Preventing cracks in concrete

Chennai: Giving an important solution to the construction industry, researchers from IIT Madras have come up with the solution for the early cracking in concrete which has become a big problem in recent years for the industry.

They have found that mixing small polypropylene fibers in the concrete prevents the early cracking in the concrete. A common complaint among builders and contractors is that floors and slabs crack just after the concrete are placed, especially during the hot days. “We are finding that as soon as the concrete is placed in about an hour or so there are cracks. This happens more and more in cities like Chennai where the climate is hot and dry,” said Professor Ravindra Gettu, Department of Civil Engineering, IIT Madras.

The water in the concrete evaporates when it is very hot and if there is a lot of wind. If the concrete is poured in large areas like a roof or slab and then crack develops. Such cracking causes leakage and necessitates costly repair and it also delays the construction.

To find the solution to the problem, Professor Ravindra Gettu and  Moghul Sirajuddin, a post-graduate scholar has studied different types of concretes for the last three years at the IIT Madras.

“If we mix small polypropylene fibers in concrete at the rate of one kg per every cubic meter, we can prevent early cracking in concrete. This is the cheapest solution to the problem,” Ravindra Gettu said.

“The fiber is holding the concrete and making sure it does not open. It also prevents some evaporation from occurring as it holds water inside the concrete. Even in concrete, which is very prone to cracking we have found that we were able to mitigate it,” he added.

It will add the cost around Rs.300 per cubic meter of concrete, but it will prevent the early cracking. They also found that concretes that have large amounts of fly ash and slag or pozzolana Portland cement (PPC), can experience more and earlier cracking than conventional concretes made only with ordinary Portland cement (OPC).

In India, nearly 60 per cent to 70 per cent  of types of cement have flyash or slag. The problem of early cracking is being reported more and more very recently.
“Earlier, there was no proper study on the relation of early cracking and fly ash. We clearly related it. It doesn’t mean we should not use fly ash. Fly ash is waste material and we are promoting its use. They should be aware of the mitigation measures,” he said.

It also suggested other measures like adding glycol-based shrinkage reducing agents or spraying the fresh concrete with acrylic-based curing compounds to reduce the evaporation of water from the surface.