Effect of Recycled Aggregates on Strength and performance of Recylced Aggregate Concrete

- This study is taken up to utilise the recycled coarse aggregate and recycled fine aggregate as replacement of natural aggregate in concrete mix. It is required to find the percentage of recycled coarse aggragate and recycled fine aggregate, as the strength of concrete can not be achieved by using higher percentaged. The purpose of study is to compare between recycled coarse aggregate and recycled fine aggregate with natural coarse aggregate and sand in terms of specific gravity, water absorption, particle size distribution. Further, this stydy will also consider the difference between the performance of Recycled Aggregate Concrete for different percentages of recycled coarse aggregate and recycled fine aggregate i.e for 0%, 10%, 15%, 20%, 25%, 30%, 35% replacement. The present study is an experimental investigation on the behaviour of recycled aggregate concrete (coarse& fine aggregates) with respect to the strength and performance.


Introduction
The most common material used in the world is water. After water Concrete is the most important construction material used through out the world in different types of civil engineering activities. Day by day scarcity of quality coarse aggrgate and fine aggregate is taking place. Restrictions on mining of aggregates is increasing day by day due to greater awareness of environmental protection. This leads to search for substitute material. It forces to reuse aggregate extracted from the construction and demolition waste (C&D waste) in new concrete. C&D waste generally contains Concrete rubble as major share. This concrete rubble can be crushed and sorted out for recycled coasre aggregate and fine aggregate. These can be used as a replacement material for natural aggregates in concrete or as a sub-base or a base layer in pavements. The material which is extracted from Construction and Demolition waste and used again in making concrete is called as recycled aggregate. The natural aggregate can be replaced with reused aggregate up to 25%. Beyond this percentaget the strength starts to reduce [1]. Based on the quantity and size of recycled aggregate, a regression model has been modified appropriately by test results [2]. The increase of Recycled aggregate content and w/c ratio decreases the durability of concrete [3]. Concrete with acceptable strength and durability can be produced along with high packing density is achieved [4]. The absorption and drying shrinkage of Recycled Aggregate Concrete linearly increase with the increase of replacement percentage of Recycled Aggregate Concrete, but decrease when certain amount of fly ash is mixed in the Recycled Aggregate Concrete [5]. As the age goes on old structures become unserviceable.  To know the performance of recycled aggregate concrete.

A. Portland cement
Cement is tested for its physical peoperties in the laboratory as per the Indian standards. When cement reacts with water it liberates considerable heat and this reaction is termed as exothermic. Due to the reaction Calcium Silicate Hydrates are formed, which are responsible for the good properties of concrete. It is better to use cement produced within three months from the date of production.

(i) R-Sand
Ordinary river sand is used. Specimens are casted using the sand passing through 2.36 mm sieve. As per the methodology mentioned in IS2386 (Part-I)-1963Sieve analysis for the sand is carried out in the laboratory. Sand plays key role in reducing shrinkage of concrete in the process of curing. Sand will also help in reducing the cost. As the availability of sand is becoming scarce, Manufactured sand can be used in making concrete. Recylced fine aggregate can also be used in making concrete. Sand can be tested as per Indian Standards in the laboratory.

Split Tensile strength test
The dimensions of cylinder used to conduct the split tensile strength test in accordance with IS 5816: 1999 is 100mm x 200mm. Two samples are used to test the split tensile strength test at the age of 7, 28 days curing.

Rapid Chloride Permeability Test (RCPT)
The size of cylinders used to conduct Rapid chloride permeability test is 100 mm x 50 mm. This test is carried out at the age of 28 days. The RCPT test consists of moulds with electrodes, connecting wires and RCPT machine.

Proposed Methodology
The laboratory work is carried out in to two phases. Basic tests were performed on materials in first phase. Specimens were casted in second phase to assess the performance and strength of concrete. The concrete is prepared by reused coarse aggregate and reused fine aggregate with various percentages i.e 10%, 15%, 20%, 25%,30% and 35% and 0.5 water cement ratio. Workability test on Green concrete was done. C.S, S.T.S tests on Hardened concrete were done after 3, 7 and 28 days of curing. Durability of concrete is assessed by using Rapid Chloride test.

Outcomes Expected
It is estimated that the recycled aggregates beyond the limits will decreases the workability and strength of concrete. Shape and size of aggregate will affect the strength of the concrete greatly. Further it is estimated that the voids in the concrete will reduce due to reused fine aggregate and increases the strength. Use of recycled aggregate makes concrete economical.