Environmental Benefits of Green Concrete - IEEE Xplore

Environmental Benefits of Green Concrete A. Abbas

Department of Civil and Environmental Engineering, Carleton University, Ottawa, Ontario, Canada

G. Fathifazl


O.B. Isgor


A.G. Razaqpur

Department of Civil Engineering, McMaster University, Hamilton, Ontario, Canada

B. Fournier

CANMET - MTL, Ottawa, Ontario, Canada

S. Foo

Public Works and Government Services Canada, Gatineau, Quebec, Canada ABSTRACT Of the approximately 11 million tonnes of annual solid concrete and demolition waste (C&D) in Canada, concrete accounts for about 52% by weight. However, most of this concrete is used as highway base or sent to landfills for disposal; only a very small portion of the concrete waste is reused in building construction. Considering the fact that usable natural aggregate (NA) supplies are diminishing, there will be a high demand for recycled concrete aggregates (RCA) to be used in the so called "green concrete (GC)." Using recycled concrete as aggregate will help reduce the total cost of concrete production because aggregates need not be hauled from remote locations, but obtained locally. The combination of RCA with significant quantities of fly ash or slag as replacement for Portland cement is particularly attractive from both economic and environmental perspectives. GC will reduce the demand for natural resources, the associated energy consumption, and green house gas (GHG) emissions required to produce aggregates and cement. These reductions can be considered as one of the construction industry's major contributions to Canada's GHG emission reduction objective. Although there are some guidelines/specifications established by different countries such as the UK and Japan, currently, there are no established guidelines for producing GC in Canada. This paper presents the environmental and economic benefits of increasing the use of GC in the construction industry and highlights the objectives of an ongoing research by the authors on GC. Key words: Recycled concrete aggregates (RCA), green concrete, green house gas (GHG), aggregate recycling

INTRODUCTION

Concrete is the most common material used in the construction of civil engineering structures. Due to its environmental impact, it is also one of the most costly ones. Ordinary concrete typically contains about 12% cement and 80% aggregate by mass (Neville, 1996). Global construction industry uses approximately 1.6 billion tonnes of cement and 10 billion tonnes of sand, gravel, and crushed rock every year (Mehta, 2001). The world's yearly cement production of 1.6 billion tonnes accounts for about 7% of the global loading of carbon dioxide (CO2) into the atmosphere (Mehta, 2001). Mining large quantities of raw materials for the production of cement such as limestone and clay, and fuel such as coal, often results in extensive deforestation or denudation and top-soil loss (Mehta, 2001). Concrete structures have service lives of several decades to more than a century. Those structures that are no longer able to fulfill their original purpose after their service life will be demolished. The demolished materials are considered 1-4244-0218-2/06/$20.00 C)2006 IEEE.

as construction and demolishing (C&D) waste, and concrete constitutes a large part of this waste. The annual worldwide output of concrete and masonry rubble has been estimated roughly as one billion tonnes (Mehta, 2001). In Canada, the C&D waste is estimated as 11 million tonnes per year, and approximately 42% (by weight) of this amount is reused or recycled. Concrete constitutes 52% of C&D waste, and approximately 73% of it is reused in low-value applications as filler material or as road sub-grade (George and Michael, 2001).

In Canada, the total aggregate supply is around 350.5 million tonnes per year in 2003 figures (Panagapko, 2003). Continuous use of natural aggregates (NA) and cement to produce conventional concrete has negative effects on the environment. These effects can be summarized as follows: 1. The effect on the habitat: As stated by Winfield and Taylor (2005), the extraction of aggregates from pits and quarries results in the destruction of the natural habitats of

many organisms and in the disturbance of the pre-existing stream flow and water resources. 2. Quality of water resources: Impact of the NA production on the quality of the surface and groundwater resources is a significant concern. The excavation of aggregate resources alters the slope of the land, and hence changes water drainage patterns. In addition, by excavating the aggregate deposits that serve as underground water reservoirs, the water storage capacity of the ground is diminished.

3. Increased transportation costs: The transport distance of hauling the aggregates from quarries to crushing plants and/or to ready-mix concrete plants has been rising due to the depletion of nearby quarries. As the hauling distances increase, direct costs associated with the transportation of NA also increase.

