Puma Bitumen. Bitumen Basics

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2 Index Introduction and Historical Perspective Introduction and Historical Perspective Bitumen Sources and Types Applications Manufacturing Process Test Proceedures Optimising Bitumen Performance Glossary The description of bitumen as mankind's oldest engineering material can be supported by a considerable amount of evidence from scholars. Nearly 3000 years BC the Sumerians in Mesopotamia used bitumen to fasten into the eye sockets of statues the materials such as ivory or mother-of-pearl pieces that represented the eyes. They also sculptured votive offerings out of a mixture of bitumen and clay. Some thousand years later, bitumen was being used by the early Babylonians as a building material because of its properties as an adhesive and water-proofing agent. With the passing of centuries, it became the standard material used in civil engineering and architectural projects to hold bricks and stones together and line drains, watercourses and grain silos. It was also used to create damp courses and seal the flat roofs of the houses in the same way as it is used today. Its importance in paving was also appreciated. About 600 BC King Nebuchadnezzar of Babylon had the city wall, intended to restrain the waters of the Euphrates, rebuilt with burnt bricks and bitumen because the wall of dried clay bricks had failed to keep the waters at bay. The Babylonians developed a technique for building houses from layers of bricks, bitumen and clay, reinforced with reeds. The system was so successful that they were able to build towers up to twelve storeys high. Nearly two thousand years later, archeologists excavating the site of the ancient city found traces of the bitumen that had been used for building. Apart from its properties, the reason why bitumen was widely used in this area was its availability in various forms. It oozed out of the ground in certain places and was even found floating in lumps on waterways that were so useful for moving it to where it was wanted. It was also available as a solid material in the form of bituminous limestone, which was used as the basis for small carvings. Given its general availability, it is not surprising that bitumen has a part to play in many of the great legends of Biblical and pre-biblical times. It is said to have been used in the building of the Tower of Babel and for the waterproofing of Noah's Ark and Moses' wicker basket. The Romans were enthusiastic about the medicinal qualities of bitumen for preventing and curing a number of ailments including boils, toothache and ringworm. It was also in favour amongst Roman ladies as a means of beautifying their eyebrows. As civilisation developed in Europe, it did so without significant use of bitumen as it was not a widely available material. Christopher Columbus and Sir Walter Raleigh found the lakes of asphalt in Trinidad useful for re-caulking their ships for the return voyage. Apart from maritime usage, bitumen was used mainly for medicinal, cosmetic and crop protection purposes. The extent of knowledge about bitumen in these times was quite variable. On the one hand, the German metallurgist Georg Agricola was writing in the early part of the sixteenth century that "Bitumen is produced from mineral waters containing oil, also from liquid bitumen and from rocks containing bitumen. Liquid bitumen sometimes floats in large quantities on the surface of wells, brooks and rivers and is collected with buckets or other pots. Small quantities are collected by means of feathers, linen towels and the like. The bitumen easily adheres to these objects and is collected in big copper or iron vessels and the lighter fractions evaporated by heating. The residual oil is used for different purposes and some people mix it with pitch, others with used axle oil to make it thicker." On the other hand, the entry for bitumen in Blount's Glossary published in 1656 defined it as " a kind of clay or slime naturally clammy, like pitch, growing in some countries of Asia." By the middle of the nineteenth century, serious attention was being given to the problem of the dust raised by the horse-drawn traffic in towns. The availability of a regular supply of coal tar from local coal-gas works led to its use in treating streets and pavements. The realisation that the horseless carriage was here to stay and would need streets and roads constructed to a hitherto unimagined standard of smoothness and durability resulted in serious attention being given to the elements needed for their creation. Rock asphalt and the Trinidad lake were the sources of bitumen first used to bind mixtures of aggregates in road building in the modern style. By the turn of the century the potential of petroleum as a readily available source of low-cost, high quality bitumen was being exploited on a small scale. As bitumen production grew with the rise of the motorcar and the universal demand for paved highways, so too did the proportion of bitumen derived from petroleum refining to the extent that today most bitumen is sourced from the distillation of crude petroleum oil. In the USA, bitumen is referred to as asphalt or asphalt cement. In the term rock asphalt, it defines a mineral substance that may be impregnated with bitumen or pitch. Outside the USA, the word asphalt means a mixture of bitumen and mineral aggregates laid as a road surface. 2 1

3 Bitumen Sources and Types What is Bitumen? Bitumen is a non-crystalline, black or dark brown viscous material, which is substantially soluble in organic solvents, such as toluene and carbon disulphide, and which possesses adhesive and water-proofing qualities. It consists essentially of hydrocarbons and typically comprises at least 80% carbon and 15% hydrogen. The remainder is oxygen, sulphur, nitrogen and traces of various metals. Sources of Bitumen Bitumen can be obtained from various sources. As mentioned earlier, it occurs naturally, but for most purposes it is petroleum on which the world relies for its supplies of bitumen. The bitumen content of crude petroleum oil can vary between 15% and 80%, but the more normal range is 25% to 40%. The three broad classifications for crude oils are: bitumen based paraffin based bitumen and paraffin based. Depending on the type of crude petroleum oil, bitumen is present either in the form of a colloidal dispersion, or in a true solution. During the refining process, as petroleum oils are taken away by distillation, the proportion of oil to bitumen particles changes. Instead of these particles being dispersed