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Assessment of Carbon Sequestration of Hemp Concrete

Authors:

Abstract

Lime Hemp Concrete (LHC) or Hemp Concrete is a carbon negative building material that uses Hemp and Lime. This research was focused on quantifying the already established carbon sequestration capability of LHC. An LHC test cube was manufactured, CHN Elemental analysis of hemp and XRD analysis of binder was conducted to determine the quantity of carbon sequestration. Carbon sequestration potential of 470.3 kg of CO2 per m3 of LHC was predicted using stoichiometry. At the age of 28 days, it was found that the cube had achieved a carbon sequestration of 307.26 kg of CO2 per m3 of LHC.
ASSESSMENT OF CARBON SEQUESTRATION OF HEMP CONCRETE
Tarun Jami (1)* and Sumit Kumar (2)
(1) Former MS Student, IR&D, Gujarat Forensic Sciences University, Gandhinagar, India
(2) Research Scholar, Entrepreneurship Development Institute of India, Ahmedabad, India
Abstract
New forms of building materials have been emerging, where natural fibres (biomass) are
used along with zero emission or low emission pozzolans or binder materials such as lime, fly
ash, furnace slag, etc. to reduce CO2 emissions from construction industry. One such building
material uses Hemp and lime, and is called Lime Hemp Concrete (LHC). This research was
focused on quantifying the already established carbon sequestration capability of LHC by
formulating a LHC mix, manufacturing a test cube and, conducting CHN Elemental analysis
of hemp and X-Ray Diffractometer analysis of binder. The analyses results are computed to
determine the quantity of carbon sequestration. A stoichiometric analysis was conducted on
the functional unit of dimensions 7*7*7cm3 to establish a predicted carbon sequestration
potential of 161.31 g of CO2, translating to 470.3 kg of CO2 per m3 of LHC. At the age of 28
days, it was found that the cube had achieved a carbon sequestration of 105.39 g of CO2,
translating to 307.26 kg of CO2 per m3 of LHC. It was found that these results were better
than those of published by other researchers. Reasoning for the same and future work has
been suggested in the paper.
1. INTRODUCTION
Curbing carbon emissions from construction is becoming increasingly important. Many
researchers are paving a path in this direction, essentially tackling the problems of climate
change and global warming. Development of environmentally conscious buildings that create
a healthy indoor environment as well as a healthy outdoor environment has taken priority. This
objective is practically unachievable by using current, prevalent conventional building
materials and methodologies.
Total CO2 emissions in India amounted to about 2.47 billion tonnes in the year 2015, as
opposed to 2.3 billion tonnes in 2014, out of which roughly 99 million tonnes of CO2 were
emitted by the manufacture of cement alone [1]. It was also found that cement production
(non-combustion processes) accounted for 8% of global CO2 emissions [1]. The answer to the
environmental problems presented by the conventional carbon intensive building materials is
what is relatively a new, yet a “traditional” building material concept that uses natural fibers
(hemp, straw, animal hairs, bamboo…) and binder (lime, clay, mud, etc.,) called Cellulose
Aggregate Concrete (CAC). Called Lime Hemp Concrete (LHC), Hemp Concrete or
Hempcrete, this type of CAC uses hemp shives as the natural fiber / cellulose aggregate and
lime-based binders. Hempcrete has been categorized as a carbon-negative material because it
has displayed a lower ecological impact as opposed to other Portland cement based
construction materials [2].
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In a study conducted by K. Ip et al. [3], it was found that the LHC wall they studied had a
total carbon sequestration of 275.7 kg of CO2 for 1 m3 of LHC. They also concluded that, for
their manufacturing process, a functional unit of dimensions 1m x 1m x 0.3m sequestered
82.71kg of CO2, thereby compensating for 46.43kg of manufacturing CO2 emissions and also
enabling a further storage of 36.08 kg of CO2.
