Rocky Road to sustainability

Sustainability in road construction is not as easy as it seems. This is one of the most difficult sectors for decarbonisation, not least because it is disorganised and all stakeholders, from researcher to mason, work in silos. Our expert panelists at the Smart Mobility Expo 2023 — Dr Ambika Behl, Senior Principal Scientist, Flexible Pavement Division, CSIR-CRRI; Neha Vyas, Senior Environment Specialist and India Environment Risk Management, Coordinator, The World Bank; Bovin Kumar, CEO, Cube Highways and Transportation Assets Advisors Pvt. Ltd. and Satin Sachdeva, Secretary General, Construction Equipment Rental Association, discussed how research in new technologies, material recycling techniques, equipment technology can drive sustainability in the construction industry, the challenges and the way forward.

We can replace 100% natural aggregates with slag-based aggregates. This also allows you to have carbon reduction and sustainability where there is depletion of aggregate resources. Another is recycling, where pavements need to be recycled more and more. We just did almost 25 projects with NHAI and we calculated the kind of savings we achieved. The aggregates saved was almost 30 lakh tonnes, and bitumen, 62,000 tonnes.

Dr. Ambika Behl
Flexible Pavement Division, CSIR-CRRI

The real culprit

A study done by IPCC revealed that almost 48% of carbon emissions were from offsite and the rest, onsite. Material, which was considered the highest emitter, was found to contribute to only 20% of the carbon emission. The major share was from construction equipment, machinery and transportation. These three entities need to be worked on to achieve decarbonization. From the technology perspective, materials that can lead to decarbonisation are available. Design, BPR and schedule, however, have to be organized such that transportation can be optimized leading to less emission. Plant, equipment and machinery need to operate on alternate fuels like bio-diesel, bio-fuel or electricity rather than on fossil fuels and aggregates to achieve decarbonisation.

Cradle-to-cradle approach

A concrete pavement will look sustainable because it lasts longer and gives less emissions during construction. However, if one considers carbon emissions generated during the production of cement, the concrete pavement is four times more polluting than an asphalt one. The cradle-to-grave concept is now being replaced by the cradle-to-cradle concept where anything that is produced is recycled. To this end, asphalt pavements are sustainable as they can be recycled multiple times.

Flexible pavement

In India, 90% of roads are flexible and 2%, concrete. Flexible pavement is very material extensive and sensitive. Research projects have brought in alternate material and technology for every layer of the four-layer structure from subgrade to surface where processes and construction methodology have been modified to bring in sustainability.

Waste plastic technology, warm mix asphalt, stabilization, recycling of pavements, all deal with construction methodology and material and adopting them can reduce carbon by 30% during construction.