**1. Introduction**

In the last decades, due to the modern lifestyle, the progresses in industry and technology had led to an important increase in the amount and type of wastes. The problem of waste accu‐ mulation every year is all over the world. These industrial and agricultural wastes are byproducts, slag, rice husk ash, bagasse, fly ash, cement dust, brick dust, sludge, glass, tires, etc. The wastes represent a major problem for the environment because the air pollution (the dust and very fine particles which spread in the atmosphere) and leaching toxic chemicals (arsenic, beryllium, boron, cadmium, cobalt, lead, manganese, mercury, molybdenum, selenium, strontium, thallium, hydrocarbon compounds, etc.) when are dumped in landfills, quarries, rivers or oceans. The capitalization of waste is difficult because of their variety, as well as their unknown properties over time.

Lately, the environmental sustainability became an important problem from the point of view of natural resources and that of wastes. The construction and the building materials sectors are involved in both processes: building industry is the largest user of natural materials and in addition a large amount of wastes results from the demolition of constructions.

The building material industry is a domain of interest for using the wastes and researchers have tried to produce new construction materials incorporating wastes. The new generation of building materials is developing on other theories in concordance with the sustainability of environment.

Concrete is obtained from natural aggregates, cement and water, compounds which make it a cheap material and easy to produce anywhere. Usually, ordinary concrete contains about 12% cement, 8% water and 80% aggregates by mass. Aggregates and water are from natural resources, only cement must be produced in fabrics, processes which are polluted the envi‐ ronment (for producing 1 m3 of concrete a quantity of 480 kg of CO2 is liberated in the

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atmosphere). For reducing the aggregate and cement consumption, the replacing materials obtained from wastes were studied.

Because the cement industry is responsible for 5-7% of worldwide emission of CO2, (which means 1.6 billion tons of carbon dioxide into the atmosphere), in preparing concrete, the cement dosage can be reduced by using mineral additions, strategy that also can contribute to environment protection by preserving the energy and consume the huge quantities of wastes.

Near cement concrete other building materials are obtained by using wastes, such as: high strength concrete, which has in the mix different additions (silica fume, fly ash, etc.), asphalt concrete, bricks, pavements, roof tiles, prefabricated units, claddings, etc.

Some building materials are totally obtained from wastes, such as "green" materials. The new concept of green buildings offers more energy-and resource efficiency. This concept means the greening of building industry by using only green materials. The technologies of obtaining green materials are available, but their use in construction industry is limited.

The building material and construction industry is one of the principal users of wastes in the processes for obtaining materials or products, for constructing bridges or highways, in soil stabilization, in hydraulic construction, etc. From environmental considerations an extensive waste utilization in construction is recommended, although particular wastes may be too risky to use.
