Microstructure and durability of alkali-activated materials as key parameters for standardization

Abstract

Alkali-activated concrete (AAC) has been commercialised as a low-CO2 construction material, but its adoption still faces several challenges, including standardisation, lack of a dedicated supply chain, limited service track record, and the question of whether laboratory durability testing can predict service life. This paper outlines how using different precursors leads to the formation of different AAC phase assemblages, and how AAC can be recognised in standards using a performance-based approach independent of binder chemistry. Microstructural assessment of pastes, strength development, water permeability and chloride migration of two AACs (100% slag and 1:1 slag:fly ash) are presented, and compared to Portland cement concrete. Manipulation of binder chemistry leads to differences in the properties of the AACs; however, both AACs assessed exhibited technical benefits in a performance-based comparison. AACs can meet the requirements of the equivalent performance concept, independent of the binder chemistry, supporting their scale-up, regulatory acceptance and wider adoption.

Influence of fine aggregates on the microstructure, porosity and chemico-mechanical stability of inorganic polymer concretes

“…Even though the presence of fines automatically increased the strength and reduced the pore threshold, it appeared that amorphous cementitious materials generate high moisture content detrimental for the durability of the matrices [19]. These observations agree with the results found by van Deventer et al [26] for geopolymers obtained with slag and fly ash. Analyzing the results of their prediction of durability concerning the alkali-activated matrices, it appeared that the crystallinity of the raw materials plays an important role.…”

Effects of Curing Conditions on Shrinkage of Alkali-Activated High-MgO Swedish Slag Concrete

“…The results from the SEM-EDX analysis are shown in the form of ternary diagrams; CaO, Al 2 O 3 and SiO 2 , Figure 10. Based on earlier studies typical regions for CSH, N(A)-S-H and C(A)-S-H are marked (Garcia-Lodeiro et al, 2011;Van Deventer et al, 2014). The values obtained from spot analyses of the binder matrix appeared to be located in the area predominantly assigned to C(A)-S-H phase, thus further supporting earlier formulated conclusion.…”

Phase evolution of C-(N)-A-S-H/N-A-S-H gel blends investigated via alkali-activation of synthetic calcium aluminosilicate precursors

“…The elemental composition is comparable with that of alkali-activated slag and slag/fly ash blends [52,58] as well as that of synthetic C-(A)-S-H and N-A-S-H gels formed by a sol-gel method [6], and reveals important compositional changes induced by differences in reaction mix chemistry.…”