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Background and Justification of project

Buildings are climate modifiers which provide indoor environments. These are essential to the well being and the social and economic developments of mankind. However, they are also intensive resources consumers and hence, they require enormous amount of materials and energy in their construction and maintenance. During the construction period and while they are demolished at the end of their life, buildings generate huge amount of solid wastes and various types of emissions, such as particulates, noise and various kinds of liquid effluents.

According to Hall (2003 ) and Anink (1996) the building industry accounts for around one-tenth of the world’s GDP, at least 7% of its jobs, half of all resources used and up to 40% of energy used and green house gas emission. Hill and Bowen (1997) discussed how the applications of modern technology, together with the increasing population, are leading to the rapid depletion of the earth’s physical resources. Hall (2003) also estimated that by 2025, the world population would reach 8 billion and 98% of the increase in the population would be in developing countries. With time, the construction industry is expanding and the rate of resource depletion is not sustainable.

As it can be imagined, construction materials and products are essential to life – with respect to both buildings and infrastructure. Humans spend around 80% of their time (on average) in some type of building or on roads. Construction products play a major role in improving the energy efficiency of buildings and also contribute to economic prosperity (Edwards, 2003). On the other hand, construction products also produce a considerable impact on the environment. The Worldwatch Institute estimates that 40% of the world’s materials and energy is used in buildings. However, according to Anink (1996), the construction sector is responsible for 50% of the material resources taken from nature and 50% of total waste generated. Also, Rodman and Lenssen (1993) pointed that buildings account for one-sixth of the world’s freshwater withdrawals, one-quarter of its wood harvest, and two-fifths of its material and energy flows. The impact of construction products relative to the overall lifetime impact of a building is currently 10-20%. For infrastructure this value is significantly higher, greater than 80% in some cases.

In Mauritius, nearly all the main resources in a building are imported, e.g. steel and cement. An average of 600 000 tonnes of cement are imported annually in Mauritius. As our country is currently going through a boom in the construction sector, the figures are expected to increase. The price of crude oil has more than doubled on the world market during the past years. This has had a direct impact on nearly all the construction materials which are imported and produced locally. While choosing for construction materials, many do not think about the impacts that the material have on the environment.

The environmental impacts of building materials are increasing day by day. Therefore, environmental impacts have become an increasingly important consideration in selecting building materials for the construction. Consequently, life cycle assessment has become an important tool in analysing natural resources and emissions generated in manufacturing processes. Winistorfer and Zhangjing (2004) said that life cycle assessment refers to the analysis of the environmental impact of a product through every step of its life. It includes environment impacts while the product is manufactured, used and disposed. The objective of a life cycle analysis is to quantify environmental influences of a product through input and output analysis.

Aim and Objectives

The aim of the project was to calculate all the resource energy and associated greenhouse gas emissions linked to construction of a typical residential house in Mauritius. Simapro Life Cycle Analysis software was used to calculate all the resource energy and greenhouse gas emission from the building.

The objectives were to:

  • quantify all the resources required for the construction of the typical residential house
  • estimate the weight of the building
  • minimise the use of resources in building thereby reducing the greenhouse gas emission and ensuring a cleaner production.

To satisfy the aim and objectives of the project, a virtual house was selected to carry out the analysis. The house used was obtained from the central statistics office. It represents the most common type of building in Mauritius. The size of the house is 128m2. All the quantities of materials used for the construction of the building were calculated. Using Simapro life cycle assessment software, the energy requirement and CO2 emission of each material was obtained. Also, the weight of the house was calculated using the unit weight of reinforced concrete and concrete blocks.

Structure of Report

A literature search was done and the findings were included in chapter 2. The latter describes how the building consumes all the different resources, energy requirements and the environmental impacts of building. Also, the benefits of sustainable building and of recycling waste, in order to recover the energy, were discussed. A detailed methodology, which was adopted to achieve the aim and objectives of the study, was described in chapter 3. The key results and discussions were presented in chapter 4. Finally, conclusions, recommendations and further works were dealt with in chapter 5.

Literature Review

Building: direct consumption of resources

There is growing concern that human activity is affecting the global and local ecosystem severely enough to potentially cause permanent changes to some ecosystems and potentially cause them to crash. Boyle (2005) suggested that there must be a reduction factor of 20 to 50 in resource consumption and efficiency in order to achieve technologies which are sustainable.

Sustainable technologies will be particularly significant to the construction industry which is a major consumer of resources. The pie chart below gives a repartition of all the primary materials resources used in the construction industry in 1998.

