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As environmental performance of construction materials is steadily gaining attention of construction industry, responsible sourcing emerges as a holistic approach to ensure and further improve the transparency of sustainable properties in a product and its influence, directly or indirectly, on three main aspects of sustainability: economy, environment, and social. This report tries to analyse different materials based on the aspects mentioned in BRE's BES6001 certification about responsible sourcing, including the products' origin, properties, impacts, and issues regarding the three main aspects above.
This report analyses two sets of material, one of which will be opted to be used in a head office building commission project, and focuses on each material's influence on the three aforementioned aspects of sustainability. The two sets are:
Set A: Precast concrete frame, precast concrete floor, concrete blockwork walls
Set B: Steel frame, Slimdek floor system, timber stud partition and plasterboard walls
The report is divided into four parts, where the first two parts provide information about the two material set options, focusing on their sustainability performance. These parts provide analysis on each material and their constituents including potential issues regarding them and actions that may be taken to optimize the aforementioned performance.
Findings of the first two parts of this report become the basis of analysis in part three, where each option are compared to decide which one is more viable to be used in the project, based on the parameters of responsible sourcing mentioned above.
In part 4, some recommendations and suggestions are presented to conclude which set of materials is more preferable in order for the project to achieve better overall score in BREEAM sustainability assessment.
Part 1 - Set A: Precast Concrete Frame, Precast Concrete Floor, and Concrete Blockwork Walls
ÂThe materials mentioned in the first set are basically products of precast concrete. Precast concrete is a type of concrete that is produced off-site, typically using mechanical machines under controlled environment. Concrete block can also be considered as precast concrete since it is manufactured in similar way.
1.1 Origins and Availability
Precast concrete, as well as typical concrete, basically consists of aggregates (rock and sand), hydraulic cement, and water. This discussion will be explained separately for each of concrete's constituents to provide deeper analysis.
Concrete consists of two kinds of aggregates, coarse (rock) and fine (sand), which are normally extracted from mines widely available throughout the United Kingdom (UK). Great Britain alone is noted to have about 1,300 aggregate quarries, inland and offshore (NERC, 2012). This shows how aggregate is locally available throughout the country.
Cement consists of various minerals (limestone, sand, bauxite, etc.) that normally extracted from mineral mines. Data from Mineral Products Association (MPA) (MPA, 2012a) shows that on September 2012, MPA-member companies in UK need only to import 4,000 tonnes (~0.6%) of cement to fulfil the demand of 649,000 tonnes (Table 1). Based on this data, UK can be said to have sufficient local supply of cement for concrete manufacture.
Table 1. Monthly cement supply data from MPA member companies (MPA, 2012a)
Water source is available locally through main water supply. However, there are some efforts on reducing dependence on main water supply by adopting water recycling system, using harvested rainwater, or mixing water-reducing admixtures. Report shows that in 2010, 36% of water used to make the products came from these non-mains sources (MPA, 2010).
1.2 Sustainability Advantages of Precast Concrete Products
1.2.1 Quality Control
Precast method provides advantage of having better and tighter quality control on the products, including the raw materials, mixing ratio control, pre-delivery storage condition, etc., which leads to many benefits, such as less defective products and precise product dimensions.
Picture 1. Possible defect on in-site concrete, rarely happens on precast products (Civil Engineering World, 2012)
Precast concrete frame, floor, and concrete blockwork normally are available in ready-stocks from suppliers (except for special demands like non-standard forms). Products are also ready to be installed once it arrived on construction site. These will help the project to save valuable time and resources.
Durable and Maintainable
Concrete has been widely known to last in long time and requires relatively low maintenance. Research by Idorn and Thaulow (1983) showed that in some cases, concrete may last over a hundred years with "little maintenance".
Hazardous combustible waste can be used as alternative power supply for cement clinker and low-density aggregate, as applied in about half of plants in North America (Bremmer, 2001).
Precast concrete produces little waste, since the amount of ingredients used is measured accurately under controlled environment.
Concrete waste is totally recyclable by crushing it into debris and reusing the debris as aggregate for new concrete production.
1.2.5 Low Embodied Energy
Based on the Inventory of Carbon & Energy (Hammond & Jones, 2011), precast concrete relatively emits low rate of pollutant and uses low energy to produce. As seen on Table 2, better results can even be achieved by adding some percentage of fly ash (or other recycled/organic alternatives) to replace cement.
