P. [TUKOVNIK et al.: CEMENT COMPOSITES WITH THE ADDITION OF PHASE-CHANGE MATERIALS AS ...
379–386
CEMENT COMPOSITES WITH THE ADDITION OF
PHASE-CHANGE MATERIALS AS INNOVATIVE CONSTRUCTION
MATERIALS FOR MAINTAINING A PLEASANT LIVING
ENVIRONMENT
CEMENTNI KOMPOZITI Z DODATKOM FAZNO SPREMENLJIVIH
MATERIALOV KOT INOVATIVNI GRADBENI MATERIALI ZA
ZAGOTAVLJANJE PRIJETNEGA BIVANJSKEGA OKOLJA
Petra [tukovnik
1
, Violeta Bokan Bosiljkov
1
, Marjan Marin{ek
2
, Tina Skalar
2*
1
Faculty of Civil and Geodetic Engineering, Jamova 2, 1000 Ljubljana
2
Faculty of Chemistry and Chemical Technology, Ve~na pot 113, 1000 Ljubljana
Prejem rokopisa – received: 2023-10-14; sprejem za objavo – accepted for publication: 2024-04-10
doi:10.17222/mit.2023.997
The aim of this work was to investigate the possibility of the addition of phase-change material (PCM) to mortar mixtures and
its effect on the material’s mechanical and thermal properties. This work included the preparation of mortar mixtures with two
different water-to-cement (w/c) ratios as well as various PCM volume-fraction additions. The main objectives were to determine
the effect of the w/c ratio as well as the PCM addition on the mechanical properties of the mortars after (3, 7, and 28) d of cur-
ing. Additionally, we examined the microstructure of the prepared mortar composites and evaluated their thermal behaviour.
Microstructural analysis revealed the uniform distribution of PCM microcapsules throughout the mortar matrix, which contrib-
utes to the efficient storage and release of thermal energy. Thermal properties were analysed by repeated heating and cooling cy-
cles of the mortar composites. The repeatability of the cyclic testing results showed a reversible melting and solidification phase
change of the PCM and indicated the potential use of such composites as an energy-efficient building material. The study high-
lighted the potential incorporation of the PCM into mortar mixtures to improve their thermal properties while maintaining the
mechanical integrity. The research findings provide valuable insight into the development of sustainable building materials with
greater energy efficiency and structural reliability.
Keywords: Mortars with PCM addition, thermal analysis, energy efficiency, sustainability
Namen prispevka je bil preu~iti vpliv vgradnje fazno spremenljivega materiala (PCM) v maltne me{anice na njihove mehanske
in toplotne lastnosti. Delo je vklju~evalo pripravo me{anic malte z razli~nimi vodo-cementnimi razmerji w/c in prostorninskimi
razmerji PCM. Glavni cilji so bili dolo~iti vpliv razmerja w/c na mehanske lastnosti malt, ter oceniti vpliv dodatka PCM na
upogibno in tla~no trdnost po (3, 7 in 28) d strjevanja. So~asno smo preu~ili tudi mikrostrukturo pripravljenih maltnih kompo-
zitov z dodatkom PCM in ocenili njihovo toplotno obna{anje. Mikrostrukturna analiza je potrdila enakomerno porazdelitev
mikrokapsul PCM v matrici malte, kar pripomore k u~inkovitemu shranjevanju in spro{~anju toplotne energije. Toplotno
obna{anje je bilo analizirano s cikli~nim testiranjem segrevanja in ohlajanja maltnih kompozitov. Ponovljivost rezultatov
cikli~nega testiranja je pokazala reverzibilno fazno spremembo taljenja in strjevanja PCM ter nakazala na potencialno uporabo
tak{nih kompozitov kot energetsko u~inkovitega gradbenega materiala. [tudija je poudarila smiselnost vklju~evanja PCM
v maltne me{anice za izbolj{anje njihovih toplotnih lastnosti ob hkratnem ohranjanju mehanske celovitosti. Ugotovitve
raziskave zagotavljajo dragocen vpogled v razvoj trajnostnih gradbenih materialov z ve~jo energetsko u~inkovitostjo in
strukturno zanesljivostjo.
