## 3 Results and Discussion
Interestingly, the blend of ground granulated blast furnace slag and hydrated lime stabiliser has comparable performance to hydrated lime in reducing swelling but is slightly less effective in reducing compression (Figure 6b). Figure 6: Summary of the (**a**) vertical strains obtained in the swelling tests under various vertical stresses, i.e., positive values indicate swelling whereas negative values indicate consolidation and (**b**) magnification of the results for specimens stabilised. A series of shear box tests were conducted on specimens stabilised with 3% on a dry weight basis of additive. To evaluate the role of the stabiliser in the shear strength behaviour two different test conditions were investigated, i.e., shear behaviour representative of the as-compacted condition and post yield behaviour after inundation. The latter condition was adopted to simulate the loss of strength potentially incurred as a result of a rainfall event leading to water infiltration in a road pavement underlain by expansive soils. As expected, in the specimens tested in as-compacted condition (Figure 7a,c) the addition of the stabiliser has a substantial effect on the stress-strain behaviour. While all specimens mainly showed a strain softening and dilation response, this behaviour is more pronounced in the specimens treated with HL, PC and BFS/HL. Moreover, the specimens treated with HL and BFS/HL achieved comparable peak stresses (80-82 kPa), while those prepared with PC showed slightly lower peak stress (71 kPa). Interestingly, while there was a substantial increase in peak stress compared to the unstabilised specimen, this was not observed for ultimate states. In fact, with exception of the specimen treated with PC (50 kPa), all other specimens approached ultimate state at approximately the same stress level (42-45 kPa). This seems to indicate that when the ultimate state is reached, the shear strength of these specimens is relatively independent of the level of treatment. This is likely due to a process of destructuralization of the soil microstructure taking place during shearing. The results of the shear behaviour of the specimens inundated at yield (i.e., specimen allowed to reach yield stress before saturation) is shown in Figure 7b,d. It can be observed that for all specimens, the soil still retains its ultimate shear strength (saturated) in the secondary shearing phase. Similarly, to as-compacted condition, the unstabilised specimen achieved the lowest shear strength at ultimate state (19 kPa), with the specimen stabilised with PC showing the highest ultimate stress (34 kPa). Additionally worthy of note is the fact that all the specimens stabilised still retained shear strength during inundation, with the specimen treated with PC showing the smallest decrease in shear stress. While this may not seem the most intuitive behaviour at first sight, it may be explained from a microstructural standpoint. As a result of the pozzolanic reactions taking place during hydration (as-compacted water content), the cementation products bind the soil particles resulting in a residual shear strength upon inundation. The cementation products are more evident in the specimens treated with PC as verified by SEM micrographs (Figure 8), hence the smaller reduction in shear strength despite showing comparable ultimate shear stresses, i.e., 24 kPa, 28 kPa and 34 kPa for HL, BFS/HL and PC, respectively. In addition, in post inundation only the specimen treated with PC showed a predominantly strain softening behaviour. The untreated specimen also experienced the greatest degree of swelling upon inundation (e.g., 4.4% of the specimen original height) while the treated specimens showed much smaller level of swelling upon inundation, although the specimen treated with BFS/HL showed the largest swell (0.34 mm). Furthermore, during the secondary shearing only the specimen treated with PC exhibit mainly dilative response, while those prepared with HL and BFS/HL showed mild compression, in line with the stress-strain response observed.