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Construction : Cover Story | April 2017 | Source : Equipment India

Construction Challenges

Ben W James, CEO & Co-founder, Global Road Technology, explains the different types of stabilisation techniques that need to be adopted in challenging rural areas, sub-Himalayan regions and north-east states.

The Indian road sector has undergone phenomenal growth over the last decade and is growing exponentially now due to the new government's focus on the sector. The pace of road construction is even higher in rural areas, sub-Himalayan regions, international border areas and north-eastern (NE) states, as part of providing better connectivity and access for defence requirements.

Accordingly, soil/aggregate requirements for infrastructure, especially roads, has increased and reached a level where availability of these materials has become a major challenge. Non-availability of suitable soil and aggregates has made projects unviable and cost prohibitive. These factors have delayed several important projects and are even blocking development in certain aggregate deficient regions - predominately in the NE.

Aggregate scarcity will increase further as part of the government's environmental conservation rules and restrictions on quarry activities. Apart from this, road projects in NE states and sub-Himalayan regions have many other engineering and financial challenges; a few of them have been itemised below:

  • Constraints for road construction;
  • Difficult terrain, weather conditions and geography;
  • Unstable rock geology giving rise to landslides;
  • High intensity and heavy rainfall which also induces slope failure;
  • Lack of suitable quality rock and other construction material in general;
  • Long haul distance for manufactured construction items like steel and cement;
  • Small construction window for road construction;
  • Fragile environment and ecosystems.

Considering the above constraints, a fresh look is required in terms of new and proven technologies and methods of road construction required for rural, sub-Himalayan/NE states. The basic requirements of these new technologies would include:
  • Reduction in aggregate requirements;
  • Recycling of existing road materials;
  • Work at high speed to be fitting in smaller construction window;
  • Use marginal materials available locally;
  • Environment friendly;
  • Technically better and cheaper in terms of life-cycle cost compared to traditional methods.

Considering all the factors mentioned above, 'Cold-In-Place-Recycling (CIPR)' and different types of stabilisation techniques will need to be adopted in these challenging areas.
The stabilisation of soil/aggregate is being used worldwide towards optimal usage of the threatened reserves of the same. Though soil stabilisation exists in Indian codes, the concept is yet to be exploited on the ground to aim at critical mass. The concept of CIPR has recently been incorporated in IRC-37(2012), the CIPR and Cement Treated Base (CTB) has been approved by the National Highways Authority of India (NHAI) in a few projects, but is yet to be applied as general practice.
Soil/aggregate stabilisation and CIPR provide a comprehensive solution for rehabilitation of existing road networks and greenfield road construction, that will suit the requirements of the sub-Himalayan and NE regions.

Major components of road stabilisation technology
The road stabilisation process can be divided into three major components: Design Process and codes: Stabilisation and CIPR requirements in Indian design codes have been adopted from AUSTROADS and need further updating with respect to gradation requirements of materials to be stabilised. The material requirements and envelope shall include larger-size particles and shall be flexible as soon as strength requirements are met. This particular modification will allow engineers to utilise existing materials to a large extent up to GSB layers. This will also allow usage of locally available marginal materials. Specialised laboratory equipment are also required to be developed in India; currently these lab equipment are being imported at high cost. Stabilisation agents (materials): The stabilisation process can use a wide range of stabilisation agents, i.e., soil-aggregate mix, lime, cement, fly ash, foundry sand, slag, foamed bitumen, emulsion, polymers and other proprietary chemical stabilisers.

Stabilisation equipment: Specialised heavy road recyclers capable of cutting existing soil/aggregate/asphalt, mixing in place, adding water and other stabilisation agents as per requirement, speed independent stabilisation agent spreader (cement, lime, polymer, etc.), heavy padfoot rollers (20 t static and 40 t dynamic capacity) and pneumatic tyre rollers are essential components of the stabilisation process in general.

Advantages of soil/aggregate stabilisation and CIPR tech Major advantages of using soil/aggregate stabilisation and CIPR technology are as follows:

  • Provides opportunity for recycling existing road materials;
  • All types of soils, i.e., gravel, sand, clay, old bituminous/granular materials including black cotton soils can be stabilised effectively with different stabilisation agents;
  • A wide verity of stabilisation agents, e.g, lime, cement, fly ash, foundry sand, slag, foamed bitumen, emulsion, polymers and other proprietary chemical stabilisers can be used, depending upon local availability;
  • The stabilised road layers are more robust, resilient and flexible than traditional roads and perform much better over a wide range of loading, moisture and temperature conditions;
  • The stabilised pavements offer superior strength and longevity, even in extreme climatic conditions. This reduces maintenance cost in the long run while providing better riding quality to road users;
  • Eliminates or reduces need for quarried rocks and other raw material;
  • Cheaper than traditional road construction;
  • Savings in foreign exchange as it reduces thickness of bituminous layers;
  • All designs for pavement are in accordance with IRC-37(2012) for major highways and IRC-72(2015) for rural roads;
  • It is possible to construct a rural/main road pavement in one pass using state-of-the-art road stabilisers at a rate of 1.5 km/1 km per day under ideal conditions;
  • Cuts water usage in construction and maintenance of haulage roads;
  • Because the construction speed is manifold (depending upon site) compared to traditional methods, it delivers considerable savings on traffic diversions and minimises disruption in traffic.

The environmental and social benefits of using stabilisation in road construction can only be counted but can never be listed in full. A few of them are listed below:

  • Reduced consumption of non-renewable road-building materials (aggregates, bitumen, sand, moorum, water);
  • Improved air quality (less trucking and quarrying);
  • Locally available marginal materials can be effectively used with stabilisation;
  • Improved road safety as diversion requirements are eliminated, or reduced traffic chaos for road users due to high speed of construction;
  • Protection of flora and fauna in quarrying area due to reduced or no quarrying operations;
  • Reduced dust/noise/air pollution and improved health in quarrying area due to reduced blasting and quarrying operations;
  • Reduced greenhouse gas emissions;

Epidemic control through control of airborne infections as it reduces dust being generated from treated areas.
It is high time that all government agencies responsible for road construction give sincere appraisal and focus on road construction in rural/sub-Himalayan/NE states, and implement proper guidelines for the use of stabilisation techniques that can reduce the need for aggregates, cut costs and ensure adherence to critical project time lines.
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