Recent studies have reported that 50% of repaired concrete fails again after a few years (25% within 5 years of repair, 75% within 10 and 95% within 15), resulting in recurring and costly interventions, material consumption and operational carbon footprint. New strategies, emphasizing zero- or minimum-maintenance, are vital to reduce the sector's operational carbon footprint and meet the UK net-zero target. Self-healing cementitious composites (SHCC) are an interesting alternative to conventional concrete. They contain mineral or biologic agents that react with water percolating through cracks to produce compounds that seal openings and heal the material before significant damage occurs. The dominant approach in the literature uses a uniform deployment of self-healing agents in a significant volume of the components due to uncertainties associated with the production process and crack positions. Nevertheless, research has pinpointed several issues associated with the implementation of self-healing materials in the construction sector and, among them, the initial investment in material cost. Re3DSkin proposes a shift in the deployment strategy and functionalisation of components - using modern methods of construction - to enable selective deposition of self-healing agents in a superficial layer with a variable concentration tailored to the likelihood and degree of cracking in each portion of the component's surface. This surface layer acts as an optimised regenerative skin to enhance the asset's performance. 3DP technology can offer the required deposition control and accuracy to optimise the layer's mesostructure and thickness, facilitating variable placement via in-line admixture addition. Re3DSkin's broad scientific objectives are to: (1) adapt the 3DP process for deposition of surface layers with variable self-healing agent concentration, and with enhanced distribution precision and accuracy; (2) understand the influence of 3DP layer thickness and variable deposition on the self-healing mechanism and efficiency; (3) compare the self-healing mechanism and material efficiency of components with a layer of variable agent concentration to equivalent components with uniform self-healing agents across the entire volume and (4) evaluate and demonstrate - in the lab and industry - the feasibility of the novel strategy via production of the world's first full-scale building component with this solution. Re3DSkin will enhance the resilience of newly built and existing assets by extending service life and address the UK's critical vulnerability of ageing assets. Developed solutions could reduce labour-intensive repair, maintenance and dependence on increasingly scarce skilled labour. Re3DSkin's findings can also reduce the use of carbon-intensive materials in SHCC and overall demand for repair materials during the whole-life of assets. Re3DSkin outcomes will contribute to a more productive, more sustainable and more internationally competitive construction sector.

The Government's Industrial Strategy highlights the need for the construction industry to embrace digitally-driven, automated manufacturing if it is going to deliver the planned infrastructure development, building and renovation of the built environment. The group funded through this award understands this need and envisages an industry that routinely deploys digitally-driven, off-site-manufacturing technologies to deliver customised and unique precision components to enable the rapid, just-in-time assembly of the built environment. Seamless digital workflow and accurate process simulation will reduce the time from design to product from weeks to hours, delivering buildings faster. It will facilitate the optimisation of components, removing unwanted material (reduced resource use and embedded CO2), designing out interfaces and reducing assembly time and complexity, both during installation and at end of life. 3D Concrete Printing (3DCP) is a digitally-driven, off-site manufacturing technology that is establishing itself worldwide as a viable manufacturing process, but its potential beyond aesthetic objects is fundamentally limited by the manufacturing tolerances achievable. The work undertaken by this group will develop the next generation, Hybrid Concrete Printing (or HCP), technology that uses 3DCP to create a near-net-shape (an object slightly larger than the desired object) and then uses subtractive process (cutting, milling and drilling) to remove a small amount of material to create the net-shape - the desired object to sub-millimetre precision. HCP technology will enable the intelligent integration of building performance and energy production and storage technologies, freed from traditional constraints on form and finish. This will unlock the potential for accurate interfaces and assemblies and, hence, open the gateway for a revolution in design and manufacture of buildings and the wider built environment. The team will develop research that answers three central goals of the Industrial Strategy Challenge Fund's Transforming Construction initiative: - Designing and managing buildings: We will develop and promote new design tools and design capabilities for UK design practise that will create globally marketable expertise; - Constructing quality buildings: HCP, a digitally-driven off-site manufacturing technology, will realise greater precision in manufacture than is currently possible, enabling repeatable, high quality components to be manufactured with a much shorter lead-time; and, - Powering buildings: The technology gives the designer close control of surface finish and component geometry, enabling them to add value through function and to design in order to integrate other active components as part of automated assembly.