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Bitumen Modification Basics

Bitumen Modification

Bitumen modification is the process of adjusting bitumen properties by mixing it with polymer additives or using modern production techniques.

To achieve good properties of this construction material, increase its temperature and deformation resistance, the dispersion phase must be influenced. Three approaches currently exist:

  1. Compounding of peroxidized bitumen containing large amounts of asphaltene with deasphaltation asphalt, tower bottoms or selective oil purification extract. Oil products with significant content of low molecular aromatic oils, with low viscosity and a relatively low settling temperature, can be used in the process.
  2. Catalytic oxidation. This approach is used relatively rarely. Some of the catalysts used are phosphorus oxide or iron chloride. Bitumen, obtained in this manner, features higher penetration and lower brittle temperature than bitumen made by regular oxidation process.
  3. Modification of bitumen with highly elastic materials. This approach is the most promising. Most often, polymers are used as modifiers. Researchers have tested practically every material of this nature, but the best performance was demonstrated by carbon chain polymers with direct or branched chain, which contain no heteroatoms: rubbers of various structure, polyethene and polypropylene.

Introduction of even a small amount of polymer into bitumen improces its quality: increases softening temperature and reduces penetration.

Besides, polymer modifiers reduce bitumen brittle temperature and increase heat resistance. Many years of observing roads constructed with modified bitumen indicate that using these materials extends the durability of the road top.

When polymer swells, the dispersed structure of bitumen is transformer. The weight part of oil fraction and redistribution of oils associated by asphaltenes is observed. Removing them from the surface of asphaltenes leads to restructuring of dispersion system, with the end result of asphaltenes coagulation into a solid phase.

The amount of polymer added is defined by future application of the material. It should be noted that the presence of 1-3% of polymer by weight, the interval of plasticity expands mostly in the low temperature range, while with 5% and above, the heat resistance of the material is significantly increased.

Asphalt Emulsion Properties

Asphalt Emulsion Properties

Asphalt Emulsion Properties. Asphalt emulsion, like any other material, has a certain range of properties, which define the requirements to its production, storage and use.

Viscosity. Viscosity is a very important performance parameter. If viscosity is low, the emulsion is not thick enough, while excessively high viscosity means the emulsion will stay on the surface without permeation of the underlying materials.

Viscosity is influenced by the amount of asphalt in the emulsion, temperature and the type of emulsifier used. Besides, not all asphalt types give the same viscosity to emulsions. However, this can be adjusted by mixing calcium chloride into the emulsion.

Flocculation. Flocculation is the phenomenon when particles of a certain material attach to each other. In asphalt emulsions, a large droplet often assembles several smaller ones. To prevent this, simple stirring is usually enough.

Coalescence. This is a continuation of flocculation; it means that emulsion droplets stick to one another, creating larger particles. If this process is not stopped, the asphalt emulsion simply separates.

Coalescence may occur due a number of reasons:

  • incompatible type of asphalt;
  • incorrect selection of emulsifier;
  • insufficient amount of emulsifier;
  • incorrect temperature in the production process;
  • incorrect storage temperature;
  • mechanical influence, such as operation of a circulation pump for a long time or transportation.

Sedimentation. Viscosity of asphalt may exceed that of water, causing the droplets to lower to the bottom of the tank. If a solvent is added, the viscosity of asphalt is reduced and it may float to the top of the container.

To prevent this, the following methods are possible:

  • better storage conditions (higher temperature and stirring at regular intervals);
  • reduction of asphalt density by adding a thinner;
  • increased asphalt content;
  • increases emulsion viscosity;
  • change stabilizer and emulsifier type and concentration;
  • change emulsion рН.

Separation. One of the main requirements to asphalt emulsions is the stability in storage, transportation and use. Ensuring stability for cationic emulsions is easier, since their separation depends on the contact with mineral materials. The emulsifier is positively charged causing mutual attraction. Separation can be controlled by using a certain type of emulsifier in correct concentrations.

In case of anionic asphalt emulsions, the situation is somewhat more complicated. They do not chemically separate, and the desired effect is only achievable by evaporation of water, which often occurs slower than desired.

Asphalt Emulsion Production Equipment

Asphalt Emulsion

To make asphalt emulsion on industrial scale, special equipment is required.

A standard emulsion plant is composed of the following:

  • a homogenizer colloid mill, a component designed for dispersion;
  • heated insulated bitumen storage tanks;
  • emulsifier, thinner and finished product tanks;
  • control system;
  • a heating system (steam or oil).

