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

Periodic Reporting for period 1 - DuRSAAM (PhD Training Network on Durable, Reliable and Sustainable Structures with Alkali-Activated Materials)

Reporting period: 2018-11-01 to 2020-10-31

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 Ordinary Portland Cement (OPC)-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. As such, DuRSAAM will deliver world-leading training 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 will be 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 initially 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 is under study, 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. The baseline concrete mixtures reported in RILEM TC 247-DTA, appeared not suited for FRAAM. Newly adapted mix designs are investigated for 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.
3) Durability.
The study on durability of AAM concrete looks 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. The study on carbonation (reaction between atmospheric CO2 and cementitious materials) is ongoing. The literature study on creep and shrinkage has been completed and the experimental campaign has been planned, in this respect, more results are expected in the coming months. The research on steel bar corrosion in AAM concrete exposed to chloride ingress has shown high chloride resistance for selected AAM mixes demonstrating the possible application of AAM in marine environment. Furthermore, indications are obtained to optimize AAM concrete mixtures with respect to corrosion. The influence of temperature on AAM concrete has been primarily investigated by heating AAM concrete cubes in an oven up to 800°C. Obtained results have shown the detrimental effect of AAM concrete spalling, though performance may vary considerably depending on the type of constituents of the AAM concrete.
4) Service life and life cycle assessment.
The research on service life extends on the ongoing durability investigations and looks also on combined environmental and mechanical actions on the properties of AAM concrete. Predictive service life models are under investigation for example for the combined influence of chloride ingress and carbonation. The life cycle assessment (LCA) currently focusses at the material level, looking into 1m3 of different AAM concrete mixtures (results so far for 3 mixtures) compared to a reference ordinary Portland cement (OPC) concrete with equivalent compressive strength. The initial results have indicated that AAM mixes can lower the CO2 emission up to 75%.
DuRSAAM will leap forward the state of the art, 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 will allow to deliver a flexible numerical model and practical design guidelines for AAM concrete mix proportioning. A significant understanding on the structural application of AAM will be 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 numerical simulation, there will be further understanding in the performance of AAM concrete which is elemental toward design guidance for partitioning engineers. This will include also various durability aspects, including resistance against chloride ingress in AAM concrete as a function of the calcium content of constituents and more advanced insight on carbonation with respect to different AAM compositions. Numerical models will become 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, will be enlarged by developing analytical tools for the prediction of AAM-based structural elements exposed to fire and delivering recommendations on fire design of AAM structure. A service life predictive model for AAM concrete exposed to carbonation and chloride ingress will be delivered. Finally, life cycle assessment of AAM concrete will provide more in-depth understanding of the gain in reducing environmental impact and to indicate the sustainability of the AAM concrete technology more precisely.
Alkali activated concrete for new and existing structures