Benefits

Many kinds of research efforts demonstrate that by modifying bitumen with polymer additives we can make a PMB – polymer modified bitumen, which under stress behaves as reinforced material. Included additives are structure-forming; they disperse or create their own structure in the bitumen. The polymer frame limits, on the one hand, flow at higher temperatures and brittle at lower temperatures, on the other hand, increasing the range of application of polymer materials. Nowadays, compounding bitumen with polymer modifiers is one of the most promising methods of making high-quality bitumen materials used for construction applications.

The market shows that polymer modified bitumen materials are in high demand. PMB is a highly customized product, made for a specific client, more expensive than straight bitumen, but vastly more efficient. PMB is different from regular bitumen in terms of stability under temperature variations, resistance to rutting and better adhesion. A correctly done PMB can serve as long as 20 years. The market share of polymer modified bitumen in Europe is 10%, with a 15% share in China and the United States, including Alaska, the coldest state, where PMB holds 48% of the market, yet another proof of its stability.

Composition properties

The first production of PMB began in the 1960s. Polymers are very efficient in regulating the dispersed structure of bitumen binder. Polymers used as additives with bitumen are classified as organic or heteroorganic compounds of one of four types: rubber line polymers and elastomers, thermosetting plastics and thermoplastics. The most common additives in road construction bitumen are elastomers and thermoplastics. The latter has the ability to transition into a highly elastic state and back, depending on the temperature.

There are certain important criteria polymers must meet to be efficient in bitumen modification. Polymer macromolecules must have a tendency to associate and immobilize the maximum volume of the dispersed medium. A polymer must also be able to distribute well in bitumen without losing its structure and form a network in bitumen to remain strong at high and elastic at low temperatures.

If polymer concentration in bitumen grows to approximately 12% and above, the phases are inverted, i.e. bitumen becomes the filler, while the polymer becomes the matrix material. The properties of such a system are close to the properties of the polymer; that is, flexibility and elasticity increase by two orders of magnitude, fatigue properties are improved, etc.

Production

The necessary condition of PMB production is the ability of a polymer to dissolve or swell in bitumen. Therefore, the methods of production are based either on dispersing the polymer in bitumen at high temperatures or dissolving the polymer in a solvent and then mixing the solution with bitumen.

An analysis of the known PMB production processes shows that of all them involve high process temperature (150-200оС) and intensive stirring of the ingredients. Most polymers decompose at a temperature much higher than the process temperature, so polymers remain practically intact. It should be noted that the structure of PMB usually remains the same even after cooling. This is due to the sharp increase of PMB viscosity at lower temperatures, which prevents the separation of the ingredients. At room temperature and under normal operating conditions PMB is usually a micro- or macroheterogenic system, i.e. a composite material. Of all polymer types, only two are commercially successful in the polymer bitumen modifier market: thermoplastics and thermoelastic rubbers. The former group is represented most by atactic polypropylene (APP), a byproduct of isotactic polypropylene production. The other type of polymers is represented almost exclusively by block copolymers styrol butadiene styrol (SBS). However, the seasonal nature of demand, small production volume, and other factors limit the large scale production of some polymer bitumen materials at oil refineries. GlobeCore company manufacture equipment for the production of any type of PMB, allowing to produce it with the different available materials.

About a hundred years ago, oil residues were treated with sulfur to produce sulfated bitumen. But the introduction of an air-purified bitumen production technology significantly reduced the usage of sulfur in this area.

This chemical element is able to remove hydrogen and turn ordinary links into double links. The unsaturated compounds formed are polymerized with time.

When sulfur is added to bitumen, its content in asphaltenes increases significantly. It is affected by both the amount of added substance and the duration of the mechanical effect and heating.

The addition of sulfur during the production of road concrete mixtures considerably improves the adhesion properties of bitumen. At the same time, the production of sulfur-bitumen mixtures causes emissions of harmful gases generated by heating. This problem needs to be solved if sulfur is selected as the bitumen modifier.

Lots of countries use cheap and affordable sulfur to create highways with sulfuric bitumen binders to reduce inefficient bitumen consumption. In some cases, the sulfur content in building mixtures can reach 60-70%. A good example is a sulfex plasticized hydrocarbon coating.

