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Lightweight Composites Containing Hemp Hurds
Article in Procedia Engineering · December 2013
DOI: 10.1016/j.proeng.2013.09.013
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Nadezda Stevulova
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Technical University of Kosice - Technicka univerzita v Kosiciach
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Procedia Engineering 65 (2013) 69 – 74
Concrete and Concrete Structures 2013 Conference
Lightweight Composites Containing Hemp Hurds
Nadezda Stevulovaa,*, Lucia Kidalovaa, Julia Cigasovaa, Jozef Junaka, Alena Sicakovaa,
Eva Terpakovaa
a
Kosice, Slovakia
Abstract
This paper deals with preparation of lightweight composites based on hemp hurds and alternative binders. Impact of hemp hurds
properties (mean particle length) on the behavior of composites (mechanical and physical properties) based on alternative binders
(hydrated lime without and with cement; zeolite, MgO-cement) is studied. The results show that the most suitable binder is MgO
cement. Hemp nature as well as mean particle size of hemp hurds slices influences the behavior of composites.
2013 The
The Authors.
Authors. Published
Published by
by Elsevier
Elsevier Ltd.
Ltd.
© 2013
Selection and
and peer-review
peer-review under
under responsibility
responsibility of
of University
University of
of Zilina,
Zilina, Faculty
Faculty of
of Civil
Civil Engineering,
Engineering,Department
Departmentof
ofStructures
Structures
Selection
and Bridges
Bridges.
and
Keywords: hemp hurds; alternative binders; mechanical properties; physical properties; lightweight composites;
1. Introduction
Traditional building materials are increasingly being replaced by advanced composite materials in accordance
with sustainable development requirements. Fiber reinforced polymers (FRPs) and fibre reinforced cement (FRC)
represent this group of new composites with advantageous properties [1]. Trends in research and development of
the limited and non-renewable limited material resources to easily renewable raw material resources. A large group
of renewable raw materials are materials of plant origin. The use of natural fibres as well as waste from the
processing of plants as reinforcement of composite materials is one of the most important targets in recent materials
research [2, 3]. A great importance to technical hemp (Cannabis Sativa) like a fast renewable material to produce
* Tel.: +421556024126.
E-mail address: nadezda.stevulova@tuke.sk.
1877-7058 © 2013 The Authors. Published by Elsevier Ltd.
Selection and peer-review under responsibility of University of Zilina, Faculty of Civil Engineering, Department of Structures and Bridges
doi:10.1016/j.proeng.2013.09.013
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Nadezda Stevulova et al. / Procedia Engineering 65 (2013) 69 – 74
bio-composite is attached [4-6]. The most common material obtained from hemp are cellulosic fibres which are
extremely strong and durable. The woody core part of the hemp stalk called shives or hurds is considered as a
waste in the hemp industry. New bio-based composite materials containing natural fibres and/or shives are low
density materials yielding relatively lightweight composites; they demonstrate various attributes like the
combination of good mechanical, thermal and acoustic properties that allow these types of materials to be used for
different applications. Many authors have studied the use of hemp fibres as reinforcement for building materials
based on cement, hydraulic lime and gypsum binders [7-12]. They have studied the effect of hemp fibers on the
physical and mechanical properties of the fibre composites. These properties depend on the nature and morphology
of the fibre, matrix properties and the fibre/matrix interaction. However, at present only a few works are devoted to
the application of hemp hurds to produce lightweight composite [13].
Our research has been focused on the utilization of hemp hurds - particles representing non-fibrous fraction of the
hemp stem as filler into lightweight composites [14, 15]. Based on previous paper [16], an increase in compressive
strength with increasing binder (MgO cement) content was found and a relationship between increasing density
and compressive strength was determined. In this paper, impact of hemp hurds properties (mean particle length) on
the behavior of composites based on alternative binders (hydrated lime without and with cement; zeolite, MgOcement) is studied.
2. Materials and methods
2.1. Components of mixture
2.1.1. The filler- Hemp hurds
Hemp hurds used in the experiments (Hungarohemp Rt, Nagylak, Hungary; bulk density = 115 kg.m-3 and
Netherlands company Hempflax; bulk density = 117.5 kg.m-3) had a wide particle size distribution. Six samples of
hemp hurds (2 original samples and 4 fractions) of various origins were used. Mean particle length values
(calculated from granulometric analysis) of all samples are given in Table 1.
Table 1. Mean particle size (dm) values of hemp shives samples
Hepm
Hungarohemp
Hempflax
Sample
Granularity (mm)
dm (mm)
1
8- 0.063
4.29
2
8- 4
7.42
3
4- 0.063
2.33
4
8- 0.063
1.94
5
8- 2
3.22
6
2- 0.063
0.94
2.1.2. The binders
Hydrated lime in powdered form was used as a binder. Calcium hydroxide used for the preparation of our
composites had a density of 2.240 kg m-3. Portland cement CEM I 42.5 R was used for mixtures in this study. To the
mixtures based on hemp hurds slices we added zeolite as a cement replacement (ZeoSand, Zeocem, a.s., Bystre,
Slovakia), and MgO-cement as a conventional binder replacement. MgO-cement consists of magnesium oxide
obtained by low temperature decomposition of natural magnesite (CCM 85, SMZ a.s. Jelsava, Slovakia), silica sand
(Sastin, Slovakia) with dominant component of SiO2 (95 - 98%) and the last component of the binder is sodium
hydrogen carbonate (NaHCO3) p.a. The granulometric composition of the magnesium oxide and silica sand and the
effect of magnesium oxide and zeolite milling were published in [14].
