The modern concrete used in everything from roads to buildings and bridges can break down in as little as 50 years, but its longevity is highly dependent on the environment and the materials used in its construction. Building codes and policies often require buildings to survive several decades, but deterioration can begin in as little as 10 years. In terms of carbon mass, our built environment is outstripping the natural one. The degradation of concrete can have several causes, such as fire, aggregate expansion, the effects of seawater, bacterial corrosion, calcium leaching, physical damage and chemical damage.
A good rule of thumb is that concrete takes approximately 30 days to dry for every inch of concrete poured. Steel formwork pinches the top surface of a concrete slab due to the weight of the next slab to be constructed. The setting time of concrete is usually 24 to 48 hours. Alternative materials for reinforcement, such as stainless steel, aluminium bronze and fibre-polymer composites, are not yet in widespread use.
DEF causes concrete to expand due to the formation of ettringite in the paste and can severely damage concrete structures. A good concrete mix will provide a concrete that can withstand severe weather conditions and changes without any sign of deterioration. Environmental scientist Vaclav Smil estimates that replacing mud floors with concrete in the world's poorest housing could reduce parasitic diseases by almost 80 per cent. However, none of these developments can solve the inherent problem that putting steel into concrete ruins its potentially great durability.
For example, a concrete floor that is inside a building will last decades longer than a concrete pavement that is outside and exposed to the elements. The main effect of chloride ions in reinforced concrete is to cause pitting corrosion of the steel reinforcing bars (rebar). Concrete rehabilitation is becoming increasingly important, and everything that is built with concrete must be renovated in the next few years. Unfortunately, the mass production of housing projects today has resulted in countless buildings being constructed with substandard materials.
While repair may be justified to preserve iconic 20th century buildings, it is questionable whether it is affordable or desirable for the vast majority of structures.