## 1 Introduction  
The use of natural fibers in construction--a technology used since ancient Egypt, with a history of more than 5000 years--is one of the most effective and promising solutions that may effectively increase in the sustainability of buildings in the modern era, hence contributing to the implementation of the concept of Bioarchitecture. Indeed, the analysis of natural elements that may be used as building components--a topic that is traditionally included in the scientific sector of Rural Buildings, i.e., one section of the widest field of Agricultural and Biosystems Engineering--may strongly contribute to the respect of the principles of sustainability, in the framework of a circular economy model aimed to improving the quality of life, by establishing a balanced relationship between nature and the built environment, satisfying the current needs without compromising the opportunities for future generations [1, 2]. Concrete has traditionally been regarded as one of the most cost-effective building materials due to its low cost, availability, long durability, ease of shaping and sizing, capacity to withstand adverse weather conditions, and excellent compressive strength [3, 4, 5]. However, it has a variety of issues that raise significant concerns in the construction industry, such as poor tensile strength, which is about 1/10 of its compressive strength [3, 6, 4]. Many researchers have looked at the viability of employing natural fibers as reinforcement materials in concrete blocks, to offset this disadvantage, due to the fibers' unique qualities, low cost, and low environmental impact. At the same time, these applications may help to value residual biomass from the agricultural sector [7; 8], resulting in positive benefits on the agricultural production chain [9] and rural landscape [10; 11; 12]. Material reinforced with natural fibers is the oldest form of composite material which, indeed, has always been obtained, at low cost, from materials present in nature, using local labor and technology and with reduced energy consumption. Due to these characteristics, the use of natural fibers as a form of concrete reinforcement is of particular interest for less-developed regions, where building materials have high costs and require the use of skilled labor. Among the natural fibers most studied and investigated by many researchers, flax fiber [13; 14; 15; 16; 17] has very significant mechanical properties that are superior to glass fiber [18; 19; 20; 21] or hemp fiber [22; 23; 24; 25; 26; 27], which are widely used in multiple building applications [28] due to their excellent mechanical strength and stiffness [29]. Remarkable mechanical and thermal properties, by comparison, were shown by [PERSON] and [PERSON] [30] in 2008 in jute fiber, which is also used in the development of a low-cost construction material reinforcement for many applications [31; 32; 33], whereas sisal fiber [34] has shown high tensile strength and stiffness [35]. Other natural fibers have also been investigated as reinforcing material in composite materials, such as bagasse fiber [36] or kenaf fiber [37; 38] which showed mechanical and workability properties of reinforced concrete comparable to normal concrete [39]. Some authors [40] studied the mechanical properties of coconut fiber-reinforced concrete [41], which showed mechanical strength and stiffness higher than that of glass fiber [42]. The effects of coconut fiber length and content on concrete properties were particularly analyzed by other authors [43], and the behavior of coconut fiber-reinforced building materials [44; 45; 46; 47; 48; 49], for their use in a variety of applications, was also investigated [50; 51; 52; 53]. Among the less common natural fibers used as reinforcement in building materials [54; 55], we would definitely mention artichoke [56], okra [57], isora [58], ferula [59], althaea [60], piassava [61], sameveria [62], and buriti [63].