• POLIMER MODIFIED BITUMEN• BITUMEN RUBBER MIXES• STONE MATRIX ASPHALT• WARM MIX ASPHALT

Pavement CompositionAsphalt/ BitumenBitumen Materials Used in IndiaPolymer Modified BitumenBitumen Rubber MixesStone Matrix AsphaltWarm Mix Asphalt

Pavement Composition

Sub-base Base Surface

Asphalt, also known as bitumen, is a sticky, black and highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product ; it is a substance classed as a pitch.

Pitch is a name for any of a number of viscoelastic-solid polymers. Pitch can be natural or manufactured, derived from petroleum, coal tar or plants. Various forms of pitch may also be called tar, bitumen or asphalt.

OPEN GRADED MIXES:

o Bituminous Macadam (BM)

o Semi Dense Bituminous Concrete (SDBC)

o Dense Bituminous Macadam (DBM) Grading 1

DENSE GRADED MIXES:

o Dense Bituminous Macadam (DBM) Grading 2

o Bituminous Concrete (BC) Grading 1

o Bituminous Concrete (BC) Grading 2

Polymer Modified Bitumen (PMB)

Natural Rubber Modified Bitumen (NRMB)

Crumb Rubber Modified Bitumen (CRMB)

Stone Matrix Asphalt (SMA)

Warm Mix Asphalt (WMA)

PMB, NRMB, CRMB for high traffic roads.

SMA for very heavy-trafficked roads with

overloading.

VG-30 Bitumen is normally used nowadays.

Modified bituminous materials can bring real

benefits to highway maintenance/construction,

in terms of better and longer lasting roads, and

savings in total road life cost.

But the choice of what materials to choose and

how they perform has to be said is a bit of a

minefield at present with little truly

independent advice available, and this guide

may help in making the necessary decisions.

A polymer is a large molecule,or macromolecule, composed of many repeatedsubunits. Because of their broad range ofproperties, both synthetic and natural polymersplay an essential and ubiquitous role in everydaylife. Polymers range from familiarsynthetic plastics such as polystyrene tonatural biopolymers suchas DNA and proteins that are fundamental tobiological structure and function.

SYNTHETIC POLYMERS

These are polymers that have been manufactured in a chemical process to combine particular molecules in a way that would not occur naturally.And although various synthetic polymers have been capable of being produced since the early part of this century it is the more recently developed polymers that are now being used to modify bitumens and produce the "new" bituminous binders.The new polymers being the result of research and development by the large petro-chemical industries.

NATURAL RUBBER

Rubberised asphalt, mainly surface course

(wearing course) but also binder course

(basecourse), has been used with a fair degree

of success for over 40 years.

Rubber is a natural polymer and its action in a

bituminous mix is similar to that of the

synthetic thermoplastic rubbers (TR's).

Bitumen is so useful in the road making and road maintenance industries because of its basic thermoplastic nature, i.e. it is stiff/solid when cold and liquid when hot, (well with penetration grade bitumens anyway).(The modifying polymers used in bitumen are also thermoplastic in nature.)

The basic properties of bitumen can be modified by the addition of flux oils or volatile oils to produce bitumen of various grades.These grades are specified by their viscosity, (penetration), and their softening point, this information, along with other physical characteristics is specified in.

Polymers change the physical nature of

bitumen, and they are able to modify physical

properties such as the softening point and the

brittleness of the bitumen.

Elastic recovery/ductility can also be

improved.

Thermoplastic Rubbers, (TR's)

This may be regarded as a group name / description for a number of polymers/copolymers used in the modification of bitumen.A copolymer is a polymer that has more than one type of molecule incorporated in the polymer.These polymers are made up of many thousands of individual monomers/molecules built up into chains by the various polymerisation processes developed by the large chemical industries.

Styrene Butadiene Styrene, (SBS)

This is a thermoplastic rubber.

