Interfacial Transition Zone Strengthening in Aeolian Sand Concrete via ssDNA Anchored CNTs on Alkali-Activated Surface Layer

The use of aeolian sand as a fine aggregate in concrete production provides a sustainable pathway to valorize abundant aeolian resources while alleviating the global shortage of natural construction aggregates. However, the high ultrafine particle content of aeolian sand results in the formation of highly porous interfacial transition zones (ITZ) between sand particles and cement paste, which is the primary cause of the inherent brittleness and inferior mechanical performance of aeolian sand concrete. To overcome this critical limitation, an alkali-activated surface layer (ASL) was constructed on aeolian sand via 4 mol/L KOH activation. This process induced the surface micro-dissolution of minerals to create high-density active ion sites (specifically Ca2+, K+, Na+, and Fe3+). These sites facilitated the precise anchoring of carbon nanotubes (CNTs) through the chemical coordination of single-stranded deoxyribonucleic acid (ssDNA). The influence of the ASL and the ssDNA/CNTs nanocomposite on the ITZ was elucidated through macro-mechanical testing and multi-scale microstructural characterization. Experimental results demonstrated that compressive strength, flexural strength, and compressive energy dissipation increased by 48%, 67%, and 42%, respectively. Microstructurally, the modification promoted a pore refinement mechanism, reducing the proportion of harmful (pores > 0.1 μm) from 51% to 20% and narrowing the ITZ width from 20–40 μm to 10–15 μm (a 67% reduction). The observed performance enhancement is attributed to the synergistic effect of the ASL and ssDNA/CNTs, which transforms the inherently weak ITZ into a chemically reinforced interfacial phase via molecular-scale coordination bonding and optimized stacking of cement hydration products.