Figure 2.1 - Repartition of primary resources in the construction industry (Source: Construction Resource Efficiency Review, 2006)

Despite the fact that every house makes use of different quantity of resources, according to US DOE Energy Efficiency and Renewable Energy Network, a standard wood-frame house uses 4047 m2 (one acre) of forest and produces 3-7 tonne of waste during construction. Lippiatt (1999) stated that building consumes 40% of the gravel, sand and stone, 25% of the timber, 40% of the energy and 16% of the water used globally per year.

Boyle (2005) estimated that in UK itself, about 6 tonnes of building materials were used annually for every member of the population. Much of the waste and consumption of resources occurred during the extraction and processing of the raw materials. For example, mining requires water and energy, consumes land and produces significant quantities of acidic contaminated gas, liquid and solid wastes (Boyle, 2005). A second example which can be used is that of timber. The cultivation of trees requires significant space for cultivation and amount of fertilizers. Moreover, the harvesting and processing phases of timber make use of considerable amounts of energy. Trees are also grown in plantations which require old-growth forest and significantly reduce biodiversity.

Energy is also used extensively in the transportation of raw materials. Fossils fuels are used for the transportation, extraction and harvesting of the material, thereby releasing greenhouse gases and a range of air pollutants. Processing of metals and mineral often results in major gas emissions. The concrete industry is a major producer of carbon dioxide whereas on the other hand, aluminium smelting produces perfluorocarbons (Boyle, 2005). These two are very powerful greenhouse gases. According to the Construction Resource Efficiency Information Review (2006), emissions to the air by the construction industry in 1998 were just over 30 million tonnes in total, of which over 97% was carbon dioxide. Of the 30 million tonnes of emissions, over 70% came from mineral extraction and product manufacture.

The table below shows the total carbon dioxide equivalent emissions generated by the construction industry in UK.

Table 2.1 - Carbon dioxide equivalent emissions generated by the construction industry in UK (Source: Construction Resource Efficiency Information Review, 2006)

Emission generated by:

Tonnage (Kt )

Mineral extraction, product and material manufacture

19,817

Transport of product and material

2,543

Transport of secondary and recycled product

675

Construction and demolition site activity

3,764

Transport related to construction and demolition site activity

1,291

Transport of waste from product and material manufacture

20

Transport of construction and demolition waste

219

Total CO2 equivalent emissions to the atmosphere

28,327

As it can be seen, from Table 2.1, a total of 28 327 Ktonnes of CO2equivalent emissions were generated by the construction industry in UK and much of these emissions occurred during the mineral extraction and product and material manufacture.

Over the lifespan of a building, the material will have to be maintained and stored in good condition whereas, in some cases, replaced. Every five to fifteen years, exterior coatings, guttering, piping, walls, and flooring will require repair or replacement. By effective maintenance, requirements for replacement are reduced by a significant amount. The decisions here are not taken by the builder or designer regardless of the original design. Concerning the material used for the repair and the maintenance of the building, it is the owner who takes the decision.

During the lifespan of a building, the overall investment of resources into the building needs to be considered (Boyle, 2005). Buildings can be constructed and designed in such a way that they can last for more than hundred years. Additionally, many traditional buildings are designed in such a way that they can last beyond 200 years (Morel, 2001). However, many designers are now planning buildings for a lifespan of only 50 years or even less despite using durable materials requiring minimal maintenance. Such materials reduce the requirement for repairs or replacement. Hence, simply designing and maintaining a building for 400 years rather than 50 can potentially reduce its environmental effect from material resources by up to a factor of 4 (Boyle, 2005).

Energy requirements of a building

Cole and Carnan (1996) found that the energy that is consumed during the life cycle of a residential building includes energy used in producing building materials and constructing the structure. Also, energy is used in occupying and maintaining the building, and in demolishing or deconstructing the structure at the end of its serviceable life. According to Cole and Carnan (1996), the energy consumed in building can be classified in three categories:

1) energy to initially produce the building;

2) energy to operate the building, and;

3) energy to demolish and dispose of the building at the end of its effective life.

During the extraction, processing and transportation of material as well as during the construction as mentioned earlier large amount of energy is consumed. Morel et al. (2001) found that costs could be reduced by more than a factor of 6 during construction by the use of energy of local materials. The local materials studied by Morel et al. (2001) included rammed earth, stone, timber which were compared to the use of imported concrete. Consequently, Morel et al found that the imported concrete required significant energy for processing. Treloar et al. (2001) found that, by using a concrete binder, rammed earth had an energy load equivalent to that of a brick veneer construction due to the energy required in processing the cement.

