CONCRETE RECYCLING IN BUILDING WASTE

MATERIALNathan Taghizadeh

N8403040

introductionThe amount of Building waste and/or construction

waste generated through the construction industry in Australia each year is about 7.8 million tons, but only 57 percent of that will be recycled. This means that 43 percent of construction material, (around 4.45 million tons), will end up as landfill and will have a massive impact on the environment both now and into the future. [25] some other countries such as Japan have achieved to the maximum recycling of concrete about 100 percent that will encourage construction industry and special in Australia to compete with such market.

MASONRY IN WASTE AND BUILDING CONSTRUCTION

Masonry materials are heavy materials such as Asphalt, Bricks, and Concrete. (Consulting, 2011). These materials are required in greater quantities for construction and developments. Hence, extra volume and space are needed for recycling these type of materials in a building cycle.

Bulk excavation and demolition are the main contributing factors to masonry construction waste with materials such as soil, cement, bitumen and aggregate making up the majority of this waste.

MASONRY IN WASTE AND BUILDING CONSTRUCTION

The table below shows the percentage of waste and recycled material from just one office building in Melbourne.

(Crowther P. , 2000)

TYPES OF MASONRY MATERIALSAsphalt Concrete - 20 to 40-millimeter thick,

smooth road pavement layer that is mixed with gravel and bitumen.

Bricks and Blocks - made of a mixture of water and clay and processed through high-temperature kiln firing.

Concrete - made of Portland cement, aggregate, reinforcement bars, and water. The strength of a concrete is designed depending on the type of concrete needed and the construction purpose.

CONCRETE WASTEIn Australia is recorded at about 7.8 million

tons a year, but only 57 percent of that will be recycled.

43 percent of construction material, around 4.45 million tons, will end up in a landfill.

Impact on the environment is significant.The density of concrete is the major

contributing factor to damage to the environment.

LANDFILLDesignated landfill areas are chosen by Local

Authorities or the Commonwealth government to allow disposal of construction waste.

Landfill volume has been increasing due to population growth in recent years.

Landfill levies are too low to be an incentive to reduce waste generation and waste disposal

LANDFILL LEVIES AND GUIDELINES ARE REGULATED BY THE ENVIRONMENTAL PROTECTION

AUTHORITY.

LANDFILL SIZES IN AUSTRALIA The bulk landfill in Australia is small, however, the

majority of this landfill is located in about 152 facilities in Queensland.

The size of the landfill may seem small in Queensland, but there is a definite increase in the of dumping construction waste and civil waste is increasing according to the Australian Bureau of Statistics.

The growth of the construction industry in Queensland will continue to put increasing demand on the number of location landfill is dumped at in the near future

LANDFILL SIZES IN AUSTRALIA

Landfill Size analysis by State [17]

TYPES OF LANDFILLThere are three different types of landfill in Australia, these are;

Solid, inert waste infill material only.

Prescribed waste, solid inert waste, fill material and some forms of prescribed industrial waste

Hazardous and Prescribed (Liquid and Solid) waste

(Australian Government Productivity Commission , 2006)

LEACHATE IN LANDFILLLeachate is a hazard substance that is produced from waste material in landfill. This usually occurs in two different forms - dissolved and suspended materials. The leachate is a common cause of groundwater contamination that has the potential to put human health at risk. The risks are not usually related to concrete itself, but contamination from other materials mixing within kilns.

CONTAMINATION MAY BE CAUSED BY:

Variations to the content of the material.

Variations in the percentage of Sulfates and Alkalis in the fine powder.

The amount of toxic material in cement kiln produced from fuel used in cement.

CONCRETE CONSTRUCTION’S IMPACT ON THE ENVIRONMENT

Concrete has numbers of issues for the environment due to the processed involved in its

production:Air Quality – Portland Cement manufacturing

causes both dust and carbon dioxide to be released into the atmosphere.

Cost and Durability - Portland Cement production could have a massive impact on increasing Carbon Dioxide emissions, power consumption and the overuse of raw materials

Carbon Dioxide – the burning of coal during production releases large quantities of CO2 into the atmosphere. (1 tonne per annum).

CEMENT IN CONCRETE AND ITS IMPACT ON THE ENVIRONMENT

The manufacturing process of cement requires large amounts of energy and the use raw

materials.

Manufacturing cement has a significant impact on the environment. Worldwide the production of cement has reached 2.8 billion tonnes per

annum.

This figure shows Global Cement Production (Schneider 2011)

ENERGY AND ENVIRONMENTAL ISSUES

The amount of energy used in clinker production has a considerable environmental impact due to the burning of fossil fuels such as coal and natural gasses.

During the production about 850 kcal per kg of clinker is consumed in the kiln.

ENERGY ISSUES INCLUDE:

1. Lack of energy efficient plants can affect investment into new technologies. Japan and China have already adopted these plant kinds.

2. Moisture in raw materials consumes more energy.

3. Kiln Size affects the amount of energy consumed.

RAW MATERIAL ISSUESCement is made of organic materials extracted from

a large quarry as per table below. The quantity of raw materials taken from the environment is dependent on population growth rates, which when it increases the demand on cement usage in the construction industry also rises. This increase puts pressure on the mining industry to supply raw materials for cement manufacture to satisfy the market demand. The demand for the excavation and extraction of raw materials will put the environment at risk, even to the point that raw material resources are no longer available, and construction practices are unsustainable for future generations.

