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Is Wollastonite Capable of Improving the Properties of
Wood Fiber-cement Composite?
Ali Hassanpoor Tichi,a Behzad Bazyar,a,* Habibollah Khademieslam,a
Hossein Rangavar,b and Mohammad Talaeipour a
Effects of wollastonite substitution were investigated relative to the
mechanical, physical, and microstructural properties of a wood fibercement composite. Wollastonite content of 0%, 3%, 6%, and 9% and
lignocellulosic material (kraft fibers) content of 10%, 20%, and 30% were
used based on the dry weight of cement. Then the lignocellulosic material
and the resulting board samples were compared to a control (without
wollastonite). Modulus of rupture (MOR), modulus of elasticity (MOE),
water absorption, and fire resistance tests were conducted to examine the
characteristics of the board composite. The results showed that the
mechanical properties of wood fiber-cement composite were improved by
the 9% wollastonite substitution. The fire-resistance of the composite
board was improved when the wollastonite content was increased.
Furthermore, cement boards with 9% wollastonite exhibited lower water
absorption in comparison to the other specimens. Scanning electron
microscopy (SEM) results showed that the calcium hydroxide formed
hydrated calcium silicate gel (C-S-H gel) after the addition of wollastonite.
The SEM images showed that the micro-structure of the boards were
improved by increasing the nano-wollastonite content.
Keywords: Kraft fibers; Cement boards; Fire resistance; Wollastonite
Contact information: a: Department of Wood and Paper Science, Faculty of Natural Resources and
Environment, Science and Research Branch, Islamic Azad University, Tehran, Iran; b: Department of
Wood Industries, Faculty of Civil Engineering, Shahid Rajaee Teacher Training University (SRTTU),
Tehran, Iran; *Corresponding authors: bazyar@srbiau.ac.ir
INTRODUCTION
Wood fiber-cement composite are produced and have been used since 1895 (Alpar
2009). The most known product types include wood wool (excelsior) boards, cement
bonded particle boards, fiber-cement products, and building blocks (Alpar 2000). Woodcement products are already used worldwide for roofs, floors, and walls. They have
numerous advantages when compared to panels produced with organic resins, such as high
durability, good dimensional stability, good acoustic and thermal insulation properties, and
low production cost (Na et al. 2014). The main problem with producing WCC is the
incompatibility of cement and wood. Hydration and MOR and MOE of WCC are sensitive
on wood extractives. Water dissolves water-soluble chemicals of wood and some of these
are inhibitors, such as sugars (e.g., hexoses: mannose or glucose), tannin, and
hemicellulose (e.g., glucomannan, xylan, arabinogalactan, or galactan), and these hinder
or stop this hydration of cement. Hardwoods due to higher amount of wooden extractives
(soluble xylans) are generally less compatible than softwoods (Naji Givi et al. 2010).
Tichi et al. (2019). “Kraft fiber-cement composites,” BioResources 14(3), 6168-6178.
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The use of admixtures in wood-cement to accelerate the curing process can be
further subdivided into the use of mineral and chemical admixtures. Chemical admixtures
include magnesium chloride (MgCl2), calcium chloride (CaCl2), water glass (Na2SiO2),
and aluminum silicate (Al2(SO4)3) (Alpar 2009). The most common mineral admixture
used as an accelerator is microsilica, or silica fume, ash, and wollastonite. This material,
as cement curing accelerators, helps to improve wood-cement compatibility. Alternatively,
the use of pretreatments, such as aqueous extraction, to remove inhibitory substances from
wood is another method to improve matrix compatibility (Na et al. 2014). Commercial
grades of wollastonite are typically high in purity because most ores must be beneficiated
by wet processing, high-intensity magnetic separation, and/or heavy media separation to
remove accessory minerals. The minerals most commonly found associated with
wollastonite are calcite (calcium carbonate), diopside (calcium magnesium silicate), and
garnet (calcium aluminum silicate). Wollastonite is hard, white, and alkaline (pH 9.8). It is
exploited for its chemistry as a source of CaO and SiO2, and its low ignition loss, low oil
absorption, low moisture absorption, and fire-retarding properties (Ciullo 1997(. The effect
of wollastonite has been reported to improve the dimensional stability of solid woods
(Poshtiri et al. 2013), and to increase the thermal conductivity coefficient of mediumdensity fiberboards (MDF) (Taghiyari et al. 2013). Fire-retarding properties of wollastonite
have been noted in the literature when it is used in solid wood and wood composite
materials (Poshtiri et al. 2013; Taghiyari et al. 2013). Khosrviyan (2009) found that the
physical and mechanical properties of wood-plastic composite were improved with the
addition of wollastonite. Moreover, wollastonite has antifungal properties (Taghiyari et al.
