# Rheology, Hydration, and Microstructure of Portland Cement Pastes Produced with Ground Acai Fibers
## 1 Introduction  
The reuse and recycling of waste, whether industrial or agro-industrial, in cement materials, represents in many cases economic, technological and environmental advantages [1]. An example of solid waste generated in large quantities around the world is rubber waste from fires: this material is widely studied for applications in asphalt coatings [2], waterproofing [3], and as fillers in masonry mortars [4]. A study by [4] evaluated the feasibility effect of using fly ash and rubber wastes with Portland cement in mortars to coat masonry, concluding that mixes containing 10% Portland cement, 70%, and 60% fly ash and 20% and 30% of tire rubber particles showed technological properties suitable for masonry applications. Another study evaluated the production of controlled low-strength material without cement (CLSM) as a function of the pozzolanic reaction between the waste glass powder (GP) and hydrated lime (HL). In this study, the various mixes were technologically characterized as to their durability and microstructure, concluding that there is the possibility of applying, on a large scale, waste glass in the cement industry, promoting the sustainability of this production chain [5]. Another possibility of applyingglass waste is its addition as a finely ground powder in concrete, aiming at reducing the amount of cement and improving the internal filling of the matrix. Thus, [6] evaluated the effect of this addition on mechanical properties, water absorption, and durability in concrete, showing that the glass waste was beneficial in these applications, functioning as matrix filling. The reinforcement of cementitious materials with fibers, whether natural or traditional, is the object of many studies that evaluated their technological properties, performance, and durability. Traditional fibers, such as glass, steel, and carbon, are used in order to improve flexural strength, as assessed by [7], who concluded that the use of glass fibers in mortars increased their flexural strength, as well as improved their fracture strength and ductility. A disadvantage of using fiberglass is the degradation resulting from the alkalinity of cementitious materials [8], which is also seen as a problem in the use of natural fibers without treatments [9]. Another study evaluated the use of other traditional fibers, such as basalt, which can help with durability in an alkaline environment but can represent high costs [10]. In the case of carbon fiber mortar reinforcement applications, they showed the ability to conduct electricity in mortars [11] and improve their performance against fire [12]. A great advantage of using natural fibers over traditional ones is its low cost of exploitation, due to its abundance, and lower energy consumption for its production, however, as a disadvantage there is the need for surface treatment to improve its durability in the cement matrix and great variability of its properties, depending on the type of fiber [12]. The wide diversity of natural fibers available in various parts of the world has contributed to the advancement of research on their reuse [13]. The applications of natural fibers can cover various types of filling matrices, such as ceramics [14], geopolymer [15], polymer [16], and Portland cement [17], behaving as a reinforcement material. Fiber-reinforced composites had their biggest development during and after the Second World War due to the great need to develop alternative materials with superior technological characteristics, such as greater lightness [18]. The introduction of the use of natural fibers, which can be extracted from different parts of a plant, revolutionized the textile [19] and composites industries for ballistic purposes [20], guaranteeing significant performance improvements. However, the civil construction sector has been requesting new materials, more environmental-friendly and advantageous in terms of performance [17].