Bitumen is used in road construction due to various properties and advantages it has over other pavement construction materials. Advantages of bitumen for road construction is discussed.
Why is Bitumen Used in Road Construction?
Bitumen gain certain unique properties that are inbuilt in it during its manufacture. The bitumen as a raw material in flexible road construction and bitumen as a mix (composing other materials i.e. aggregates/ pozzolans) serves certain advantages, that prompt to use bitumen widely in road construction.
Use of Bitumen in Flexible Road Construction
The reason behind the significant application of bitumen in flexible pavements are explained below:
1. Production of Bitumen is economical
is a by-product of crude oil distillation process. Crude oil itself is a composition of hydrocarbons. The primary products that are available are the petrol, diesel, high octane fuels and gasoline.
When these fuels are refined from the crude oil, the bitumen is left behind. Further treatment of by-product, to make it free from impurities give pure bitumen.
As the primary product demand is of utmost importance to the society, the bitumen as a by product has survival for long. This by product is utilized as a new construction material, without going for any other new resource.
2. Physical and Rheological Properties of Bitumen bring Versatility
The physical and the chemical properties of Bitumen are found to be a function of load level, temperature and the duration of loading. It is a thermoplastic and viscoelastic material.
These dependencies make us to truly access the traffic on the road so that a bitumen mix properties can be varied based on the stress levels calculated. This versatility of bitumen results in a large variety of bitumen mix, based on the road application.
3. The Melting Point of Bitumen is low
It is highly appreciable about the fact that bitumen has a favorable melting point, that helps in both surface dressing and wearing resistance with ease.
The melting point of the bitumen should not be too high, that it can be melted easily during laying the pavement. At the same time, bitumen has a melting point, which would not let the already casted road pave to melt and deform under high temperatures.
In areas of high temperatures, along with this quality of bitumen, the aggregate composition helps to cover up the effect of large temperature.
4. Bitumen can undergo Recycling
As the melting point of bitumen is favorable, it can be melted back to its original state. This is called as asphalt recycling process.
The torn-up asphalt pieces are taken up to the recycling plant, instead of sending them to landfills. This recycled mix can be reused. If necessary, the old bitumen is mixed with new bitumen and new aggregates to make the mix live again.
5. Bitumen gain Adhesive Nature
As explained in the production of bitumen, it is free from hydrocarbon and hence not toxic. The by product is refined to maximum to get rid of organic materials and impurities.
The bitumen has a highly adhesive nature, which keeps the materials in the road mix bind together under strong bonds. These become stronger when the mix is set i.e. ready for vehicle movement.
6. Bitumen has Color Variety
The traditional bitumen is black in color. This is because the dense organic material within bitumen is black in color. Now, when certain pigments are added to bitumen, the color of our choice can be obtained. These are colored bitumen.
It is costly than the normal colored bitumen. The disadvantage of colored bitumen is that it requires more chemical additives and materials.
Requirements of Bitumen Mixes for Road Construction
An overall bitumen mix is used in the construction of flexible pavement to serve the following needs.
- Structural Strength
- Surface Drainage
- Surface Friction
The figure below shows a typical cross section of flexible pavement, that was developed in the USA. The structural bitumen layer composes of:
- Bituminous surface or wearing course
- Bituminous binder course
- Bituminous base course
The primary purpose of these bitumen mixes is structural strength provision. This involves even load dispersion throughout the layers of the pavement. The loads involved are dynamic or static loads, which is transferred to the base subgrade through the aggregate course.
A granular base with a bituminous surface course is only provided for roads of low traffic. It is just sufficient and economical.
The rebounding effect of bitumen upper layers helps in having resistance against high dynamic effect due to the heavy traffic. Rebounding property is reflected by the stiffness and the flexibility characteristics of the bitumen top layers. When looking from bottom to top, the flexibility characteristics should increase.
Studies have shown that the above mentioned characteristics of aggregates are attained using densely graded bitumen mixes. This mix should make use of nominal maximum size aggregate (NMAS), that must decrease from the base course- binder course – surface course.
The nominal maximum size aggregate (NMAS) = One sieve larger than first sieve-to retain more than 10% of combined aggregate.
There is a higher amount of bitumen content in the wearing course, that make the layer more flexible. This would help in increasing the durability.
Surface Drainage of Bituminous Pavements
Subsurface drainage can be facilitated using granular sub base in the construction of flexible pavement. Permeable asphalt treated base (PATB) can be used to provided positive surface drainage in major highways. This would behave as a separate course for facilitating subsurface drainage.