Klju~ne besede: Malte s PCM dodatkom, termi~na analiza, energijska u~inkovitost, trajnost
1 INTRODUCTION
The most commonly used primary energy sources in
the world are, unfortunately, still fossil fuels. In indus-
trialised countries (including Slovenia), the residential
sector is responsible for more than 40 % of the overall
energy end-use,
1,2
of which almost 35 % is consumed for
heating and cooling. The above facts represent a clearly
significant economic cost for individual households as
well as adversely affecting the environment due to the
way energy is produced.
One of the possibilities for the more efficient use of
energy to achieve favourable living conditions in build-
ings is the greater use of so-called smart materials in
construction, which includes materials with a mineral
binder (mortars, plasters, and concretes) with the addi-
tion of phase-change materials (PCMs).
3
PCMs are a
group of functional materials with the intrinsic capability
of absorbing, storing, and releasing thermal energy in the
form of latent heat
4
during phase transition cycles at their
operating temperatures under isothermal conditions. The
principle of the PCM is simple. As the temperature in-
creases, the material changes phase from solid to liquid.
The reaction being endothermic, the PCM absorbs the
heat. Similarly, when the temperature decreases, the ma-
terial changes phase from liquid to solid. The reaction is
Materiali in tehnologije / Materials and technology 58 (2024) 3, 379–386 379
UDK 666.971.4:543.57 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 58(3)379(2024)
*Corresponding author's e-mail:
tina.skalar@fkkt.uni-lj.si (Tina Skalar)

exothermic, so the PCM releases the heat.
5
The addition
of PCM to mortars, plasters, or concretes, therefore,
changes the specific heat capacity of the mortar. The use
of PCM in mortar would, therefore, reduce the need for
the cooling and heating of buildings.
According to chemical origin, PCMs are divided into
i) organic, ii) inorganic and iii) materials of eutectic ori-
gin.
6–9
The organic materials that exhibit phase-changing
properties are paraffins and fatty acids. PCMs of organic
origin are satisfactorily stable, chemically inert, afford-
able, mostly of natural origin and have a fairly high la-
tent heat of fusion/crystallisation. Their main disadvan-
tage is a relatively poor thermal conductivity and, in the
case of paraffin PCMs, flammability.
10
Inorganic PCMs
are mostly hydrates of inorganic salts. These PCMs show
relatively high latent heat of fusion/crystallisation and
have relatively good compatibility with inorganic com-
posite matrices; however, their price is higher than or-
ganic PCMs, and the phase transition usually results in a
large volume expansion, which is the main limitation for
their use in mortar as rigid systems.
11
Eutectic PCMs are
a mixture of two or more organic or inorganic com-
pounds, which, depending on the phase diagram under a
given composition and thermodynamic conditions, form
a liquid or solid. The main advantage of using eutectics
is that they allow the properties of PCMs to be ad-
justed.
12
The selected PCM in construction must meet
the following properties: 1) chemical inertness, 2) ther-
mal resistance, 3) high specific heat capacity, 4) good
thermal conductivity, 5) high latent heat, and 6) the
phase-transition temperature must be in an area suitable
for its application.
13,14
To ensure chemical inertness, the
PCM is usually not added directly to the mortar but is
encapsulated prior to admixing (indirect method of PCM
incorporation).
2,15
This reduces the potential impact of
the PCM on hydration reactions during the solidification
of the mortar mix, as well as subsequent chemical reac-
tions during the ageing of the mortar.
In construction, regarding the temperature range of
the phase transition, the use of encapsulated organic
PCMs, especially paraffins, is mostly considered. For
many paraffins, the solid/liquid phase transition is pre-
cisely in the temperature range favourable for human liv-
ing temperatures. Also, paraffins do not cause corrosion
of reinforcement in mortar. It is evident from the scien-
tific literature that the functional properties of mortars
can be changed with the addition of PCMs.
13
The
hydration of cement is an exothermic reaction that can
lead to the formation of cracks in the core of the mortar
element and, consequently, the weakening of the mortar.
It has been reported that the addition of PCM delays the
development of the temperature profile due to hydration
and lowers the maximum hydration temperature.