Boyle (2005) stated that energy is the major resource consumed in buildings and 90% of the energy consumption is over the operational lifespan of the building. Therefore, significant decrease in energy consumption assists in reducing the resource consumption and improving efficiency. Although a house can be designed to a totally self-sufficient condition for energy and water, much depends on the location, that is, the climate, the availability and potability of local water sources as well as the attitude of the user. The designer or builder can incorporate some energy saving devices and design such a water heater, passive heating, and composting toilets, which are suitable for local conditions. Furthermore, such devices and designs will only be incorporated if a significant profit can be generated. Many developers resist including energy- saving measures unless they are required by local councils or are considered essentially by buyers in the local community. Cole and Kernan (1996) found that the energy used to heat, cool, provide artificial lighting, and power typically used appliances in buildings accounts for more than 30% of Canada’s national energy use. Approximately two-thirds of this consumption is attributed to residential buildings and the remainder to commercial buildings. The US DOE Energy Efficiency and Renewable Energy Network estimated that, the annual average energy consumption for one story concrete building, the annual average energy consumption is 63GJ.

However, Zydeveld (1998) pointed out that up to 80% savings in heating water and improving the indoor air quality and thermal comfort could be made in the Netherlands with the inclusion of passive solar design with an additional 10% cost in construction. Therefore, savings of 90% could be achieved. Four major design principles enabled architects and builders to incorporate passive solar design into their buildings: solar orientation; maximizing the solar gain through low surface loss and high internal volume; high mass within the insulation and avoiding of shading.

The rise in use of material in the low energy building can, however, mean that there is an increased consumption of material and energy overall. Thormark (2002) discovered that up to 45% of the total energy used is in the embodied energy in a low-energy building and that such a building could have a greater total energy use than that of a building with a higher operating energy consumption. Besides, he also said that 37-42% of the embodied energy could be recovered by recycling of materials.

Embodied Energy

According to an unknown author (2007), Embodied Energy is the amount of energy that has gone into the making of a material or things made with materials. A very high percentage of the world’s energy is derived from fossil fuels which, when burnt, release vast amounts of CO2. As the production of energy from fossil fuels is environmentally unfriendly, materials and things that have a lower embodied energy are more sustainable than those with a higher embodied energy.

On average, 0.098 tonnes of CO2 are produced per gigajoule of embodied energy (Sustainable built environment 2007).

Source: Sustainable Technologies (1996)

Figure 2.2: Embodied Energy of the different building materials

The embodied energy per unit mass of materials used in a building varies enormously from about two gigajoules per tonne for concrete, to hundreds of gigajoules per tonne for aluminium.(Figure 2.2). The reuse of materials commonly saves about 95% of embodied energy which could otherwise be wasted (Sustainable Built Environment 2007).

According to Fichtner Report (1999), in Mauritius, steel is the only waste material generated from the construction industry which is recycled, implying that most of the embodied energy of the materials is wasted.

Resource Efficiency in a building

According to the report “Construction Resource Efficiency Review” (2006), resource efficiency is about the sustainable use of resources. Indeed, there should be effective use and management of all the resources available to the industry while at the same time optimising output and profit. There is much emphasis on the use of all the physical resources (water, energy, etc) and materials used in the production and operation cycle. As minimum resource is used in the manufacture of the product, profits can be made by increasing productivity. Resource efficiency can also be achieved by reducing the wastes.

As far as the construction industry is concerned, there is a need to focus on sustainable consumption of resources. Buildings can be built with fewer resources while looking at the same time at the impacts of the building on the environment.

Sustainable Buildings

Buildings have a tremendous impact on our environmental quality, resource use, human health and productivity. According to Nicholas S. (2003), sustainable building meets current building needs and reduces impacts on future generations by integrating building materials and methods that promote environmental quality, economic vitality, and social benefit through the design, construction and operation of our built environment. Sustainable building, also referred as green building, involves the consideration of many issues, including land use, site impacts, indoor environment, energy and water use, lifecycle impacts of building materials, and solid waste.

