Article

Thermophysical Properties of Sawdust and Coconut Coir Dust

Incorporated Unfired Clay Blocks
Nusrat Jannat 1,2, * , Jeff Cullen 1 , Badr Abdullah 1 , Rafal Latif Al-Mufti 1 and Karyono Karyono 1,3

1 School of Civil Engineering & Built Environment, Liverpool John Moores University, Byrom Street,
Liverpool L3 3AF, UK
2 Department of Architecture, Chittagong University of Engineering & Technology,
Chattogram 4349, Bangladesh
3 Faculty of Engineering and Informatics, Universitas Multimedia Nusantara, Scientia Garden, Gading Serpong,
Tangerang 15810, Indonesia
* Correspondence: n.jannat@2019.ljmu.ac.uk

Abstract: Sawdust and coconut coir dust are agro-wastes/by-products which are suitable for use
as raw materials to manufacture unfired clay blocks due to their excellent physical and mechanical
properties. A limited number of studies have been conducted on the utilisation of these agro-wastes
in clay block production, and they have mostly been devoted to investigating the physicomechanical
properties, with less attention given to the thermal properties. Moreover, the majority of the studies
have used chemical binders (cement and lime) in combination with agro-waste, thus increasing
the carbon footprint and embodied energy of the samples. Furthermore, no research has been
performed on the thermal performance of these agro-wastes when incorporated into clay blocks
at the wall scale. Therefore, to address these limitations, the present study developed unfired clay
blocks incorporating sawdust and coconut coir dust (0, 2.5, 5, and 7.5% by weight), without the use
of chemical binders, and evaluated their thermal performance, both at the individual and wall scales.
The experiments were divided into two phases. In the first phase, individual sample blocks was tested
for basic thermal properties. Based on the results of the first phase, small walls with dimensions
Citation: Jannat, N.; Cullen, J.;
of 310 mm × 215 mm × 100 mm were built in the second phase, using the best performing mixture
Abdullah, B.; Latif Al-Mufti, R.;
from each waste type, and these were assessed for thermal performance using an adapted hot box
Karyono, K. Thermophysical
Properties of Sawdust and Coconut
method. The thermal performance of the walls was evaluated by measuring the heat transfer rate
Coir Dust Incorporated Unfired Clay from hot to cold environments and comparing the results to the reference wall. The results showed
Blocks. Constr. Mater. 2022, 2, that thermal conductivity decreased from 0.36 W/mK for the reference sample, to 0.19 W/mK for
234–257. https://doi.org/10.3390/ the 7.5% coconut coir dust sample, and 0.21 W/mK for the 7.5% sawdust sample, indicating an
constrmater2040016 improvement in thermal insulation. Furthermore, the coconut coir dust and sawdust sample walls
Received: 25 August 2022
showed a thermal resistance improvement of around 48% and 35%, respectively, over the reference
Accepted: 28 September 2022 sample wall. Consequently, the findings of this study will provide additional essential information
Published: 8 October 2022 that will help in assessing the prospective applications of sawdust and coconut coir dust as the
insulating material for manufacturing unfired clay blocks.
Publisher’s Note: MDPI stays neutral
with regard to jurisdictional claims in
Keywords: agro-wastes; clay blocks; thermal; unfired; wall
published maps and institutional affil-
iations.

1. Introduction
Copyright: © 2022 by the authors. The tropics survey report [1] states that over half of the world’s population will
Licensee MDPI, Basel, Switzerland. be residing in tropical regions by 2050, resulting in a considerable rise in demand for
This article is an open access article indoor thermal comfort. The high temperatures and high humidity features of tropical
distributed under the terms and climates necessitate the development of high thermal resistance building technologies to
conditions of the Creative Commons improve thermal comfort in residential housing. Since the Intergovernmental Panel on
Attribution (CC BY) license (https://
Climate Change [2] predicts an increase in global mean surface air temperature of +1.3
creativecommons.org/licenses/by/
to +4.5 ◦ C by the end of the twenty-first century, thermal comfort improvement in this
4.0/).

Constr. Mater. 2022, 2, 234–257. https://doi.org/10.3390/constrmater2040016 https://www.mdpi.com/journal/constrmater

Constr. Mater. 2022, 2 235

region is now a key concern [3]. Therefore, researchers have been attempting to alleviate the
consequences of global warming by developing novel materials to improve thermal comfort
and energy savings in tropical dwellings [4–13]. Earth-based materials have been used for
building construction for centuries and are still used in most developing countries [14].
The popularity of these materials is attributed to their easy availability, workability, as well
as advantageous hygro-thermal properties [15,16]. Earthen construction generally has a
massive thickness, which is responsible for its higher thermal inertia. This feature improves
the thermal efficiency of buildings in certain climates by lowering heating and cooling
energy demands, resulting in lower operating costs [17,18]. However, in addition to the
lack of strength and durability, earthen materials require regular maintenance [15,19,20].
Therefore, there has been growing concern in recent decades about addressing these issues
in earthen construction, and different types of stabilisers have been employed to enhance
the properties of the earthen materials. Among the various stabilisers, calcium-based
materials, such as cement and lime, are widely used due to their easy adaptability and
robustness [21,22]. Though such conventional chemical stabilisers can improve several
properties of earthen materials, they have certain drawbacks, such as high CO2 emissions,
energy consumption, and cost [23]. Consequently, the development of new stabilisers for
earthen material construction with lower environmental impact and processing costs seems
to be of great interest among researchers.
The statistics reveal that global agro-waste generation is around 998 million tonnes
each year [24,25], and the processing of these wastes is a major issue in developing countries,
as most of these wastes are dumped in landfills or burned, which causes serious environ-
mental pollution [26,27]. A number of studies have presented that agro-wastes can be
transformed into low-energy and sustainable construction materials, solving a major prob-
lem in waste management [28,29]. Sawdust and coconut coir are agro-wastes/by-products
which are abundant in tropical countries [30–32]. According to several studies [32–35],
these agro-wastes can be used as raw materials in the construction industry due to their
excellent physical and mechanical properties. However, a limited number of studies
have been carried out using these two agro-wastes in the production of unfired bricks.
Khedari et al. [36], Thanushan et al. [37], and Thanushan and Sathiparan [38] produced
soil-cement blocks utilising coconut coir fibre and reported that bulk density and compres-
sive strength decreased with the increase in fibre percentage. Moreover, fibre inclusion
resulted in a decrease in thermal conductivity [36] and an increase in water absorption
rate [38]. On the other hand, the study by Danso et al. [39] revealed that the incorporation of
coconut coir fibre into soil blocks remarkably improved mechanical strength and durability.
Additionally, the study showed that higher fibre content decreased the linear shrinkage and
density, but increased the water absorption rate of the blocks. Sangma et al. [40] assessed
the physicomechanical properties of the unfired earth blocks by varying the coconut coir
fibre length from 20 mm to 80 mm. The test results demonstrated that the compressive
and tensile strength of the samples improved when the fibre length was increased up to
40 mm. Purnomo and Arini [41] developed unfired bricks using lime in combination with
treated coconut coir fibre and examined their physicomechanical properties under various
humidity conditions. It was observed that better properties were achieved in a high humid
environment. Demir [42], Ouattara et al. [43], Vilane [44], and Jokhio et al. [45] investi-
gated the compressive strength of sawdust-incorporated unfired clay bricks and found
that the presence of sawdust enhanced the compressive strength. However, according to
Ganga et al. [46], Tatane et al. [47], and De Castrillo et al. [48], the compressive strength of
the samples decreased with the addition of sawdust. Furthermore, the density and thermal
conductivity of the samples declined, whereas capillary water absorption increased with
increasing sawdust content [47,48]. Charai et al. [49] also studied the thermal properties of
sawdust–clay composites and concluded that sawdust had a positive effect on improving
the thermal properties of the samples. The findings of previous studies show that sawdust
and coconut coir have the potential to enhance the characteristics of earthen materials.
Constr. Mater. 2022, 2 236