Currently in Canada, there are no major studies underway to evaluate the applicability and long-term performance of GC in structural applications. As a consequence of this lack of research, there are no established guidelines regarding the production of GC using RCA and fly ash/slag. There are, however, extensive guidelines for producing concrete with supplementary materials, including fly ash. This paper will present the objectives and environmental benefits of an ongoing research for development of the guidelines for the production of GC as a structural material with comparable mechanical and physical properties as conventional concrete.

Figure 1: Canada Greenhouse Gas Emission (source: ECGC, 2006b; EC-GC, 2006c)

4. Increased greenhouse gas (GHG) emissions: There are two major sources of GHG emissions associated with concrete production: -,

(a) The mining, processing, and transport operations

involving large quantities of aggregate consume considerable amounts of energy, produce large quantities of GHGs, and adversely affect the ecology of the areas they are extracted from. As the hauling distances between the quarries to the processing plants and processing plants to construction sites increase, GHG emissions associated with the transportation of NA also increase.

(b) The manufacturing of cement involves emission of considerable amount of GHG in the atmosphere. It is estimated that producing one tonne of Portland cement requires about four giga-joules of energy, which in turn emits 1.25 tonnes of carbon dioxide into atmosphere (Wilson, 1993). Increased emissions of GHGs is considered to be the main reason for the climate change that we have been experiencing over the past century. Although Canada's GHG emissions account for 2.5 percent of global total, it is the world's third largest per capita emitter of these gases, following the US and Australia (IPCC-GC, 2005a and ECGC, 2006). According to the Kyoto Protocol, 38 industrialized countries are committed to cut their emissions of GHG between 2008 to 2012 to 5.2 percent below 1990 levels. However, Canada's target is to reduce the net GHG emissions to 6 percent below 1990 levels (Figure 1).

Global demands for regulating concrete production and recycling of the C&D waste arise from the growth of these environmental and economic issues. With Canada's commitment to Kyoto protocol, every sector, including the construction industry, has the obligation to reduce its GHG emissions. As a result of this necessity, the concept of "green concrete (GC)" as an environmentally friendly alternative to conventional concrete has been emerging. GC in this paper is considered to be the concrete produced with a combination of RCA and NA, and large quantities of fly ash or slag, used as partial replacement for regular Portland cement. It is intended that the replacement of NA with RCA and regular Portland cement with fly ash or slag will diminish the environmental impact of the conventional concrete production.

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A large portion of Canada's building stock and infrastructure are made of concrete. Many of these buildings were built in the 50's or 60's, and are near the end of their design life. It is expected that during the next two decades, a large amount of concrete, resulting from the demolition of these buildings and structures, will be available for either disposal or for being recycled for reuse as RCA. However, only a very small portion of the concrete waste is reused in building construction. During the next two decades, a large amount of concrete, resulting from the demolition of these structures, will need to be disposed. This would require extensive new landfills and possibly distant transportation away from cities and farming communities. In addition, in order to replace the demolished structures, vast quantities of fresh aggregates will need to be manufactured, which will result in extensive use of new resources and the degradation of the natural environment. One method of conserving these resources is to increase the use of RCA as coarse aggregate in structural grade GC.

Currently, most NA are obtained from crushed stone since

natural sand and gravel sources that do not require any processing are limited. As stated in the Environmental Council of Concrete Organization information sheet (ECCO, 1999), the cost and transport distances of NA will continue to increase as the natural sources grow scarce. From this point of view, RCA, whereby it will be used locally, is the most environmentally friendly alternative. In the United States, according to Wilburn and Goonan (1998), the

processing cost for RCA is around $10 per tonne depending on the size of the operation. The large operations produce cheaper products due to lower distribution cost over more units of output. The unit cost of producing natural sand and crushed stone in processing plants range from $ 6.5 to $8 per tonne (MOTH, 1999). It can be seen that the use of RCA will not create significantly high additional costs in the production stage as long as the quality-related issues regarding RCA and its use in GO can be addressed.

As the quantity of construction debris rise, the number of accessible landfills is falling; hence the dumping fees will most likely increase (ECCO, 1999). Therefore, seeking alternative means of disposal of concrete from C&D operations to protect the environment and to gain economic benefits is obvious. As participation from the aggregate producers increase, more disposal sites will be opening up for recycling purposes and contractors will be incorporating recycling into their operations to decrease disposal costs.

