Chloride diffusion in alkali-activated fly ash/slag concretes: Role of slag content, water/binder ratio, alkali content and sand-aggregate ratio

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 x 10(-12) m(2)/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 Na2O content of similar to 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. (C) 2020 Elsevier Ltd. All rights reserved.