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PhD Training Network on Durable, Reliable and Sustainable Structures with Alkali-Activated Materials

Periodic Reporting for period 2 - DuRSAAM (PhD Training Network on Durable, Reliable and Sustainable Structures with Alkali-Activated Materials)

Reporting period: 2020-11-01 to 2023-02-28

The design, durability and performance of structures play a crucial role in fostering societal and economic growth. Concrete structures are used extensively for buildings, transport, infrastructure and maritime applications. By using concrete extraordinary structures can be realised, and these are often designed for long service lives to gain optimal value from the material, environmental, intellectual and financial input into the making of the structure. In Europe, around 4 tonnes of concrete per capita are consumed annually. The downside of using concrete is associated with durability issues and huge environmental costs, as the cement industry accounts for 8% of global anthropogenic carbon dioxide emissions; and around 60% of all non-renewable resources are used in construction, making it one of the least sustainable industries. There is a clear demand for a new, sustainable generation of construction materials, since Portland cement based concrete cannot meet all the challenges of modern society concerning durability and sustainability.

The aim of DuRSAAM is to strengthen the European research area on eco-efficient construction materials and the increased competitiveness of Europe's construction sector, in applying concrete technology based on alkali-activated materials (AAM) for a more sustainable build environment. The AAM concrete fits in a vision of using local available by-products, so as to simultaneously avoid the use of primary raw materials and reducing the carbon footprint. As such, DuRSAAM provided world-leading training and a leap forward in the state-of-the-art in this multidisciplinary field through 13 PhDs in interrelated aspects of AAM concrete, fibre reinforced high-performance concrete, and textile-reinforced mortar, as well as sustainability assessment. The outcomes are instrumental in delivering a sustainable future in Europe’s construction industry, which is increasingly driven by the growing demand for durable yet cost-effective solutions, driving a greater focus on reliable and comprehensive eco-efficient material technologies such as AAM.
The DuRSAAM action was successful in setting up a PhD program and to provide dedicated training focussed on eco-efficient concrete by means of alkali-activated materials (AAM). Four main aspects have been approached by literature studies and then investigated by numerical/experimental research as follows:
1) Mix design and microstructure.
The research on mix design of AAM concrete focussed on mix trials and rheological testing, starting from the reference mixtures reported by RILEM TC 247-DTA. This has allowed to get acquainted with AAMs and the technical equipment, and to progress into new AAM concrete mixtures with good workability and strength performance and making use of locally available mineral powders as one of the main constituents of the AAM concrete. The AAM microstructure has been studied, considering the change in the chemical composition of the AAM during the hydration process and the influence of the microstructure on transport properties of concrete being exposed to the environment.
2) Structural applications.
Next to more mainstream application of AAM for reinforced concrete, the use is also investigated for steel fibre reinforced AAM (FRAAM), the use of AAM for textile reinforced mortar (TRM) strengthening systems, including its application for seismic retrofitting of existing structures. Regarding FRAAM, optimal AAM concrete mixture with short fibres have been achieved with good workability and strength, considering different types of steel fibres. The use of the AAM-TRM technique has been studied looking into the optimization of the mortar composition by characterizing the workability and strength properties of the selected AAM mixtures, and looking further into the bond performance, and structural performance of members strengthened with AAM-TRM.
3) Durability.
The study on durability of AAM concrete looked mainly into carbonation, creep and shrinkage of AAM concrete, corrosion of internal steel reinforcement by chloride penetration and the influence of elevated temperature on AAM concrete. A more deep understanding on these durability aspects for AAM-concrete has been achieved, allowing for performance based durability design of AAM concrete. A high-fire resistant AAM concrete mix with local by-products has been achieved.
4) Service life and life cycle assessment.
The research on service life extended on the durability investigations and looked also on combined environmental and mechanical actions on the properties of AAM concrete. Predictive service life models have been investigated e.g. for the combined influence of chloride ingress and carbonation. The life cycle assessment (LCA) more precisely quantified environmental performance of the developed AAM mixes, not only at material level, but also in due consideration of the service life. The results have indicated that AAM mixes can lower the CO2 emission up to 75%.
DuRSAAM improved knowledge and insights along the value chain of AAM concrete starting from mix design and microstructure, over structural applications and durability, up to life cycle assessment, as follows. The microstructure characterisation of AAM allowed to deliver a flexible numerical model and practical design guidelines for AAM concrete mix proportioning. A significant understanding on the structural application of AAM has been delivered not only on the use of AAM concrete for new structures (traditionally reinforced or by means of short fibres), but also on using AAMs for retrofitting of existing structures. Furthermore, by experimental tests and analytical work, further understanding in the performance of AAM concrete has been achieved that is elemental toward design guidance for partitioning engineers. This includes also various durability aspects, amongst other resistance against chloride ingress and more advanced insight on carbonation. Models are made available to predict the AAM behaviour under combined environmental-mechanical loading and creep and shrinkage. The understanding of AAM under elevated temperatures, in view of applications where fire resistance is of concern, has been enlarged. A service life predictive model for AAM concrete has been issued in due consideration of the durability performance. Finally, life cycle assessment of AAM concrete is providing more in-depth understanding of the gain in reducing environmental impact and to indicate the sustainability of the AAM concrete technology more precisely. To lower implementation hurdles on AAM concrete technology, an open access e-handbook 'The Urban Concrete Innovation' has been issued.
The Urban Concrete Innovation (DuRSAAM/URBCON e-book cover)
Alkali activated concrete for new and existing structures