Properties of magnesium silicate hydrate (M-S-H) cement mortars
containing chicken feather fibres
1Tingting Zhang, 2,3Elena Dieckmann, 3Shizhuo Song, 1Jingyi Xie,
1Zewei Yu, 3Christopher Cheeseman*
1Faculty of Infrastructure Engineering, Dalian University of
Technology, Dalian, Liaoning, China
2Dyson School of Design Engineering, Imperial College London,
UK
3Department of Civil and Environmental Engineering, Imperial
College London, UK
*Corresponding author: [email protected]
Abstract
Fibres derived from waste chicken feathers have been used to
reinforce magnesium silicate hydrate (M-S-H) cement mortars and
Portland cement mortars using up to 5% of fibres by weight of
dry binder. The properties of the feather fibre mortar composites
including pH, density, flexural strength, compressive strength,
toughness, thermal conductivity and microstructure are reported.
Feather fibres bond very effectively into M-S-H cement mortars
which has significantly lower pH (~10.8) than Portland cement
mortars (pH ~ 12.6). Increasing the feather fibre content reduces
the density, compressive strength, bending strength and thermal
conductivity of samples but increases mortar toughness. The optimal
feather fibre addition was determined to be 4 wt.% by weight
of dry binder content, based on ease of mixing the samples and the
strength, toughness and thermal conductivity data. Potential
applications for feather fibre reinforced M-S-H cement mortars
boards are discussed.
Keywords: Magnesium silicate hydrate; chicken feather; pH;
Microstructure
1. Introduction
Magnesium silicate hydrate (M-S-H) mortars have high strength
and low pH compared to Portland cement systems (Zhang et al.,
2011). They can be formed by reacting 40 wt.% of reactive MgO with
60 wt.% silica fume (SF). Significantly improved properties are
obtained if 1-2 wt.% of sodium hexametaphosphate is added to the
mix (Zhang et al., 2014). This acts as a dispersant, reducing the
water to binder ratio for mixing and significantly increasing the
strength and density of M-S-H mortar samples. The addition of sand
to produce mortars also improves dimensional stability during
drying so that cracking in M-S-H pastes is avoided (Zhang et al.,
2016).
Chicken feathers are a problematic waste produced by the poultry
industry. In the UK ~1,000 tonnes of chicken feathers are produced
each week and the main application for this is as the raw material
for production of a low-grade animal feed. Chicken feathers are
~91% keratin, 8% water and 1% lipids (Kock, 2006). Keratin is
strong and durable protein containing the amino acids cysteine,
glycine, proline and serine (Gupta et al., 2011). Intermolecular
cross-linking is formed by disulfide and hydrogen bonds and these
contribute to the high toughness, lightweight, excellent thermal
properties and sound insulating properties of feathers (Staron et
al., 2011).
Natural cellulose fibres such as flax and hemp have been used to
reinforce cementitious materials and the composite materials formed
are low cost, but have good mechanical properties (Khorami and
Ganjian, 2011; Mostefai et al., 2015). The properties of the
composite materials formed depend on the bond strength between the
cement matrix and the fibres (Afroughsab et al., 2016) and this is
effected by the highly alkaline environment in Portland cement
composites which degrades cellulose fibres. Feather reinforced
Portland cement composites have been reported and the high pH
causes feather fibre degradation (El-Hawary and Hamoush, 1994;
Staron et al., 2011).
M-S-H cements have an inherently lower pH than Portland cement
and therefore M-S-H may provide a more suitable matrix for natural
fibres that are pH sensitive, such as feather fibres. In this
research feather fibres have been used to reinforce M-S-H cement
mortars and Portland cement mortars. The effect of feather fibre
addition on the properties and microstructure of the composite
materials formed is reported and the properties of the two mortar
systems are compared.
2. Materials and methods
M-S-H cement mortars were prepared using MgO (MagChem 30, M.A.F.
Magnesite B.V., The Netherlands), silica fume (920U, Elkem
Materials Ltd, China) and 2 wt.% sodium hexa- metaphosphate
(NaPO3)6, (NaHMP, China National Pharmaceutical Group Corporation,
China). The chemical composition of these materials and Portland
cement (42.5R, Dalian Xiaoyetian Cement Corporation, China) are
shown in Table 1. A standard silica sand with particle sizes
between 0.21 and 0.36 mm was used to form mortar samples
(Xinlian Silica Sand, Zhuanghe, China).
