Highly alkaline (pH 9-13) drainage waters can result from the weathering of by-products from globally important industries such as steel manufacture, cement production and electricity generation. The extreme alkalinities of the waters reflect the highly basic nature of the source residues which include lime-rich steel slags and fly ashes. These residues have traditionally been landfilled or stockpiled, historically with little or no control of leachate migration. Drainage waters leaving such disposal sites are of such high pH that they absorb carbon dioxide from the atmosphere and precipitate solids (predominantly calcite: CaCO3) so prolifically that streams and rivers are smothered to the point where little or no aquatic life can be sustained in the waters. In addition, elevated concentrations of metals/metalloids (especially arsenic, chromium, selenium and vanadium) and high sulphate loadings can be of significant environmental concern, and a barrier to compliance with statutory water quality standards such as those set out in the EU Water Framework Directive. Established treatment options for alkaline leachates, such as acid dosing, active aeration and/or recirculation of leachates over stockpiled residues, are very expensive. Given that generation of high pH leachates is now known to continue for many years after the operational life of the associated industrial operations, sustained treatment by these traditional methods is rare, and untreated leachates can produce a legacy of persistent environmental damage. Recent NERC research has highlighted the effectiveness of natural wetlands in lowering the pH and alkalinity of these drainage waters. Microbial respiration in the organic-rich wetland substrate appears to accelerate calcite precipitation, a process which lowers alkalinity. These calcite-rich solids can also serve as a sink for some potentially toxic metals. The work proposed in this study aims to commercially develop constructed treatment wetlands as a low-cost, environmentally sensitive passive option for treating highly alkaline waters. Passive treatment systems are characterised by an initial capital outlay but low running costs for infrequent (albeit regular) maintenance. In addition, constructed wetlands create valuable wetland habitat, provide a useable green public space and integrate well with the wider ecological restoration of post-industrial landscapes. This research will develop some of the technical components of constructed wetlands to ensure effective pollutant treatment with regard statutory environmental quality standards, in liaison with one of the project partners: the Environment Agency. Economic feasibility will also be assessed through quantifying calcite precipitation rates and establishing relationships for sizing and costing treatment systems based on water flows and chemistry. This will be carried out through the construction and monitoring of a pilot wetland system at a site belonging to project partner Corus. The principal focus of the work will however be to engage with potential industrial end-users of the treatment technology and develop opportunities for commercial exploitation. While the technology is unlikely to yield any formal intellectual property rights, the technical know-how for successful design of these treatment systems is a valuable asset. The HERO Group at Newcastle University has a strong track record in commercially-exploiting this know-how for the design of novel treatment systems for other post-industrial pollution sources. End-user engagement will come through various avenues, but will be principally undertaken by project partner the Mineral Industry Research Organisation (MIRO) who count in their membership a range of aggregate and process companies who own problem sites. Workshops and meetings convened with potential end-users will be used to demonstrate the technical capabilities of treatment wetlands and encourage industrial uptake of the technology.

177 million tonnes of virgin aggregates, 15 million tonnes of cement and 2 billion bricks were used to build houses, civic and commercial buildings, roads and railways, etc, in the UK in 2016. Meanwhile, 64 million tonnes of waste arose from construction and demolition. Materials from construction and demolition are mainly managed by down-cycling with loss of the value imparted to them by energy-intensive and polluting manufacturing processes; for example, high value concrete is broken down into low value aggregate. Environmental damage is associated with the whole linear life cycles of mineral-based construction materials, and includes scarring of the landscape and habitat destruction when minerals are extracted from the earth; depletion of mineral and energy resources; and water use and emission of greenhouse gases and other pollutants to air, land and water, during extraction, processing, use and demolition. It is important to take action now, to return materials to the resource loop in a Circular Economy, and reduce the amount of extraction from the earth, as the amount we build increases each year. For example, the UK plans spend £600 billion to build infrastructure in the next decade. The UKRI National Interdisciplinary Circular Economy Research Centre for Mineral-based Construction Materials therefore aims to do more with less mineral-based construction materials, to reduce costs to industry, reduce waste and pollution, and benefit the natural environment that we depend on. There is potential for mineral-based construction materials to be reused and recycled at higher value, for example, by refurbishing rather than demolishing, or by building using reusable modules that can be taken apart rather than demolished, so all the energy that went into making them isn't wasted. It may also be possible to substitute minerals from natural sources by other types of mineral wastes, such as the 76 million tonnes of waste arising from excavation and quarrying, 