and relatively few in number, they become closer to one another and their size increases. At the point when the distillation process is usually stopped, the petroleum bitumen is a colloidal dispersion of black solids (hydrocarbons). These are known as asphaltenes, which are dispersed in an oily brown-yellow liquid, known as the maltenes fraction. Also present to act as a stabilising agent to keep the asphaltenes in suspension are another group of hydrocarbons known as resins. Bitumen is found in nature in several forms, from the hard, easily crumbled bitumen in rock asphalt to the softer, more viscous material found in oil sands and so-called asphalt lakes. It is commonly mixed with varying proportions of mineral or vegetable impurities that need to be extracted before it can be used effectively as an engineering material. Bitumen may also be found as asphaltite, natural bitumen without impurities that varies in the extent to which it is soluble in carbon disulphide. Natural bitumen, like petroleum, occurs as the result of the special decomposition of marine debris. It will have been moved over many thousands of years through porous rocks such as limestone or sandstone, often by volcanic action. In some areas notable for their petroleum resources, for example the Middle East, semi-fluid bitumen can be found oozing out of fissures near hot springs or seeping out of the ground. Figure 1: The decomposition of marine debris over millions of years produces natural bitumen in a petroleum residue, which is extracted through the refining process. Rock asphalt, with its variable and relatively low content of bitumen, tends to be found away from the places where bitumen is needed. It is costly to move around and to process. It is important to draw the distinction between bitumen and coal tar. Although coal tar is black and viscous like bitumen, it is obtained from the carbonisation of coal and therefore has very different chemical properties. Engineering projects in every part of the world, from the construction of transcontinental highways to the waterproofing of flat roof surfaces, rely on the particular properties of bitumen. Crude petroleum oil processed by the petroleum industry provides all but a small percentage of this vital material. Properties Bitumen is a strong and durable adhesive that binds together a very wide variety of other materials without affecting their properties. Its durability is essential to major engineering projects such as roads and waterways where it must perform for up to 20 years or more. Bitumen is insoluble in water and can act as an effective waterproofing sealant. It also resists action by most acids, alkalis and salts and does not contaminate water, so it can be used to line watercourses. Bitumen is a thermoplastic material: it softens and becomes liquid with the application of heat and hardens as it cools. It can be spread relatively easily in the areas where it is required because it can readily be liquefied by one of three methods: applying heat dissolving it in petroleum solvents dispersing it in water (emulsification). Bitumen gives controlled flexibility to mixtures of mineral aggregates, which is why so much of the total annual production is used in road building. It is available at an economic cost virtually all over the world. Types of Bitumen There are six major classifications of petroleum bitumen produced by the refining and manufacturing process: Paving grade bitumen (or asphalt cement in the USA) is the most widely used bitumen and is refined and blended to meet road engineering and industrial specifications that take into account different climatic conditions. Paving grade bitumen may also be considered as the parent bitumen from which the other forms are produced. Cutback bitumens consist of bitumen that has been diluted in solvent (cutter or flux) to make it more fluid for application. The fluidity of cutback bitumens (or cutbacks as they are known) depends on the degree of hardness of the bitumen and the proportion of diluent. Cutbacks are classified according to the time it takes for them to cure, or become solid due to the evaporation of the diluent. Classifications are rapid curing (RC), medium curing (MC) or slow curing (SC). A cutback varies in behaviour according to the type of cutter or flux used as the diluent with white spirit commonly used for RC grades, kerosene for MC and diesel for SC. Bitumen emulsions are dispersions of bitumen in water. Hot bitumen, water and emulsifier are processed in a highspeed colloid mill that disperses the bitumen in the water in the form of small droplets. These droplets or particles of bitumen are normally in the 5-10 micrometre size range but may be even smaller. The emulsifier assists in forming and maintaining the dispersion of fine droplets of bitumen. Bitumen emulsions normally comprise between 30% and 80% bitumen by volume. If the bitumen starts to separate from the water solution in storage, the emulsion can usually be easily restored by gentle agitation to redisperse the droplets. Bitumen emulsions have a low viscosity compared to the bitumen from which they are produced and can be workable at ambient temperatures. Their application requires controlled breaking and setting. The emulsion must not break before it is laid on the road surface but, once in place, it should break quickly so that the road can be in service again without delay. 40 micrometres Limit of visibility to the naked eye 25 micrometres White blood cells 8 micrometres Red blood cells 2 micrometres Bacteria 100 micrometres Grain of salt 70 micrometres Diameter of human hair Figure 2: Particles of bitumen dispersed in water to make bitumen emulsions are usually between 5 and 10 micrometres in size. This diagram gives an indication of relative size. 2 3

