## 1 Introduction  
According to the latest estimations, the building materials market will reach USD 1.5 trillion by 2027, a consequence, among other factors, of the accelerated growth of infrastructure in emerging economies [1]. Thus, this increase in market share linked to construction's intensive nature will be related to an increase in the consumption of natural resources and energy, leading to a strong environmental impact in terms of greenhouse gas emissions and waste generation [2]. Construction and demolition waste (CDW) is produced in the process of construction, maintenance, demolition and deconstruction of infrastructure and buildings [3]. This waste, mainly solid, has a very heterogeneous and generally inert nature [4]. According to the latest UN figures, each citizen in an economically developed region contributes approximately two tons of CDW per year, which implies more than 500 million tons of CDW per year [5].  
Unfortunately, the vast majority of these CDW are disposed of in landfills in large cities, posing a risk to health, the environment and wasting resources [6]. The European Union, aware of this global problem, has promoted the efficient use of resources in construction for responsible economic growth through the European Green Deal [7]. For this reason, in recent decades, several lines of research have emerged that are committed to the incorporation of circular economy criteria and the redesign of traditional construction products. In this work, the study of the physical and mechanical properties of masonry mortars made with recycled concrete aggregate and natural fibers is addressed, thus seeking to promote the application of eco-friendly materials in the construction sector.  
Concrete is the most consumed building material on the planet, generating a strong environmental impact due to the high energy consumption required for its production [8], while at the same time it is responsible for most CDW (between \(100\cdot 10^{9}\) and \(340\cdot 10^{9}\) kg in the EU alone [9]). The use of recycled concrete aggregates (RCA) is essential for CDW recovery and revalorization, as it allows the production of sustainable mortars and concretes with a lower demand for original raw materials [10]. In general terms, the physical and mechanical characteristics of RCA, such as their high content of surface impurities as a result of the cementitious layer adhered to the aggregate during the crushing and grinding of these wastes [11], make it difficult to use them in structural elements. This mortar layer that covers the RCA decreases its mechanical strength the lower the quality of the old mortar adhered and can also compromise the durability of the composites made with these secondary raw materials as a result of their higher porosity and water absorption capacity compared to natural aggregate [12].  
On the other hand, these RCA have a higher content of fine particles, which means that it is necessary to use a higher content of mixing water or to use chemical superplasticizing agents in the dosing of mortars [13]. This aggregate particle size can be corrected to some extent by introducing washing and sieving stages prior to the use of the aggregate, although it is true that qualitatively its physical properties do not usually improve with respect to natural aggregate [14]. Another consequence of the use of these aggregates in the manufacture of masonry mortars is the increase in shrinkage during the setting process, which causes surface cracks that can compromise their durability [15].  
For this reason, reinforcement fibers have become a technically and economically viable alternative to improve the properties of mortars and concrete made with these recycled aggregates.