2014a, 2014b). A wide variety of fibers, from different forms and origins, have been used
to reinforce cementitious matrices, while kraft pulp is the most common fiber form used.
This is because lignocellulosic fibers are a cheap raw material that are used by the paper
industry; they can be easily dispersed in water and can represent a basic component for the
production of cementitious materials. ACI 544 recommends that kraft pulps are favored
for their use in cement-based materials due to their low lignin and hemicelluloses levels,
which are less alkali resistant than cellulose that has been obtained from the kraft pulping
process (ACI 544, 2002).
The production of waste biofiber wood fiber-cement composite reinforced with
nano-SiO2 particles as a substitute for asbestos cement composites showed that the addition
of silica nanoparticles to mixtures increases mechanical properties. Additionally, the
physical properties was improved by the addition of up to 1% silica nanoparticles
(Hosseinpourpia et al. 2012). Increasing the wollastonite microfiber content resulted in a
compressive strength comparable to or higher than that of the control mixture without
microfibers. Wollastonite microfibers reduced shrinkage strains and increased cracking
resistance compared to that of the control mixture. However, no noticeable improvement
in the flexural behavior was achieved with the addition of wollastonite microfibers due to
a sudden rupture of microfibers within the matrix (Soliman 2011). Del Meneéis et al.
(2007) produced oriented strand board (OSB) from pine (Pinus tadea) and Portland cement
by mixing them in a 1:1 ratio. Cement was partly substituted by silica fume (SiO2) in
proportions of 0%, 10%, or 20%. The best results were observed for the board made with
cement that had 10% SiO2 substitution.
This research reports the preparation and the properties of wood fiber-cement
composite that were reinforced with wollastonite. The morphological, mechanical,
Tichi et al. (2019). “Kraft fiber-cement composites,” BioResources 14(3), 6168-6178.
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physical, and fire retardancy properties of the wood fiber-cement composite with different
compositions were also investigated.
EXPERIMENTAL
Materials
The cement used in this study was type II Portland cement; it was purchased from
Abyeik Company (Qazvin, Iran). The natural fibers used in this research were kraft pulp
fibers obtained from Mazandaran Wood and Paper Industry (Sari, Iran). Commercial
wollastonite (WOLL) and calcium chloride were purchased from Vard Manufacturing
Company of Mineral and Industrial Products (Tehran, Iran) and Merck Company
(Darmstadt, Germany), respectively.
Sample preparation
Specifications of the wollastonite composition are given in Table 1. Kraft pulp
fibers were applied at three proportions (10%, 20%, or 30%, with respect to the total
content of binder in each mixture), and different wollastonite substitution levels (0%, 3%,
6%, or 9%) for cement.
