The consideration of sustainability has become a very important factor, because of the negative impacts posed by the production of Ordinary Portland Cement (OPC). This study investigates the influence of fine aggregate fineness modulus (FM) on the durability properties of AACs exposed to harsh environmental conditions (high temperatures, sea water, and sulfate solutions). Furthermore, this paper aims to statistically derive and validate a linear model that can be utilized in predicting the compressive strength (CS) of AACs of ground granulated blast furnace slag (GGBFS) using ultrasonic pulse velocity (UPV) a non-destructive evaluation. The FM of 2.4, 2.8, and 3.2, which represent fine, medium, and coarse particle sizes of fine aggregate, respectively, were adopted in this study, with other parameters kept constant. GGBFS was activated with a combined alkaline activating solution of sodium silicate (Na 2 SiO 3 ) and a 12 M concentration of sodium hydroxide (NaOH) in a 2 to 1 ratio. The CS, UPV, density, and microstructural morphology as well as statistical analysis investigating linear relationships between UPV and CS were all evaluated in different harsh environments. The results showed that specimens immersed in 7 % magnesium sulfate (MgSO 4 )and sea water after 6 months exhibited an increase in densities, CS, and UPV, with 2.4 FM having the highest enhancements, followed by 3.2 FM due to void filling action. However, mixes containing 2.8 FM were more resistant to residual incremental change produced by 7 % MgSO 4 and sea water. The statistical analysis shows that; besides the simplicity and robustness of the linear model, it also gives a higher coefficient of determination compared to an exponential model, making it a better fit for the UPV and CS relationship.

The clinker in cement largely determines the environmental footprint of concrete. Therefore, concrete recycling should focus on retrieving high-quality cementitious fractions to replace clinker. This requires a shift from current traditional recycling techniques towards innovative recycling methods, enabling recovery of not only clean secondary aggregates, but also residual cementitious fines (RCF), potentially eliminating the carbon dioxide emissions associated with them. The production and upcycling of RCF offer new implementation routes that were previously deemed unfeasible. However, the properties of RCF may vary based on their origin, affecting their replacement and upcycling potential. Consequently, assessing the original concrete quality, with a focus on the binder type, before demolition is important. A handheld x-ray fluorescence technique appears promising for this purpose. To achieve effective separation of clean secondary aggregates from the original cementitious content, innovative crushing and separation techniques are needed. Additionally, electrostatic separation shows significant research potential for further optimizing RCF.

This paper presents a study investigating for the first time the effects of the inclusion of graphene nanoplatelets (GNPs) on the mechanical and microstructural properties of alkali activated binders produced with fly ash and slag and using superplasticizer for the GNPs dispersion in the mixing water. Compressive strength and water absorption of mortar cubes, flexural strength of mortar beams, X-ray computer tomography scanning and mercury intrusion porosimetry, Fourier transform infrared spectroscopy, scanning electron microscopy with Energy Dispersive X-Ray Spectroscopy, and X-ray diffraction, were carried out on samples cured either at room temperature or at 40 °C. Results showed that the inclusion of GNPs at a dosage of 0.05% provided a considerable increase in compressive strength at both curing conditions. Microstructural observations suggested that the presence of GNPs improved the formation of hydrated gel, and the research demonstrated through porosity measurements the shift from the capillary to the gel pore region due to the inclusion of GNPs. This study represents a step forward in understanding the effects of GNPs inclusion on alkali activated binder microstructure.