Properties of sulfur-modified bitumen are determined not only by sulfur as a chemical element, but also by its injection temperature, content and duration of mixing.

Studies show that sulfur combines with bitumen better at the temperature 100-120° C. The form of modification (powder, alloy, etc.) does not affect the properties of the finished product.

In general, perfect conditions for the sulfur modification are as follows:

• process temperature: 120-140⁰ С;
• mixing time: 10-20 minutes (depends on the amount of modifier introduced);
• sulfur content: 5-7%.

As you could notice, the required temperature of bitumen for the production of asphalt mixture is 160⁰C. Modification at this temperature will lead to the formation of hydrogen sulfide and sulfur oxides. That is why bitumen must be cooled to 120 ° C before modification, which may be somewhat inconvenient.

In the USA and Canada, a sulfur-bitumen mixture is widely used as a binder in asphalt mixtures. Sulfur content improves durability, theramal resistance, cracking resistance, adhesion and chemical resistance. In addition, the use of this material reduces the thickness of the asphalt coating and the consumption of bitumen.

During road construction works tack coat is an important step that is made in order to prepare the surface for asphalt concrete or for surface treatment. Such measures ensure reliable traction between layers. Priming can be done with emulsion or liquid bitumen. The emulsion huge benefit is its low viscosity. This allows an even distribution over the surface and a 20-30% economy of bitumen.

The main three purposes of surface treatment are:

• to restore traction between vehicle wheels and the road;
• to create a wear layer.
• renewal of road waterproofing;

The perfect conditions for surface treatment are dry weather with daily average temperatures above 10 °С. The specific type and method of treatment are selected depending on the traffic load and the condition of the surface:

• single-layer dressing (binder/macadam);
• double-layer dressing (binder/macadam/binder/macadam);
• single-layer dressing with double macadam application, binder/macadam/macadam;
• sandwich-type treatment (macadam/binder/macadam).

The consumption amount of emulsion and macadam depends on the type of surface treatment, emulsion concentration, and macadam size. The machines used in the process are motorized binder spreaders, aggregate spreaders (towed or attached) and combined or pneumatic asphalt compactor rollers. The number of compactor passes required for a proper result is usually three to five, and compaction speed is 3 kph for the first three passes and 10 kph subsequently. Compaction should only be started when the emulsion begins to breakdown. The sign for that is a change in the color of the emulsion from brown to black.

Single-layer dressing with double macadam layers are both compacted after each macadam layer is applied.

The double surface treatment layer is only compacted after the second macadam layer is applied.

Sandwich type layers are compacted immediately after the application of the second macadam layer.

The quality of the surface treatment depends on the weather conditions, traffic loads, traffic speeds and the timely measures taken to ensure normal settling conditions, such as:

• the road is opened for traffic one hour after final compaction, with the speed limited to 40 kph in the first seven days.
• excess macadam on the surface must be removed by mechanical brushes to prevent the destruction of the forming layer structure.
• the final formation is complete in the first six weeks after making the layer at a minimum midday temperature of +10 °С.

If the temperature of the surface exceeds 35°С during treatment and it is possible that macadam may be dislodged from the layer, small macadam is distributed across the surface (2-5 mm) to prevent the binder from sticking to vehicle wheels and protect the surface dressing. The amount of such macadam application is 2-4 kg/m2.

Bitumen emulsions are usually made using a colloid mill, although other dispersion devices are possible. In the colloid mill energy is applied to the system by passing the mixture of hot bitumen and water  phase between a rotating disc, cone or flywheel and a stator. The rotor as well as stator may be grooved or have teeth in order to create a turbulent flow.

Bitumen emulsion can be produced either in a batch or an in-line process plant. The batch process involves at least two process stepswater phase (soap) preparation and the actual emulsion production. The water phase is prepared in a tank into which heated water, emulsifier and other emulsion chemicals are metered and the solution properly mixed. In the emulsion production process the bitumen and the pre-made water phase are dosed to the colloid mill. If solvent is to be added to the bitumen, then a batch tank is needed for bitumen as well, or the solvent must be dosed in-line.

In the batch plant the emulsion production itself involves only a few material  flows, which allows manual process control. However, proper metering of the various components are decisive for the quality of the emulsion and automatic or semi-automatic control will make the manufacturing more efficient and reduce human error.

