IIT-M research shows concrete made from clay may replace cement

Chennai: Indian Institute of Technology Madras (IIT-M) on Friday said its new study shows that concrete made from clay fly ash, and limestone hold promise as replacements for cement.

The IIT-M researchers have provided clarity on the link between microstructural development and durability performance of concrete through their investigation on concrete with ternary blended cements, which will help the construction industry to produce more eco-friendly concrete than available now.

Concrete is the most widely used construction material in the world - seven cubic kilometres of concrete are manufactured each year, which works to one cubic metre of concrete for every human on earth.

Conventional concrete is made of cement, fine aggregate particles such as sand and coarse aggregate particles from rock, mixed with water; this mixture hardens with time because of the reaction of cement with water, the Institute said.

Modern concrete, however, includes chemical and mineral additives that impart unique properties. It is common today to find the cement to be a mixture of two or three different ingredients.

The current research, funded by Swiss Agency for Development and Cooperation, deals with the exploration of properties of a three-component cement.

"Worldwide, there are research efforts in developing alternative concrete additives and energy efficient binders that can produce a more sustainable form of concrete. The UN Environment Programme (UNEP) has stressed on the need for cement substitution to decarbonise cement industry," said Professor Manu Santhanam, Department of Civil Engineering, IIT Madras.

According to the researchers, the study unravels the complex nature of interactions of this three-component system involving ordinary cement, limestone powder and calcined clay, called LC3, which leads to the production of highly durable concrete in aggressive environments such as sea water.

The research team studied the role of physical structure alterations on three binder types - plain Portland cement, fly ash-based binder and calcined clay-limestone binder (LC3).

The researchers adopted a fundamental approach based on cement chemistry and identified the chemical composition of the blended cement system as a critical factor in the development of nanoscale pore structure, which is the key to concrete durability.

The evolution of pore structure decides the permeability of concrete to water and aggressive chemicals - the finer the pore structure, the lesser the permeability.

Ternary blended systems such as LC3 impart a finer pore structure to concrete at early ages, which is not possible with plain cement or even fly ash blended cement.

Further, the unique reaction chemistry of the three components in LC3 results in a complex arrangement of cement reaction products, which make the concrete microstructure denser and helps to attain strength and durability at an early age.

"While several composite cementitious materials are being explored, clear understanding of the microstructure-dependant factors that lead to these superior performance characteristics in concrete is not yet available," Santhanam added.

The governing factors controlling durability performance must be analysed in order to understand how the various components contribute to the performance of the concrete, according to the Institute.

"Our primary focus was always to understand the behaviour at the scale of cement reaction and further integrate this information with concrete performance, which is a challenging task," said study co-author Yuvaraj Dhandapani, PhD Student.

"Since we have clarified and fine-tuned performance at the microscale, all type of concretes made with LC3 could attain superior performance to ingress of water or chlorides along with excellent early strength development," Dhandapani added.

"To facilitate practical adoption, we have also confirmed these characteristics on a range of different concrete types used in the construction activities," he added.