· DEFINITION:
A non-crystalline solid or viscous material having adhesive properties derived from petroleum either by natural or refinery processes, and substantially soluble in carbon disulphide. Bitumen is black or brown in colour. This may occur naturally but are usually made as end products from distillation of, or extracts from, selected petroleum oils.
· NOMENCLATURE:
Bitumen and asphalt are both generic terms. In USA, the word asphalt is used as synonymous with bitumen- the refinery product which has now largely replaced the natural asphalts that occur in Trinidad, Venezuela, Cuba etc. Outside USA however, the word asphalt is generally taken to mean a mixture of refinery bitumen with a substantial proportion of solid mineral matter.
· SOURCES:
· Bitumen does occur naturally, but for all intents and purposes it is petroleum on which the world relies for its supplies of bitumen today. The bitumen content of crude can vary between 15% and 80%, but the more normal range is 25% to 40%.
· In fact the three broad classifications for crude oils are:
1) Bitumen based
2) Paraffin based
3) Bitumen and paraffin based
· Depending on the type of crude, bitumen is present either in the form of colloidally dispersed particles 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 being dispersed and relatively few in number, the particles become closer to one another and the size of the particles increases.
· At the point when the distillation process is usually stopped, the petroleum bitumen is a colloidal dispersion of black solids (hydrocarbons), known as asphaltenes, in a dispersion medium, which is an oily brown yellow liquid known as malthene fraction. Also present to act as a stabilizing 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 tar sands and 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.
· However it may be found as an asphaltite, natural bitumen without impurities that varies in the extent to which it is soluble in carbon disulphide. Natural bitumen occurs, as does petroleum, 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.
· 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. The latter is obtained from the carbonization of coal and, although it is black and viscous in appearance,it 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 oil processed by the petroleum industry provides all but a small percentage of this vital material.
· FIRST USE OF BITUMEN:
· The first recorded uses of asphalt as a road-building material in Bbylon.The ancient Greeks were also familiar with asphalt. The asphalt comes from the Greek “asphaltos” meaning “secure”. The Romans used it to seal their baths, reservoirs and aqueducts.
· But Main Contribution from U.S and Canada.
· COMPOSITION:
· On average, Bitumen is composed of:
Carbon - 83.2%
Hydrogen - 10.4%
Oxygen - 0.94%
Nitrogen - 0.36%
Sulphur - 4.8%
· The remaining content is made up of small quantities of methane and hydrogen sulphide, along with traces of nickel, iron and vanadium.
· TYPES OF BITUMEN:
· There are five major classifications of petroleum bitumen produced by the refining and manufacturing process:
1) Paving grade bitumen
2) Cutback bitumen
3) Bitumen emulsions
4) Industrial bitumen
5) Modified bitumen
6) Bitumen Binder Modifiers
· Paving Grade Bitumen:
It’s also called as Asphalt Cement & is refined and blended to meet road engineering and industrial specifications that take into account different climatic conditions. As a product it is the most widely used bitumen. It may also be considered as the parent bitumen from which the other types, listed below, are produced.
· Cutback Bitumen:
They consist basically of bitumen that has been diluted in order to make it more fluid for application, mainly in road making. Their fluidity depends on the degree of hardness of the bitumen base and the proportion of diluent (or flux) to bitumen. They are classified according to the time it takes them to become solid, as rapid curing (RC), medium curing (MC) or slow curing (SC) cutbacks. The cutback varies according to the flux, white spirit commonly being used for RC grades, kerosene for MC and diesel for SC. They set as the flux evaporates. This evaporation is currently regarded as a potentially undesirable characteristic from the point of view of the environment and health and safety, so cutback bitumen’s are looked upon less favorably than the more modem bitumen emulsions.
