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

The use of natural lignocellulosic fibers has become popular all over the world, as they are abundant, low-cost materials that favor a series of technological properties when used in cementitious composites. Due to its climate and geographic characteristics, Brazil has an abundant variety of natural fibers that have great potential for use in civil construction. The objective of this work is to present the main concepts about lignocellulosic fibers in cementitious composites, highlighting the innovation and advances in this topic in relation to countries such as Brazil, which has a worldwide prominence in the production of natural fibers. For this, some common characteristics of lignocellulosic fibers will be observed, such as their source, their proportion of natural polymers (biological structure of the fiber), their density and other mechanical characteristics. This information is compared with the mechanical characteristics of synthetic fibers to analyze the performance of composites reinforced with both types of fibers. Despite being inferior in tensile and flexural strength, composites made from vegetable fibers have an advantage in relation to their low density. The interface between the fiber and the composite matrix is what will define the final characteristics of the composite material. Due to this, different fibers (reinforcement materials) were analyzed in the literature in order to observe their characteristics in cementitious composites. Finally, the different surface treatments through which the fibers undergo will determine the fiber-matrix interface and the final characteristics of the cementitious composite.

Development of Alkaline-Activated Self-Leveling Hybrid Mortar Ash-Based Composites.

This study investigated the reactivity properties of self-leveling hybrid alkali-activated cements, such as ordinary Portland cement (OPC) and its residual precursors, coal bottom ash (BA), and rice husk ash (RHA). Due to the relatively low reactivity of BA, binary mixes were produced with OPC using contents of 2.5⁻30% in the treated BA samples. Furthermore, ternary mixes were prepared in proportions of 25%, 50%, and 75% with RHA as a replacement material for the OPC (mix with 90%:10% BA:OPC). For all of the mixes the spreading behaviors were fixed to obtain a self-levelling mortar, and dimensional changes, such as curling and shrinkage, were performed. Mortars with 30% OPC reached a compressive strength of 33.5 MPa and flexural strength of 7.53 MPa. A scanning electron microscope (SEM) and X-ray powder diffraction (XRD) were used to indicate the formation of N-A-S-H and a (N,C)-A-S-H gel, similar to the gel with trace of calcium. The best performance was achieved when the binary mix produced 10% OPC. A hybrid mortar of OPS-BA presented 10 times lower susceptibility to curling than an OPC mortar. The results showed that both ashes reduced the shrinkage and curling phenomena.