Research Significance
The literature review presented in the previous section reveals that most of the studies
have focused mainly on the investigation of the physicomechanical properties, and limited
research is available regarding thermal properties tests. Moreover, the majority of the
studies have used chemical binders, such as cement and lime, with agro-wastes to produce
the samples. These chemical binders are responsible for environmental degradation, with a
high carbon footprint and embodied energy [50]. Hence, the production of agro-wastes
incorporated into unfired earth blocks without these binders provides the greatest advan-
tages in terms of sustainability. This study, therefore, investigated the thermophysical
properties of the sawdust- and coconut coir dust-blended unfired earth blocks, without any
chemical binders.
The literature also shows that studies which measured the thermal properties of the
sawdust- and coconut coir dust-incorporated brick are at the individual sample scale. No
research has been performed on the thermal performance of these agro-wastes-incorporated
clay blocks at the wall scale. The examination of heat transfer rates through building wall
materials is important for determining building energy efficiency. Consequently, this study
not only measured the thermal properties of individual samples, but also evaluated the
thermal performance of the constructed walls in the laboratory using an adapted hot
box method. Finally, the test results were compared to the reference sample to reach
a conclusion.
The outcomes of this study will support the assessment of the potential application
of sawdust and coconut coir dust as insulating materials in the manufacturing of unfired
clay blocks.

2. Materials and Methods

2.1. Materials
The materials used to produce the samples were red clay, coconut coir dust, sawdust,
and tap water. Square mesh sieves were used to sieve the raw materials to obtain particle
sizes between 2 mm–1.18 mm, 1.18 mm–300 µm, and 600 µm–425 µm for red clay, coconut
coir dust, and sawdust, respectively (Figure 1). The maximum dry density (2320 kg/m3 )
and optimum moisture content (15.50%) of the clay were determined by the standard
Proctor compaction test [51], while the Atterberg limit (liquid limit: 31.61%, plastic limit:
19.25, plasticity index: 12.36%) was established following the BS 1377-2:1990 standard [52].
Scanning electron microscopy (SEM) with a conductive coating was used to study the
morphology of the raw materials. Moreover, X-ray fluorescence (XRF) and X-ray diffrac-
tion (XRD) analysis were used, respectively, for the evaluation of chemical composition
and mineralogical phases of raw materials. Furthermore, the thermal characteristics of
the raw materials were determined by ISOMET 2114 equipment using a needle probe
(Figure 2). The thermophysical properties and chemical compositions of the raw materials
are given in Tables 1 and 2, respectively. SEM micrographs revealed that sawdust particles
vary in size and form, with heterogeneous fibres and rough surfaces (Figure 3b). On the
other hand, the spongy structure of coconut coir dust particles contains numerous pores
(Figure 3c). The XRD analysis showed that red clay mainly contains quartz (SiO2 ), kaolinite
(Al2 (Si2 O5 )(OH)4 ), and haematite (Fe2 O3 ) (Figure 4a), which was also supported by the
XRF results presented in Table 2. Coconut coir dust and sawdust were amorphous in form,
as observed by the disordered XRD patterns (Figure 4b).

Table 1. Thermophysical properties of raw materials.

Properties Red Clay Sawdust Coconut Coir Dust

Density (kg/m3 ) 1430 230 130
Specific gravity 2.32 1.14 0.61
Thermal conductivity (W/mK) 0.30 0.06 0.05
 Constr. Mater. 2022, 2 237

Table 1. Cont.

Properties Red Clay Sawdust Coconut Coir Dust

Volumetric heat capacity (×106 J/m3 K) 1.29 0.24 0.21
Specific heat capacity (J/kgK) 902.80 1040.43 1583.08
Porosity 0.38 5.09 7.65
Natural moisture content (%) 6.47 5.02 5.62
str. Mater.
nstr. Mater. 2022,
2022, 3,
3, FOR
FOR PEER
PEER REVIEW
REVIEW
Water absorption after 24 h under water (%) 27.57 127.66 195.16
Colour Red Light brown Brown

(a)
(a) (b)
(b) (c)
(c)

Figure 1.
1. Photographs
Figure
Figure Photographs of
ofofraw
1. Photographs rawmaterials:
raw (a)
materials: (a)
materials: red
red
(a) clay;
clay;
red (b)
(b) sawdust;
(b) sawdust;
clay; (c)
(c) coconut
(c) coconut
sawdust; coir dust.coir
coconut coir dust.
dust.

Figure
Figure 2.
2. Thermal
Thermal
Figure conductivity
conductivity measurement
conductivity
2. Thermal measurement of of
measurement of raw
rawraw materials.
materials.
materials.

Table 2. XRF analysis of the raw materials.

Weight (%)
Elements
Red Clay Sawdust Coconut Coir Dust
SiO2 41.454 0.348 4.059
Al2 O3 15.214 0.390 1.206
K2 O 1.636 0.340 3.942
MgO 5.114 0.408 0.767
Fe2 O3 8.104 0.186 1.184
Na2 O 1.027 0.926 1.183
Constr. Mater. 2022, 2 238

Table 2. Cont.

Weight (%)
Constr. Mater. 2022, Elements
3, FOR PEER REVIEW
Red Clay Sawdust Coconut Coir Dust
TiO2 1.411 0.171 0.596
CaO 0.633 1.681 2.782
SO3 0.047 0.049 0.275
BaO 0.216 0.074 0.089
MnO 0.040 0.026 0.013
ZrO2 0.035 0.002 0.011
P2 O5 0.250 0.021 0.094
SrO 0.011 0.000 0.005
CuO (a) 0.006 (b) 0.003 0.002
(c)
ZnO 0.007 0.004 0.006
Figure 1. Photographs of raw materials: (a) red clay; (b) sawdust; (c) coconut coir dust.
Y2 O3 0.006 0.001 0.001
F 0.050 0.050 0.050
Cl 0.040 0.040 0.040
Co2 O3 0.007 0.002 0.001
Rb2 O 0.004 - -
NiO 0.003 - -
BaO 0.097 - -
Cr2 O3 0.016 - -
Br - - 0.001
CHO 24.572 95.278 83.693
Figure 2. Thermal conductivity measurement of raw materials.

