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Bitumen is described as 'mankind's oldest engineering material'. This fact is supported by some evidence. Back at the time, nearly 3000 years BC, the Sumerians in Mesopotamia used bitumen to fasten ivory or pearl into the eye sockets of their statues. They also sculptured votive offerings which the mixture of their sculpture is originally from bitumen and clay.
From the finding, it is proven that some thousand years later, bitumen was being used by the early Babylonians as a building material because of its properties as a cement and water proofing agent. Later, bitumen became the standard material and being used in civil engineering and architectural projects to hold bricks and stones together which used to line drains, watercourses and grain storage. It was also being used to create damp courses and seal the flat roofs of the houses in the same way as it is used today. It is also important in paving (Ask.com, 21 Dec 2010).
Other Evidence found that, about 600 BC King Nebuchadnezzar of Babylon rebuilt the city wall, which he intends to restrain the water of the Euphrates with burnt bricks and bitumen because the old wall which is made of dried clay bricks had failed to keep the waters at the bay. The Babylonians had developed a technique using layer of bricks, bitumen and clay which they reinforced with reed for construction purposes. The system was so successful whereas they were able to build towers up to twelve storeys high. The evidence is proven when archeologists excavating the site of the ancient city and they found traces that bitumen had been used for the construction of the building.
Instead of using bitumen for construction, the reason why bitumen was widely used in this area was its availability in various forms. It can be found in certain places where we can find it easily. It was also available as a solid material in the form of bituminous limestone, which was used as the basis for small carvings. Because of its availability, bitumen has taken parts in many great legends of Biblical and pre-Biblical times. It is said that, bitumen has being used in the building of the Tower of Babel and for the waterproofing of Noah's Ark and Moses' wicker basket (Zayn Bilkadi, Dec 1984).
The Romans used bitumen for medicinal purposes whereas they use bitumen for preventing and curing a number of ailments including boils, toothache and ringworm. Meanwhile, Roman ladies used bitumen for cosmetic purposes whereas they used bitumen as a means of beautifying their eyebrows. Bitumen also was being used for maritime usage whereas Christopher Columbus and Sir Walter Raleigh found that the lakes of asphalt in Trinidad are 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.
On the other 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, the usage of bitumen for the road construction is to solve the problem of the dust raised by the horse-drawn traffic in towns. The availability of supply of tar from local coal-gas works led to the use of tar for treating streets and pavements. They started to realize the important of streets and road which would lead to the unimagined standard of smoothness and durability for the elements needed for their creation in the future. 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. (Asphalt Origin,)
Nowadays, a small scale of high quality bitumen can be exploited from petroleum which is a readily available source of low cost. The production of bitumen grew with the rise of the motorcar and the universal demand for paved highways. The proportion of bitumen which is resulted from petroleum refining whereas lead that today most bitumen sources is from the distillation of crude petroleum oil. (BP , 2010).
Bitumen is a versatile material that is widely used in civil engineering. Bitumen is a mixture of organic liquid that are black, oily, highly viscous that is a naturally occurring organic product by product of decomposed organic materials. This basically consists of hydrocarbons ,carbon hydrogen the rest becomes oxygen, sulfur, nitrogen and trace the various metals such as nickel, vanadium, lead, chromium, mercury and also arsenic, selenium and other toxic elements. Bitumen can provide good preservation of plants and animal fossils.
Bitumen and asphalt is two different things. In American asphalt used to mean bitumen but outside American asphalt refers to the mixture of bitumen and aggregate laid as a road surface.
Figure 2.1: Bitumen
2.3 Sources of bitumen
Bitumen can be derived from different type of sources. It occurs naturally, but for most occasions, the world relies on petroleum for the supplies of bitumen. The bitumen consists of crude petroleum oil that normally varies between 25% and 40%, but content of crude oil can vary between 15% and 80% (BP 2010). There are three categorization for crude oil bitumen that is bitumen based, paraffin based or bitumen and paraffin based.
Bitumen present in the form of colloidal dispersion or in a true solution based on the type of crude petroleum oil. In the refining process, the proportion of oil to bitumen particles changes because of petroleum oil is taken away by distillation. Relatively in few numbers, this particle become closer to one another and their size increase when it is dispersed.