· Bitumen Emulsion:
§ The basic bitumen has also been diluted in order to facilitate application. Hot bitumen, water and emulsifier are processed in a high-speed colloid mill that disperses the bitumen in the water in the form of globules that are normally in the 5-10 micrometer size range but may be even smaller. The emulsifier produces a system in which fine droplets of bitumen, of between 30% and 80% of the volume, are held in suspension. If they separate in storage, the emulsion can easily be restored by agitation.
§ Bitumen emulsions have a low viscosity and can be workable at ambient temperatures, which makes them ideal for use in road building. This 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. Particles of bitumen are dispersed in water to make bitumen emulsions are usually between 5 and 10 micrometers in size. This diagram gives an indication of relative size.
§ The mechanical performance of bitumen emulsions can be tailored like that of other construction materials.
And Bitumen emulsions are divided into three categories:
1) Anionic with negatively charged globules
2) Cationic with positively charged globules
3) Non-ionic with neutral globules.
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 engineering demands. The first emulsions were the anionics. They are currently less favoured than the cationics because the positively charged globules of bitumen coat the aggregates more thoroughly and have greater adhesion. Use of cationic emulsions is therefore increasing.
· Industrial bitumen:
These are also called as Oxidized Bitumen’s and these are made by blowing air through hot paving grade bitumen. The result is a product that softens at a higher temperature than that at which paving grade bitumen softens. It also has more rubber like properties and its viscosity is much less affected by changes in temperature than is the case with paving grade bitumen.
· Modified bitumen’s:
These are formulated with additives to improve their service performance by changing such properties as their durability, resistance to ageing, elasticity and/or plasticity. As well as natural rubbers, polymers such as styrene butadiene styrene (SBS), thermoplastic rubbers and ethylene vinyl acetate (EVA) are commonly used to modify bitumen and some companies, including BP, have their own proprietary technology using special polymers or polymer blends. This is an exciting development of growing importance due to the ability of modem technology to satisfy the demands of the bitumen market internationally. For example, polymers that extend the range of temperatures at which bitumen is worked will enable road builders to work effectively for more months of the year. A modified bitumen that increases the extent to which a road 'bounces back' after being subjected to heavy traffic, in terms of weight and volume, will contribute towards a longer road life and lower maintenance costs.
· Bitumen Binder Modifiers:
Some asphalt cements require modification in order to meet specifications. Asphalt cement modification has been practiced for over 50 years but has received added attention in the past decade or so. There are numerous binder additives available on the market today. The benefits of modified asphalt cement can only be realized by a judicious selection of the modifier(s); not all modifiers are appropriate for all applications. In general, asphalt cement should be modified to achieve the following types of improvements (Roberts et al., 1996):
· Lower stiffness (or viscosity) at the high temperatures associated with construction. This facilitates pumping of the liquid asphalt binder as well as mixing and compaction of HMA.
· Higher stiffness at high service temperatures. This will reduce rutting and shoving.
· Lower stiffness and faster relaxation properties at low service temperatures. This will reduce thermal cracking.
· Increased adhesion between the asphalt binder and the aggregate in the presence of moisture. This will reduce the likelihood of stripping. Figure 4 shows two aggregate samples from the same source after they have been coated with asphalt binder. The asphalt binder used with the sample on the left contain no anti-stripping modifier, which resulted in almost no aggregate-asphalt binder adhesion. The asphalt binder used with the sample on the right contains 0.5% (by weight of asphalt binder) of an anti-stripping modifier, which results in good aggregate-asphalt binder adhesion.
Figure 4: Effects of an Antistripping Modifier
· OTHER FORMS OF ASPHALT/BITUMEN USED IN PAVING:
Besides asphalt cement, three other forms of asphalt are used prominently in the paving industry:
· Emulsified asphalt. Emulsified asphalt is a suspension of small asphalt cement globules in water, which is assisted by an emulsifying agent (such as soap). Emulsions have lower viscosities than neat (plain) asphalt and can thus be used in low temperature applications. After an emulsion is applied the water evaporates away and only the asphalt cement is left. Emulsions are often used as prime coats and tack coats.