(a)

Figure 3. Cont.
Constr. Mater. 2022, 2Constr. Mater. 2022, 3, FOR PEER REVIEW 239

(b)

(c)
Figure 3. SEM micrographs of raw materials: (a) red clay; (b) sawdust; (c) coconut coir dust.
Figure 3. SEM micrographs of raw materials: (a) red clay; (b) sawdust; (c) coconut coir dust.
Constr. Mater. 2022, 3, FOR PEER REVIEW 6
Constr. Mater. 2022, 2 240

(a)

(b)
Figure
Figure 4.
4. XRD
XRD spectra
spectra of
of raw
raw materials:
materials: (a)
(a) red
red clay;
clay; (b)
(b) sawdust
sawdust and
and coconut coir dust.
coconut coir dust.

TableIn
1. this
Thermophysical properties
study, sample of raw materials.
preparation was executed by hand compaction, since most
Properties earthen material building projects in practice employ
Red Clay Sawdustmanual compaction.
CoconutTable
Coir3 lists
Dustthe
proportions in which the waste materials were added to the clay during sample prepara-
Density (kg/m3) 1430 230 130
tion. The reference case consisted of the sample without waste material. First, dry clay
Specific gravity 2.32
and waste material were thoroughly combined1.14using a mechanical0.61mixer. Then, normal
Thermal conductivity (W/mK)tap water was added and the 0.30mixture was blended
0.06 until it became 0.05
homogeneous. The
Volumetric heat capacity (×10proportion
6 J/m3K) 1.29 for each series
of water was adjusted 0.24 0.21 the same consis-
of the mixture to retain
Specific heat capacity (J/kgK) tency for moulding. The standardised
902.80 mould sizes of 100 mm × 100
1040.43 mm × 100 mm and
1583.08
Porosity 100 mm × 100 mm × 215 mm
0.38were used for casting
5.09 the samples. 7.65 wet mixture was
The
poured into the mould in two equal layers, and manual compaction was conducted using
Natural moisture content (%) 6.47 5.02 5.62
a square flat section steel rod with 25 blows. A plastic membrane was used to cover the
Water absorption after 24 h under water (%) 27.57 127.66 195.16
samples for 24 h to avoid rapid loss of moisture. The samples were kept in the moulds
Colour Red of 23 ◦ C to 26Light
for 7 days at a room temperature brown
◦ C and Brown of 30% to 34%
a relative humidity
achieve firmness suitable for demoulding. Before the tests, the demoulded samples were
stored for another 21 days in the same environment to dry naturally.
Constr. Mater. 2022, 2 241

Table 3. Mix composition.

Waste (%) Waste (g)

Mix Designation
Red Clay (g) Coconut Coconut
of Samples Sawdust Sawdust
Coir Dust Coir Dust
R 550 0 0 0 0
S-2.5 550 2.5 0 13.75 0
S-5 550 5 0 27.50 0
S-7.5 550 7.5 0 41.25 0
C-2.5 550 0 2.5 0 13.75
C-5 550 0 5 0 27.50
C-7.5 550 0 7.5 0 41.25

2.2. Testing Methods

2.2.1. Thermophysical Properties of Individual Samples
The density of the samples was determined from the mass and volume of the samples
according to BS EN 771-1 [53] using the following Equation (1):

ρ = M/V (1)

where ρ (kg/m3 ) is the density, V is the volume (m3 ), and M (kg) is the mass of the samples.
The thermal properties (thermal conductivity and volumetric heat capacity) of each
mixture were measured using a portable apparatus, ISOMET 2114 model, that directly
measures the value via a surface probe attached to a temperature sensor (Figure 5). The ex-
periment was conducted in a laboratory room environment with a temperature of 25 ± 1 ◦ C
and a relative humidity of 32 ± 2%. Prior to the test, each sample was cleaned with a cloth
to remove dust or any interferents. During the experiment, the samples were positioned
on a polyurethane block of 50 mm thickness to avoid any potential interference from the
adjacent apparatus. For each mix design, two measurements were taken, and the mean
was calculated. Knowing the volumetric heat capacity and density of the sample, specific
heat capacity was calculated by dividing the volumetric heat capacity by the density value.
Furthermore, thermal diffusivity and thermal effusivity were determined by the following
Equations (2) and (3) [54]:
α = λ/ρC p (2)
q
τ = λρC p (3)

where α (m2 /s) is the thermal diffusivity, τ (Ws1/2 /m2 K) is the thermal effusivity, λ (W/mK)
is the thermal conductivity, ρ (kg/m3 ) is the density, and Cp (J/kgK) is the specific heat
capacity.
 𝜏= 𝜆𝜌𝐶 (3

where α (m2/s) is the thermal diffusivity, τ (Ws1/2/m2K) is the thermal effusivity, λ (W/mK
Constr. Mater. 2022, 2 242
is the thermal conductivity, ρ (kg/m³) is the density, and Cp (J/kgK) is the specific hea
capacity.

(a) (b)

Figure 5. Thermal
Figure 5. Thermaltests:
tests:(a)
(a) 100 mm××100
100 mm 100mm
mm × 100
× 100 mmmm sample;
sample; (b)
(b) 100 mm100
× mm × 100
100 mm mm
× 215 × 215 mm
mm
sample.
sample.

