Author: Susan McGarry, civil engineer and LEED Green Associate, environmental manager with Ecocem Ireland for the past four years
Since its pioneering use in the construction of the Jack Lynch Tunnel in 1999, Ground Granulated Blastfurnace Slag - or GGBS - has become well established in Irish construction. With six sources in the market, two producers and four import facilities, GGBS is now widely available nationwide in readymix concrete, precast concrete and 25kg bags. GGBS is used as a direct replacement for ordinary Portland cement to produce lower carbon concrete.
Technical advantages
Commonly specified at 50 per cent for its strength and durability, GGBS has now become the cement of choice for high performance concrete. I.S EN 206-1: 2002, 'Concrete - Part 1: Specification, performance, production and conformity standard' allows for a direct replacement of ordinary Portland cement by GGBS up to a limit of 70 per cent with a CEM I or CEM II.
Ecocem GGBS was specified at 50 per cent in the Rosie Hackett Bridge (Engineer’s Ireland Project of the Year 2015) where a strength of 130MPa was achieved. This is believed to be the strongest concrete ever produced and placed in Ireland. As the construction sector begins to recover, sustainability has moved up the agenda and GGBS is now being increasingly specified for the carbon reductions it can provide to the sector.
Lower carbon footprint
Global cement production accounts for seven per cent of CO
2 emissions annually. Traditional cement (CEM I) is made up of 95 per cent clinker and has an estimated carbon footprint of 850kg of CO
2 per tonne due to calcination and the burning of fossil fuels to 1450°C during the production process.
Welcome developments in the cement industry have resulted in a reduced carbon alternative, CEM II, becoming the more dominant choice in the market. This reduction is achieved through the substitution of clinker by alternative materials like fly ash and limestone.
Further carbon reduction has been made through the burning of secondary fuel sources such as bone meal, SRF and other wastes instead of fossil fuels. However, with an estimated carbon footprint of 750kgCO
2 per tonne, and with scope for further reductions limited, the time has come to consider lower carbon alternatives.
GGBS, a by-product from the production of iron, involves no quarrying and requires very little energy to manufacture. This gives Ecocem GGBS an extremely low carbon footprint of 42kgCO
2/tonne, which is a 95 per cent reduction when compared with CEM II.
To verify the low environmental impact associated with GGBS, Ecocem commissioned a full life cycle analysis of the product and produced a third party verified Environmental Product Declaration (EPD). The EPD gives a full cradle to gate breakdown of all impacts associated with the manufacturing of GGBS from the granulating process at the steel works, shipping by sea from Europe and processing in the plant in Dublin port before it leaves the gate.
The impact categories range from carbon footprint to acidification and eutrophication. This is the first EPD produced by a cement supplier in Ireland and gives engineers transparent and directly comparable environmental information on the product.
I.S EN 15804 'Environmental Product Declarations Product Category Rules for Construction Products' was published in 2012. However there is no national database of embodied carbon or life cycle data in Ireland and no Irish body exists for third party verification or review of these EPDs.
The only option currently available to Irish suppliers is to have their products assessed through other European certification bodies. Ecocem use the Dutch system, MRPI, to verify and publish their EPD until a national system is put in place. EPDs are a clear way of avoiding green wash, as the clearly defined scope and transparent demonstration of results allows for direct comparison of different materials.
The lack of a national database means engineers and architects cannot readily assess and compare materials during the specification process. There is also potential to include EPD information into Building Information Modelling (BIM) objects to generate an embodied carbon figure on a project-by-project basis.
Building rating systems
As well as helping to make more informed decisions around material specification, EPDs also fit into many of the green building rating systems such as BREEAM and LEED. These systems have grown in popularity as the construction industry has started to recover and sustainability has become a priority.
Large industrial projects such as the Diageo Brewhouse and the Kerry Innovation Centre have used LEED to construct state-of-the-art facilities. Extra credits were achieved by the specification of Ecocem GGBS on both of these projects.
GGBS is a low carbon material and has many environmental benefits which are rewarded in LEED and BREEAM. As a recycled product with a third party verified EPD it increases the percentage recycled content across a project and gains credits for life cycle assessment. The whiter colour of GGBS concrete has a much higher reflectance value which helps reduce the 'heat island effect'.
This can be a huge advantage when trying to reduce cooling costs in industrial settings. The high reflectance also means less artificial lighting is required. Approximately 30 per cent less lighting is required for lighter coloured concrete surfaces to achieve the same visibility when compared with darker asphalt surfaces.
This point is of particularly importance in car parks and external walkways for night-time security. Sourcing raw material from a short supply chain in Europe means Ecocem GGBS counts as a regional material and this has also helped achieve BES 6001 'Certification for Responsible Sourcing' for the product.
Overall, GGBS can contribute up to 14 credits in LEED new construction projects and feeds into the materials calculator in BREEAM. Achieving a high rating in these systems can increase the rental and resale value of commercial properties.
Obligations
At present there is no legal obligation on engineers to consider the environmental impacts of the materials being specified. To date this has been a client driven task or limited to the moral obligations of companies. However, the EU Commission’s Communication on Integrated Product Policy encouraged member states to draw up publicly available national action plans for greening their public procurement across different sectors.
The publication of Green Public Procurement guidelines for the Irish construction sector will change the way materials are selected by the specifier and will require suppliers to assess and publish the environmental impacts of their products. It will mean engineers will have to take due consideration to the environmental impacts of their choice of construction materials.
As we await the imminent publication of Irish GPP guidelines, guidance is available from 'Green Public Procurement Criteria for Design, Construction and Management of Office Buildings' draft document published in December 2014 by the European Commission. This document relies heavily on life cycle assessment and Environmental Product Declarations as the best method of material assessment.
Conclusion
It is estimated that 90 per cent of the embodied carbon of concrete is attributed to the cement - consequently replacement with 50 per cent GGBS offers an immediate 52 per cent saving and a quick win for carbon reduction.
Building sustainably is of critical importance as the construction industry starts to recover and material selection will play a big part in achieving this. The specification of one material, GGBS, is a quick win for carbon reduction already accommodated by I.S EN 206 and a simple change that can be made in most construction projects to lower embodied carbon.
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Susan McGarry[/caption]
Ecocem has a complete technical service offering to help promote the use of GGBS and assist on all stages of a project from design, environmental assessment, lab testing and on site assistance. We have a team of chartered engineers and concrete technologists to help with any technical queries around GGBS use.
Susan McGarry, environmental manager and LEED Green Associate can provide assistance on GGBS concrete in LEED and BREEAM projects. If you would like to learn more about GGBS, Ecocem is a registered training provider with Engineers Ireland and can deliver a registered CPD to your company. www.ecocem.ie