Cutback asphalt. A cutback asphalt is a combination of asphalt cement and petroleum solvent. Like emulsions, cutbacks are used because their viscosity is lower than that of neat asphalt and can thus be used in low temperature applications. After a cutback is applied the solvent evaporates away and only the asphalt cement is left. Cutbacks are much less common today because the petroleum solvent is more expensive than water and can be an environmental concern. Cutbacks are typically used as prime coats and tack coats.
Foamed asphalt. Foamed asphalt is formed by combining hot asphalt binder with small amounts of cold water. When the cold water comes in contact with the hot asphalt binder it turns to steam, which becomes trapped in tiny asphalt binder bubbles (World Highways, 2001). The result is a thin-film, high volume asphalt foam. This high volume foam state only lasts for a few minutes, after which the asphalt binder resumes its original properties. Foamed asphalt can be used as a binder in soil or base course stabilization, and is often used as the stabilizing agent in cold in-place recycling (CIPR).
· There is another type of Oxidized Bitumen Mainly Existing and Using in U.S,that is TIKI Bitumen
· In this too many varieties are there.
· Detailed explanation is as follows.
· Tiki Oxidized bitumen comply with International Standards. Tiki Oxidized bitumen has got a range of uses. It can be used in industries as an adhesive, protective coating, bonding agent, electric insulator and structures below ground. Because of their softening point, it shows excellent physical stability, no exudation or bleeding in contact with highly absorptive material and a remarkable resistance against atmospheric corrosion.
· Grades of Oxidized TIKI Bitumen:
85/25, 85/40, 90/15, 115/15, 135/10, 155/6
· Tiki Anti Stripping Agent:
Tiki Anti Stripping Agent is a highly stable anti stripping agent for increasing adhesion between asphalt and aggregates. It has been specifically designed for use in the manufacture of high performance emulsions, Cutbacks and hot mix. It may be used in polymer asphalt systems. It is NOT an amine and so is also useful as a bitumen additive.
Anti Stripping agent is ‘Heat Stable’ for 10 days at 1600C It have No smell, Non flammable, and contain no volatile solvents. It is liquid in nature and easy to use. It’s USE is recommended to avoid stripping even under submergence in water.
· Tiki Cut Back:
Tiki Cut Back Bitumen is a low viscosity, cold applied bituminous primer. Cutback Bitumen is produced by fluxing bitumen with distillates of petroleum for use in road construction. A bituminous prime coat is an initial application of low viscosity liquid material to an absorbent surface preparatory to any super-imposed treatment or construction. The object of priming is to promote adhesion between the existing surface and super-imposed treatment or construction. The choice of a bituminous primer shall depend upon the porosity characteristics of the surface to be primed. Cutback bitumen Primer is classified into Rapid Curing (RC), Medium Curing (MC) & Slow Curing (SC) based on viscosity.
· Tiki Bitumen(Paving Grade: 60/70 & 30/40):
Paving Bitumen shall be prepared by the distillation of suitable crude, petroleum oil without subsequent blending with other grades. The material shall be homogenous and shall not foam when heated to 175 deg C. No mineral matter other than naturally contained in the material shall be present.
Paving Bitumen (Straight Grade) used in construction and maintenance of Roads, Airfields & Allied Constructions.
· TIKI CRMB(Crumb Rubber Modified Bitumen):
TIKI CRMB is a blend of selected grades of bitumen and crumb rubber modifier. The modifier restores the required visco-elastic balance of the Bitumen binder, which improves binder resistance to any form of permanent deformation while maintaining high resistance to fatigue, thermal and low temperature cracking. When using TIKI CRMB, the maintenance free life of pavement will increase one and half to two times as compared to roads built using unmodified neat bitumen binders. TIKI CRMB has good adhesion to different types of aggregates which therefore reduce, rutting, cracking, deformations, etc. TIKI CRMB meets the performance- based specification of IRC: SP 53-2002.
· Advantages of TIKI CRMB:
· Excellent Resistance to Thermal and low temperature cracking.