Waste chicken feathers were obtained from the feather press of a
major poultry processing facility in the UK (Cargill Ltd, Hereford,
UK). The feathers were washed, disinfected and dried. They were
then ball milled for 4 hours in a laboratory scale mill. This
removed the majority of the vane from the feather and produced
fibrillated chicken feather fibres consisting of the feather
quills, as shown in Figure 1. These processed feather fibres were
much easier to process than the as received washed chicken
feathers.
The composition of M-S-H mortar samples prepared are shown in
Table 2. NaHMP was first dissolved in water and then the mix of MgO
and silica fume (SF) slowly added as the mix was continuously
stirred. Silica sand was then added using a rotary mixer to form
M-S-H mortar.
The required weight of feather fibres were mixed by hand into
the M-S-H mortar. This ensured that all the fibres were coated by
the mortar mix. It was found that 5 wt.% relative to the weight of
dry binder was the maximum amount of feather fibre that could be
effectively mixed using this method. The feather fibre mortar mix
was then pressed by hand into steel moulds to form 160 x
40 ×40 mm prism and 40 x 40 x 40 mm cube samples. The
moulds were vibrated for approximately 3 minutes to minimise air
voids and the samples then cured at a 95% relative humidity at
20°C. The samples were de-moulded after 24 hours and then stored
under at 95% relative humidity for 7, 14 and 28 days prior to
testing.
The composition of the Portland cement feather fibre composites
prepared are shown in Table 3. These are identical to the samples
prepared using M-S-H mortars except Portland cement paste replaces
the combination of MgO and silica fume (SF). The Portland cement
(42.5R) was mixed with water in a rotary mixer and the silica sand
added to form mortar samples. Feather fibres were then added and
the samples cured using the same procedures as for feather fibre
reinforced M-S-H mortar samples.
The pH was determined by crushing 28 day cured samples. The
crushed samples were sieved and 1 g of the < 250 µm fraction
mixed with 5mL of distilled water. The mix was then rotated for
24 hours and the pH determined using a standard glass pH
electrode.
The density of samples was obtained following BS-EN12467.
Samples were dried at 105°C for 24 hours and the dry mass
determined. The saturated volume was obtained by immersing samples
in water for 24 hours. The apparent density was then
calculated from the ratio of oven-dried mass to the saturated
volume. Compressive and flexural strength tests used a universal
testing machine (WAW-1000), following BS EN 196-1. Three 40
x 40 x 40 mm samples of each mix type were tested in
compression at a loading rate of 2400 Ns-1. Three 160 x
40 x 10 mm specimens of each sample type were tested in
3-point bending using a 100 mm span and a loading rate of
50 Ns-1.
Scanning electron microscopy (SEM, QUANTA 450, FEG) was used to
analyze gold coated fracture surfaces of selected samples.
The thermal conductivity of composites was determined using the
hot wire technique (TC 3000E, Xiatech). A line source probe was
placed between two test samples. After thermal equilibrium was
achieved, a constant electrical current was applied and the
temperature increase recorded. The thermal conductivity was then
calculated from the temperature rise. Three 160 x 40 x
10 mm specimens of each mix were dried 105°C for one week
before testing and the thermal conductivity values were measured
using two sample faces.
3. Results
The feather fibre reinforced M-S-H cement mortar had a pH of
10.9, while Portland cement samples had a pH of 12.6, independent
of feather fibre loading. The apparent density of 28-day feather
fibre reinforced M-S-H and PC mortars composites are shown in
Figure 2. The density falls with increasing feather fibre content
from 1981 kg/m3 to 1716 kg/m3 for the M-S-H mortar samples and from
2233 kg/m3 to 1597 kg/m3 for the PC mortars.
Figure 3 shows the load deflection curves for 28-day cured
samples tested in compression. The M-S-H mortar feather fibre
composites have higher compressive strengths than the PC composites
at all mix ratios and they retain significant load after the
initial cracking occurs. PC composites exhibit much greater load
reduction compared to the M-S-H composite samples after initial
cracking.
Figure 4 shows the effect of curing time and feather fibre
content on compressive strength. Figure 4 (a) shows that the
strengths of M-S-H composites are high and the decrease in strength
associated with increased feather fibre content is low. PC mortar
composites show lower compressive strengths than M-S-H composite
samples and increasing feather fibre content significantly reduces
the compressive strength as shown in Figure 4 (b). The error bars
(plus and minus one standard deviation) indicate the typical
variation expected in compressive strength testing.
The load-deflection curves for samples tested in 3-point bending
are shown in Figure 5. The maximum loads for both M-S-H and PC
composites decrease with increasing feather fibre content. The
increased area under the load-deflection curves indicate the
feather fibres have improved reinforcing effect in M-S-H composites
compared to PC composites, suggesting greater fibre bonding. The
reduction in the load to initiate first cracking results from the
reduction in stiffness that occurs with increased feather fibre
addition. The M-S-H samples show much greater decline in stiffness
with feather fibre addition compared to the PC samples.
