PRESENTATIONRECYCLED AGGREGATE CONCRETE

BY -- Garima RanaBRANCH -- Civil engineeringYear -- 4th year(8th sem)

CONTENTS INTRODUCTIONWHAT IS RECYCLE AGGREGATE CONCRETE?CHARACTERISTICS OF RECYCLE AGGREGATE CONCRETECLASSIFICATION OF RECYCLE AGGREGATE CONCRETEPROCESS OF RECYCLE AGGREGATE CONCRETEHOW TO PRODUCED RECYCLE AGGREGATE CONCRETEUSE OF RECYCLE AGGREGATE CONCRETEAPPLICATION OF RECYCLE AGGREGATE CONCRETE BENEFIT OF RECYCLE AGGREGATE CONCRETE CONCLUSION

INTRODUCTIONTo achieve sustainable issue in construction area, researchers and companies focus on using waste concrete as a new construction material. It is called recycled aggregate which can be produced by concrete crusher.RAC or Recycled Aggregate Concrete is one of the most important use of waste concrete and is being used throughout the world .It is manufactured by using previously prepared concrete as aggregate with fresh cement matrix. It is sustainable and environment friendly as it recycles the concrete which would have been discarded as waste and had to be dumped off.It reduces the construction cost and when used properly gives similar performance as virgin aggregate concrete.

It has lower density , elastic modulus, strength and a higher water absorption capacity.recycled aggregate has a proportional mortar which attached to aggregate, it gives a higher porosity and a lower strength to RAC than the normal concrete.In addition, since recycled aggregates require a more amount of water than natural aggregate, shrinkage issue could be a problematic to use RAC in practically.

What Is Recycle aggregate concrete

The strength of RAC greatly depends on the micro structural interfaces present in it.There are two interfaces in RAC: Old interfacial Transition Zone(Old ITZ):It is the zone formed between natural aggregate and old cement matrix.New Interfacial Transition Zone(New ITZ):It is the zone formed between Recycled Coarse Aggregate(RCA) and new cement matrix. The study of interfaces is important as they are a prime source of internal micro cracks which greatly affect the strength and durability of concrete.

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NORMAL MIXING APPROACH(NMA)It is traditional mixing approach in which all the ingredients are mixed all together.It has been used for a long time and is effective for the production of virgin aggregate concrete.

TWO STAGE MIXING APPROACH(TSMA)In this method, the RCA is firstly mixed with cement paste, which is followed by adding sand to the mixture, thus making a two stage mixing. The two-stage mixing can help to form a layer of cement slurry on the surface of RCA to fill up the initial damage such as micro-cracks and voids, leading to an improved interfacial zone at the pre-mix stageSOME TERMS AND DEFENITIONS

Characteristics of recycle aggregate concreteRecycle aggregate concrete has a Crushed stone and clean waste concrete of at least 95% by weight of concrete with typical total contamination lower than 1% of the bulk mass The characteristic of recycled aggregates could be different by its parent concrete because the parent concrete was designed for its purposes such as permeable, durable and high strength concrete

Less Specific gravity.High Water absorption.Less Bulk density.Relatively less Compressive strength.Less Modulus of elasticity of 15% from natural aggregate.Flexural strength (0.95 7.2MPa).Splitting tensile strength (0.3 3.1MPa).

PROPERTIES OF RECYCLED CONCRETE

Classification & properties of recycle aggregate concreteMaterial composition is the basis for classification of recycled concrete aggregate in two main types- 1) Crushed concrete 2) Mixed materialEach of these types is divided in a class for bound and a class for unbound use

Crushing ageBulk specific gravity Bulk densityAbsorption(%)Crushing value(%)1 daysCoarseMediumFine 2.59

2.352.231433

122013423.2

9.711.225.4

n/a

n/a3 daysCoarseMediumFine2.60

2.382.251433

123413423.4

8.111.425.3

n/a

n/a28 daysCoarseMediumFine2.55

2.32

2.231433

127813212.3

8.0

12.724.3

n/a

n/a

crushed concrete- This materials generally resulted in increased water demand and decreased workability.Mixed concrete- mixed concrete remain plastic for a short time. This properties are important because they affect the quality and in place cost of the hardened concrete

Process of recycle aggregate concreteProcess of recycle aggregate concrete- crushing pre-sizing sorting screening contaminant elimination

How to produce recycle aggregate concreteCrushing and screening systems start with primary jaws, cones and/or large impactor taking rubble from 30 inches to 4 feet.

