Microstructural evolution and chloride diffusion behavior of multi-component cementless materials made from industrial by-products

This study investigated the mechanical properties and durability of novel multi-component cementless binders formulated entirely from industrial by-products, including co-fired fly ash (CFA), slag, reactive ultra-fine fly ash (RUFA), and fly ash (FA). The performance of these water-activated systems was compared with that of traditional alkali-activated materials (AAMs) through compressive strength monitoring, chloride migration tests, and microstructural analyses using MIP, XRD, and SEM. The results revealed that the water-activated binders demonstrated superior reliability, achieving compressive strengths of up to 22.2 MPa and exceptional resistance to chloride ingress, with chloride diffusion coefficients ranging from 1.91 ×10 -12 m 2 /s to 2.82 ×10 -12 m 2 /s. In contrast, the alkali-activated systems exhibited significant instability; specifically, high-slag AAMs suffered from severe strength loss (5.9 MPa) attributed to matrix brittleness and extensive microcracking. Microstructural analysis confirmed that the water-activated system employed a self-activation mechanism to form a dense C-A-S-H gel. In contrast, the incorporation of RUFA facilitated the growth of a unique, interlocked crystalline network dominated by Latiumite and Kottenheimite, which effectively severed pore connectivity. This research innovatively demonstrated that leveraging the self-activation potential of sulfate-rich CFA with ultra-fine particle modification could yield a sustainable, cementless binder with durability characteristics surpassing those of conventional alkali-activated systems. • Novel cementless binders were developed using 100% industrial by-products. • Water-activated systems showed superior reliability over alkali-activated ones. • RUFA promoted the formation of a unique interlocked Latiumite crystalline network. • Self-activated binders demonstrated exceptional resistance to chloride ingress. • High-slag alkali-activated matrices failed due to brittleness and microcracking.