Nowadays, the recycled concrete is widely used to produce aggregates for non-structural construction such as general bulk fills, base or fill for drainage structures, pavement base and sub-base, lean-concrete bases, concrete blocks, and wall sound barriers in highways. Although the use of RCA in structural concrete is limited, various quantities of RCA were used successfully in the construction of concrete pavements and low-rise buildings in the UK (Collins, 1998) and in a small number of projects in Japan (Takenaka, 1999). The main reasons behind the limited use of RCA in structural concrete can be listed as: (1) technical problems, (2) commercial barriers, (3) quality control problems, (4) lack of suitable regulations and experience, and (5) poor image of recycled materials.

Currently, there are no specifications or guidelines available in North America, which can be followed to consistently produce structural-grade concrete made with RCA. The commercial barriers arise from the unsteady supply of structural-grade RCA, which cannot compete with efficient and stable supply of traditional concrete materials. The steady supply of normal concrete materials makes it very

difficult for a new material such as RCA to enter the market. The quality of RCA depends on the equipment used to produce the RCA, and it varies from one plant to another. This variation may cause concerns about the quality of structures made using RCA. The poor image of RCA arises from the fact that the recycled materials in general have the problem of low quality. However, this poor image is based on the preconceived notion that RCA can not yield good quality concrete. There is ample evidence (Dhir et al., 1999) to challenge this presumption. Figure 2 is taken from the ongoing study carried out by the authors of this paper about the effect of RCA on the mechanical properties of GC. It is obvious from this figure that with proper material selection and mix design procedure, GC using RCA can reach the compressive strength req u ired for structural-grade applications (i.e. ~-30 MPa and higher). Similar observations have also been made for other mechanical properties of GC produced with large quantities of RCA, fly-ash/slag. In general, all difficulties described above can be overcome by developing sound technical specifications and quality control and quality assurance methodologies for producing structural-grade concrete.

Figure 2: Compressive Strength vs. Water-Cement Ratio of GC produced with 1 0000 RCA 50. Non-air-entained concrete

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ENVIRONMENTAL BENEFITS OF GC

The extensive use of GC in the construction industry has a number of environmental benefits. These benefits can be classified as: (1) energy conservation, (2) GHG reduction, (3) conservation of natural resources and land, and (4) reducing landfill costs. These benefits will be discussed in the following sections.

Energy Conservation and GHG Reduction

Extensive use of GC in the construction industry will result in savings in energy consumption and consequently reductions in GHG emissions in the long term. In order to understand these benefits, it is imperative to understand the energy demand of concrete production process. Energy required for concrete production technology, can be categorized as follows: 1.

Energy required to produce cement: Producing a tonne of Portland cement requires about four giga-joules of energy. Using fly-ash or slag as replacement for cement will decrease the demand for cement production and its associated energy consumption. The research on fly-ash and/or slag addition to concrete is quite extensive, and the use of these supplementary materials in concrete is already common practice.

2.

Energy required for producing aggregates: As natural sand and gravel sources generally require significantly less processing, the production from such sources requires less energy compared to the energy required to produce crushed aggregates. The Portland Cement Association (1993) indeed estimates energy requirements for the processing of sand and gravel to be 5.8 M-joules per tonne, while crushed aggregates, on the other hand, require approximately 54 M-joules per tonne. It is reasonable to expect that manufacturing RCA would require almost the same amount of energy as for producing crushed natural aggregates since they use similar equipment and processes (e.g. crushers, screens, transfer equipment, and devices for removal of foreign matter).

3.

Energy required for transporting aggregate materials to processing plants: As the supply for natural sand and gravel will be increasingly limited, the proportion of the

required aggregates for new construction obtained from crushed stone processing plants is expected to increase significantly. It is also expected that the hauling distances will increase over the years, resulting in higher transportation costs. The RCA production plants being closer to the construction sites, hauling distances will be shorter. It is estimated that the total required energy for hauling the aggregates for processing stage can be reduced as much as 80%. This translates into significant energy savings. 4.

Energy required for transporting processed aggregates to ready-mixed concrete plants: It is estimated that 2.7

M-Joules per tonne-km for sand and gravel, and 3.8 MJoules per tonne-km for crushed aggregates, are required to transport these materials to ready-mixed concrete plants (PCA, 1993). The energy required to transport RCA to ready-mixed concrete plants can be expected to be the same as for crushed aggregates, except that the hauling distance may be significantly less in the case of RCA. 5.