RAW MATERIAL ISSUES

Raw Materials for Clinker Production [19]

CONCRETE CONSTRUCTION’S IMPACT ON THE ECONOMY

Concrete has varied benefits on the economy, a few of which are outlined below; [1]

Concrete is a high quality and affordable product. [1]

The thermal mass of concrete can be used to increase the energy efficiency of a building. [1]

Concrete buildings provide improved indoor air quality (Australia, 2016) [1]

C & D MANAGEMENT PLANS AND POLICIES IN AUSTRALIA

The waste construction program was initially started in 1997 between 5 major construction companies and the government, aiming to reduce the amount of construction waste.

. There are also other organizations that are working to reduce the amount of waste in Australia such as:

Partner Advancing the Housing Environment (PATHE) 1999

Lifecycle Assessment in Building and Construction

Also, the major responsible agencies are:

The Commonwealth Government

State and Territory Governments

Local Government

EPA (Environment Protection Authority)

CONSTRUCTION AND DEMOLITION POLICIES

Table 4 (Legislation, and Waste Minimization Strategies and target for waste recycling in Australia) [25]

CONSTRUCTION AND DEMOLITION POLICY ISSUES

There are a few policy and other issues in relation to landfill and demolition waste such as: [16]

There is no National Guideline to control waste minimization

No specific rules and legislations exist in regards to the quantity and quality of waste disposed

The levy and prices for waste recycling are too low, so this does not deter dumping or encourage construction companies to reduce waste.

There are not many waste recycle companies

There is little motivation for companies to manage waste in ways to reduce costs

Financial costs of alternative waste technologies and most dedicated energy-from-waste facilities are much higher that the financial costs of landfills

The external costs and levies may not increase in the future which means companies don’t need to factor in increasing cost as they continue to expand their construction development projects.

SUSTAINABLE ENVIRONMENT AND CONSTRUCTION WASTE

According to Australian State and Territory Government legislation, regarding the minimisation of waste disposal to landfill, companies will need to endeavour to maintain the environment, using sustainable practises to safeguard it for future generations. The Environment 1992 agreement was created to ensure the Australian government was responsible for national environmental matters such as: [2]

Monitoring closely Australian environmental policies to match International policies and also negotiating and entering into National agreements

Ensuring that policies are identical and practical across every State and Territory

Referencing and replication of the National Environmental Standards and Guidelines [2]

RECYCLED CONCRETE Economic, Environmental and Health benefits are just some of

the issues that are closely related to the recycling of concrete and reductions in the manufacturing of cement. These methods can be monitored by each state and territory to achieve maximum performance to reuse materials in the industry.

There number of issues are considerable for recycling concrete such as:

The Council of Recycle has argued that the focus of most recycling is ‘just recycling’ rather than focussing on the performance and quality of recycled materials, which could have a negative impact on the market.

Most recycled materials are just used as road base, instead of using it for all aspects of the construction industry. This has come about due to a lack of standard indicators and regulations for recycled material.

CONCRETE RECYCLED METHODSBASIC METHOD

Basic methods of concrete recycling are similar to the same processes used to produce raw material such as:

Crushing

Sizing

Stockpiling

The main stages of recycling aggregate are as below:

Sieves

Sorting devices

Screening

CONCRETE RECYCLED METHODSADVANCED METHOD Method Details of the method

Heating and grinding method The heating and grinding method makes the hardened cement paste which adheres to concrete waste soften by heating concrete waste to about 300 degrees . After that parts of the hardened cement paste adhered to original aggregate in the concrete mass can then be separated by a grind process resulting in clean original aggregate from the concrete waste.

 

Screw grinding method The screw grinding method uses a shaft screw consisting of an intermediate part and an exhaust part with a warping cone to remove mortar adhered to the aggregate’s surface.

 

Mechanical grinding method The mechanical grinding method uses a drum body which finely separates partition boards with same-sized holes. The steel balls can move horizontally and vertically by rolling the drum. The quality of aggregate can then be improved in narrowing the inside space by using the partition boards

Gravity concentration method After processing with a jaw crusher, an impact crusher and an improvement rod mill, aggregate of over 8 mm are divided into recycled coarse aggregate and mortar particles. Aggregate with sizes under 8 mm are divided into two types: recycled fine aggregate of sizes 5 mm and 5-8 mm . The wet gravity concentration machine is used to move: i) light weight things such as mortar particle and wood waste upward; and ii) heavy-weight things such as aggregate grain downward.

(Recovery Rates of Common Recyclable Material) [26]

CONSTRUCTION WASTEConstruction waste recycling in Australia has increased since 1995. Figure 8 shows that there has been a slight increase in the recycling of concrete from 36% to about 37% between the years of 2010 to 2011 [13] Even this small increase in the recycling percentages reflects a positive response to the Australian C&D policies.

composition of recovered masonry (by weight), South [13]

CONCLUSION Construction waste is the second biggest source of pollution,

(Air quality being the biggest issue today) and this is due to the fact that most construction waste will end up in landfill. Construction and demolition policies must enforce construction companies to reduce the amount of waste by paying levies to the government, especially in the area of dumping waste as landfill. Levies today are not effective in the reduction of construction waste because the costs required are too low for large construction companies. Australia has achieved the maximum levels required to recycle waste in accordance with international environmental guidelines, however quality of recycled material is not competitive with market standards. This is unlike some other countries such Japan that has managed to recycle 100 percent of concrete waste by using new recycling technologies of to increase the levels of recycled concrete.

DISCUSSION AND QUESTIONS