Tuesday, July 21, 2020

Recycled Concrete Aggregate - Properties, Advantages, Disadvantages

Recycled Concrete Aggregate

Recycled Concrete Aggregate

Introduction

Recycled concrete aggregate is also termed as “crushed concrete aggregate”. When we demolish a building (ex- blasting of a structure/old structure), the mix of quarry crushed stone is screened, the dirt is removed and the waste is processed by crushing the large stones into smaller size and the recycled concrete aggregate is extracted from that.

Normally the process is carried out with the help of portable crushers on the site itself. The benefit of the portable crushers is, it eases the relaxation of the transportation cost i.e shifting of material from the site to the recycling plant.

Crushed concrete aggregate cannot be used in all types of concrete grades, on excessive use it may tend to lower down the strength of the concrete.

The specifications of recycled coarse aggregate come under ACI 555R-01, British Standard, and Building Contractors Society of Japan.

Why should we use Recycled concrete aggregate?

1. Depletion Of Natural Resources

(i) As the rapid growth of construction, we see the depletion of the natural resources, the rocks we are cutting for the manufacturing of aggregates, dust, etc are becoming less in number.

(ii) Due to the depletion of the natural resources, the government impose a high tax on the new quarried rocks. So, it is economical to use crushed concrete aggregate.

2. Shortage Of Disposable Area

(i) There is a shortage of areas where we can dispose of the demolished materials due to the growth of construction industries and others already filled with old demolished concrete.

3. Energy Efficient

(i) It takes less energy to screen and filtering of the demolished concrete, compared to mining.

4. Provides Sustainability

The use of natural resources is reduced by using the alternative of recycled concrete aggregate, even the problem of deposing of the demolished material is solved which results in making it eco-friendly, thus contributing to the sustainability of the environment.

5. Reduce Carbon Footprints

Due to the crushing process in mining, a lot of carbon is released, this is reduced by the reuse of crushed concrete aggregate resulting in the reduction of carbon footprints.

Recycled Concrete Aggregate - Material Properties

Recycled concrete aggregate is different compared with the natural aggregate, so the properties of crushed concrete aggregate show different nature compared with the natural aggregate. The properties can vary from performance, workability, strength, etc to conventional concrete.

1. Particle Size

After performing the sieve analysis test, it is observed that the RCA meets the standard requirements which are observed in natural aggregate.

2. Specific Gravity

(i) It is observed in a range between 2.35 - 2.58

(ii) It is less compared to natural aggregate.

3. Water Absorption

(i) The range is between 3.05% to 7.40%

(ii) High water absorption is observed in more fines.

(iii) Higher than natural aggregate is observed.

4. Aggregate

Grading

 

(i) More mix of recycled aggregate will lead to more absorption of water, as fines required more water.

(ii) Since water is inversely related to strength, more water absorption will lead to lower strength of the mix.

5. Modulus of elasticity

(i) The modulus of elasticity of the crushed aggregate is observed 15% less than the natural aggregate.

(ii) It is low because the cement sticks to the surface of the aggregate.

6. Porosity

(i) Higher porosity is observed in crushed concrete aggregate.

7. Freezing & Thawing Resistance

 

(ii) It is observed the same for recycled concrete aggregate and natural aggregate.

8. Compressive Strength

(i) Reduced strength of 2-15% is observed of recycled aggregate compare to natural aggregate.

9. Effect of Admixture present on recycled aggregate

(i) There will be no change in the new concrete mix by the recycled aggregate extracted from the old concrete with admixture.

Note - If the old concrete may contain a high range of water chloride ions, then it will affect the new concrete, leading to corrosion of the steel bars.

10. Crushing value and Impact value.

(i) The recycled concrete aggregate fulfills all the specifications and requirements of BIS.


Area’s Recycled Concrete Aggregate Is Used

(i) When the crushed aggregate is not processed or screened, then they are used in the areas where the bulk filling is required, in a huge quantity.

Example- Berms in canals for the protection of water to raise up, Base of the road, Backfilling of the excavated area’s, etc

(ii) The processed recycled aggregate can be used in areas where not much strength is required.

 Example - Sewer lines, Dowla in canals area, the base of the foundation, plain cement concrete, plumb concrete, etc. 

Advantages - Recycled Concrete Aggregate

Cost-efficient

Environment friendly

Sustainable material

No need for extra space for disposal

Disadvantages - Recycled Concrete Aggregate

High use of crushed aggregate can lead to lowering the strength of the concrete.

Should ensure the aggregate to be properly cleaned before use else it will lead to the generation of cracks in the concrete surface.

To achieve the desired strength compared to the natural aggregate, certain admixtures are added.

Proper inspection is required before the use.

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