Introduction: structural and infrastructure applications. However, in spite

Introduction:

The use
of composites started centuries ago with the use of natural fibers. Clay was
reinforced with straw to build walls in the ancient Egypt. However, the
interest on the natural fibers reduced in the further times as more strong
materials like metals were introduced. The rise of composite materials began
when glass fibers were introduced with a possibility of combining them with
tough resins to produce strong composites 1. Advanced polymeric composites that
use high strength fibers like graphite, aramids, glass, etc. gained more
importance in the decades that followed due to their high strength and low-density
properties in comparison with metals and these are gradually replacing the
metals. These composites were initially developed for aerospace industry and
now they are being used in variety of applications like automotive parts, sporting
goods, structural and infrastructure applications. However, in spite of their
strength and versatility, the major problem associated is their degradability and
the replenishibility of the sources. Since the products are mainly derived from
petroleum products, these are not sustainable and their disposal after their
useful life is a major issue concerning the amount of waste generated from
different end uses and the cost of processing the waste and landfills which in
turn leads to pollution. The growing environmental
concern in the current times has led to a renewed interest in the use of
natural fibers and resins as a substitute of synthetic fibers and in the
composite materials. The fact that natural
fibers are sourced from plants which are renewable in origin and the fact that
they can be easily biodegraded has encouraged more research into this field.

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Fully green composites can be developed from both natural fibers and resins
that are derived from natural, sustainable and renewable sources. Commercially available
forms of fibers such as loose fibers, yarns, woven and knitted fabrics or non-woven
mats make it possible to combine them in different layers and engineer them for
varied applications. The composites can be manipulated according to the
mechanical properties of the fibers used. Furthermore, high strength cellulosic
fibers, protein fibers and bio based resins have been developed that have
excellent properties and can be used as reinforcements 2. This paper aims to review the use of fully green composites
in structural and infrastructure applications. While
large multistoried structures or bridges need the high strength and stiffness
of advanced composites to be used as structural elements, smaller structures
such as single room cabins, temporary housings or shelters, etc., may not need
composites with such high strength. For such structures composites with
moderate mechanical properties, comparable to wood, would work well. Further,
non-load- bearing components such as walls, ceilings, etc., may also use
composites with moderate mechanical properties. Some of the structural elements
of single houses/ cabins would still need somewhat higher strength,
particularly if light weighting of the structure (e.g., for transportation
ease) is desired. While wood is considered as sustainable, one of its biggest disadvantages
is that it can only be harvested after the trees are grown to their maturity,
which, depending on the variety, can take 20 to 30 years. However,
plant-derived fibers (e.g., jute, hemp, sisal, ramie, banana, pineapple,
henequen, flax, kenaf, etc.), which can be used as reinforcement, as well as
resins (e.g., plant-based proteins and starches) are yearly renewable.

Composites made using plant-derived fibers and resins can be engineered to
obtain properties better than those of wood and would be excellent for smaller
structures. Furthermore, if high strength fibers are used along with the same
resins, advanced green composites having high mechanical properties may be
fabricated. These advanced green composites can be used as primary structural
elements for construction. In addition to their good mechanical properties, the
rich variety of sensorial properties possible in green composites due to the
natural fibers, gives this material family a great advantage in comparison to
its oil- based predecessors and many other panelized materials on the market,
such as fiber cement and aluminum 2. The
main impetus in pursuing the use of green composites instead is the ecological
benefit: natural composites offer the potential to create large volume,
biodegradable structural components using only renewable resources, resulting
in reduced quantities of embodied energy. Using materials like natural
composites that reduce construction waste and increase energy efficiency would
provide a solution to immediate infrastructure needs while promoting the
concept of sustainability 3.