One of the most critical problems we are facing today is acid rain.
One of the main causes is the burning of fossil fuels, and as a
result, sulfuric acid and carbon dioxide are added to the
atmosphere. These gases have detrimental effects on building
materials. Thus, there are two problems: (1) to decrease the gas
emission, and (2) to produce construction materials more durable to
the aggressive pollutant gases and acid rain.
The environmental aspects involved in the production and use of
cement, concrete and other building materials are of growing
importance. CO2 emissions are 0.8-1.3 ton/ton of cement production
in dry process. SO2 emission is also very high, but is dependent
upon the type of fuel used. Energy consumption is also very high at
100-150 KWT/ton of cement produced. It is costly to erect new
cement plants. Substitution of waste materials will conserve
dwindling resources, and will avoid the environmental and
ecological damages caused by quarrying and exploitation of the raw
materials for making cement. To some extent, it will help to solve
the problem otherwise en-countered in disposing of the wastes.
Partial replacement of clinker or portland cement by slag, fly ash,
silica fume and natural rock minerals illustrates these aspects.
Partial replacement by natural materials that require little or no
processing, such as pozzolans, calcined clays, etc., saves energy
and decreases emission of gases. The output of waste materials
suitable as cement replacement (slags, fly ashes, silica fumes,
rice husk ash, etc.) is more than double that of cement
production.
These waste materials can partly be used, or processed, to
produce materials suitable as aggregates or fillersin concrete.
These can also be used as clinker raw materials, or processed into
cementing systems. New grinding and mixing technology will make the
use of these secondary materials simpler. Developments in chemical
admixtures: superplasticizers, air entraining agents, etc., help in
controlling production techniques and, in achieving the desired
properties in concrete.
Use of waste products is not only a partial solution to
environmental and ecological problems, it significantly improves
the microstructure, and consequently the durability properties of
concrete, which are difficult to achieve by the use of pure
portland cement. The aim is not only to make the cements and
concrete less expensive, but to provide a blend of tailored
properties of waste materials and portland cements suitable for
specified purpose. This requires a better understanding of
chemistry, and materials science.
There is an increasing demand for better understanding of
material properties, as well as better control of the
microstructure developing in the construction material, to increase
durability. The combination of different binders and modifiers to
produce cheaper and more durable building materials will solve to
some extent the ecological and environmental problems.
General
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