The production of cement and concrete contributes significantly to global greenhouse gas emissions. Alkali‐activated concretes (AACs) are a family of existing alternative construction materials that could reduce the current environmental impact of Portland cement (PC) production and utilisation. Successful applications of AACs can be found in Europe and the former USSR since the 1950s and more recently in Australia, China and North America, proving their potential as construction materials. However, their utilisation is limited presently by the lack of normative and construction guidelines. Raw materials’ non‐uniform global availability and variable intrinsic properties, coupled with the lack of specific testing methods, raise questions regarding reproducibility and reliability. The mechanical and chemical behaviour of AACs has been investigated extensively over the past decades, strengthening its potential as a sustainable substitute for traditional PC‐based concrete. Although a wide amount of studies demonstrated that AACs could meet and even exceed the performance requirements provided by European design standards, a classification of these broad spectra of materials, as well as new analytical models linking the chemistry of the system components to the mechanical behaviour of the material, still need further development. This report gives an overview of the potential of alkali‐activated systems technology, focusing on the limitations and challenges still hindering their standardisation and wider application in the construction field.

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The fib Model Codes aim at integrating in a single document the relevant knowledge for the structural design with concrete. Fibre reinforced concrete is already integrated in fib Model Code 2010 (fib MC2010) as a general category of materials. The group of flowable concrete consists of clusters of different types of concrete among others Self-Compacting Concrete, Ultra High Performance Concrete and Strain-Hardening Cementitious Composites. Being highly flowable is the distinguishing characteristic, flowable concrete might contain or not contain fibres. Although the fibre contribution on the structural level can be assessed on short-term, the structural behaviour also depends on the behaviour of the fibres and the matrix in which they are embedded. fib Task Group 4.3 worked on identifying and characterising different types of flowable concrete and discusses in a fib bulletin the most relevant aspects with regard to mix design, manufacturing, material performance and structural behaviour of flowable concrete which can allow innovative applications to be developed and realised. This paper discusses recent developments with regard to flowable concrete in a broader perspective and addresses the progress with regard to standardisation.@en

This paper investigates the development of the alkalinity and its impact on carbon steel reinforcement embedded in alkali-activated fly ashes (AAFA) and alkali-activated fly ashes with ten percentage mass (wt%) of blast furnace slag (AAFAS)-based materials (geopolymer–GP). The pH analysis of eluates indicates a remarkable decrease of alkalinity in AAFA and AAFAS in the first hours of the geopolymerization process. Phenolphthalein solution and pore solution tests on concretes also show a sharp decrease of alkalinity with increased Ca content in the binder due to carbonation. Micro X-ray computer tomography (µXCT) and electrochemical techniques indicate that the changed pH in the GP systems was accompanied by a decrease in the corrosion rates of steel reinforcement when compared to ordinary Portland cement (OPC) systems. In contrast to calcite and vaterite, which were detected in OPC and AAFAS after a carbonation process, only sodium carbonate natron was determined at lower levels in AAFA by X-ray diffraction (XRD).@en