At the time the distillation process stopped, the petroleum becomes a colloidal dispersion of black solid known as asphaltenes. This asphaltenes are dispersed in an oily brown yellow liquid, known as the maltenes fraction. It also react as a stabilizing agent to keep the asphaltenes in suspension are another group of hydrocarbon known as resins.
Normally bitumen is found in a few forms, from the hard, easily crumbled bitumen in rock asphalt to the softer, more viscous material found in tar sands and so-called asphalt lakes. It is normally consist of varying proportions of mineral and vegetable impurities that need to be extracted before in can be used as engineering material. Bitumen also can be found as asphaltite. It is natural bitumen without an impurity that varies in the amount the asphaltite can be dissolve in carbon disulphide. Natural petroleum like bitumen naturally occurs as the result from the special decompositions of marine debris.
After thousands of years it has been move through porous rock such as limestone and sandstone often by volcanic action. In certain areas notable for their petroleum resources, like in the Middle East, semi fluid bitumen can be found oozing out of fissures near hot spring or seeping out of the ground. Rock asphalt, it is more costly to move around and to process. This is because it's variable and relative low content of bitumen and tends to be found away from the places where bitumen needed.
It is important to distinguish between bitumen and coal tar. Even though coal tar is black and viscous like bitumen, it is obtained from the carbonization of coal that why it is very different chemical properties. Many part of the world in engineering project, from the construction of transcontinental highways to the waterproofing of flat roof surfaces, depending on the specific nature of asphalt. Petroleum crude oil processed by the industry to provide all but a small part of this material is important.(BP, 2010)
2.4 Manufacturing process
Manufacturing of bitumen consist of three processes which is refinery process, storage and distribution.
2.4.1 Refinery process
In oil refinery process, the crude oil is divided into different groups based on their boiling range. The first stage of refinery process is atmospheric distillation. In this process the crude oil is heated about 3000 C to 3500 C and the more volatile components in the crude oil such as petrol and kerosene are distilled off. Residue from this process called atmosphere residue, which is need further distilled under vacuum. Because of the applied vacuum, the effective distillation point is 5000 C - 5600 C. this vacuum distillation process produce more volatile products called as vacuum distillates and leaves vacuum residue which is a non volatile residue of high viscosity.
Based on the crude oil origin, the vacuum residue can be used directly as bitumen and for some cases of crude oil it needs additional process to meet certain specification such as air blowing of the residue. To ensure consistent product, the air blowing needs careful selection and control of process temperature, air rate and residence time. In other hand bitumen are produced by blending vacuum residue with asphaltenes which is derived from the production of lubricating oils. The selection of crude is the most important element of bitumen manufacture because it is required expertise and experience to yield a satisfactory product.
Large permanent tank made of mild steel plate use to stored bitumen at refineries with capacities of between 100 and 10000 tones. To make sure the bitumen remain fluid, steam or hot oil is pumped during heating oils in the heavily insulated tanks.
To make sure the bitumen not cool and unworkable the product must be kept between 150Â°C-190Â°C throughout the supply chain.Â The temperature of bitumen can fall about 7oC to 10oC when it is loaded into a road tanker and it will continue to fall further while in transit. Most of the bitumen will be transferred from the refineries using the road tankers with capacities of 10 to 40 tones. The road tanker is insulated by single-compartment tanks, normally with some kind of heating such as heating tubes. Insulated rail cars are sometimes used to transport bitumen to intermediary depots with reheating facilities.
2.5 Properties of Bitumen
Bitumen is a durable and strong adhesive use as a binder in many applications with other material without affecting their properties. Its durability is important to major engineering part such as road and water ways. Bitumen is insoluble in water and can be used as an effective water proofing sealant. Bitumen can be used to line watercourses because it resist and do not react with acid, alkalis, salt and does not contaminate water.
Bitumen is soften and thermoplastic material. Bitumen becomes liquid when heated and hardens when it cools. Bitumen can used easily in the area where its need to used because it can readily be liquefied by one of three methods that's applying heat, dissolving it in petroleum solvents or dispersing it in water (emulsification).
Total production of bitumen is larger use in road construction. This is because bitumen gives flexibility to the mixed mineral aggregates that been used in road construction. It is available with economic cost all around the world.
