Designing waste-derived materials to produce sustainable concrete – a potential mine for the future?
CIWM Early Careers Ambassador, Dr Sadish Oumabady & Dr Rory Doherty FCIWM spotlight their research project that provides a circular solution to help two of the most polluting industries, agriculture (poor water quality) and construction (carbon emissions).
Biochar based concrete
The project in Queen’s University Belfast is an industry-led collaboration funded through the Centre for Advanced Sustainable Energy (CASE) with Agri-Food Biosciences Institute (AFBI), United Renewables, Mineral Products Association NI, Mannok Build, Breedon Group, Irish Cements and Northstone NI as research partners.
The root cause
Agricultural intensification and the subsequent spreading of slurry onto the land caused run-off from non-point sources that allowed nutrient leaching (primarily Nitrogen and Phosphorus) into catchments and Lough Neagh.
Lough Neagh is the largest freshwater lake on the island of Ireland and in the British Isles and supplies drinking water to about 40.7% of Northern Ireland’s population.
Eutrophication of the lake happened in 2022 causing a major environmental issue affecting water companies, the eel fishing industry, tourism and recreational users of the Lough, as it is likely to happen again and again.
This triggered an outcry from the local population and the Northern Ireland government is now rapidly seeking management strategies.
A mitigation strategy in progress
The simplest solution to help Lough Neagh is to prevent farm waste (slurry) from being returned to land.
Valorising the farm waste through Anaerobic Digestion (AD) promotes renewable energy generation (biogas) and the nutrient rich slurry (digestate) is derived as a byproduct.
The subsequent usage of dried digestate for syngas production through pyrolysis yields biochar, contributing to Biomass Carbon Capture and Storage (BCCS). Biochar production from AD digestate contributes to the reduction of sector’s emission between 54 and 160kt CO2e.
With the current electricity output of 213 GWh, the AD sector in NI produces 110kt of digestate dry matter and this could yield 32kt of biochar upon pyrolysis.
Considering the UK Climate Change Committee’s 2050 biomethane target for NI, an estimated 184kt of biochar could be produced annually.
Industrial scale applications of biochar as an energy source, as a filter for wastewater treatment and as a soil amendment are well established.
Our initial analysis of the elemental composition of the digestate biochar showed that it was over 55% carbon but also confirmed the presence of significant quantities of essential components for cementitious mineral formation in concrete manufacturing.
The construction industry is responsible for up to 8% global CO2 emissions, in Northern Ireland it emits up to 900kt of CO2e.
The 2024 requirement by the Irish government for low-carbon cement mandate a minimum 30% reduction in clinker use demonstrate the time is right to scale up the biochar production for use in the construction industry.
Biochar production and its usage in concrete manufacturing provides tangible benefits in terms of emission reductions (potentially up to 75%), volume shrinkage and helping achieve the UK’s net zero target by 2050.
How our work plan contributes
Utilising locally available materials to produce biochar serves as a decentralised solution to valorise waste and an effective resource consumption tool.
We have currently optimised the proportion of biochar in concrete for non-structural precast mixes, such as roof tiles, paving stones, facades, curbing, and barriers, etc.
The resultant low-carbon concrete products have comparable benefits in terms of aesthetic quality, durability, faster curing, and facilitate industrial mass production due to the supplementary cementitious properties of the biochar.
Our lab scale tests have demonstrated evidence of self-repair capabilities and early strength attainment of biochar-concrete mixes in a factory environment.
Additionally, biochar imparts a black shade to the final products ideally replacing the need of an imported black pigment.
Designing biochar-based concrete products could serve as an initiating point for the reduced dependency on Carbon black imports to the UK which was valued at ~£65 million in 2023.
This could benefit the local economy through lowered VAT/customs/excise duties and help the industries prepare for the UK Government’s plan to introduce CBAM (Carbon Border Adjustment Mechanism) in 2027 on GHG emissions from imports.
The way forward
With one of our industrial partners, we have performed factory trials on optimised mix proportions that still adhere to industry standards.
This promoted an advancement in the Technology Readiness Level (TRL) of our research and ensured its operation readiness.
Biochar concrete cubes and roof tiles from factory trials
The workflow and baseline work for the Life Cycle Analysis (LCA) of biochar-concrete mixes and industrial trials will deliver an improved aspect of techno-economic capabilities from the project outcomes.
This eventually creates a circular economic pathway for wider industrial acceptance and a global audience to achieve sustainability.
A curiosity
Aside from the above-mentioned work, a curious question arises in using this nutrient rich biochar to make sustainable concrete. Could this be mapped digitally using Building Information Modelling (BIM) systems and be used to mine nutrients in the future as part of design for deconstruction?
