# Mechanical Properties and Decay Resistance of  Hornbeam Cement Bonded Particleboards

Authors: Antonios N. Papadopoulos
Journal: Research Letters in Materials Science
 (2008)

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## Abstract

Cement bonded particleboards were manufactured from hornbeam (Carpinus betulus L.) wood particles.  Hydration tests were carried out to determine the inhibitory index in order to characterise wood-cement compatibility. The results revealed that the mixture of hornbeam-cement can be classified as moderate inhibition. Two wood: cement ratios were applied in this study, namely, 1 : 3 and 1 : 4, for the board manufacture. It was found that an increase of cement-wood ratio resulted in an improvement in all properties examined, except MOR. All properties of the boards made from 1 : 4 wood: cement ratio surpassed the minimum requirements set forth by the building type HZ code. Boards were exposed to brown and white rot fungi, Coniophora puteana, and Trametes versicolor, respectively. Overall, both fungi failed to attack the cement-bonded boards.


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## Body

## 1. Introduction

Cement-bonded particleboard has
been manufactured using conventional technology, where the boards are kept
under pressure for consolidation for several hours. The pressure is necessary
because the hydration of the cement is a slow process. The cement hardening is
usually completed in three to four weeks. The characteristics that make such type of boards desirable to various
construction applications are decay and fire resistance and good dimensional stability.A significant problem however, when
these products are manufactured, is the compatibility of wood with cement. The term compatibility, when applied in the area of
wood-cement composites, refers to the degree of cement setting after mixing
with water and with a given wood in fragmented form. Generally, if the chemical
process of cement hardening is undisturbed by the presence of wood, it is
considered that cement and wood are compatible. On the other hand, if cement hardening is impaired by the presence of
wood, then cement and wood are referred as incompatible [1].
The latter is commonly expressed by a lowering of the physical and mechanical
properties of the final product. Weatherwax and Tarkow [2] described a
method to quantify differences among species by using the term inhibitory
index, which compares the extension of wood-cement inhibition based on the
percentage increase in setting time. Hofstrand et al. [3] incorporated
maximum temperature and the maximum slope of the temperature time curve of the
wood-cement mixture and neat cement, respectively, into the inhibitory index
calculations. The inhibitory index of any species can be computed from the
values of maximum temperature of hydration, the maximum slope of the exothermic
curve and the hydration time needed to reach maximum temperature of the
inhibited cement when compared, respectively, with the values of the
uninhibited cement. The lower the inhibitory index, the higher the
compatibility between cement and wood. Objective of this communication was to manufacture wood cement
particleboards using particles of hornbeam, a less utilised wood species in Greece, and to evaluate the mechanical properties and decay resistance of the boards.


## 2. Materials and Methods

### 2.1. Hydration Test

The hydration tests were
carried out as previously described [4]. To calculate the inhibitory index (l) of the species, the following
equation was used:(1)l=100[(t2−t2′t2′)*(T2′−T2T2′)*(S2′−S2S2′)], where t2: time to
reach maximum temperature of the inhibited cement in seconds (wood-cement-water
mixture), t2′: time to reach maximum temperature of the
uninhibited cement in seconds (cement-water mixture), T2: maximum hydration temperature of the inhibited cement in °C (wood-cement-water
mixture), T2′: maximum hydration temperature of the
uninhibited cement °C (cement-water mixture), S2: maximum temperature-time slope of inhibited cement °C (wood-cement-water
mixture), S2′: maximum temperature-time slope of
uninhibited cement °C (cement-water mixture).