Table 1. Inorganic Composition of Wollastonite Used in This Study (Taghiyari et
al. 2013)
Inorganic Component
SiO2
CaO
Fe2O3
Al2O3
TiO2
K2O
MgO
Na2O
SO3
Percentage (%)
46.96
39.77
2.79
3.95
0.22
0.04
1.39
0.16
0.05
Composite production
First, the cement powder and kraft pulp fibers were mixed together by hand. Next,
water and wollastonite were mixed using a mortar mixer at a moderate speed (200 rpm) for
2 min. Finally, all the materials were stirred at a high speed (600 rpm) for 4 min. The
mixture was then poured into molds with the dimensions of 40 cm × 30 cm ×4 cm. The
obtained mat was pressed (30 kg/cm2) using a Burkle LA-160 flat press (Babol, Iran) for
10 min at room temperature to obtain a target thickness of 12 mm. The density was kept
constant for all treatments (1.1 g/cm3). The boards were conditioned at standard conditions
(20 ± 1 °C, 65 ± 2% relative humidity) for an additional 28 days for the cement to cure.
Methods
Mechanical tests
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The samples were then evaluated for flexural moduli of elasticity and rupture
according to DIN EN 634 parts 1 and 2 (1995) using a universal testing machine (model
GT-TCS-2000; Taichung Industry Park, Taichung, Taiwan) at the speed of 10 mm/min.
The specimens were trimmed to the dimensions of 350 mm × 50 mm × 12 mm for the
mechanical tests. Three samples were evaluated for each treatment. The load and deflection
were continuously recorded and the data were used to calculate flexural modulus of
elasticity (MOE) and modulus of rupture (MOR) according to Eqs. 1 and 2,
FL
bd 2
(1)
FL3
4bd 3 D
(2)
MOR 1.5
MOE
where F is the maximum force (N), L is the span length (mm), b is the sample width (mm),
d is the sample thickness (mm), and D is the deflection.
Physical tests- Water absorption
The effect of composite formulation on the water uptake was determined in samples
with the dimensions of 50 mm × 50 mm × 12 mm according to DIN EN 634 parts 1 and 2
(1995). The sample was initially oven-dried for 48 h at 103 °C, and the mass was recorded.
The sample was then soaked in distilled water for 2 h and 24 h. Water uptake was then
calculated based on the initial oven-dried mass and the wet mass values.
Mass loss due to fire activation
The specimens (150 length × 100 width × 12 thickness, mm3) were prepared
according to the ISO 11925 (2010) specifications for the fire resistance tests. Mass loss of
the samples due to fire exposure was vertically mounted on a holder up-straight and
exposed to a Bunsen-type burner (with the internal diameter of 11 mm) hold at 45 degrees
to the surface of the specimen for 120 seconds in accordance with method described by
Ayoub Esmailpour et al. (2017).
Scanning electron microscopy (SEM)
To confirm the distribution of wollastonite, SEM imaging was carried out at the
thin-film laboratory, FE-SEM lab (Field Emission), School of Electrical and Computer
Engineering, University of Amir Kabir, Tehran, Iran. One specimen with dimensions of 10
mm × 10 mm was prepared for SEM imaging for each treatment.
Statistical analyses
Statistical analyses were performed using Statistica software (Dell Inc., v.13,
Landolock, TX, USA) at a significance level of α = 0.05. The obtained results were
analyzed statistically, and an analysis of variance (ANOVA) was performed to determine
the significance of the tested parameter. A Duncan’s multiple range test (DMRT) was
performed to compare treatment means.
RESULTS AND DISCUSSION
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Mechanical Properties
The results from the mechanical testing are shown in Figs. 1 and 2. As shown, the
MOR and MOE values increased in the cement boards that contained wollastonite
compared to the cement boards without wollastonite.
For the sample containing 9% wollastonite and 10% kraft pulp fibers, the MOR
value increased up to 7.84 MPa, which was 36% higher than the control sample (0%
wollastonite). The MOE values were higher with the wollastonite treatments. The highest
MOE value (12,400 MPa) was observed with 9% wollastonite substitution and 10% fibers,
which was 29% higher than the control. Because water and cellulosic materials were added
to the cement, the pH of the wood–cement mixture increased to approximately 12.5, which
facilitated the dissolution of wood constituents, particularly low molecular-weight
carbohydrates, and extractives materials (phenolic and sugars). These compounds could
have inhibited cement hydration (Sandermann and Kohler 1964), which could have
reduced the wood fiber-cement composite strength. The high silica (SiO2) level of
wollastonite cause the formation of calcium silicate hydrates, which increases the heat of
hydration of cement and improves the connection between fibers and cement (Naji Givi et
al. 2010).
