08-02-2010, 06:28 AM
CONSTRUCTION WASTE RECYCLING
[attachment=1800]
INTRODUCTION
The promotion of enviornmental management and the mission of sustainable development
have exerted the pressure demanding for the adoption of proper methods to protect the
enviornment across all industries including construction.
Construction by nature is not an eco-friendly activity.
Construction,renovation and demolition activities leads to the formation of waste.
NEED FOR ADOPTION OF PROPER METHODS OF RECYCLING
It reduces the demand up on new resources.
Cuts down the cost and effort of transport and production.
Use waste which would otherwise be lost to landfill sites.
CONSTRUCTION WASTE PROBLEM
WASTE- Material by-product of human and industrial activity that has no residual
value.
Need for Comprehensive construction waste management in every site.
Every personnel,from the management to the operational level should work for the goal
of construction waste management.
AGGREGATE FROM CONSTRUCTION AND DEMOLITION WASTE
Recycled precast elements and cubes after testing (the aggregate could be relatively
clean with only cement paste adhering to it).
Demolished concrete building(aggregate could be contaminated with bricks and tiles,
sand and dust, timber, plastics, cardboard and paper and metals.)
Used as a subtitle for natural coarse aggregates in concrete
FACTORS THAT ASSESS THE QUALITY OF RECYCLED AGGREGATE
Size distribution
It has been generally accepted that recycled aggregates either fine or coarse
can be obtained by primary and secondary crushing and subsequent removal of
impurities.
The best particle distribution can be achieved by primary crushing and then
secondary crushing, but a single crushing process is more effective from the economic
point of view.
Absorption
The water absorption in Recycled Aggregates ranges from ( 3-12% ), this value
is much higher than that of natural aggregates whose absorption is about ( 0.5- 1 %
).
Abrasion resistance
Use of such aggregates as sub base in flexible pavements show promising
results. These recycled aggregates have also been used in generating concrete that is
further used in rigid pavements .
PROPERTIES OF FRESH RECYCLED AGGREGATE CONCRETE
The air content of recycled aggregate concrete is slightly higher ( 4-5 % ) than
concrete with natural aggregate. This increased air content in the recycled concrete
leads to reduction in the density of fresh concrete.
The bulk density of fresh concrete made with natural aggregates is in the range of
2400 kg/m3, where as the concrete made with recycled aggregates is significantly
lighter, 2150 kg/m3.
VIABLE TECHNOLOGY ON CONSTRUCTION WASTE RECYCLING
When considering a recyclable material, three major areas need to be taken in to
account are:
Economy
Compatibility with other materials
Material properties
DIFFERENT WASTES IN A CONSTRUCTION SITE
Brick
Bricks arising from demolition may be contaminated with more mortar, plaster
and are often mixed with other materials such as timber and concrete.In recent years,
bricks are commonly crushed to form filling materials.
Concrete
The most usual way to recycle concrete rubble is categorized as:
a) Bound ( natural aggregate replacement in new concrete )
b) Un bound ( road base, trench etc )
Ferrous Metal
It is by far the most profitable and recyclable material.
In India more than 80% scrap arising is recycled. Scrap steel is almost totally
recycled and allowed repeated recycling. 100% steel can be recycled to avoid wastage
at construction site.
Masonry
Masonry is normally crushed as recycled masonry aggregate.
A special application of recycled masonry aggregate is to use it as thermal
insulating concrete.
Another potential application for recycled masonry aggregate is to use it as
aggregate in traditional clay bricks.
Non Ferrous Metal
The main non ferrous metal collected from construction and demolition sites
are alluminium, copper, lead and zinc .
In India alluminium usage is up to 95000 tonnes with about 70% recycled in 2004.
Copper is recycled up to 119000 tonnes out of a national market of 262000 tonnes.
Paper And Cardboard
Paper and paper board comprise approximately 37% construction and demolition
wastes by volume.It usually attracts recyclers to reprocess them as new paper product
by purification.
Timber
Timber waste from construction and demolition works is produced in large
quantity all over the world.
Whole timber arising from construction and demolition works can be utilized easily
and directly for reused in other construction projects after cleaning, denailing and
sizing.
BARRIERS IN PROMOTING USE OF RECYCLED MATERIALS
Lack of appropriately located recycling facilities.
Absence of appropriate technology.
Lack of awareness
CONCLUSION
In order to reduce the construction waste, during the time of construction
order only the correct amount of raw materials. Proper care should be taken to ensure
the protection of materials being delivered and stored in the site. When a structure
is being demolished, salvage as much of the more valuable fittings and materials as
possible. Any suitable substitute for aggregate should be considered during the
construction. It is the duty of an engineer to revaluvate technical specification for
materials where strength and safety do not have to be compromised to permit the use
of recycled materials. As sorting and recycling facilities become more wide spread
and better developed it will be easier to redirect our waste from landfill.
