# Microstructure, Durability and Mechanical Properties of
## 5 Conclusions  
In view of the results obtained, firstly it is important to highlight that the studied mortars showed a progressive refinement of their microstructure, as suggested by the rise with time of the relative volume of finer pores, revealed by mercury intrusion porosimetry results, and the increasing tendency of electrical resistivity. This pore refinement would be produced as a consequence of the development of slag and clinker hydration and fly ash pozzolanic reactions. Regarding the services properties, this microstructure refinement overall produced a reduction of the chloride diffusion coefficient and the enhancement of mechanical performance of the mortars. Furthermore, at early ages, reference mortars without additions and mortars with slag generally presented lower porosities, lower diffusion coefficients, higher mechanical strength and higher ultrasonic pulse velocities, compared to specimens with fly ash. However, at later ages, mortars which incorporated fly ash in the binders showed a high pore refinement, a noticeable reduction of diffusion coefficient and an improvement of their mechanical properties. These results were related to the delay of fly ash pozzolanic reactions compared to slag and clinker hydration. This delay would be revealed by the differential thermal analysis performed, with the reduction of area of portlandite peak area from 28 to 250 days, noted for binders with fly ash. Despite that, in general, the incorporation of slag and fly ash in the binary and ternary binders would produce a higher microstructure development and better durability and mechanical properties. This could be due to the effects of the hydraulic activity of slag and the pozzolanic activity of fly ash. On the other hand, the highest total porosity, the lowest pore refinement, the lowest electrical resistivity, the highest diffusion coefficient, the smallest compressive strength and the lowest ultrasonic pulse velocity have been observed for binary mortars with only the addition of limestone. This could be explained in relation to the fact the limestone acts as an inert material, without hydraulic or pozzolanic activity, so its beneficial effects in the microstructure and properties development is limited compared to slag and fly ash. Regarding the absorption after immersion parameter, it reached similar values in the long term for mortars made with ternary binders compared to reference specimens. Then, the use of these binders would not worsen the performance of the mortars regarding this parameter. Finally, in relation to the ternary binders studied, in general the best performance was noted for the mortars which incorporated both slag and fly ash as additions (SF series), compared to those with limestone (SL and FL series). This would show the improvement of incorporating two active additions in the binder, produced by the combined synergetic effects of slag hydration and fly ash pozzolanic reactions. These effects were more noticeable regarding the compressive strength of the mortars. Conceptualization, [PERSON] and [PERSON]; methodology, [PERSON], [PERSON] and [PERSON]; investigation, [PERSON], [PERSON] and [PERSON]; data curation, [PERSON] and [PERSON]; writing--original draft preparation, [PERSON]; writing--review and editing, [PERSON]; supervision, [PERSON] and [PERSON]; funding acquisition, [PERSON]. The results included in this paper were obtained in the PhD thesis carried out by [PERSON] at University of Alicante (Spain), under the supervision of [PERSON] and [PERSON]. All authors have read and agreed to the published version of the manuscript. This work was supported by the Conselleria de Educacion, Investigacion, Cultura y Deporte (presently re-named as Conselleria de Innovacion, Universidades, Ciencia y Sociedad Digital) de la Generalitat Valenciana, Spain (grant code GV/2019/070). Not applicable.