Surface Friction of Bituminous Roads
It is essential for the pavement layer to provide enough skid resistance and friction, during vehicle passage, especially in wet condition. This would ensure the safety of the passengers. The macro and the micro surface texture of the asphalt mix contributes towards the surface friction.
The mix gradation i.e. open graded or dense graded will contribute to macro surface texture. The open graded mix have higher macro surface than dense graded. The water is squeezed out from the bottom of vehicle tire when the high macro surface texture is implemented.
The micro surface texture is contributed by the aggregate surface, that is exposed when the above bitumen layer is torn.
1. A smooth Ride Surface
It does not make use of any joints; Hence provide a smooth surface to ride. It also gives less sound emission when compared with concrete pavements. The wear and tear are less in the bituminous pavement, thus maintaining the smoothness.
2. Gradual Failure
The deformation and the failure in the bituminous pavement is a gradual process. The concrete pavement shows brittle failures.
3. Quick Repair
They have an option to be repaired to be quick. They don’t consume time in reverting the path for traffic; as they set fast.
4. Staged Construction
This helps in carrying out staged construction in a situation when problems of fund constraint or traffic estimation problems are faced.
5. Life Cost is Less
The initial cost and overall maintenance cost of bituminous pavement are less compared to concrete pavement.
6. Temperature Resistant
They act resistant against high temperature from melting and are not affected by de-icing materials.
Disadvantages of Bituminous Pavement
- Bituminous pavements are less durable
- Low tensile strength compared to concrete pavement
- Extreme weather and improper weather conditions tend to make bituminous pavement slick and soft.
- Bitumen with impurities can cause pollution to soil, hence ground water by their melting. These may have hydrocarbons in small amounts.
- Clogging of pores and drainage path during construction and service life
- More salting- to prevent snow during winter season
- Cost of construction high during extreme conditions of temperature
The National Highways Authority of India (NHAI) is preparing to start the process of monetizing toll-based operational road assets under the toll, operate and transfer (TOT) model, aimed to bring new investments to the highways sector.
“We have not as yet floated tenders to monetize road assets, but are preparing to do so. We expect to begin doing this in 2-3 months’ time under the TOT model,” NHAI chairman Raghav Chandra said in an email response to queries from Mint.
This will be India’s first exercise in auctioning NHAI’s operational projects after a cabinet clearance in August. The proceeds will fund new highway projects under various models.
NHAI is currently working on the guidelines for TOT, under which the investor will collect tolls and be responsible for operation and maintenance of the project. The TOT model will be essential to attract long-term foreign investment, financial investors and investment bankers told Mint.
NHAI can lease up to 75 national highway projects which are fetching tolls for at least two years to various entities on the TOT model. The overall annual toll collected from these projects is about Rs2,700 crore, against which NHAI can expect to raise Rs25,000-30,000 crore by granting 30-year concessions, said Ashish Agarwal, director (infrastructure) at investment bank Equirus Capital.
The TOT model is long overdue, said Gautam Bhandari, partner at I Squared Capital, a US-based investor in road projects. “We are hopeful that NHAI finally does launch its TOT programme so that it can serve as a model for other sectors as well. As a global investor, we believe that NHAI’s TOT model, if executed properly, could be a win-win for everyone. Proceeds from TOT auctions will free up valuable taxpayer capital that can then be recycled for much-needed new infrastructure projects,” he said.
I Squared is looking to invest as much as $1 billion in Indian infrastructure. It has invested more than Rs1,000 crore through its investment platform Cube Highways and Infrastructure Pte. Ltd in three road projects so far.
IDFC Alternatives, which has bought controlling stakes in operational road projects, is waiting to see the fine print. “The good part is that in the TOT model, there are far less variables and concerns to be addressed as compared to projects with embedded construction risks. The differences in the bids here would be more a function of how differently each investor views the traffic growth rates, maintenance costs, synergies with other projects in one’s portfolio, if any,” said Aditya Aggarwal, partner (infrastructure), IDFC Alternatives.
There is significant interest from international infrastructure funds in the Indian road sector, said Rahul Mody, managing director, Ambit Corporate Finance Pvt. Ltd. “The TOT model is an excellent idea. The model takes away two key risks in the road sector—delays or cost overruns and initial traffic discovery—as the assets that will be offered under this (model) will be operational with some tolling history; hence it should attract considerable interest from Indian companies as well as foreign investors,” Mody said.