4 Applications Fine Coarse Figure 3: Microscopic representation of emulsion structures. The mechanical performance of bitumen emulsions can be tailored like that of other construction materials. Bitumen emulsions are divided into three categories: Anionic with negatively charged droplets Cationic with positively charged droplets Non-ionic with neutral droplets. The main grades for bitumen emulsions are classified as follows: Anionic Cationic ARS CRS Rapid setting AMS CMS Medium setting ASS CSS Slow setting The development of bitumen emulsions is an area where technological progress is still being made to meet current and emerging engineering demands. The first emulsions were the anionic types. They are currently less favoured than the cationic types because the positively charged globules of bitumen in cationic emulsions better coat the majority of aggregate types and result in greater adhesion. Use of cationic emulsions is therefore preferred in most applications. Modified bitumens are formulated with additives to improve their service performance by changing such properties as their durability, resistance to ageing, elasticity and/or plasticity. The most important modifiers are polymers. Polymer modified binders (PMB) are a major advancement in bituminous binder technology as these materials better satisfy the demands of increasing traffic volumes and loads on our road networks. As well as natural rubbers, polymers such as styrene butadiene styrene (SBS), polybutadiene (PBD) and ethylene vinyl acetate (EVA) are commonly used to modify bitumen. Multigrade bitumen is a chemically modified bitumen that has the properties of a hard paving grade bitumen at high service temperatures coupled with the properties of a soft paving grade bitumen at low temperatures (i.e. it has properties that span multiple grades). Multigrade bitumens provide improved resistance to deformation and reduce the detrimental effects of high service temperatures, whilst providing reduced stiffness at low service temperatures than exhibited by a similar normal paving grade bitumen. Industrial bitumens (or oxidised bitumens) are made by blowing air through hot paving grade bitumen. The so-called blowing process results in harder bitumen that softens at a higher temperature than that at which paving grade bitumen softens. Industrial bitumens also have more rubber-like properties and their viscosities are much less affected by changes in temperature than is the case with paving grade bitumen. Bitumen Handling The four major factors involved in handling bitumen are: the high handling temperatures and the need for purposedesigned storage and transport tanks and equipment the flammable nature of certain grades, particularly cutbacks the need to safeguard the health and safety of personnel the training of personnel. Owing to their high viscosity, almost all bitumen and bituminous products must be heated to make them sufficiently fluid for bulk distribution and application. Contact with bitumen or the equipment involved in transporting, storing or applying it can cause severe skin burns at the recommended handling temperatures. For example, even a fleeting touch at 80 C can be expected to burn unprotected skin. It is essential that anyone working with bitumen or bituminous products make themselves familiar with the necessary health, safety and environmental considerations. Users are advised to always refer to product Material Safety Data Sheets (MSDS) for a full description of hazards associated with the use of bitumen products. Road Construction and Maintenance Over 80% of the 100 million tonnes of worldwide annual bitumen consumption is used for paving applications in the construction and maintenance of roads. The remainder is used for various purposes. The use of bitumen in road maintenance can be up to four times its use in road construction. An understanding of how roads are built is necessary for an appreciation of the importance of the role played by bitumen. Modern road design and construction techniques are aimed at building flexible road layers or courses so that the tensile and compressive stresses imposed by passing traffic are distributed evenly through these layers, according to their relative strengths. This ensures that neither the ground supporting the road nor the individual layers are permanently deformed by these concentrated stresses. The courses must also be made weather resistant and durable. Bitumen plays a major part in meeting this requirement because it strongly binds the aggregate particles and seals and fills the voids between them. Its effectiveness depends on the aggregate specification, the size and number of voids and the type of bitumen. By sealing the gaps, bitumen makes it difficult for water to penetrate the road courses and damage the natural foundation of the road. In the context of road building, the entire road structure is called the pavement. The lowest layer of a road is the natural soil of the subgrade. For a new road the subgrade is carefully prepared by modern machinery, but for an old road this layer consists of whatever has been left by generations of traffic. The rest of the road is made up of layers of aggregates and bitumen, each designed to do a specific job (see Figure 4 on page 9). Aggregate is the term used to describe hard non-metallic minerals such as crushed rock, gravel, sand and slag. Aggregates must meet engineering specifications that include shape, strength, surface characteristics and size. The subbase is the first layer put down by the road builder and consists of compacted granular material stone, gravel or sand. Its function is to contribute towards the strength of the road and give the road building machinery an operating platform. The base course is a mixture of aggregates and bitumen used as a structural layer. It adds to the strength of the road and is an even surface foundation for the top layer. The wearing course is the top layer normally consisting of a more finely textured mixture of aggregates and bitumen. Its role is to act as a smooth running surface for traffic. It must also be as weather-proof as possible and resist the continual action of the abrasive forces imposed by the vehicles as they pass along it. The wearing course should also disperse surface water effectively to minimise the danger of skidding. Where appropriate, a tack coat of bitumen may be applied between courses to ensure adhesion of the layers. The layers of asphalt in a road pavement can vary widely in maximum stone size used and thickness laid, from as low as 15mm thickness using 5mm maximum stone size up to 250mm layers using up to 40mm maximum stone size. Variable Design Factors The exact make-up of a road will depend on several variable factors such as the weight and volume of traffic it has been designed to carry, local climatic conditions and the availability of mineral aggregates. In most cases, bitumen will be needed for its properties of waterproofing and durability and as the cheapest adhesive generally available. A minor secondary road may use bitumen only for its top two courses, at the rate of 7 tonnes per kilometre. A highway engineer may call for three asphalt courses, with tack coats in between, because of asphalt's superior load bearing properties. In this case, bitumen consumption can amount to 1,000 tonnes per kilometre. The bitumen percentage in asphalt is usually between 4-8%. GENERAL ROAD CONSTRUCTION AND MAINTENANCE APPLICATIONS Examples of use C170 C320 C600 Cutback manufacture Emulsion manufacture Hotmix asphalt Sprayed seals Tack coat Paving grades Cutback grades Emulsions Low viscosity High viscosity Table A: This table defines some typical road construction and maintenance applications for different types of bitumen. Modified bitumens 4 5

