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Currently it is necessary to find alternatives towards a sustainable construction, in order to optimize the management of natural resources. Thus, using recycled fine aggregate (RFA) is a viable recycling option for the production of new cementitious materials. In addition, the use of polymeric microfibers would cause an increase in the properties of these materials. In this work, mortars were studied with 25% of RFA and an addition of polyacrylonitrile PAN microfibers of 0.05% in cement weight. The microfibers were obtained by the electrospinning method, which had an average diameter of 1.024 µm and were separated by means of a homogenizer to be added to the mortar. Cementing materials under study were evaluated for compressive strength, flexural strength, total porosity, effective porosity and capillary absorption, resistance to water penetration, sorptivity and carbonation. The results showed that using 25% of RFA causes decreases mechanical properties and durability, but adding PAN microfibers in 0.05% caused an increase of 2.9% and 30.8% of compressive strength and flexural strength respectively (with respect to the reference sample); a decrease in total porosity of 5.8% and effective porosity of 7.4%; and significant decreases in capillary absorption (approximately 23.3%), resistance to water penetration (25%) and carbonation (14.3% after 28 days of exposure). The results showed that the use of PAN microfibers in recycled mortars allowed it to increase the mechanical properties (because they increase the tensile strength), helped to fill pores or cavities and this causes them to be mortars with greater durability. Therefore, the use of PAN microfibers as a reinforcement in recycled cementitious materials would be a viable option to increase their applications.

In this research, the effect of the addition of carbon fiber (FC) and graphite powder (GP) in a mortar with recycled aggregate was evaluated to know the percolation threshold with a water / cement ratio 0.6, sand / cement 1, PG / cement 0.5,1 and 0.1,0.3,0.5,1,1.5% of FC by weight of cement, the determination of the electrical conductivity of the mortar was carried out by the four-point method, obtaining the threshold of percolation from 0.3% FC by weight of cement for percentages greater than 0.5% the conductivity remains approximately constant, the increases in electrical conductivity are defined by the contact between the FC and the PG simultaneously, forming conductive routes with higher performance in their electric conductivity.