Table 2. Embodied energy of Precast concrete RC 40/50 (Hammond & Jones, 2011)
Sustainability Issues and Challenges on Precast Concrete Products
Fast construction rate of precast concrete means that few days, or even several hours of tardiness in delivery could affect the whole construction's schedule, especially for commercial projects such as office building. Congestions and method of delivery also pose environmental issue where more times wasted on the road means more pollution emitted from the transporting vehicles. There is also matter of vehicle's fuel consumption efficiency.
There are two main side products of concrete manufacturing, CO2 which mostly come from cement production (average Portland cement emits 1 kg of CO2 for each kg produced (Bremner, 2001)) and NOX, which usually comes from fuel burning reaction on generating power for precast concrete's production process.
1.3.3 Waste Disposal on Water Body
On average day, 2 - 4% of whole country's concrete order is returned, counting both ready-mix and precast, producing about 300kg of solids waste that is usually washed out by thousands litres of water (Bremner, 2001). Although the number is significantly less for precast concrete, it is still an issue worth addressed.
1.3.4 Worker's Health & Safety
There is no in-site issue about precast concrete construction aside from standard safety working procedures, but in production factory, employees' health may be affected by increased chromium content in cement.
Ozone, which is formed when nitrous oxides react with volatile compounds catalysed by sunlight, has been identified to be the cause of health problem, such as asthma, sore throat, coughing, etc., as identified by Bremner (2001).
1.4 Possible Strategies to Counter the Issues
1.4.1 Good Planning and Management
Well-planned project planning and management is a crucial factor that may ensure the success of a project. Use suppliers that are located near construction site and avoid busy hours to make sure products are delivered on time. In some cases, using air or water route instead of road may be faster (and may also be more environmentally viable).
1.4.2 Use Organic / Recycled Materials to Reduce Environmental Impacts
Emission during manufacture can be reduced by using organic compound in concrete production mixture. Table 2 in previous page shows how using fly ash as cement replacement may reduce overall embodied energy of the product.
As mentioned in point 1.2.5, using recycled concrete in producing new products is a good way to reuse concrete waste. UK's BS8500 standard allows 20% of coarse recycled aggregates to be reused in making RC 40/50 quality concrete (BSI, 200X).
1.4.3 Increase Attention on Worker's Health
Well-assessed suppliers need to put attention on their employees' health and safety by applying certain regulations and policies. Contact with elements that may pose negative effects on health (cement, fresh concrete) can be minimized with proper warning and training. Using recycled materials can also reduce the use of the mentioned elements.
Precast concrete products are created from elements that are available locally, supported by the availability of local precast concrete suppliers throughout the country.
Although there are several issues need to be addressed, precast concrete shows to be a sustainable option, and there are many suppliers (78% in 2011 (MPA, 2012b)) that have undergone proper assessment and clarified to provide transparent, responsible, and traceable source of their products.
Some points mentioned in this part are applied effectively during production phase, which is why choosing product suppliers that put these into consideration is crucial. It's preferable to choose suppliers that has undergone proper assessment and held BES6001 certification.
Part 2 - Set B: Steel Frame, Slimdek Floor, and Timber Stud Partition with Plasterboard Walls
2.1 Origins and Availability
As with the first part, this section will discuss about origins and availability of each products mentioned and their main constituents separately.
2.1.1 Steel Frame: Iron ore
There are numerous UK-based construction steel suppliers, but iron ore mines as well as other mineral mines, which act as the source of raw materials, are not fully available locally. Recent study shows that two-thirds of steel supplies in UK are imported from China, Brazil, and Australia, and the rest are supplied by Corus (now part of Tata Steel) (Klusell, 2008).
2.1.2 Galvanized Steel
Galvanized steel is the main constituent of "Slimdek", a pre-manufactured floor system licensed to Tata Steel (UK-based company). The manufacture process involves coating steel with zinc. Zinc supplies in UK are mostly originated from imported raw materials, with the same reason as steel. There is no recent data regarding whether the product has undergone a responsible sourcing assessment.
2.1.3 Concrete (Ready-mix or site-manufactured)
Concrete is poured on top of installed slimdek floor system, creating a solid layer of around 60-70mm above the panels. This phase is done on site, with concrete source may come from ready-mix trucks or produced on site (the latter one is more unusual). See point 1.1 for origins and availability of concrete and its constituents.