5 Hot Mix The mixing of aggregates and bitumen to produce asphalt may take place at a purpose-built plant located away from the road construction site, or it may be done at the site itself. Controlled amounts of various size aggregates, which have been carefully blended and graded to meet the required specification, are dried and heated before being mixed with a measured quantity of hot bitumen. All this takes place in a purpose-built plant. The hot mixture, or hot mix, at a temperature of up to 160 C, is carried to the construction site and laid while still hot. The above describes, in simple terms, a process in which skill and experience are combined with computerised control systems to carry out a complex series of operations. Various sizes of aggregate dry out, gain and retain heat at different rates. Their temperature must be controlled so that the bitumen does not cool when it is mixed with the aggregates. The supply of aggregates is continuously weighed by scales linked to the pump metering the bitumen to ensure that a constant ratio of aggregate to bitumen is maintained. The mixing time should be no longer than is necessary for the uniform distribution of the bitumen as a coating for the aggregate particles, otherwise the bitumen film will harden due to oxidation as it is exposed to air. The durability of the mixture will be impaired if the mixing process takes too long. Continuous operation of the plant is required to provide consistent high quality mixtures. This, in turn, means that all parts of the operation must be integrated so there are no hold-ups as the drying, screening, mixing, transporting and laying processes are carried out. Bitumen supplies are ordered daily to meet the production schedules on the road gangs' programs for the following day. As bitumen storage capacity is usually limited, delivery has to be made on a 'when required' basis, often within thirty minutes of the target time based on the moment when the aggregates have been heated to the right temperature for mixing with bitumen. Any delay means that expensive fuel is wasted in keeping the aggregate at the right temperature. This precision in delivery calls for a high degree of commitment on the part of the supplier in terms of capital equipment, logistics and technical expertise. Direction of load Wearing course Tack coat Base course Tack coat Sub-base Formation level Subgrade (natural soil) Figure 4: Distribution of load through a bituminous road 6 7

6 s Figures 5 and 6: This purpose-built asphalt mixing plant grades and dries the aggregates and then mixes them with bitumen. All aspects of the mixing plant are carefully controlled from the computer console. (Pictures courtesy of Boral Asphalt). Asphalt and Other Treatment Types Asphalt mixtures have been classified into a number of different types, which may be simply stated as: Dense-graded Asphalt or Asphaltic Concrete: a dense, continuously graded mixture of coarse and fine aggregates, mineral filler and bitumen, having a carefully controlled air void content. Hot Rolled Asphalt: a sand-based material, bound with high viscosity grade bitumen, and having approximately 30% selected stone content, with larger stones rolled into the surface. Stone Mastic Asphalt: a high stone content mixture where the large stones form a load-bearing matrix within the mixture to provide high resistance to deformation with the interstices substantially filled with bitumen/filler mastic. Bitumen content % Air voids content % COMPOSITION OF ROAD SURFACE Dense-graded Asphalt 4-7% 3-5% Hot Rolled Asphalt 6-9% 3-5% Table B: Asphalt mixture compositions Stone Mastic Asphalt Open-graded Asphalt 6-8% 5-7% 2-4% 18-20% Open-graded Asphalt: a mixture of graded aggregates and bitumen produced to provide an open texture and high air voids content to allow ready drainage of water through the finished asphalt layer also known as Porous Asphalt and Drainage Asphalt. Tack Coat: a thin layer of emulsified or cutback bitumen that bonds a layer of road to the layer beneath. Current practice is to favour the use of bitumen emulsions in place of cutbacks in this application. Sprayed Seal: also known as surface dressings and chip seals, these involve spraying a coating of bitumen onto the surface of a wearing course or granular pavement. Sprayed seals can be sprayed as an emulsion, a cutback or as neat paving grade bitumen. Either a single or double coating of aggregates or stone chippings is applied. These treatments are applied to renovate and waterproof old roads that require maintenance or to protect unbound granular pavements in new constructions. An example of a remedial treatment is a fog seal, which is a coat of bitumen emulsion applied to an existing surface to seal cracks or to replenish aged bitumen as a maintenance treatment. Bituminous Slurry Surfacing: an important maintenance treatment for the surface in which a mixture of fine aggregates, filler and emulsified bitumen is applied to a structurally sound road surface for minor shape correction and to improve skid resistance. It has the advantage that it can be applied rapidly and at a relatively low cost by a truckmounted mixing plant. Road Recycling The techniques of road recycling reclaim the materials used to build roads. They offer benefits in terms of reduced demands for aggregates and energy. The layers of road surface are ripped up, crushed and reprocessed with varying proportions of fresh aggregate, new bitumen or bitumen emulsion and, if necessary, a recycling agent. The process may be carried out on site (in situ), or the reclaimed material can be transported to and from the site to be mixed in a dedicated static plant. Such reclaimed material is known as RAP or reclaimed asphalt pavement. Industrial Usage The use of bitumen in industrial applications accounts for less than 20% of world bitumen consumption. It is nevertheless important to those manufacturers and engineers who rely on its particular properties as an economical binder and protector. In many parts of the world it is used extensively to waterproof the roofs of houses, often in the form of shingles, which are strips of felt first impregnated with bitumen and then covered on both sides with harder bitumen and a coating of mineral granules. A similar construction technique involves sheets of bitumensaturated felt laid onto a flat roof with layers of bitumen below, between and above them. By contrast, bitumen is also used in damp-proofing and floor tiles. Other materials, particularly felts and papers, are impregnated with bitumen to improve their performance as insulators. Packaging papers, printing inks, linoleum, sound deadening felts hidden inside car bodies and undersealing compounds beneath them, electrical insulating compounds and battery boxes are some of the hundreds of industrial and domestic products likely to contain industrial grade bitumen. 8 9