Benefits of Sustainable Building

There are a number of environmental, social, and economic benefits which we can enjoy from a sustainable building. Miriam L. (1999) gives some benefits of sustainable building to the environment, which are as follows:

  • air and water quality protection
  • soil protection and flood prevention
  • solid waste reduction
  • energy and water conservation
  • climate stabilization
  • ozone layer protection
  • natural resource conservation
  • open space, habitat, and species/biodiversity protection

Also, sustainable building can have other benefits for designers, contractors, occupants, construction workers, developers, and owners. These benefits include:

  • Improved health, comfort, and productivity/performance

As mentioned earlier, people spend 80 % of their life in some buildings. It is reported that 30 % of new and remodeled buildings worldwide may be linked to symptoms of sick building syndrome (WHO 1984). Particular Symptoms are:-

- Headache

- Eye, nose or throat irritation

- Dry cough

- Dizziness

- Fatigue

- Sensitivity to odors

Sick building syndrome (SBS) is normally caused by fungi and bacteria that build up because of inadequate fresh air ventilation in structures. Therefore, improving the indoor environment of the building can reduce the effect of SBS.

Lower construction costs

The cost of the building can be lowered by reducing the use of material and saving on disposal costs because of recycling. For example, recycled aggregate can be used as filler material.

Lower operating costs

As discussed earlier in chapter 2.10, the use of energy can be reduced in a building by designing the building such that it gets maximum sunlight, and in so doing, cutting down expenses concerning electricity. This has a great impact for people with low income, who spend much of their salary in paying utility bills.

Life Cycle Assessment

“….Life Cycle Assessment is a process to evaluate the environmental burdens associated with a product, process, or activity by identifying and quantifying energy and materials used and wastes released to the environment; to assess the impact of those energy and materials used and releases to the environment; and to identify and evaluate opportunities to affect environmental improvements. The assessment includes the entire life cycle of the product, process or activity, encompassing, extracting and processing raw materials; manufacturing, transportation and distribution; use, re-use, maintenance; recycling, and final disposal….” Guidelines for Life-Cycle Assessment: A 'Code of Practice', SETAC, Brussels (1990).

There are four main components of LCA, which are as follows:

- Goal definition and scoping:

Identify the LCA's purpose and the expected products of the study. Also, he needs to determine the boundaries and assumptions based upon the goal definition

- Life-cycle inventory:

Quantify the raw material and energy inputs during each stage of production. Moreover, environmental releases are also taken into account.

- Impact analysis:

Assess the impacts on human health and the environment associated with energy, raw material inputs and environmental releases quantified by the inventory.

-Improvement analysis:

Evaluate opportunities to reduce energy, material inputs, or environmental impacts at each stage of the product life-cycle.

For this project, only the environmental impacts (carbon dioxide emission) and energy used from the manufacture of all the materials utilised in the construction of a typical residential house were considered.

Construction Waste

The construction energy generates an enormous amount of waste. Rogoff and Williams (1994) pointed out that in the USA, wastes from the construction industry contributed to approximately 20 %, in Australia 30% and in UK more than 50 % of the overall landfill volumes in each country. The Building Research Establishment (1982) has defined waste as the difference between materials ordered and those placed for fixing on building projects. Serpell and Alarcon (1998) defined construction waste as any material by product that does not have any residual value.

But this is not true for the construction and demolition waste as much as the waste can be reduced or recycled. By reducing the level of waste in the construction industry, it benefits the environment and lowers the cost of the project.

Bossink and Brouwers (1996) estimated that about 1-10% by weight of the purchase construction material leaves the site of residential projects as waste. However Guthrie et al. (1998) found that at least 10 % of all the raw materials which are delivered on most construction sites are wasted through damage, loss and over-ordering.

A study carried by Dabycharun (2004), pointed out that a residential house in Mauritius generates about 0.2-0.5 tonne/m2 of waste. He carried out questionnaire interview in order to get this figure. However, the Fichtner report (1999) states that during the construction of an average private house of 140 m2, 8-10 tonne of mixed waste are generated.

Skoyles and Skoyles (1987) identified two main kinds of building construction waste and finishing waste. Structure waste consists of fragments, reinforcement bars, abandoned timer plate and pieces which are generated during the finishing stage of a building. For example it comprises of surplus cement motar arising from screeding scatters over the floors inside the building.

There are two distinct procedures in minimising the amount of in landfill sites through the construction process. The first one is to reduce the amount of waste generated through source reduction techniques both on site and during the design and procurement phases of a building project. The second procedure is to improve the management of the unavoidable waste generated on site. In managing the unavoidable waste, there are three options in order of preference. They are as follows:

  • Reuse
  • Recycling
  • Disposal

The balance between the three will depend upon the nature of the materials wasted, legislative requirements for the specific materials and the cost effectiveness of each option. The cost will in turn depend upon the availability of reusing and recycling options and the opportunities for reuse on a specific project.