Fig. 1. Effect of varying levels of kraft pulp fiber and wollastonite on the MOR; letters on each
column indicate Duncan’s grouping at the 95% level of confidence
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Fig. 2. Effect of varying levels of kraft pulp fiber and wollastonite on the MOE; letters on each
column indicate Duncan’s grouping at the 95% level of confidence
Silica in the wollastonite is converted calcium hydroxide, which is released by the
hydration to CaCO3 and accelerates the thermal reaction of cement hydration. Additionally,
increasing the mechanical strength via increasing the wollastonite addition produces the
reaction between calcium chloride, calcium hydroxide, and wollastonite, which provides
the required heat for cement hydration and formation of calcium silicate gel. High
substitution levels of wollastonite mitigated the negative effect of the extractive materials
(Karimi et al. 2012; Ma and Wang 2012). Consequently, the mechanical properties were
improved.
Physical Tests
Water absorption
The water absorption of the samples is shown in Fig. 3. The lowest water absorption
was observed for 9% wollastonite and 10% kraft fibers, and the highest was observed for
the sample without wollastonite and 30% fibers (control). The wollastonite decreased the
water absorption of samples at 2 h and at 24 h. A reason for this observation could be
related to the hydrophobic character of wollastonite (Hosseinpourpia et al. 2012).
Khosrviyan (2009) reported similar results for wood-plastic composite and proposed it was
associated to the hydrophobic characteristic of wollastonite.
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Fig. 3. Effect of varying levels of kraft pulp fiber and wollastonite on the water absorption (WA);
letters on each column indicate Duncan’s grouping at the 95% level of confidence
Fig. 4. Effect of varying levels of kraft pulp fiber and wollastonite on the mass loss (ML) due to fire
exposing; letters on each column indicate Duncan’s grouping at the 95% level of confidence
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Fig. 5a. Weak structure of cement composites
without wollastonite
Fig. 5c. SEM image of fiber-cement composites with
6% wollastonite
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Fig. 5b. SEM image of fiber-cement composites
with 3% wollastonite
Fig. 5d. SEM image of fiber-cement composites with
9% wollastonite
Mass Loss due to Fire Exposure
Fire retardancy is an important characteristic when using lignocellulosic composite.
The results indicated that the fire-retarding properties of the samples were improved by the
addition of wollastonite (Fig. 4). The lowest mass loss was noted with the sample
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containing 9% wollastonite and 10% kraft fibers. An important characteristic of
wollastonite is its fire resistance; thus, boards containing wollastonite exhibited higher fire
resistance and a lower percentage of mass loss when compared to the control samples
without wollastonite (Hosseinpourpia et al. 2012). Wollastonite has a high thermal
conductivity, which facilitates heat transfer (Taghiyari et al. 2014c). Therefore,
wollastonite increased fire-resistance in Populus wood. The heat-conductivity of
wollastonite limited the accumulation of heat at one spot. Furthermore, it acted as a
physical barrier to deter heat and mass transfer between the gas and the condensed phase.
Consequently, fire-retarding properties were improved, and could decrease the weight loss
percentage in the boards with wollastonite (Haghighi Poshtiri et al. 2013; Esmailpour et
al. 2018). Research by Haghighi et al. (2013) reported that fir wood saturated by
wollastonite had a higher fire resistance than samples without wollastonite, which mirrored
the results observed in this research.
