WASTE & RECYCLED MATERIAL IN CONCRETE TECHNOLOGY
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World wide consumption of concrete amounts to more than 1000 Kgs/person
The demand is expected to increase in future
Concrete comprises in quantity the largest of man made material
Concrete made with Portland cement ,water admixtures and aggregates comprises in quantity the largest of all man made material
Historically whenever new compounds were produced ,or waste materials accumulated in industries ,they were incorporated as one of ingredients of concrete. Typical examples are fly ash phosphogypsum,blast furnace slag, saw mil waste, rice husk, cotton etc.The wide spread need for conserving resources & environment will be reflected major emphasis on the use of wastes & by products.
Recycling of concrete materials also offers some promise. Attempts are already being made to use municipal refuse & waste oil as partial substitutes for the fuel in the production of cement clinker
NEED OF RECYCLING OF WASTE MATERIALS
Rise in population
Large scale demand for housing
Over stressing the reserves of traditional building materials
Cement material presently not in a position to cope the millions of the country
The enormous amount of waste materials
Recycling becoming imperative & mandatory
ROLE OF WASTE MATERIAL IN CEMENT CLINKER PRODUCTION
Many waste materials contain basic ingredients that are needed for the manufacturing of cement clinker
Fly ash can also be used as a source of raw material
Lime sludge can be used as a substitutes for lime stone
Red mud a waste material from the production of alumina used as a raw material for cement clinker production
Phosphogypsum as a mineralizer for making clinker
PORTLAND CEMENT MANUFACTURED FROM WASTE MATERIALS
FLY ASH CEMENT
BLAST FURNACE SLAG CEMENT
RICE HUSK ASH CEMENT
FLY ASH CEMENT
Fly ash is the ash component of Coal liberated during combustion .
Fly ash can be incorporated into Portland cement in one of the three ways.
Fly ash can be used as a admixture or as replacement of Portland cement.
Fly ash addition to Portland cement results in increased workability.
In fly ash cement development of compressive strength is slow
At longer periods of curing Fly ash concrete develops higher strengths than the normal concrete
INFLUENCE OF FLY ASH ON STRENGTH DEVELOPMENT IN CONCRETE
PERMEABILITY OF FLY ASH CONCRETE
ADVANTAGES OF FLY ASH CONCRETE
Addition of fly ash to concrete minimize or eliminates the expansion due to alkali aggregate reaction
TIME OF SETTING
DURABILITY OF FLY ASH CONCRETE
Sufficiently cured fly ash concrete has dense structure & hence more resistance to deleterious substances.
This reduces the corrosion of reinforcement.
Class F fly ash reduces alkali-silica reactivity because of the dense structure & hence expansion is reduced which increases durability.
Because of the reduced permeability the chloride ingress is reduced.
STRUCTURES USED FLY ASH ASH
BLAST FURNACE SLAG CEMENT
Portland blast furnace slag cement can replace Portland cement where high strength is not required.
It is produced by intergrinding Portland cement clinker & granulated blast furnace slag.
The workability of this cement is as good as Portland cement concrete.
This is resistant to a number of aggressive agents including sulphates of Al,Mg,NH4 etc…
The rate of hardening is slower than the normal Portland cement concrete.
The 90 days strength is ≤ of Portland cement concrete.
More resistant to sea water &other chemical agents than Portland cement.
RICE HUSK ASH CEMENT
In the rice milling operation one ton of rice paddy produces 400 kg of husk. Burning of the husk results in 20% by a weight of ash. Blending this ash with cement produces a suitable blended cement
The rice husk ash cement on hydration produces practically no Ca(OH)2 &hence is superior to Portland.
RECYCLING OF CONCRETE
Except structures which have to be preserved as moments a great number of them have to be demolished sooner or later.
Concrete accounts of nearly 75% by weight of all construction material.
Millions of tons of concrete debris are generated by natural disaster.
Depletion of normal aggregate sources, stricter environmental laws & waste disposal problems make recycling of concrete.
USES OF RECYCLED CONCRETE
Smaller pieces of concrete are used as gravel for new construction projects.
Sub base gravels laid down as the lowest layer in a road.
Recycled concrete can also be used as the dry aggregate for brand new concrete.
Larger pieces can be used for erosion control.
Lead paint contamination.
MINING & QUARRYING WASTES
Large amount of wastes produced in mining & quarrying operations.
Mineral mining wastes are “waste rock” or “mill tailings”.
Manufacturing of bricks ,light weight aggregates & autoclaved concrete blocks.
APPLICATION OF MISCELLANEOUS WASTES
In coal operations about one half of the material is separated & discarded as colliery soil.
This soil is used to fill in road embankments.
It can also be used to produce light weight concrete.
Millions of tons of waste glass are generated annually..
The strength of concrete less than with gravel aggregate.
This is used to make light weight aggregates.
Red mud is a waste product resulting from the extraction of alumina from bauxite ore.
It is sufficiently plastic to be moulded into balls.
Firing at about 1260 to 1310 c produces a strong dense aggregate.
Concrete contains burnt clay has high fire resisting capacity.
Saw dust concrete is used only to a limited extent because of its low strengths.
The addition of sand can improve strength.
Saw dust cement has a good insulation value .
Low thermal conductivity.
Concrete containing large amounts of saw dust is flammable.
ROLE OF WASTE MATERIALS AS AGGREGATES
Use of waste & byproducts as aggregates has greater potential because 75% of concrete is composed of aggregates.
Various aggregates examined includes reclaimed concrete mining & quarrying wastes, colliery soil, waste glass, red mud, burnt clay & saw dust.