2.2.2. Thermal Properties of Wall Samples

Based on the thermophysical properties of individual samples, the optimal percentage
of each waste was chosen to construct small walls to evaluate thermal transmittance.
The walls were constructed using two 100 mm × 100 mm × 215 mm blocks and two
100 mm × 100 mm × 100 mm blocks joined together with earth mortar similar to each
sample composition. Each wall had a vertical surface area of around 310 mm × 215 mm
and a thickness of 100 mm.
Thermal transmittance, also known as the U-value (W/m2 K), is one of the key pa-
rameters used to assess the thermal performance of a building envelope, and it can be
determined theoretically or experimentally. The theoretical method for calculating the
U-value is described in the BS EN ISO 6946 standard [55]. The results obtained from the
theoretical method often differ from the in situ U-values [56–58]. The in situ U-value is
widely measured following the heat flow meter method specified in the BS ISO 9869-1
standard [59]. In this method, the U-value is calculated by measuring the heat flux through
a wall and the temperature difference between the two surfaces (inside and outside) of the
wall, since heat is transferred from the warmer to the colder side when there is a tempera-
ture difference between two surfaces of a wall. The standard recommends the minimum
duration for the test is three days, if the temperature around the heat flux meter is kept
steady, but it should be at least seven days to obtain consistent results. Gaspar et al. [60]
showed that temperature differences of more than 19 ◦ C require a 72 h test length for
low U-value facades, whereas lower temperature differences necessitate a 144 h test time.
However, since the temperatures of the hot and cold boxes are controlled in the laboratory,
the test duration can be adapted, considering the temperature stability [61].
This study followed the adapted hot box technique [59] (Figure 6), which is a reliable and
accurate method for measuring thermal transmittance in laboratory experiments [62–65]. In this
method, heat flux between hot and cold chambers was estimated using heat flux sensors.
The hot chamber (800 mm × 600 mm × 650 mm) was made of commercially available
50 mm thick polyisocyanurate insulation boards (PIR, λ = 0.022 W/mK, R = 2.25 m2 K/W),
which have a thin aluminium foil covering on both sides to keep them isolated from the
outside environment. The λ value of this insulation material is comparable to polystyrene
foam (0.035 W/mK) [62], expanded polystyrene (0.034 W/mK) [63], and foam polyurethane
(0.0245 W/mK) [66], which were used in previous studies to build the hot chamber.
Two thermostatic tubular heaters (DIMPLEX ECOT1FT 40 W, 230–240 V) were placed
inside the hot chamber as an internal heat source. On the other hand, the cold chamber
(450 mm × 600 mm × 750 mm) was a refrigerator used to cool the inside air. The tempera-
tures of the hot and cold chambers were controlled by the EMKO ESM-3711-H temperature
controller. The sample wall was positioned between the hot and cold chambers in a sample
holder made of double insulation boards (100 mm). Additionally, any gaps between the
wall and the sample holder were filled with insulation material (polyisocyanurate insula-
Constr. Mater. 2022, 2 243

tion, λ = 0.022 W/mK, R = 2.25 m2 K/W) and then sealed with aluminium foil tape to ensure
that heat propagation could only occur through the exposed wall surfaces. Furthermore,
Constr. Mater. 2022, 3, FOR PEER REVIEW 11
inside both chambers, a small fan was placed to prevent any thermal stratification and to
ensure uniform heating and cooling [63].

Figure
Figure 6.
6. Test
Test setup
setup of
of thermal
thermal transmittance
transmittance measurement.
measurement.

The surface temperature of the sample wall was measured using thermocouple K-type
sensors attached to the sample wall. On either side of each block of the sample wall, two
thermocouple K sensors were installed. In addition, two heat-flux sensors (gSKIN-XB 26 9C)
were installed on the sample wall facing the cold room (Figure 7). In order to prevent any
influence of air gaps, sandpaper was used to smooth the wall surfaces where the sensors
were installed, and adhesive tape was used to fix the sensors to the wall, ensuring that all
sensors had good thermal contact with the wall surface. All the sensors were connected to
a data logger (Pico USB TC-08) to record the continuous readings for 3 days (72 h), with
a sampling period of 5 min. A temperature and relative humidity data logger was also
Constr. Mater. 2022, 2 244

Constr. Mater. 2022, 3, FOR PEER REVIEW 12

installed inside both chambers to monitor the temperature and relative humidity of the
chambers. Table 4 lists the main materials and equipment used in this experiment.

Figure 7. Configuration of the sample wall and position of the sensors.

Figure 7. Configuration of the sample wall and position of the sensors.
Table 4. Equipment used for thermal transmittance test setup and measurement.
3. Results and Discussions
Equipment Model Parameters Values
3.1. Thermophysical Properties of Individual
◦ Samples
Temperature sensor K-type thermocouple Accuracy ( C) ±1.5
Table 5 presents the results of the thermophysical properties of different agro-waste-
Range (kW/m2 ) −150 to +150
blended samples. As shown in the table, the bulk density decreased as the waste content
2 1.5 studies, where the inclusion
increased. Similar results Sensitivity
gSKIN-XB 26 9C
[µV/(W/m
were observed )]
in several previous
Heat flux sensor
of natural fibres or aggregates into the
Calibration formulation
accuracy (%) of unfired
±3 earthen blocks resulted in a
gradual decrease in bulk density [68–70].
Resolution (W/m ) This
2 can be explained
0.41 by the fact that when com-
paratively lighter sawdust and coconut coir dust particles (see Table 1) were incorporated
Temperature controller EMKO ESM-3711-H Accuracy (%) ±1
into the mixture, they displaced the heavier clay particles, which eventually decreased the
density. Moreover, duringVoltage
sampleinput ±70
range (mV)the hydrophilic
preparation, sawdust and coconut coir
dust (see water absorption values in range
Temperature ◦
Table(1)C)swelled by absorbing
−270 to +1820water. After drying,
Data logger Pico USB TC-08
they returned almost to their former size,
Temperature leaving
accuracy (◦ C)very small
Sum air
of ±voids between
0.2% of reading their
and ±outer
0.5
periphery and the clay particles. Consequently, the more sawdust and coconut coir dust
Voltage accuracy (µV) Sum of ±0.2% of reading and ±10
were added to the mixture, the more air voids were created [71]. The samples with saw-
Temperature range ◦
( C)3 to 1638.64 −35 to +80
dust had densities ranging from 1837.05 kg/m kg/m 3 for 2.5% to 7.5% content,

Temperature and relative while for the same coconut Relative humidity
coir dust range
content, the (%)
density0 to 100
declined from 1725.44 kg/m3 to
EL-USB-2 RH/TEMP
humidity data logger 1552.52 kg/m3 corresponding to a decrease
Temperature accuracy of(up
◦ C) to 22%±and
0.5 26%, respectively, for saw-
dust and coconut coir dust in comparison to the waste-free
Relative humidity accuracy (%) ±2.25
clay sample.