Figure 6 shows the effect of feather fibre addition on bending
strength after curing for 7, 14 and 28 days. The M-S-H composite
samples have strengths which remain largely independent of feather
fibre addition, although the strengths are lower than for PC
samples. The relatively high variation in flexural strength
relative to the absolute value for both the M-S-H and PC feather
fibre composites results from the variation in flaws that
predominantly form at the feather fibre cement mortar
interface.
Figures 7 and 8 show polished surfaces of the M-S-H and PC
samples. Figure 7 is the 4 wt.% fibre reinforced M-S-H composite
and this seems to indicate good adherence between the fibres and
the M-S-H mortar. Figure 8 shows the 4 wt.% feather fibre
reinforced PC composite. Significant feather degradation seems to
have occurred and more voids are present compared to 5 wt.% M-S-H
composite.
The thermal conductivity data for M-S-H and PC mortar composites
containing different feather fibre additions are shown in Figure 9.
For both types of samples the thermal conductivity decreases with
increasing feather fibre content. The thermal conductivity of M-S-H
composites are lower than PC containing samples at all feather
fibre additions. The PC mortar samples decrease from 1.93 W/mK
to 1.39 W/mK, while the M-S-H mortar samples decrease from 1.51
W/mK to 1.22 W/mK.
4. Discussions
Feather fibres have a unique combination of properties that make
them potentially useful for reinforcing cementitious materials.
Each feather has a complex structure with high tensile strength and
toughness, extremely lightweight and excellent thermal insulating
properties. The shaft and barbs are hollow and this contributes to
the low density and low thermal conductivity of feathers. Uses for
waste feathers are currently limited and only a very small
percentage of the waste feathers produced worldwide are used. The
vast majority of chicken feathers produced by the poultry industry
are an industrial waste, with annual waste feather production in
the EU reported to be ~3.1 million tonnes per annum. Waste poultry
feathers are autoclaved to produce ‘feather-meal’, a low-value,
low-grade animal feed.
Using feather fibres to reinforce cements would beneficially
reuse some of this material and has potential to produce new
construction materials with reduced thermal conductivity which is
critical for energy efficient buildings. Fibre durability is a key
issue for biomaterials used as reinforcing fibres in cementitious
materials and this work has compared feather fibres in PC and M-S-H
cement mortars.
The pH of the binding systems has an important role in
controlling fibre durability. The keratin in chicken feathers is
extremely insoluble in water and organic solvents. However, it will
dissolve in NaOH solutions and feather fibres are not expected to
be highly stable or durable in the high pH environment of PC
mortars. As a result the reinforcing performance is likely to
decline over time. The pH of pore water in PC systems was found to
be around 12.6 which is likely to adversely affect feather fibres.
After 28 days of curing the feather fibres in the PC mortars appear
to have degraded, producing voids in the microstructure that limit
the mechanical strengths of the composites. Compared with PC, the
lower pH of ~10.6 associated with M-S-H systems provides a more
suitable environment for keratin, resulting in an improved bond
between feather fibres and the M-S-H cement mortar. M-S-H cement
mortars have low toughness and by adding feather fibres the
composite becomes more ductile and are able to carry significant
load after initial failure.
M-S-H composites have significantly lower density and lower
thermal conductivity than PC feather fibre composites. The 28-day
compressive strengths of M-S-H composites are higher than
comparable PC cement samples, particularly for samples with
3~5 wt.% of feather fibre. The feather fibres bond well into
the M-S-H cement mortar and exhibit far less degradation during the
28 day curing period than the feather fibres in PC composites. A
4 wt.% addition of feather fibres to M-S-H mortar was found to
be optimal taking into account mechanical properties and ease of
processing. Further work is investigating the use of lightweight
fillers in the M-S-H feather fibre composites to produce low
density thermally insulating board products and as an alternative
to plasterboard or plywood for tiling on floors and walls.
5. Conclusions
Waste feathers are readily available from the poultry industry.
Feather fibres have high strength and toughness and can be used to
reinforce cementitious materials. The reduced pH of M-S-H cement
mortars makes this a more suitable matrix for reinforcing using
feather fibres than Portland cement mortars. The addition of
feather fibre to M-S-H cement mortar has potential to form boards
with low density, high strength and low thermal conductivity. The
optimum feather fibre addition was 4% by weight of M-S-H
binder.
Acknowledgement
The Dyson Foundation is acknowledged for supporting the
research. The laboratory work was partly supported by the National
Natural Science Foundation of China (Grant No. 51778101).
