Geopolymer Reinforced with Bamboo for Sustainable Construction Materials

Geopolymer Reinforced with Bamboo for Sustainable Construction
Materials
Ruy A. Sá Ribeiro1,2,a, Waltraud M. Kriven1,b, Marilene G. Sá Ribeiro2,c, Kaushik Sankar1,d,
Ires P. A. Miranda2,e, Fernando L. Almeida2,f
1
UIUC-University of Illinois at Urbana-Champaign, Materials Science and Engineering,
1304 West Green St., Urbana, Illinois, 61801 USA
a
2
[email protected], [email protected], [email protected]
INPA-National Institute for Amazonian Research, Structural Engineering Laboratory, Av.
André Araújo, 2936, Petrópolis, Manaus, AM 69067-375, Brazil
a
[email protected], [email protected], [email protected],
f
[email protected]
Keywords: Geopolymer composites, bamboo reinforcement, metakaolin, Amazon, SEM,
XRD.
Abstract. The objective of this project is investigate the use of bamboo as a structural reinforcement
for geopolymer composites. The bamboo-reinforced geopolymer composites (GPCBs) are intended
to replace conventional cements and concretes. This preliminary project uses randomly aligned
bamboo fibers from the Amazon region and metakaolin based geopolymer matrix activated by
potassium water glass. While fly ash-based geopolymers are now an established technology,
metakaolin-based cements and concretes still need to be developed and optimized based on the
knowledge of the specific characteristics and properties of local resources. As part of this
collaborative research, chopped bamboo fibers were prepared at INPA and the composites were
mechanically evaluated at UIUC laboratories. The GPCBs strengths were tested in four-point flexural
loading according to ASTM standards. In addition, x-ray diffraction and scanning electron
microscopy techniques were used to characterize the material. Test results demonstrate the potential
for GPCB as a green and sustainable construction material.
Introduction
The term polymer refers to organic molecules with large repeating units. Geopolymeric materials
are obtained from the polycondensation of aluminosilicate solids, activated by a concentrated aqueous
solution of alkali hydroxide or silicate. Such reactions produce poly-silicoaluminates or simply
polysialates, these materials generally called “geopolymers”, or inorganic polymers [1]. The main
application of geopolymers is as a binding phase, replacing Portland cement. It can also be used to
improve the mechanical properties of cements and concretes.
In 1983, large U.S. companies (Lone Star Industries) started along with the European (Geopolymer
Institute) to develop geopolymeric binders and cements composed of geopolymers and water. A year
later, a mixture of Portland cement to geopolymer called PBC (Portland Blended Cement), was
developed with properties similar to the pozzolanic cement currently known. The PBC has become
recognized in the market as the ideal for industrial paving and repair of highways material as it
hardened quickly and gained a compressive strength of 20 MPa, after 4 hours of its molding at room
temperature [2].
Several applications of high technology and added value for geopolymers have emerged since
then, among which worth noting are cements with low CO2 emissions. These materials can be made
by using aluminum silicon sources like fly ash, which replace the minerals or other natural materials.
Fly ashes are ashes of fine texture entrained by the combustion gases in the combustion of pulverized
coal, which occurs at thermoelectric power plants. They are extracted from the gases through a postfilter collecting system or by use of an electrostatic precipitator. The fly ash is mixed with Portland
cement (OPC) to contain up to 60% by volume to obtain an environmentally sustainable cement,
cement HVFA (high volume fly ash).
The usual route is the basic processing route, based on the steps of mixing, molding (compression)
and curing, similar to the production process of the concrete. The optimum curing temperature is
between 40-65 ºC. Geopolymers are immune reactions to the type alkali-aggregate. The mechanical
properties are superior to Portland cement in general, but are influenced by the content of the liquid
phase in the mixture, the curing temperature and the final porosity of the body. They have high fire
resistance (can withstand temperatures of 1000-1200 °C without losing functional characteristics)
[3,4], high chemical stability and inertia, which gives them excellent durability. They have low
thermal conductivity values ranging from 0.24 to 0.3 W/MK. The energy required to produce
geopolymer cement concrete (GCC) is considerably lower than that required for concrete mixes of
Portland (CPC) cement, resulting in up to 90% reduction in carbon emissions. The primary curing
time (25 MPa compression) varies from 4-48 hours [1]; studies indicate that geopolymers acquire
about 70% of the compressive strength in 4 hours. Full curing occurs around 28 days, which may
result in a geopolymer compressive strength of 100 MPa [2]. A composition used in the literature
provides a mixture by weight of 57% fly ash and 15% calcined kaolin (metakaolin) and alkali as a
binder, 3.5% sodium silicate, 20% water and 4% potassium or sodium hydroxide. This composition
resulted in a threshold compressive strength of 75 MPa after full cure. Duxson et al. [5,6] carried out
extensive research on the relationships between composition, processing, microstructure and the
properties of metakaolin-based geopolymers (MKGPs). Rashad [7] presented a thorough review on
alkali-activated MKGPs.
