Large quantities of waste materials and by-products are generated from manufacturing
processes, service industries and municipal solid wastes, etc. As a result, solid waste
management has become one of the major environmental concerns in the world. With the
increasing awareness about the environment, scarcity of land-fill space and due to its ever
increasing cost, waste materials and by-products utilization has become an attractive alternative
to disposal. High consumption of natural sources, high amount production of industrial wastes
and environmental pollution require obtaining new solutions for a sustainable development.
Utilization of waste materials and by-products is a partial solution to environmental and
ecological problems. Use of these materials not only helps in getting them utilized in cement,
concrete, and other construction materials, it helps in reducing the cost of cement and concrete
manufacturing, but also has numerous indirect benefits such as reduction in land-fill cost, saving
in energy, and protecting the environment form possible pollution effects. Further, their
utilization may improve the microstructure, mechanical and durability properties of mortar and
concrete, which are difficult to achieve by the use of only ordinary Portland cement.
Latest researches are on the use of fly ash, clean coal ash, coal bottom ash, foundry sand, waste
glass and RHA in cement-based materials.
involves processing used materials into new products to prevent waste of
potentially useful materials, reduce the consumption of fresh raw materials, reduce
usage, reduce air pollution (from
) and water pollution (from
reducing the need for "conventional" waste disposal, and lower
compared to virgin production.
Recycling is a key component of modern waste reduction
and is the third component of the "
Recyclable materials include many kinds of
. Although similar in effect, the
or other reuse of
– such as
– is not typically considered recycling.
Materials to be
recycled are either brought to a collection center or picked up from the curbside, then
sorted, cleaned, and reprocessed into new materials bound for manufacturing.
In a strict sense, recycling of a material would produce a fresh supply of the same material,
for example used office
to more office paper, or used
polystyrene. However, this is often difficult or too expensive (compared with producing the
same product from raw materials or other sources), so "recycling" of many products or
materials involves their
in producing different materials (e.g.,