320 Kilometres for Fly Ash
This week, a story about what happens when the most critical ingredient in your RCC mix is 320 kilometres away. Every dam engineer understands concrete technology. Fewer understand the logistics that determine whether that technology can actually be delivered on site.
A.K. Sthapak, Managing Director, PCCI
From the Field
Roller compacted concrete needs fly ash. Not as an optional additive, but as a fundamental component of the mix. At Teesta Low Dam Stage IV in West Bengal, the RCC mix used 135 kg/m³ of fly ash against 85 kg/m³ of cement: a 61% fly ash replacement ratio. Without that fly ash, there would be no RCC dam.
The problem was sourcing it.
Teesta Low Dam IV is NHPC's first RCC dam, located at Kalijhora in the Kalimpong district of West Bengal. The nearest fly ash source of acceptable quality was NTPC Kahalgaon Super Thermal Power Station in Bihar, approximately 320 km away by road.
At normal production rates, the dam site consumed approximately 115 tonnes of fly ash per day. During peak placement, that rose to 210 tonnes. HCC, the civil contractor, deployed 29 bulker trucks running continuously to maintain supply. The trucks ran through the Siliguri corridor and then climbed narrow hill roads to the dam site. A five to fifteen day buffer inventory was maintained on site to absorb any transport disruption.
The fly ash was just one supply line. Peak days also required 135 tonnes of cement, over 4,000 tonnes of aggregate, and 2,500 tonnes of boulders. The batching plant ran 24 hours a day. Any interruption in any material stream could create a cold joint in the dam.
At normal production rates, the dam site consumed approximately 115 tonnes of fly ash per day. During peak placement, that rose to 210 tonnes. HCC deployed 29 bulker trucks running continuously to maintain supply from NTPC Kahalgaon, approximately 320 km away.
HCC case study, Equipment India
HCC completed the 196-metre RCC section in 196 calendar days, placing 167,000 m³ of RCC. It was India's third RCC dam after Ghatghar and Middle Vaitarna, and the first built in the Sub-Himalayan geological zone.
The technical achievement is impressive. But the lesson for the industry is logistical, not structural.
India's RCC dam pipeline is growing. The pumped storage programme alone envisions 100 GW of new capacity by 2036. Every one of these projects will need fly ash in volumes measured in hundreds of tonnes per day. The thermal power plants that produce it are concentrated in Bihar, Uttar Pradesh, Madhya Pradesh, and Maharashtra. The dam sites are in the Himalayas, the Western Ghats, and the Northeast.
The gap between where fly ash is produced and where it is needed is not shrinking. Engineers who plan concrete technology for new dam projects must plan the supply chain with equal rigour, or the best mix design in the world will remain a laboratory exercise.
The lesson: RCC dam construction depends on fly ash supply chains as much as it depends on mix design. If you cannot guarantee 200+ tonnes per day of consistent-quality fly ash at a remote site for the entire construction season, the RCC option needs a logistics plan before it gets a mix design.
Did You Know?
340 million tonnes
of fly ash generated in India yearly.
Indian coal contains 25-45% ash, compared to 10-20% in imported coal. India generated 340 million tonnes of fly ash in FY 2024-25, but only about 27% went to the cement industry. The government reports approximately 98% overall utilization, but most goes to roads, bricks, and mine backfilling. For dam engineers, the question is not whether fly ash exists. It is whether the right quality can reach a remote site reliably for years.
Sources: Ministry of Railways/NTPC (2025), MDPI Minerals (2022)
Worth Knowing
SCM Strategies for Dam Concrete: Fly Ash, GGBS, Silica Fume, and Calcined Clay
A comprehensive guide to selecting the right SCM at the right replacement rate for each application within a dam, from the body RCC to the spillway face.
Cement Optimization in Mass Concrete: Reducing Cost and Carbon Without Sacrificing Strength
Performance-based mix design with SCMs can reduce cement content by 30-50% while maintaining or exceeding target strength. The economics and the engineering.
ASTM C618: Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan
The international benchmark for fly ash quality in concrete. Covers Class F and Class C designations, LOI limits, fineness, and chemical requirements.
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