From dust and debris

Construction and demolition waste (CDW) is one of the heaviest and most voluminous waste streams generated in the GCC.

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Crane

Construction and demolition waste (CDW) is one of the heaviest and most voluminous waste streams generated in the GCC, arising from activities such as the construction of buildings and civil infrastructure and demolition of buildings as well as road planning and maintenance.

Mega projects such as the FIFA World Cup, Doha Metro, Gulf railway, and other infrastructural projects, have cemented Qatar as the fastest growing construction and infrastructural market within the GCC, forecasted to spend USD 24 billion on construction in 2015 according to the EC Harris report ‘Middle East Major Construction Programmes’. Projects like these will only amplify the existing problem of construction waste.

According to the Ministry of Development Planning and Statistics, some 77 percent of the 12,163 million tonnes of the solid waste generated in Qatar, was from construction sector, occupying huge amount of space and posing serious health hazards.

There is a high potential for recycling and re-use of CDW, since some of its components have a high resource value. In particular, there is a re-use market for aggregates derived from CDW waste in roads, drainage and other construction projects. Technology for the separation and recovery of construction and demolition waste is well established, readily accessible and in general inexpensive.

This technology has been widely accepted and welcomed all over the world, as many countries are looking to encourage sustainable construction work, which has the advantage of avoiding deposits of large quantities of construction waste at landfills while greatly reducing the use of borrow material in construction projects.

In India, for example, nearly 50 percent of construction and demolition waste is being re-used and recycled, while the remainder is mostly landfilled. The EU is also aiming to push towards a recycling society with a high level of resource efficiency. Although the level of recycling and material recovery of CDW varies greatly (between less than 10 percent and over 90 percent), the European Commission has issued Waste Framework Directives, calling member states to take the necessary measures to achieve a minimum of 70 percent (by weight) of non-hazardous construction and demolition waste by 2020. At present, around 30 percent of the materials used by the European construction industry come from recycled sources.

Roads made of waste – roads of the future

Qatar has decided to introduce new environment friendly technologies as well. The Minister of Environment, H.E. Ahmed Amer Mohamed Al Humaidi, recently issued Qatar Construction Specifications (QCS) 2014, one of the core objectives of which is to reuse the huge amount of debris coming from the construction sector.

In a project called ‘Innovative use of recycled aggregate in construction’ undertaken by TRL (UK Transport Research Laboratory) together with Qatar Standards (part of the Ministry of Environment), Qatar University and the Public Works Authority (Ashghal), reclaimed rubble has been used in construction of roads in Qatar (one kilometre of access road to the landfill at Rawdat Rashid near Salwa was constructed as part of the project initiative in cooperation with Boom Construction).

Dr. Khaled Hassan, regional manager of TRL, tells bq magazine there is great scope for recycled aggregates to be used widely in road construction in Qatar and other GCC countries. TRL is planning a series of demonstration projects using recycled aggregates in a number of different construction applications, including roads and buildings. All these projects will be carried out in collaboration with Ashghal and Qatar Standards to ensure they meet the relevant standards and give confidence to the industry on the use of recycled aggregates.

How many kilometres of new roads can be constructed using recycled construction waste depends on how wide and thick the road is, and what would be the expected levels of traffic. In Doha’s industrial estates, a road needs about 3,600 tonnes of recycled aggregate as unbound sub base – the granular layer below the asphalt – over a length of about 450m, explains Dr. Hassan.

Knowing that the current generation of construction and excavation waste is about 12 million tonnes per year, and approximately 2 million tonnes are processed and used as recycled aggregates brings us to the conclusion: “If the recycled aggregate is fully used for road sub base it would stretch for something like 200,000 km! Processing more recycled aggregate than 2 million tonnes per year will result in more roads and longer lengths to be constructed by recycled aggregate,” says Dr. Hassan.

Waste recyclingAward-winning applications

In addition, recycled aggregates can be used in a number of other applications. Under the 2014 edition of the Qatar Construction Specifications, they can be used as partial replacement for gabbro in structural and non-structural concrete and concrete blocks. TRL, for example, constructed three small buildings at the Ashghal premises in Najma to demonstrate these uses; this trial won the Qatar Contractors Award for most innovative project in 2013 and the 2014 Green Mind Award for the Best Green Innovation project in the Middle-East and North Africa (MENA), Dr. Hassan tells bq.

One of the first major construction waste recycling projects is already underway. All the waste material excavated for the purpose of the construction of the two metro stations (West Bay Central and West Bay South station) will be reused during the construction of the long-distance GCC railway, using overhead conveyers, which will transport the dirt instead of mass truck transportation fleets.

Cheaper and with lower carbon footprint

Although the transport of feedstock to the processing sites and from them has environmental impacts associated with it, such as carbon emissions and noise, the wide scope of benefits tips the scales in favour of using recycled rubble materials. Dr. Hassan points out transport is greatly reduced if recycled aggregates are used.

