# Rheology, Hydration, and Microstructure of Portland Cement Pastes Produced with Ground Acai Fibers
## 1 Introduction
Countries that have great agricultural potential, such as Brazil, generate huge amounts of fibers that are often discarded as waste after some processing process, as is the case with acai fibers [21]. Axi (_Euterpe olercea_) is a typical fruit from the Amazon region, located in South America, which is used in cosmetics, medicines, and food industries, being widely consumed in Brazil and currently exported to several countries such as the United States and Canada [22]. During its beneficiation process, two agro-industrial wastes are generated--the lump (Figure 1a) and the fibers (Figure 1b)--which are disposed of in large volumes in landfills, generating financial costs for the industries. Figure 1: Acai waste: (**a**) Lump; (**b**) Natural acai fibers [23]; (**c**) Ground acai fibers. Some research has been developed over the last few years aiming at the reuse of these wastes in the development of alternative construction materials. For example, [PERSON] et al. [24] investigated the use of ground lump in ceramic matrices for the production of structural blocks, proving that up to 15% lump incorporation in traditional ceramic mass burned at 1050 \({}^{\circ}\)C produced blocks with high mechanical and physical properties, which can be applied for the development of more ecological and economical materials. [PERSON] et al. [25] evaluated the application of natural açai fibers in cement- and lime-based mortars, with addition ratios of 1.5%, 3.0%, and 5.0% by cement weight, both in natura (i.e., untreated) and treated with NaOH. In addition, the fibers were characterized regarding their physical, chemical, and morphological conditions, besides the fresh and hardened properties of the mortars [8]. The results revealed that additions of 3% of treated fibers provided good reinforcement in mortar, which is beneficial for its application in civil construction. However, such a study evidenced a usual problem of the application of natural fibers in cementitious matrices: their durability in high alkalinity medium (such as in Portland cement matrix) that can compromise the integrity of the composite. In this regard, [PERSON] et al. [26] evaluated issues and parameters related to the durability of mortars containing açai fibers, such as their exposure to wetting and drying cycles, salt spray, and thermal shock. The authors observed that the addition of the treated fibers mitigated the mechanical strength reduction after the different exposure cycles, corroborating its reinforcement purpose. In addition, 1.5% fiber incorporation resulted in the best overall performance. The main studies of cementitious materials reinforced with natural fibers are intended to evaluate mechanical parameters, such as strength and durability, due to the effect that fibers usually have on this type of matrix [17; 27]. In turn, studies focusing on the condition of the fluid paste, such as rheological behavior or even its interaction with the heat release throughout the cement hydration process, are still few in the literature of cement materials with additions of natural fibers [28]. The rheological parameters are essential to the knowledge of pastes and their behavior regarding workability, which is related to the casting capacity of the fresh mix and can affect its performance parameters in the hardened state [29]. The use of natural fibers can reduce the workability of pastes and mortars [30]; however, treating these fibers can lead to positive changes in the rheology and hydration of the cementitious matrix. The objective of this work is an experimental investigation on the rheology, hydration, and microstructure of Portland cement pastes with the addition of açai fibers in different conditions (in natura and treated, in dry and saturated conditions), at different contents. It is noteworthy that because it is a fiber little explored in the literature, there are no consistent studies aimed at this type of addition in cementitious pastes.