RECYCLED AGGREGATE CONCRETE USING POZZOLANIC MATERIALS

Abstract

Construction is a process of developing new ventures and is a never-ending activity. The aggregates are the raw materials, which constitute 70-80% in the concrete mixture. Every year, it is estimated that the construction industry in India generates about 10-12 million tonnes of waste annually. Concrete is the most versatile material which is used extensively in the construction field. There is a need to think of alternate materials because of the scarcity of natural aggregates.

The use of this recycled coarse aggregate is mainly for two reasons: To decrease CO2 emission which is harmful to environment and to reduce the cost of construction material / cost cutting/ reduce the budget of the construction. C&D waste can be reduced, re-used and recovered, dramatically reducing the dumping of demolished waste. The main purpose of recycling is to minimize the amount of waste to be deposited and to preserve natural resources.

The present investigation is carried out for evaluation of properties of natural and recycled aggregate concrete. Pozzolanic materials like Fly Ash and Silica Fume are used as mineral admixtures for good workability and for better strength. Cement is replaced with 10% SF and 20% FA in design mix. RAC20 made with different grades of recycled aggregates of GA20, GA25, GA30, GA35 and GA40 with different replacements 50%, 75% and 100%. During mix proportion presoaking of aggregates is done before the mixing of concrete. Three stage mixing approach is adopted for the production of concrete. The density of concrete, compressive strength and water absorption of PC & RAC were determined at ages of 7 and 28 days. The results of compressive strength are found to be lower than target strength. With GA20 at 50% replacement, 95% of the target strength is achieved (27.55MPa). Strength could have achieved with increase in curing period.

It is also concluded that the water absorption and density of RAC is lower than NAC.