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• Chloride resistance was evaluated by natural chloride diffusion test. • W/b and slag content significantly impacted chloride transport. • Sand-aggregate ratio decided workability instead of D f. • D f was related to the threshold pore diameter and pores > 5 nm. The widespread application of alkali-activated fly ash/slag (AAFS) concrete requires the satisfaction of a series of performance criteria both from its early age properties (e.g. workability, strength) and long-term stability. In this study, long-term (till 180 days) natural chloride diffusion tests were conducted to evaluate the chloride diffusion in AAFS concretes prepared with different slag content, water/binder (w/b) ratio, alkali content, and sand-aggregate ratio. The results revealed that AAFS concretes obtained in this study were generally regarded as flow/high flow concretes (slump > 100 mm) with compressive strength > 50 MPa at 28 day. The free chloride diffusion coefficient (D f) of AAFS concretes was between 0.4 and 1.8 × 10-12 m2/s. The slag content and w/b were found as dominant parameters affecting the long-term chloride transport in AAFS concretes, while the sand-aggregate ratio presented a limited effect. The formation of more C-A-S-H gels (by increasing slag content ≥ 50%), and lower w/b (≤0.45) at Na 2 O content of ∼ 5% was preferred for AAFS concretes with good workability, strength and durability. MIP results indicated that capillary pores in AAFS reached percolation and became disconnected after 180 days. The long-term chloride diffusivity of AAFS concretes was closely related to the threshold pore diameter and volume of pores > 5 nm. The more larger pores, the higher chloride diffusion coefficient was. [ABSTRACT FROM AUTHOR]

[Display omitted] • Products with different composition in alkali-activated flay ash were synthesized. • Chlorides were physically adsorbed on the surface of synthetic reaction products. • The chloride adsorption capacity of zeolites was lower than N-A-S-H gel. • The chloride adsorption capacity was related to the surface properties of products. Compared to ordinary Portland cement, reaction products in alkali-activated fly ash (AAF) exhibit different characteristics, dramatically influencing their chloride adsorption ability. This paper extensively characterized the chloride adsorption behavior of individual reaction products in AAF. First individual reaction products, including NASH gels, P zeolite and analcite, were synthesized and their composition, morphology and structure were extensively evaluated. The chloride adsorption ability of the above synthetic reaction products was then investigated. The synthetic reaction products mainly physically adsorbed chlorides on their surface. When Si/Al ratio of NASH gel increased, its chloride adsorption ability was enhanced, which was mainly related to the positive shift of zeta potential. The synthetic P zeolite and analcite exhibited lower zeta potential and specific surface area, thus their chloride adsorption ability was lower than synthetic NASH gels. [ABSTRACT FROM AUTHOR]