In a life cycle assessment study, it was found that 1 kg of hemp shives sequester an
equivalent of 2.1 kg of CO2, and a functional unit of dimensions 1m x 1m x 0.3m was able to
sequester 75.7 kg of CO2, thereby amounting to 251.67 kg of CO2 equivalent for 1 m3 of LHC
[4, 5]. The net emissions incurred when constructing a LHC timber frame structure,
inclusive of transport, construction and manufacturing processes were found to be -35.5 kg of
CO2 equivalent per m3 of LHC [4, 5].
2. SCOPE AND METHODOLOGY
This aim of this research was to quantify the total carbon sequestration achieved by hemp
concrete through its biogenic and non-biogenic components. It is an established fact that
hemp concrete stores carbon within itself through photosynthesis undertaken by the hemp
plant; and carbonation undertaken by the lime based binder. For this purpose, the
methodology adapted was to manufacture a test cube with accordance to a mix design derived
from the studied literature [2, 6 – 12] and, undertake X-Ray Diffractometric (XRD) and CHN
Elemental analyses.
The XRD Analysis is used to estimate the carbon sequestration achieved by the binder
component, while the CHN Elemental analysis reveals the carbon dioxide already captured by
the hemp shives through photosynthesis. As a precursor to conducting the aforementioned
analysis, a stoichiometric evaluation of the available binder content in the LHC cube is carried
out to estimate the maximum amount of carbon sequestration that can be achieved through
carbonation of the binder. The summation of the quantities of CO2 consumed by Hemp shives
and Lime binder gives the total carbon sequestration achieved. The carbon sequestration
values of hemp concrete published by other authors (see section 1) are used as the benchmark
to compare our results against.
3. EXPERIMENTAL
The functional unit is a 7cm*7cm*7cm cube with a wet/green density (density of the fresh
mix at the time of casting) of 950.43 kg/m3 and a dry density (after 28 days) of 567.05 kg/m3.
The constituents of the hempcrete mix were Hemp Shives, 90% Hydrated Lime (binder) and
water, and were batched according to the quantities and mass ratios as tabulated in Table 1.
Furthermore, the cube (see Figure 2(a)) was divided into 3 zones for the purpose of
analysis, with the innermost zone, denoted as Zone 3, being a small cube having volume of
2.69 x 10-4 m3, middle zone, denoted as Zone 2, being a hollow cube having a LHC volume of
7.134 x 10-5 m3 and the outermost zone, denoted as Zone 1, being a hollow cube having a
LHC volume of 2.744 x 10-6 m3. Figure 2(b) shows the graphical illustration of segregation of
LHC block into separate zones.
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Table 1: Mass ratios and quantities of Hemp Shives, Lime binder and Water
Binder to Shiv (B/S) Mass Ratio Water to Binder (W/B) Mass Ratio
2.15 1.3
Hemp Weight (Ws)
(g)
Binder Weight (Wb)
(g)
Water Weight (Ww)
(g)
80 172 223
(a) (b)
Figure 1: (a) Hemp stalks (b) Hemp shives processed from hemp stalks by hand [2]
(a) (b)
Figure 2: (a) Lime Hemp concrete test cube (b) 2-D Illustration of division of cubes into
different zones (not to scale)
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3.1 Theoretical estimation of carbon consumption through carbonation of lime
The carbonation of lime is governed by the following double replacement reaction:
Ca(OH)2 + CO2 >CaCO3 + H2O (1)
The amount of lime binder available in the fresh test cube is 117.9g.
Therefore, since the binder is 90% Hydrated lime and only lime undergoes carbonation in
the given mixture, the equivalent weight of hydrated lime is 106.11g.
Molar masses of calcium hydroxide and carbon dioxide are 74.093 g/mol and 44.01
g/mol, respectively.
By calculating the number of moles of calcium hydroxide present in the test cube by
using its molar mass value, the number of moles of CO2 required to carbonate the available
Ca(OH)2 (Portlandite) can be estimated from equation (1). This gives us the estimated carbon
consumption through carbonation of the binder in the test cube.
The estimated maximum carbon capture the functional unit can achieve through
carbonation of the lime binder is calculated at 70.03g.
