Road Construction Advances in India with Open Graded Asphalt Friction Course
Advances in road construction technology have given rise to an ambitious plan that mainly includes the friction course for the construction of open graded asphalt in India.
road asphalt texture
Open Graded Asphalt Friction Layer (OGFC) is an open graded hot mix asphalt with interconnected voids to provide better surface drainage during rainfall.
This article describes these advancements in materials, mix design, specialty asphalt mixes, and recycling. Keeping pace with the latest technology requires integrating these advancements.
Before July 2006, India used 60/70 isotonic graded asphalt for paving. This grading system is based on experimental penetration testing conducted at 25oC.
Penetration testing measures the consistency of asphalt. While two 60/70 inlet asphalt samples from different refineries may have the same consistency at 25oC, one may be softer than the other when tested at 60oC, which is close to the maximum pavement temperature on a hot summer day.
Asphalt that is too soft at high temperatures is undesirable because it can create rutting on asphalt pavements under heavy loads.
Although progress has been made, it is necessary to move forward by adopting Performance Graded (PG) bitumen, especially on national highways. For over 20 years, viscosity grading systems have provided outstanding performance results in the United States.
However, viscosity grading systems, while more reasonable than osmotic grading systems, are based on experience. The so-called Superpave performance grading system includes new asphalt tests and specifications with the following key features:
The tests and specifications apply to asphalt "binders," both modified and unmodified.
The physical properties measured by the Superpave bitumen test are directly related to field performance, not only based on experience, but also on engineering principles.
The tests and specifications are designed to eliminate or reduce three specific types of asphalt pavement problems: rutting, fatigue cracking and thermal cracking. Rutting usually occurs at high temperatures, fatigue cracking at moderate temperatures, and thermal cracking at low temperatures.
road asphalt layers
The entire pavement temperature range experienced at the project site was considered. For this purpose, new test equipment was developed/adopted to test bitumen. A rotational viscometer is used to measure asphalt viscosity at 135oC.
A dynamic shear rheometer was used to measure the viscoelasticity of the asphalt at two temperatures: a high temperature corresponding to the highest 7-day pavement temperature in summer at the project site, and an intermediate temperature corresponding to the annual average pavement temperature.
Aggregate
Numerous advances have been made in the characterization of coarse aggregate, fine aggregate, and mineral filler used in planned asphalt manufacturing equipment for testing fine aggregate (FAA). However, simple tests for particle size and surface texture characterization of 4.75 mm fine aggregate (sand) are readily available in India.
In asphalt pavements, it is desirable to include angular fine aggregate particles in the mixture to resist rutting. While the edges and corners of coarse aggregate (placed on a 4.75mm sieve) can be assessed with the naked eye, this is not easy for fine aggregate particles. A schematic diagram of the test equipment used to measure fine aggregate angularity (FAA).
It is easy to make in India. Adopt the FAA test procedure standard as AASHTO Test 304.
Mix Design
Marshall mix design is currently used to design asphalt mixes in India. In any hybrid design, it is desirable to compact laboratory samples to the density expected on asphalt pavements after 2-3 years of compaction in traffic conditions.
Designed for heavy traffic asphalt mixes, Marshall impact hammers were used on both sides of the specimen every 75 strokes. This level of laboratory compaction has worked well in the past. However, in the 1980s, it was found that the areal density of asphalt pavements in use in the United States was significantly higher than the laboratory design density obtained using 75 Blow.
This is thanks to the truck's improved tire pressure and a new tire design with stiffer sidewalls. Therefore, the 75-compaction level is insufficient. Increasing the number of blows is not advisable as it will only erode the particles accumulated in the sample.
Open Graded Asphalt Friction Course
Open graded hot mix asphalt is combined with an asphalt friction course grades to provide better drainage during rainfall. Rainwater penetrates vertically through the OGFC into the impermeable underlying asphalt layer and then reaches the shoulders of the OGFC's sunlit (exposed) edge.
In addition to minimizing the likelihood of skidding in the rain and providing improved friction values on wet surfaces, the OGFC has the following advantages over other densely graded surfaces: (a) reduced water spray and water jets to the rear of the vehicle, (b) reduced tire pavement noise, (c) improve visibility of pavement markings, and (d) reduce nighttime surface brightness in wet weather.
Many U.S. states that currently use OGFC have demonstrated superior performance in terms of safety (improved wet surface friction) and durability.
This is achieved through one or more of the following: the use of polymer modified bitumen binders, relatively high bitumen content (using cellulosic fibers), and/or a relatively open gradation.
The authors have written a manual detailing guidelines for the design, construction, and maintenance of OGFCs for use by practicing engineers in the United States.
For economic reasons, OGFCs in India should be selectively used on roads with heavy rainfall and slip-and-fall accidents on wet surfaces.
Warm Mix Asphalt
On US Interstates, the right lane has OGFC and the left lane has densely graded hot mix asphalt. Note that the right lane is free of standing water and splash/spray. Warm mix asphalt (WMA) is a rapidly emerging new technology that has the potential to revolutionize the production of asphalt mixtures.
WMA technology allows asphalt mixtures to be mixed, laid and compacted at much lower temperatures than hot mix asphalt (HMA).
This technology can reduce production temperatures by up to 30%. Asphalt mixtures are typically produced at temperatures of 150°C or higher, depending on the type of binder used. WMA blends can be produced at temperatures around 120°C or lower.