· Superior resistance to any form to permanent deformation.
· Better adhesion between aggregate and binder.
· Overall improved performance in extreme climatic conditions.
· Higher fatigue life of mixes.
· Highly flexible and stability
· Cost effective.
· TIKI PMB(Polymer Modified Bitumen):
This invention relates to the process for the preparation of a polymer and rubber based modified binder which is useful for the construction of roads catering to heavy traffic and also for the formation of airfields and surfacings, besides its use as binder for stress absorbing membrane (SAM) and stress absorbing membrane interlayer (SAMI) for sealing of cracks, preventive maintenance of flexible pavement and delaying reflective cracking. Modified Bitumen performs better than ordinary Bitumen in high rain fall area and in situation where the aggregates are prone to stripping.
· Advantages of TIKI PMB:
· Improves resistance in cracking resulting in stronger and more durable overlays even in extreme climatic conditions.
· Reduces deformation on the roads even at temperatures of ( 50-70 degrees C)
· Polymer and Rubber based modifer binder extend life of pavement by 50-70% compared to conventional bitumen.
· PMB act as a multigrade bitumen and are economical when life cycle cost is taken into consideration.
· PROPERTIES OF ASPHALT OR BITUMEN:
“Asphalt" is a dark brown to black, highly viscous, hydrocarbon produced from petroleum distillation residue. This distillation can occur naturally, resulting in asphalt lakes, or occur in a petroleum refinery using crude oil. In 2001, the U.S. produced almost 35 million tons of asphalt at a rough value of around $6 billion. Roads and highways constitute the largest single use of asphalt at 85 percent of the total (Asphalt Institute, 2002). In HMA, asphalt functions as a waterproof, thermoplastic, viscoelastic adhesive. By weight, asphalt generally accounts for between 4 and 8 percent of HMA and makes up about 25 - 30 percent of the cost of an HMA pavement structure depending upon the type and quantity. The paving industry also uses asphalt emulsions, asphalt cutbacks and foamed asphalt.
“Asphalt cement" refers to asphalt that has been prepared for use in HMA and other paving applications. This section uses the generic term, "asphalt binder", to represent the principal binding agent in HMA because "asphalt binder" includes asphalt cement as well as any material added to modify the original asphalt cement properties.
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Figure 1: Trinidad Lake Asphalt | Figure 2: Chevron Hawai'i Refinery |
· PHYSICAL PROPERTIES OF ASPHALT
Bitumen's main property is that of a very 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 do its job for 20 years or more.
Bitumen is insoluble in water but is soluble in numerous organic solvents. As it is highly waterproof, it can act as an effective sealant. It also resists action by most acids, alkalis and salts. It does not contaminate water so it can be used to line watercourses.
It is a thermoplastic material: it softens and becomes liquid with the application of heat and hardens as it cools. Bitumen can be spread relatively easily in the areas where it is required because it can readily be liquefied by one of three methods:
1) Applying beat
2) Dissolving it in petroleum solvents
3) Dispersing with 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.
Asphalt can be classified by its chemical composition and physical properties. The pavement industry typically relies on physical properties for performance characterization although an asphalt's physical properties are a direct result of its chemical composition. Typically, the most important physical properties are:
· Durability. Durability is a measure of how asphalt binder physical properties change with age (sometimes called age hardening). In general, as an asphalt binder ages, its viscosity increases and it becomes more stiff and brittle.
· Rheology. Rheology is the study of deformation and flow of matter. Deformation and flow of the asphalt binder in HMA is important in HMA pavement performance. HMA pavements that deform and flow too much may be susceptible to rutting and bleeding, while those that are too stiff may be susceptible to fatigue cracking.
Safety. Asphalt cement like most other materials, volatilizes (gives off vapor) when heated. At extremely high temperatures (well above those experienced in the manufacture and construction of HMA) asphalt cement can release enough vapor to increase the volatile concentration immediately above the asphalt cement to a point where it will ignite (flash) when exposed to a spark or open flame. This is called the flash point. For safety reasons, the flash point of asphalt cement is tested and controlled.
