Dr. Ambika Behl, Dr. G. Bharath, Dr. Siksha Kar, Central Road Research Institute, New Delhi

Construction of Sustainable Pavements Through Recycling

Increased connectivity and improved road infrastructure developed in the country in the recent past has resulted in significant increase in the growth of traffic in terms of the number of vehicles and axle loads. However, the increased construction activities have resulted in an increased demand of materials and thereby allowing depletion of naturally occurring materials like stone aggregates. This has made the concerned engineers to explore the alternate methods including re-use of materials from existing pavements. Beneficial utilization of recycled materials can result in an important opportunity to save the mining and use of virgin materials, preserve energy, and save landfill space.

The main components of asphalt mixture are asphalt binder and aggregate, which have the potential to be replaced by recycled materials. The largest portion of pavement in terms of mass and volume are aggregates. The unit price of the aggregates is comparatively low with relatively low environmental impact on production. Correspondingly, because aggregate is exercised in large quantities, is non-renewable, and incapable to mine near its point of use, it can play a vital role in pavement sustainability.

Milling of distressed pavements for their complete or partial use is an accepted norm now to save fresh aggregates and bitumen. Recycling or reuse of pavement material is a very simple but powerful concept. In a time when highway professionals determine pavement rehabilitation techniques based on cost, performance, and environmental sustainability, in-situ recycling processes offer the best alternative to optimize these benefits. With strict attention paid to pre-engineering, mix design formulation, construction, and quality control, pavements constructed using these techniques offer the ability to decrease life-cycle costs and the environmental impact.

The conventional method of providing bituminous surfacing on flexible pavements requires significant amount of materials and energy. Therefore, in order to reduce consumption of fuel and aggregates, pavement recycling technology may be adopted for Indian roads (Reddy et al., 2013). Also, there is a problem of the scarcity of aggregates, which forces truck delivery of materials from long distance. The use of diesel for running these trucks contributes to emission of pollutants such as particulate matter, nitrogen oxides, carbon dioxides and sulphur dioxides. Many of the diesel engine emissions have been identified as carcinogenic, and harmful to the human health, even at occupational and environmental levels of exposure. For a lead of 200 km (which is common in north India), requires 18 million liters of diesel in transportation alone (Mallick and Veeraraghvan, 2010).

Based on the process adopted in recycling the asphalt mix, it can be broadly classified as central plant recycling and in-situ recycling. If the RAP (recycled asphalt pavement) is modified at a plant, away from construction site then the process is known as central plant recycling. In-situ recycling process the RAP modified in place, where from it is available. Further, the RAP could be heated to condition it. If heat is applied, then the process is known as hot mix recycling. In case of cold mix recycling, old materials are conditioned using recycling agent (like, low viscosity emulsion or foamed bitumen) without application of heat.

CSIR-Central Road Research Institute (CSIR-CRRI) has recommended recycling of pavement in several projects of maintenance, rehabilitation and up gradation of roads. This article presents the case study of rehabilitation and up grading of two road sections in India, Ranchi Ring Road using hot in place recycling (HIPR) and NH-31, using cold in place recycling (CIPR).

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