Of 3.1 million hectares of woodland in UK, 44% are sustainably managed, as certified by individual certification body (Forestry Commission, 2012). However, UK is also noted as one of the largest net importers of forest products, with sawn wood import (used on timber stud construction) reaches 4.9 million cubic meters in 2012, where most of the amount is originated from Europe (49%) (Forestry Commission, 2012).
2.1.5 Gypsum & Paper Sheet
Gypsum is the main constituent of plasterboard, produced by drying gypsum then mixing it with water. Gypsum mines are available in several places in UK, but the country also imported some from other nations (Mostly from European countries, with Spain has the biggest exporter).
To complete the production process, gypsum plaster is pressed between two thick paper sheets, and then dried in a drying chamber. Paper sheet can be assumed to have the same origin as timber (since its main material is wood pulp).
2.2 Sustainability Advantages of Set B Materials
2.2.1 Quality Control
Prefabricated properties of steel, slimdek plates, timber stud, and plasterboard ensures high quality control and less waste for the products.
2.2.2 Fast Construction
As well as precast concrete, these materials are usually available as ready-stock. Steel frame are relatively easy to transport and installed from separate parts, providing efficiency for time and labour cost.
2.2.3 Design Flexibility
Steel frame can be ordered and casted in various forms, depend on engineering and design requirements of each projects. Slimdek floor system is available in various dimension and technical properties. Timber stud partitions can be assembled into different forms, with plasterboard is easily cut and adjusted.
2.2.4 Recyclable / Environmentally Friendly
Steel is highly recyclable. Klusell (2008) even points out that 99% of structural steel found in demolition is either re-cycled or re-used.
Timber is made from natural material and may serve as carbon storage, seeping and storing CO2 during its lifetime, and it's also recyclable as other timber-based products (board, paper, furniture, etc.). Table below shows timber's carbon footprint data compared to other typical construction elements.
Table 3. Carbon footprints of timber vs. other building materials (TDA, 2012)
17% of plasterboard used in construction is wasted but recyclable (Camp and McKee, 1998). Recycled plasterboard can be used to make new plasterboard.
2.3 Sustainability Issues and Challenges on Set B Materials
As the case with precast concrete, prefabricated elements such as steel, timber, and plasterboard needs to be transported from supplier's storage to construction site, with potential issues of carbon emission and traffic congestions to be addressed.
2.3.3 Fire Resistance and Use of Fireproof Coating
Timber is considered relatively vulnerable to fire, and although steel structures are incombustible, their strength reduces significantly at high temperature. Use of fireproof coatings may increase the resistance, but at the cost of additional resources to apply and maintain (Johnson, n.d.). Chemical substances in fireproof coating products may also bear high embodied energy rate or other environmental issue.
A study conducted by Wright (1997) shows that Slimdek floor has quite good fire resistance rate from the help of concrete casted on top of it (60 minutes with 60mm thick of lightweight concrete on SD225 type deck).
Timber also has an issue regarding fire resistance, but the use of plasterboard (which has high fire resistance property) can minimize the risk.
2.3.4 Energy Intensive
Production of steel frame and plasterboard are quite energy intensive, as shown in the high embodied energy rate on table below (Hammond & Jones, 2011)
Table 4. Embodied energy of steel, timber, and plasterboard (Hammond & Jones, 2011)
Plasterboard and timber have low embodied energy and carbon, but still far higher than those of concrete (discussed further in Part 3).
2.3.5 Deforestation and Illegal Lodging
Annual amount of 13 million hectare forest conversion into land use (FAO, 2010) has been a major global problem. This problem has been identified as the main cause of many other environmental and social issues, such as biodiversity losses, erosion, and CO2 emission.
There have been many cases of timber sourced from unsustainable timber harvesting and illegal logging, as described by Damette and Delacote (2011) which also lead to illegal practice of workmanship (child labour, bad work environment), biodiversity loss, and higher carbon footprint as cost of the lower price rate.
2.3.6 Maintenance Problems with Timber
Timber, as organic material, has problems of damp and mould need to be addressed. Chemical treatments that are usually used to keep timber in good shape over years may lead to toxic waste, additional amount embodied energy, and may cause timber to be unrecyclable, losing one of its best advantages.
2.3.7 Health & Safety Issues
Chemical reaction involved in plaster production involving silica may improve chance of cancer and silicosis (although rare).
