The construction sector has traditionally been a source of employment in African regions. However, due to policy changes, cut backs in public investments as well as a fall in the number of employments in the private sector have been observed in many countries . Furthermore a shift from registered companies to informal contractors could be noticed [1-3]. Many contractors offer services they do not provide permanently or for which the required equipment has to be borrowed. A study that was published in 2000 about the situation in Tanzania pointed out that only ca. 15% of the enterprises that offer concrete works own a concrete mixer . The building practice with concrete varies widely over the African continent. Whereas the level of technology and the infrastructure for cement and concrete in South Africa is elaborate, in East Africa and particularly those that were heavily suffering from civil war during the nineties of the last century, the availability of cement and concrete is poor and these materials are far from being everyday building practice. Most of the population relies on indigenous forms of construction requiring wood obtained from felling of forest trees and ultimately contributing to de-forestation. Informal settlements in South-Africa and Kenya are literal evidence where originally green natural vegetation has been turned into artificial desert-like landscapes.
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