7 Manufacturing Process Refinery Processes In an oil refinery, the crude oil being processed is separated into different cuts on the basis of their boiling range. In atmospheric distillation, which is the first stage of this continuous process, the crude oil is heated to 300 C-350 C and the more volatile components, e.g. petrol and kerosene, are distilled off. This leaves a residue called atmospheric residue, which is then further distilled under vacuum. The actual processing temperature of the residue is 350 C- 390 C, but because of the applied vacuum, the further effective distillation cut point is 500 C-560 C. This vacuum distillation process yields further volatile products known as vacuum distillates and leaves a non-volatile residue of high viscosity, which is called vacuum residue. Depending on the crude origin, the vacuum residue may be used directly as bitumen without further processing. For some crude oils though, or to meet particular specifications, additional processing may be required, such as mild air blowing of the residue. The air blowing process demands careful selection and control of process temperature, air rate and residence time to ensure consistent product. Sometimes bitumens are produced by blending vacuum residue with asphaltenes derived from the manufacture of lubricating oils. For example, propane-precipitated asphalt (PPA) is commonly used in the manufacture of bitumens when lubricating oils are produced at the same refinery. The selection of crude is an important aspect of bitumen manufacture, requiring expertise and experience to yield a satisfactory product not all crude can be used to make bitumen. Few of the nearly 1500 available crude petroleum oils are suitable for the manufacture of good quality bitumen. Within the Australian context, a very small number of crude oils are able to be used to manufacture bitumen compliant with the current Australian Standard. Cutback bitumens are produced by diluting the paving grade bitumen with a cutter or flux. Bitumen emulsions are made in a colloid mill by dispersing paving grade bitumen in water with the aid of an emulsifying agent. For industrial bitumens, in order to produce a material that will soften at a higher temperature than paving grade bitumen of equivalent penetration, severe air blowing is required. The product is therefore also known as air-blown or oxidised bitumen. Typically the blower feedstock has a lower initial boiling point than for paving grade bitumens. It is this, combined with severe blowing, that gives industrial bitumens their special physical properties. The production of high quality bitumen relies on a combination of skills, experience and modern refinery technology. These are used extensively to ensure the suitability of feedstocks and to monitor and control all stages of the process. Storage Bitumen is stored at refineries and large depots in large permanent tanks made of mild-steel plate, with capacities of between 100 and 10,000 tonnes. Steam or hot oil is pumped through heating coils in the heavily insulated tanks so that the bitumen remains fluid. Smaller depots and big users store bitumen in small permanent or semi-mobile tanks of up to 60 tonnes capacity, typically heated by electricity or flame heater tubes. Distribution As bitumen cools, it gradually becomes unworkable. Therefore the delivery of paving grade bitumen not only calls for the supply of bitumen to be provided at the right quality and quantity at the right time, but the product must also be kept between 150 C-190 C throughout the supply chain. When it is loaded into a road tanker, the temperature can drop by about 7 C-10 C and continue to fall by a further one or two degrees per hour while in transit. Road tankers with capacities of between 10 and 40 tonnes are normally used to take most of the bitumen from the refineries. They have insulated single-compartment tanks, usually with some kind of heating such as heating tubes. To transport bitumen to intermediary depots with reheating facilities, insulated rail cars are sometimes used. Their capacity ranges from 10 tonnes to 50 tonnes and they are also fitted with electric heaters or direct oil-fired flame tube heaters. When bitumen is moved by sea, it can be shipped in a variety of vessels from 300 tonne barges to ocean-going tankers of up to 30,000 tonnes capacity. The temperature of the hot-loaded bitumen is maintained by high pressure steam or hot oil passing through coils in the bitumen tanks. Crude Oil C Vacuum Distillation C Mild Air Blowing C Atmospheric Distillation Wax Distillate Atmospheric Distillation The crude oil is split into different boiling-point fractions. Vacuum Distillation Atmospheric residue is split into different boiling-point fractions. Air Blowing By blowing air through bitumen at high temperature under controlled conditions, the heavy molecules are enlarged. Emulsification In an emulsion mill bitumen is dispersed in water; chemicals are also added to stabilise the emulsions. Mixing High energy mixing process to disperse polymer into bitumen. Blending The viscosity of bitumen is reduced by blending in various amounts of flux oil (solvents). Vacuum Residue Light Distillate: Naphtha, Kerosene, Gas-oil Cutter Oil Flux Oil Severe Air Blowing Water and Emulsification Agent Emulsification Polymer Mixing Blending Main Refinery Processing Industrial Bitumen Bitumen Emulsion Polymer Bitumen Emulsion Polymer Modified Binder Cutback Bitumen Fluxed Bitumen Paving Grade Bitumen Figure 8: A refinery process diagram illustrating a typical off-take for bitumen products