### 2.2. Board Manufacture

Hornbeam particles that
previously passed the1×1 mm sieve were the raw
material used in this study. The
bonding agent employed was commercial grade Portland cement, type I. The wood: cement ratios applied in this study were 1 : 3 and 1 : 4, based on the oven
dry weight. Calcium chloride (CaCl2-3%
based on weight of cement) was introduced into cement slurry to accelerate
cement set during hydration. The boards manufactured according to methodology
described in Okino et el. [5] and Fuwape [6]. A predetermined amount of air-dried wood particles and a CaCl2 distilled water solution were thoroughly blended. Cement was subsequently added
and the constituents were mixed until the cement paste was completely hydrated. The quantity of distilled water added was
calculated using a relationship applied by other researchers as well [6–8]. In his formulation, the water requirement was
determined as follows:(2)water(litres)=0.35C+(0.30−MC)W, where C = cement weight (Kg), MC (%) =
wood strands moisture content (oven-dry basis), W = oven-dry
wood strand weight (Kg).After 15 minutes of manual mixing, the cement-wood water mixture was
screened onto to a caul. The mat was evenly distributed to provide as uniform a
density as possible and prepressed to a thickness of approximately 50 mm. Cold pressing took
place under an initial pressure of 5 MPa, to a 15 mm thickness, after which the
board was retained in compression for 24 hours. Target board density was 1200 Kg/m3. A total of six boards were made, each
measuring 40×40 cm.
To minimise cement capillary desiccation and enhance hydration, boards were
misted with distilled water, then wrapped in cellophane before storing for
curing at 20°C and 65% relative humidity for a month. After manufacturing, the boards were conditioned at 20°C and 60%
relative humidity and tested for IB (internal bond, sample size 50×50 mm), MOR-MOE (moduli of
rupture and elasticity, sample size 300×50 mm), TS (thickness swelling, after 24 hours
immersion in water, sample size 50×50 mm) according to procedures defined in the
European Union standards EN 310, EN 317, and EN 319.One way analysis of
variance (ANOVA) at 5% level of significance was used to compare the properties
of the panels between different wood cement ratios.


### 2.3. Decay Tests

60 samples, measuring50×50×15, were
packed in an argon atmosphere and sterilised by irradiation (2.5 Mrad.) prior
to decay tests, using the methods described in DD ENV 12038: 1996. Laboratory pure strains of the brown rot
fungi Coniophora puteana (No FPRL 11E) and white rot fungi Trametes versicolor (CTB 863A) were used, grown on malt agar. 48 blocks
(24 for each fungi) were planted on sterile specimen supports placed on the
cultures of the test fungus actively growing on 5% malt agar in 500 mL capacity
jars. An additional set of 12 sterile control samples was used to assess
operational control losses. The closed jars were incubated for 16 weeks, at 22±1°C and 75±5% relative humidity to evaluate the efficacy of the treatments. After incubation, the samples were removed
from the jars, cleaned, weighed, conditioned to constant weight as above, and
reweighed. Weight loss (WL) was expressed as a percentage of the initial weight
of the sample. Weight losses from sterile controls were subtracted from the
decay results to give corrected data.


## 2.1. Hydration Test

The hydration tests were
carried out as previously described [4]. To calculate the inhibitory index (l) of the species, the following
equation was used:(1)l=100[(t2−t2′t2′)*(T2′−T2T2′)*(S2′−S2S2′)], where t2: time to
reach maximum temperature of the inhibited cement in seconds (wood-cement-water
mixture), t2′: time to reach maximum temperature of the
uninhibited cement in seconds (cement-water mixture), T2: maximum hydration temperature of the inhibited cement in °C (wood-cement-water
mixture), T2′: maximum hydration temperature of the
uninhibited cement °C (cement-water mixture), S2: maximum temperature-time slope of inhibited cement °C (wood-cement-water
mixture), S2′: maximum temperature-time slope of
uninhibited cement °C (cement-water mixture).


