Properties of Fibre Reinforced Concrete Using Recycled Aggregates and Flyash

Introduction

Concrete is the basic engineering material used in most of the civil engineering structures, it is the premier construction material used widely across the world in most types of engineering works. According to research, concrete stands second to water on volume consumption basis Concrete is a composite material made up of cement, fine aggregates, coarse aggregates and water mixed in desired proportion based on strength requirement. Concrete solidifies and hardens after mixing with water and placement due to a chemical process known as hydration. The water reacts with the cement, which binds the other components together, eventually creating a robust stone-like material. Concrete is used more than any other man-made material in the world. Concrete like other engineering materials needs to be designed for properties like strength, durability and workability. Concrete mix design is the science of deciding relative proportions of ingredients of concrete, to achieve the desired properties of concrete. Use of mineral admixtures like fly ash, slag, metakaolin and steel fibre have revolutionized the concrete technology by increasing its strength and durability of by many folds. The concrete in which steel reinforcement bars, plates or fibres have been incorporated to strengthen a material is called reinforced concrete.

Now a days, construction and demolition industry is one of the country’s largest waste producers. The waste produced by demolition can be minimized and could be utilized again. Concrete recycling is an increasingly common method of disposing of dismantled concrete structures which was once routinely shipped to landfills for disposal. But recycling is now increasing due to improved environmental awareness, government laws and economic benefits. In India, about 14.5 MT of solid wastes are generated annually from construction industries, which include waste sand, gravel, bitumen concrete bricks, masonry, & concrete. However, some quantity of such waste material is being recycled and utilized in building materials. Most of the waste materials produced by demolished structures disposed off by dumping them in land fill. Dumping of wastes on land is causing shortage of dumping place in urban areas. Therefore, it is necessary to start recycling and re-use of demolition concrete waste to save environment. Concrete recycling gains importance because it protects natural resources and eliminates the need for disposal by using the readily available concrete as an aggregate source for new concrete or other applications. Large-scale recycling of demolished concrete will help conserve natural resources, and solve a growing waste-disposal crisis. The future for recycled aggregates will be driven by reduced landfill availability, greater product acceptance, continuing government recycling mandates, and the continuing decay of a large stock of existing infrastructure, as well as by the demands of a healthy economy.

The term "fly ash" is often used to describe any fine paniculate material precipitated from the stack gases of industrial furnaces burning solid fuels like coal. The characteristics and properties of different fly ashes depend on the nature of the fuel and the size of furnace used. Fine grade fly ash has acquired considerable importance in the building materials sector. Disposal of fly ash not only causes air and ground water pollution but also requires huge land area. It is estimated that 72 to 75 thermal power stations across country are presently producing more than 90 Million Tonne of fly ash per annum. For disposal of 400 to 500 MT of ash generation about 100 to 125 acres of waste land is required to dump fly ash. But now a days fly ash can be utilized in many ways in civil engineering works and it can save up to 15 to 25 % of construction cost.

Fibre-reinforced concrete (FRC) is concrete containing fibrous material which increases its structural integrity. It also increases speed of construction and in some cases may even eliminate the need for conventional reinforcement. It contains short discrete fibres that are uniformly distributed and randomly oriented. Fibres include steel fibres, glass fibres, synthetic fibres and natural fibres. Within these different fibres that character of fibre-reinforced concrete changes with varying concretes, fibre materials, geometries, distribution, orientation and densities. Fibre-reinforced normal concrete are mostly used for on-ground floors and pavements, but can be considered for a wide range of construction parts. Fibres are usually used in concrete to control cracking due to both plastic shrinkage and drying shrinkage. They also reduce the permeability of concrete and thus reduce bleeding of water. Some types of fibres produce greater impact, abrasion and shatter resistance in concrete. Steel is the strongest commonly-available fibre, and come in different lengths and shapes. Steel fibres can only be used on surfaces that can tolerate or avoid corrosion and rust stains.

It is expected that this study involving combination of waste materials i.e. recycled course aggregates with full replacement of fresh course aggregates and fly ash with partially replacement of cement and also addition of steel fibre to concrete, will be useful to the existing construction methodology.