Heating source DIMPLEX Average values andHeat

Table 5.ECOT1FT outputof(W)
coefficient 40
variation (% in parenthesis) of thermophysical properties
thermostatic tubular
of the sample heater
blocks. Capacity (V) 230–240
Fan 400 portable USB fan Capacity (V) Heat
Volumetric 5 Thermal
Thermal Specific Heat Thermal
Density,
Conductivity, Capacity, Capacity, Diffusivity, Effusivity,
Sample ID ρ
λ ISO 9869-1-2014 [59]
BS ρCpspecifies the averageCp progressiveαmethod to determine
τ the U-
(kg/m3)
value(W/mK) (×10 J/m
in steady-state conditions.6 This
3 popular, since(×it10
K)method is(J/kgK) simplifies
−6 the calculating
m /s) (Ws
2 1/2 /m K)
2

R procedure, despite
2090.96 ± 2.55 (0.32) 0.36 ± 0.02 (0.14) the longer test period.
1.66 ± 0.25 (0.33) The reliability
794.75 of this method
0.217 depends
774.70 on the
S-2.5 temperature difference
1837.05 ± 2.36 (0.08) 0.26 ± 0.01 (0.22) between the two
1.51 ± 0.23 (0.31) chambers. The
824.12 higher the
0.173 temperature
629.44 difference,
the more reliable the results. Meng et al. [67] revealed that raising the temperature differ-
S-5 1735.85 ± 2.35 (0.13) 0.24 ± 0.01 (0.30) 1.47 ± 0.22 (0.33) 849.41 0.161 591.14
ence on both sides of walls reduces the maximum system error (measurement error) and
S-7.5 1638.64 ± 2.34 (0.09) 0.21 ± 0.01 (0.41) 1.42 ± 0.21 (0.43) 865.39 0.145
◦
recommended maintaining a temperature difference of over 20 C on both sides 539.96of the wall
C-2.5 1725.44 ± 2.54 (0.24) 0.25 ± 0.01 (0.23) 1.46 ± 0.22 (0.41) 848.68 0.168 600.19
C-5 1638.79 ± 2.56 (0.25) 0.22 ± 0.01 (0.32) 1.41 ± 0.21 (0.39) 859.45 0.159 561.19
C-7.5 1552.52 ± 2.59 (0.27) 0.19 ± 0.01 (0.47) 1.38 ± 0.21 (0.47) 886.20 0.142 517.77
Constr. Mater. 2022, 2 245

to decrease the maximum system error. Hence, in this study, throughout the test period,
the average air temperatures of the hot and cold chambers were maintained at 40 ◦ C and
10 ◦ C, respectively. The heat flux was measured at two locations on the sample wall over
a period of at least 3 days (72 h), fulfilling the minimum duration requirement stipulated
by the standard. Using Equation (4) from the standard, the U-value of the sample wall
was derived by dividing the heat flux data through the wall by the temperature difference
between the two surfaces (hot and cold) of the wall.
q
U= (4)
( Th − Tc )

where q is the density of heat flow rate (W/m2 ), Th is the hot side temperature (◦ C), and Tc
is the cold side temperature (◦ C) of the sample.
The thermal resistance or R-value (m2 K/W) of the wall can be obtained by inverting
the total thermal transmittance determined (R = 1/U).

3. Results and Discussions

3.1. Thermophysical Properties of Individual Samples
Table 5 presents the results of the thermophysical properties of different agro-waste-
blended samples. As shown in the table, the bulk density decreased as the waste content
increased. Similar results were observed in several previous studies, where the inclusion
of natural fibres or aggregates into the formulation of unfired earthen blocks resulted
in a gradual decrease in bulk density [68–70]. This can be explained by the fact that
when comparatively lighter sawdust and coconut coir dust particles (see Table 1) were
incorporated into the mixture, they displaced the heavier clay particles, which eventually
decreased the density. Moreover, during sample preparation, the hydrophilic sawdust
and coconut coir dust (see water absorption values in Table 1) swelled by absorbing
water. After drying, they returned almost to their former size, leaving very small air voids
between their outer periphery and the clay particles. Consequently, the more sawdust and
coconut coir dust were added to the mixture, the more air voids were created [71]. The
samples with sawdust had densities ranging from 1837.05 kg/m3 to 1638.64 kg/m3 for
2.5% to 7.5% content, while for the same coconut coir dust content, the density declined
from 1725.44 kg/m3 to 1552.52 kg/m3 corresponding to a decrease of up to 22% and 26%,
respectively, for sawdust and coconut coir dust in comparison to the waste-free clay sample.

Table 5. Average values and coefficient of variation (% in parenthesis) of thermophysical properties

of the sample blocks.

Thermal Volumetric Heat Specific Heat Thermal Thermal

Density,
Conductivity, Capacity, Capacity, Diffusivity, Effusivity,
Sample ID ρ
λ ρCp Cp α τ
(kg/m3 )
(W/mK) (×106 J/m3 K) (J/kgK) (×10−6 m2 /s) (Ws1/2 /m2 K)
R 2090.96 ± 2.55 (0.32) 0.36 ± 0.02 (0.14) 1.66 ± 0.25 (0.33) 794.75 0.217 774.70
S-2.5 1837.05 ± 2.36 (0.08) 0.26 ± 0.01 (0.22) 1.51 ± 0.23 (0.31) 824.12 0.173 629.44
S-5 1735.85 ± 2.35 (0.13) 0.24 ± 0.01 (0.30) 1.47 ± 0.22 (0.33) 849.41 0.161 591.14
S-7.5 1638.64 ± 2.34 (0.09) 0.21 ± 0.01 (0.41) 1.42 ± 0.21 (0.43) 865.39 0.145 539.96
C-2.5 1725.44 ± 2.54 (0.24) 0.25 ± 0.01 (0.23) 1.46 ± 0.22 (0.41) 848.68 0.168 600.19
C-5 1638.79 ± 2.56 (0.25) 0.22 ± 0.01 (0.32) 1.41 ± 0.21 (0.39) 859.45 0.159 561.19
C-7.5 1552.52 ± 2.59 (0.27) 0.19 ± 0.01 (0.47) 1.38 ± 0.21 (0.47) 886.20 0.142 517.77

The thermal conductivity of building materials is an important factor for evaluating