## 2.2. Board Manufacture

Hornbeam particles that
previously passed the1×1 mm sieve were the raw
material used in this study. The
bonding agent employed was commercial grade Portland cement, type I. The wood: cement ratios applied in this study were 1 : 3 and 1 : 4, based on the oven
dry weight. Calcium chloride (CaCl2-3%
based on weight of cement) was introduced into cement slurry to accelerate
cement set during hydration. The boards manufactured according to methodology
described in Okino et el. [5] and Fuwape [6]. A predetermined amount of air-dried wood particles and a CaCl2 distilled water solution were thoroughly blended. Cement was subsequently added
and the constituents were mixed until the cement paste was completely hydrated. The quantity of distilled water added was
calculated using a relationship applied by other researchers as well [6–8]. In his formulation, the water requirement was
determined as follows:(2)water(litres)=0.35C+(0.30−MC)W, where C = cement weight (Kg), MC (%) =
wood strands moisture content (oven-dry basis), W = oven-dry
wood strand weight (Kg).After 15 minutes of manual mixing, the cement-wood water mixture was
screened onto to a caul. The mat was evenly distributed to provide as uniform a
density as possible and prepressed to a thickness of approximately 50 mm. Cold pressing took
place under an initial pressure of 5 MPa, to a 15 mm thickness, after which the
board was retained in compression for 24 hours. Target board density was 1200 Kg/m3. A total of six boards were made, each
measuring 40×40 cm.
To minimise cement capillary desiccation and enhance hydration, boards were
misted with distilled water, then wrapped in cellophane before storing for
curing at 20°C and 65% relative humidity for a month. After manufacturing, the boards were conditioned at 20°C and 60%
relative humidity and tested for IB (internal bond, sample size 50×50 mm), MOR-MOE (moduli of
rupture and elasticity, sample size 300×50 mm), TS (thickness swelling, after 24 hours
immersion in water, sample size 50×50 mm) according to procedures defined in the
European Union standards EN 310, EN 317, and EN 319.One way analysis of
variance (ANOVA) at 5% level of significance was used to compare the properties
of the panels between different wood cement ratios.


## 2.3. Decay Tests

60 samples, measuring50×50×15, were
packed in an argon atmosphere and sterilised by irradiation (2.5 Mrad.) prior
to decay tests, using the methods described in DD ENV 12038: 1996. Laboratory pure strains of the brown rot
fungi Coniophora puteana (No FPRL 11E) and white rot fungi Trametes versicolor (CTB 863A) were used, grown on malt agar. 48 blocks
(24 for each fungi) were planted on sterile specimen supports placed on the
cultures of the test fungus actively growing on 5% malt agar in 500 mL capacity
jars. An additional set of 12 sterile control samples was used to assess
operational control losses. The closed jars were incubated for 16 weeks, at 22±1°C and 75±5% relative humidity to evaluate the efficacy of the treatments. After incubation, the samples were removed
from the jars, cleaned, weighed, conditioned to constant weight as above, and
reweighed. Weight loss (WL) was expressed as a percentage of the initial weight
of the sample. Weight losses from sterile controls were subtracted from the
decay results to give corrected data.


## 3. Results and Discussion

### 3.1. Hydration Test

The results obtained from the hydration test
are shown in Table1. From this, it can be seen that the mixture of hornbeam-cement
was classified as moderate inhibition. When
CaCl2 was incorporated, the mixture was graded as low inhibition.
The value of inhibitory index is negative, probably due to the capacity of the
CaCl2 to buffer or minimise the adverse effect of the soluble sugars
and extractives and also to accelerate the cement hardening and setting.Table 1
Inhibitory index of hornbeam wood species used in this study. (Standard
deviations in parentheses.)
Wood speciesInhibitory index (%)Without additiveWith additive (3% CaCI2)Hornbeam39.15(a) (4.3)−0.92 (0.08)(a)Each value represents
the mean of four replicates.