Colloid mills of varying design are used in asphalt emulsion plants. The resulting quality of the product is influenced by the rotation speed and the gap between the rotor and the stator of the homogenizer. It is interesting that colloid mills had been developed long before asphalt emulsions were first used in road construction and repairs. These devices usually consist of a cast iron body, a heating jacket, two disks, a replaceable ring and seals.

Since the internal surface of the ring and the external surface of the disks are conical, and the disks rotate, the radial axial gap changes. This parameter is very important, since it directly influences the rate of production and quality of the emulsion. The smaller the gap, the finer the product dispersity.

The European experience of asphalt emulsion production indicates that the colloid mill is the optimal design for a dispersion device. It is used in the UVB-1 units by GlobeCore. These units allow to:

  • produce high quality asphalt emulsion regardless of the initial bitumen quality by adding plasticizers, adhesion additives and thinners;
  • produce all types of cationic and anionic asphalt emulsions;
  • ensure safety of operation (interlocks to stop the unit in case of faults);
  • produce asphalt emulsions fully compliant with the ASTM D 2397-98 and D977-98 standards;
  • make the process of emulsion production easy and simple.

GlobeCore specialists always stand ready to assist at the stage of selecting asphalt emulsion equipment and also built it according to custom order (if necessary).

Using Bitumen Emulsions for Reinforcement of Coating

Bitumen Emulsions

One of the possible uses of bitumen emulsions is reinforcement of fine sand in the top layer of earth roadbed, as well as running sands of border strips in road construction. Such measures are especially important in desert areas.

The process can be performed with regular emulsion, but before application ot should be diluted with water or emulsifier solution. The consumption of emulsion is 1 to 1.5 liters per m2; the material is applied by mobile sprayers.

Dust prevention on unpaved roads is the fixation of running sands within the limits of the road border strip. After applying, the emulsion permeates the sand to the depth of 10-15 cm, creating a protective layer which prevents the growth of grass and ground erosion.

Such operations can be performed with anionic bitumen emulsion made from 130/200 and 200/300 bitumen. Running sands must be secured with emulsion diluted with 2 – 6 parts water.

Bitumen emulsions used for dust prevention on roads can also be made from 130/200 and 200/300 bitumen. It is possible to achieve the result with slow thickening 70/130 bitumen.

Dust prevention is performed with anionic emulsion diluted before use with water or emulsifier to obtain 30% bitumen concentration.

Before the process, the road must be cleaned and moisturized. Emulsion is applied in the amount of 0.8-1.2 l/m2. Sand is applied above emulsion in the amount of 5-10 kg/m2, then the surface is compacted by several passes of a light roller.

Preparation of Road Construction Emulsions

The production process of bitumen emulsions is inextricably connected with bitumen emulsification. Currently there are several approaches to the production of this material: mechanical, acoustic, chemical and aeration.

Mechanical method means grinding of initial bitumen by compression, impact, stretching, friction and other external forces. With the acoustic method the properties of ultrasonic waves are used for bitumen milling. Chemical method causes bitumen breaking by the reaction between injected substances (acids) and binder. Interfacial tension is reduced and further simple mixing results in emulsification.

Emulsion facilities are usually equipped with:

  • a bitumen-emulsion production unit;
  • bitumen melting plant for bitumen dehydration and heating;
  • a soap boiling tank;
  • tanks for caustic soda preparation;
  • agitator for preparation of emulsifier water solution;
  • emulsifier feeding tanks;
  • water softening unit;
  • pumps;
  • portioning units.

To eliminate the risk of foaming and ejection of the mix out of the emulsifying unit, the temperatures of bitumen and emulsifier solution are set so as not to exceed 200ºС total. The temperature of bitumen is kept unchanged, while the temperature of the product at the outlet of the emulsifying unit must not exceed 90ºС.

The process of bitumen emulsion preparation starts from the supply of emulsifier solution into the unit, followed by bitumen. If using acoustic dispersers, the duration of mixing is 5 to 7 minutes after supplying the full batch of bitumen, and in case of a vane mixer it takes 5 to 8 minutes after supplying the solution when inverse emulsions are made. If slotted dispersers are use, the mixing process is continuous.

Road Bitumen Emulsions

Road Bitumen Emulsions

Bitumen emulsion is a dark brown water-bitumen mix. It is produced by bitumen dispersion in water with various emulsifiers.

Anionic bitumen emulsions interact with various minerals in different ways. This defines its area of application. Road construction tasks are much better solved by cationic bitumen emulsions.