Morphology of Composite
The morphology of the wood fiber-cement composites was examined using SEM
analysis. In Figures 5a, 5b, 5c, and 5d, can see different amounts of nano wollastonite
percentages in the boards. Also, by increasing the percentage of nano wollastonite from
zero to 90 percent, the formation of the C-S-H gel increased and in the opposite direction,
the micro cavities decreased. The SEM images illustrate a uniform distribution in the wood
fiber-cement composite structure with incorporation of 9% wollastonite (Fig. 5d). This can
be attributed to the role of wollastonite in bridging the microcracks leading to a delay in
micro crack coalescence. Figure 5d is a sample containing 9% wollastonite and 10% kraft
fibers; this composition was also effective in the microstructural improvement of a cement
matrix. As shown, the lower amounts of harmful crystals, such as Ca(OH) 2 and ettringite,
were observed because of the wollastonite behavior in the cement matrix, which reinforces
the matrix and turns the harmful crystals of Ca(OH) 2 to a C–S–H gel. The presence of
Ca(OH)2 crystals and needle-like ettringite, as well as fibrillated C–S–H gel, can be
observed at low levels in the composite without wollastonite in Fig. 5a. In this image, some
of the kraft fibers did not perform well in terms of bending strength due to the lack of
adhesion with cement hydration products. The micro-cavities in the control specimens
(without wollastonite) increased the sample’s water absorption. This observation was
similar to the reports of Hosseinpourpia et al. (2012).
CONCLUSIONS
1. The mechanical and physical properties of wood-cement panels mixed with
wollastonite were examined. The results indicated that the wollastonite addition to the
board composite improved the MOE and MOR, decreased the water absorption, and
decreased the mass loss of the composite when exposed to fire.
2. Wollastonite improved the compatibility of kraft pulp fibers with the cement matrix.
The decrease in water absorption of the boards was attributed to the hydrophobic
characteristic of wollastonite.
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3. The high thermal conductivity of wollastonite increased heat transfer, which improved
the fire resistance of the composite boards.
4. It is recommended that wood fiber-cement composite boards contain 10% kraft fibers
and 9% wollastonite to obtain the highest values of mechanical properties and the
lowest mass loss when exposed to fire.
ACKNOWLEDGEMENTS
The authors express their gratitude to Mr. Mohammad Hossein Vardi, the
Managing Director of VARD Mineral and Industrial Products Company, who provided the
wollastonite. The authors gratefully acknowledge Sheikh Kazemi and Hadi Ghasemi for
their considerable assistance in conducting the tests to prepare the kraft pulp fibers.
REFERENCES CITED
ACI Committee 544 (2002), State of the Art Report of Fiber Reinforced Concrete (ACI544.1R -96) (Reapproved 2002), American Concrete Institute, Farmington Hills, MI,
EUA.
Alpar, T. (2000). Methods on Accelerating Curing of Cement when Producing Cement
Bonded Particle Boards, Ph.D. Dissertation, University of Sopron, Sopron, Hungary
(in Hungarian).
Alpar, T. (2009). Wood-cement Compatibility, Ph.D. Dissertation, Georg August
University, Göttingen, Germany.
Ciullo, P. A. (1997(. “The Industrial Minerals,” in: Industrial Minerals and Their Uses,
William Andrew – Elsevier, USA, pp. 75-77.
Del Meneeis, C. H. S., Castro, V. G., and Souza, M. R. (2007). “Production and
properties of a medium density wood-cement boards produced with oriented strands
and silica fume,” Maderas-Cienc. Tecnol. 9(2), 105-115.
DIN EN 634-1. (1995). “Cement-bonded particleboards - Specifications - Part 1: General
requirements,” German.
DIN EN 634-1. (1995). “Cement-bonded particleboards - Specifications - Part 2:
Requirements for OPC bonded particleboards for use in dry, humid and external
conditions,” German.
Esmailpour, A., Taghiyari H. R., Nouri P., and Jahangiri A. (2017). “Fire-retarding
properties of nanowollastonite in particle-board,” Fire and Materials. DOI:
10.1002/fam.2493
Haghighi Poshtiri, A., Taghiyari, H. R., and Karimi, A. N. (2013). “The optimum level of
nano-wollastonite consumption as fire -retardant in poplar wood (Populus nigra),”
Int. J. Nano Dimension 4(2), 141-151.