### 3.2. Mechanical and Physical Properties

The mechanical properties of the boards are presented in Table2. Table 2 shows that an
increase of cement-wood ratio resulted in improvement in MOE, IN, and
TS properties, and this improvement is significant at 5% level of significance.
However, the MOR value was significantly decreased, as the cement-wood ratio
increased. This is in line with the observations made by Moslemi and Pfister [7]
and Papadopoulos et al. [9]. They found that the modulus of elasticity, internal bond strength, and thickness
swell increased linearly with greater cement-wood ratio. The relationship between cement-wood ratio
and MOR values is considerably different from that of MOE or IBS or TS. The MOR
decreased with an increase of cement-wood ratio since higher proportion of wood
in the board may enhance the flexural property of the board. When wood occupies
more volume in the board, the areas of stress concentration around the
component particles are more diffused, resulting in increased applied stresses [6]. The results reported here are in conformity with those made by
other workers [7–9] regarding the use of cement in particleboard, flakeboard, and OSB manufacture.
All properties of the boards, if we exclude the IB value of boards made from
1 : 3 wood: cement ratio, surpassed the minimum requirements set forth by the
building type HZ code, as shown in the last line of Table 2. This is in line
with the results published by Okino et al. [10]. They manufactured cement-bonded
boards with 1 : 3 wood: cement ratio and used cypress particles.Table 2
Mechanical and physical properties of cement-bonded hornbeam boards. (Standard deviations in
parentheses.)
Wood: cementDensity(a) (Kg/m3)MOR(b) (N/mm2)MOE(b) (N/mm2)IB(a) (N/mm2)TS(a) (%)1 : 31270 (0.18)12.68 (0.5)6009.6 (32.1)0.35 (0.07)1.75 (0.6)1 : 41280 (0.12)10.56 (0.8)7056.4 (199.3)0.56 (0.04)0.67 (0.1)BISON type HZ1.209.030000.401.2–1.8(a)Each value represents
the mean of twelve replicates.
(b)Each value represents
the mean of eight replicates.


### 3.3. Decay Resistance

The results obtained after a 16-week incubation period are presented in Table3. Overall, both fungi failed to attack the
cement-bonded boards. Visual examination revealed a slight presence of mycelium
in the surface of the tested samples. Boards showed weight gain instead of
weight loss. This according to Okino et al. [5, 10] was a consequence of
the final curing process of the cement, at this high cement: wood ratios. Research
in durability of cement-bonded panels is not very common in the literature. Tests conducted by Dinwoodeie and Paxton [11]
and Pirie et al. [12] suggested that conventionally made cement-bonded
particleboards are very resistant to the attack of the white rot fungus Pleurotus ostreatus and to the brown rot
fungus Coniophora puteana. Similar results were also reported by Okino et al. [10] in cement-bonded
boards made from cypress particles. The present study was the first study, as
far as the author is aware, that examined the decay resistance of oriented
strand board using cement as a binder.Table 3
Weight loss (WL) of cement-bonded hornbeam boards. (Standard deviations in parentheses.)
Brown rotWhite rotWood: cementWL(a) (%)WL(a) (%)1 : 30.85 (0.07)−1.88 (0.40)1 : 4−2.92 (0.20)−1.45 (0.66)(a)Each value represents the mean of twelve replicates.


## 3.1. Hydration Test

The results obtained from the hydration test
are shown in Table1. From this, it can be seen that the mixture of hornbeam-cement
was classified as moderate inhibition. When
CaCl2 was incorporated, the mixture was graded as low inhibition.
The value of inhibitory index is negative, probably due to the capacity of the
CaCl2 to buffer or minimise the adverse effect of the soluble sugars
and extractives and also to accelerate the cement hardening and setting.Table 1
Inhibitory index of hornbeam wood species used in this study. (Standard
deviations in parentheses.)
Wood speciesInhibitory index (%)Without additiveWith additive (3% CaCI2)Hornbeam39.15(a) (4.3)−0.92 (0.08)(a)Each value represents
the mean of four replicates.