Recycled materials, while requiring transportation and reprocessing, consume significantly fewer resources compared to the extraction and processing of raw materials. This is particularly true for metal such as iron, copper and aluminium. These metals can be reproduced to a quality equal to that of raw material processing. Both concrete and timber can be recycled or reused but with the defect that the quality of the final product is often diminished. By crushing concrete, we can reuse it as an aggregate for some purposes, particularly like paving (Boyle, 2005). But, it was found by Millard and al. (2004) that from the recycled aggregate found in the construction and demolition waste, concrete blocks can be manufactured. Also, coarse recycled aggregates can be used in new concrete (Limbachia, 2004). Good grade timber can be used in the making of furniture. It is strongly stated not to use supporting timber since it is difficult to determine whether a used timber beam has stress cracks or other weak points. In other countries, plastics can be recycled into a number of construction products, including tiles, lumber, heating and wire insulation and carpet. According to Huang and Hsu (2003), each year in Taiwan over 10x106 tonnes of construction material are extracted for their usage and more than 40x106 tonnes of construction waste are disposed without recycling. Significant amounts of asphalt were present in the waste. However, if it was recycled, this would have decreased the amount of asphalt which was imported. Thormark (2002) pointed out that recycled concrete, clay brick and lightweight concrete can meet the total need for gravel in new houses and in renovation.

Materials and Methods

The next part of the dissertation was the methodology. In this section, an analysis was carried out on the different resources used for the construction of a single-storey house and the CO2 emission from each of the different resources. Therefore, a house had to be selected to carry out the analysis

Selection of a typical house

The house model used for the analysis was basically a virtual detached house which occupied a space of 128.30 squares metres floor area. The floor area was measured at plinth level to the external face of the external wall. The plan of the typical house model was obtained from the Central Statistics Office which was originally provided by the Mauritius Housing Company Limited. The house represented the most common type of residential house in Mauritius. The plan of the house is found in appendix A.

The building constitutes of two bedrooms, a living-dining room, a kitchen, a toilet, a bathroom, a verandah and an attached garage. It was assumed to be built up of concrete block walls, reinforced concrete flat roof, internal flush plywood doors, glazed metal openings, screened floor and roof, tiling to floor and walls of W.C, and bathroom and kitchen worktop; the ceiling and walls were rendered and painted both internally and externally.

It should also be noted that in the event the single-storey building would need to be converted into a two-storey house, an additional provision of more substantial foundation and of stub columns of the roof has already been made.

Calculation of different resources

Various materials and other resources were needed during the construction of the house.

These can be broken down in different input categories. The input categories (different components) for the construction comprised of labour, hire of plant, materials and transport. The materials were further broken down into hardcore fillings (remplissage), cement, sand, timber for carpentry and joinery, metal openings, ceramic tiles, glass and putty, plumbing, sanitary installation, electrical installation and other miscellaneous expenses.

The weightage of the components, shown in table 3.0, was calculated by a private firm of Quantity Surveyors for the Central Statistics Office’s use. The firm had identified nineteen stages through which the construction of the house had gone through. The cost for each stage was calculated. Detailed cost of each inputs in terms of plant, labour, materials and transport that go into the construction of typical residential house were calculated. According to the Statician, Jagai D. (pers. Comm., 19 November 2007), the construction of the single storey building, in the year 2001, was estimated by the quantity surveyor to be Rs 550,000. the weight was calculated so that each input category represented a fraction of the price for the residential building.

Table 3.0 - Weightage of different Input categories

(Source: construction price index,2007)

Input categories

Weight / %

Labour

Skilled workers

Unskilled workers

16.8

17.7

Plant

Mixer

Breaker

Metal plaques

0.7

0.9

1.4

Materials

Hardcore

Cement

Rocksand

Aggregate

Block

Steel bars

Galvanised corrugated iron sheeting

Timber

carpentry

joinery

Metal openings

metal sections

metal fittings

garage door

Ceramics tiles

Glass

Putty

Paint

Plumbing

pipes

fittings

water tank

Sanitary

lavabo

toilet

sink

fittings

Electrical

wires

fittings

Other

1.0

10.0

6.1

2.9

4.4

5.8

1.2

3.9

4.2

2.2

1.7

2.2

1.3

0.6

0.1

2.0

0.2

0.3

1.0

0.3

0.7

0.3

1.0

1.0

1.6

1.2

Transport

5.3

∑ = 100

The various materials from the input categories which had been used for the analysis were Cement, Rockand, Aggregate, Block, Steel bars, Glass and Ceramic tiles. As it can be observed from table 3.0, all the different components have been attributed a weightage to tally 100 for all the input categories used in the construction of the single-storey house in the base year 2001.

