This report presents a meticulous synthesis of collaborative interlaboratory research conducted within the purview of the RILEM Technical Committee 294-MPA, with two expert groups named RRT1 and RRT2, and encompassing ten participants from Belgium, China, Finland, India, Italy, Japan, the Netherlands, and the United Kingdom. The RRT1 expert group mainly focused on the ground granulated blast furnace slag-based alkali-activated concrete (GGBFS-based AAC) mix design and mechanical properties. In turn, the RRT2 expert group focused on the fresh properties of GGBFS-based AAC. The investigation, conducted between 2020 and 2024, aimed to establish globally reproducible mix design and mixing protocols for GGBFS-based AAC. Developed by the RRT1 and RRT2 expert groups, these protocols have emerged through iterative experiments followed by a comprehensive interlaboratory study. The outcomes highlight the reliable production of GGBFS-based AAC across participants, with minor deviations in fresh and mechanical properties that are largely consistent with those observed in Portland cement concrete (PCC). The primary objective of the developed GGBFS-based AAC mix design was to achieve a defined consistence class S4, while targeting a compressive strength threshold of approximately 50 MPa at 28 days. This objective was effectively realized, with the average compressive strength values reaching 56 MPa at 28 days and 64 MPa at 720 days. While the average splitting tensile strength stabilized at 3.2 MPa over the 720 day period. These findings underscore the growing importance of AAC within the construction sector, particularly due to its reproducible and reliable experimental results, as the industry increasingly shifts toward more sustainable alternatives to traditional cement-based materials.

With the development of waste recovery techniques, previous research has revealed that coarse fractions of municipal solid waste incineration (MSWI) bottom ash (BA) after proper treatment could be applied in the construction sector, while the fines are seldom recovered in practice and normally landfilled. This study explores the potential application of fine MSWI BA (0–2 mm) as a supplementary cementitious material (SCM) in Portland cement (PC) mixtures. Mechanical and chemical pre-treatment approaches have been designed with various conditions to optimize the treating process. The chemical and mineralogical compositions, as well as the metallic Al content in BA were characterized before and after the pre-treatment. It was found that both methods are effective in removing the metallic Al content in BA, Moreover, BA derived from mechanical treatment exhibited more contribution to the hydration reaction in PC mixtures, as revealed by the amount of reaction products and mineral phases formed in hardened trial mixtures. BA obtained was further partially blended in PC mortars to evaluate the performance as compared to SCMs and inert fillers. It was found that treated BA resulted in a slight retarding effect on the reaction kinetics. Treated BA behaved better than the coal fly ash to contribute to the strength development, while the inclusion of BA did not lead to significant influences on the workability.

The proper control of the rheological performance of silicate-based alkali-activated slag (AAS) mixtures is problematic, as the conventional superplasticizers become less effective in alkaline media. Nevertheless, several methods have been proposed to improve the workability of silicate-activated AAS, such as by extending the mixing time, and replacing sodium silicate with sodium carbonate activators. However, the underlying fluidizing mechanism is not yet well understood in the literature, which is crucial knowledge to achieve proper rheology control of silicate-activated AAS. In this study, the effects of mixing conditions and activator anionic species on the rheology of silicate-activated AAS concrete have been assessed. The reaction products, particle size and interparticle interactions, as well as the reaction kinetics in AAS, have been further investigated to understand the distinct fluidizing mechanisms. By using a longer mixing time, it was found that the solid particles formed at early ages are broken down into smaller particles, accompanied by a slight increase in the amount of reaction products to improve the fluidity. With the sodium carbonate substitution, the calcium ions dissolved from slag particles are entrapped into calcium carbonate precipitates to slow down the accumulation of C-(A)-S-H phases, leading to a better dynamic flow. However, the interparticle interactions are intensified due to the formation of larger particles and the declined dispersing effect induced by silicate activators.