding agents. In addition, fewer trucks are needed to transport materials, reducing environmental pollution compared to new construction.

- Materials for constructing bound and unbound roads are 100% recycled.

- The number of trucks required for transport to and from the construction site is reduced by up to 90%, relieving pressure on the road network.

- Recyclers complete several process steps in a single machine.

- Fast and efficient construction method, minimizing construction time and traffic disruption.

- Saves 10-12 liters of fuel per ton of paving material compared to conventional rehabilitation methods (hot mix).

- Reduced fuel consumption and emissions thanks to advanced engine technology with intelligent control systems.

- The KMA 220 mobile cold recycling plant allows for in-plant processing close to the project site, minimizing environmental impact.

COMPREHENSIVE RANGE OF MODERN SUPPORT SERVICES

The exchange of experience during site visits has helped convince road construction authorities.

Trade presentations, practical demonstrations, articles in trade journals, and expert lectures have created awareness, making foamed bitumen a technology that is now firmly established worldwide.

Wirtgen specialists provide individual, customized application support on site. Machine operators worldwide are trained and supported on the job site by experienced training specialists.

Wirtgen - Always at the Forefront of Innovative Technologies

The company sees itself as an enabler of highly efficient cold recycling technology. In addition to the machines required for the process, it offers its customers an all-round service. Close cooperation with users in this field provides the impetus for further development of the equipment. The company then shares its experience in the field to help customers exploit the advantages offered by this open market.

Consulting services for specific projects and training courses at different levels for target groups are other key points that ensure the project is carried out cost-effectively.