2.6 Types of Bitumen
There are several types of the bitumen below based on BP bitumen 2010:
2.6.1 Paving grade bitumen
This type of bitumen considered as a parent bitumen of the other form of bitumen produced below. It is refined and blended to fulfill the industrial and road engineering specification that considered different climate condition.
2.6.2 Cutback bitumen
This type of bitumen has lower viscosity than other types of bitumen. This bitumen has been diluted in order to make it more flow able and suitable for application. Cutback bitumen mostly is used for cold weather bituminous, road construction and maintenance. In cutback bitumen suitable solvent is used to lower the viscosity of the bitumen. Fluidity of bitumen depends on the proportion of solvent and degree of hardness of the bitumen base. Cutback bitumen classified based to the time it takes to become solid, as rapid curing (RC), medium curing (MC) or slow curing (SC). RC is recommended for surface dressing and patchwork.
MC is recommended for premix with less quantity of fine aggregates. SC is used for premix with appreciable quantity of fine aggregates. The solvent used for preparation of cutback of bitumen are white spirit commonly used for RC grades, kerosene for MC grades and diesel for SC grades. In view of the environment, health and safety cutback bitumen cause a problem because the solvent used evaporates and currently the evaporation is regarded as a potentially undesirable characteristic.
2.6.3 Bitumen emulsions
Frequently the bitumen that been applied to mineral aggregates substrates in road construction is in the form called bitumen emulsion. Bitumen emulsions are the dispersion of bitumen in an aqueous continuous condition and been stabilized by the addition of emulsifier. Bitumen emulsions are the ideal binder can be used in hill road construction which the process of heating the bitumen or aggregates are not easy in that area.
Rapid setting emulsions usually used for surface dressing work, Medium setting emulsions use for premix jobs and patch repairs work and slow setting emulsions are ideal use during rainy season. Around 60% of bitumen content in the emulsion and the left over is water (Tom V. Mathew and K V Krishna Rao, 2007). During the road construction, these emulsions will breaks down resulting in released of water and the mix will starts to set. Grade of bitumen affect the time of setting. Bitumen emulsion is ideal for used in road construction because it have low viscosity and workable in ambient temperatures.
But to apply this bitumen in road making process, it requires controlled breaking and setting. Bitumen should not break before it is laid on the surface of road but, once it placed, it should break quickly. This implies that the road can be in service without delay.
2.6.4 Modified bitumen
Modified bitumen is bitumen treated with modifiers. Certain additives added as bitumen modifiers to improve the service performance by changing such properties as their durability and hardness. Natural rubber, polymer and thermoplastic are commonly used to modify bitumen. This is an exciting development of growing importance due to the ability of modem technology to satisfy the demands of the bitumen and international market. Modified bitumen will contribute towards a longer road life and lower cost maintenance.
2.6.5 Multi-grade Bitumen
This type of bitumen is chemically modified bitumen. It has multi properties that are properties of hard paving bitumen at high service temperature with the properties of soft paving grades bitumen at low temperature. Multi-grade bitumen gives improvement in resistance to deformation
2.6.6 Industrial bitumen
Industrial bitumen also known as oxidized bitumen. This bitumen is made by blowing air through hot paving grade bitumen called blowing process. The result from blowing process is a product that softens bitumen at higher temperature than provide by paving grade bitumen softens. It also has rubberlike properties and its viscosity is less affected by changes in temperature than is the case with paving grade bitumen.
2.7 Requirement of Bitumen
The some requirement properties of bitumen depend on the mix type and construction. In general, Bitumen should fulfill the following properties: (Prof. Tom V. Mathew, 2009)
The bitumen should not be highly temperature susceptible: during the hottest weather the mix should not become too soft or unstable, and during cold weather the mix should not become too brittle causing cracks.
The viscosity of the bitumen at the time of mixing and compaction should be adequate. This can be achieved by use of cutbacks or emulsions of suitable grades or by heating the bitumen and aggregates prior to mixing.
There should be adequate affinity and adhesion between the bitumen and aggregates used in the mix.
2.8 Modification of bitumen
Many studies have been conducted in order to improve the performance of bitumen used in road pavement by modified bitumen with other material. Additional materials such as rubber, polymer and epoxy resin have been used as modifier in bitumen in the previous research. This study stresses on the usage of fly ash as an additive in bitumen.