Purity. Asphalt cement, as used in HMA paving, should consist of almost pure bitumen. Impurities are not active cementing constituents and may be detrimental to asphalt performance.
· GRADING SYSTEM OF BITUMEN(US PROCEDURE):
Asphalt binders are typically categorized by one or more shorthand grading systems according to their physical characteristics. These systems range from simple to complex and represent an evolution in the ability to characterize asphalt binder. Today, most state agencies use or are planning to switch to the Super pave performance grading (PG) system.
· Penetration Grading:
Based on the depth a standard needle will penetrate an asphalt binder sample when placed under a 100 g load for 5 seconds (see Figure 3). The test is simple and easy to perform but it does not measure any fundamental parameter and can only characterize asphalt binder at one temperature (77°F). Penetration grades are listed as a range of penetration units (one penetration unit = 0.1 mm of penetration by the standard needle). Typical asphalt binders used in the U.S. are 65-70 pen and 85-100 pen. This system is not used in Hawai'i, although the current asphalt used would meet 805-100 pen specifications.
Figure 3: Penetration Needle
· Viscosity Grading:
Measures penetration (as in penetration grading) but also measures an asphalt binder's viscosity at 140°F and 275°F. Testing can be done on virgin (AC) or aged (AR) asphalt binder. Grades are listed in poises (cm-g-s = dyne-second/cm2) or poises divided by 10. Typical asphalt binders used in the U.S. are AC-10, AC-20, AC-30, AR-4000 and AR-8000. Viscosity grading is a better grading system but it does not test low temperature asphalt binder rheology.
· Superpave Performance Grading (PG) System:
The Superpave PG system was developed as part of the Superpave research effort to more accurately and fully characterize asphalt binders for use in HMA pavements. The PG system is based on the idea that an HMA asphalt binder’s properties should be related to the conditions under which it is used. For asphalt binders, this involves expected climatic conditions as well as aging considerations. Therefore, the PG system uses a common battery of tests (as the older penetration and viscosity grading systems do) but specifies that a particular asphalt binder must pass these tests at specific temperatures that are dependant upon the specific climatic conditions in the area of intended use. Therefore, a binder used in Hawai'i would be different than one used in, say, Alaska.
Superpave performance grading is reported using two numbers – the first being the average seven-day maximum pavement temperature (in °C) and the second being the minimum pavement design temperature likely to be experienced (in °C). Thus, a PG 64-16 is intended for use where the average seven-day maximum pavement temperature is 64°C and the expected minimum pavement temperature is -16°C. Notice that these numbers are pavement temperatures and not air temperatures. The typical PG grade used in Hawai'i is a PG 64-16. Realistically, pavement temperatures in Hawai'i will never dip down to -16°C, but the typical asphalt binder used will meet this standard so it is graded as such.
· SPECIFICATIONS OF DIFFERENT GRADES OF BITUMEN:
Sr.No. | Characteristics | 80/100 | 60/70 | 30/40 | 10/20 |
1 | Specific Gravity at 27 0C min | 0.98 | 0.99 | 0.99 | 1.00-1.05 |
2 | Water percent by wt.max | 0.2 | 0.2 | 0.2 | - |
3 | Flash point, 0C | 175 | 175 | 175 | 225 |
4 | Softening point 0C | 35-50 | 40-55 | 50-65 | 65-80 |
5 | Penetration at 25 0C, 100 g 5 sec in 1/100 cm | 80-100 | 60-70 | 30-40 | 10-20 |
6 | Ductility at 27 0C, in cm. min | 75 | 75 | 50 | 2.5 |
7 | Loss on heating, percentage by wt.Max | 1 | 1 | 1 | 0.10 |
8 | Penetration of residue | 60 | 60 | 60 | - |
9 | Percent by wt. soluble in carbon di- sulphide, min | 99 | 99 | 99 | 99 |
· TEST PROCEDURES:
All Test procedures Depends on
1. Characteristics
2. Test Development
3. Specifying Authorities
4. Cutback Bitumen’s
5. Bitumen Emulsions
Characteristics:
The main characteristics that bitumen must have are as follows:
Consistency: the degree of fluidity or viscosity of the bitumen at a standard temperature. As the viscosity of bitumen varies according to its temperature, when comparing grades of bitumen it is essential to carry out the tests at a standard temperature.
