Question:
Describe about Engineering Construction for Coke Production.
Answer:
Asphalt
The definition of asphalt is a black or brown, tar-like substance that is used to cover roadways and is usually mixed with gravel.
Types of asphalt
- Coal tar pitch
This is a type of asphalt that results from coke production. It is the byproduct of black residue that remains in the distillation still after the process of distillation has been completed. Moreover, this type of asphalt is usually similar to the refined tar with an exception to its physical properties (Oikonomou, 2005). The most common method to distinguish this asphalt with the refined tar is the substance softening point. The tar pitch does emit a special smell when heated to high temperatures.
- Petroleum asphalt
This is the residue of crude oil after distillation. The asphalt is usually dark in color with a shiny outlook. It is also resistance to very high temperatures and contains little volatile organic compounds due to the high temperature that it is usually subjected to the distillation process. Even though, there are usually some hydrocarbons that exist which can cause danger to humans.
- Natural asphalt
This kind of asphalt is usually found deposited in the underground as a result of their accumulation over time. Fortunately, such asphalts are usually harmless to humans due to their natural evaporation and oxidation.
- Porous asphalt
This asphalt allows water and other liquids to pass through the ground surface into the underground beds. This type of asphalt is found below the car parking lots where they assist in the enhancement of stormwater so as to improve its quality as it seeps underground.
5. Hot Mix Asphalt
This asphalt is the most recommended for the construction of the driveways. This is because it gives the best design features and finished appearances. In addition, it is usually strong and can withstand thawing and freezing. The hot mix asphalt is also resistant to salt water and requires low maintenance (Zimmermann, 2002). Generally, the asphalt is the cheapest among the types of asphalt discussed above.
- Mastic asphalt
It is also known as sheet asphalt. It contains fewer amounts of bitumen content. As such , it is the most suitable for the construction of floors, roofs, footing paths.
Key ingredients of asphalt
Importance
Aggregate do play an important part in providing strength to concrete during the construction process. In addition, the transition zones of concrete is the region between an aggregate and cement paste and is responsible for providing compressive strength to cement (Hollon, 2001).
Properties of rock types
Although aggregate is considered inert filler, it is a necessary component that defines the concrete’s thermal and elastic properties and dimensional stability. Aggregate is classified as two different types, coarse and fine. Coarse aggregate is usually greater than 4.75 mm (retained on a No. 4 sieve), while fine aggregate is less than 4.75 mm (passing the No. 4 sieve). The compressive aggregate strength is an important factor in the selection of aggregate (Linden, 1997).
Asphalt production
Asphalt can be manufactured from either oil refinery of naturally through deposition. For example, a manufacturer from crude petroleum oil is obtained through separation of various fractions through the distillation process. After the separation of the fractions from the distillation, the end products are usually paraffin, gasoline, asphalt, lubricating oil among others. Due to the high density of asphalt, it is usually deposited at the base of the distillation chamber. The refining process begins at the piping of the crude from the storage tank to the tubers where the temperature is highly raised (Geller, 2004). This always happens to achieve primary distillation. After this, it is made to enter atmospheric distillation tower. Here, the crude oil is subjected to pressure which makes the lighter and most volatile components to vaporize. It is then separated on further heating and pressurization to obtain gasoline, kerosene and diesel oil among other petroleum products. The heavy residue that is left is referred to as topped crude (Evangelista and Brito, 2007). The topped crude is usually moved to vacuum distillation which removes high boiling fractions so as to reach the asphalt.
Artificial aggregate is a light mixture of fly ash binders and water. They are usually round shaped. However, it can be made into any other irregular form.
Artificial aggregates are usually advantageous in that it is very firm, have a very fast absorbability and a low volumetric weight. This property usually makes it to be used in concrete mortar without changing their consistency.
Grading of aggregates
Fine aggregates- according to the international standards specification for the architects, such aggregates pass 4.75 mm in diameter size. The aggregates may be described as natural sand, crushed stone sand or crushed gravel sand (Zakaria et al., 2006).
Uses of aggregates
Aggregates are usually important in that they provide strength during the construction process. The fine aggregates, for instance, the fine aggregates ensures that there is no weakness in the construction structure. In addition, the fine aggregates are responsible for the maximum surface area coverage with the concrete to achieve a smooth layer (Paranavithana and Mohajerani, 2006).
Aggregate shape and texture
The shape and texture of aggregate are usually important for effective compaction, workability and construction purposes. Different shapes of an aggregate are preferred by different purposes in which it serves. For instance, the shape of an aggregate defines its ability to interlock with each other therefore providing stiffness and strength in the construction process. There are also rounded particles that are known to create less particle to particle interlocking as compared to the angular counterparts.
Classification of aggregates based on origin
- Natural aggregates
Natural aggregates are those that are naturally occurring and are buried within the river, lakes or ocean beds. They are characterized with round shaped, smooth surfaces with waterborne fragments of rocks. They are usually graded in different sizes. There are those with larger gravel pieces while others have smaller gravel sizes (Van et al., 2000). They are constituted with minerals such as the granite, limestone, sandstone among others.
