The material and process of manufacturing contribute to reduced CO2 emissions

A research collaboration between India and Switzerland on a new cement material that can reduce carbon dioxide emissions in the manufacturing process is set to take off into implementation.

The construction sector is a major contributor to global carbon dioxide emissions. Though this is known, it appears difficult to reduce the scale of construction, especially as it is a route to establishing more equitable conditions in developing countries like India. One way of mitigating the emissions factor is the use of Limestone Calcined Clay Cement or the LC3 technology.

Traditional processes that manufacture cement from clinker-limestone or clinker-calcined clay combinations are well known. LC3 effects a synergy between these processes. The combination of the new method and the material properties effectively reduces carbon dioxide emissions by 30% as compared to the traditional way of manufacturing cement. Research on this evolved over ten years in Karen Scrivener’s lab at the Swiss Federal Institute of Technology (EPFL) at Lausanne, in Switzerland. Partners in this research are IIT Delhi, IIT Madras and TARA (Technology and Action for Rural Development).

Emissions and substitution

In manufacturing portland cement, limestone and materials like clay are heated together in huge kilns to high temperatures (approximately 1,450 degrees C), so that they fuse without melting to give clinker. “This is the most CO2-intensive part of the whole process. The carbon dioxide comes both from the burning of the fuel needed to create that temperature and due to the breakdown of limestone into calcium oxide and carbon dioxide. The latter part accounts for 60% of the CO2 emissions in manufacture of cement, ” says Prof. Scrivener. The best thing to do would be to substitute CO2-intensive clinker with a different material.

In India, fly ash – a waste produced in the burning of coal for producing energy – is used in the manufacture of blended cement. However this is used in a lower proportions and only where available; therefore, for effectively reducing emissions, more clinker is to be substituted with calcined clay and limestone. This reduces emissions by 30% with respect to portland cement.

Lab to commerce

To take this product from the lab to commercial use requires that the cement be certified by reputed research and testing centres, and for this purpose, Prof. Scrivener’s team has collaborated with Indian and Cuban agencies. The results of the Indian tests were published in The Indian Concete Journal, special issue on cements. Nearly ten tonnes each of four blends of LC3 (50% clinker, 30%calcined clay, 15%crushed limestone and 5% gypsum) were produced in India. To obtain a variation, clays and limestones of two different qualities were used. The LC3 obtained was used to manufacture solid and hollow concrete blocks, door and window frames, low duty paving blocks and roofing tiles, and to make roads. “Good results were obtained from the blends despite the sub-optimal conditions of production of the cement, demonstrating the viability and robustness of the technology,” Shashank Bishnoi of IIT Delhi and other authors write in the paper. The authors compared the strength of the various LC3 samples with Ordinary Portland Cement (OPC, a popular type of cement) and Portland Pozzolanic Cement (PPC, a variation of OPC in which locally available fly ash was added). They found that the strength of the LC3 made with low quality clay was comparable to the OPC and the samples of LC3 containing superior quality clay was higher than the OPC.

In fact, there is an added advantage to the new material when used in coastal areas where reinforced concrete can be damaged by chloride diffusing through the material. “The new cement has less porosity and it is more difficult for the chloride to get in and damage the steel rods,” says Prof. Scrivener. This gives the new cement a longer service life.

“From the beginning we have been in talks with the industry and the stakeholders,” says Ravindra Gettu, Professor, Department of Civil Engineering, IIT Madras. “In India, the first company [J K Lakshmi Cements] has made the industrial trials at its own expense, and we’re working to set up the second set with a different company in a few months,” adds Prof. Scrivener.

Though there is an initial cost, the payback times are of the order of five years, adds Prof. Scrivener.