Safety: to ensure that bitumen may be used safely, it is essential 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.
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 levels.
However, there are two important points to be taken into account when considering these test procedures.
First, 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. Modem technology is continually being employed by major bitumen manufacturers at their research centers and in industry sponsored university research projects to find new ways of measuring the physical properties of bitumen, and translating these into specifications relating to 'road performance'. Specifying Authorities Second, various organizations representing bitumen manufacturers and users have laid down standard test procedures. Major internationally used methods are:
IRC Indian Road Congress
ASTM American Society for Testing and Materials (USA)
AASHO American Association of State Highway Officials (USA)
DIN Deutsche Industrie Norm (Germany)
IP Institute of Petroleum (UK)
LCPC Laboratoire Centrale des Ponts at Chaussées (France)
SA Standards Australia (Australia)
Paving Grade Bitumens:
The test procedures used for paving grades of bitumen are as follows:
Penetration test
Viscosity
Flash Point
Ductility
Solubility
Effect of Heat and Air
Softening Point
Solubility: indicates the degree of contamination of the bitumen by other matter and therefore the presence of pure bitumen, the active adhesive or binding element. The 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 movi ng film of bitumen is heated in an oven at 163°C for 60 minutes. The viscosity is measured before and after treatment. Also, the ductility is measured after treatment.
Cutback Bitumens:
For cutback bitumen’s, in addition to the viscosity and flash point tests, the following test is included in specifications:
Distillation test
Bitumen Emulsions:
Bitumen emulsions are subject to their own test procedures. Some of the tests used for determining their properties are as follows:
Consistency (Engler Viscosity test)
Water Content test
Sedimentation test
Stone Coating Ability and Water Resistance test
Particle Charge test
Sieve Residue test
Residue from Evaporation test
· USES AND MIXTURES:
1) Road Construction and Maintenance
2) Variable Factors
3) Hot Mix
4) Mixture Specifications
5) Road Recycling
6) Industrial Usage
Road Construction and Maintenance:
For many years well over 80% of world consumption of bitumen, which is estimated at 100 million tonnes, has been used for paving applications, the construction and maintenance of roads. The rest 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. Therefore, 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
in 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 contact of roadbuilding, 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 it 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.
Aggregates is the term used to describe a mixture of hard non-metallic minerals such as crushed rock, gravel, sand and slag. Aggregates must meet engineering specifications as regards shape, strength, surface characteristics and size. The sub-base is the first layer put down by the roadbuilder and consists of compacted stone,
gravel or sand. Its function is to contribute towards the strength of the road and give the roadbuilding machinery an operating platform.
The roadbase is the main working layer of the road that gives it strength and flexibility. it is
made up of graded mineral aggregates. When roads have to carry a great deal of traffic, the roadbase mixture also contains bitumen because the load bearing performance is twice that of a non-treated granular base. The base course is a mixture of aggregates and bitumen. 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 aggregate and bitumen. It has not only to act as a smooth running surface for the traffic but 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 combined depth of the bituminous layers is usually between 20 and 200 millimetres.
Variable 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 tones per kilometer. A highway engineer may call for bitumen to be applied to three courses, with tack coats in between, because of the mixture's superior load bearing properties. In this case bitumen consumption can amount to 1000 tones per kilometer. The bitumen percentage in an aggregate/bitumen mixture is usually between 4-8%.