SBS is a copolymer that you will come across

in bitumen modification, it was originally

developed for use in the production of tyres

and the soles of shoes, but is suitable for the

modification of bitumen.

Natural Rubber Modified Bitumen (NRMB) :

using latex or rubber powder.

Crumb Rubber Modified Bitumen (CRMB) :

using crumb rubber powder from discarded

truck tires further improved by additives.

Polymer Modified Bitumen (PMB) : using

polymers like Ethylene Vinyl Acetate (EVA)

or Styrene Butadiene Styrene(SBS) etc.

Polymer, typically in either crumb, pellet or powder form is added to hot asphalt which penetrates the polymer particles and causes them to swell and flow.

Improved aggregate adhesion in highly

stressed areas.

Superior load carrying capacity for a given

thickness compared to conventional bitumen.

Higher cohesive strength to withstand

stripping action of high speed traffic.

Higher viscosity at elevated temperatures

combats bleeding of binder.

Lower susceptibility to temperature variations.Higher resistance to deformation at elevated pavement temperature.Better age resistance properties.Higher fatigue life of mixes.Overall improved performance in extreme climatic conditions.Reduction in overall life cycle cost of overlays.Higher stiffness modulus.Better resistance to creep.

Stone-matrix asphalt was developed in

Germany in the 1960s.

It provides a deformation resistant, durable

surfacing material, suitable for heavily

trafficked roads.

SMA has found use in Europe, Australia, the

United States, and Canada as a

durable asphalt surfacing option for residential

streets and highways.

SMA has a high coarse aggregate content that interlocks to form a stone skeleton that resists permanent deformation. The stone skeleton is filled with a mastic of bitumen and filler to which fibers are added to provide adequate stability of bitumen and to prevent drainage of binder during transport and placement. Typical SMA composition consists of 70−80% coarse aggregate, 8−12% filler, 6.0−7.0% binder, and 0.3 per cent fiber.

The deformation resistant capacity of SMA stems from a coarse stone skeleton providing more stone-on-stone contact than with conventional dense graded asphalt (DGA) mixes (see above picture). Improved binder durability is a result of higher bitumen content, a thicker bitumen film, and lower air voids content. This high bitumen content also improves flexibility. Addition of a small quantity of cellulose or mineral fiber prevents drainage of bitumen during transport and placement.

SMA is mixed and placed in the same plant as that used with conventional hot mix. In batch plants, the fiber additive is added direct to the pug mill using individually wrapped press packs or bulk dispensing equipment. Mixing times may be extended ensure that fiber is homogeneously distributed throughout the mix and temperatures controlled in order to avoid overheating or damage to the fiber.In drum plants, particular care must be taken to ensure that both the additional filler content and fiber additive are incorporated into the mixture without excessive losses through the dust extraction system.

Filler systems that add filler directly into the drum rather than aggregate feed are preferred.Pelletized fibers may be added through systems designed for addition of recycled materials, but a more effective means is addition through a special delivery line that is combined with the bitumen delivery, so that the fiber is captured by bitumen at the point of addition to the mixture.

The primary difference in placing SMA, compared to DGA is in compaction procedures.Multi-tyre rollers are not used due to the possible working of binder-rich material to the surface of the asphalt and consequent flushing and pick-up. Trafficking of the newly placed asphalt while still warm may have the same effect and it is generally preferable for surfaces to cool below about 40°C before opening to traffic. The preferred method of compaction is to use heavy, non-vibrating, steel-wheeled rollers. If these are not available, vibrating rollers may be used but vibration should be kept to a minimum to avoid fracture of coarse aggregate particles, or drawing of binder to the surface of the mix.

The use of polymer modified binder may decrease mix workability and necessitate increased compactiveeffort to achieve high standards of compacted density. Achieving high standards of compacted density and low field air voids has been identified as an important factor in the performance of all SMA work. SMA is normally placed with a minimum layer thickness of 2.5 to 3 times the nominal maximum aggregate particle size. Greater layer thicknesses assist in achieving appropriate standards of compacted density.