As mentioned earlier, the total cost of the single storey house in the base year 2001 was Rs 550,000. While following up on the various increases in the individual prices of the different components from the base year to September 2007, it has been noted that the prices of the materials have experienced an average increase of 51.6% in the total price (Construction price index, 2007). Hence, applying the 51.6% increase, the cost of the house as at September 2007 has reached up to Rs 833,800. Therefore, we can now have an idea of the quantities of each component, based on the total cost, which would be needed for the construction of the building. To illustrate this, cement was taken as an example.

It has been calculated from the Index that cement makes up 10% of the total weightage of the materials used. Therefore, it can be deduced that the total amount of cement for the construction of the building will cost (10% x 833,800) Rs 83,380 as at 30 September 2007. Hence, using the index, the cost of each component can be computed individually. For example, if the price of one cement bag is known, the number of bags of cement needed for the construction of the building can also be calculated.

To check whether the weightage allocated by the quantity surveyor was adequate or not, a quantity take off exercise work was carried out on one of the materials used. Block work was selected for that purpose. By knowing the weightage attributed to the block and the unit price, 2174 blocks was obtained. However, by quantity takeoff, 2216 blocks was calculated. There is a marginal difference in the number of blocks. Therefore, the weightage allocated can be considered to be realistic and reliable. Similarly all the different materials were calculated.

Calculation of energy resources and green house gas

The Simapro Life-Cycle Assessment Software was used to calculate the greenhouse gas emission and energy resources of each of the calculated materials in section 3.2. The resource energy is an estimation of all the energies which have been used for the different processes to manufacture the material. Similarly, during each process, green house gas is emitted.

Estimating the weight of the building

Every house has a weight which is being supported on the soil. In order to have an estimate of it, unit weight of reinforced concrete, concrete block and ceramic tiles were used.

Concrete work

Concrete work included concrete for slabs, columns, beams, floor, strip footing and pad footing. Knowing the unit weight of reinforced concrete, the total weight of the concrete used in the house can be calculated. In this case, a unit weight of 25 KPa for the reinforced concrete was used. However, concrete work excludes all finishing works.

Blocks

A unit weight of 2.85 KPa was used for calculating the weight of blocks in the building. It included for the rendering of the blocks and the mortar between the block’s joint. Therefore, having the weight of each unit, the total weight of the blocks used in the house can be calculated.

Ceramic tiles

Assuming that the tile is of 30 cm by 30 cm and having a weight of 0.2 kg, the total weight of the ceramic tiles used in the house can be estimated.

Therefore, if the weight of all the materials in the house is known, an estimate of the overall weight of the building can be found.

Results and Discussion

Introduction

In order to satisfy the aim of the project, calculations and a quantity take off exercise were carried out and using the Simapro Life Cycle Analysis Software greenhouse gas emissions and resource energy were obtained. The calculation is presented in the Appendices B and C. The main results are discussed in the following section.

Results for Steel bars used

For the pad foundation, 12mm diameter steel bars (Y12) were used. Moreover, 10mm diameter bars (Y10) were used in columns and beams, 8mm diameter (Y08) for the bottom bars (B1 and B2) and one of the top bars in slabs and stirrups had a diameter of 6mm (R06). It was assumed that the length of standard size of a regular steel bar to be 9m. By doing bar bending schedule, 180Y10 were used, in the 20 columns which were found in the typical residential house. Moreover, 44.5Y10 were used in the beams. And 159Y08 and R06 were used in the slabs and in the columns as shear links. The total price of all these is Rs 48 296 (Appendix B)

The table 4.0 below shows the quantities obtained for different diameters of steel bars used. The mass of each steel bar was also calculated by multiplying the length of the steel bars by the quantity and the multiplying factor.

Table 4.0 - Total mass and quantity of steel bars used

Bar diameter/ mm

Quantity

Multiplying factor

Total Mass/ Kg

12

20

0.888

159.84

10

44.5

0.616

246.71

8

159

0.395

565.25

6

159

0.222

317.68

∑= 1289.48

1289 kg of steel were required for the construction of a 128 m2 (1381 Sq. feet) house.