Geopolymers fall into an interesting interdisciplinary context of engineering (ceramics, polymeric
materials, environmental, civil), and other important knowledge areas: chemistry, geology,
archeology, history. They present themselves as an environmentally friendly and still unexplored with
great prospects as a sustainable engineered material solution. In addition to the mineral reserves
containing aluminosilicates, Brazil has many industrial processes that generate fly ash and other byproducts as sources of aluminosilicates, so it has the raw material for exploitation of this technology
in abundance. Moreover, the introduction of fibers, particles and strip of native or natural materials
grown in the Amazon (such as bamboo) in the production of geopolymeric composites, promote
higher strength, rigidity, and workability, generating green high-performance materials. The use of
regional and local materials in the production of geopolymeric composites reduce environmental
impacts and raise their practicality in different situations.
Herbal biocomposites (natural fibers), have low density, low cost and low energy consumption, as
well as neutralizing CO2. Characteristics of bamboo fibers include: low cost, high strength and
biodegradability; absorption of CO2 and production of O2 three times more than other plants. Bamboo
is a fast growing and high yield renewable resource, readily available in Brazil, which received
governmental support for plantation and technological research. Bamboo can yield 40-50 culms per
clump, and add 10-20 culms yearly. It reaches maximum height in 4-6 months with a daily increment
of 150-180 mm; and it takes only 4 years to mature.
In the pursuit of tough or semi-ductile and high strength green geopolymer composites, several
researchers used natural fibers, such as basalt [8,9], corn husk [10], wool [11], jute [12], rice stem
[13], fique [14], for reinforcement of MKGP. Adding 10 wt.% of 13 µm by 6.35 mm long basalt
fibers to potassium-based geopolymer composites yielded 19.5 MPa three-point flexure strength [8].
Increasing the chopped basalt fibers length to 12.7 mm yielded 27.07 MPa three-point flexure strength
[9]. Sodium-based geopolymer reinforced with corn husk fiber bundles resulted in 14.14 MPa fourpoint flexure strength [10]. Sodium-based geopolymer reinforced with 5 wt.% wool fiber bundles
yielded 8.1-9.1 MPa three-point flexure strength [11]. Sodium-based geopolymer reinforced with 30
wt.% untreated jute weave resulted in 20.5 MPa four-point flexure strength [12]. Potassium-based
geopolymer reinforced with 6.4 wt.% rice stem yielded 18.45 MPa three-point flexure strength [13].
Potassium-based geopolymer reinforced with 30 wt.% alkali-treated fique fibers yielded 11.4 MPa
four-point flexure strength [14]. Up to this date, we found no published work on MKGP reinforced
with bamboo fibers.
The objective of this research is investigate the use of bamboo as a structural reinforcement for
geopolymer composites. The bamboo-reinforced geopolymer composites (GPCBs) are intended to
replace conventional cements and concretes, using low carbon emission and producing sustainable
green materials.
Experimental Procedures
Bamboo Fibers (BFs) Processing. Amazonian tropical bamboo specie Guadua angustifolia was
selected based on abundance, accessibility, mechanical properties, durability and commercial size
criteria. Four-year old Guadua culms were collected from a research plantation area [15,16] at INPA
in Manaus, Brazil, and immersed in water for three days for better machine workability. The green
bamboo culms (Fig. 1) were chopped through a chipper PZ8 Pallman and the chips were transformed
into fiber bundles through a Hammer Mill Bison at INPA’s Particleboard Laboratory. The Guadua
bamboo fiber bundles (GBFs) (Fig. 1) were air-dried and filtered by an Allgaier sifter machine
through a mesh #4 (12.51 – 40 mm). Bamboo main chemical constituents are 60% cellulose and 32%
lignin and hemicellulose [17]. Minor constituents are resins, tannins, waxes, inorganic salts. At the
Geopolymer Laboratory of UIUC, before utilization the GBFs were washed with deionized water and
set to dry-in two layers of paper towels.