Energy required for producing concrete: Producing new concrete using RCA requires the same amount of energy as producing concrete with NA, and this energy can be approximately estimated as 1.3 to 2.4 GJ/m3 (George and Michael, 2001).

Based on the abovementioned energy demands for producing concrete, the reduction in the energy consumption and GHG emissions by using GC will come from two sources: (1) reduced cement consumption due to replacement of cement with fly-ash and slag, (2) reduced transportation distance of unprocessed rock/stone from quarries to the processing plants. The amount of GHG emission as a result of transportation of coarse aggregate to processing plants can be calculated if the following assumptions are made:

(a) transportation by a 35-tonne truck consumes 0.56 liters/km of fuel (or 63 MJ/km), which results in the release of 1.5 kilograms of GHG per kilometer (Clayton Research and MHBC, 2004; TPPF, 2004), (b) taking 2002 figures as reference (Panagapko 2003, OARC 2002), annual Canadian coarse aggregate demand is approximately 350 Million tonnes. Based on these assumptions, the amount of GHG emitted in Canada by transportation of coarse aggregates (RCA or NA), unprocessed rock/stone or disposed concrete, can be calculated as: j(1.5)

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The practical interpretation of this is that using RCA instead of NA will reduce 15,000 tonnes of GHG emissions for every 1 km increase in average traveling distance of the trucks used in the transportation operations. Although this modest amount is only a small portion of Canada's annual

GHG emissions, reducing the GHG emissions due to aggregate transportation as much as 80% by using RCA instead of natural resources will help Canada achieve her Kyoto targets. It should also be noticed that transportation distances associated with delivering the natural stones to the processing plants and hauling the processed aggregates back to the construction sites will continue to increase as the natural resources for producing construction-grade aggregates diminish. Table 1 summarizes the energy consumption and GHG emissions for production of conventional concrete and GC. Table 1: The Energy Consumption and GHG Emission for Production of conventional concrete and GC

GHG Emission and Energy Consumption

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From Aggregate hauling1 (per km) 15,000 63

7,5006 31.5

(1) Based on 30% replacement by supplementary materials (2) Assuming 35 - tonne trucks are used (3) Assuming 50% reduction in transportation costs by use of RCA

Conservation of Water Resources and Natural Habitat

The impact of the NA production on the quality of the surface and groundwater resources and natural habitat of many species is a serious concern. As stated by Winfield and Taylor (2005), the excavation of mineral sources and aggregates changes the slope of the land and vegetation; hence changes water drainage patterns. Also aggregate deposits behave as underground water reservoirs. By excavating the aggregate, the water storage capacity of the ground is lost. Increased use of GC in the construction industry will alleviate the demand for these resources; hence conserve water resources and protect natural habitat.

Reducing Landfill Costs and Saving Space

Landfill costs for construction and demolition waste continue to rise and landfills become more heavily regulated. Hence, the dumping fees will most likely increase (ECCO, 1999). For instance, the dumping fee in Holland has increased almost six-fold per tonne within only a few years during the past decade (De Vries, 1993). Table 2 shows the average tipping fees in different countries. The construction waste tipping fee in European countries varies from $43 (CDN) to $79 (CDN) /tonne. In Canada, tipping fees vary greatly; nominal mass-based dumping fees are $25-$90 per tonne, depending on the type of waste material (Wikipedia, 2005). Therefore, it makes economic and environmental sense to seek alternative means of disposal of concrete from C&D operations. Aggregate processors are beginning to accept this reality and consider receiving reclaimed concrete for a "tipping fee" significantly lower than the cost of landfilling the material and to supply RCA of sufficient quality for many applications. Depending on the

size of the recycling facility, entry into the aggregates recycling business requires a capital investment between $6 and $10 per tonne of annual capacity (Wilburn and Goonan, 1998). Table 2: Average Tipping Fees in different countries Country Tipping fee (CD$/ tonne) Holland 66 Denmark 79 Sweden 43 Canada 58 Ottawa 73* 70* Canada GGuelph Hartland 75* Range 25 - 90 * Tipping fee for concrete

