Author: Jennifer Couperthwaite – Waste Engineer at GCX ZeroWaste
A circular economy requires the re-examining of processes, raw material and the way “waste” materials are viewed in order to conserve natural resources and reduce environmental impact. One such overlooked natural resource is sand and stone for use as a building material which is being rapidly depleted worldwide. A need for alternatives has prompted initiatives to use inert solid waste in the construction industry to replace conventional material. Despite being in its infancy, the waste-to-building-material industry is a potential method. Alleviating pressure on the sand and stone industry and the environment.
Sand and stone, termed aggregate by the industrial sector, accounts for the largest volume of solid material mined globally. Aggregates have a wide variety of applications. This includes the construction of buildings and roads, land reclamation, and by foundries in the formation of moulds. Sand is used as an abrasive in sandblasting and quartz containing silica is used in the construction of glass, solar panels and electronics. Sand and gravel are typically generated over time through the disintegration of larger rocks by ice, water and wind. According to the United Nations Environmental Programme, demand for aggregates has exceeded the rate at which they are being replenished.
Aggregate for construction is mined predominantly from riverbanks and quarries. A dramatic increase in demand has resulted in marine and beach sand mining being more common. Despite plenty of desert sands, different erosion results in the sand being too rounded and fine to hold well as a construction material. Many countries have limited access to appropriate building sand and import it from other countries. Dubai, for example, has exhausted its own marine sand supplies and imports all required aggregate despite being a desert city.
The transport of the material over vast distances has significant costs and associated carbon emissions. The mining itself is also energy intensive and causes the destruction of natural habitat, loss of biodiversity, and pollution of rivers and groundwater.
Immense volumes of waste created daily by households and industries alike. This represents another challenge that countries all over the world are facing. Some industries have already drawn the link between waste and building material as a potential solution. Most waste, especially household waste, is solid, durable, inert, abundant and cheap. This makes it appropriate for building material in many ways. Contributing to a circular economy.
In 2011, South Africa generated approximately 108 million tons of waste according to the National Waste Information Baseline. Landfill space in SA is becoming limited. To encourage waste diversion from landfill and reach set diversion targets, the cost of disposal to landfill has increased.
We also generated 58 million tons of general waste or municipal solid waste (MSW) in 2011. This consists of organic waste, non-recyclables and recyclables which are too contaminated and to be recovered. This fraction is the most suitable for use as building material.
The recovery of recyclables in SA is estimated by GreenCape at only 10% of the total waste produced. Furthermore, organic waste is still widely landfilled. Although removal of recyclable and organic waste is preferable. Beneficiation and recycling methods already exist for these waste types. They too can be converted into building material using some technologies.
How can the Circular Economy approach help?
Waste streams differ in make up between producers and can be pre-processed to be suitable for the chosen technology type. One technique is to shred the waste, mix it with the appropriate binders and compact it into bricks. Some technologies melt plastics together to form bricks. Some bricks are moulded in such a way that they stack and lock together easily to avoid the use of mortar.
The use of waste materials has several benefits over and above diverting it from landfill. Waste is universally produced and if it could be processed into building materials and used for construction in the same city in which it was generated, the financial and environmental cost of transport could be reduced.
In some cases, such as the use of non-recyclable plastics, the resultant building material is a better insulator. They are also lighter than conventional building material, making them easier to handle even preferable over their regular counterparts.
In SA, construction waste or builders rubble is landfilled. A circular economy approach would crush the builder’s rubble. This can then be used in foundations and fill base layers in roads and parking lots in place of aggregate. GreenCape estimated that in Cape Town alone, 92 000m3 of crushable builder’s rubble was produced per month in 2015.
The waste-to-building-material industry stands to do more than ease pressure on landfill space and natural resources. It is particularly attractive in developing countries such as South Africa. A large part of the population live in informal settlements and new developments are re-occurring. A waste-to-building-material industry could stimulate hundreds of small businesses and generate thousands of jobs. It is a solution which enables SA to embed circular economy into our approach to developments in the future.