Low Carbon Precast Concrete

We attended Flood & Coast this year and exhibited a small L wall that was cast with our low carbon 80% GGBS mix.  GGBS (ground granulated blast slag) is a cementitious material which can be used to replace Portland Cement.  Our source of GGBS has a carbon footprint of 32kg CO2 eq/t compared to Portland Cement at 884kg CO2 eq/t.

This mix has been rated A++ using the recommendations published in the Low Carbon Concrete Routemap.  The mix is classified as a CEM IIIB cement combination as per BS 8500-1 Table A6.

We are now using this method of carbon rating to asses the environmental impact of our concrete mixes right across the company.

Basalt fibre reinforcment

Basalt rebar is used as an environmentally friendly alternative to steel.  Basalt is naturally resistant to attacks from alkali, water or chemical – making it perfect for use in the marine environment where corrosion is continuous concern.  Basalt reinforced structures may be designed to the code ACI 440 which allows for greater design crack widths as the durability risk to the unit is reduced.

Using non-ferrous reinforcement in coastal locations, allows the cover to reinforcement to be reduced hence reducing the overall section size.  The unit design with basalt fibre rods in place of steel reinforcement which has reduced the unit volume by 25%.  Basalt rebar is also significantly lighter than steel rebar while retaining greater strength properties.

Less concrete = Less carbon: Thinner design means that less concrete is needed, reducing the overall carbon footprint of the unit.

Reduce transport carbon: Thinner units are lighter and more can be fitted on a lorry for transport, meaning less loads are needed – again reducing the overall carbon footprint of your project.

By using basalt rebar as opposed to steel we are able to design smaller, lighter units which allow for a significant carbon reduction in both production and transport – without compromising structural integrity.

Assessing the Carbon Footprint of Products and Mixes

In September 2022 Moore Concrete published Environmental Product Declarations for:

• Bebo Arches
• VSOL Retaining Panels
• Bunker retaining walls
• L shaped cantilever retaining walls
• Box Culverts
• Suspended flooring for cattle

This exercise enabled us to map our processes and quantify the carbon emissions generated across the whole year 2021.  Using this 3rd party accredited information, we are able to accurately assess the carbon footprint of products produced at our facility and use this information to inform choices during the design process.

Comparing the basalt and steel reinforced walls

Using the above mentioned indices, we have determined that the cradle to grave carbon footprint for a 1m length of basalt reinforced wall is 34kg CO2 eq compared to 48kg CO2 eq for a steel reinforced wall.

The differences are highlighted below:

Due to the significantly lighter basalt reinforcement and the reduced section size for the wall, it can be seen that using basalt reinforcement can achieve a reduction in carbon footprint for this unit of 30%.

Challenges and Opportunities

Moore Concrete are continuing to develop the mix design of their 80% GGBS mix to improve workability and finish.

80% GGBS mixes have a long curing period before formwork can be stripped, this needs to be accommodated within the works programme.

The basalt reinforcement used in this wall has been supplied by Orlitech who are in the process of achieving BBA approval for their mesh and rod products.

Our 3 year Knowledge Transfer Partnership with Queens University Belfast is underway to further research and implement other low carbon options in precast.

Follow us on LinkedIn to hear more about our Net Zero Pathway activities.