Aggregates used in SMA must be of high quality – well shaped,resistant to crushing and of suitable polish resistance.

Binders used in SMA include:Class 320 bitumen - used in many general applications.Multi grade binder - used to provide enhanced performance at higher traffic levels.Polymer modified binder - increasingly used in heavy traffic conditions to provide additional resistance to flushing and rutting.Cellulose fiber is most commonly used in SMA work in Australia. Other fibre types, including glass fiber, rock wool, polyester, and even natural wool, have all been found to be suitable but cellulose fiber is generally the most cost-effective. Fiber content is generally 0.3% (by mass) of the total mix.

SMA provides a textured, durable, and rut resistant wearing course.The surface texture characteristics of SMA are similar to Open graded asphalt (OGA) so that the noise generated by traffic is lower than that on DGA but equal to or slightly higher than OGA.SMA can be produced and compacted with the same plant and equipment available for normal hot mix, using the above procedure modifications.SMA may be used at intersections and other high traffic stress situations where OGA is unsuitable.SMA surfacing may provide reduced reflection cracking from underlying cracked pavements due to the flexible mastic.The durability of SMA should be equal, or greater than, DGA and significantly greater than OGA.

Increased material cost associated with higher asphalt binder and filler contents, and fibre additive.Increased mixing time and time taken to add extra filler, may result in reduced productivity.Possible delays in opening to traffic as the SMA mix should be cooled to 40°C to prevent flushing of the binder to the surface (bleeding).Initial skid resistance (lack of Friction) may be low until the thick binder film is worn off the top of the surface by traffic. In critical situations, a small, clean grit, may need to be applied before opening to traffic.

Warm-Mix Asphalt was developed in Europe in response to EEC countries signing the 1997 Kyoto Treaty to reduce greenhouse gases.Warm mix asphalt concrete (commonly abbreviated as WMA) is produced by adding zeolites, waxes, asphalt emulsions, or sometimes even water to the asphalt binder prior to mixing. This allows significantly lower mixing and laying temperatures and results in lower consumption of fossil fuels, thus releasing less carbon dioxide, aerosols and vapors.

Not only are working conditions improved,

but the lower laying-temperature also leads to

more rapid availability of the surface for use,

which is important for construction sites with

critical time schedules.

The usage of these additives in hot mixed

asphalt (above) may afford easier compaction

and allow cold weather paving or longer hauls.

Reduces Plant Fuel Consumption – Studies have shown that running your plant at 35° F – 100° F lower will reduce fuel consumption by an average of 15%.Reduces VOC Stack Emissions – The EPA has found that volatile organic compounds (VOC) released through the stack of an asphalt plant are well within required EPA guidelines. The use of WMA has been shown to reduce these emissions between 50-90%.Easy to Compact. WMA has been found to be easier to compact, especially very stiff mix designs. Some contractors have eliminated a roller from the paving train. This saves money, time and energy resources.

Increased RAP Usage – The reduced viscosity of the WMA

allows for easier coverage of the RAP and because the asphalt

cement is not being aged at higher temperatures, the virgin

asphalt binder may help to rejuvenate the inherent binder of

the RAP. The increased use of RAP is a savings to contractors,

agencies, and creates sustainable pavements by reducing the

need for petroleum and virgin aggregates.

Fume and Smell Reduction – The largest source of

emissions from an asphalt plant is the result of fuel

combustion during the drying and heating process. The

decrease in fuel consumption is directly correlated to reducing

these emissions. In addition, reducing temperature at load out

and paving has a direct correlation to fumes at the plant and

asphalt pavers.

Better Work Environment – The reduction in temperature behind the paver makes a more comfortable environment for employees and government workers.Reduces “Aging” Asphalt Cement – The heating of asphalt cement oxidizes the material for every 25° F it is heated.2 By decreasing the temperature needed to produce WMA we may be decreasing the “aging” of the asphalt binder and thereby creating longer lasting pavements.