The term “urban heat island” describes built up areas that are hotter than nearby rural areas due to human behaviours and activities. Heat islands can affect communities by increasing summertime peak energy demand, air conditioning costs, air pollution and greenhouse gas emissions, heat-related illness and mortality, and water quality.

Urban Heat Island Effect

Many techniques are currently being employed to combat the heat island effect including:

• Increase shade around your home by planting trees and other vegetation or shade cloths.
• Installing green/cool roofs: These will either absorb heat through vegetation or reflect sunlight.
• Using energy-efficient appliances and equipment.

Climatologists have been studying heat islands for decades but only recently has attention turned from vegetation and roofing strategies to cool pavements. 

“Interest in cool pavements has been growing, and an emerging body of research and pilot projects are helping scientists, engineers, and practitioners to better understand the interactions between pavements and the urban climate.”  ​- Environmental Protection Agency, Reducing Urban Heat Islands: Compendium of Strategies, 2014.

Research from the Lawrence Berkeley National Laboratory (USA) recently showed interesting results. Berkeley researchers created a lifecycle tool to assess energy, greenhouse gas emissions, air temperature and air quality consequences of urban pavement choice over a 50-year lifecycle. This lifecycle also took other factors into consideration such as manufacture, installation and disposal/recycling, including the use of slag.

The use of slag in pavements and roads is seen to reduce the heat island effect due to its lighter colour, which can increase the reflectivity of the finished pavement. A 2007 study measured a solar reflectance of almost 60% for cement with slag, versus about 35% for a conventional concrete mix.

In contrast, fly ash tended to darken con­crete unless counterbalanced by materials such as slag. However, substituting FA for a portion of the Portland cement reduces greenhouse gases and other emissions associated with producing Portland cement. The results found that extra energy and emissions that went into cool pavement materials usually exceeded the energy and emissions savings resulting from reduced cooling needs of surrounding buildings.

“Over the life cycle of the pavement, the pavement material matters substantially more than the pavement reflectance,” Berkeley Lab’s Ronnen Levinson said.

Dr Levinson also said that “The development of lower energy and lower carbon cool pavement solutions is still necessary.”

To read more about the research conducted by US’s Lawrence Berkeley National Laboratory click here. http://www.sciencedirect.com/science/article/pii/S0378778817309908