thermal performance, since it has a direct influence on heat losses and energy consumption
in the building [72–74]. The thermal conductivity of a material is affected by various
 The thermal conductivity of building materials is an important factor for evaluating
thermal performance, since it has a direct influence on heat losses and energy consump-
tion in the building [72–74]. The thermal conductivity of a material is affected by various
variables, including its morphology, density, and homogeneity [75,76]. The results in Ta-
ble 52022,
Constr. Mater. indicate
2 a gradual decrease in thermal conductivity values with the increase in waste 246
percentages. This drop can be attributed to both the lower thermal conductivity of the
agro-waste materials employed (see Table 1) and an increase in the amount of air in the
sample combination. variables,
The thermal including its morphology,
conductivity of adensity,
material andishomogeneity [75,76]. The results
inversely proportional to in
Table 5 indicate a gradual decrease in thermal conductivity values with the increase in
its porosity [77]. The addition of agro-wastes reduces the density of the samples, resulting
waste percentages. This drop can be attributed to both the lower thermal conductivity of
in a higher void volume, whichmaterials
the agro-waste is usually filled (see
employed with air.1)Due
Table and anto increase
the lowinconductivity
the amount of air ofin the
air (0.024–0.026 W/mK),samplethe thermal conductivity
combination. of the samples
The thermal conductivity decreases
of a material as the
is inversely volume to its
proportional
porosity [77].
of air in the void increases [78–80]. The addition of agro-wastes reduces the density of the samples, resulting in
In Figure 8, thea thermal
higher void volume, which
conductivity is usually
values filled
of the with air.tested
samples Due toarethe plotted
low conductivity
against of air
(0.024–0.026 W/mK), the thermal conductivity of the samples decreases as the volume of
their density. Thereairisina the linear
void connection between sample density and thermal conduc-
increases [78–80].
tivity, with lower density samples having lower
In Figure 8, the thermal conductivity thermal conductivity
values of the samplesthan higher
tested density
are plotted against
samples. The findings theirare consistent
density. There with the conclusions
is a linear reached
connection between in previous
sample investiga-
density and thermal con-
ductivity, with
tions [68,72,81,82]. Moreover, thelower density samples
microscopic having of
examination lower
the thermal conductivity
raw materials than3)
(Figure higher
density samples. The findings are consistent with the conclusions reached in previous
revealed that sawdust and coconut coir dust particles exhibited cellular porous structures
investigations [68,72,81,82]. Moreover, the microscopic examination of the raw materials
that may contain air, explaining
(Figure 3) revealedtheir
that low
sawdustthermal conductivity
and coconut values.exhibited
coir dust particles Furthermore,
cellular it
porous
appears that the usestructures
of coconut coir contain
that may dust leads to marginally
air, explaining their lowbetter
thermalinsulation
conductivity (i.e., lower
values. Further-
thermal conductivity more, it appears
values) thanthat the use of
sawdust. coconut
This maycoir be dust
dueleads to marginally
to the lower bulk better insulation
density
(i.e., lower thermal conductivity values) than sawdust. This may be due to the lower bulk
and spongy structure of coconut coir dust particles, containing more air voids than saw-
density and spongy structure of coconut coir dust particles, containing more air voids
dust. The lowest thermal conductivity
than sawdust. The lowestvalues
thermalforconductivity
the coconut coir for
values dust
theand sawdust
coconut coir dustsam-
and saw-
ples was achieved at a 7.5%
dust samplescontent, whichatwas
was achieved about
a 7.5% a 46%
content, andwas
which 43% decrease
about compared
a 46% and 43% decrease
to the reference sample.
compared to the reference sample.

Sawdust Coconut coir dust

0.260
Thermal conductivity (W/mK)

0.250

0.240

0.230

0.220

0.210

0.200

0.190
1500 1550 1600 1650 1700 1750 1800 1850
Density (kg/m3)

Figure 8. Correlation Figure

between thermal conductivity
8. Correlation and
between thermal density. and density.
conductivity

The volumetric heat Thecapacity

volumetricofheat
thecapacity of the agro-waste-incorporated
agro-waste-incorporated samples
samples droppedbe-
dropped because
of the considerable decrease in the samples’ density (see Table 5). However, the specific
cause of the considerable decrease
heat capacity of thein the samples’
samples increased density (see Tablewaste
with the increasing 5). However,
percentage, the
since the
specific heat capacity of the samples
agro-wastes, increased
which have a lowerwith
mass the increasing
content than clay,waste percentage,
had greater since
specific heat capacity
the agro-wastes, which have
values [68].aThe
lower mass content
experimental resultsthan clay,that
revealed hada greater specific
7.5% coconut coir heat ca- 7.5%
dust and
sawdust
pacity values [68]. The addition raised
experimental the specific
results heat capacity
revealed that a from
7.5%848.68 J/kgK
coconut to 886.20
coir dust J/kgK
and and
824.12 J/kgK to 865.39 J/kgK, resulting in an increase of about 12% and 9%, respectively,
7.5% sawdust addition raised the specific heat capacity from 848.68 J/kgK to 886.20 J/kgK
over the reference sample. Moreover, the coconut coir dust samples had a slightly higher
and 824.12 J/kgK to 865.39 J/kgK, resulting in an increase of about 12% and 9%, respec-
tively, over the reference sample. Moreover, the coconut coir dust samples had a slightly
Constr. Mater. 2022, 2 247

specific heat capacity than the sawdust samples. The higher porosity in coconut coir dust
samples than in sawdust samples might be responsible for this, as the pores are primarily
filled with air, which has a specific heat capacity of 1005 J/kgK [83].
The thermal inertia of buildings contributes to both thermal comfort and a reduction in
energy consumption by keeping the indoor air temperature stable. There are two forms of
inertia: transmission and absorption. Transmission inertia is defined by thermal diffusivity,
whereas absorption inertia is described by thermal effusivity. In buildings, materials with
low diffusivity and high effusivity should be used to improve thermal inertia [84,85]. In
areas where cooling is a major issue, using low thermal diffusivity materials can delay heat
transfer from the outside of the building to the inside, decreasing the indoor temperature of
the building and reducing the demand for air conditioning during the summer. Materials
with high thermal effusivity can also help to keep the indoor temperature of a building
stable in the summer by storing and releasing heat. When the internal temperature of a
building rises above the comfort level, the walls absorb heat until a steady temperature
is attained. This heat is released when the building’s internal temperature falls below a
comfortable level. Similarly, in the winter, these high effusive materials can also aid in
the reduction in heating demand [86,87]. As a result, it is recommended that two distinct
materials be used to improve indoor thermal comfort: one with low diffusivity on the
exterior side as an insulating material and the other with high effusivity on the interior side
of the building wall as a structural material [84].
Table 5 also shows that the thermal diffusivity and thermal effusivity of the sam-
ples decreased when the percentage of agro-wastes increased in the mixture. Laborel-
Préneron et al. [68] also observed a similar trend in results using hemp shiv, corn cob,
and barley straw in unfired earthen bricks. The thermal diffusivity decreased from
0.178 × 10−6 m2 /s to 0.142 × 10−6 m2 /s and 0.173 × 10−6 m2 /s to 0.145 × 10−6 m2 /s,
respectively, when the coconut coir dust and sawdust content increased from 0.25% to 7.5%,
indicating a positive influence of agro-wastes on dampening the thermal diffusion in the
produced clay blocks [88]. It was also found that the thermal effusivity values declined from
600.19 Ws1/2 /m2 K to 517.77 Ws1/2 /m2 K and 629.44 Ws1/2 /m2 K to 539.96 Ws1/2 /m2 K,
respectively, for increasing the same amount of coconut coir dust and sawdust. According
to the results, the addition of agro-wastes to the unfired clay block increases the transmis-
sion inertia, while decreasing the absorption inertia. These types of materials would be
better suited to the construction of exterior walls to delay the transmission of heat from the
outside to the inside [68].

