• 1. Good thermal mass- when combined with good architectural design and allow air changes to the exposed concrete surface, the transfer of heat throughout the building would provide more stable temperatures during the day whilst preventing overheating. [¹]

• 2. Aesthetics - Concrete planks can be left exposed and finished off neatly for industrialised looks, which in turn would create extensive savings in gypsum materials (Resulting in less material needed to be transported to the site, thus less CO₂ emissions during construction, and less material used) [¹]

• 3. Hollow Core benefit- the hollow cores provide the benefit of serving as channels to pass services, preventing chasing, unnecessary lengthy cables, etc… [¹]

• 4. Form work – concrete planks do not require formwork to be set-up. [¹]

• 5. Reinforcement – prestressed planks & prestressed predalles work out at a reduced thickness & use much less steel as compared to the traditional cast in-situ ceiling. [¹]

• 6. Speed of construction – A general benefit of precast elements, is that they expedite a projects time-frame. [¹]

• 7. Re-usability – Hollow concrete planks can potentially be re-used once a building’s life span expires. [¹]

• 8. The role of the structural engineer, as part of a multi-disciplinary design team, is to develop structural solutions that contribute to reducing energy consumption, and to deliver buildings with a long life and a low embodied carbon footprint. The embodied carbon of the construction of the building (excluding fit out), spread over a 60 year design life, is between 6 to 15 kgCO₂e/m² on an annual basis. Taking a typical value of 5 kgCO₂e/m² for a typical office building and assuming the structure (primarily steel and concrete) represents 50% of this, then the structure accounts for an annual 2.5 kgCO₂e/m² , with the other 50% approximating to the annual energy consumption of the building. If the structural engineer can, through clever design and material specification, reduce this by 30% then the saving is 0.8kgCO₂e/m². [²]

• 9. Annual energy consumption – operating carbon footprint. Real energy consumption is hugely variable and depends on: Building type. Thermal performance of the fabric. Typical operational energy and carbon figures for buildings. Type and efficiency of heating, cooling, ventilation, lighting, domestic hot water and other systems. Equipment plugged in. Hours of operation. Average climate that year (warmer or colder). Control strategy. The expectations and behaviour of the building occupants. [²]

• 10. Embodied versus operating carbon The embodied carbon for new construction of office buildings should typically tend to be between 500 and 900 kgCO₂e/m² of GIA (Gross internal area). This is equivalent to five to ten years of the CO₂e emissions due to the energy consumption. The 10 years is for an office building with the 5 years for a lower grade building. [²]

• 11. Embodied versus renewables The contribution that onsite renewables can make to reducing the whole carbon footprint of a building varies significantly depending on the building type and configuration, including the area of roof available for solar panels. But for example, a ten-storey 10,000m² office building with a roof full of photovoltaics could reduce annual carbon emissions by around 2 kgCO₂e/m². [²]

• 12. Besides drinking water, concrete is the most used man-made material on earth, with 14 billion m³ produced each year. As a result, the production of cement, the active binding agent in concrete, accounts for around 7% of global CO₂ emissions. While concrete production emissions arise from a range of sources, cement production is responsible for almost 60% of the embodied carbon in reinforced concrete. Thus, with 2050 rapidly approaching, action must be taken to reduce emissions and realise net-zero commitments. To address this, many companies are developing lower carbon concrete technologies. However, publicly available information about these technologies is often limited and inconsistent, making it difficult to draw comparisons with conventional concrete. [³]

• 13. The 3C’s of Innovation in Low-Carbon Concrete, examining decarbonising solutions across the clinker, cement and concrete production stages: It is not expected, or recommended, that engineers should try to provide detailed specification clauses to optimise concrete for carbon. Rather, this optimisation should be delivered by the supplier or an independent project concrete technologist if appropriate, to incorporate the construction requirements. Thus following collaboration and discussion with the engineer and contractor as early as possible, it will not be possible to achieve carbon savings in all concretes but discussions with concrete suppliers to optimise carbon of conventional concrete can lead to immediate savings of between 5 - 15%. [³]

• 14. The following tables 1-3 show the embodied carbon for each concrete plate predalles & hollowcore prestressed concrete plank produced by GMF. The embodied carbon is measured per square meter on plan. The values below only account for the production stage of the precast elements (A1-A3). These stages are identified as: A1: Supply of raw material A2: Transport of raw material to manufacturing facility A3: Manufacturing of the product (predalles or hollow prestressed concrete planks)

• 15. The following table 4 is a comparison of the GMF products as compared to utilising solid reinforced concrete comparing the embodied carbon. The embodied carbon values to be shown in the table below are calculated from the supply of raw material up till the construction on site (A1- A5). A1: Supply of raw material A2: Transport of raw material to manufacturing facility A3: Manufacturing of the product (hollow prestressed concrete plank) A4: Transport of the manufactured product to the construction site A5: Construction and installation process including any wastage that might occur on site

• Prestressed hollow core slabs are supported at each end with a reinforced C30 sulletta having a height of 1 course (filata) and a width of 9”, reinforced with 4 T16 steel bars. This is included in the embodied carbon.

• Embodied carbon for cast in-situ concrete slabs includes the formwork required.

• Waste factors included are: - Predalle: C25 concrete topping - Prestressed hollow core slabs: C30 concrete, T16 reinforcement and C30 grouting between the planks - Cast in-situ: C25 concrete, high yield reinforcement and formwork

• An advantage of using precast elements over cast-in-situ concrete is that generally, precast elements have an embodied carbon varying between 13% - 35% of cast-in-situ concrete. On spans above 6m, precast elements can be circa 35% cheaper when compared to cast-in-situ concrete.

References

• Brooker, O. (2009) Concrete Buildings Scheme Design Manual: A handbook for the istructe chartered membership examination, based on Eurocode 2. Camberley: The Concrete Centre, part of the Mineral Products Association.

• Gibbons, O.P. et al. (2022) How to calculate Embodied Carbon. 2nd edn. London: The Institution of Structural Engineers.

• Concrete Technology Tracker (2024) The Institution of Structural Engineers. Available at: https://www.istructe.org/resources/guidance/concrete-technology-tracker/ (Accessed: 17 April 2024).