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 aggregates, which have been carefully graded to meet the 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, at a temperature of up
to 160°C, is carried to the construction site and laid while still hot.
This describes in simple terms a process in which skill and experience are combined with computerized control systems to carry out a complex series of operations. Various sizes of aggregates 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 supply of bitumen, so 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 as it is exposed to air. If the mixing process takes too long the durability of the mixture will be impaired. To provide consistent high quality mixtures, continuous operation of the plant is required which 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 based on the road gangs' programmes 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 a 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. With cutbacks and bitumen emulsions, lower aggregate (stone) temperatures (30-100°C) can be used: mixing may be carried out on site or by using mobile mixing plants. This is one of the significant advantages of using these bitumen’s when the design of the road allows them to be specified.
Mixture Specifications:
Asphalts have been classified into a number of different types, which may be simply stated as:
Asphaltic Concrete: a dense, continuously graded mixture of coarse and fine aggregates, mineral filler and bitumen produced hot in a mixing plant. It is delivered, spread and compacted while hot.
Bituminous Macadam: a road with a graded aggregate and bituminous coating, in which the mechanical interlock of the aggregate particles contributes significantly to its strength.
Open-graded Asphalt: an asphaltic mix using aggregates containing only small amounts of fine material and providing a high percentage of air voids.
Stone Mastic Asphalt: a gap-graded wearing course mix with a high proportion of coarse aggregate content which interlocks to form a stone-on stone skeleton to resist permanent deformation. The mix is filled with mastic of bitumen and filler.
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 more modem bitumen emulsions in place of cutbacks.
Surface treatments: including dressings and coats, involve spraying a coating of bitumen onto the surface of a wearing course. It can be sprayed as an emulsion, a cutback or paving grade bitumen. Either a single or double coating of fine aggregates or stone chippings is applied. These treatments are applied to renovate and waterproof old roads that require maintenance. An example of such a treatment is a fog seal which is a coat of bitumen emulsion applied to an existing surface to seal cracks as maintenance
treatment.
Bituminous Slurry Surfacing: an important maintenance treatment for the surface in which a mixture of fine aggregates and filler and emulsified bitumen is applied to a structurally sound road surface for minor shape corrections and to improve skid resistance. It has the advantage that it can be applied rapidly at a relatively low cost by a truck-mounted 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 emulsions 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.
Industrial Usage:
The use of bitumen in industry accounts for less, than 20% of world bitumen production. 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 bitumen saturated felt laid onto a flat roof with layers of bitumen below, between and above them. In more complex roofing projects, bitumen is to be found holding in place a protective coating of chippings on the cantilevered roof of a sports stadium. By contrast, bitumen is also used in damp proofing and floor composition tiles. Other materials, particularly felts and papers, are impregnated with bitumen to improve their performance as regards insulation. Packaging papers, printing inks, linoleum, sound deadening felts hidden inside car bodies and the under sealing compounds beneath them, electrical insulating compounds and battery boxes are some of the hundreds of industrial and domestic products likely to contain bitumen.
· RATE ANALYSIS OF BITUMEN:
A) Take 1 km road, then what is the quantity of bitumen required?
B) For that first we have to know the crust details of general section of road.
C) Generally Bitumen mixes which are using for Base and Surface(Black Topping) layers are
1) B.C (Bituminous Concrete)
2) D.B.M (Dense Bitumen Macadam)
3) B.U.S.G (Built Up Spray Grout)
D) Out of this we are taking B.C for estimating the rate of Bitumen Concrete
E) Here we have to observe that we can’t find only bitumen quantity as well as bitumen rate for 1 km.
F) Instead of that we can take some particular quantity of B.C mix then we can estimate the cost of B.C only but not bitumen.
G) So we are taking 205 cumec standard quantity for calculating B.C, then we will find rate per cumec of B.C
The calculation is follows like this.