8 Test Procedures Characteristics The main bitumen characteristics of interest are its viscosity and its ability to be handled safely. Viscosity: the degree of fluidity of the bitumen at a standard test temperature. The viscosity of bitumen varies according to its temperature; therefore when comparing grades of bitumen, it is essential to carry out tests at standard temperature. Safety: to ensure that bitumen may be used safely, it is critical that its flash point occurs at a much greater temperature than that at which road construction work is carried out. The flash point is the temperature at which the heated bitumen will release fumes that will ignite (flash) in the presence of a naked flame or a spark. SA Standards Australia Austroads The association of Australian and New Zealand road transport and traffic authorities AusSpec ASTM AASHTO DIN IP LCPC Joint Venture between Standards Australia and the Institute of Public Works Engineering Australia (IPWEA) American Society for Testing and Materials (USA) American Association of State Highway and Transportation Officials (USA) Deutsche Industrie Norm (Germany) Institute of Petroleum (UK) Laboratoire Central des Ponts et Chaussées (France) Viscosity: is a more scientific measure of consistency than Penetration. Various tests are used to measure the resistance to flow of bitumen and to thereby define its consistency. Results are given in units of Poise (P), centistokes (cst) or Pascal seconds (Pa s) as standard units of measurement, the relationship between these units depending on the specific gravity of the bitumen. Different types of viscometers are used according to the type of bitumen being tested and the preferences of local specifying authorities. The capillary tube viscometer with a means of applying a partial vacuum is most commonly used for testing paving grade and cutback bitumens at 60 C. The time taken for the bitumen to flow between two points is taken and multiplied by a calibration factor to give a value in Pascal seconds. Vacuum viscometer To vacuum Vent to atmosphere Water bath heated to 60 C Timing marks Sample Gravity viscometer Upper filling mark Sample Water bath heated to 135 C Timing marks Lower filling mark Figure 10: The recognised methods used to measure viscosity. Test Development Experience in using bitumen in engineering projects has led to the adoption of certain test procedures that are indicative of the characteristics that identify adequate performance. However, there are two important points to be taken into account when considering these test procedures. 1. Strict adherance to the specified test procedures. 2. Different specifying authorities use different standard test procedures. Paving Grade Bitumens The test procedures used for paving grades of bitumen are as follows: Penetration Test: used to determine the consistency of bitumen by measuring the distance that a standard needle will penetrate vertically into a sample under specified conditions of loading, temperature and time, i.e. load of 100g at a temperature of 25 C for 5 seconds, reported in tenths of a millimetre. A vacuum is sometimes not required when testing paving grade bitumen at 135 C as the bitumen is fluid enough to pass through the tube within a reasonable time under gravity alone. The time taken for its passage is also multiplied by a calibration factor and the result is expressed in Pascal seconds. Another type of viscometer used for cutbacks and bitumen emulsions is the efflux viscometer. This measures in seconds the time a specified quantity of bitumen takes to flow through an orifice of specified dimensions under standard temperature conditions. Flash Point: used to measure the temperature to which a sample of bitumen may be safely heated by establishing the temperature at which a small flame causes the vapour above the sample to ignite or flash. Various methods may be used but the most common is the Cleveland Open Cup (COC) test in which a brass cup filled with a specified amount of bitumen is heated and a flame is passed over the top at specified intervals of time. The flash point is the temperature reached when the vapour causes an instantaneous flash. A modified Pensky-Martens closed tester is used in the Australian Standard test. Some of the tests have evolved with the development of the industry and are empirical methods. Consequently it is essential that they are carried out in strict compliance with the recommended procedures if they are to be accurate measurements of the bitumen s properties. Modern technology is continually being employed by major bitumen manufacturers at their research centres and in industrysponsored university research projects to find new ways of measuring the physical properties of bitumen, and translating these into specifications relating to road performance. Dial set at zero Time = 0 seconds 100g Water bath heated to 25 C Before test Dial reading Time = 5 seconds After test A fourth viscometer is the Brookfield Viscometer. A spindle is suspended in a sample of bitumen. When the spindle is twisted, the resistance to rotation is recorded through a calibrated spring connected to a dial where the reading is taken. Modern Brookfield Viscometers utilise digital displays which directly show the viscosity of the material being tested. Thermometer Vapour rising from sample Cleveland brass cup Naked flame to be passed over sample at specified intervals Temperature is noted when flash occurs Specifying Authorities Various organisations representing bitumen manufacturers and users have laid down standard test procedures. Major test methods specifiers are: Sample Needle set just touching surface Needle position after test = dial reading in tenths of a millimetre Figure 9: The penetration test as applied to bitumen. Heat source Figure 11: This test establishes the temperature at which a sample of bitumen will ignite, i.e. flash point