16
Some
authors are also of the opinion that the addition of a
PCM reduces the damage to mortar due to freezing and
thawing cycles.
17
The addition of microencapsulated
PCMs, in contrast, reduces the workability and flow-
ability of mortar, but there are no definitive answers in
the literature on the acceptable amount of PCM to be
added, as well as the method and timing of PCM addi-
tion to keep the mortar workable.
18
The addition of mi-
cro-encapsulated PCM further reduces the density of the
mortar, as PCM in mortar partially replaces higher-den-
sity material (e.g., aggregate), which can consequently
affect the mechanical properties of the mortar product
(e.g., compressive strength). The compressive strength of
mortar is an essential element to consider when design-
ing a structure. Specifically, mortar withstands compres-
sive loads well and is thus used as a load-bearing compo-
nent of the structure. In the case of PCM addition, it is
therefore highly desirable to minimise the loss of com-
pressive strength of the mortar. The prevailing opinion in
the literature is that the cracking of microcapsules and,
consequently, the increased porosity of the mortar with
an addition of encapsulated PCM contributes mostly to
the reduction of compressive strength.
19
However, the re-
duction in the strength of the mortar with the addition of
PCM has not yet been definitively investigated, but it is
assumed that the reduction in compressive strength of the
mortar is related to the amount of added PCM. Despite
the latter, the compressive strength of mortar with the ad-
dition of PCM is still believed to be suitable for use in
structural applications. Furthermore, the addition of a
PCM is also expected to affect the thermal properties of
mortar, both its thermal conductivity and specific heat
capacity. Most studies find that the addition of micro-en-
capsulated PCMs reduces the thermal conductivity of
mortar.
20
The reasons for this effect are the increase in
porosity due to entrapped air caused by the addition of a
PCM as well as the partial replacement of the aggregate
with PCM particles, which, in principle, have poorer
thermal conductivity. In contrast, the addition of mi-
cro-encapsulated PCMs increases the heat capacity of
the mortar, especially in the PCM melting temperature
range due to the latent heat of the PCM phase transition.
It is also worth mentioning the influence of the addi-
tion of a PCM on the resistance of the mortar during fire.
Organic PCMs are certainly combustible. However, some
literature studies suggest that the addition of a PCM in
the initial stages of a fire even lowers the temperature of
the mortar, which further suggests that the time required
for the building construction material to decay during a
fire is actually longer.
21
The aim of the proposed project is to critically evalu-
ate the possibility of using selected PCM based on en-
capsulated wax for the preparation of special mortars as
modern building materials in construction.
2 EXPERIMENTAL PART
2.1 Materials
The cement mortar samples were prepared using do-
lomite aggregate from the north-east part of Slovenia, ce-
ment CEM I 42.5N (EN 197-1) and superplasticiser
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380 Materiali in tehnologije / Materials and technology 58 (2024) 3, 379–386

Cementol Hiperplast 481 in accordance with
22
. The ag-
gregate was produced by crushing the parent rock. Only
a 0/4 mm fraction was used for the specimens’ prepara-
tion. Water absorption of the aggregate was 0.8 %, and
its density was 2810 kg m
–3
. The result of a quantitative
X-ray analysis showed that the aggregate was composed
predominantly of the minerals dolomite (98.1 %) and
calcite (representing only  1.9 %). The Blain-specific
surface area of used cement is 3388 cm
2
g
–1
, and its den-
sity is 3.05 g cm
–3
. The chemical composition of the used
CEM I 42.5N is given in Table 1.
The chosen PCM was based on encapsulated paraffin
wax with a melamine-formaldehyde membrane. The
melting point of the wax in the used PCM is between
25 °C and 29 °C, and its heat storage capacity is in the
160–185 J g
–1
range. The particle size of the encapsu-
lated PCM is 2–10 μm (Figure 1). During the prepara-
tion of the cement mixture, the PCM was added as an
aqueous dispersion (slurry with 28.2 % PCM content).