3.2 Empirical determination of carbon storage through binder carbonation
At the age of 28 days, the cube was made to undergo a compressive strength test in a
Compressive Strength Testing machine, thereby destroying the cube. It was found that the
compressive strength of the sample cube was negligible. Samples from Zones 1, 2 and 3 were
extracted for X-Ray Diffractometric (XRD) analysis. The binder was extracted from the
samples and was ground into a fine powder individually, before conducting analyses.
The results are furnished in section 4.1.
Figure 3: XRD Spectral Analysis of Zone 1 sample
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Figure 4: XRD Spectral Analysis of Zone 2 sample
Figure 5: XRD Spectral Analysis of Zone 3 sample
Page 5
3.3 Determination of percentage of carbon in Hemp Shives
To determine the amount of carbon dioxide equivalent present in the Hemp component of
the mixture, it is necessary to determine the percentage of carbon that hemp shives are
constituted of. This quantity of carbon is translated into an equivalent quantity of carbon
dioxide consumed by the hemp component through photosynthesis, which is governed by the
following equation:
6CO2 + 6H2O >C6H12O6 + 6O2(2)
A representative sample of the hemp shives was taken by quarter-sampling technique and
dried in a hot air oven for a period of 6 hours at 105 OC; and powdered for the CHN
Elemental Analysis to identify the quantity of carbon stocks present in the hemp component
of LHC. The determination of percent composition of Carbon in the hemp shives is carried
out in a CHN (Carbon, Hydrogen, Nitrogen) Elemental Analyser. The results are furnished in
section 4.2.
4. RESULTS AND DISCUSSION
(a) (b)
Figure 6: (a) SEM image of hemp particle from test cube at 2µm scale, (b) SEM image of
hemp particle from test cube at 10µm scale
4.1 X-Ray Diffractometer Analysis
A quantitative phase analysis of the XRD spectral data on Calcite and Portlandite revealed
that, at the age of 28 days, in Zone 1, 27.93% of the binder was Calcite (CaCO3) and 72.18%
was portlandite (Ca(OH)2) approximately. Whereas, Zone 2 and Zone 3 contained very small
amounts of calcite, 5.13% and 5.66% respectively. X-Ray diffractograms of Samples 1, 2 and
3 are shown in Figures 3, 4 and 5 respectively. It can be seen that Calcite peaks as well as
Portlandite peaks were consistent in all the three diffractograms at d-values of 3.11 – 3.03 for
calcite; and 2.63 – 2.67 and 4.91 along with other minor peaks for portlandite. Figure 6 shows
the deposition of calcium carbonate on the hemp shiv/particle that was extracted from the test
cube for SEM analysis.
Page 6
This data was used to calculate the quantities of the calcium carbonate present in the
binder and the results are as follows:
Zone 1: 30.59 g
Zone 2: 1.49 g
Zone 3: 0.03 g
From the above-furnished information, the number of moles of calcium carbonate was
calculated and applied in equation (1) to elicit the amount of carbon dioxide consumed. The
resulting values are as follows:
Zone 1: 13.46 g of CO2
Zone 2: 0.65 g of CO2
Zone 3: negligible
The summation of the amount of carbon dioxide by the binder in each zone gives the total
carbon dioxide consumed through carbonation of hydrated lime in LHC.
Therefore, the total CO2 consumed by the binder at the age of 28 days is 14.11g.
4.2 CHN Elemental Analysis Results
The dried and powdered hemp shives were carefully weighed and subjected to CHN
Elemental analyses to determine the percent composition of carbon in them. Three samples
were analysed and the results are as follows:
Sample 1: 45.25%
Sample 2: 45.78%
Sample 3: 45.24%
Average: 45.423%
The mass of hemp shives in the test cube calculated using the mass ratios and green
weight is 54.84g.
From the average CHN Elemental analysis results, it is established that mass of carbon
present in the form of hemp shives in the test cube is 24.91g.