ONGOING RESEARCH ACTIVITIES Considering the vast benefits of using RCA, many countries have taken the lead in preparing guidelines or specifications to utilize recycled aggregates in one way or the other. In the UK, the use of C&D waste as RCA has been permitted since the publication of BS EN 12620:2002 "Aggregates for concrete". Specification for their use in concrete is given in BS EN 8500-2:2002 ConcreteComplementary British Standard to BS EN 206-1 (Dhir et al., 2004). In Japan, the draft standard for use of RCA was published in 1977. However, the Recycling Law was established in 1991 to suppress the increase of waste and promote recycling of useful resources (Noguchi and Tamura, 2001). In Germany, the national standard "DIN 4226-1000 Aggregates for Concrete and Mortar, 2002" set the guideline for RCA content in concrete aggregates. In Netherlands, the Dutch standard NEN 6720:1995 "Construction Requirements and Calculation Methods", allows the use of concrete aggregate by certain percentage of NA (Corinaldesi, et al, 2002). In Denmark, use of RCA for certain structural applications in mild environments was allowed in 1990 (Hansen, 1992). In the US, since 1982, ASTM C33 "Standard specifications for concrete aggregates", defines coarse aggregate as including crushed hydraulic cement concrete. ASTM C125 "Standard definitions of terms relating to concrete and concrete aggregates" defines manufactured sand as including hydraulic cement concrete. Similarly the US Army Corps of Engineers has changed its specifications and guides to encourage the use of RCA as aggregate. Some State Highway Departments have developed their own specifications for RCA in pavements (ASTM C33, 2001; ASTM C125, 2000). In Canada, the Ministry of Transportation Ontario's (MTO) specifications for road construction, "Special Provisions for Provincial Highways," allows the use of reclaimed aggregates, concrete and asphalt pavement in highway construction, subject to qualifying criteria (Winfield and Taylor, 2005). The use of RCA included in Ontario Provincial Standard Specification (OPSS) to be used as road or parking lot base and sub-base aggregate as well as sewer bedding and backfills. Furthermore, a guideline on the use of RCA as a filling material exists in Quebec (BNQ, 2002). This guideline does not address the processes and methods to produce structural-grade concrete from RCA.

However, CSA Standard A23.1 -04, "Concrete Materials and Methods of Concrete Construction", included the use of RCA in notes under Section 4.2.3.1. RCA as aggregate should be evaluated in a manner similar to the evaluation of normal-density aggregate with particular attention to durability characteristics; deleterious materials; potential alkali-aggregate reactivity; chloride contamination; and the workability characteristics of concrete manufactured with the material (CSA A23.1 -04, 2004). Despite these efforts, current use of GC in new structural applications is limited by several technical and practical uncertainities. There is still a strong global reluctance in using RCA and GC as structural material. In addition, the unique circumstances imposed by Canada's environmental conditions, and the extensive use of de-icing salts that may cause pre-contamination of RCA, require comprehensive investigation of the durability properties of concrete produced with these aggregates. The objectives of an ongoing joint research being untaken by the authors include the comprehesive investigation of material and structural performance of concrete procuded with RCA and the development of technical tools for the design and contruction of such concrete, with special emphasis on Canada's unique environmental conditions. This research is believed to be the first comprehensive study in Canada into the material, mechanical and physical properties of concrete using RCA, with an objective to establish preliminary requirements for the design and construction of structural concrete.

Key activities of the research include:

(a) Material characterizatation of RCA, (b) Investigation of mechanical and durability properties of GC produced with RCA, fly ash and/or slag, (c) Testing of structural members produced with GC, (d) Development of mixture design procedures for GC, (e) Development of QA and QC procedures, (e) Development of a guide on the use of GC in structural applications. Preliminary results on determining material characterization of RCA and mechanical properties of GC are very promising. A test for the determination of residual mortar content of RCA has already been developed (Abbas et al., 2006), and it is expected that the proposed methodology will be submitted to ASTM for consideration as an international procedure.

CONCLUSIONS

Based on the investigation of the environmental benefits of using GC in the construction industry, the following

conclusions are reached: 1.

RCA is currently used in Canada, the US, Japan and many European countries mostly as base and subbase materials in road construction. The use of RCA as substitute for natural coarse aggregates in concrete is presently rather limited worldwide.

2. The recycling of old concrete as coarse aggregates and replacing cement with fly-ash or slag in new concrete will save fresh minerals and aggregate resources, reduce landfill disposal and the extent of

aggregate quarrying. Less quarrying will prevent land denudation and ecological degradation.

Concrete Aggregates.1 st International Structural Specialty Conference. Calgary, Alberta. May 23-26.

3. The use of fly ash/slag and RCA could potentially reduce overall energy consumption in concrete production, and this will contribute to the efforts for reducing GHG emissions.