“The model can be an avenue for NHAI to raise upfront capital to fund the EPC and HAM projects; opportunity to feed the increasing number of pension funds and infrastructure investors having access to low cost capital and further deepen the infrastructure market; and allowing players to choose better the nature of risk-reward play they want to play in the road sector,” Agarwal said.
The global bitumen market
is forecast to grow at a Compound Annual Growth Rate (CAGR) of four percent between 2015 to 2020, and the world’s largest energy traders such as the Vitol Group and the Trafigura Group Pte. are in a race to increase their market share.
The bitumen market
was valued at around $75 billion in 2014 and is expected to reach $94 billion in 2020, according to a report by Zion Research, titled, “Bitumen (Paving Bitumen, Oxidized Bitumen, Cutback Bitumen, Bitumen Emulsion, Polymer Modified Bitumen
and Others) Market for Roadways, Waterproofing, Adhesives, Insulation and Other Applications - Global Industry Perspective, Comprehensive Analysis and Forecast, 2014 – 2020”.Bitumen
is a semi-solid form of petroleum, which is used to make asphalt for roads, waterproofing for roofs, insulation, and adhesives. It is either obtained by distillation of petroleum or is available naturally, such as in Canada’s oil sands.Bitumen
is used mainly in road manufacturing. A surge in road construction activity in Asia will propel growth for the product going forward. 75 percent of the global consumption of bitumen was used for road construction in 2014.
Waterproofing of roofing and building construction was the second major consumer of bitumen in 2014. Increased construction of homes to cater for the growing population is likely to add to the bitumen demand in the future.
Along with roofing, polymer modified bitumen
(PMB), which is used as a chemical additive and adhesive, will witness rapid growth compared to other forms of bitumen
Trucks, trains, and barges have been used traditionally to transport bitumen from refineries to local consumers; however, a drop in supply from the aging refineries in the U.S. and Europe has necessitated the use of oceangoing tankers, to supply the material from its source of production to the end consumer.
Vitol, the largest independent oil-trading house teamed up with U.S.-based Sargeant Marine Inc., which distributes asphalt to customers worldwide to form Valt, which operates the world’s largest dedicated asphalt fleet, handling parcel sizes from 20 metric tons up to 37,000 metric tons through its fleet of fourteen specialist vessels, according to its website.
“It used to be mostly a small distribution business,” Chris Bake, a senior executive at Rotterdam-based Vitol, said in an interview. “Now it is more of a whole arbitrage business requiring a global reach and shipping capacity,” reports Bloomberg.
Trafigura group is also not far behind. Its Singapore-based unit, Puma Energy has added four new bitumen vessels, taking the total number of vessels to 11, which cater to the Asian markets.
“We see a definite upward trend in the number of nautical miles for bitumen,
” said Valt Chief Commercial Officer Nick Fay, who estimates an annual increase of about 7 percent. “All the new refineries that are getting built don’t make bitumen
,” reports Bloomberg.
The Guvnor Group is planning to invest in the Perth Amboy asphalt refinery and storage facility in New Jersey, which has been shut since 2008, reports Bloomberg.
There is hardly any public information about the bitumen market, which makes it ideal for the large energy traders, who use their energy expertise and global connection to supply to far-off markets.
“There is a perception that the world is going to be more disconnected -- supply and demand-wise -- and we are there to help connect the dots,” Klintholm said.
Nonetheless, increased use of asphalt for roads and environmental concerns with bitumen manufacturing could pose a risk for the growth of the bitumen industry
in the future.By Rakesh Upadhyay for Oilprice.com
Asphalt plant manufacturers agree that recycled asphalt is a valuable resource that is too good to waste - Mike Woof writes
Around the globe there is growing interest in the use of recycled asphalt pavement (RAP). The technology to utilise RAP in asphalt mixes has been available for some time, with a range of asphalt plant manufacturers in the US and Europe having developed a number of solutions. However, take-up of this technology has varied, with the US pushing ahead with the use of RAP while progress has been much slower in Europe. But many European countries are now becoming more aware of the need to lower the reliance on new aggregates through the use of RAP. And other markets, too, are seeing greater interest in the use of RAP, with the Chinese authorities, for example, having set requirements for this material to be used in road building.
Using RAP can lead to substantial savings in both production costs and indirect CO2 emissions. A paper by Ammann’s commercial manager, Peter Maurer, highlights the fact that RAP is not a waste material but one that can be re-used efficiently. This is a key issue that all the specialists building equipment for the asphalt sector, such as Astec, Benninghoven, Günter Papenburg, Intrame, Lintec and Marini, will agree with Ammann upon.