3.2. Thermal Properties of Wall Samples

According to the results of the thermophysical properties of the individual samples,
the S-7.5 and C-7.5 samples had the lowest density, thermal conductivity, and diffusivity,
as well as the highest specific heat capacity values. Hence, the S-7.5 and C-7.5 samples
were used to make small walls to evaluate their thermal transmittance and resistance.
Instead of collecting data immediately, data was collected for at least 24 h after the system
attained a thermal steady-state condition. Thermography analysis was performed on both
sides of the walls to check for any irregularities introduced by the heating and cooling
sources. According to Figure 9, the wall surface areas are not affected by any probable
source of error.
The temperature profiles of the two sides (hot and cold) of the wall surfaces (72 h) are
shown in Figure 10. The figure shows that all the walls have nearly similar temperatures
on both surfaces, indicating that wall surface temperatures are unaffected by the material
properties, which was also confirmed by the experimental results of Bruno et al. [89]. The
slight temperature difference is due to the position of the temperature sensors on the surface
of the sample block. Despite the sensors being attached as near to the surface as feasible, a
gap between the sensor and the surface may be created, leading it to record the temperature
of the surrounding air at some point.
 Constr. Mater. 2022, 2 248

Figure 11 illustrates the monitored relative humidity inside the hot and cold chambers
during
Constr. Mater. 2022, 3, FOR PEER REVIEW the test period. The recorded average relative humidity during the last 24 h test 15
period in the hot chamber varied between 14.62% and 15.35%, while it varied between
39.09% and 41.29% in the cold chamber.

Hot side Cold side

(a)

Hot side Cold side

(b)

Hot side Cold side

(c)

Figure
Figure9.9.Thermographs
Thermographsof
ofdifferent
different wall surfaces:
surfaces: (a)
(a)reference
referencewall;
wall;(b)
(b)sawdust
sawdust wall;
wall; (c)(c) coconut
coconut
coir dust
coir dustwall.
wall.

The temperature profiles of the two sides (hot and cold) of the wall surfaces (72 h)
are shown in Figure 10. The figure shows that all the walls have nearly similar tempera-
tures on both surfaces, indicating that wall surface temperatures are unaffected by the
material properties, which was also confirmed by the experimental results of Bruno et al.
[89]. The slight temperature difference is due to the position of the temperature sensors
on the surface of the sample block. Despite the sensors being attached as near to the sur-
face as feasible, a gap between the sensor and the surface may be created, leading it to
record the temperature of the surrounding air at some point.
Figure 11 illustrates the monitored relative humidity inside the hot and cold cham-
bers during the test period. The recorded average relative humidity during the last 24 h
test period in the hot chamber varied between 14.62% and 15.35%, while it varied between
39.09% and 41.29% in the cold chamber.
Constr. Mater. 2022, 3, FOR PEER REVIEW 16
Constr. Mater. 2022, 2 249

(a)

(b)

Figure 10. Wall surface temperature profiles

profiles (72
(72 h):
h): (a) hot side; (b) cold side.
side.
Constr.
Constr. Mater.
Mater. 2022, 3,
2 FOR PEER REVIEW 17
250

(a)

(b)
Figure 11. Relative humidity (72 h): (a) hot chamber; (b) cold chamber.
Figure 11. Relative humidity (72 h): (a) hot chamber; (b) cold chamber.
Constr. Mater. 2022, 2 251

Constr. Mater. 2022, 3, FOR PEER REVIEW 18

Table 6 lists the results of the last 24 h of the different wall sample test. The heat
flux measured through the walls exhibited a similar pattern (Figure 12), but with different
Table 6 The
magnitudes. lists reference
the resultswall
of the
hadlast
the24 h of the
highest different
heat wallof
flux value sample
548.17test.
W/m 2 , followed
The heat flux
measured
by the heat through
flux in the thesawdust
walls exhibited
wall, with a asimilar
value ofpattern
407.53(Figure 2
W/m ,12), whilebutthe
with
heatdifferent
flux of
magnitudes.
the coconut coirThedust
reference wall hadthe
wall showed thelowest
highest heatofflux
value value
369.96 W/m 2 . TheW/m
of 548.17 lower 2, followed
thermal
by the heat flux
conductivity andindensity
the sawdust
of the wall,
coconutwithcoira value
dust of 407.53may
sample W/mcontribute
2, while the heat flux of
to the lower
the coconut coir dust wall showed the lowest value of 369.96
heat flux. Materials with a higher thermal transmittance, or U-value, lose more W/m 2 . The lower thermal
heat,
conductivity
whereas thoseandwithdensity
a lower of U-value
the coconutlosecoir
lessdust
heat.sample may contribute
The results show that to thethe lower coir
coconut heat
flux.sample
dust Materials
hadwith a higher
the lowest thermalindicating
U-value, transmittance, or U-value,
the highest thermallose more heat,
resistance, as whereas
thermal
resistance
those withisainversely proportional
lower U-value to the
lose less heat.thermal transmittance.
The results show thatThe thethermal
coconutresistance
coir dust
of the coconut
sample had thecoir dustU-value,
lowest and sawdust sample
indicating thewalls
highestincreased
thermalby around 48%
resistance, and 35%,
as thermal re-
respectively, as compared
sistance is inversely to the reference
proportional sample transmittance.
to the thermal wall. The thermal resistance of
the coconut coir dust and sawdust sample walls increased by around 48% and 35%, re-
Table 6. Average
spectively, results of last
as compared 24 hreference
to the of the wallsample
test. wall.

Table Wall ID
6. Average results of last 24 h of the wall test.
Measurements
R S-7.5 C-7.5
Wall ID
Measurements
Thickness (mm) 100 100 100
R S-7.5 C-7.5
Surface Temperature
Thickness (mm) (hot side) (◦ C) 37.32100 37.40 100 36.46
100
Surface
SurfaceTemperature (cold
Temperature side)
(hot (◦ C)(°C)
side) 13.4437.32 13.32 37.40 13.42
36.46
Average values (Last 24 h) Surface Temperature
Temperature ◦ C)
Difference ((cold
side) (°C) 23.8813.44 23.08 13.32 13.42
23.04
Average values (Last 24 h) Temperature Difference
2
Heat Flux (W/m ) (°C) 23.88
548.17 407.5323.08 23.04
369.96
Heat Flux (W/m2)
U-value (W/m2 K) 1.85 548.17 1.37 407.53 1.24369.96
U-value (W/m2K) 1.85 1.37 1.24
R-value (m2 K/W) 0.54 0.73 0.80
R-value (m2K/W) 0.54 0.73 0.80

Figure 12.Heat
Figure12. Heatfluxes
fluxesacross
acrossthe
thewalls
walls(72
(72h).
h).