2.2 Samples preparation
During the experimental work, four samples were
prepared: a reference mortar sample without added PCM
and three mortar samples with added PCM (Table 2). In
the case of the reference sample and two mortar samples
with added PCM, the water-to-cement (w/c) ratio used
was 0.46, and the addition of the PCM slurry into the ce-
ment mixture was 5 /% or 10 /% for samples A 0.46-5
and B 0.46-10, respectively. Additionally, in order to al-
ter the workability of the fresh mortar paste, the C 0.53-5
sample was prepared with a water-to-cement ratio of
0.53 and 5 /% of added PCM. After the casting of mor-
tar bars with dimensions of (40 × 40 × 160) mm, the
samples were cured in an environment with a relative hu-
midity higher than 90 % and a temperature of 20±1°C
for (3, 7 and 28) d.
2.3 Methods
Microstructure characterisations of the samples were
performed using electron microscopy (FE-SEM Zeiss
Ultra Plus microscope equipped with EDS Oxford
X-Max SDD 50 mm
2
detector and INCA 4.14 5 X-ray
microanalysis software). To better distinguish the phases
present in the samples, back-scattered electrons (BSEs)
were used for SEM imaging and the Cameo+ option in
Inca software, which allows the emitted X-ray light to be
presented in the visible part of the spectrum.
The workability tests of the fresh mortar mixtures
(including mortars’ flow tests and density) were carried
out in accordance with the SIST EN 1015-3:2001 stan-
dard method.
23
Porosity tests of the fresh mortar mixture
were measured in accordance with the SIST EN
1015-7:1999 standard.
24
The flexural (3 parallel samples)
and compressive (6 parallel samples) strengths of the
cast and cured mortar bars were determined according to
the EN 1015-11 standard
25
by using universal testing ma-
chines Roel-Amsler with capacities of 100 kN and
500 kN, respectively. The E-modulus of ready-mixed
mortars with PCM addition was measured using a
Proceq Pundit PL-200 ultrasound according to the
method described in
26
. The freeze-thaw tests of the cast
and cured mortar bars with de-icing salts were performed
using an alternative method described in the CEN/TS
12390-9 standard.
27
In each test, 20 freeze/thaw cycles
were conducted. Each cycle lasted 24 h and consisted of
16 h of freezing at a temperature of –15±2°Cfollowed
by8hoftha wing at a constant temperature of 20±2°C.
After every fifth cycle, the samples were removed from
the solution, cleaned with running water to remove all
P. [TUKOVNIK et al.: CEMENT COMPOSITES WITH THE ADDITION OF PHASE-CHANGE MATERIALS AS ...
Materiali in tehnologije / Materials and technology 58 (2024) 3, 379–386 381
Table 1: Chemical composition of CEM I 42.5N
SiO2 (w/%) Al2O3 (w/%) Fe2O3 (w/%) CaO (w/%) MgO (w/%) SO3 (w/%) Na2O( w/%) K
2O( w/%) Cl (w/%)
19.68 4.82 2.88 63.49 1.54 2.74 0.34 0.72 0.06
Table 2: Designation and composition of samples.
Sample name used cement
aggregate size
fraction
w/c ratio
superplasticizer ad-
dition /%
PCM addition
/  /%
Ref CEM I 42.5N 0/4 0.46 1 /
A 0.46-5 CEM I 42.5N 0/4 0.46 1 5
B 0.46-10 CEM I 42.5N 0/4 0.46 1 10
C 0.53-5 CEM I 42.5N 0/4 0.53 1 5
Figure 1: SEM image of used PCM

the particles that fell off the surface and dried. Such sur-
face dry samples were weighed in order to calculate the
mass of the lost material.
All thermo-analytical tests were recorded using a
Metter Toledo DSC1/778/700 module. Each test was per-
formed on approximately 5 mg of crushed mortar sample
in synthetic air (20 mL min
–1
20  /%O
2
and 80  /%
Ar) following consecutive steps in a temperature pro-
gram: 1) dynamic cooling from room temperature to
–10 °C (cooling rate =2Kmin
–1
), 2) isothermal step at
–10 °C for 2 min, 3) dynamic heating from –10 °C to
50 °C ( =2Kmin
–1
), 4) isothermal step at 50 °C for
2 min, 5) dynamic cooling from 50 °C to –10 °C
( =2Kmin
–1
), 6) isothermal step at -10 °C for 2 min
and 7) dynamic heating from –10 °C to 50 °C
( =2Kmin
–1
).
