Plant fiber reinforced geopolymer – A green and high performance cementitious material
Rui Chen (Graduate Student), Saeed Ahmari (Graduate Student), Mark Gregory (Undergraduate Student), Lianyang Zhang (Advisor)
Department of Civil Engineering and Engineering Mechanics, The University of Arizona
Sweet Sorghum Fiber
Sweet sorghum is a potential crop for large scale production of
biofuel. After the juice is extracted from sweet sorghum stalks for
ethanol production, a large amount of bagasse is left behind. For
large scale bioethanol production, it is a great challenge to handle
the significant amount of bagasse. Because the bagasse contains
high content of fibers, however, it has a great potential to be used
for reinforcement of cementitious materials.
(a)
(b)
30
Fiber content (%)
25
0
20
1
2
15
3
10
6.0
5.0
4.0
5
3.0
0
Fly ash
Alkali (NaOH)
Water
Geopolymer paste
2
3
4
5
0.0
6
1.0
Sweet sorghum bagasse: (a) As received; and (b) After treatment
2.0
3.0
Fiber content (%)
(b)
(a)
(a) Split tensile test load and displacement curves; and (b) Effect of fiber
content on tensile strength of geopolymer paste samples
Research Approach
SEM images of the failed surface of a split tensile test sample
Toughness
The project takes a multi-scale and multi-disciplinary approach to
investigate sweet sorghum fiber reinforced fly ash geopolymer.
40
Pull-out Test
Flexural Tests
SEM/EDS Imaging
Toughness (Nm)
XRD Characterization
25
20
15
10
5
AFM Nano-indentation
Durability Tests
Conclusions:
30
Force
Split Tensile Tests
35
Micro/Nano–Scale
Investigation
Macro–Scale Study
Conclusions & Future Work
Post-peak toughness
Unconfined Compression
Tests
0
Displacement
0.0
1.0
2.0
3.0
Fiber content (%)
(a)
DEM Simulations
(b)
(a) Definition of post-peak toughness; and (b) Effect of fiber content on postpeak toughness of geopolymer paste samples
Preliminary Results
Different failure modes
Unit Weight & Unconfined Compression Strength
(a)
30.0
16.0
Future Work:
UCS (MPa)
15.0
14.0
The unit weight of geopolymer paste samples decreases with
higher sweet sorghum fiber content, which is beneficial for
producing light weight cementitious material.
The inclusion of sweet sorghum fibers in geopolymer paste
samples slightly decrease the UCS.
The tensile strength increases with the content of sweet
sorghum fibers up to 2% and then decreases to be lower
than that of the plain geopolymer paste sample.
The post-peak toughness increases significantly with the
content of sweet sorghum fibers up to 2% and then slightly
decreases but is still much higher than that of the plain
geopolymer paste sample.
There is a clear transition from the brittle failure of the plain
geopolymer specimen to the “ductile” failure of the
geopolymer paste specimen containing sweet sorghum
fibers.
(b)
25.0
Unit weight (kN/m 3)
The fly ash-based geopolymer is produced by using Class F fly
ash in reaction with an alkaline hydroxide solution of 10 M
concentration at ambient or slightly elevated temperature, which
has an amorphous to semi-crystalline interconnected polymeric
structure.
1
Displacement (mm)
This project investigates the reinforcement of fly ash-based
geopolymer with sweet sorghum fiber, a residue after sweet
sorghum is used for production of biofuel.
Fly Ash-Based Geopolymer
SEM Imaging
7.0
0
Recently, geopolymer has been of great research interest as an
ideal OPC alternative for sustainable development. Geopolymer
not only provides performance comparable to OPC in many
applications, but has many additional advantages, including
rapid curing, high acid resistance, excellent adherence to
aggregates, immobilization of toxic and hazardous materials,
and significantly reduced energy usage and greenhouse gas
emissions. As OPC, however, geopolymer exhibits brittle
behavior with low tensile strength and is sensitive to cracking.
These shortcomings not only impose constraints in structural
design, but also affect the long term durability of structures.
Research has been conducted on utilizing steel, carbon, and
glass to reinforce geopolymer. Although these fibers can
effectively increase the tensile strength, ductility and toughness
of geopolymer, they are all produced by a high energyconsuming process and there is concern about how to do with
them at the end of their life cycle. Growing environmental
awareness and the need to ensure sustainability of construction
materials have led to efforts to look for alternative fibers. Recent
years have witnessed an increasing interest in natural plant
fibers because they are abundant, reproducible and
environmentally friendly. So far researchers have studied
utilization of natural fibers to reinforce OPC cementitious
materials and very promising results have been obtained; but
very little research has been conducted on utilizing natural fibers
to reinforce geopolymer.
Preliminary Results (Cont.)
Split Tensile Test
Tensile strength (MPa)
Ordinary Portland cement (OPC) is widely used in construction
industry; but the utilization of OPC imposes an enormous impact
on the environment. The manufacturing of OPC not only
consumes significant amount of natural materials and energy
but also releases substantial quantity of greenhouse gases. To
produce 1 ton of OPC, about 1.5 tons of raw materials is
needed and 1 ton of CO2 is released to the atmosphere.
Worldwide, the cement industry alone is estimated to be
responsible for about 7% of all CO2 generated. Another
drawback for OPC is that it may not provide the required
properties for specific applications, such as rapid development
of mechanical strength and high resistance to chemical attack.
Preliminary Results (Cont.)
Force (kN)
Background
Conduct DEM simulations to investigate how the distribution
and orientation of fibers affect the mechanical properties.
Conduct wet/dry cycling experiment to test the durability of
the composite.
20.0
15.0
10.0
13.0
5.0
Acknowledgement
0.0
12.0
0.0
1.0
2.0
3.0
0.0
2.0
1.0
Fiber content (%)
Fiber content (%)
(a)
(b)
(a) Unit weight versus fiber content; and (b) UCS versus fiber content for
sweet sorghum reinforced geopolymer paste samples
3.0
Different failure modes of geopolymer paste samples containing (a) no fibers;
and (b) 1% sweet sorghum fibers
The research is supported by the National Science Foundation.
The Campus Agriculture Center (CAC), University of Arizona,
provided the sweet sorghum bagasse and the Salt River
Materials Group, Phoenix, Arizona provided the Class F fly ash.