Application of bitumen emulsions has a range of advantages compared to hot mix:

  • reduction of bitumen consumption;
  • no need for heating (reduction of labour and power costs);
  • no toxicity (no pollution of environment);
  • no fire-hazard;
  • efficiency of application (can be applied on wet surfaces).

Bitumen emulsion production plants make emulsions of three types: fast-, middle- and slow-breaking emulsions.

The invention of cationic bitumen emulsions opened up a range of new possibilities in the area of “cold” technologies, possessing some undeniable advantages in comparison with bitumen, which requires heating. Those are:

  • low viscosity of emulsion. This material can be spread over and mixed with mineral substances at ambient temperature. There is no need to heat the emulsion. Besides the reduction of power costs, emissions to the atmosphere are also reduced. There is no way for personnel to get burned, so labour safety is improved;
  • the job does not depend of weather conditions. The ability to interact with wet materials makes it possible to repair roads even at +5ºС;
  • flexibility of job planning. Emulsion-mineral mixes can be stored for up to 6 months without breaking;
  • better adhesion of binder and base due to application of an emulsifier. Road top made of bitumen emulsion is noted for high durability, resistance to cracking and rutting;
  • applicability of mineral materials with natural moisture content to make gravel-emulsion mixes.

The table shows areas of application of bitumen emulsions depending on breakdown rate.

Table 1. Area of application of bitumen emulsions depending on breakdown rate

#

Type of emulsion

Area of application

1

Fast-breaking

Road surface treatment, protective wearing course and tack coating
2

Middle-breaking

Dust laying, arrangement of wearing course, “Slurry seal”, preparation of black crushed-stone and vesicular gravel mixes, road surface treatment, tack coating
3

Slow-breaking

Preparation of bitumen-mineral mixes, topping of road by means of penetration method

Currently the sphere of application of bitumen emulsions is quite wide. This construction material enables to expand the road construction technology in the following directions:

  • preparation of cold asphalt-concrete mixes;
  • production of impregnated macadam surfacing for construction of road bottom layer and road surface dressings;
  • laying of protective coatings for old road surface treatment;
  • gravel compaction of surface course;
  • sand sealing for treatment of road surface with many cracks;
  • “Slurry seal” type cover for application of thin layers of cold asphalt-concrete surfacing.

Among other processes we’d like to note:

  • ground stabilization;
  • dust consolidation on dirt roads;
  • recycling of asphalt-concrete;
  • black-topping of  garden road lanes;
  • curing of newly-laid cement concrete mixes.

For production of bitumen emulsions, GlobeCore manufactures UVB-1 plants designed for 1 to 8 m3/hour capacity range.

This product has the following advantages:

  • capability to produce high-grade bitumen emulsion irrespectively of raw material quality due to the addition of plasticizers, adhesion additives and flux oils;
  • production of all type of emulsions, such as CRS, CMS and CSS-1,2, as well as anionic emulsions of  corresponding types, including sub-type h;
  • dilution of blending concentrate with water is performed directly in the plant;
  • safety (automatic emergency stop);
  • emulsion produced complies with the ASTM D 2397-98 and D977-98 standards;
  • small footprint;
  • simple maintenance and operation.

Polymer Bitumen Roofing Materials

Currently, there are over a hundred brands of polymer bitumen materials available in the market. There is no need to analyze them based on the product name, since any producer comes up with a new name, although the structure, composition and properties of these materials are near identical.

In general, a polymer bitumen material includes a base covered with polymer bitumen binders and protective layers on both sides. The upper layer offers protection from solar radiation, while the lower layer prevents sticking of layers in a roll.

No prize for guessing from the name: polymer bitumen binder consists of two components, bitumen and polymer. As a rule, the part of the polymer component does not exceed 12%. Modifiers raise the quality and durability of roofing materials considerably. Among the most popular additives are Styrene Butadiene Styrene (SBS), which is an artificial rubber, as well as atactic (APP) and isotactic (IPP) polypropylene.

Atactic polypropylene gives the bitumen higher heat endurance, resistance to weather and extra flexibility. Introduction of Styrene Butadiene Styrene gives even more flexibility to the binder, but at the same time makes it more sensitive to ultraviolet rays. Some other characteristics of roofing materials are also improved.

Protective coating can be fine or coarse dressing compounds.

If the material is used as the upper layer of roofing, the front surface should be dusted with coarse dressing compound, while the underside is covered with a polymer micro perforated film or a fine dressing compound.

Although the above roofing materials have similar components, structure and production technology, they differ in properties due to several factors:

  • varying quality of raw materials;
  • varying amount of modifiers added;
  • type of modifiers applied.