Equation (2) shows that CO2 reacts with H2O to form C6H12O6 and that for every atom of
C in C6H12O6 one mole of CO2 is consumed. From (2) it can be determined that 91.28g of CO2
was consumed by the hemp component of the LHC test cube.
4.3 Total carbon sequestration achieved
The aforementioned results in sections 4.1 and 4.2 are summed to determine the total
carbon sequestration achieved by the LHC test cube, which amounts to, 105.39 g of CO2.
However, the predicted carbon sequestration potential of the test cube, calculated by
summing the results of sections 3.1 and 4.2, was 161.31 g of CO2 for the test cube.
5. CONCLUSION
A Lime Hemp Concrete cube was manufactured and its components were subjected to
XRD analysis and CHN Elemental analysis. It was found in this research that, 1 m3 of this
particular mix of LHC has a carbon sequestration potential of up to 470.29 kg of CO2, while,
at the age of 28 days, the functional unit was able to sequester an equivalent of 307.26 kg of
CO2 per m3 of LHC.
The carbon sequestration results achieved by the LHC mix formulated for this research
was higher than the values (275.7 kg of CO2 [3] and 251.67 kg of CO2 [4]) published by other
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authors mentioned before in section 1 (see Figure 7). The possible reason for this may be
attributed to the use of 90% Hydrated Lime as binder instead of commercially available
binders such as Tradical®, that incorporate other materials (industrial wastes) such as Fly
Ash, Slag, etc., that do not undertake active carbon sequestration. However, the use of such
industrial wastes reduces direct as well as indirect emissions, thereby effecting net carbon
emissions of the product, and also its impact on climate change.
Figure 7: Graphical illustration of results and comparison to benchmark values
The mechanical strength of the LHC cube manufactured for the current study was
negligible, indicating a need for developmental research in this particular parameter. One of
the reasons for the same was that, the binder used was 90% Hydrated Lime of the non-
hydraulic variety because of which there was an underdevelopment of strength and lack of
complete carbonation (or carbon storage) as witnessed in the XRD results, despite the
sample’s age of 28 days. It shall be interesting to see the carbon sequestration that hydrated
lime can achieve when other pozzolans and relevant industrial wastes are added as additives
to change the chemical composition of the binder mix.
Further to the exercises carried out in this research, the total emissions of the individual
raw materials used for the manufacture of the current mix need to be audited to establish the
net carbon emissions. Life Cycle Assessment exercises on different mix designs and
Hempcrete structures need to be conducted in the Indian context (adaptation with prevalent
construction methods such as RCC Structures, Steel frame structures, load-bearing walls, etc.)
to establish more statistical data on net carbon emissions of Lime Hemp Concrete. Also, a
need for developmental research into the advancement of the various mechanical attributes of
hemp concrete is identified.
ACKNOWLEDGEMENTS
This research, which was carried out at IR&D, Gujarat Forensic Sciences University as
part of the Masters thesis of Mr. Tarun Jami, was funded and supported by Bombay Hemp
Company Pvt. Ltd. (BOHECO), Mumbai, India. The authors would like to thank BOHECO
for providing hemp for this research; Mr. Sumit Mathur, Sigma Minerals Ltd., Jodhpur, RJ,
India for providing Hydrated Lime; Institute for Plasma Research, Gandhinagar, India for
carrying out XRD Analysis; Sophisticated Instrumentation Centre for Applied Research &
Testing (SICART), Charutar Vidya Mandal, Vallabh Vidyanagar, Anand, India for carrying out
CHN Elemental analysis.
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... In the year 2012 study reviewing the potential of various NETs, cellulose aggregate concrete was purported as a possible geoengineering strategy (McLaren 2012). Indeed, many researchers since then have studied cellulose aggregate concrete, also known as bio-based building materials, bio-aggregate concrete, and vegetal concrete, and their potential for carbon capture was published (Amziane and Sonebi 2016;Amziane and Collet 2017;Arrigoni et al. 2017;Pretot et al. 2014;Pittau et al. 2018;Ip and Miller 2012;Jami et al. 2019;Jami et al. 2016;Jami 2016;Ahmad et al. 2020). ...
