In Pakistan, flooded lanes, roads and underpasses are a common sight during the monsoon season. In addition to causing massive traffic bottlenecks, vehicle breakdowns and accidents, puddles of water in and around residential and commercial areas make commuting in public or private transport difficult and dangerous, disrupting people’s routines.
An effective method to address this problem is to use porous concrete that absorbs rainwater completely, leaving the roads (and any other surface on which it is used), dry.
Developed in the UK six years ago, porous concrete is now widely used globally to build roads, parking lots, walking and biking pathways and driveways; it can absorb nearly one thousand liters of water per square meter in a minute.
Conventional concrete is made from finely crushed stone held together by a binder. Contrary to this, porous concrete comprises two layers; the upper layer uses a mix of crushed stones that slowly release water into the ground below and the lower layer contains large rocks that make it porous, allowing the absorption of large amounts of water.
Porous concrete works well in all climates except regions where there is extreme snow or on roads that attract heavy traffic.
The life of porous concrete is 20 to 30 years and although it is expensive (Rs 1,000-1,250 per square foot) compared to conventional concrete (Rs 85-120 per square foot), it is a worthwhile investment in countries prone to flooding and/or heavy monsoon rains.
Depending on the specific set of needs, three types of porous concrete are available in the market:
- Full infiltration permits all water to pass through and be absorbed in the soil underneath. This is suitable for areas where the collection and recycling of rainwater is not a priority.
- Partial infiltration uses a semi-permeable barrier beneath the top surface that acts as a drainage system and directs water into nearby sewers or waterways.
- Full shrinking allows storage of all the water under the road through specially designed tunnels that direct the water to a collection unit. This option is useful in areas where water shortage can be eliminated by collecting and recycling rainwater.
By Uzma Khateeb Nawaz