Furthermore, the chemicals used may be hazardous as well as corrosive, which means closed dosage systems rather than open tanks and portable pumps are preferable in order to ensure safe work and environmental conditions.

In the in-line process the water heating and all material dosage are done continuously using individual dosage pumps for each material. No batch tanks are used. Instead, the water phase system must further be designed to provide sufficient reaction time for the chemicals so that adequate neutralization and solution take place before the water phase meets the bitumen.

The process needs to be automatically controlled using flow meters for all material dosage except acid, which should be controlled by the pH in the water phase. Various special additives such as latex, SBS or bitumen dope may be used and will then require special components and technical solutions. Latex for example is shear sensitive and may coagulate in pumps and lines. SBS modified bitumens usually require the emulsion to be produced above the boiling point of water, which requires production under pressure and cooling before release to atmospheric pressure in the storage tank.

Heavy oil and natural bitumen are oils set apart by their high viscosity (resistance to flow) and high density (low API gravity). These attributes reflect the invariable presence of up to 50 weight percent asphaltenes, very high molecular weight hydrocarbon molecules incorporating many heteroatoms in their lattices. Almost all heavy oil and natural bitumen are alteration products of conventional oil. Total resources of heavy oil in known accumulations are 3,396 billion barrels of original oil in place, of which 30 billion barrels are included as prospective additional oil. The total natural bitumen resource in known accumulations amounts to 5,505 billion barrels of oil originally in place, which includes 993 billion barrels as prospective additional oil.  When natural bitumen is mobile in the reservoir, it is generally known as extra-heavy oil. As natural asphalt, bitumen has been exploited since antiquity as a source of road paving, caulk, and mortar and is still used for these purposes in some parts of the world. The direct use of mined asphalt for road paving is now almost entirely local, having been replaced by manufactured asphalt, which can be tailored to specific requirements.

Fundamental differences exist between natural bitumen, heavy oil, medium oil, and conventional (light) oil, according to the volatilities of the constituent hydrocarbon fractions: paraffinic, naphthenic, and aromatic. When the light fractions are lost through natural processes after evolution from organic source materials, the oil becomes heavy, with a high proportion of asphaltic molecules, and with substitution in the carbon network of heteroatoms such as nitrogen, sulfur, and oxygen.

Therefore, heavy oil, regardless of source, always contains the heavy fractions, the asphaltics, which consist of resins, asphaltenes, and preasphaltenes (the carbene-carboids). No known, that  heavy oil fails to incorporate asphaltenes. The large asphaltic molecules define the increase or decrease in the density and viscosity of the oil.

Due to scientists research asphaltenes are defined formally as the crude oil fraction that precipitates upon addition of an n-alkane, usually n-pentane or n-heptane, but remains soluble in toluene or benzene.

It is possible to form heavy oil and natural bitumen by several processes. First, the oil may be expelled from its source rock as immature oil. There is general agreement that immature oils account for a small percentage of the heavy oil. Most heavy oil and natural bitumen is thought  be expelled from source rocks as light or medium oil and subsequently migrated to a trap. If the trap is later elevated into an oxidizing zone, several processes can convert the oil to heavy oil. These processes include water washing, bacterial degradation and evaporation.

It is apparent that bitumen is different to conventional petroleum and heavy oil of liquid fuels and other products. Heavy oil, found in various reservoirs, and bitumen, found in tar-sand deposits.

Tar sand (also known as oil sand and bituminous sand) is a sand deposit that is impregnated with dense, viscous material that is usually immobile under reservoir conditions. Tar-sand deposits are found throughout the world, often in the same geographical areas as petroleum, including and heavy oil.

The heavy oil in various reservoirs and the bitumen in various tar-sand deposits represent a potentially large supply of energy. However, many of the reserves are available only with some difficulty and optional refinery scenarios will be necessary for conversion of these materials to liquid products, because of the substantial differences in character between conventional petroleum and heavy oil when compared to tar-sand. The definition of heavy oil has been very loosely based on the API gravity or viscosity.

Most important, the flow properties of heavy oil are reduced relative to conventional crude oil and heavy oil is much more difficult to recover from the subsurface reservoir. These materials have a high viscosity (and low API gravity) relative to the viscosity (and API gravity) of conventional petroleum and recovery of heavy oil usually requires thermal stimulation of the reservoir.