October 2, 2017
February 17, 2017
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
Bitumen 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
Structural Strength of Bituminous Pavements
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.
Advantages of Bituminous Road Construction Over Concrete Pavements
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
Source - enggfeed
July 20, 2016
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
May 18, 2016
The straight road, to be funded by the Centre, is expected to cost about Rs.18,000 crore and once ready, the travel time between the two cities will be just six hours.
A team of officials comprising Roads &Buildings Principal Secretary Sam Bob, Engineer in Chief and others left for San Francisco on a study tour on execution of such projects, he said.
Addressing a media conference here on Tuesday, Mr. Raghava Rao detailed the work done by the department ahead of the Andhra Pradesh Government completing two years on June 8.
While the length of roads under R&B is 45,000 km, nearly 4,000 km single-lane roads were widened into two-lane roads.
“While the 10-year rule by the Congress left the roads in a shambles, Chief Minister N. Chandrababu Naidu took it upon himself to improve their condition in the State and also lay new roads. Roads are the basic infrastructure required for the industrial development”, he said.
The Government’s objective was to connect rural areas to mandal headquarters, mandals to district headquarters and the district headquarters to the new Capital City Amaravati.
In the current financial year another 2,517 km of single-lane roads would be widened into two-lane roads, 38 km of two-lane roads would be developed into four-lane roads.
The department also proposes to construct nine Road Over Bridges and 25 bridges. Special repairs would be taken up on 2,412 km of roads.
The National Highways Authority of India gave a commitment to convert 1,205 km of State Highways into National Highways. The Roads &Buildings Department allocated Rs.3,000 crore during current fiscal for development of State highways and link roads.
In the 2014-15 fiscal, 1,336 km of roads were widened into two-lane roads and another 3,089 km of roads were repaired and three Road over Bridges and another 20 bridges constructed.
In the 2015-16 financial year, 2,636 km single-lane roads were developed into two-lane roads and special repairs were carried out on 2,890 km of roads besides constructing five RoBs and 18 bridges.
World Bank funds
The roads being laid with World Bank funds such as Rajahmundry to Kakinada were monitored and the contractors who do not execute quality work removed. The R&B also took over 5,420 km of Panchayat Raj roads recently and tenders were being called shortly to develop 545 km of roads.
For the Krishna Pushkaram, R&B would spend Rs.389 crore on improvement of roads and the works completed by July-end, he said.
Source- The Hindu
February 18, 2016
Repairs continue on Northern Territory's Buntine Highway after massive flood washes away sections of road
Updated 18 minutes ago
PHOTO: The NT Department of Infrastructure's Gordon Atkinson says recent rain events were bigger than anything seen over the past 10 years. (ABC Rural: Nathan Coates )
The clean-up is continuing after recent severe flooding across the Top End's Victoria River District caused sections of the Buntine Highway to be washed away.
The NT Department of Infrastructure has confirmed that whole five-metre sections of bitumen had lifted and been carried away by rushing water.
The department's Gordon Atkinson said the rain events had been bigger than anything seen over the past 10 years.
He said it was normal for road surfaces to be ripped up by such intense events.
"The bitumen has water running over the top of it and the water gets underneath and helps to lift it as well, a bit like an aeroplane wing," he said.
Mr Atkinson said the priority was to repair damage and make the highway operational, and that a longer road improvement would continue in the background.
"All our major repairs are finished, so the Buntine Highway is open to major traffic and there are no weight restrictions," Mr Atkinson said.
He said the last bits of resealing required would happen soon and drivers were safely doing 100 kilometres per hour over those sections.
Mr Atkinson said the "mountains of organic debris" left on bridges had been largely cleaned up, with a large quantity of snakes and spiders keeping workers on their toes.
"Nobody got bitten," Mr Atkinson said. "They are used to it now. They've got gloves on, they are using pitchforks, poles and chainsaws on long chain bars.
"They are ready to start running when the snakes appear."
December 21, 2015
Each winter, when climate forecasters predict snow or icy circumstances, native governments deploy vans that mud roads with salt, or different chemical mixtures to assist forestall ice build-up. Residents escape their very own provide to maintain their walkways and driveways from freezing over and turning into dangerously slick.
However the de-icer does not keep on the streets for lengthy. Melting snow and automobiles driving by wash or pressure it off, making re-application crucial. To interrupt this cycle, Seda Kizilel and colleagues needed to see if they might devise a method to ice-proof the street itself.
The researchers began with the salt potassium formate and mixed it with the polymer styrene-butadiene-styrene. They added this combination to bitumen, a serious element of asphalt.
The ensuing materials was simply as sturdy as unmodified bitumen, and it considerably delayed ice formation in lab research. The brand new composite launched de-icing salt for 2 months within the lab, however the results might final even longer when used on actual roads, the researchers observe.
In that occasion, the salt-polymer composite can be evenly embedded all through the asphalt. Thus, as automobiles and vans drive over and put on away the pavement, the salt might regularly be launched—probably for years.
Extra info: Derya Aydın et al. Gelation-Stabilized Useful Composite-Modified Bitumen for Anti-icing Functions, Industrial & Engineering Chemistry Analysis (2015).
Ionic salts as anti-icing brokers have been extensively used to get rid of accumulation of ice on asphalt surfaces. Nevertheless, salt may be simply eliminated by rain or cars and requires frequent software on roads.
Apart from this financial consideration, anti-icing brokers compromise the mechanical properties of asphalt and have a adverse influence on dwelling organisms and the setting when utilized in giant quantities.
Incorporation of hydrophilic salts into bitumen, a hydrophobic asphalt binder, and managed launch of particular molecules from this hydrophobic medium can present an efficient answer for decreasing ice formation on pavements.
Bitumen has beforehand been modified by numerous polymers, together with styrene-butadiene-styrene (SBS) for improved power and thermomechanical properties. Nevertheless, an anti-icing perform was not thought-about in these earlier designs. In a earlier research, we developed a useful polymer composite consisting of potassium formate (HCOOK) salt pockets dissolved in a hydrophilic gel medium and dispersed in a hydrophobic SBS polymer matrix.
Right here, we developed an revolutionary technique to acquire polymer composite-modified bitumen and investigated additional the anti-icing properties of the practical bitumen. We improved incorporation of this polymer composite into bitumen and demonstrated correct distribution of the composite inside bitumen by means of morphological and rheological evaluation.
We characterised the anti-icing properties of modified bitumen surfaces and demonstrated vital will increase in freezing delay of composite-modified bitumen in comparison with base bitumen in a temperature- and humidity-controlled chamber. As well as, we characterised the discharge of HCOOK salt from polymer composite-modified bitumen and noticed salt launch inside the vary of 1.07–10.eight% (w/w) in 67 days, relying on the composite content material. The outcomes show the potential of this polymer composite-modified bitumen for anti-icing performance and for industrially related purposes.
Source- Sunnews Journal