## 1 Introduction
[26] showed an increase in the California Bearing Ratio (CBR) of soil when using limestone powder with lime. Similar results were found by [PERSON] et al. [27] for marble dust used with ordinary Portland cement for soil stabilization. Due to the lack of other similar studies, some ideas can be extracted from the by-product's chemical nature and the research about other materials with similar composition. In this sense, [PERSON] et al. [28] found that the addition of CaCO\({}_{3}\) nanoparticles in a cement-stabilized soil can improve the compressive strength of the soil due to the nucleation effect and the filling function of these particles. This nucleation effect has been extensively reported when studying cementitious materials such as mortars or concretes [29; 30; 31]. The nucleation effect of limestone powder increases with a decrease in the particle size of CaCO\({}_{3}\) or an increase in the amount of CaCO\({}_{3}\)[32]. [PERSON] et al. [31] also concluded that the pore structure of cementitious materials can be refined by incorporating CaCO\({}_{3}\) as a fine limestone powder. In this sense, an improvement in the hydration degree of cement and a denser structure due to its filling effect at an early age was reported by [PERSON] et al. [33] when limestone powder was used for the preparation of blended cements. [PERSON] et al. [34] studied the use of marble dust waste in the production of ternary blended cements, concluding that this by-product could be valorized as a cementitious addition for cement replacement. There have been fewer studies about the use of CaCO\({}_{3}\) with lime. In this sense, [PERSON] et al. [35] studied the influence of recycled limestone filler additions on lime mortars, concluding that a positive impact on the mechanical strength was observed after 56 days due to the nucleation effect. Previous research on limestone powder waste as a ternary element for soil stabilization is very limited and has not covered the strength and microstructure of mixed soil. Former studies have focused on the effect of limestone powder on cement-based materials, but the mineralogy of soils can change this effect. Thus, the study of the microstructure of mixed soil using natural stone industry waste as a ternary additive with lime or cement with different techniques is a novelty in this work. Sulfates are sometimes present in soils and groundwater due to their geological origin or other causes. It is well known that sulfates can negatively affect lime and cement-stabilized soils [10], resulting in the phenomenon termed sulfate-induced heave [36]. Ettrin-gite, a highly expansive mineral, is formed when the calcium from the binder reacts with soil sulfates in the presence of aluminum compounds in an alkaline environment caused by binder hydration. The harmful effect of sulfates can be modified when using industrial by-products. For example, ground granulated blast furnace slag on lime-stabilizedsulfate-bearing soils reduces the harmful effect of sulfate in soils [37; 38]. Then, the use of limestone powder in soil stabilization with calcium-based stabilizers can also affect the durability conditions of the mixed soil. Nevertheless, the effect of an aggressive medium on the microstructure of the soil mixed with limestone powder waste as a ternary element has not been previously investigated. This issue is also a novelty of the present work. Therefore, although the subject is not new, this study represents a considerable increase in the information currently available.