ASTM C33. 2001. Standard Specifications for Concrete Aggregate, Annual Book of ASTM Standards, Vol. 04.02, American Society for Testing and Materials (ASTM), West Conshohocken, PA, USA.

4. There are a number of reasons for the limited use of RCA in concrete. Among these are the lack of adequate technical knowledge and experience with RCA, the lack of general design guidelines and specifications, and a preconceived notion that concrete made with RCA is inherently inferior.

ASTM C125. 2000. Standard Terminology Relating to Concrete and Concrete Aggregates, Annual Book of ASTM Standards, Vol. 04.02, American Society for Testing and Materials (ASTM), West Conshohocken, PA, USA.

5.

Limited research so far has indicated that in a properly designed concrete mixture with RCA, mechanical strength can be equal to or even superior to the strength of the original mix from which the RCA was extracted.

6. Concrete made with RCA can be economically competitive if sufficiently large quantities of concrete can be retrieved to keep an aggregate crushing plant fully operational. 7. The use of RCA may also be economical if portable aggregate crushers and cleaners are used to process demolished concrete at the demolition site. This may substantially reduce transportation and handling charges. Such crushers are already used in some countries.

8. To render GC, a commonly acceptable construction material, research is needed to fully characterize all its physical, mechanical and chemical properties. Based on these results, mixture and structural design specifications and methods can be developed. 9.

Research is also needed to develop quality control and quality assurance procedures/programs for (a) the operations involved in producing high quality RCA concrete mixes, and (b) for constructing high quality structures using RCA concrete.

10. In order to maximize beneficial environmental impact, recycled aggregate concrete technology could be combined with other environmentally favourable concrete technologies, such as the use of fly ash, slag and silica fume, in order to reduce cement consumption and to produce a truly "green concrete."

ACKNOWLEDGEMENTS

The authors gratefully acknowledge the technical and financial support of the Public Works and Government Services Canada (PWGSC) and the Natural Resources Canada (NRCan) and the financial support of the Natural Sciences and Engineering Research Council of Canada (NSERC).

REFERENCES

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Bureau de normalization du Quebec (BNQ). 2002. Classification and characteristic of recycled material from concrete construction debris coated with bitumen and bricks. Recycle material specifications. Quebec.NQ2560600/2002

Clayton Research and MHBC. Regional & Urban Planning & Resource Development. 2004. The Implications of Restricting Aggregate Supply in the GTA, pg. 13. Collins, R., 1998. Recycled aggregate in readymix - Dr. Rod Collins describes two practical applications of RCA in concrete and evaluates their success. Concrete Engineering International, 2 (2): 49 -54.

Corinaldesi, V., Giuggiolini, M., and Moriconi, G. 2002. Use of rubble from building demolition in mortars. Waste Management, 22 (8): 893-900. CSA A23.1-04. 2004. Concrete Materials and Methods of Concrete Construction, standard, CSA International, Toronto, ON. Dhir, R.K., Limbachiya, M.C., and Leelawat, T. 1999. Suitability of recycled concrete aggregate for use in BS

5328 designated mixes. Proceedings of the Institution of Civil Engineers - Structures and Buildings, 134 (3): 257 274.

Dhir, R., Paine, K., and Dyer, T. 2004. Sustainable concrete construction - Recycling construction and demolition wastes in concrete. Concrete - Crowthorne, 38(3): 25-28. De Vries, P. 1993. Concrete Recycled. Concrete (London), 27 (3): 9-13. Environment Canada, Government Canada (EC-GC), 2006a. [Online]. Available:

www.ec.gc.ca/pdb/ghg/inventory report/2003 report/c2 e.c fm, January issue [Retrieved January 2006] Environment Canada, Government Canada, 2006b. [Online]. Available: www.ec.gc.ca/climate/kyoto-e.html, December issue [Retrieved January 2006] Environment Canada, Government Canada, 2006c. [Online]. Available: http://www.ec.gc.ca/press/2001/010711 b e.htm July issue [Retrieved January 2006]

Environmental Council of Concrete Organization, ECCO. 1999. Recycling Concrete and Masonry. [online]. Available: http://ecco.org/. [August, 2004]

Wikipedia, the free encyclopedia. 2005. [Online] Available: http://en.wikipedia.org/wiki/Tipping fee [Retrieved January 2006]

George J.V, Michael N. .2001. Waste streams from building construction and demolition, with a specific focus on concrete reuse and recycling report submitted to public works Government Services Canada, Gatineau, Quebec, Canada.