3 RESULTS AND DISCUSSION
3.1. Mechanical properties of mortars
The mechanical properties of mortars are of prime
importance in construction. Some basic characteristics of
fresh mortars, as obtained on a flow table, are presented
in Table 3. It is evident that the ability of fresh mortars
to flow is mainly influenced by the w/c ratio in the fresh
mortar mixture and very little by the amount of added
PCM. Such results are expected since a higher w/c ratio
dilutes the system and thus lowers its viscosity. Conse-
quently, with a higher w/c ratio, the workability of the
mortar increases, and such systems can be mixed, placed,
consolidated, and finished more easily with minimal loss
of homogeneity. Additionally, the measured porosity val-
ues further imply that a higher w/c ratio also reduces the
aeration of the mortars. In this regard, the PCM addition
has very little effect. In contrast, the addition of PCM
has a significant effect on the bulk density of the pre-
pared fresh mortars. When compared to the reference
sample (without added PCM), the bulk density of the
prepared fresh mortars decreases with increasing volume
fraction of the PCM additive. The main reason for such
an observation is the fact that PCM, as an organic phase,
has a lower density than any other solid phase in mortars.
Since PCM partially replaces other solid components in
the mortar composite mixture, it also lowers its bulk den-
sity.
Table 3: Basic characteristics of fresh mortars as obtained on a flow
table.
Sample name
ability to flow
/mm
bulk density
/kgm
–3
porosity
/%
Ref 106 2402 3.9
A 0.46-5 103 2387 4.0
B 0.46-10 104 2276 3.8
C 0.53-5 172 2290 3.6
Figure 2 shows the evolution of the flexural and
compressive strengths of the cast and cured mortar com-
posites in the time periods of (3, 7, and 28) d. As ex-
pected, both compressive and flexural strengths increase
over time for all the samples. When comparing the refer-
ence and the PCM samples, it is evident that the flexural
and compressive strengths of the samples with the addi-
tion of PCM are lower. At the age of 3 d, sample A
0.46-5 reaches close to 54 % of the compressive strength
of the reference sample, sample B 0.46-10 reaches
 59 % of the reference strength, while sample C 0.53-5
reaches  69 % of the reference mixture compressive
strength. At the age of 7 d, the compressive strength of
the reference samples is around 61 MPa, and the samples
with the added PCM achieve an average of around 67 %
of that value. At the age of 28 d, the reference sample
reaches a compressive strength of 69.31 MPa, while the
compressive strengths of the samples A 0.46-5,
B 0.46-10 and C 0.53-5 are 52.51 MPa, 51.54 MPa and
56.61 MPa, respectively, which is around 77 % of the
reference value. The fact that the C 0.53-5 sample exhib-
its relatively higher strength values during the early
stages of curing compared to the A 0.46-5 and B 0.46-10
samples can be attributed to the better workability of the
C 0.53-5 sample.
Regarding flexural strength, the gap between the ref-
erence sample and the samples with added PCM is
smaller than the compressive strength. At the age of 3 d,
the samples with added PCM reached, on average, 72 %
P. [TUKOVNIK et al.: CEMENT COMPOSITES WITH THE ADDITION OF PHASE-CHANGE MATERIALS AS ...
382 Materiali in tehnologije / Materials and technology 58 (2024) 3, 379–386
Figure 2: a) Compressive and b) flexural strength of cast and cured
mortars

(28 % gap) of the flexural strength of the reference mix-
ture. After 7 d of hardening, this difference is down to
23 %, and at the age of 28 d, the gap in flexural strength
is, on average, only 13 %.
The above numbers suggest that the reference sample
hardens faster than the PCM samples; however, the gap
in compressive or flexural strength between the reference
and the PCM samples gradually becomes narrower with
hardening time. It is, therefore, rational to expect that
prolonged curing time will bring the compressive and
flexural strengths of the PCM samples even closer to the
reference value.
