Manufactured Limestone (M-LS) carbon negative aggregate creates the opportunity for genuine low carbon or carbon negative construction. M-LS can be used in a variety of construction applications including in the manufacture of medium density building blocks or used in low strength concretes. O.C.O Technology has developed a versatile process – Accelerated Carbonation Technology (ACT) – that utilises carbon dioxide gas as a resource to treat and valorise a wide range of wastes. ACT is a genuine carbon capture and utilisation (CCU) process with significant volumes of carbon dioxide being permanently captured. Many residual materials react naturally with carbon dioxide. If the conditions are carefully controlled, this natural reaction can be accelerated to take place in minutes rather than years. This results in the formation of calcium carbonate (limestone) and other very stable complex compounds.
The ACT process has been applied in the UK to the treatment and recycling of ‘fly ash’ residues from modern Energy from Waste (EfW) facilities. Known as air pollution control residues (APCr) the material is a hazardous waste and historically has been treated and landfilled. The ACT process allows the recycling of APCr into an aggregate product that is used in the manufacture of building blocks. The quantity of APCr in the UK is increasing due to the growth in EfW facilities, so the deployment of the ACT is opportune as it reduces the requirement for landfill and provides a recycling solution. ACT not only recycles the residual material, it also captures CO2 in the process to create a carbon negative aggregate. The aggregate has a carbon footprint in the region of -40 to -50 kg CO2 eq per tonne of aggregate produced. In the financial year ending September 2020, O.C.O treated 132,000 tonnes of APCr to create 316,000 tonnes of aggregate, permanently capturing approximately 15,000 tonnes of CO2.
The M-LS is used used in multiple applications in the construction industry. Predominantly used in the manufacture of medium dense blocks for builders alongside being incorporated into 6 series materials and as a blend in Type 1. Extensive research and R&D into using the aggregate in concrete and foam mix asphalt applications is currently taking place. By using the material as a blend, it allows the quarries to control the utilisation of their virgin aggregates in a more sustainable manner.
M-LS offers a saving of -44kg per ton of CO2. This has been independently verified and certificated to a PAS 2050 standard.