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Nadezda Stevulova et al. / Procedia Engineering 65 (2013) 69 – 74
2.2. Mixture and composite preparing
Composition and designation of mixtures prepared with various binders is given in Table 2. The amount of
binder in experimental mixtures was 29 %. Mixtures 1 - 3 and 5 were prepared according to the recipes published in
[12].
Table 2. Designation of the experimental mixtures
Mixtures
Component content in experimental mixtures [vol.%]
Hungarohemp
Hemp hurds
Hydrated lime
Portland cement
Zeolit
MgO- cement
Water
1
40
24
5
-
-
31
2
40
24
2.5
2.5
3
40
24
-
5
-
31
4
40
-
-
-
29
31
5
40
24
5
-
-
31
6
40
-
-
-
29
31
31
Hempflax
Experimental mixtures based on different mean particle length of hemp were prepared in the same composition
like mixture 6. Designation of these mixtures is corresponding to hemp hurds samples in Table 1.
Homogenization of the mixtures based on polydisperse hemp and its fraction was carried out in labor mixer.
Standard steel cube forms of dimensions 100 mm x 100 mm x 100 mm were used for forming the test samples.
Compacting of samples was carried out by tamping process. Next day the composites were taken out of the forms
and cured under laboratory conditions according to standard procedures during 28 days.
2.3. Methods
The density, thermal conductivity coefficient, compressive strength and water absorption were measured on
hardened composite samples. Density was determined in accordance with standard STN EN 12390-7 [17]. The
thermal conductivity coefficient, as the main parameter of heat transport, was determined by measuring thermal
conductivity, thermal diffusivity, and volumetric heat capacity, using the commercial device ISOMET 104.
Compressive strength of the cube concrete specimens, at particular ages under controlled conditions, was
determined as the maximum load per average cross-sectional area. Water absorption (after one hour) was specified
in accordance with the standard STN EN 12087/A1 [18].
3. Results and discussion
3.1. Influence of binder
Table 3 shows the results of density and compressive strength of the composites containing hemp hurds and as a
binder hydrated lime, Portland cement, zeolite and MgO - cement after 28 days of hardening. The values of
composites density are in the range of 720 1110 kg/m3. Compressive strength takes the values from 0.3 MPa to
2.73 MPa in dependence on used binder. In the case of composites prepared with hydrated lime with addition of
cement or zeolite the lowest values of compressive strength in comparison to composites based on MgO cement
have been observed. Based on published data [11] the water soluble constituents of the hemp are responsible for
affecting the behavior of lime binder. Pectin as a partially soluble hemp constituent reacts with the calcium ions in
hydrated lime resulting in less Ca2+ available for the formation of hydration products [19]. The high absorption of
water by hemp particles results in insufficient water levels required for the hydration process. The highest values of
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Nadezda Stevulova et al. / Procedia Engineering 65 (2013) 69 – 74
this parameter reached sample 4 - 2.73 MPa and sample 6 - 1.86 MPa. These results suggest that the MgO - cement
is a suitable alternative binder into the lightweight composites.
Table 3. Density and compressive strength of composites
Mixtures
Density [kg/m3]
Compressive strength [MPa]
1
790
0.3
2
760
0.27
3
720
0.23
4
1040
2.73
5
1110
0.73
6
1110
1.86
3.2. Influence of mean particle length of hemp hurds slices
Based on above mentioned results, MgO cement as a binder was used in composite preparing for study of the
impact of mean particle length of following hemp hurds slices originating from two sources on mechanical
properties. The results of measurement of physical (density, thermal conductivity coefficient, water absorption) and
mechanical properties (compressive strength) of composites samples after 28 days of hardening are given in Table 4
and in Figure 1.
Table 4. Density, thermal conductivity coefficient and absorbability of 28 days hardened composites based on hemp hurds with different mean
particle length
Sample
Density [kg. m-3]
Thermal conductivity coefficient [W/m.K]
Absorbability [%]
1
0.111
21.38
2
0.115
25.81
3
0.110
11.88
4
0.082
14.33
5
0.069
7.59
6
0.074
6.30
As is shown in Figure 1, compressive strength of prepared lightweight composites from hemp hurds depends on
mean particle size of used filler material and also undoubtedly the hemp origin has a great effect on the mechanical
properties of composites. Compressive strength of composites increases with decreasing mean particle length of
hemp hurds. Higher strength parameter values were observed for composites based on Hungarian hemp hurds. This
fact is probably due to creating a stronger structure with smaller pores, which also leads to higher values of thermal
conductivity coefficient in comparison to composites based on the Netherlands hurds.
Nadezda Stevulova et al. / Procedia Engineering 65 (2013) 69 – 74
Compressive strength [MPa]
6
5
4
Hungarohemp
3
Hempflax
2
1
0
0
2
4
6
8
mean particle size [mm]
Fig. 1. Dependence of compressive strength on mean particle size of hemp hurds
The values of the water absorbability increase in the dependence on decreasing mean particle size of hemp hurds
slices, whereas the effect of mean length of hemp hurds slices on thermal conductivity coefficient was not
confirmed.
4. Conclusion
The results of research aimed at study of impact of various alternative binders on compressive strength of 28 days
hardened hemp composites confirmed that the most suitable binder for lightweight biocomposites is MgO- cement.
Low values of compressive strength obtained for composites with binder based on hydrated lime are likely
connected with the hemp properties influencing the formation of hydration products.
Hemp nature as well as mean particle size of hemp hurds slices influences the behavior of composites.
Compressive strength of composites increases with decreasing the mean particle size of hemp hurds.
Properties of hemp biocomposites predetermine this material as a sustainable and carbon negative which can be
applied as a non load bearing material such as interior panel walls with thermal - insulating properties.
Acknowledgements
The authors are grateful to the Slovak Grant Agency for financial support of the project VEGA1/0231/12.
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