Waste ash make concrete stronger

Waste ash can make concrete stronger

6:33 AM, 17th November 2015
Waste ash can make concrete stronger

CHENNAI, INDIA: The use of cement might add strength to a concrete mix and eventually to a structure. But adding a small quantity of wastes disposed in thermal power plants or a steel factory to the concrete mixture can help the structure last a lifetime, a study conducted in Indian Institute of Technology, Madras (IIT-M) has found.

Following a series of tests done on different types of concrete, the study by the civil engineering department of IIT-M showed that a proportion of by-products like fly ash and ground granulated blast furnace slag (GGBS) added to the concrete mix can give durability and life to reinforced structures including buildings and bridges.

It recommends that cement used for durable construction be partially replaced with or should contain at least 15 percent fly ash or 30 percent slag, along with the use of low water content in the concrete.

A higher fly ash and slag content can deter penetration of chlorides into concretes of offshore and coastal area structures for a longer duration than usual and, consequently, protect the steel reinforcement from corroding.

Thermal power plants in the country generate nearly 200 million tonnes of fly ash a year, but less than 30 million tonnes are utilised.

“The use of these mineral admixtures improves the relative performance of the concrete in chloride rich environment, from 4 to 13 times more than usual. While these by-products are available for a relatively cheaper price, their use can bring down the cost to some extent during construction,” said prof Manu Santhanam.

“But what matters is that such structures save costs on a long term due to its durability because a design based on strength alone does not ensure durability,” said prof Ravindra Gettu.

Extensive use of these byproducts like fly ash not only cuts down the use of cement proportionately and subsequently reducing carbon dioxide emission in the production of cement, but also lowers environmental pollution if they are dumped in wastelands.

The findings come at a time when numerous cases of premature deterioration of reinforced structures and consequent failure were being reported across the world. The study involved more than 3,000 tests done over four years on more than 50 types of concrete,” added prof Gettu.

The microstructure, evolution of compressive strength, resistivity to corrosion, permeability, potential for limiting the ingress of chlorides both from sea and ground water into the concrete were examined.

The professors said that fly ash has a high amount of silica and alumina. When cement in the concrete mix reacts with water, one of the compounds it produces is lime, which leads to deterioration of concrete when it is attacked by aggressive environmental agents like water, sulphates and carbon dioxide.

These reactive elements in fly ash convert lime and help it bind with the aggregates, thereby adding more strength to the concrete.

© Times of India News

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