Pervious Concrete Will Help Avoid Flood Damage

Pervious Concrete Will Help Avoid Flood Damage

16th September 2015

Staying with our series on concrete, today we’re going to take a look at Pervious Concrete which is also known as porous concrete, permeable concrete, no fines concrete and porous pavement.  As its names suggest, pervious concrete is a type of concrete with a high porosity and is used for concrete flatwork that allows water (both rainwater and other types of water) to pass directly through it which reduces runoff and allows the groundwater to recharge.

Many parts of the UK have suffered severe flooding in recent years – we’ve all seen the news reports showing homes and businesses underwater while residents are evacuated to areas that have not been hit by the flooding.  Flooding has become a major problem in our cities, towns, villages and the countryside.  Urban flooding in particular is a real problem that needs to be dealt with and managing flood risks is vital if we want to prevent future news reports depicting these horrendous floods that impact directly on so many people’s day to day life.

One of the factors that has contributed to an increase in flooding is that so many areas (especially in towns and cities) have been concreted over in recent years.  Driveways, patios, pavements, etc. – all of these surfaces prevent rainwater from sinking into the ground where it belongs.  Pervious concrete is becoming part of the solution here – it allows the rainwater to seep right through it, rather than running off into drainage systems that just can’t cope with the sheer volume of water following heavy rainfall.

Pervious concrete consists of cement, coarse aggregate and water with little or no fine aggregates in the mix.  Adding a small amount of sand will increase the strength of the mix which has a water to cement ratio of 0.28 to 0.40 with a void content of 15 – 25%.  The correct quantity of water in the concrete is critical as too little water may cause surface failure. 

To prevent a reduction in permeability, pervious concrete needs regular cleaning and maintenance – this involves wetting the surface and then vacuuming off the residue. 

There have been some concerns about pervious concrete’s ability to resist the freeze-thaw cycle in cold weather.  The addition of a small amount of fine aggregate to the mix increases the durability of pervious concrete while entrained air can help to protect the paste as in normal concrete.  During freezing weather, it’s vital to avoid saturation in order to preserve the longevity of pervious concrete.

While the use of pervious concrete may seem a modern development, it was first used in the 1800s in Europe as pavement surface and load bearing walls – this was in order to save costs by using a smaller amount of cement.  Pervious concrete was used in England for building two storey homes in the 1920s and really came into its own during the rebuilding of many towns and cities in Europe following the Second World War when cement was scarce.  In the future, it looks as if the use of pervious concrete is going to play a significant part in the sustainable infrastructure landscape as use of this material increases.