Fig. 1 Water-treated Guadua bamboo culms ready to be chopped, and mechanically attained air-dried
fiber bundles
Geopolymer Composite Processing. Geopolymer was prepared at the Geopolymer Laboratory with
potassium water glass and Metamax metakaolin (1.3 µm) mixed at a high shear mixer. This mixture
was put in a mixer and degassing machine for fine removal of bubbles. GBFs 5 wt.% was slowly
added to the geopolymer slurry and manually mixed until complete integration occurred. The
geopolymer composite slurry was poured onto a high strength plastic mold attached to a vibration
table for more uniform distribution of GBFs and less voids formation. The filled mold was wrapped
in plastic wrap to prevent water loss during setting and curing. It was pressed, and then cured for 24
hours in a 50 ºC oven. Then, the GPCB plate was demolded and set to dry at room temperature.
Third-Point Loading Flexural Strength. Seven (155 x 25 x 4 mm) GPCB specimens (Fig. 2) were
cut from the plate for third-point loading flexural strength test according to ASTM standard C1341-
13 [18]. The average density of GPCB is 1.35 g/cm3. Tests were carried out by an Instron testing
machine at the Advanced Mechanical Testing and Evaluation Laboratory (AMTEL) of UIUC. The
test span to depth ratio was 25:1, and the crosshead displacement rate was 0.10 mm/s. Strain was
measured by crosshead displacement.
Fig. 2 GPCB tested specimens
Microscopic Analysis. The nature of the interactions between the fiber bundles and the geopolymer
matrix was analyzed by scanning electron microscopy (SEM) using a JEOL JSM-6060 LV
microscope. Phase characterization of the tested GPCB was performed by x-ray diffraction (XRD)
on a Siemens/Bruker D-5000.
Results and Discussion
SEM micrographs of the structure of the GPCB bar (Fig. 3) showed gaps between the bamboo
fibers and the geopolymer matrix. Crack propagation through the geopolymer matrix deflected around
the fibers. These gaps and crack development are characteristics of a weak interface. This may be due
to the roughness and shrinkage of the untreated bamboo fibers. Large displacement was observed in
all samples before the initial vertical crack at the central point. Central displacement continued until
the fibers stretched to breaking, accompanied by some fiber pullout. This behavior is also reflected
in the shape of the stress–strain curve (Fig. 4), showing very smooth behavior without sharp kinks.
(a)
(b)
Fig. 3 SEM micrographs of GPCB tested specimen showing gaps and crack propagation in (a) back
scattered (BES) mode, 30x; (b) secondary electron (SEI) mode, 75x
Fig. 4 Typical stress-strain curve for GPCB tested in third-point loading bending
The average value of the four-point flexural strength (σu) for the GPCB tested specimens is 4.64
MPa.
X-ray diffractogram for potassium-based GPCB is presented in Fig. 5. XRD pattern shows GPCB
as x-ray amorphous with a pronounced hump at 2ϴ-28º, which confirms geopolymer formation.
Fig. 5 XRD pattern of GPCB
Conclusions
This preliminary investigation reinforcing geopolymer composite with untreated bamboo fibers
resulted in the following:
1) SEM micrographs reviewed a weak interface between the fibers and the geopolymer matrix.
However, the stress-strain curves were very smooth, and yielded a reasonable flexural strength
of 4.64 MPa.
2) X-ray diffraction pattern confirmed amorphous geopolymer formation with a hump at 2ϴ-28º.
3) The bamboo-reinforced geopolymer composite is a potential sustainable green material for
construction.
Acknowledgements
Bamboo collection and fibers preparation and conditioning were done at the Structural
Engineering Laboratory (LTEE-INPA) and at the Particleboard Laboratory (LA-INPA). SEM and
XRD were carried out at the Frederick Seitz Materials Research Laboratory Central Facilities (FSMRL). Flexural strength tests were done at AMTEL-UIUC.
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