He explains local limestone is supplied from a number of quarries in various parts of Qatar, most of which are further from Doha than Rawdat Rashed. The really big savings though, are by comparison with imported gabbro. This is transported approximately 700 km by ship from quarries in the United Arab Emirates and landed at Mesaieed and Lusail. The distance from Masaieed to Doha is similar to that from Rawdat Rashed.

“We carried out a carbon footprint analysis of imported aggregates and recycled aggregates and found that the carbon emissions from recycled aggregates were 50 percent or less of those from imported gabbro,” Dr. Hassan says. Truth be told, recycled aggregate production does produce more dust than virgin aggregates, but as the site is out in the desert this does not cause any problems, he adds.

Such practices will also lower the costs of construction as price of recycled material is usually lower than conventional, which is especially welcome in Qatar which faces shortage of local aggregate and depends on imports. In addition, solid waste has commercial potential as well.

According to a Qatar Development Bank (QDB) report, the revenue from recycling construction and demolition debris would potentially raise QR 387.25 million (USD 104 million).

“We estimate using recycled aggregates will lead to cost savings of up to 40 percent compared to using virgin aggregates. The highest saving is when recycled aggregate replaces imported gabbro such as in concrete and asphalt applications. The price of imported gabbro is quite variable, so the savings may be greater than this,” says Dr. Hassan.

However, the greatest benefits of the use of recycled and secondary aggregates are not in the lower costs of construction, but in protecting the environment by saving natural resources, while reducing the accumulation of waste, and the carbon emissions associated with the extraction and transporting of virgin aggregates, Dr. Hassan points out, adding the cost of aggregates is a relatively small part of the total cost of concrete and asphalt construction.

While in the West there are some concerns over environmental impact of recycled aggregates, such as loss of agricultural land (or removal from use for many years), scarring of landscape, fuel, noise and traffic, most of these are irrelevant in Qatar’s case, as sites are placed in the desert and do not pose any hazards to the environment. In addition, in the hot desert climate of Qatar, the pollution of soil and groundwater is most unlikely, especially from properly managed sites.

Quality up to standards

While usage of recycled material lowers the costs and hazards for environment and health, what about the quality of the constructed objects? Dr. Hassan ensures that recycled aggregate does not affect the quality of concrete and the constructed roads, because the aggregates have to comply with the requirements of the Qatar Construction Specification in the same way as local limestone and imported gabbro aggregates.

“All aggregate producers are audited regularly by Qatar Standards and only those who meet the requirements of the Qatar Construction Specification, are permitted to supply aggregates for construction projects. It is not rubble material that is used in construction; it is aggregates produced from rubble and excavation material. The aggregates are produced under a Quality Control System in the same way as virgin aggregates he specifies.

Currently construction waste is not sorted before being taken to Rawdat Rashed, so a lot of it contains contaminants such as wood, paper, plastic and tyres and this material cannot be processed into aggregate because of the contamination. There are limits on the amount of contamination as specified in the Qatar Construction Specifications 2014. The limits are checked as part of the Quality Control Procedures and certified by Qatar Standards.

The contractor at Rawdat Rashed has recently installed equipment that will enable the company to process this material, but it would be very helpful if the material was sorted before leaving the site to remove as much contamination as possible.

“We need to make it clear that recycled aggregates are permitted to contain small amounts of foreign materials (contaminants) but if you see recycled aggregates that are full of such materials, they have probably been produced by an unofficial producer who does not have proper quality control procedures in place. Inform Qatar Standards if you see any such material,” warns Dr Hassan.

Industrial potential

Given that the majority of the Gulf countries are ranked amongst the top ten globally in terms of waste production per capita, and with the rapid growth of the construction sector in the GCC, multiple countries in the region are introducing new technologies and developing sustainable programmes.

In the UAE, Abu Dhabi’s Urban Planning Council has developed the Community Sustainable Responsibility initiative, Estidama CSR 2030, and one of its key segments is recycling of construction waste. In 2010 Abu Dhabi authorities opened the Al Dhafra facility, a plant designed to process between 5,000 and 7,000 tonnes of CDW on a daily basis, while producing a range of materials including road base, sub base, structural fill, trench bedding, hardstand and low dust asphalt products.

While the benefits of the technology are obvious, there seem to be some reservations as well. “It may be difficult to persuade people to use recycled aggregates in concrete. The construction industry tends to be conservative, and we will have to put in more effort and do more trials to achieve a significant change in behaviour,” Dr. Hassan admits. Most importantly, one of the main obstacles was removed with the changes in the 2014 edition of the Qatar Construction Specification, which permits the use of recycled aggregates in a range of applications.

Application of the Codes of Practice would improve the quality of feedstock for recycled aggregate production, which would lower the cost of producing aggregates that comply with the Qatar Construction Specification. Further demonstration projects planned with Ashghal and Qatar Standards will help to convince clients and the construction industry to use recycled aggregates, as will the cost savings and certainty of supply.

Dr. Hassan is convinced that further development and appliance of this innovation will place Qatar as a leader in sustainable construction, not just in the Gulf but in the world.

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