... This is mainly because of the carbon capture in the photosynthesis process undertaken by the hemp plant during its growth. The plant absorbs carbon dioxide from the atmosphere and converts it into carbon compounds deposited within the Fig. 11 Relationship between thermal capacity and relative humidity (RH) (Evrard 2008) Current Trends in Applications of Cannabis/Hemp in Construction 229 plant as it grows (Jami 2016;Jami et al. 2016). About 50% of the hemp shivs are carbon, implying that each kg of the hemp hurds captures 1.85 kg of CO 2 (Arrigoni et al. 2017). ...
... Made from the dried woody core of hemp stalks and a lime-based binder, hempcrete can be cast just like concrete. Hempcrete can sequester 307 kg of CO 2 per cubic meter (19 pounds per cubic foot), roughly the equivalent of the annual carbon emissions of three refrigerators ( Jami and Kumar, 2017). Because of its superior thermal properties, hempcrete has great potential to be used for walls, floors, and roof insulation (Ellis, 2014). ...
Chapter
Industrial hemp (Cannabis sativa), a member of the family that includes marijuana, has great potentials as a renewable feedstock for a sustainable society. Unlike marijuana, industrial hemp has a high cannabidiol (CBD) content and only < 0.3% tetrahydrocannabinol (THC), the psychoactive compound in marijuana. Moreover, every part of hemp can be used. For instance, hemp bast can be used as a fiber source for textile and paper production. Hemp seeds are a good source of oil, which is rich in omega-3, omega-6, and unsaturated fatty acids for cooking and supplements. Hemp flowering materials (leaves and flowers) are rich in CBD oil, which has medicinal properties for the treatment of Dravet syndrome, Parkinson's disease, schizophrenia, and anxiety disorder. Last but not least, hemp hurd, a soft inner core of hemp stalks and stems, can be used as a starting material for biofuel, bioproducts, and construction materials. Considering the hemp's versatility, the cultivation of industrial hemp and hemp-derived products have increased rapidly. In this chapter, we described selected potential uses of industrial hemp in the following aspects: (1) value-added materials, (2) foods and bioproducts, and (3) biofuels and biochemicals.
... The biogenic component of the material, hemp shivs, are 45% carbon (Jami, 2016), which is a direct result of the atmospheric carbon dioxide absorbed by the plant through photosynthesis during its growth. The non-biogenic component of hemp concrete is the lime binder, which engulfs the hemp shivs in a hardened matrix and also consumes carbon dioxide through carbonation (Jami and Kumar, 2017). Jami et al. (2016) in their study had found the total carbon sequestration of hemp concrete to be 307.26 ...
Article
The growing concerns surrounding the rising carbon emissions have impelled the leaders around the world to make efforts to prevent catastrophic manifestations of climate change and global warming. This has led to the resurrection of vegetal concrete building materials using biomass, which have the added benefits of carbon sequestration apart from low embodied energy and renewability. Vegetal concretes are made up of an organic or inorganic binder, and biomass originating from agro-forestry industries such as rice husk, straw bale, hemp, kenaf, cork, and so on. Hemp concrete, a variety of vegetal concrete has been widely researched and is arguably one of the most researched building materials in current times. This paper presents a review of the state-of-the-art of hemp concrete research, with a view to identifying research gaps that shall guide future research for its implementation in the fast-growing green buildings industry. The reviewed aspects of hemp concrete include properties of hemp relevant to construction, binder characteristics, mechanical properties, durability, hygric and thermal properties, environmental credentials, manufacturing processes, and current applications. Several research gaps with regards to the hydraulicity of the binder, strength and durability, and fire resistance of hemp concrete were identified. It was also established that hemp concrete has very low embodied carbon and embodied energy, making it ideal for green building applications. The paper ends with a discussion outlining the need and direction for future research on improving the manufacturing processes and mechanical performance of hemp concrete for wider adoption by the construction industry.
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