Production and Performance of Aggregates Using Two Types of Fly-ash for Lightweight Concrete using Glass Powder as Binder

Abstract

In India despite the government commitment to increase energy production primarily by renewable sources and nuclear plants the main source for power production are coal fired thermal plants; its projected that by year 2020 India annual consumption of coal will rise to 1.5 billion tonnes. These coals fired thermal plants produce large quantity of finely divided fly-ash as by product which are collected be electrostatic precipitators from flue gases. Fly-ash in large quantities are still disposed of in landfills and storage lagoons. Such practices of disposal lead to environmental damage by causing air and water pollution on a large scale. Most of the previous research works were done by using conventional fine and coarse aggregates in concrete and replacing cement with fly-ash or by replacing the natural aggregates by fly-ash spherical aggregates. In this research work, the coarse aggregates were replaced entirely by fly ash angular aggregates in concrete.
For determination of physical properties tests like specific gravity, water absorption, etc. are performed on fly-ash, glass-powder, fine aggregates and coarse aggregates.
Fly-Ash aggregates are made from briquettes, which are casted by mixing glass powder and fly-ash in ratios of 10:90, 15:85 and 20:80 were adopted with a suitable water fly-ash ratio tried for every glass powder and fly-ash ratio. These briquettes after sintering were crushed to produce angular lightweight aggregates.
These lightweight aggregates performance were checked against sudden impact and progressive crushing by impact test and crushing test respectively.
Concrete mix design procedures recommended for lightweight aggregate concrete varies completely from normal aggregate concrete mix design. Lightweight aggregates are highly porous which has adverse effect on compressive strength and also reduces the free water available in paste matrix; so in the case of light weight concrete mixes the net water cement ratio required cannot be established with sufficient accuracy. The ACI standard ACI 213-03123 have suggested to overcome these difficulties by incorporating the concept of ‘Specific Gravity Factor’. In view of this lightweight concrete mixes are usually proportioned by trial and error method.
The mix design for fly-ash glass powder ratio of 15:85 was done for M20 grade concrete, because of the segregation problem natural aggregates are completely replaced by lightweight aggregates. In the fine trial compressive strength on 7th-day crossed the desired strength of 21 MPa requirement. Cubes are casted and tested for their compressive strength on 7th-day and 28th-day. Cylinders and Prisms are casted and tested on 28th Day for split tensile test and flexural strength test respectively.
From the studies, it can be concluded that the fly-ash aggregates can be used as a substitute of natural aggregates in construction works.