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Chloride resistance is important for the durability of geopolymers used in construction applications, particularly in coastal and saline areas. In this study, the workability, mechanical performance, and chloride resistance of class C/class F fly ash-based geopolymer mortars were investigated. First, the effects of the water-to-fly ash ratio, class C fly ash content, and sand-to-ash ratio, on the fluidity, and mechanical properties of the geopolymers were examined. Second, based on the results, geopolymer mortars with three different strength grades were chosen for chloride resistance tests. After these were subjected to a NaCl solution, their weight change, ultrasonic flight-time, and compressive strength were determined. Moreover, corrosion products were evaluated by conducting microstructural analysis. The results indicated that a high class C fly ash content, small water-to-fly ash ratio, and small sand-to-ash ratio led to low fluidity and a high compressive strength of the specimens. The ultrasonic flight-time and the pore structures of the geopolymers were strongly related. Furthermore, after corrosion, the hydration products appeared as new crystalline zeolite phases in the low-strength samples. Compared with the high- and medium- strength mortars, the low-strength samples showed excellent chloride resistance.

Alkali-activated slag (AAS), an environmentally friendly material, has recently attracted increasing attention for applications in soil improvement. However, most of the studies focused on the geomechanical behavior of non-liquefiable soils strengthened with AAS. The objectives of this study are to examine whether AAS is effective for strengthening liquefiable soil and to evaluate the effectiveness of AAS in deep soil mixing (DSM) technology for mitigation of liquefaction. The mechanical properties and microscale mechanism of the improvement of liquefiable soil by AAS under standard curing, water curing, and seawater curing conditions are studied first. Then, the strengthening effect of the DSM technique using the soil-AAS mixture on the soil-pile-superstructure system is studied by three-dimensional numerical analyses. The results show that the compressive strength of the soil-AAS mixture is much greater than that of the soil-cement mixture. Compressive strength of 32 MPa was obtained for a soil-ASS mixture with 25% slag content under 28-day standard curing. Moreover, the DSM technique using the soil-AAS mixture is an effective method for liquefaction mitigation; the maximum lateral displacement of the pile during shaking can be reduced by half when the area improvement ratio is 20 %.