# Microstructure, Durability and Mechanical Properties of
## 1 Introduction  
At present, to lessen the greenhouse gases emissions produced by the most contaminant industrial sectors is an important field of research [1, 2, 3, 4]. In this topic, the construction sector and the cement industry in particular have put into practice several strategies for becoming less pollutant, in order to contribute to the global sustainable development goals, which aim to reduce global warming. Several of these strategies are related to the components of cement-based materials, such as the use of supplementary cementitious materials, recycled or lightweight aggregates, among others, as well as the combination of them, in order to develop more eco-friendly materials [5, 6, 7]. Regarding supplementary cementitious materials (SCMs), they are key components of sustainable, low carbon footprint cements, replacing partially or totally clinker [8, 9]. The use of these eco-friendly cements presents several benefits [9, 10, 11, 12, 13]. Firstly, these cements contribute to reduce CO\({}_{2}\) emissions produced by the cement industry, because the SCMs replace a proportion of clinker [8, 9], then a lower amount of this component is required. In addition, the most popular SCMs are residues produced in other industrial sectors. Therefore, their reutilization in cement production also causes advantages from an ecological point of view. Furthermore, it has been observed that several SCMs improve theperformance of cement-based materials, so their influence are still today a relevant field of research [9; 14; 15; 16; 17]. Among the different SCMs, it is important to highlight the active additions, such as fly ash and ground granulated blast furnace slag. In relation to slag, the development of their hydration reactions produces the formation of additional CSH phases, increasing the microstructure refinement [18] and improving the materials' properties [19; 20]. Fly ash addition shows comparable influence in the pore network and service performance of cement-based materials, although this addition has pozzolanic activity, being capable of reacting with portlandite [15], formed as a product of clinker hydration. As a consequence of the pozzolanic reactions development, new hydrated phases are produced, making the microstructure of the material more dense [9; 15]. On the other hand, there are additions without hydraulic or pozzolanic activity, which are also used for replacing clinker in cement production. One of the most popular is limestone, which has mainly a filler effect in cement-based materials, improving their pore size distribution, as well as their fresh and hardened properties [21; 22; 23]. In relation to the production of commercial cements with SCMs, those made with binary binders, incorporating one addition as a clinker replacement, are mostly produced nowadays. Nevertheless, the use of ternary binders, in which clinker is partially replaced by two additions, for manufacturing commercial cements is very low, at least in Spain. Therefore, to explore the performance of mortars and concretes prepared using cements made with ternary binders [21; 24; 25; 26], focused on their application for commercial cements production, could be a promising research field for providing more solutions to improve the sustainability of the cement industry. In addition, the synergetic effects of combining two additions could entail an improvement of the behavior of these cement-based materials made using ternary binders [27; 28; 29; 30]. Therefore, the objective of this research is to study the effects in the long term produced by ternary binders which combine the additions of ground granulated blast furnace slag, fly ash and limestone in the microstructure, durability-related parameters and the mechanical performance of mortars. Those additions were chosen because they are the most used in the production of blended commercial cements in Spain.