Recycled Concrete Aggregates: Its Properties & Uses

In recent years, conscience of humanity is strongly awakened to the need to protect environment and preserve it. As the most intelligent being on the earth, man has constantly manipulated nature by using his inventive genius and disrupting the ecological balance. Thus, air, water and soil are all polluted and, this is posing a threat to the substance of humanity. This goes without saying that, protection of environment is of major concern today. Innumerous human activities are carried out haphazardly under the name of development. Such activities, at times, consume a lot of natural energy; whereas some leads to excess use of natural raw materials, thereby increasing pollution and exploitation wastage of materials on the earth. Understanding need of the hour, when we talk in reference to the construction industry, there are various structures such as homes, schools, offices, hospitals, roads, dams and runways, canals, and so on, which not only consume natural materials but produce a lot of waste as byproduct.
As per the Greece researcher ‘Oikonomou N.D. (2015)’ (Published in, Recycled concrete aggregates), all over the globe the construction industry takes 50% of raw materials from nature, consumes 40% of total energy and produces 50% of total waste.

Recycled Concrete Aggregates Image

Bad Impact of Construction Waste on Environment

If the construction demolition wastes are not handled properly, it may create a bad impact on the environment leading to water Pollution, air pollution and noise pollution. Sources of water pollution on building sites include diesel and oil; paint, solvents, and other harmful chemicals; and construction debris and dirt which either penetrate into land or clogs the flow of natural water bodies ultimately resulting into soil pollution and in worst cases, contamination of water sources. All construction sites generate high levels of dust (typically from concrete, cement, wood, stone, silica) and’ this can carry for large distances over a long period of time increasing the health risks of inhalation. Thus, apart from land pollution, it as well as create land pollution, creates aesthetical discomfort, produce dust leading to major health concern.

These concerns have lead the attention towards sustainable development. Hence, the use of recycled concrete aggregates from the construction demolition waste looks like a potential application in the construction of buildings or house as a sustainable alternative to natural aggregates. Use of recycled concrete aggregates reduces the amount of virgin aggregates to be created, hence less exploitation of natural resources. It also helps reducing the space and energy required for the landfill disposal as well.

What is Recycled Concrete Aggregate?

Crushed Concrete Aggregates

Recycled concrete aggregates are manufactured from waste concrete or demolished concrete. In simple words, it’s the byproduct of the concrete building demolition or concrete demolition. Recycled concrete aggregate as such, holds original aggregate with hydrated cement paste. Hence first, that demolished concrete is cleaned from dirt and other loose particles. After that, it is broken into smaller pieces to produce aggregate known as recycled concrete aggregate. Recycled concrete aggregates are available in size of 20mm to 50mm.
Recycled concrete aggregate is also referred to as crushed concrete aggregate and its abbreviated form is RCA. The quality of recycled crushed concrete mainly depends on two things:
01. The characteristic of the original aggregate
02. The condition of the demolished concrete

Use of Recycled Concrete Aggregates

Recycled concrete as aggregates are used for the normal grade concrete as well as high strength or structural grade concrete.
Its applications are mentioned below:
01. Various types of general bulk fill and base or fill for drainage structures.
02. In the construction of bank protection such as embankment
03. In the road construction like pavements, shoulders, median barriers, sidewalks, freeways etc.
04. In the airport runways
05. In the bridge foundations and decks
06. For the lean-concrete
07. For the bituminous concrete
08. In the oil & gas civil construction projects
09. In the construction of curbs, gutters, noise barriers
10. For the bases of soil-cement pavement.

Classification of Recycled Concrete Aggregates

According to the ‘BRE Digest 433’ (1998) (Building Research Establishment-UK), crushed concrete aggregates are classified into three types:
01. Class RCA (I):
In this class of RCA, the origin of RCA is brickwork. It contains 0-100 % of brick content or block masonry by its weight. It’s the lowest quality material which contains high amount of impurities and has low strength.
02. Class RCA (II):
In this class of RCA, the origin of RCA is crushed concrete. It contains 0- 90 % of concrete and significant amount of natural aggregate, and 0-10% of brick content. It’s a relatively high-quality material which has high strength, toughness and low amount of impurities.
03. Class RCA (III):
In this class of RCA, the origin of RCA is crushed concrete as well as brick masonry. It contains 0-50% of crushed concrete and natural aggregate and, other 0-50% of brick content. It’s a mixed material which has almost the same level of impurities as class (I), but the potential usage of this aggregate is extensive compared to class (I).

Properties of Recycled Concrete Aggregates

  • Density:

Recycled concrete as aggregate contains residual adhered mortar on the particle of aggregate. Due to which the density of RCA is normally lower than the density of natural aggregate. The main reason for the lower density is that the adhered mortar is lighter in weight compared to the same volume of natural aggregate, which decreases the density. The density of RCA is not constant for all the crushed concrete aggregate. It depends upon the specific aggregate.

  • Porosity and Water Absorption:

The crushed concrete aggregate has greater water absorption capacity due to high porosity; which is because of adhered mortar. On the other side, the source of natural aggregate is rock, which tends to have low porosity and low water absorption.

  • Specific Gravity:

As described above, the origin of the natural aggregate is the hard rock with old adhered mortar. So, the specific gravity of the crushed concrete aggregates is lower as compared to the natural aggregate.

  • Shape and Gradation:

The shape and gradation of recycled concrete aggregates are dependent on the production method and type of crusher used for the manufacturing of RCA. The crushed concrete aggregates have a rounded and spherical shape and can be grainy in texture.
For further information regarding the shape of aggregates, please refer our article – shape wise classification of aggregates.

  • Strength:

Recycled concrete as aggregates are relatively weaker in strength as compared to natural aggregates. Crushing and abrasion value of RCA is also lower than the natural aggregates.
You can check the various strength of aggregates by performing the different tests of aggregate such as crushing value test, Los Angeles abrasion test, impact test etc. and understand the technical aspect of it in a better way.
On the final note, recycled concrete aggregates have long been used in India, UK, Japan and other countries. However, the developing countries like India, Bangladesh, Nepal, Nigeria etc. needs to take some serious urgent measures to unleash the scope of RAC. And if done so, concrete recycling will become one of the most important elements for construction sustainability. There is larger quality control required due to the lack of standard specifications, although RCA can be successfully used for various purposes in the new concrete by comparing the standard specifications for natural aggregate, and hence can be used for various purposes i.e. lower grade concrete application and high-quality concretes as high-strength, high-performance, and self-consolidating concrete by appropriate materials selection and mix design.

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