Hosseinpourpia, R., Varshoee, A., Soltani, M., Hosseini, P., and Ziaei Tabari, H. (2012).
“Production of waste bio-fiber cement-based composites reinforced with nano-SiO2
particles as a substitute for asbestos cement composites,” Constr. Build. Mater. 31,
105-111. DOI: 10.1016/j.conbuildmat.2011.12.102
Tichi et al. (2019). “Kraft fiber-cement composites,” BioResources 14(3), 6168-6178.
6177
PEER-REVIEWED ARTICLE
bioresources.com
ISO 11925 (2010). “Reaction to fire tests - Ignitability of building products subjected to
direct impingement of flame - Part 2,” International Organization for Standardization,
Geneva, Switzerland.
Karimi, A., Poshtiri, A. H., Taghiyari, H. R., Hamzeh, Y., and Enayati, A. A. (2012).
“Effects of nano-wollastonite impregnation on fire resistance and dimensional
stability of poplar wood,” in: The International Research Group on Wood Protection,
Kuala Lumpur, Malaysia.
Khosrviyan, B. (2009). The Study of Mechanical, Physical, Thermal and Morphological
Properties of Hybrid Multi-Structures and Nano Hybrid Polypropylene Wood
Flour/Wollastonite Multi- Structures, M.S. Thesis, University of Tehran, Tehran,
Iran.
Ma, X. X., and Wang, C. G. (2012). “Hydration characteristics of mixture of grapevine
and cement,” Journal of Nanjing Forestry University 36(3), 157-159.
Naji Givi, A., Abdul Rashid, S., Aziz, F. N. A., and Salleh, M. A. M. (2010). “Experimental investigation of the size effects of SiO2 nano-particles on the mechanical
properties of binary blended concrete,” Compos. Part B- Eng. 41(8), 673-677.
Sandermann, W., and Kohler, R. (1964). “Studies on inorganic-bonded wood materials.
Part 4: A short test of the aptitudes of woods for cement-bonded materials,”
Holzforschung 18(1-2), 53-59.
Soliman, A. M. (2011). Effect of Wollastonite for Compression Strength of Concrete,
Ph.D. Dissertation, University of Western Ontario, London, Canada.
Taghiyari, H. R, Mobini, K., Sarvari Samadi, Y., Doosti, Z., Karimi, F., Asghari, M.,
Jahangiri, A., and Nouri, P. (2013). “Effects of nano-wollastonite on thermal
conductivity coefficient of medium-density fiberboard,” J. Nanomater. Mol.
Nanotechnol. 2(1), 1-5. DOI: 10.4172/2324-8777.1000106
Taghiyari, H. R., Bari, E., Schmidt, O., Tajick Ghanbary, M. A., Karimi, A., and Tahir,
P. M. D. (2014a). “Effects of nano-wollastonite on biological resistance of
particleboard made from wood chips and chicken-feather against Antrodia vaillantii,”
Int. Biodeter. Biodegr. 90(7), 93-98. DOI: 10.1016/j.ibiod.2014.02.012
Taghiyari, H. R., Bari, E., and Schmidt, O. (2014b). “Effects of nanowollastonite on
biological resistance of medium-density fiberboard against Antrodia vaillantii,” Eur.
J. Wood. Prod. 72(3), 399-406. DOI: 10.1007/s00107-014-0794-8
Taghiyari, H. R., Ghorbanali, M., and Tahir, P. M. D. (2014c). “Effects of the
improvement in thermal conductivity coefficient by nano-wollastonite on physical
and mechanical properties in medium-density fiberboard (MDF),” BioResources 9(3),
4138-4149.
Article submitted: June 23, 2018; Peer review completed: January 12, 2019; Revised
version received: May 5, 2019; Accepted: May 6, 2019; Published: June 17, 2019.
DOI: 10.15376/biores.14.3.6168-6178
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