Cement 2 Zero (C2Z) has officially launched in the UK this week. The project is an industrial scale pilot of the Cambridge Electric Cement (CEC) process. The Materials Processing Institute will lead on this stage with two-year funding of around Euro7m provided by UK Research and Innovation (UKRI). Partners include the University of Cambridge, Atkins, Balfour Beatty, Brewster Brothers, Celsa Group, Day Aggregates and Tarmac.

CEC’s method uses recycled concrete paste in place of lime-flux in steel recycling. Slag is formed as the steel melts and this is then used in place of clinker to make more cement. This way of making cement cuts out the decarbonisation of limestone step from conventional clinker production. If renewably-sourced electricity is used to power the heating and grinding parts of manufacture, then cement production in this way could potentially cut out most of its CO₂ emissions. The first phase of trial melts by C2Z will be conducted by the Materials Processing Institute using a 250kg induction furnace and this will be scaled up to 6t in an electric arc furnace (EAF). Later, industrial scale melts will be tested in Celsa Steel's EAF in Cardiff, Wales.

CEC is taking a similar approach to HeidelbergCement with its research into using recycled concrete paste. However, HeidelbergCement says it is using the paste to help capture CO₂ in an enforced carbonation step it is testing at cement plants. It too though wants to create a secondary cementitious material (SCM) afterwards. There are also links here to construction and demolition waste and electric cement kilns as covered by Global Cement Weekly previously. The latter is different with regards to what CEC is doing because it is recycling concrete waste to produce an SCM (slag) rather than using an electrically powered kiln to make clinker from limestone. Coolbrook, VTT and the like have had to build electric kilns effectively from scratch or adapt technology from elsewhere for their approaches whilst CEC appears to be about to use existing EAFs in its industrial scale pilot.

Figure 1: Projection of how the Cambridge Electric Cement production process could be used at scale in the UK. Source: UK FIRES. Click to view larger version.

CEC’s forecast of how its process could be used at scale in the UK can be seen above in Figure 1. If the majority of the country’s steel scrap was recycled in this fashion each year then 2.4Mt/yr of CEC cement could be produced. This would represent a quarter of the c10Mt of cement sales reported by the MPA in 2021. Assuming the EAFs were powered by renewables then this could reduce the cement sector’s CO₂ emissions significantly. Although it would still leave the industry looking for other decarbonisation routes for the other three-quarters of cement demand.

C2Z and CEC offer a novel spin on cement production by recycling concrete waste, using an electrical heating step and dodging the process emissions associated with normal ordinary Portland cement (OPC) clinker production. If it did progress to a commercial stage then it would see a continued relationship between steel and cement producers. Currently this is mainly centered around iron and steel slag usage as a SCM. One point of interest here would be how much higher levels of steel recycling and a process like CEC being used regularly would affect existing slag usage as an SCM. It doesn’t look like CEC could solve the cement sector’s CO₂ emission problem all on its own but it could certainly make a difference if it progressed to a commercial stage. As ever with cement sector decarbonisation there appear to be a range of options available to producers.