31 October 2012

Concrete waste: discard or recycle?

By Dr Wong Kien Kuok

Concrete, a construction material made from a mixture of cement, aggregate (sand or stone) and water, had been and still is the most widely used building material worldwide. According to Global Cement Report 2011, China dominated the world’s cement consumption of 1851 million tons in 2010. The report also noted that Turkey and Bangladesh were the leading exporter and importer of cement and clinker, and predicted cement consumption to peak to 3859 million tons in 2012.

Proportionally, about 25 billion tons of concrete is produced annually worldwide for development and construction purposes. At the same time, the volume of construction waste and debris from demolished structures has increased correspondingly, making disposal sites for such wastes to be in high demand.

Construction waste and debris need to be disposed of after the completion of a project. They can be sorted into three major categories: masonry rubbles and concrete waste (about 40-45%); timber (about 30-35%); and metal (6%). Masonry and concrete make up the largest component and are hazardous to the environment. As landfill sites are saturated or become scarce, a higher landfill levy will be imposed on additional waste so as to encourage the recycling of such material. The high production of concrete also translates to the depletion of natural aggregate. With these environmental concerns in mind, the feasibility of using recycled construction waste and debris for the making of concrete needs to be examined.

The use of demolished concrete as recycled aggregate is an established technology. It can be crushed and used again as partial replacement for natural aggregate.

In some countries, tax on waste dumping, the importing of sand and stone, and landfill levies has been implemented. This has contributed to the emergence of concrete-related industries which recycle used concrete. Belgium, the UK, the Netherlands, Germany and Switzerland are among some of the major users of recycled aggregate. In the US, it is estimated that 68% of recycled sand and stone is used as road base while the rest is utilized for new concrete mixes, asphalt hot mixes, high-value riprap (a protection embankment to prevent erosion), low-value products like general fill, and others. Australia, Korea, Japan, Germany, Portugal, Hong Kong, the UK and the US, are among some of countries which have set up requirements for recycled aggregate concrete.

In Malaysia, rapid development has increased the consumption of cement, where about 16.5 million tons is consumed annually. The high dependence and demand for concrete has significantly depleted natural aggregate in Malaysia although supply is still regarded to be sufficient. Not surprisingly, awareness of recycling concrete is still generally low in the country and many contractors choose to dispose of the waste illegally, dumping them in isolated areas or into rivers. As such, concrete waste recycling industry has not taken off.

Despite studies proving recycled aggregate as suitable for non-structural and structural use, local engineers remain conservative when it comes to the utilisation of the material. This may be due to the lack of extensive investigation and comprehensive results to demonstrate the robustness and durability of recycled concrete. For the past decade, studies had been carried out by local universities on the use of secondary recycled materials such as rubber, glass, steel slag, mining and quarry waste, by-products from power plant, rice husk, natural fibers, plastic, wood chip and polystyrene as substitutes for sand and stone.

The reuse and recycling of concrete waste or leftover concrete will only become viable if the governing body supports it. Contractors must also self-regulate and exercise transparency in concrete waste disposal. Additionally, researchers must be well funded to carry out extensive research and experiments. Awareness campaigns on reuse and recycling must also be sustained. In fact, the Malaysian Ministry of Energy, Green Technology and Water, had budgeted RM1.5 billion as soft loans for manufacturers and consumers through the Green Technology Financing Scheme in 2011. Building owners certified with the Green Building Index (GBI) are entitled to income tax exemption while home buyers with GBI certification will be exempted for stamp duty on documents of transfer. These measures encourage green technology industries, including the use of recycled aggregate and recycled concrete.

In the years to come, Malaysia will have plenty of room to consider the use of concrete waste and other secondary recycled materials as recycled aggregate. It is hoped that local builders and engineers will one day adopt recycled aggregate and new recycled concrete as construction materials.

Dr Wong Kien Kuok is a lecturer with the Faculty of Engineering, Computing and Science at Swinburne University of Technology Sarawak Campus. He is contactable at kwong@swinburne.edu.my