The white settlers introduced animals for sentiment or for sport; later, the belief developed that New Zealand's native flora and fauna must eventually be replaced by the European. There was thus a vigorous policy of acclimatisation lasting from the 1840s to the first quarter of the present century. Some 53 exotic mammals were introduced (most of them deliberately) and of these 31 are at present living in a free state.
Concrete is a composite material composed of aggregate bonded together with a fluid cement which hardens over time.Most use of the term concrete refers to Portland cement concrete or to concretes made with other hydraulic cements, such as ciment fondu.However, road surfaces are also a type of concrete, asphaltic concrete, where the cement material is bitumen. lower water-to-cement ratio yields a stronger, more durable concrete, whereas more water gives a freer-flowing concrete with a higher slump. Impure water used to make concrete can cause problems when setting or in causing premature failure of the structure.
Commonly rectangular, concrete blocks are manufactured as a solid block of concrete or with hollow chambers. Although concrete blocks are strong and durable, cracks sometimes develop. As a home or structure settles, for example, sideways or shifting force can put pressure on the concrete block, resulting in a crack.Fortunately, do-it-yourselfers can fix the damage.lthough concrete blocks are strong and durable, cracks sometimes develop. As a home or structure settles, for example, sideways or shifting force can put pressure on the concrete block, resulting in a crack. Fortunately, do-it-yourselfers can fix the damage.