Chennai: Indian Institute of Technology Madras researchers have provided clarity on the link between microstructural development and durability performance of concrete through their investigation on concrete with ternary blended (i.e. three component) 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 – 7 cubic kilometres of concrete are manufactured each year, which works to 1 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.
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 study deals with the exploration of properties of a three-component cement. 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 IIT Madras 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.
The research, funded partially by Swiss Agency for Development and Cooperation, and the Department of Science and Technology, Government of India, has been published recently in the reputed peer-reviewed journal Cement and Concrete Research. The paper has been co-authored by Mr. Yuvaraj Dhandapani, PhD candidate, IIT Madras, and Prof Manu Santhanam, Head, Department of Civil Engineering, IIT Madras.
Speaking about this research, Prof Manu Santhanam, Department of Civil Engineering, IIT Madras, said, “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.”
Prof Manu Santhanam added, “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.”
The governing factors controlling durability performance must be analysed in order to understand how the various components contribute to the performance of the concrete.
“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. 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. To facilitate practical adoption, we have also confirmed these characteristics on a range of different concrete types used in the construction activities,” said, Mr. Yuvaraj Dhandapani, PhD Student.
The study provides critical insights into the structural development mechanisms with ternary blended cementitious systems, and paves the way for effective utilization of such cementitious combinations to produce durable concrete.