Both the aggregates and bitumen contained in RAP can meet the standards allowing re-use. Adding some quantities of new aggregates and bitumen can ensure that quality is maintained.
Clearly, the use of recycled asphalt pavemen (RAP) will only increase across the globe, with asphalt plant manufacturers having already developed ingenious solutions to make best use of this material.
Maurer’s paper details a number of fundamental points for the use of large quantities of RAP in an asphalt plant, which all of the key suppliers in the market segment would agree with. First, legislation must allow the use of RAP in asphalt mixes. Second, there must be a sufficient supply of the material available to a user to make the investment in the extra equipment needed worthwhile. Assuming that the material can be used and is available, the asphalt plant owner then has to provide separate storage facilities for different grades of RAP being received. Careful monitoring of the RAP supply has to be carried out, with laboratory-based testing to assess the quality. And the higher the percentage of RAP being used in the mix, the greater the importance of assuring the quality of the RAP feed.
Marzio Ferrini, head of product marketing at Marini, emphasised that determining the quality of the RAP is essential. He said that quality testing of road materials being milled off should be carried out so that the contractor knows exactly what grade is being recovered. He said, “You need to know the source of the RAP.”
Ferrini added that weather protection is also important for the RAP storage area, as this helps to reduce the moisture levels in the material, lowering the quantities of fuel used for heating the plant. This is a technical point on which Marini’s rivals are in broad agreement.
Batching-type plants are favoured by users in many markets, because of their versatility and adaptability. Modern batching plants are now often constructed in modular form with prewired components, allowing faster commissioning onsite while they can also be set up to handle a wide range of mix specifications. This versatility in construction also helps these plants to use RAP in the mix (although it is worth noting that continuous-type plants can also be configured to handle RAP).
Accurate weighing of the RAP entering the mixer is necessary to ensure that the correct quantities of materials are used, a point on which Benninghoven’s sales manager Rainer Böllinger, as well as Ferrini and Maurer all agree. The feed conveyor systems can be equipped with load scales on the belt so that the quantities can be monitored continuously.
With regard to the use of cold RAP in the mix, there is considerable discussion too as to how much can be used efficiently, however.
Böllinger said that Benninghoven’s latest granulators play a key role in the production process by breaking up the RAP prior to being used in the feed. Böllinger said, “The granulator is a key factor for high-quality recycling management. You need soft crushing to protect the stone and you remove the fines in the end products. You can increase the percentage of recycled feed in the plant by 5-10%; because you remove the fines efficiently, you don’t destroy the stone and you retain the bitumen.”
The source of the RAP has to be identified and lab testing is crucial to determine the material quality.
According to Böllinger, using the granulator helps recoat the bitumen around the stone and avoids the need for long mixing cycles in the mixer, with a boost to productivity. He said that the material being delivered to the mixer is more homogenous, allowing a conventional mixing cycle of 45 seconds.
Another important feature is the slow feed rate for the RAP into the mixer box, which reduces the quantity of steam being released. Ammann’s and Benninghoven’s burners are controlled by an inverter system, which it claims also helps to boost overall plant efficiency. When the plant has a low level of throughput into the drier drum, the burner reduces the fuel consumption.
Ferrini pointed out that the mix design must be modified to incorporate RAP, while the plant has to have the necessary features to accommodate this. The recipe has to be checked using software, with continual monitoring of all the feed components.
The introduction of the RAP in the feed can generate large quantities of steam from the mixer, so the Marini plants have a special tube that operates under negative pressure as an extractor.
Marini’s approach to allowing a high percentage of RAP into the mix, however, is to use a larger mixer. Because of the heat-exchange process to the cold RAP, the mixing time is typically increased to 50 seconds, compared with the 45 seconds for a conventional mix using virgin materials. Ferrini said, “If you want good quality, you need more time to heat the material and allow the bitumen to cover the stone.”
He said that a batching plant using fresh aggregates and with an output of 240tonnes/hour will typically have a 5tonne mixer and a mixing time of 45 seconds for each batch. But when cold RAP is used in the mix, extra time is required for the heat-transfer process so that the mixing time will be increased to 50 seconds, so to ensure the output remains the same at 240tonnes/hour, the mixer capacity has to be increased to 6tonnes. “The bigger batch compensates for the longer time,” he said. “The more cold RAP you use, the longer the time you need.”
