Behavior of Cement Concrete Using Recycled Concrete Aggregates

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Introduction

The requirement of concrete aggregate in India is large. Corresponding to the current annual production of cement of 300 million tons, total requirement of coarse and fine aggregate for use in cement concrete, mortar and plasters of about 1500 metric tons per year is a safe estimate. There is difficulty in obtaining natural aggregates within economic distances. Search for alternate sources of aggregates thus assumes importance. One such alternative is recycled concrete aggregate derived from construction and demolition wastes, which allow conservation of natural resources and land.

Aggregate in concrete constructions typically accounts for 75 per cent of the total volume. The majority of concrete constructions till date essentially resort to aggregate materials derived from natural resources conforming to IS : 383. However, due to the need for conserving natural resources and issues relating to sustainability, environmental considerations and economy, increasing the use of recycled and secondary aggregate has been forecasted.

Objectives of the Project

1. To compare the compressive strength of Recycled Coarse Aggregate for Constructional Concrete with the Conventional concrete.
2. To know its applications in the construction industry.
3. To reduce the pressure on naturally available materials by replacing it with recycled aggregate.
4. To compare the physical characteristics of natural aggregate with recycled aggregate.
5. To study the behaviour of fresh and hardened concrete reinforced with recycled coarse aggregate.

Advantages & Disadvantages of Recycled Concrete Aggregates

Advantages

First, discuss the advantages. We have the following advantages of using recycled aggregates.

1. It is cost-saving.
2. It is better for controlling the alkali-silica reaction.
3. To save the environment, recycled aggregates may be used.
4. It saves time.
5. It also has less emission of carbon.
6. Up to 20% replacement of natural aggregate with RCA or RMA without a need for additional testing. For all concrete up to a characteristic strength of 65 mega Pascal as per Indian Standard is permitted.

Disadvantages

There are also some disadvantages, such as-

1. Less quality.
2. Duration of procurement of materials may affect the life cycle of the project.
3. Land, special equipment machineries are required.
4. Very high water absorption.
5. It has higher drying shrinkage.

Properties of Concrete Aggregate

Properties of Recycled Concrete Aggregates

Physical Properties of Fresh Concrete Containing Recycled Concrete Aggregates

Physical Properties of Hardened Concrete Containing Recycled Concrete Aggregates

Quantity of Normal & Recycled Concrete Aggregates Used in the Experiment

We used the following quantities of cement, sand, coarse aggregates and water for slump test.

For Compressive Test With normal aggregates, recycled aggregates and brickbats, we used the following quantities of cement, sand, coarse aggregates and water.

And, For Compressive Test with Partial Replacement of Cement with Fly Ash, we replaced the cement content by 25%, 50% and 75% in three different samples.

Experimental Program

We conducted 3 experiments to know the basic properties of fresh and harden concrete. These experiments are –

1. Specific Gravity & Water Absorption Test of Aggregates.
2. Slump Test of Fresh Concrete.
3. Compressive Test of Concrete as per IS 456: 2000.

To know the details about the experiments, watch the full video.

Result of Experiments

For the Specific Gravity and Water Absorption test of Coarse Aggregate, we got the following results.

We also get the Slump Value of Concrete as 15 mm.

Compressive Strength Using Normal Coarse Aggregates, we have the following results.

When we replaced some normal coarse aggregates, with Recycled Coarse Aggregates, we got the following compressive strength.

And, When we replaced some normal coarse aggregates, with brickbats, we got the following compressive strength.

Now, if we compare the Compressive Strength, we have these values for Different Coarse Aggregates

And here is the graphical representation of the compressive strength, using different course aggregates.

When we replaced the cement content with fly ash, we have the following Compressive Strength for different percentages of Fly Ash.

Concluding Remarks

Recycling and reuse of building wastes have been found to be an appropriate solution to the problems of dumping hundreds of thousands of tons of debris accompanied by a shortage of natural aggregates. The use of recycled aggregates in concrete proves to be a valuable building material in technical, environmental and economic respect.

There are several reliable applications for using recycled coarse aggregate in construction. However, more research and initiation of a pilot project for application of RCA is needed for modifying our design codes, specifications and procedure for use of recycled aggregate concrete.

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