## 3.2. Mechanical and Physical Properties

The mechanical properties of the boards are presented in Table2. Table 2 shows that an
increase of cement-wood ratio resulted in improvement in MOE, IN, and
TS properties, and this improvement is significant at 5% level of significance.
However, the MOR value was significantly decreased, as the cement-wood ratio
increased. This is in line with the observations made by Moslemi and Pfister [7]
and Papadopoulos et al. [9]. They found that the modulus of elasticity, internal bond strength, and thickness
swell increased linearly with greater cement-wood ratio. The relationship between cement-wood ratio
and MOR values is considerably different from that of MOE or IBS or TS. The MOR
decreased with an increase of cement-wood ratio since higher proportion of wood
in the board may enhance the flexural property of the board. When wood occupies
more volume in the board, the areas of stress concentration around the
component particles are more diffused, resulting in increased applied stresses [6]. The results reported here are in conformity with those made by
other workers [7–9] regarding the use of cement in particleboard, flakeboard, and OSB manufacture.
All properties of the boards, if we exclude the IB value of boards made from
1 : 3 wood: cement ratio, surpassed the minimum requirements set forth by the
building type HZ code, as shown in the last line of Table 2. This is in line
with the results published by Okino et al. [10]. They manufactured cement-bonded
boards with 1 : 3 wood: cement ratio and used cypress particles.Table 2
Mechanical and physical properties of cement-bonded hornbeam boards. (Standard deviations in
parentheses.)
Wood: cementDensity(a) (Kg/m3)MOR(b) (N/mm2)MOE(b) (N/mm2)IB(a) (N/mm2)TS(a) (%)1 : 31270 (0.18)12.68 (0.5)6009.6 (32.1)0.35 (0.07)1.75 (0.6)1 : 41280 (0.12)10.56 (0.8)7056.4 (199.3)0.56 (0.04)0.67 (0.1)BISON type HZ1.209.030000.401.2–1.8(a)Each value represents
the mean of twelve replicates.
(b)Each value represents
the mean of eight replicates.


## 3.3. Decay Resistance

The results obtained after a 16-week incubation period are presented in Table3. Overall, both fungi failed to attack the
cement-bonded boards. Visual examination revealed a slight presence of mycelium
in the surface of the tested samples. Boards showed weight gain instead of
weight loss. This according to Okino et al. [5, 10] was a consequence of
the final curing process of the cement, at this high cement: wood ratios. Research
in durability of cement-bonded panels is not very common in the literature. Tests conducted by Dinwoodeie and Paxton [11]
and Pirie et al. [12] suggested that conventionally made cement-bonded
particleboards are very resistant to the attack of the white rot fungus Pleurotus ostreatus and to the brown rot
fungus Coniophora puteana. Similar results were also reported by Okino et al. [10] in cement-bonded
boards made from cypress particles. The present study was the first study, as
far as the author is aware, that examined the decay resistance of oriented
strand board using cement as a binder.Table 3
Weight loss (WL) of cement-bonded hornbeam boards. (Standard deviations in parentheses.)
Brown rotWhite rotWood: cementWL(a) (%)WL(a) (%)1 : 30.85 (0.07)−1.88 (0.40)1 : 4−2.92 (0.20)−1.45 (0.66)(a)Each value represents the mean of twelve replicates.


## 4. Conclusions

The aim of this paper was to manufacture wood cement particleboards using particles of hornbeam and to evaluate the mechanical
properties and decay resistance of the boards. Based on hydration tests, it was
found that the mixture of maple-cement can be
classified as moderate inhibition. Two wood: cement ratios were applied in this study, namely, 1 : 3 and 1 : 4, for
the board manufacture. It was found that an increase of cement-wood ratio
resulted in an improvement in all properties examined, except for MOR. All properties of the boards
made from 1 : 4 wood: cement ratio surpassed the minimum requirements set forth
by the building-type HZ code. Boards were exposed to brown and white rot fungi,Coniophora puteana and  Trametes versicolor, respectively. Overall, both fungi
failed to attack the cement-bonded boards.



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*Source: 379749-2008-03-30.xml*