Bitumen Roofing Materials

Bitumen felt is a roofing material produced by saturating cardboard with liquid bitumen. With this material a dressing compound for the front surface is not required.

Bitumen felt is produced in 1000, 1025 and 1050 mm rolls. The total area of one roll can reach 40 m2.

This roofing material has the following specifications:

  • 20% max absorption of water by weight;
  • 220… 320 N tension breaking strength.

Bitumen felt is predominantly used as the lower or middle layer of roof cover and as a vapour barrier in structures.

The main difference between ruberoid and bitumen felt is the number of layers. The production technique is similar: bitumen felt is saturated with low-melting bitumen, but then both sides are coated with a composition made of high melting bitumen filled with mineral powder.

The front surface of ruberoid is covered with protective or decorative dressing compound consisting of mineral materials. The underside is dusted with fine limestone or talcum. This is required to avoid adhesion inside the roll.

The main disadvantages of ruberoid as a roofing material are its low lifespan and decay.

Short service life was the reason why application of ruberoid was seriously limited and prohibited entirely in some countries. Now this material is mostly used for roofing of temporary buildings.

Bicrost is a roofing material produced by double application of air blown bitumen and filler on polyether or glass base. Consumption of the binder in this case is 3.5-4 kg/m2.

The front surface is protected by coarse and flaky, dusty and fine dressing compounds. The base can be polyester, glass-fibre mat or glass cloth.

Bicrost is used for roofing of buildings and waterproofing of structural elements. Lifespan of bicrost roofing is 10 years on average.

The Difference Between Modified Bitumen and Concrete

To separate the terms “modified bitumen” and “modified concrete”, one needs to understand what these materials are, their use and methods to adjust their properties.

Scientists refer to modified concrete as the concrete of the millenium. Additives can control the process of material formation and create highly functional construction materials. Modified concrete has higher density, better cold-endurance and water resistance.

Application of additives helps to improve durability of concrete structures built of monolithic or composite concrete. The amount of modifiers used is usually less than one tenth or even one hundredth of percent of cement mass.

Depending on their functionality, additives are divided into four groups:

  • additives designed for alteration of mineral binders without chemical interactions;
  • additives interacting with binders, resulting in hardly soluble and poorly dissociated complex compounds;
  • additives which become crystallization nodes;
  • organic surfactants.

The scope of application of modified concrete is little or no different from the application of usual concrete: repairs of asphalt concrete roads, reconstruction of hydroengineering structures, bridge construction, underground development, etc.

Modified bitumens in turn found industrial application in road construction, as well as roofing and waterproofing.

Bitumens are most often modified by introduction of polymers, allowing to achieve better performance, such as:

  • improved performance at high and low temperatures;
  • improvement of elasticity;
  • increased fatigue resistance;
  • improvement of cohesion and adhesion with fillers;
  • increased aging resistance.

The practical difference between modified bitumen and concrete is in the type of the basic material influenced by additives. In the former it is bitumen, in the latter case it is cement.

Production of Bitumen Emulsion

Bitumen emulsions are produced by special continuous or batch units, usually based on a colloid mill.

First, the solution of emulsifier and bitumen passes through a mill, where emulsifying occurs. Production of cationic bitumen emulsions require a soap solution. It contains water, acid and emulsifier mixed together in ratio ensuring the proper acidity. A special solvent is often added to bitumen emulsions, usually kerosene, diesel or white spirit.

To eliminate the risk of local overheating, the temperature difference of bitumen and emulsifier solution must be minimized. However, bitumen temperautre should be sufficient for pumping.

Batch type plants

The identifying feature of batch plants is production and dilution of emulsifier solution in a dosing tank. If solvent must be mixed with bitumen, an additional dosing tank for bitumen can be be used; solvent can be injected continuously.

High volume components like bitumen or water can be measured by level marks on a tank. For fewer amounts, a more accurate measuring unit is used.

Continuous plants

The main difference of continuous operation plants is that there aren’t any dosing tanks. Bitumen and emulsifier solution are injected directly from supply tanks.

Emulsifier solvent is prepared automatically according to input formula by injection of emulsifier, acid and stabilizer into a water supply line. Before the water enters the colloid mill, emulsifier and acid must react chemically.

Water is heated to the required temperature by a continuous heater. Emulsifiers must be easily dispersible in water. This is required for faster reaction with acid. Dosing of acid is controlled by a sensor fixed on the water line just before the colloid mill. Bitumen and solvent (if required) are supplied to the colloid mill is continuously as well.

Continuous operation plant works while the materials are available and there is free space for product output.