2.4 Possible Strategies to Counter the Issues
2.4.1 Good Planning and Management
Same case and same strategy as precast concrete, good planning and management, especially when choosing the right suppliers of these materials may help on increasing the traceability and reliability of products from manufacture until delivery.
2.4.2 Use Organic-based Compound in Coatings
There are lists of local suppliers in UK that provides environmentally-friendly coatings for fire protection or to preserve timber quality. However, there is no reliable data or studies found that can confirm whether these products have undergone proper assessment regarding responsible sourcing.
2.4.3 Utilize the Use of Recycled Materials
As shown on Table 4, before, recycled steel have considerably lower environmental impact than virgin steel. The same principles also logically apply to the other materials.
2.4.4 Pick Right Suppliers to Avoid Illegally-harvested Timber
Choosing suppliers with right certification is a simple and effective way to avoid environmental and social issues described in point 2.3.5. Unfortunately, there is no clue of certified timber suppliers holding proper certification of responsible sourcing in the UK.
Suppliers of set B materials are available locally in the country, but several constituents are not sufficiently provided from local source.
Set B consists of materials manufactured off site, each of which has different advantages and disadvantages regarding responsible sourcing assessment.
Main challenges for set B are potential need to use additional elements and compounds to tackle some risks they possess (fire resistance, damp, mould), as well as the relatively high embodied energy value they possess.
Part 3 - Comparisons and Analysis
This part will discuss each set's advantages and disadvantages, based on three main aspects of sustainability and responsible sourcing: economic, environmental, and social.
3.1 Economic Aspects
There are several certification bodies in UK (BSI, BRE Global, CPC) that provide service on responsible sourcing assessment of construction product companies as way to ensure the ethical business practice within the company, as well as management transparency and traceability of each material, including related supply-chains and legal compliances.
Choosing products that has been assessed and possess certification from the mentioned bodies ensures that the product's suppliers have provided sufficient concern regarding the importance of responsible sourcing.
3.2 Comparisons and Analysis: Environmental & Social Aspects
Below is a comparison table showing each material's performance regarding aspects of responsible sourcing, as mentioned in Part 1 and 2:
UK has local availability of concrete, from its raw materials to companies that supply the products to construction site, while set B's raw materials need to partially depend on sources outside the country. Using local sources, supported with good management and planned delivery method, not only reduces environmental impact caused but also increases employability of local human resources.
Precast concrete products have lower embodied energy value and emission rate than steel, timber, or plasterboard.
All materials mentioned are able to be recycled or reused into various range of products.
Precast concrete has an issue regarding waste disposal on water body that can be omitted by recycling the waste. Illegal logging and deforestation's effect can be avoided by choosing certified timber products sourced from sustainable forests.
Steel and timber requires some additional treatments to overcome issues regarding materials' fire, damp, and mould resistance.
Cement and plasterboard production has some health issues identified.
Slimdek floor and timber are not listed as materials that have undergone responsible sourcing assessment (GreenBookLive 2012).
Part 4 - Conclusions and Recommendations
Both options studied in this report have shown how materials have different performance and issues based on aspects of responsible sourcing.
The two options discussed consist of products manufactured in controlled environment before transported to construction site to optimize time and resources spent while retaining their qualities. All of them are also highly recyclable.
However, set B materials have crucial issues regarding risks of fire, corrosion, mould, and humidity, where the additional treatments viable to overcome the issues may cause other issues regarding health, emission, embodied energy, and disposability. Precast concrete also have an advantage in the number of product suppliers holding responsible sourcing certificate (GreenBookLive, 2012). As explained before, using products that have proper certifications is the simplest and easiest way to ensure the traceability of product's source alongside transparent records of ethical economic practice and proper social conducts.
Other notable advantages are that set A materials has all of their extraction and production process available inside the country and happen to have lower overall emission and energy impact than the other options. These advantages may affect some other factors mentioned in BREEAM assessment (aside from responsible sourcing), as the project is aimed to achieve BREEAM score of 'Excellent'.
Based on the study and analysis in this report about responsible sourcing aspects of materials, it is concluded that precast concrete frame, precast concrete floor, and concrete blockwork walls are more likely to ensure sustainability objectives throughout the products' project supply chain.
It is highly recommended that the project utilizes proper products from suppliers that have undergone responsible sourcing assessment and held the particular certifications.