Wilburn, D.R., Goonan, T.G., 1998. Aggregates from natural and recycled sources, Economic assessments for construction applications, a materials flow analysis, U.S. Geological survey circular 1176.

Hansen, T.C. 1992. Recycling of Demolished Concrete and Masonry, RILEM Report 6 - Report of Technical Committee 37-DRC Demolition and Reuse of Concrete, E&FN Spon, Chapman & Hall, London, U.K. Intergovernmental Panel on Climate Change (IPCC), Government of Canada, 2005a. [Online]. Available: www.climatechange.gc.ca/english/climate change/factshee t_en.pdf [Retrieved January 2006]

Intergovernmental Panel on Climate Change, Government of Canada, 2005b. [Online]. Available: www.climatechange.gc.ca/english/climate change/greenho use.asp, March issue [Retrieved January 2006] Mehta, P.K. 2001. Reducing the environmental impact of concrete. Concrete International, ACI, October issue, pp: 61-66.

MOTH. 1999. Construction Aggregates Sector Trends. British Columbia Ministry of Transport and Highways Neville, A. M. 1996. Properties of Concrete. Longman Group Limited, Essex

Noguchi, T., and Tamura, M., 2001. Concrete design towards complete recycling. Structural Concrete, 2 (3): 155167 Ontario Aggregate Resources Corporation (OARC). 2002. Mineral Aggregates of Ontario Statistical Update, 2002 [Online]. Available: http://www.toarc.com/publications statistics.asp [Retrieved December 2005] Portland Cement Association (PCA), 1993. Cement and Concrete- Environmental considerations: Environmental Building News, v. 2, no. 20, Skokie, IL.

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BIOGRAPH IES

A. Abbas, M.Sc., P.Eng. Department of Civil and Environmental Engineering, Carleton University, Ottawa, Ontario, Canada Mr. Abbas received his B.Sc. degree from University of Khartoum in Sudan in 1994 and M.Sc. degree from Vrije University Brussels in Belgium in 1999. He is a member of Professional Engineers of Ontario (PEO) since 2001. Currently, he is carrying out his Ph.D. studies in the Department of Civil and Environmental Engineering at Carleton University in Ottawa, Ontario, Canada

G. Fathifazl, M.Sc. Department of Civil and Environmental Engineering, Carleton University, Ottawa, Ontario, Canada Mr. Fathifazl received his B.Sc. and M.Sc. degrees from University of Guilan and Iran University of science and Technology (IUST) in Iran in 1995 and 2002, respectively. Currently, he is carrying out his Ph.D. studies in the Department of Civil and Environmental Engineering at Carleton University in Ottawa, Ontario, Canada.

O.B. Isgor, Ph.D., P.Eng. Department of Civil and Environmental Engineering, Carleton University, Ottawa, Ontario, Canada 0. Burkan Isgor is an assistant professor of civil engineering at Carleton University, Ottawa, Ontario, Canada. His research interests include analysis, design and durability of reinforced concrete structures, corrosion of steel in concrete, use of recycled materials in civil engineering applications, and multi-scale and multi-physics modelling. A.G. Razaqpur, Ph.D., P.Eng. Department of Civil Engineering, McMaster University, Hamilton, Ontario, Canada A.G. Razaqpur is a professor of civil engineering at McMaster University, Hamilton, Canada. His research interests include analysis and design of reinforced concrete structures, advanced mechanics of concrete, bridge engineering and durability of reinforced concrete structures.

B. Fournier, Ph.D., P.Eng.

CANMET - MTL, Ottawa, Ontario, Canada

Dr. Benoit Fournier is research scientist with the Concrete Technology Program of CANMET-MTL, Ottawa, Canada. His research interests are in the various aspects of the durability of concrete, especially concrete incorporating supplementary cementing materials (SCM) and the various aspects of alkali-aggregate reaction in concrete.

S. Foo, Ph.D., P.Eng. Public Works and Government Services Canada, Gatineau, Quebec, Canada S. Foo is an Engineering Specialist (Risk Management) with research interest in risk management and sustainability of assets. He is a member of ISO/TC59/SC17 "Sustainability in Building Construction" and CSA Technical Committee on "Sustainable Buildings".