14 million tonnes of mineral wastes that come from other industries, or 4 billion tonnes of historical mining wastes. We can also be more frugal in our use of mineral-based construction materials, by designing materials, products and structures to use less primary raw materials, last longer, and be suitable for repurposing rather than demolition, and using new manufacturing techniques. First, our research will try to better understand how mineral-based construction materials flow through the economy, over all the stages of their life cycle, including extraction, processing, manufacture, and end-of-life. The Centre will work to support the National Materials Database planned by the Office of National Statistics, which will capture how, where and when materials are used and waste arises, so that we have the information to improve this system. We will also study how any changes we might make to practices around minerals use would affect the environment and the economy, such as greenhouse gas emissions, costs to businesses, or jobs. Second, we will work on technical improvements that we can make in design of mineral-based products and structures, and in all the life-cycle stages of mineral-based construction materials. Third, we will look at how changes in current business models and practices could support use of less mineral-based construction materials, such as how they might be able to move more quickly to new technologies, or how they might use digital technologies to keep track of materials. We will explore how the government can support these changes, and how we can provide education so that everyone working in this system understands what they need to do. In the first 4 years of our Centre, 15 postdoctoral researchers will gain research experience working in the universities for 2y and will then work with an industrial collaborator for a year, to implement the results of their research. More than 20 PhD and 30 MSc students will also be trained in the Centre.

The construction industry is heavily reliant on production of Portland cement and, in the UK alone, 12 MT of cement is produced per annum. Depending on the specific production processes used, manufacture of 1 kg of Portland cement produces 0.7 kg - 1.0 kg of CO2. Many sources suggest that cement manufacture accounts for up to 5% of the world's CO2 emissions. There is an urgent need for a step change in technology to achieve the radical reductions in carbon emissions necessary to stabilise climate change. Many different approaches can be used to mitigate the effects of cement production. Considerable improvements have been made with kiln efficiency and waste fuels are now commonly used. However, during the production process, calcium carbonate decomposes into calcium oxide and carbon dioxide. This calcination reaction causes over half the CO2 emissions from the production process so there is limited scope for improvement. A number of initiatives have examined cement alternatives or replacement materials to reduce the Portland cement requirement of concrete. "Novacem" is an innovation from Imperial College London that made significant progress on a radical alternative to calcium-silica based cements based on magnesium oxide produced from magnesium silicates. Although these developments are encouraging, this process would require entirely new plant and with world production of cement at 2.5 billion tonnes per annum, this technology will take a long time to make a significant impact. Other initiatives such as "Ecocem" in Australia are based on cement replacement materials. A considerable amount of research and development of cement replacement materials has been carried out but replacement levels have specified maximum limits in current standards to ensure concrete behaviour does not differ significantly from Portland cement concrete. Fly ash is a by-product from coal-fired power stations which can be used as a partial cement replacement in concrete. It reacts with calcium hydroxide (produced during hydration of Portland cement) to form stable calcium silicate and aluminate hydrates - the pozzolanic reaction. Fly ash typically replaces 20% - 35% of the cement content within a concrete mix but there are obvious environmental benefits for incorporating higher proportions of cement replacement. However, the pozzolanic reaction between the fly ash and calcium hydroxide occurs quite slowly, which increases setting times and reduces the rate of strength gain of the concrete. This can cause problems associated with surface finishing, delayed removal of formwork etc. which can increase the cost and duration of a construction project. Researchers have consistently found that the higher the proportion of fly ash, the lower the early age strength of the concrete. Therefore, improvement of early age strength of fly ash concrete, particularly when incorporating high volumes of fly ash, warrants investigation. This project has been developed by Coventry University after detailed discussions with key industry figures representing cement, fly ash and admixture suppliers and concrete users. A comprehensive experimental programme will investigate the use of mineral activators to reduce setting times and enhance early age strengths of HVFA concretes. Cement kiln dust is a by-product of the cement manufacture process and its high alkalinity makes it a suitable activator of fly ash. Waste gypsum is also available in abundance and has been shown to increase the rate of strength gain of fly ash concrete. The aim of this study is to incorporate these by-products into HVFA concrete mixes to give comparable early age performance to equivalent Portland cement concretes. The effect of intergrinding the cementitious materials and activators will also be assessed. Also, a range of fly ash sources will be investigated to account for variations in chemical composition of the fly ash, which have been shown to affect concrete strength.