One of the fundamental parameters when designing
mortar or mortar structures is the elastic modulus (E
c
). In
general, it is defined as the ratio of the applied stress to
the corresponding strain. Not only does it demonstrate
the ability of the mortar to withstand deformation due to
an applied stress, but also its stiffness. In other words, it
reflects the ability of the mortar to deflect elastically and
is thus a good overall indicator of its strength. From this
definition, it is also possible to connect the evolution of
E
c
with progressing mortar or mortar hardening. Accord-
ing to the results presented in Figure 3, the addition of a
PCM to the mortar mixtures affects their E
c
values (E
c
is
calculated through the velocity measurements of longitu-
dinal ultrasound waves v
US
). It is evident that the refer-
ence mixture starts hardening 3.55 h after casting. The
mixture with added 5 % PCM (A 0.46-5) starts harden-
ing within 4.40 h, while the B 0.46-10 mixture starts
hardening another 35 min after the A 0.46-5 sample. Ad-
ditionally, the C 0.53-5 sample with 10 % PCM and
0.53 w/c ratio behaves similarly to the A 0.46-5 sample
with regard to hardening time and, thus, E
c
evolution.
As expected, the dynamic modulus of elasticity after
48 h is the highest for the reference mixture, around
 45 GPa. After the same time period, mortars with a
PCM addition exhibit lower E
c
values ranging between
 32.2 GPa and  32.4 GPa. Furthermore, regarding the
E
c
values during this early curing time, the gap between
he reference sample and the mortars with added PCM
appears to widen. The latter suggests that the initial mor-
tar hardening is a more complex process if the PCM is
added to the mixture and that the PCM capsules affect
the stress-strain behaviour and, thus, the deformation of
mortars under load.
Successive freeze-thaw cycles and the disruption of
paste and aggregate can cause some immediate micro-
structural changes and, eventually, permanent mortar
damage. The main reason for such an observation is the
fact that the liquid-to-solid phase change of water results
in a volume expansion of about 9 %. As the water in the
mortar freezes, it produces pressure in the pores of the
mortar. If the pressure developed exceeds the tensile
strength of the mortar, the cavity will dilate and rupture.
Therefore, the freeze-thaw resistance is one of the many
parameters which define mortar durability and should be
carefully studied.
The results of the freeze-thaw tests are summarised in
Figure 4. It is evident that the reference sample, as well
as samples A 0.46-5 and C 0.53-5, have practically negli-
gible mass loss after the 10
th
freeze-thaw cycle. In these
three cases, after the 10
th
freeze-thaw cycle, only minor
surface erosion can be visually observed. Further, at the
end of the 20
th
freeze-thaw cycle, total mass losses for
samples Ref, A 0.46-5 and C 0.53-5 were measured as
0.87 g, 1.80 g and 1.07 g, respectively. These values are
still fairly low, suggesting that relatively low PCM addi-
tions only slightly affect the freeze-thaw durability of the
investigated mortars. In contrast, the B 0.46-10 sample
exhibits an 2 g mass loss and a rather rough surface af-
ter the first five freeze-thaw cycles. Surface erosion in-
creases noticeably with each further freeze-thaw cycle,
resulting in a 17.63 g mass loss after the 20
th
cycle
(which is 3 % of the initial mass). The final surface of
the B 0.46-10 sample is heavily degraded with numerous
craters, voids and cracks, making such mortar inappro-
P. [TUKOVNIK et al.: CEMENT COMPOSITES WITH THE ADDITION OF PHASE-CHANGE MATERIALS AS ...
Materiali in tehnologije / Materials and technology 58 (2024) 3, 379–386 383
Figure 4: Freeze-thaw tests of mortars with various additions of PCM
(the inner picture presents B 0.46-10 mortar bars after the 20
th
freeze-thaw cycle)
Figure 3: Evolution of dynamic modulus of elasticity (top) and veloc-
ity of longitudinal ultrasound waves (bottom) in the prepared mortar
mixtures

priate to use in extreme weather conditions or limiting its
use only for potential applications inside buildings.
