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In this paper, we present a methodology for measuring the reaction degree of ground granulated blast furnace slag (GGBFS) in alkali-activated cements using neural network based image analysis. The new methodology consists of an image analysis routine in which the segmentation of the back scattered electron (BSE) (SEM) images is based on a deep learning U-net. This methodology was applied to and developed for NaOH-activated slag cements and validated against independently measured XRD results. In a next step the developed method was applied to NaOH-Na

The similarity of the fine fraction of dredged freshwater sediments to natural clays stimulates the valorization in a product similar to expanded clay aggregates, obtained by bloating at high temperature. The impact of the ratios between different flux elements (Fe2O3 + CaO + MgO + K2O + Na2O) on the melting behavior is quantified using thermodynamic modeling and validated with experiments. The total content of alkalis is found to be key in controlling melting and bloating. Increased alkali content triggers the formation of alkali feldspars that start to melt at low temperature and give rise to a gradual increase of the amount of melt with temperature. The ratio (CaO + MgO + K2O + Na2O)/Al2O3 should preferably be smaller than or close to 1 to avoid excessive pyroxene formation, which causes complete meltdown of the granules around 1150 °C. The chemical composition has a complex influence on the melting behavior, even when on the same location on the SiO2–Al2O3–flux diagram. The conventional approach of trying to modify the composition towards a certain range in the ternary diagram does not work for all materials, and therefore, the understanding of the melting behavior using the phase composition at high temperature (= the metallurgical approach) provided in this work is shown to be crucial to produce lightweight aggregates from materials with a higher chemical variability.

Ternary cements are a promising option to further reduce CO2 emissions and environmental impact from cement production. The current study investigates in detail the impact of water to binder ratio (0.4, 0.5, 0.6) and curing temperature (5, 20, 40 °C) on the hydration kinetics of a ternary cement comprising clinker, slag and limestone in a 50:40:10 mass ratio, respectively. The results show that the water to binder ratio mainly affected the hydration degree of slow reacting phases, such as slag and belite, at later ages. The curing temperature accelerated the hydration of alite to a lesser extent than that of C3A and slag, which could lead to changes in the hydration reaction sequence at elevated curing temperatures. Elevated temperature curing did not lead to cross-over effects in terms of slag hydration degree at later ages but led to reductions in the portlandite and ettringite levels.

Applied Sciences 11(9), 4028 (2021). doi:10.3390/app11094028 special issue: "Special Issue "Eco-Performance of Alternative Binder Systems" / Special Issue Editors: Dr. Philip Van den Heede, Guest Editor ; Dr. Natalia Mariel Alderete, Guest Editor", Published by MDPI, Basel