A new CCU composite structure with a novel demountable connection towards CO2 sequestration and material recyclability.

Project Information

CCU Structure

Grant agreement ID: 101105930

DOI

10.3030/101105930

Project closed

EC signature date 25 October 2023

Start date 1 March 2024

End date 28 February 2026

Funded under

• Marie Skłodowska-Curie Actions (MSCA)

Total cost

No data

EU contribution

€ 199 694,40

Coordinated by

AALTO KORKEAKOULUSAATIO SR
Finland

Periodic Reporting for period 1 - CCU Structure (A new CCU composite structure with a novel demountable connection towards CO2 sequestration and material recyclability.)

Reporting period: 2024-03-01 to 2026-02-28

Summary of the context and overall objectives of the project

The construction sector faces two closely linked challenges: reducing the carbon footprint of building materials and improving the reuse of structural components at the end of service life. Conventional cement-based materials are associated with high embodied carbon, while many steel–concrete composite systems rely on permanent connections that make non-destructive disassembly difficult and limit high-value reuse. In the context of Europe’s transition towards a low-carbon and more circular built environment, there is a clear need for structural solutions that address carbon reduction, material circularity, and reliable mechanical performance. This project responded to that need by developing a new CCU composite concept that integrates a CO2-mineralising cementitious component with a practical demountable connection.

The overall objective was to establish the scientific and technical basis for a reusable steel–cementitious composite system capable of both CO2 storage and disassembly for reuse. To achieve this, the project developed strain-hardening magnesia-based cementitious slab components, designed a novel bolt–wedge demountable connection to improve slip resistance while preserving demountability, and investigated how material gradients, interface friction, and connector configuration influence structural load transfer. The project pathway to impact lies in providing a basis for prefabricated structural systems that link low-carbon material use with improved potential for disassembly and reuse, thereby supporting more resource-efficient construction practices.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The project combined material development, connection design, structural testing, and numerical modelling to establish the proposed CCU composite concept. On the material side, strain-hardening magnesia-based cementitious composites were developed and assessed under CO2 curing, including component-scale slab fabrication and depth-resolved characterization of carbonation penetration, strength development, phase assemblage, microstructure, and CO2 uptake. On the connection side, a novel bolt–wedge demountable connection was designed and validated through push-out tests under different wedge slope ratios, bolt pretension levels, surface conditions, and loading protocols, supported by finite-element modelling and analytical interpretation. These two research lines were then brought together in prefabricated steel–SHMC push-out specimens to investigate how carbonation-induced material gradients affect interface shear behavior in reusable steel–cementitious assemblies.

The project achieved its main technical objectives. The developed SHMC system exceeded the target compressive strength of 50 MPa after CO2 curing, and the natural-fibre-reinforced slab reached a one-way carbonation depth of about 65 mm. The bolt–wedge connection improved slip resistance by converting bolt pretension into enhanced interface compression, and its behavior was captured through experiments, finite-element modelling, and a closed-form analytical model. At the structural level, the steel–SHMC studies showed that carbonation-induced through-thickness gradients strongly influence load transfer, stiffness evolution, and damage development at the interface. Compared with steel–C50 reference specimens, the steel–SHMC interfaces provided lower peak shear resistance but much greater deformation capacity and energy absorption, while also offering substantial CO2 uptake potential. Overall, the project delivered an integrated set of results linking carbon-sequestering cementitious materials, demountable connection design, and reusable composite interface behavior.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The project advanced the state of the art by linking three aspects that are often addressed separately: CO2-mineralising cementitious materials, demountable connection design, and structural interface performance. On the materials side, it showed that CO2-cured magnesia-based strain-hardening composites can be developed not only as low-carbon materials, but also as structurally relevant slab components with measurable through-thickness gradients in carbonation, strength, and CO2 uptake. On the connection side, it delivered a novel bolt–wedge demountable concept that improves slip resistance while preserving disassembly potential, supported by experimental validation, finite-element modelling, and a closed-form analytical model. At structural level, the project went beyond conventional material or connector studies by demonstrating how carbonation-induced gradients in the cementitious component influence load transfer, stiffness evolution, and damage development in reusable steel–cementitious interface assemblies.

Taken together, these results provide an integrated basis for future reusable and lower-carbon composite construction. They indicate that carbon-sequestering cementitious components and demountable interface systems can be combined within one prefabricated concept, while also showing that material non-uniformity must be considered in structural design and assessment. For further uptake, additional work will be needed on larger-scale demonstration, long-term performance under service and environmental loading, design-oriented validation across wider parameter ranges, and, in the longer term, support from standardization and practical design guidance for reusable steel–cementitious systems. The bolt–wedge connection concept and the related protection-oriented output also provide a basis for future technical development and potential exploitation.

concept-of-prefabricated-and-demountable-steel-shmc-composite-system-with-bolt-wedge-connections.jpg