Evaluation Of The Cost Benefit Analysis Construction Essay

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Edeoghon Otibho Stephanie

E-mail Address:

 o.edeoghon@lancaster.ac.uk

Dissertation Working Title:

Life Cycle Assessment of Aggregates

Introduction

Aggregates are the most widely excavated and used building materials in the construction industry. This definition is also supported by the European standards which defines aggregates as "granular materials used in structural constructions/ buildings (EN12620: 2002 and BGS, 2007). The three different sources of aggregates are classified based on the production process they undergo.

The virgin aggregate otherwise called naturally occurring aggregates are construction aggregates that are produced when naturally occurring earth minerals undergo physical extraction process like screening and crushing e.g. Sand and Gravel. Recycled aggregates are construction aggregates that are produced from the recycling of inorganic construction materials that have previously been used in a construction process. They include production from recycling of construction and demolition waste (BGS, 2007, Robinson et al., 2004). Manufacture aggregates which include; slag are aggregates that are produced from the combined industrial effect of thermal and other processing methods on mineral aggregates. (.....) Aggregates in their naturally occurring form or in combination with other materials to form asphalt and concretes are used in the construction of architectural structures such as residential or commercial building and in the construction of roads and bridges (ref..................).

The availability of virgin aggregates to meet the rising future need for aggregates by the concrete producing and construction industry gives course for concern as the annual European Union production of aggregates stands at 3 billion tonnes (EEA, 2008) . This increase in demand and the resultant effect has been felt in countries like the UK where the sand and gravel reserves have dropped from 869 million tonnes in 1997 to 616 million tonnes in 2005 (……………………….). With this projected rise in future, demand for aggregates strategies need to be put in place to curb the downward supply trend (Brown and Highley, 2006). With this, increase in aggregate demand come a need for an environmental impact assessment of the constituent makeup of the aggregates (Marinkovic et al., 2010), as it is recognisable that virgin aggregates are invaluable to the successful economic and social development of humanity and as such must be utilized and produced in accordance with sustainable development principles (Blengini and Garbarino, 2010).

It has however important to take into consideration that with this increase in demand for aggregates come increase in the production of construction and demolition waste. The environmental impact of this has to be taken into consideration as about 900 million of the 3 billion annually generated waste in the European Union countries are from construction and demolition waste ( EC, 2010) of which the UK contributes 77.4 million (DEFRA, 2010). The conservation and protection of the natural environment can be achieved by incorporating a construction and demolition waste recycling process that invariably produced recycled aggregates, preserve virgin aggregates and minimize the quantity of construction and demolition waste deposited in landfills (Blengini and Garbarino, 2010). The production of recycled aggregates from construction and demolition waste follows a two-staged process of Screening of waste to remove contaminants and materials not suitable for the construction process and a crushing process where waste are further reduced to the particulate size needed for further construction use. The quality of the recycled aggregate produced from this process is largely determined by the quality of the parent construction and demolition waste, the screening and crushing process and any other processing criteria the material undergoes (Padmini et al., 2009 and Wrap 2010).

Aggregates obtained from the recycling of construction and demolition waste (recycled aggregates) are for the most part used as sub-base for pavement construction (Al-Ali et al, 2001, Al-Ali et al, 2002, and Xu-ping, 2009) and in sand lime brick construction (Al-Otaibi and El-Hawary, 2005 and Al-Otaibi 2007). The reason for the use of recycled aggregates in lower quality construction application is attributed to the fact that recycled aggregates have a lower quality when compared to that of virgin aggregates (Marinkovic et al., 2010). The differences in the quality of recycled and virgin aggregates is linked to the presence of mortar and cement paste from parent construction and demolition waste that remains as part of the recycled aggregate produced from the recycling process ( De Juan and Gutierrez , 2009 and Marinkovic et al., 2010). The presence of the mortar affects the physical characteristics of the recycled aggregate which when compared with virgin aggregates gives the following results; an abrasion resistance decrease of up to 70% for recycled aggregate (Poon et al., 2003, Poon et al., 2004 and Lopez-Gayarre et al., 2009 ); a coarse recycled aggregate water absorption of 3.5% (Rahal, 2007 and Lopez-Gayarre et al., 2009) to 9.2% (Xiao et al., 2009) as against that of virgin aggregate which falls in a range of 0.5-5% ( Qasrawi et al., 2012) and a decrease in density of up to 10% for recycled aggregate (Hasen 1992, Poon et al., 2004 and Dejuan and Guitierrez 2009).

Aim

On the switch side, a comparative evaluation of the cost-benefit analysis (capital cost), environmental impacts ( carbon dioxide emission and energy consumption) and availability of recycled vis a vis virgin aggregates on are key information needed before major organisational decisions can be made. Hence, the questions to ask are: which aggregate use will be more cost effective in the long run, what are the environmental impacts associated with each aggregate use and which of them posses less harm to the environment in terms of energy use and carbon dioxide emission; finally which of these aggregates is readily available and accessible for use in construction (transportation)?

The main purpose of this study is to identify:

The capital cost of making a choice between the use of recycled aggregates and virgin aggregates in the construction industry.

The environmental impacts associated with the use of recycled aggregates as against virgin aggregates.

The transport cost associated with the transportation of recycled aggregate from source of origin to point of use as against that of virgin aggregates.

To address the main purpose of this study, the environmental impact assessment tool to be used is a Life Cycle Assessment (LCA) that follows the standards listed as ISO 14040:2006 (ISO, 2006a) and ISO 14044:2006 (ISO, 2006b). The LCA model has been used in the evaluation of the environmental impacts of construction materials and buildings (Wu et al., 2005 and Ortiz et al., 2009)

Methodology

The LCA is an objective process used in evaluating the environmental impact associated with a product, process or activity throughout its lifetime by identifying its input energy and material and its output waste and emissions released to the environment (Liu et al., 2010; Madival et al., 2009, Fisher et al., 2008). The result gotten from an LCA is used in the detection of fractions within the product/ process lifecycle where environmental improvements can be made (Graedel and Allenby, 2010). The LCA model incorporates four major steps namely; the goal and scope definition step, life cycle inventory analysis (LCI) step, life cycle environmental impact assessment (LCIA) step and finally the interpretation step (ISO 2006 a and b, Georgakellos, 2006, Curran, 2006)

Goal and Scope Definition

Life Cycle Inventory Analysis

Life Cycle Impact Assessment

(Classification, characterisation, normalisation and valuation)

Interpretation

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