Influence of Different Types of Treatments on Amazonian Vegetable Fibers on the Performance of Mortars Based on Portland Cement, Metakaolin and Fly Ash

Abstract

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.

A Review of the Use of Natural Fibers in Cement Composites: Concepts, Applications and Brazilian History

“…The modification of the surface of the natural fiber is a necessary method to improve the fiber–matrix adhesion and, consequently, the properties of the composite. In addition, the treatments help to: remove impurities from ash, waxes, and sugars that can delay the hardening of the fibers, improve adhesion, increase crystallinity and consequently mechanical strength, or even improve fiber durability aspects [ 98 , 99 , 100 , 101 ].…”

“…Simpler treatments also demonstrate success in improving the interfacial interaction between the fiber and the matrix, such as the hot water wash treatment performed by [ 99 ]. Fonseca et al [ 99 ] compared the fiber washing treatment with three other treatments, such as hornification, alkaline treatment with NaOH, and hybridization. Hornification consists of the application of ten cycles of wetting/drying, as performed by [ 121 ].…”

“…Hornification consists of the application of ten cycles of wetting/drying, as performed by [ 121 ]. The hybridization process consisted of a combination of the chemical and physical treatment of the fiber, such as the washing in hot water, followed by treatment with NaOH and an application of a 5% hydrogen peroxide solution for 3 h in a fiber solution ratio of 1:20 [ 99 ]. The hybridization process contributed to increasing the mechanical strength and crystallinity of the fiber.…”

“…Fonseca et al [ 99 ] observed that chemical treatments (NaOH solution and hybridization) resulted in greater water absorption. The hornification treatment alters the surface of the cellulose fibrils, promoting less water absorption, a result also found in [ 122 ], while the hot water treatment results in less water absorption due to changes in the fiber structures, which have become more rigid.…”

Effect of combined fiber-microcrystalline cellulose reinforcement on the rheology and hydration kinetics of cementitious composites

“…It is the most abundant polymer in the world, with an estimated production of 10 14 tons per year, and can be found in different forms of life such as green plants, fungi, protozoa, and prokaryotes [1]. In the wood industry, cellulose-based materials are generally used in paper production as a possible emulsifier and dispersing agent, which can minimize the carbon footprint, generating interest in biodegradable materials [2], [3]. Although it is a natural product, it has the potential to replace synthetic polymers, since they are non-petroleum-derived materials and can also be used to produce micromaterials [4], [5].…”