Results for Cement

It is a basic ingredient of concrete (grade 15 and grade 20), mortar and plaster. Concrete grade 15 was used for the casting of the blinding layer while grade 20 was used for casting of slab, columns and beams. To calculate the amount of cement required, it was assumed that the price of a 50 kg bag of cement was Rs. 208.80 (Source: local Hardware shop). Using the weight and the total price of the residential house, the total price obtained for cement was Rs. 83 270 (refer to Appendix B).

Approximately, 20 tonnes of cement were required for the construction of the house.

Results for Rocksand and Aggregate

Aggregate and rocksand were used in the making of concrete grade 15 and 20. It was assumed that the price of one tonne of Rocksand and aggregate to be Rs 380 and Rs 331 respectively. The total cost of rocksand was calculated to be Rs 50 794 and Rs 24148 for aggregate. 134 tonnes of rocksand and 73 tonnes of aggregate (14mm – 20mm) were needed for the construction of the house.

Results for Blocks

By quantity take off exercise, 2 216 blocks of size 150x200x450mm were used for the construction of the house. The blocks were used for the construction of partitioning as well as load bearing wall.

Results for glass and ceramic tiles

195 Kg of glass (3mm thick) and 428 Kg of ceramic tiles were used for the typical house.

Results for concrete

By quantity take off exercise, 50.88 m3 of grade 20 concrete and 4.37 m3 of grade 15 concrete was used for the construction of the building.

Results for resource energy and greenhouse gas emission

Table 4.1 displays the different values of greenhouse gas emission and energy resources that were obtained using the Simapro life cycle assessment software. Table 4.2, Figure 4.0 and 4.1 show the total green house gas emission and energy resources for the typical residential house.

Table 4.1 - Greenhouse Gas Emission and Resource Energy for different materials

Material

Unit

Greenhouse Gas/ Kg of CO2 equivalent

Energy resource MJ LHV

Concrete

1 kg

0.135

0.863

Cement

1 kg

0.977

4.87

Iron Bar

1 kg

1.710

31.1

Ceramic tile

1 kg

0.360

6.99

Float glass uncoated

1 kg

0.995

13.5

Sand and gravel

1 kg

1.560

25.1

Concrete block

1 kg

0.523

1.60

As it can be observed, the unit of green house gas emission is in “CO2 equivalent”. This is because methane is also included as a green house gas.

Table 4.2 - Total Greenhouse Gas Emission and Energy Resource

Material

Mass /kg

Greenhouse Gas/ Kg of CO2 equivalent

Energy resources MJ LHV

Concrete

138 125

18 647

119 202

Cement

20 000

19 540

97 400

Iron Bar

1 290

2 206

40 119

Ceramic tile

428

154

2 992

Float glass uncoated

185

184

2 498

Sand and gravel

207 000

322 920

5 195 700

Concrete block

33 240

1 7 384

53 184

∑= 381 035

∑= 5 511 095

Discussions on resource energy and C02 emission

To construct a 128 m2 (1381 Sq. feet) house, 381 tonnes of CO2 equivalent are emitted and 5 511 GJ LHV of energy is required, to produce all the material. However, this energy is only 10% of the total energy consumed over the operational lifespan of the building. While considering the construction materials, it can be noted that Iron bar requires the highest energy (31.1 MJ LHV) to manufacture and Concrete the lowest (0.863 MJ LHV). This can be explained by the fact that the manufacturing process of steel is very complex and therefore consumes a lot of energy. Furthermore, energy is only needed for mixing all the different constituents for the manufacture of concrete. The same reasoning can be applied for the value of greenhouse gas emission of Iron bar and Concrete. For the construction of the residential house, normally materials which are left over make up the majority of construction waste. Levels of waste during the construction need to be reduced, for environmental and economics reasons. The focus should be on decreasing waste at source, that is, by prevention. The advantage with this practice is a more efficient use of materials and hence a reduction of the material costs. In order to achieve sustainable use of resources, the waste hierarchy can be used.

