Ensete ventricosum natural fibres as reinforcement in textile reinforced concrete: Development, characterization, and durability investigation

The growing environmental concern and awareness of industrial pollution are driving the
construction industry to seek towards innovative materials that are abundant in supply,
durable, sustainable, economical, and environmentally friendly. Cementitious composites
reinforced with natural fibres are promising materials for sustainable engineering. Natural
fibres require only a relatively low level of industrialization to be processed, and the cost of
their production is small compared to an equivalent weight of the most common synthetic
fibres. Ensete ventricosum (Ev), also known as the False banana plant, is widely used
throughout Central and Eastern Africa, as well as in Asia and North America. Ethiopia is the
largest producer. Due to its local abundance, the fibre has an enormous valorisation potential
to make locally sourced and affordable building products in Ethiopia and beyond, which is
why the use of Ev fibre as reinforcement in cement composites is explored in this research.
To date, there has been no study on the use of aligned Ev fibres as a reinforcement in cement-
based composites. In most studies, short fibres are used as reinforcement in the cement
matrix, however this type of composite exhibits tension softening and limited tensile strength
due to the short fibre length and the limited amount of fibres that can be used. Cement
composites reinforced with aligned natural fibres are a new class of sustainable construction
materials; the few experimental studies conducted on unidirectional natural fibres have
shown significantly improved post-cracking performance, tensile strength, and toughness.
Therefore the mechanical performance of aligned Ev fibre reinforced cementitious
composites and in particular, the influence of the fibre volume fraction on the flexural
performance of the composite was evaluated in this research.
In the design of cement-based composites, consideration of durability is very important.
Particularly natural fibre reinforced cement-based composites are susceptible to degradation
due to the alkaline nature of the cement attacking the lignin of these fibres. Addressing these
durability concerns was therefore one of the main drivers of this research. Two strategies
have been explored: (i) the partial replacement of the Portland cement by different
supplementary cementitious materials (SCMs) abundantly available in Ethiopia, and (ii) fibre
surface modification, including alkaline treatment with NaOH and hot water.
The methods used in this research to steer the development of the Ev fibre reinforced cement
composites are multifold. The mechanical characterisation of the composite was performed
by four-point bending tests; a detailed investigation of the cracking behaviour was carried out
using optical Digital Image Correlation techniques and Acoustic Emission. The durability
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was investigated by exposure to both natural weathering and accelerated aging. To
characterize the fibre and to examine the effect of treatment, Fourier-transform infrared
spectroscopy, X-ray diffraction, and scanning electron microscopy were performed on fibre
bundles. Microstructural behaviour and chemical changes were studied by scanning electron
microscopy and thermal analysis. Measurements of ultrasonic pulse velocity were measured
to determine the effects of wet/dry cycles.
This study concluded that Ev fibres have physical, mechanical, and chemical properties
comparable to many other natural fibres, including abaca, flax, sisal, hemp, jute, kenaf, and
pineapple fibres, and that they can be used as reinforcement in cement composites. Under
bending, the Ev fibre reinforced cementitious composite exhibited multiple cracking. The
post-cracking stiffness, toughness, and flexural strength of Ev fibre reinforced specimens
increased with higher fibre content (test range: 3 % - 8 %). The optimal aligned fibre content
of 5 % resulted in a strength increase of almost 400 % compared to that of the reference
mortar specimen. In specimens exposed to natural weathering and accelerated aging
conditions, Ev fibre reinforced composites with 100 % Portland cement matrix however lost
all their ductility and strength, while specimens partially replaced with SCMs, and reinforced
with treated fibres exhibited significantly lower degradation. The partial replacement of
Portland cement by SCMs and surface modification of natural fibres showed to be promising
techniques to tackle the degradation of natural fibres in cement-based composites, paving the
way for the future development of Ev fibre-based cement composite sheets as locally sourced
and affordable building products.