The engineering and construction sector is the largest global consumer of resources and raw materials. The carbon emissions associated with the product of construction materials (embodied carbon), particularly cement and steel, can account for 40-50% of the carbon footprint of a building. The application of circular design strategies in the construction sector has the potential to increase our resource productivity alongside emissions reductions across the value chain.
While Ireland does not have a specific strategy for the circular economy in the construction sector, there have been some developments in recent years towards more general advancements regarding more sustainable construction practices and the use of low carbon construction materials. In this post, we looked at the practices of an Irish company that uses waste by-products in the manufacturing of construction materials, Ecocem.
The material produced by Ecocem is known as GGBS (Ground Granulated Blastfurnace Slag) and is a by-product of the iron industry. The production process comprises the rapid cooling of blastfurnace slag by adding water which granulates the material and then refining the granulated material in a milling plant, producing a fine cementitious powder.
Embracing the concepts of the circular economy, Ecocem’s up-cycling of materials which would otherwise go to landfill contributes to the maintenance and value of materials in the economy, reducing emissions and increasing competitiveness in Ireland.
The GGBS produced by Ecocem, and other Irish companies, has high performing technical properties compared to traditional Portland cements. These properties include higher strength gains, increased service due to enhanced durability which leads to longer times to first repair and replacement. In addition to the enhanced technical qualities there are benefits of higher environmental performance. GGBS is commonly specified in construction projects procured in both the private and public sectors. Ecocem GGBS is specified in a diverse range of applications such as precast products, ready-mix concrete, mining industry and soil stabilisation.
Verification and life cycle assessment
Ecocem were one of the first companies in the Irish construction sector to conduct a product life cycle assessment and establish an independently verified Environmental Product Declaration (EPD).
EPDs are the life cycle assessment methodology used in the EU to establish and communicate the environmental impacts of construction products or materials. EPDs are developed in accordance with EN15804 “Sustainability of construction works – Environmental product declarations – Core rules for the product category of construction products” and are harmonised across the EU.
There are 11 impact categories which include, Global Warming, Acidification, Eutrophication, Human Toxicity, and Ecotoxicity.
The Ecocem EPD is third party verified and covers the life cycle from the quenching process of the blastfurnace slag to the production of the final product.
This accounts for all emissions and energy consumed in each stage of extraction, production and shipping of materials from locations across Europe to Dublin, up to the point where it leaves the Dublin milling plant. This is described as a cradle-to-gate life cycle assessment in that it does not include all end use applications.
EPDs can be beneficial in terms of supporting Green Public Procurement as well as changing behaviour across sectors. EPDs aim to be a transparent communication tool that limits the potential for greenwashing. Importantly for Ecocem, EPDs also align with industry standard green building rating systems such as LEED, BREEAM and the Home Performance Index (HPI).
Challenges
Clearly cement has a number of significant challenges with regards sustainability. The cement sector alone accounts for 5% – 8% of all global CO2 emissions. This surprises many as the aviation industry accounts for 2% of global emissions but maintains a higher public interest.
A small number of stages in the production of cement account for the majority of emissions. These include the use of fossil fuels to achieve temperatures of approximately 1450℃ in kilns and breakdown of the key constituent material, limestone.
There are technically viable interventions to reduce the impact of the sector and these can be taken with relative ease and comparatively low cost. This includes upgrading or retrofitting old kilns to improve thermal efficiencies. The Carbon Disclosure Project estimates that the retrofitting of kilns could reduce the energy demand and related emissions by two-fifths.
However, in saying this, substitute cementitious materials provide an immediate opportunity to reduce environmental impacts. An essential constituent of Portland cement is a material called ‘clinker’.
This is the primary source of pollutants in the Portland cement production process. The less clinker included in the final cement mix means there is less resulting emissions.
The most common cement mix used is CEM II. This produces approximately 750 Kg of carbon for every tonne produced.
GGBS on the other hand produces 42 Kg of carbon for every tonne produced. GGBS is not typically used as a standalone material but is blended or mixed with Portland cement to achieve a final concrete mix. Under the concrete specifications in Ireland (I.S EN 206-1), up to 70% of GGBS can be blended with Portland cement. GGBS reduces significantly the amount of clinker required in the mix.
A blend of 50% GGBS and 50% Portland cement is common. Ecocem’s strategy has been to provide GGBS to the concrete producers, who in turn use this cementitious material to reduce the amount of Portland cement (clinker) in the final concrete mix, which in turn significantly reduces the environmental impacts of the concrete mix.
A common question regarding GGBS is in relation to supply risks. To date there have been no supply issues for Ireland. Ecocem, for example, have long term supply contracts agreed with the primary steel producers in Europe.
The production of steel tends to rise and fall in a similar manner as the construction sector, both of which are strongly connected with economic activity. For example, in 2012, 23 million tonnes of slag was produced in Europe and only 60% used. At the height of the ‘Celtic Tiger’ construction era, Ireland used approximately 7 million tonnes of cement per annum. As such, Ecocem is well placed to continue growing its supply into Ireland.
This article was originally published in NESC’s Moving Towards the Circular Economy in Ireland.
Building Life Cycle Assessment and Environmental Product Declarations will be extensively discussed at Re-Source 2018 conference on 21st June.
