Conserving Limestone

Conserving Limestone

There is a need to conserve the limestone used in OPC production and optimally use cement in construction, writes JD Bapat.

The cement industry in India is set on the path of growth and modernisation. However, one of the biggest challenges before the industry in the coming years is the conservation of limestone, the principal raw material for cement production.

As per the report of Working Group on Cement Industry for the 12th Five- Year- Plan (2012-17), prepared by the Ministry of Commerce and Industry, Government of India, investment in infrastructure is estimated at US $ 1 trillion, during that period.

The cement demand for infrastructure projects such as the dedicated freight corridors, upgraded and new airports and ports, housing and roads, is likely to increase substantially. The additional installed capacity requirement during the next 15 years (up to 2027) would be about 1,035 million tonnes.

As per the estimate of the Indian Bureau of Mines (IBM), the total cement grade limestone reserve available to meet the industry requirements is 89,862 million tonnes. Based on the expected growth and consumption pattern, the current available limestone reserves are expected to last only for another 35 - 41 years.

All the available limestone reserves cannot be exploited for the following reasons:

  • Deposits in inaccessible areas.
  • Lack of infrastructural facilities like rail, road network, power supply, water availability, etc.
  • Limestone deposits located near villages, towns, cultivated land, historical monuments, important civil structures like dams, forests, are blocked due to safety regulations and are not available for mining for cement manufacture.
  • Limestone mining from a simple deposit is cost- effective, as compared to intricate and complex deposits, where the fluctuations in the grade often lead to problems in cement production or require beneficiation before utilisation and also require improved fuel with low ash content.
  • The availability of potential limestone deposits has also been restricted due to environmental constraints, as many of these deposits are located in reserve forests, bio-zones and environmentally sensitive areas, near tourist centres/hill-stations or under thickly populated or cultivated fields.
  • There is a need to conserve limestone used in cement (Ordinary Portland Cement or OPC) production, on the one hand and optimally use cement in construction, on the other.

Towards that end, the he following measures are suggested:

Improving utilisation of low/marginal grade limestone in cement production:
This requires efforts in different areas, such as:

Using petcoke as fuel in cement production.
Mine planning to blend high-grade with low-grade limestone.
Enrichment of CaCO3 in limestone, through different beneficiation techniques. Using lesser lime in cement production:
Low lime cements such as belite and sulfoaluminate (C4A3S) type have been used on a commercial scale particularly in countries such as China, Japan and Russia.
The cements are manufactured in smaller batch- type process kilns and are found suitable for applications in coastal areas owing to their sulphate resistance. These have potential for utilisation of low grade limestone and industrial wastes.

Minimising clinker production: Maximising substitution of clinker with mineral admixtures such as fly ash and blast furnace slag, in the production of blended cement. The relevant changes in Indian Standards may be initiated to permit the manufacture of composite cement with more than one mineral admixture, high volume fly ash cement and limestone cement. The standards in European countries and US allow such cements.

Using lesser cement in concrete: Maximising the substitution of cement with mineral admixtures, such as fly ash, ground granulated blast furnace slag, metakaolin, rice husk ash and limestone powder. Appropriate application of high performance concrete such as self-compacting concrete, roller compacted concrete, high volume fly ash concrete may be promoted, considering the requirements of strength and durability.

Highlight: Based on the expected growth and consumption pattern, the current available limestone reserves are expected to last only for another 35 - 41 years.

Dr J D Bapat,
Independent Professional Consultant.

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