Warm mix asphalt has the following important advantages:
Energy saving. The most obvious benefit of WMA is reduced fuel consumption. Fuel is used to dry and heat the aggregate. Studies have shown that lower plant mixing temperatures associated with WMA can reduce energy consumption by up to 30%.
Extend paving season. By producing WMA at normal HMA temperatures, the paving season can be extended during the cooler months of the year or in areas with higher elevations, where the WMA additive or process can act as a compaction aid.
In addition, the cooling rate is reduced by reducing the difference between the compaction temperature and the ambient air temperature. Compared to HMA, WMA can also be transported over longer distances with reduced mixing temperature in the transport unit.
Compaction aid for hard mixes. WMA additives and processes can be used to improve the compatibility of hard mixes when the mix is produced near specific HMA production temperatures. A small drop in temperature is also possible. Europe has extensive experience in using certain types of WMAs with SMAs.
road asphalt ingredients
The technique of introducing a small amount of water into a hot asphalt binder takes advantage of this phenomenon: When water becomes steam at atmospheric pressure, its volume expands by a factor of 1,673.
This results in a substantial increase in the amount of bituminous binder, which helps coat the aggregate more easily, but also reduces the apparent viscosity of the mixture.
Procedures for introducing water into asphalt binders include foaming nozzles, the use of hydrophilic materials such as zeolites or dam aggregates. The temperature of the asphalt binder is usually the same as that used for hot mix asphalt.
Recycling of Bituminous Pavements
Reusing existing asphalt pavement materials to produce new pavement materials can result in significant savings in material, money and energy. The specific benefits of recycling can be summarized as follows:
When used properly, recycling can save a lot of money over using new materials. Additionally, on-site recycling avoids shipping costs. With tight budgets and rising material costs, economic considerations are more important now than ever.
Recycled material has been shown to be of equal or better quality than new material.
Even though they are of the same thickness, hot mix asphalt (HMA) overlays on recycled bases are expected to perform better than HMA overlays on existing surfaces because the former reduces the likelihood of cracking through surface reflections.
Recycling preserves pavement geometry as well as pavement thickness. Existing pavement structures can be reinforced through reuse without the need to add extensive overlays. In some cases, traffic disruptions are reduced compared to other recovery techniques.
Recycling can save a lot of energy compared to traditional manufacturing techniques. This factor was important during the energy crisis experienced during the 1972 Arab oil embargo.
Cold planing is described as an automated method of removing asphalt pavement to the desired depth and restoring the surface to the desired grade and grade, free from humps, ruts, and other problems. This method can be used to roughen or texture pavements to improve wear resistance.
Cold planing is carried out using self-propelled drum cold planers, and the Reclaimed Asphalt Pavement (RAP) is transferred to trucks for transport out of the site. The resulting pavement can be used immediately by regular traffic and may be covered or preserved as a textured surface at some point in the future.
Heat recovery or hot mix recycling is the process of combining recycled asphalt pavement (RAP) material with new material (sometimes with a recycling agent) to produce a hot mix asphalt (HMA) mix.
Both batch and drum type hot mix plants are used to produce recycled mixtures. RAP material can be obtained by milling or tearing and crushing operations.
When the coil is introduced into the weigh hopper of a batch plant or the drum of a drum plant, the coil is heated to ambient temperature by the superheated virgin aggregate. If the amount of RAP exceeds 15-20%, use a soft asphalt binder to regenerate the old asphalt binder in the RAP.
road asphalt composition
SPECIAL BITUMINOUS MIXES
Stone Matrix Asphalt
Stone matrix asphalt (SMA) was developed in Germany in the mid-1960 and it has been used very successfully by many countries including US as a highly rut-resistant bituminous course, both for binder (intermediate) and wearing course for heavy traffic roads.
SMA is tough, stable, rut-resistant mix that relies on stone-on-stone contact to provide strength and a rich mortar binder to provide durability.
Advances in Bituminous Road Construction Advances in Bituminous Road Construction
In a conventional dense graded mix, coarse aggregate particles (retained on 4.75 mm sieve) are separated by fine aggregate matrix, which primarily carries the load. In SMA, coarse aggregate particles have stone-on-stone contact forming a stone skeleton which carries the load.
Since SMA mix has relatively higher bitumen content, cellulose fiber is added to the mix to minimize drain down of bitumen in trucks during transportation of the mix from plant to project site.
Although the cost of SMA is typically about 25-30% higher than the cost of dense graded bituminous mix, it is still economical considering life cycle costs.
SMA has been widely used in the US since 1991 for heavy-traffic roads. It must also be used in India for heavy corridors especially when overloading is also common.
Indian Roads Congress (IRC) has recently published a tentative specification for SMA (IRC:SP:79-2008), which was drafted by the author to facilitate its use in India. A manual containing detailed guidelines for designing and constructing SMA mixtures was developed by the author in the US for practicing engineers.
In the case of remixing, the scarified RAP material is mixed with virgin HMA in a pug mill, and the recycled mix is laid down as a single mix.
The advantages of hot in place recycling are that surface cracks can be eliminated, ruts and shoves and bumps can be corrected, aged asphalt binder is rejuvenated, aggregate gradation and asphalt content can be modified, traffic interruption is minimal, and hauling costs are minimized.
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