Multi-storey car parks

Water expands when it freezes, and while the deterioration of concrete is often due to spalling of reinforcement through corrosion, general damage to the surface can often occur on the top deck of a car park or in the ground or access floor and first two ramps as a result of prolonged saturation. Tyre abrasion and the freezing and thawing of the water in the surface pores gradually roughens the surface, making it friable and more susceptible to further water ingress. In extreme conditions, potholing of the concrete can occur. Frost damage can be associated with ponding due to deflections in the slab or poor drainage arising from badly located or blocked outlets.

The effects of freeze-thaw action can result in:

• scaling in the surface;
• formation of conical 'pop-outs' (this occurs when bleed water has accumulated under a layer of flaky aggregate); and
• cracking or spalling of lumps of concrete.

The phase change from water to ice is accompanied by a volumetric expansion of around 1.09%, which generates a bursting stress in the concrete.

Surface deterioration due to frost damage in an area that is regularly saturated

Heavily tamped concrete surfaces create conditions where water is more likely to be held in the surface: while frictional resistance is good, deterioration may eventually become more pronounced. Smooth, power-floated floors perform better in this respect, although they do give rise to tyre squeal.

It might seem that the UK climate is unlikely to create the same risk of freeze-thaw damage as might be experienced in North America or Siberia, for example. However, the reverse is probably true, since in cold environments the low temperatures are maintained for far longer while in the UK or northern Europe, the frequency of freezing and thawing is greater - especially where de-icing salts are used on a regular basis.

User damage

While the effects of user damage will generally be localised, they can be severe. For example, oil spills or drips from vehicles can disrupt and soften asphalt surfaces and lead to their degradation, while gypsum-based oil absorbent materials used for cleaning or mopping up after oil spills have been known to initiate sulphate attack in concrete.

Car washing activities can lead to increased risk of saturation of a concrete deck. Also concentrations of salt and other contaminants washed off vehicles are greater in localised areas. Concentrations of chlorides can give rise to serious corrosion problems.