High Performance Concrete

CHAPTER 1

INTRODUCTION

1.1 GENERAL

Concrete is an extraordinary and key structural material in human history. Concrete holds the credit of being the most widely utilized tailored or man- made material in the construction industry and will hold good for the years to come. This credit goes to the properties of concrete like excellent strength, durability, less maintenance costs and use in many structural applications. But in the recent years the concrete industry is facing a big challenge mainly due the cement which is a vital component. International Energy Agency states that cement production accounts for 7% of total global CO2 emissions. Worldwide cement production is expected to rise about 5 billion tons by 2020. Thus, CO2 emission caused

This can be greatly achieved by the development of the concrete micro-structure. The resulting materials thus produced should have outstanding strength and durability properties, must be cost effective and most of all environmental friendly. There are some critical characteristics to be considered for particular applications like early strength, ease of placement, permeability and mechanical properties.

One such material developed to meet the above criteria and that has become attractive to civil engineers is High Performance Concrete (HPC). High performance materials are intended to reduce cross sections and the volume of concrete produced. HPC exhibits better mechanical properties and workability, and is increasingly used in the construction of high rise buildings, off shore structures and bridges. Certain characteristics of HPC are developed for particular applications and environments, so that it gives excellent performance in the structure in which it is used and in the environment where it will be

The fine and coarse aggregates were obtained from river sand, gravel and pebbles form river channels. Sand is a loose, non-cohesive ‘granular’ material whose size varies between 75 micron to 4.75 mm. River sand takes millions of years to be formed and it is a non-renewable resource and very essential part of human life. The process of extraction of river sand is very simple as there is no need of processing other than gradation. But as of now, continuous and indiscriminate sand mining causes serious environmental issues especially for erosive river beds. The depletion of these natural resources is continuing at a very fast rate mainly due to contamination, exploitation and industrial wastes which leads to scarcity of river sand. Also the transportation of river sand to the construction sites increases its cost significantly. Many of the rivers are exploited for living and non-living resources which poses ecological imbalance. In the present scenario, sand which is available in the river beds are very coarse containing large percentages of silt and clay. Presence of even minor quantities of silt and clay affects the strength of concrete to a large extent. For thousands of years, sand and gravel have been used in the construction of roads and buildings. But the presence of mica, fossils and other organic impurities in the river sand makes it inevitable for concrete