Bituminous Macadam |
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Unit = cum |
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Taking output = 205 cum (450 tonnes) |
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a) Labour |
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Mate | day | 0.840 | 209.00 | 175.56 | |
Mazdoor working with HMP, mechanical broom, paver, roller, asphalt cutter and assistance for setting out lines, levels and layout of construction | day | 16.000 | 140.00 | 2240.00 | |
Skilled mazdoor for checking line & levels | day | 5.000 | 140.00 | 700.00 | |
b) Machinery |
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Batch mix HMP 100-120 TPH @ 75 tonne per hour actual output | hour | 6.000 | 17613.00 | 105678.00 | |
Mechanical broom hydraulic @ 1250 sqm per hour | hour | 2.200 | 268.00 | 589.60 | |
Air compressor 250 cfm | hour | 2.200 | 240.00 | 528.00 | |
Paver finisher hydrostatic with sensor control @ 75 cum per hour | hour | 6.000 | 2012.00 | 12072.00 | |
Generator 250 KVA | hour | 6.000 | 900.00 | 5400.00 | |
Front end loader 1 cum bucket capacity | hour | 6.000 | 607.00 | 3642.00 | |
Tipper 10 tonne capacity | tonne.km | 450 x L | 2.00 | 2700.00 | |
Add 10 per cent of cost of carriage to cover cost of loading and unloading |
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| 270.00 | |
Smooth wheeled roller 8-10 tonnes for initial break down rolling. | hour | 6.00x0.65* | 346.00 | 1349.40 | |
Vibratory roller 8 tonnes for intermediate rolling. | hour | 6.00x0.65* | 1159.00 | 4520.10 | |
Finish rolling with 6-8 tonnes smooth wheeled tandem roller. | hour | 6.00x0.65* | 861.00 | 3357.90 | |
c) Material |
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i) Bitumen@ 3.3 per cent of mix | tonne | 14.850 | 23739.00 | 352524.15 | |
weight of mix = 205 x 2.2 = 450 tonne |
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ii) Aggregate |
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Total weight of mix = 450 tonnes |
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Weight of bitumen = 14.85 tonnes |
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Weight of aggregate = 450 -14.85 = 435.15 tonnes |
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Taking density of aggregate = 1.5 ton/cum |
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Volume of aggregate = 290.1 cum |
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*Grading I ( 40 mm nominal size ) |
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37.5 - 25 mm 15 per cent | cum | 43.510 | 371.70 | 16172.72 | |
25 - 10 mm 45 per cent | cum | 130.550 | 389.16 | 50804.41 | |
10 - 5 mm 25 per cent | cum | 72.530 | 467.71 | 33922.79 | |
5 mm and below15 per cent | cum | 43.510 | 467.71 | 20349.93 | |
or |
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GradingII(19 mm nominal size) |
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25 - 10 mm 40 per cent | cum | 116.040 | 389.16 | 45157.75 | |
10 - 5 mm 40 per cent | cum | 116.040 | 467.71 | 54272.72 | |
5 mm and below 20 per cent | cum | 58.020 | 467.71 | 27136.36 | |
* Any one of the alternative may be adopted as per approved design |
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for Grading I ( 40 mm nominal size ) |
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d) Overhead charges @ 08 % on (a+b+c) |
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| 49359.72 | |
e) Contractor's profit @ 10 % on (a+b+c+d) |
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| 66635.63 | |
Cost for 205 cum = a+b+c+d+e |
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| 732991.91 | |
Rate per cum = (a+b+c+d+e)/205 (For Grading I) |
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| 3575.57 | |
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| say | 3576.00 | |
for GradingII(19 mm nominal size) |
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d) Overhead charges @ 08 % on (a+b+c) |
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| 49785.08 | |
e) Contractor's profit @ 10 % on (a+b+c+d) |
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| 67209.86 | |
Cost for 205 cum = a+b+c+d+e |
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| 739308.49 | |
Rate per cum = (a+b+c+d+e)/205 (For Grading-II) |
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| 3606.38 | |
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| say | 3606.00 |