Ferrini said that while higher percentages of cold RAP can be used in theory, this requires a greater energy transfer, and to prevent overheating of the material, even longer times are needed and this will increase fuel consumption significantly. “We can do this but the machine must be specifically designed for it with a big mixer and a big burner and use a very good quality RAP and with a low moisture content.”
Ferrini added that in addition to the technology used for the introduction of cold RAP directly into the mixer, the firm can help increase the percentage of RAP used. This is achieved by adding RAP into the recycling ring on the dryer drum and by combining both technologies, Ferrini said that the Marini plants can reach a recycling rate of up to 60%.
The view from Ammann is broadly in agreement with Marini. And Maurer’s paper on the use of recycled asphalt details how a feed of up to 30% of cold RAP can be fed directly into the mixer. Keeping the moisture of the RAP lower than 2% allows the percentage to go up to 35% or 40%, supported by an intelligent feed of the RAP into the mixer. The paper also highlights how, by using a parallel dryer in parallel flow technology, a feed of up to 60% of hot recycled material can be used in the mix.
However, Maurer points out that Ammann is working on technology to boost the quantity of recycled materials from the current maximum of 60% when using a dried feed, having set a target of 100%. This technology, based on the counter flow drying principle in combination with a hot gas generator, and equipped with some high sophisticated air ducting details, was introduced in 2007 in a wide range of installations. It ensures gentle drying and heating of the RAP, and in some road-construction projects it was possible to use up to 98% of RAP with this technology.
Nowadays, all of the leading manufacturers in the asphalt plant field will be working in this same direction to optimise the use of RAP, although the solutions they eventually deliver may vary significantly.
source- world highways
The South African National Roads Agency (Sanral) his issued tenders to six pre-qualified bidders for each of the mega-bridges, over the Mtentu and Msikaba River gorges, that are to be part of the greenfield section of the N2 Wild Coast Road project.
This is in spite of the fact that the project, which has been dogged by controversy since its inception 15 years ago, still faces some unresolved legal issues. There was huge opposition from KwaZulu-Natal road users who expected to fund the project through increased tolling in their province. However, this opposition has fallen away as the KwaZulu-Natal section has been excluded from the project. The revised N2 Wild Coast Road Project runs from East London to the Mtamvuna River Bridge, a distance of approximately 410km.
Bizana residents fear being displaced and the Amadiba Crisis Committee has objected to the project, claiming it is linked to the Xolobeni dune mining proposal, against which they are fighting. Conservation organisations are bitterly opposed to the fact that the greenfields section of the proposed route will pass through the environmentally sensitive Pondoland Centre of Endemism, part of a global floral hot spot.
Sanral spokesman Mbulelo Peterson said that an open pre-qualification process had been followed before the issuing of the tenders. He said that, due to the size and complexity of the two bridges, which are expected to cost around R3,5-billion to construct, the tender periods were 18 weeks and 20 weeks respectively for the Mtentu and Msikaba Bridges. Tenders would close at the end of October for the Mtentu Bridge and early in November for the Msikaba Bridge. Construction of the bridges was likely to start early next year.
THE N2 Wild Coast road project was already well under way as Sanral had started working on it as soon as it had received the go-ahead from the Minister of Environmental Affairs in 2010. Mr Peterson said that, to date, Sanral had done extensive work on upgrading existing roads on the N2 between East London and Mthatha and on the future new N2 alignment along the current R61 route between Mthatha and Port St Johns.
All work already done on the N2 Wild Coast Road had been funded from non-toll funding and only the greenfields section of the route would be funded through a mix of government grant and tollings.
“Sanral, the Department of Transport and National Treasury are in discussion to finalise the funding model for the greenfields section. By law only roads funded through toll funding can be tolled and no cross-subsidisation of tolling is allowed,” he said.
This meant Sanral could not erect new toll booths or adjust tariffs at existing toll plazas within KwaZulu-Natal to fund roads in the Eastern Cape.
“New toll roads must be gazetted and go through an extensive public participation process after gazetting.”
In January this year, government gave the green light for the construction of the greenfields section of the project, between Ndwalane outside Port St Johns and the Mtamvuna River.
Mr Peterson said this part of the project would start with the construction of the massive bridges over the Mtentu and Msikaba Rivers, which border the Mkambati Nature Reserve. Once these were under way, construction of the remaining approximately 110km of road, the seven additional river bridges and four interchanges would start.
Source - Southcoast Herald