2.9 Coal combustion products
Fly ash is one of the coal combustion residues. Coal combustion residuals are formed during coal-burning processes in power plants. Coal combustion product consists of several materials: (R.Â Majko, 1996).
2.9.1 Fly ash
Fly ash is the fines ash of coal ash particles from combustion of coal. It is called fly ash because it is transported from combustion chamber by exhaust gases. Fly ash is a fine powder produce from the mineral contain in coal. It also consists of noncombustible mater in coal and a small amount of carbon that's remains because of incomplete combustion. Fly ash is usually light tan in color. It is commonly consists of silt sized and clay sized glassy spheres which is gives fly ash a consistency somewhat like talcum powder. The property of the fly ash varies based on coal composition used and plant operating system.http://www.undeerc.org/carrc/Assets/FlyAsh1.JPG
Figure 2.2: fly ash
2.9.2 Bottom ash
Bottom ash and fly ash is two different materials in physical, mineralogical and chemical. Bottom ash is a coarse, granular, and incombustible material which is collected from the bottom of furnaces of combustion of coal in generation of electricity. Different with fly ash, bottom ash coarser than fly ash with grain sizes spanning from fine sand to fine gravel. The type of the bottom ash depends on type of furnaces used to burn a coal.
Figure 2.3: bottom ash
2.9.3 BOILER SLAG
Boiler slag is normally a black granular material with numerous engineering uses. It is formed in cyclone boilers which form a molten ash that's cooled with water. Boiler slag is coarser than fly ash.http://www.undeerc.org/carrc/Assets/BoilerSlag1.JPG
Figure 2.4:boiler slag
2.9.4 FGD GYPSUM
Flue gas desulfurization (FGD) gypsum is also can be defined as scrubber gypsum. FGD gypsum is the product from an air pollution control system which is removes sulfur from the flue gas in calcium based scrubbing systems. It is composed of calcium sulfate and produced by employing forced oxidation in the scrubber. FGD gypsum is most usually used for agricultural activity and for wallboard production.
Figure 2.5: FGD gypsum
2.10 Production of fly ash
Fly ash normally produced from burning of coal for power generation.Â Normally coal is pulverized and blown with air into the combustion chamber. In this part the coal will be ignites, generating heat and producing a molten residue. Then the boiler tubes will extract heat from the boiler and then cool the gas in the chimney. This make the residue from the combustion of coal harden and produce ash known as coal combustion products. The coarse ash kwon as bottom ash andÂ it will fall at the bottom of coal furnaces. In the other hand, the light ash will the light ash will remain suspended in the flue gas and will be collected by electrostatic precipitators, baghouses, or mechanical collection devices such as cyclones.
C:\Documents and Settings\to_pek\Desktop\production of fly ash.gif
Figure 2.6: production of fly ash (ACAA, 1997)
2.11 Utilization and benefit of fly ash
Fly ash have been used many part of the engineering application around the world. The table below shows the utilization of fly ash in the engineering part. (Fly ash facts for highway engineers, 2003).
used in Portland cement concrete (PCC)
-decrease water demand
used in stabilized base course
-provide a strong and durable mixture
-suitable for using recycled base material
-increased energy efficiency
used in flowable fill
-allows placement under freezing conditions
-reach 100% density with no compactive effort
-increase soil bearing capacity
-increase the speed and ease of backfilling operations
Used in soil improvement
-eliminates need for expensive materials
-expedites construction works by improving unstable subgrade
- By improve subgrade conditions, cost saving through reduction in required pavement thickness.
Used in asphalt pavement
-reduce potential of asphalt stripping due to hydrophobic properties of fly ash
-reduce stripping because fly ash consist of lime
-a lower cost than other filler
Used in grouts for pavement subsealing
-develop high ultimate strength
-accomplished quickly with minimum effect to the traffic flow.
-used to correct undermining without
2.12 Type of fly ash
Fly ash is collected use electrostatic precipitators or bag houses and then transferred to large silos for shipment. Fly ash divided base on precise particle size requirement, thus assuring a uniform and quality of product. There are 2 different type of fly ash from combustion of coal in large power plant which is class C and class F.
