The addition of natural fibers used as reinforcement has great appeal in the construction materials industry since natural fibers are cheaper, biodegradable, and easily available. In this work, we analyzed the feasibility of using the fibers of piassava, tucum palm, razor grass, and jute from the Amazon rainforest as reinforcement in mortars, exploiting the mechanical properties of compressive and flexural strength of samples with 1.5%, 3.0%, and 4.5% mass addition of the composite binder (50% Portland cement + 40% metakaolin + 10% fly ash). The mortars were reinforced with untreated (natural) and treated (hot water treatment, hornification, 8% NaOH solution, and hybridization) fibers, submitted to two types of curing (submerged in water, and inflated with CO2 in a pressurized autoclave) for 28 days. Mortars without fibers were used as a reference. For the durability study, the samples were submitted to 20 drying/wetting cycles. The fibers improved the flexural strength of the mortars and prevented the abrupt rupture of the samples, in contrast to the fragile behavior of the reference samples. The autoclave cure increased the compressive strength of the piassava and tucum palm samples with 4.5% of fibers.

This study aimed to evaluate the physical, chemical, and mechanical properties of different Amazonian vegetable fibers to produce cementitious mortars reinforced with different types of vegetable fibers from the Amazon. Also, to analyze the influence of different types of chemical and physical treatments, on the direct tensile strength of vegetable fibers, water absorption of vegetable fibers and on the mechanical properties of compressive strength, flexural strength, and water absorption of mortars. Four vegetable fibers from the Amazon rainforest, from the Upper Rio Negro region (piassava, jute, tucum and razor grass) were used to produce cement composites with 50% Portland CPII-F cement and additions of supplementary cement materials (40% metakaolin and 10% fly ash), with cement mortar and sand trace 1:2:0.60. The cementitious composites were subjected to two types of curing: initial curing in air followed by final curing in water and curing in a pressurized autoclave with CO 2 , both for 28 days. The treatments applied to the fibers were: washing with hot water; hornification; chemical treatment with sodium hydroxide and hybridization (hot water washing coupling, hornification, sodium hydroxide (NaOH) and application of hydrogen peroxide (H 2 O 2 )). As a result, the hybridization treatment increased the mechanical strength of the tucum fiber from 67.20 MPa (untreated fiber) to 318.80 MPa (treated), corroborating the increase in the crystallinity index from 59.84% to 66.73%. The flexural strength of cementitious composites reinforced with 4.5% tucum fibers and razor grass submitted to curing in an autoclave with CO 2 was, respectively, 49.61% and 61.75% higher than the reference composite (without fibers) in the water curing. Therefore, both the autoclave cure and the hybridization treatment proved to be viable for its application in composites with vegetable fibers.