References
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Construction and Building Materials. 22(4), 573-579.
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(2016). Optimization of the MgO-SiO2 binding system for
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(2015). Microstructure and mechanical performance of modified hemp
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Table 1. Chemical composition of MgO, silica fume and Portland
cement (42.5R).
wt.%
MgO
Silica fume
Portland cement
SiO2
0.35
94.71
21.45
Al2O3
0.10
0.23
5.24
Fe2O3
0.15
0.24
2.89
CaO
0.8
0.68
61.13
P2O5
-
0.37
-
MgO
98.2
1.19
2.08
K2O
-
1.74
-
Na2O
-
0.35
0.77
SO3
0.03
0.36
2.50
Cl
-
0.09
-
Table 2. Mix designs used to prepare M-S-H cement mortar feather
fibre composites from MgO and SF (silica fume). NaHMP is sodium
hexametaposphate
Feather fibre
%
MgO
g
SF
g
Total binder
g
Sand
g
Water
g
NaHMP
g
Feather fibre
g
0
320
480
800
800
400
16
0
1
320
480
800
800
400
16
8
2
320
480
800
800
400
16
16
3
300
450
750
750
375
15
23
4
300
450
750
750
375
15
30
5
280
420
700
700
350
14
35
Table 3. Mix designs used to prepare Portland cement (PC) mortar
feather fibre composites.
Feather
fibre
%
PC
g
Sand
g
Water
g
Feather
fibre
g
0
800
800
400
0
1
800
800
400
8
2
800
800
400
16
3
750
750
375
23
4
750
750
375
30
5
700
700
350
35
Figure 1. The fibrillated feather fibres used in all
experiments.
Figure 2. Effect of feather fibre content on M-S-H mortar and PC
mortar composite density.
(a)
(a)
(b)
Figure 3. Load defection curves for samples cured for 28 days
tested in compression,
(a) M-S-H with 0 - 5 wt.% feather fibre content; (b) PC
with 0 - 5 wt.% feather fibre content.
(a) M-S-H
(b) PC
Figure 4. Comparison of the compressive strengths at curing
times of 7-day, 14-day and 28-day, (a) for M-S-H composite; (b) for
PC composite.
(a)
(b)
Figure 5. The 28-day flexural load defection curves for (a)
M-S-H with 0~5 wt.% feather fibre content; (b) PC with
0~5 wt.% feather fibre content.
(a)
(b)
Figure 6. Comparison of the flexural strengths with different
curing times of 7-day, 14-day and 28-day, (a) M-S-H composite and
(b) PC composites.
500 µm
500 µm
Figure 7. SEM images of M-S-H feather fibre composites after 28
days curing with 4 wt.% feather fibre addition.
500 µm
500 µm
Figure 8. SEM images of PC feather fibre composites after 28
days curing with 4 wt.% feather fibre addition.
Figure 9. Effect of feather fibre addition on the thermal
conductivity of the M-S-H and PC mortar feather fibre
composites.
1
012345
1500
1600
1700
1800
1900
2000
2100
2200
2300
Density
(
kg/m
3
)
Chicken feather fibre content (wt.%)
M-S-H
PC
0.00.51.01.52.02.53.03.54.0
0
10
20
30
40
50
60
70
80
Load (N)
Deflection (mm)
5%
4%
3%
2%
1%
0%
0.00.51.01.52.02.53.03.54.0
0
10
20
30
40
50
60
70
80
Load (N)
Deflection (mm)
5%
4%
3%
2%
1%
0%
012345
0
10
20
30
40
50
Compressive strength (MPa)
Chicken feather fibre content (wt.%)
28DAY 14DAY 7DAY
012345
0
10
20
30
40
50
Compressive strength (MPa)
Chicken feather fibre content (wt.%)
28DAY 14DAY 7DAY
0.00.20.40.60.81.01.21.4
0
50
100
150
200
250
Load (N)
Deflection (mm)
5%
4%
3%
2%
1%
0%
0.00.20.40.60.81.01.21.4
0
50
100
150
200
250
Load (N)
Deflection (mm)
5%
4%
3%
2%
1%
0%
012345
0
2
4
6
8
10
12
14
Flexural strength (MPa)
Chicken feather fibre content (wt.%)
28DAY 14DAY 7DAY
012345
0
2
4
6
8
10
12
14
Flexural strength (MPa)
Chicken feather fibre content (wt.%)
28DAY 14DAY 7DAY
012345
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0
Thermal conductivity ( W/mK)
Chicken feather fibre content (wt.%)
M-S-H
PC