2.12.1 Class C
Class C fly ash is produced usually from lignite and sub-bituminous coals and normally contains significant amount of Calcium Hydroxide (CaO) or lime (Cockrell et. al., 1970). Fly ash class C will harden when exposure to the water. Class C normally contains more than 15% of lime and can reach until 30% of the composition (Dr. Kamar Shah Ariffin, 2007). Higher of CaO in class C fly ash make it more special with self hardening characteristic. This is because calcium is a good adhesive agent. The existence of pozzolan properties in the fly ash class c make it different from fly ash class F.
2.12.2 Class F
Class F fly ash is produced from bituminous coals and burning anthracite .Class F is normally contains greater combination of silica, alumina and iron about 70% of the composition but low in lime content usually under about 15% of the composition (Dr. Kamar Shah Ariffin, 2007). This fly ash has Siliceous and aluminous material, which itself possesses little or no cementitious value but in finely divided form and in the presence of moisture, chemically react with
Calcium hydroxide at ordinary temperature to form cementitious compounds (Chu et. al.,
2.13 Characteristic of fly ash
2.13.1 Size and shape
Fly ash consist of powdery and fine particle that are in spherical shape, either in solid or hollow and mostly glassy in nature. The carbonaceous in fly ash consist of angular particles. The particle size distribution of bituminous coal fly ashes is usually similar to the silt which is less than a 0.075 mm or No. 200 sieve.
Sub bituminous coal fly ashes are similar to the silt size and it is slightly coarser than bituminous coal fly ashes. A coarser particle can result in a less reactive ash and could contain higher carbon contents.
Figure 2.7: Fly ash particles at 2,000x magnification
By depending on the amount of unburned carbon in the ash, the color of fly ash can be found and vary from tan to gray to black. If the fly ash contains low carbon, the color will be lighter. Lignite or sub bituminous fly ashes are typically light tan to buff in color, representing relatively low quantities of carbon in addition to the presence of some lime or calcium. However, bituminous fly ashes are usually some shade of gray, with the lighter shades of gray generally indicating a higher quality of ash. Â
Figure 2.8: typical fly ash colors
2.13.3 Specific gravity
The specific gravity of fly ash is generally varies between 2.1to 3.0 whereas the specific surface area are varies in range from 170 to 1000 m2/kg that been measured by the Blaine air permeability method.
2.13.4 Loss of ignition
Loss of ignition is a measured of remaining unburned carbon in a coal. It is a critical property of fly ash need to be measured, especially for concrete applications. High carbon levels, the type of carbon, the interaction of soluble ions in fly ash, and the variability of carbon content can cause air entrainment problem in fresh concrete and can affect the durability of the concrete. In some application of fly ash are not affected by the loss of ignition such as filler in asphalt and flowable fill can accept fly ash with high content of carbon.
Chemical compositions of the coal mainly affect the chemical constituents of fly ash. Depending on the coal combustion technology used, the fly ash can be significantly different even though they are produced from the same source and similar chemical composition. Therefore the ash hydration properties with the leaching characteristic can vary a lot between generating facilities.
The combustion and glassification process used at certain power plant will affect the quantity of crystalline material versus glassy phase material because these two substances were depends on these two process. When the maximum temperature of the combustion process is above approximately 12000 C and the cooling time is short, the ash produced is mostly glassy phase material (McCarthy et. al., 1987). Crystalline phase calcium compounds are formed where boiler design or operation allows an extra gradual cooling of the ash particles.
The factors that affect the hydration and leaching properties of fly ash such as the relative proportion of the spherical glassy phase and crystalline materials, the size distribution of the ash, the chemical nature of glass phase, the type of crystalline material, the nature and the percentage of unburned carbon (Roy et.al, 1985).
Generally, the most important factors that influenced the mineralogy of coal fly ash are (Baker, 1987):
Chemical composition of the coal
Coal combustion process including coal pulverization, combustion, flue gas clean up, and fly ash collection operations
Additives used, including oil additives for flame stabilization and corrosion control additives.
The minerals present in the coal dictates the elemental composition of the fly ash. The boiler design and operation dictated the mineralogy of the ash.
2.13.5 Chemical Requirements for Fly Ash Classification
(Dr. Kamar Shah Ariffin, 2007)
Fly Ash Class
Silicon dioxide (SiO2) plus aluminum oxide (Al2O3) plus iron oxide (Fe2O3), min, %
Sulfur trioxide (SO3), max, %
Moisture Content, max, %
Loss on ignition, max, %