A secondary cone or impactor may or may not need to be run, and then primary and secondary screens may or may not be used, depending upon the project, the equipment used and the final product desired.

A scalping screen will remove dirt and foreign particles. A fine harp deck screen will remove fine material from coarse aggregate.

Further cleaning is necessary to ensure the recycled concrete product is free of dirt, clay, wood, plastic and organic materials.

This is done by water floatation, hand picking, air separators, and electromagnetic separators.

Uses of recycle aggregate concrete

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Smaller pieces of concrete are used as gravel for new construction projects. Sub-base gravel is laid down as the lowest layer in a road, with fresh concrete or asphalt poured over it.The US Federal Highway Administration uses this techniques to build new highways from the materials of old highways.Crushed recycled concrete can also be used as the dry aggregate for brand new concrete if it is free of contaminants. Also, concrete pavements can be broken in place and used as a base layer for an asphalt pavement through a process called Rubblization. Larger pieces of crushed concrete can be used as riprap revetments, which are "a very effective and popular method of controlling streambank erosion."

For recycled concrete to be used in greater quantities in a country like India, there are certain aspects that need to be taken care of initially. The setting up of a proper institutional mechanism for taking care of all the steps, such as collection of the construction and demolition waste, transportation, and disposal is of key importance. Outsourcing of such functions to private enterprise is an idea that the concerned authorities could give a though to in this day and age of open economies.

Challenges in the Indian Context

Set up of the necessary processing infrastructure. Necessary infrastructure should also be available for testing the quality of recycled aggregates. Project developers need to be educated on on-site waste management plans. Concerned authorities need to plan an awareness campaign, using the electronic and online media to promote the virtues of recycled aggregates. Removing misconceptions about recycled aggregates as being of inferior quality among the public.

STEPS TO BE TAKEN

Application of recycle aggregate

Scope of applicationCLASS-- HNo limitation are put on the type segment for concrete & structures with a nominal strength of45 mpa or less.CLASS MMember not subjected to drying or freezing and thawing action, such as piles ,under ground beam and concrete fill in steel tubes.

CLASS-- lBackfill concrete, building concrete, and leveling concrete

There are a variety of benefits in recycling concrete rather than dumping it or burying it in a landfill.Keeping concrete debris out of landfills saves landfill space.Using recycled material as gravel reduces the need for gravel miningUsing recycled concrete as the base material for roadways reduces the pollution involved in trucking material. Crushing at the construction site using crushers reduces construction costs and the pollution generated when compared with transporting material from a quarry.

Benefit of recycle aggregate concrete

Decrease in strength & modulus.Greater moisture shrinkage potential.Higher absorption capacity range from 3% - 9%.Reduced workability due to higher absorption capacity.Lower bulk specific gravity.

Demerits

Initial moisture states of RCA is one of the most important variables that impact strength and shrinkage. When oven-dried RCA is used, strength is used to be greatly reduced but free shrinkage as measured in this study was low. The creep to free shrinkage ratio for RAC was similar to that of normal concrete at 7 days under restrained conditions. When greater volume of recycled fine aggregates and fly ash was used, free shrinkage of the specimens was reduced.

Conclusion

The use of recycled aggregate has been found to be better than that of virgin aggregates for certain applications. For example, the physical properties of recycled aggregates make them ideally suited for road base and sub-base. This is because of their physical properties which means less cement is required making them suited for sub-base use. This is in addition to the cost benefits accrued by developers in the process.

Recycled Concrete Aggregate An idea Whose Time Has Come Thanking you