- Bye product
This includes the materials that arise from industrial wastes and other engineering operations which possess best qualities of aggregates. Examples include cinder found from burning of coal locomotives.
Classification based on texture
- Fine aggregates
Fine aggregates in most cases do consist of the natural sand or even the crushed stone with the majority of the particles passing through a sieve of 9.5mm.
- Coarse aggregates
In this case, the coarse aggregates are usually obtained from the crushing or breaking down of rocks with the help of explosives and machines leaving large particles of aggregates of sizes ranging from 6mm or above. They are necessary for construction purposes as well.
Classification of aggregates based on density
The aggregates may be classified with reference to their nature of weighing. For instance, there are normal weight aggregates, heavyweight aggregates, and lightweight aggregates. The normal weight aggregates are the natural mineral aggregates and do have a bulk specific gravity of about 2.5. This is the most commonly used class of material in the developed and developing countries. The heavyweight aggregate is usually synthetic in nature and may have a typical weight of about 2100kg/m3. Some of the most common types of the heavyweight aggregates are the magnetite, hematite, limonite, and barite (Linden et al., 2003). Lightweight aggregates are usually sourced from the manufactured varieties of aggregates. They do have a bulk density less than 1100kg/m3.
Porosity of aggregates
In between the aggregate particles there exist voids filled with air. The amount of the voids does determine the nature of porosity of each given aggregate. Besides the air, the voids may also contain water particles. The size of the voids between the particles does have an effect on the design process of some construction processes. For instance, those constructions that require finely divided aggregates do have less amount of pore space. As such, if the coarsely divided aggregates are used then the resultant outcome will not be effective.
Compaction of asphalt
Asphalt compaction means the process of reducing the air asphalt mixture by means of external forces thereby making the particles to be more closely packed and arranged (Isenring et al, 1999). Compaction results in an increased density of the mixture. There are various coverage techniques that are used in the process of asphalt compaction. These techniques include
Initial Compaction by Use of a Finisher
This is done using a low pre-compaction light roller to press the mixture of air and asphalt into a dense degree. High compaction heavy rollers are not encouraged since they are prone to damaging the uniformity of the layers. Below is a diagram of the process
Static Compaction
This process is attained by using the deadweight of the roller and is mostly done using the pneumatic rollers and the tandem rollers. It has a low effect on the mixture and normally applied when the initial compaction was low.
Vibratory Compaction
This is a technique used for optimum compaction. It is always applied to increase the relationship between the density of the mixture and the deadweight (Ahmedzade and Sengoz, 2009). Below is an illustration of how it is conducted
Equipment’s used in compaction
There are various equipment’s that are used in compaction which includes the tamper, pneumatic steel roller, and the wheel roller
Tampers
These are machines that are used for compaction in situations where the large compacting machines have failed are cannot be used (Chang and Meegoda, 1999). They are powered by gasoline engines
Steel wheel rollers
These are the type of equipment that self-propelled such that they apply steel drum in the compression of the underlying mixture of air and asphalt. Normally, these rollers pose one or more drums but not more than three (Appleman et al., 2016). The most common rollers used is the 2 drum since it is static and vibratory and have a wider range of diameter. Besides, their weight can be enhanced through a process of compact effort where the wheels are ballasted with either water or sand
Below is a picture of the steel wheel roller
Pneumatic wheel rollers
These kind of rollers are also self-driven and they use pneumatic tires in compression of the underlying mixture of air and asphalt (D’Angelo et al, 2008). They employ tires that are not threaded on the axles for complete compaction. The tire contains a pressure regulating device which varies the tire pressure depending on the extent of compaction required. Below is a picture of the pneumatic wheel rollers
These wheel rollers are most preferred due to some advantages listed below
- The results into a uniform, tight and denser surface as compared to other
- They provide a stiff compaction without causing cracks on the surface
- They also provide a uniform degree of compaction
Besides, they have a disadvantage of causing deformation that is hard to repair when they contain a rubber modifier.
Test reporting for the engineer to ensure acceptance and suitability
Sampling and testing of the products should be done in accordance with set standards and specifications. The samples should then be taken to the engineer to allow or familiarity with the materials. Besides, proper sampling techniques should be applied to ensure that quality and assurance standards are met (Tayebali et al., 1992). Some of the sampling aspects should involve soil sampling, aggregate sampling and also concrete sampling.
Safe handling procedures when working with asphalt
When working with asphalt, it is important to consider some factors. Below are the safety rules when dealing with asphalt.
- Always ensure that the workers are well trained in the hazards of asphalt
- At the terminal of asphalt , the driver should ensure that no contamination of any kind is caused when loading and offloading since it may result to eruptions
- During the loading of the container having the asphalt, one should ensure that he stays upwind to prevent contamination by dangerous hydrogen fluoride fumes.
- At the mixing plant, plant operators should ensure that all connections are properly done to prevent outbreaks.
Reference
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