Porus Bhatt, Director, Genesis Infra Project Consultants
A Stone Matrix Asphalt (SMA) pavement laid at Parimal Underpass in Ahmedabad Municipal Corporation has completed 7 years. The underpass, which used to get submerged under almost 2m depth of water due to waterlogging in the monsoons every year, has not shown a single pothole, and the surface looks as good and smooth as when it was first laid. With the Indian government intending to build roads connecting every town of India, it is essential to make them maintenance-free as well.
Features of SMA
SMA roads have proven to withstand their structure for almost 20 years without needing any maintenance. SMA pavements require a higher quantity of bitumen compared to traditional flexible pavements. This generates risk of bleeding of bitumen. To prevent this, cellulose fibers are used to arrest wearing-off of the bitumen. A unique feature of this design is the stone on stone contact and the least percentage of air voids.
|Mix Design requirement for SMA as per IRC: SP: 79 : 2008 and MORTH Specification Section 515 ( 2013)|
|Bitumen||5.8 – 6.5%|
|Air voids||3 – 4%|
|Palletized Cellulose Fibers||0.3%|
|Drain down||Maximum 0.3%|
- High resistance against rutting
- Can be used at places with very high temperatures and heavy traffic
- High flexibility provides resistance against cracking which happens during cold temperatures
- Good wearing resistance
- Good adhesion between aggregates and bitumen
- Less bleeding
- Reduced traffic noise
Guidelines for laying down SMA
Measures to be taken at Plant
- Hot Mix Plant should be calibrated as per IRC 90 2010.
- Maintain stockpiles separately – No mixing of aggregates.
- Monitor gradation of incoming aggregates.
- Coarse aggregates to be added first-raise temperature to 170oC, mix for 6-7 seconds.
- Add Bitumen Coated Cellulose Fibers directly afterwards, together with filler (lime100 % passing 600µ).
- Mix for 5-6 seconds.
- For Batch Mix Plant - Mineral filler & fiber feed system, to be calibrated for plant for production & maintain interlock system.
- For Drum Mix Plant – Fiber will be dosed through conveyor belt with the mineral filler and aggregates.
- Bitumen to be added immediately after addition of filler & Cellulose Fiber pallets.
- Bitumen mixing should be for 7-8 seconds.
- Wet mixing should be for about 25 seconds.
- Maintain temperature of 160-165°C taking care bitumen is not overheated.
- Start with a clean truck.
- Use water based liquid soap for truck cleaning.
- Drain excess release agents – truck bed should be dry.
- Mix to be transported between155-160oC.
- Cover the mix during transportation.
- Measures to be taken while paving the mix at site.
- Receipt of hot mix directly on the paver.
- Maintain continuous paver operation.
- Avoid manual paving.
- Adopt number of trucks to transport to site, ensuring paver runs continuously without a break, so that the paver plate does not cool.
Measures to be taken for Compaction
- Do not use rubber tyre rollers for compaction of SMA
- Use only vibratory roller for the first pass
- For the balance passes, use 8-10MT static rollers
- Roller should be right behind the paver-minimum distance
- There should be three Compacts and six passes each direction
- Compaction should run in direction of paver
- Favorable temperature of starting compaction, between 130-165°C & should be about 110°C at end of compaction
- Hydrated Lime should be sprayed post compaction
- Surface must cool to 55-60°C and 4 hours curing before allowing any traffic is allowed on the road.
Designing a pavement on Railway Over Bridge was a challenge. In 2017, the Public Works Department of the Government of Maharashtra planned to rehabilitate SH34 under PWD Palghar. We at Genesis Infra Project Consultants (GIPC) suggested the use of Stone Matrix Asphalt (SMA). EE Er. Rahul Vasaikar and Road Secretary Shri Prakash Ingole assisted us in taking up this challenge and we successfully made the First Stone Matrix Asphalt on any ROB in India.
Genesis Infra Project Consultants supporting public and private sectors
GIPC is supporting both the public-and private sector with planning, project management, and realization of infrastructure projects. The company specializes in implementation of Stone Matrix Asphalt Technology using made-in-India Palletized Cellulose Fiber. GIPC also hand holds the contractors and guarantees the pavement for its complete defect liability period and believes in commitment and adhering to specifications. All the projects till date have achieved the Defect Liability Period without any need for any repairs/maintenance. Incorporating the findings from analysis and feasibility studies into a well-thought-out master plan, or system plan, is the basis for the projects.