9 Ductility: gives an indication of the extent to which a sample of the material can be stretched before breaking. A standard briquette of bitumen, placed in a mould in a water bath heated to 15 C, is pulled apart, usually at a speed of 5 cm per minute. The length of the thread of bitumen at the moment when it breaks, expressed in centimetres, is the ductility of the sample. Water bath heated to 15 C Each failure is indicated here Three samples set up for test Mark indicates start of test Samples are drawn through bath at a speed of 5cm per minute Figure 12: Ductility testing of bitumen samples: Above: illustrates the position at the start of the test, and Below: the points of failure. Solubility and the Presence of Insolubles: indicates the degree of contamination of the bitumen by other matter and therefore the presence of pure bitumen. The Australian test measures the percentage of matter that is insoluble in toluene. Effect of Heat and Air: is determined to simulate the conditions obtained when the bitumen is used to manufacture hot-mix. In the Rolling Thin Film Oven Test a moving film of bitumen is heated in an oven at 163 C for 60 minutes. The viscosity is measured before and after treatment. Softening Point: a measurement of the temperature at which a sample of bitumen held in a ring in a water bath allows a steel ball of specified weight to fall to a point at a specified distance below it. It is used as an indication of the temperature at which bitumen has a particular viscosity or more simply, the temperature at which it softens. Thermometer Balls Ring Sample Water Heat source Heat source Thermometer Water coolant supply Draught shield Sample heated to 360 C Wire gauze Chimney Temperature is noted at end of test When ball has dropped a previously set specified distance test has ended Figure 13: The Softening Point test ( Ring and Ball Test ) measures the temperature at which bitumen has a particular viscosity. Cutback Bitumens For cutback bitumens, in addition to the viscosity and flash point tests, the following test is included in specifications: Distillation test: a measured quantity of cutback is heated to 360 C in a distillation flask. The volatile constituents vaporise and pass into a water-cooled condenser flask where they are measured to show the percentage of the volume of the cutback that has been driven off. This indicates the volatility of the cutback. The material that remains in the distillation flask is treated as paving grade bitumen for further testing for viscosity and solubility. Condenser Figure 14: The Distillation test indicates the volatility of a sample of cutback bitumen. Bitumen Emulsions Bitumen emulsions are subject to their own test procedures. Some of the tests used for determining their properties are as follows: Consistency: Also known as the Engler Viscosity test, this measures the rate of flow of the bitumen emulsion at 25 C. The emulsion is heated to 25 C and poured into a standard container. The time taken by 200mL of emulsion to pass through a standard orifice at the bottom of the container is measured. Water Content test: determines the weight percent of water in an emulsion. This can be performed by Dean and Stark distillation or Karl Fischer titration. In the Dean and Stark distillation, a sample is heated with a solvent that is immiscible with water. During the distillation process, the solvent and the water are separated in a trap so that the amount of water can be measured. In the Karl Fischer water content method, the emulsion is dissolved in a solvent and titrated with a Karl Fischer reagent, which reacts with the water in the emulsion. The amount of Karl Fischer reagent consumed is used to determine the water content of the emulsion. Sedimentation test: indicates the extent to which the components of an emulsion sample will separate during storage. Samples are taken from the top and bottom of a 500mL sample that has stood undisturbed for three days. The samples are tested for water content. The difference between the water content of each sample is an indication of the degree to which sedimentation has taken place. Stone Coating Ability and Water Resistance test: it is essential that a bitumen emulsion stands up to the action of being mixed with aggregates, coat them as completely as possible and not be washed off by any water that may fall on it once the mixing is completed. This test shows the extent to which a sample meets these requirements. It involves coating a sample of aggregate with emulsion, spraying it with water until the water coming from it is clear. The coating on the sample is assessed. Particle Charge test: identifies the charge on the bitumen particles in an emulsion. A positive and a negative electrode are left in a sample of emulsion for half an hour and an electric current applied. If there is bitumen deposited on the negative electrode at the end of the test the emulsion is cationic; if bitumen is deposited on the positive electrode, the emulsion is anionic. Sieve Residue test: shows the presence of coarse binder particles in the emulsion. These particles may be in the form of relatively large globules or strings and may indicate instability or result in poor coating performance or clogging of equipment. The sample is strained through a 150µm sieve and the percentage mass of emulsion retained on the sieve is calculated and reported as sieve residue. Residue from Evaporation test: indicates the percentage mass of binder present in an emulsion. An emulsion sample is heated so that water and other volatile components are evaporated. Residue from evaporation is calculated from the mass of the sample and residue after evaporation.. Solvent Water content collected here Sample with solvent mix Water coolant supply Heat source Figure 15: The Dean and Stark test ( Water Content Test ) records the percentage volume of water in a bitumen emulsion 14 15

10 Optimising Bitumen Performance Glossary Background Petroleum based bitumen is a product of consistently high quality. Its production involves a heavy investment in high-technology equipment and a commitment to quality management at all stages of crude oil selection, manufacture, blending, storage and distribution. By retaining and checking samples of consignments of bitumen, the composition and quality of the bitumen at the time it was delivered to the contractor can be confirmed. The actual performance of the bitumen when it is doing its job is just one part of the total performance of an asphalt mixture or sprayed seal. Asphalt performance depends on a number of factors, including the design of the mixture, the way it was mixed, the quality of mineral aggregate used and how it was laid and compacted. Sprayed seal performance depends on similar factors and can be significantly affected by weather conditions at the time of spraying and the cleanliness of the aggregate. As bitumen is an integral part of both asphalt mixtures and sprayed seals, advice on how to avoid and correct errors would need to cover many factors and types of applications. This subject is outside the scope of this booklet. However, it is possible to put forward the following essential guidelines to optimising the performance of bitumen, mainly in hot mix asphalt, on the basis of what is known about bitumen itself. Some of the points are mentioned elsewhere but they have been repeated in this section for convenient reference. General Advice Minimise the time during which hot bitumen is exposed to air. Bitumen hardens and loses some of its adhesive property when it is exposed