In Figure 13, the experimental U-value results of different wall constructions are com-
pared to the findings of several studies in the literature [90–94]. Due to the different
Constr. Mater. 2022, 2 252

Constr. Mater. 2022, 3, FOR PEER REVIEW 19

In Figure 13, the experimental U-value results of different wall constructions are
compared to the findings of several studies in the literature [90–94]. Due to the different
thicknesses
thicknesses of of the
theexperimented
experimentedwalls
wallsand
andsince
since the
the U-value
U-value is highly
is highly dependent
dependent on the
on the
thickness of the wall, the apparent thermal conductivity values of the walls
thickness of the wall, the apparent thermal conductivity values of the walls are calculated are calculated
by
by multiplying
multiplying the theU-value
U-valueby bythe
thethickness
thickness ofof
thethe wall
wall to to obtain
obtain a better
a better comparison
comparison of of
their thermal efficiency [95]. However, it should be noted that the literature
their thermal efficiency [95]. However, it should be noted that the literature thus far re-thus far reflects
very
flectsfew
veryconducted and published
few conducted tests.tests.
and published

Figure 13. Comparison of U-values of different walls with literature results [90–94].
Figure 13. Comparison of U-values of different walls with literature results [90–94].

Ojerinde
Ojerinde [90]
[90]observed
observedthatthata a10%
10%toto30%
30%rice husk
rice ashash
husk addition
additionas aaspartial replace-
a partial replace-
ment for Portland cement in compressed earth brick production decreased
ment for Portland cement in compressed earth brick production decreased the U-value the U-value
from 1.076
from W/mK
1.076 W/m 2 2 to 1.086 W/m2K.2 In another study, Teixeira et al. [94] found a U-value
K to 1.086 W/m K. In another study, Teixeira et al. [94] found a U-value
of 2.66 W/m
of 2.66 W/m K using7%
2K using
2 7%lime
limeininthe
thecompressed
compressed earth brick
earth wall.
brick Krstić
wall. et al.
Krstić et [91] used
al. [91] used
two methods (heat flow and temperature based) to measure the in situ U-value
two methods (heat flow and temperature based) to measure the in situ U-value of a hol- of a hollow
concrete
low masonry
concrete block block
masonry wall made
wall with
maderecycled crushedcrushed
with recycled brick waste
brickand ground
waste andpoly-
ground
styrene. According to the study, the U-values for the wall without any insulation
polystyrene. According to the study, the U-values for the wall without any insulation ranged
from 1.740 W/m2K to 1.782 W/m2K for the heat flow method, while for the temperature
ranged from 1.740 W/m2 K to 1.782 W/m22 K for the heat flow method, while for the tem-
based method, the U-value was 1.363 W/m K. In the case of a burnt clay brick wall with
perature based method, the U-value was 1.363 W/m2 K. In the case of a burnt clay brick
cement plaster, using the guarded hot box method, Chowdhury and Neogi [92] reported
wall with cement plaster, using the guarded hot box method, Chowdhury and Neogi [92]
that the U-value ranged from 2.326 W/m2K to 2.488 W/m2K. Callejas et al. [93] also used
reported that the U-value ranged from 2.326 W/m2 K to 2.488 W/m2 K. Callejas et al. [93]
an adapted hot box method to determine the thermal properties of concrete block with
also used an adapted hot box method to determine the thermal properties of concrete block
recycled construction and demolition waste. Based on the results obtained, the block was
with recycled construction and demolition waste. Based on the results obtained, the block
found to have a U-value of between 2.439 W/m2K and 3.030 W/m2K in the solid area. After
was found to have a U-value of between 2.439 W/m2 K and 3.030 W/m2 K in the solid area.
reviewing the experimental results described in the literature, it can be concluded that
After reviewing the experimental results described in the literature, it can be concluded that
coconut coir dust and sawdust have great potential for improving the thermal properties
coconut coir dust and sawdust have great potential for improving the thermal properties of
of unfired clay brick.
unfired clay brick.
4. Conclusions
4. Conclusions
This study aimed to experimentally investigate the thermophysical properties of the
This study aimed to experimentally investigate the thermophysical properties of the
produced unfired clay blocks utilising sawdust and coconut coir dust wastes. The prop-
produced unfired clay blocks utilising sawdust and coconut coir dust wastes. The properties
erties measured include density, thermal conductivity, volumetric heat capacity, specific
Constr. Mater. 2022, 2 253

measured include density, thermal conductivity, volumetric heat capacity, specific heat
capacity, thermal diffusivity, and thermal effusivity. Furthermore, the thermal efficiency
of the constructed walls with dimensions of 310 mm × 215 mm × 100 mm was evaluated
using an adapted hot box method in which two surfaces of the wall were exposed to hot
and cold temperatures, and heat flow across the wall was measured concurrently.
The test findings lead to the following conclusions:
• The presence of more waste content in the mixture decreased the density and con-
sequently lowered the thermal conductivity of the samples. Based on the fact that
coconut coir dust particles are lighter than sawdust particles, samples reinforced with
coconut coir dust provided better thermal insulation than those reinforced with saw-
dust. When compared to the reference sample, the addition of coconut coir dust and
sawdust resulted in a decrease of about 26% and 22% in density, as well as 46% and
43% in thermal conductivity, respectively.
• Moreover, waste inclusion contributed to lowering the volumetric heat capacity, ther-
mal diffusivity, and thermal effusivity, while increasing the specific heat capacity of
the samples.
• Furthermore, the wall made of 7.5% coconut coir dust had the best thermal perfor-
mance, which may be attributed to the lightweight nature of the samples. Lightweight
samples contain more air voids, which reduces the amount of heat transfer from hot
to cold environments. The coconut coir dust and sawdust sample walls outperformed
the reference sample wall in terms of thermal resistance, with an improvement of
around 48% and 35%, respectively.
• Considering the thermal performance, it can be concluded that both types of agro-
waste incorporation enhanced the overall thermal properties of the produced unfired
clay blocks.
The findings of this study will contribute to the literature by adding information
related to the thermal performance of agro-wastes incorporated into unfired clay blocks.
Moreover, this study will be beneficial for building material manufacturers, as it proposes
a methodology for developing environmentally friendly unfired clay blocks. Furthermore,
the production of clay blocks with agro-wastes will provide a sustainable solution to the
waste disposal problem.
In this study, small walls were tested in the laboratory to determine the thermal
characteristics of agro-waste-incorporated unfired clay blocks, in which the findings are not
fully conclusive. Therefore, future research might employ in situ performance measurement
of the wall materials to arrive at a more realistic conclusion. Future research can also
investigate the properties of agro-waste-incorporated clay blocks using different types of
clay/soil.

Author Contributions: Methodology, N.J. and J.C.; investigation, N.J., J.C. and K.K.; supervision,
B.A. and R.L.A.-M.; writing—original draft, N.J.; writing—review and editing, B.A., R.L.A.-M. and
K.K. All authors have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Data Availability Statement: Not applicable.
Acknowledgments: The authors gratefully acknowledge the financial and laboratory assistance
provided by the School of Civil Engineering and Built Environment at Liverpool John Moores
University, United Kingdom.
Conflicts of Interest: The authors declare no conflict of interest.

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