Figure 4.1 - Waste Hierarchy

Potentials for waste minimization on site are very difficult as the amount of waste materials that will be generated is affected by many factors. Some of these factors are

- Building design

- Specification for materials

- Construction methods (whether load bearing or frame method)

- Time allocated for the construction of the building

Reduction of resource energy and CO2 emission

Some common practices in the construction of a residential house which can reduce the resource energy and CO2 emission are given below:

- Residential house can be built either using the frame method or the load bearing method. In Mauritius, nearly all residential houses are built using a combination of both methods. In load bearing construction, the inner columns are not necessary as the loads are taken by the wall. If the load bearing method is adopted, for the construction of the 128 m2, some 16 columns can be removed from a total of 20. This will reduce the cost of the house as less concrete, steel bars, formwork and labour will be used. About 4m3 of concrete could be saved if 16 columns are removed. Moreover, this will also lower the overall resource energy and greenhouse gas emission of the house by 8630 MJ LHV and 1350 Kg of C02 equivalent respectively. Also, beams that does not span on long distances can be removed. By doing so, the total resource energy for the house and green house gas emission can be reduced.

- As mentioned earlier in chapter 2, usually left over materials make up the majority of construction waste. Overestimation of materials which will be needed for the construction increases the cost through the purchase of excess products, waste handling and disposal costs. However, the excess materials can be returned to the supplier if any packaging return is adopted. Also, materials should be stored in a safe place in order to prevent damage and wastage.

- Concrete waste resulting from overpouring of concrete is an example of inefficient use of earth resources. Most of the times, block wastes can be reduced through avoiding damage to blocks during delivery. In addition, waste can be reduced by applying a more efficient blocklaying practice.

- There are volumes of waste from offcuts of ceramic tiles. Tile offcuts are affected by the design specification of the building. If tile offcuts are used, material wastage can be limited. Also, ceramic tiles must be bought in small proportion to ensure that there is minimum wastage. Overestimation of ceramic tiles which will be needed for the floor should be prevented as far as possible.

Discussion on weight of the building

The weight of the building was calculated to be 1953 KN. However by taking the sum of all the weight of the different materials used in the construction of the residential house, the weight obtained was 2670 KN. There is a significant difference between the two weights. There are several possible reasons which can explain this.

- There were many assumptions on which the analysis was based. According to Jagai D. (pers. Comm., 19 November 2007), the weightage allocated by the firm of private quantity surveyors had included 5-10% wastage in all the material used for the construction. Based on that assumption, the weight of the building should have been 2403 KN (2670 x 0.9) instead of 1953 KN.

- The estimated weight was based on estimated prices which could have been erroneous. The prices are actual rates being used by local hardware shops and by local suppliers. Normally, price of construction material varies across the island. This is because transport cost is included in the rate. In this project, the rate from one hardware shop and supplier was considered for the calculation of the resources (the prices which were used, is found in the appendix).

Conclusions

The main objective of the report was to calculate the resource energy and associated green house gas linked to construction of a typical house in Mauritius. Also, the weight of the house had to be calculated. A virtual house of 128.30m2 was selected for that purpose.

The key findings are:

  • Prior to the start of the analysis, existing literature reviews show that building consumes a lot of energy mainly for the manufacture of all the materials and during the lifespan of the building. 10% of total energy requirement is used for the manufacture of the materials.
  • The most common type of residential building in Mauritius has a size of 128m2 and it requires 20 tonnes of cement, 1290 Kg of iron bar, 428 Kg of ceramic tile, 185 Kg of glass 207 tonnes of rocksand and aggregate and finally 2216 blocks.
  • The virtual residential house emitted 381 tonnes of greenhouse gas and required 5511 tonnes of energy to build all the materials considered in the analysis.
  • The weight of the house was estimated using unit weights of concrete and block. The virtual house was found to weigh about 195 tonnes.
  • There are several ways in which the resource energy and the greenhouse gas emission can be reduced. First and foremost, waste minimization is important during the construction. Improving material efficiency will reduce purchasing and disposal costs. It also benefits the environment through more efficient use of the earth’s resources.
  • Recycling of construction waste materials would provide substantial benefits to the industry in terms reduced material supply and waste disposal cost. This will also increase sustainability and reduced environmental impacts.
  • Recommendations for future work

Only unit weight of block and reinforced concrete was used while calculating the weight of the building. It is required to calculate the weight of the building inclusive of live load. This will give a more apparent weight of the building.

While calculating the total resource energy and greenhouse gas emission, some of the construction materials such as timber, metal openings and paint were neglected. It is required to estimate the quantity which will be used and hence calculate the total resource energy and greenhouse gas emission. This will give a factual value.

As mention in the literature review, 90% of energy is consumed over the lifespan of the building, it is required to conduct an analysis on the building to calculate the energy requirement of the building during its operation phase. The value obtained can be compared to that of the materials obtained in this report.

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