to a combination of air and excessive heat. Careless mixing of bitumen and aggregate is an example of a practice that exposes bitumen to the air and heat for longer than the minimum time required to coat the aggregate. It is therefore likely to reduce the bitumen s performance as an adhesive. Keep bitumen dry and away from contamination by water at all times. When hot bitumen comes into contact with water it will foam. In extreme cases it will violently boil over from storage vessels due to the presence of small quantities of water. Keep bitumen within the range of temperatures recommended for the type and grade. Bitumen solidifies as it cools and becomes unworkable and the viscosity may increase due to oxidation if it is overheated. Keep asphalt at the lowest temperature that will permit it to be thoroughly mixed, transported and compacted to the specified density. The maximum bitumen storage temperature relating to the grade should not be exceeded during the mixing process. Temperature control is a major factor in the quality control of asphalt mixes. Avoid contaminating the bitumen, particularly with petroleum based solvents that reduce the flashpoint and the viscosity, and increase the penetration. Just 0.1% diesel in an asphalt mixture can lower the flash point and viscosity, and increase the penetration significantly. Stability is an essential quality in the performance of asphalt. It depends on friction and cohesion within the mixture. Too much bitumen will act as a lubricant for the aggregate particles, reducing friction and therefore the stability of the mix. The cohesion, or internal binding force in the mixture, increases as the proportion of bitumen in the mixture is increased, until it reaches the optimum. If the amount of bitumen increases further, stability decreases. It is therefore essential to ensure that the optimum proportion of bitumen is used in any mixture. To quote the Asphalt Institute of America directly: Finished mix should be frequently observed. No testing method or device is as quick and convenient as the human eye. The following are useful examples of what can be seen by simple observation. They can be treated as early warning signs that further checks should be made: blue smoke coming from the mixture can indicate overheating steam coming from the mixture indicates the presence of too much moisture if the distribution of bitumen on the aggregate is not uniform, the temperature in the mixing operation may be too low if the mixture looks stiff and dull rather than black and shiny there may be too little bitumen in the mixture, or overheating has excessively oxidised the binder if the mixture lies slumped on the floor of the truck the mixture may contain too much bitumen AAPA Australian Asphalt Pavement Association. adhesion agent A substance added to a bituminous binder to improve adhesion between the binder and aggregate. The term is usually applied to adhesion in the presence of water. Also commonly known as an anti-stripping agent. age hardening Hardening of a bituminous binder due to loss of volatiles and oxidation of the binder resulting from exposure to weather over a period of time. aggregate A material usually produced by crushing rock, slag, gravel, sand or similar material and screened to provide a specific size distribution. air voids The spaces within the bulk of a material, such as an asphalt mix, which is not occupied by solid matter or filled with bituminous binder. ALGA Australian Local Government Association. anionic bitumen emulsion A bituminous emulsion in which the suspended bitumen droplets are negatively charged. anti-foaming agent A substance (e.g. silicone oil) added to bitumen to reduce the surface tension and hence the frothing tendency of hot bitumen in the presence of water. application rate (aggregate) The amount of aggregate spread in a sprayed seal expressed as square metres per cubic metre (m 2 /m 3 ). Commonly known as the aggregate spread rate or coverage. application rate (binder) The amount of bituminous binder applied in a sprayed seal expressed as litres per square metre (L/m 2 ), usually expressed at 15 C. Commonly known as the spray rate. ARF Australian Road Federation. ARRB Australian Road Research Board, now known as ARRB Group Limited. asphalt A mixture of bituminous binder and aggregate, with or without mineral filler. Usually produced hot in a mixing plant and delivered, spread and compacted while hot. Also known as hot mix or hot mix asphalt (HMA). Asphalt Institute (AI) An association of international petroleum bitumen producers, manufacturers, and affiliated businesses, based in the USA. asphalt, dense-graded (DGA) An asphalt comprised of coarse and fine aggregates, filler and a bituminous binder, which is placed hot and then compacted to a dense state as a road pavement layer. The aggregate gradation of dense graded asphalt is considered to be continuous and the intimate interlocking of the aggregate particles is a major factor in the strength of the compacted asphalt. Also known as asphaltic concrete. asphalt, hot rolled (HRA) An asphalt material used as a dense wearing course, basecourse or roadbase material and which consists of a mixture of gap-graded coarse aggregate, fine aggregates, filler and bituminous binder. Common in the UK. asphalt, lake A highly viscous natural bitumen found in well-defined surface deposits e.g. Trinidad Lake Asphalt. asphalt, open-graded (OGA) An asphalt comprised of a large proportion of a single size aggregate, filler and bituminous binder, which has an interconnecting voids content of about 20% to 25%. Also known as porous asphalt and drainage asphalt. asphalt, stone mastic (SMA) An asphalt with a high coarse aggregate content and a high volume of both filler and bituminous binder, the strength of which is predominantly provided by stone-on-stone contact of the coarse aggregate particles. Also known as Splitt Mastic Asphalt. asphaltenes High molecular weight compounds in bitumen which are soluble in carbon disulphide, but insoluble in aromatic-free low-boiling petroleum solvents, such as n-heptane. asphaltic cement North American term for bitumen. asphaltic concrete See asphalt, dense-graded (DGA). atmospheric residue (atres) The residue obtained in the atmospheric distillation of crude petroleum oil. Austroads The association of Australian and New Zealand road transport and traffic authorities. AustStab Australian Stabilisation Industry Association. base course One or more layers of material immediately below the wearing course of a pavement. Also known as base or binder course