Multiscale microstructure and micromechanical properties of alkali-activated concrete: A critical review

With the rapid development of alkali-activated concrete (AAC) as a promising sustainable concrete, it is vital to thoroughly understand the microstructural characteristics and micromechanical properties, which determine the macroscopic mechanical properties and structural performance of AAC. This paper presents a critical review on the multiscale microstructure and micromechanical properties of AAC with both single and blend precursor systems, including alkali-activated fly ash (AAF), alkali-activated metakaolin (AAMK), alkali-activated slag (AAS), and alkali-activated fly ash-slag (AAFS). These types of AAC are systematically studied from nano-scale to macro-scale, covering solid gel particles (N-A-S-H, C-A-S-H and N-C-A-S-H), gel matrix (solid gel particles + gel pores), paste (unreacted particles + reaction products + pores), mortar and concrete (paste + interfacial transition zone + aggregates). The recent advances in microstructure and micromechanical properties of AAC are discussed, with special focus on microstructure-mechanical property relationships. The remaining challenges and opportunities for future research are also provided.