The presence of a PCM in the mortar mixture causes
some unique microstructural features. Namely, PCM is
an additional solid phase in a mortar composite with its
characteristic spherical morphology. The microstructure
of the A 0.46-5 sample is presented in Figure 5.Itisevi-
dent that PCM microcapsules are uniformly distributed
throughout the mortar. No PCM segregation in the A
0.46-5 hardened mortar further suggests successful mate-
rial preparation during the components’ mixing. Further-
more, all the PCM capsules are still undamaged, mean-
ing that the paraffin wax remains firmly encapsulated
within the relatively thin melamine-formaldehyde mem-
brane. The latter is important when such mortar is ap-
plied in construction. Specifically, any wax leakage out
of the membrane can influence the mortar-hardening
process and its strength evolution. The final mortar
strength is substantially lowered if the PCM capsules are
damaged and the wax spreads throughout the mortar.
Since PCM segregation is omitted by more vigorous
mixing, while less intense mixing preserves the PCM
capsules unharmed, a delicate balance in power input
during the mortar preparation must be found.
If mortars with the PCM addition are used as modern
building materials with a function to provide favourable
living temperatures, the thermal properties of such mate-
rials are essential. Specifically, the head capacity and
temperature interval of the solid-to-liquid phase transi-
tion are two basic characteristics of such modern com-
posites. To evaluate the thermal behaviour of the pre-
pared mortars, a series of DSC tests were conducted
(Figure 6). The DSC tests included two consecutive
cooling-heating cycles in order to verify the repeatability
of the measured heat effects. According to the collected
DSC results, the reference sample (mortar without PCM
addition) exhibits no measurable heat effects within the
monitored temperature window (Figure 6a). In contrast,
the pure PCM sample (Figure 6b) shows an exothermic
effect during heating and several (two major) consecu-
tive endothermic effects during cooling. The exothermic
effect is a consequence of the wax melting during heat-
ing, while the endothermic effects are due to subsequent
wax solidification during cooling. Several consecutive
endothermic peaks during cooling indicate that the wax
from the PCM is a combination of different straight-
P. [TUKOVNIK et al.: CEMENT COMPOSITES WITH THE ADDITION OF PHASE-CHANGE MATERIALS AS ...
384 Materiali in tehnologije / Materials and technology 58 (2024) 3, 379–386
Figure 5: BSE-EDS images of A 0.46-5 mortar composite (PCM cap-
sules are coloured red)
Figure 6: DSC measurements of mortars with various PCM additions: a) the Ref sample, b) the A 0.46-5 sample, c) the pure PCM, d) the B
0.46-10 sample, e) the C 0.53-5 sample

chain hydrocarbons rather than a chemically well-de-
fined single organic compound. The latter is further cor-
roborated by the fact that melting and/or solidification
intervals are rather wide. Furthermore, the melting
( 29 °C) and the solidification (main peak at  23 °C)
of the wax are separated by a temperature hysteresis. The
latent-heat storage capacities of the encapsulated PCMs
are measured as 183.0 J g
–1
, –184.1 J g
–1
and 187.0 J g
–1
during the 1
st
heating cycle and the 2
nd
cooling cycle in
the 2
nd
heating cycle, respectively (Table 4). Data from
the 1
st
cooling cycle are irrelevant since the cycle is in-
complete. If the mortars with PCM additions are tested,
the exothermic and endothermic effects due to wax melt-
ing and solidification, respectively, are still apparent,
however, with much lower latent-heat storage capacity
when compared to the pure PCM material. On average,
 H
melting/solidification
of samples A 0.46-5, B 0.46-10 and C
0.53-5 are measured as 9.7 J g
–1
,18.7Jg
–1
and 9.4 J g
–1
,
respectively, which is comparable to the work of Chris-
ten et al.
28
. These numbers can be illustrated through a
hypothetical calculation. Let us assume a room with di-
mensions of3m×3m×4mwhere the ceiling and outer
walls are plastered, applying mortar with the PCM addi-
tion. A simple calculation reveals that the plastered sur-
face equals 54 m
2
. Assuming a 2-cm-thick layer of the
applied plaster, we can further calculate the volume of
the used plaster to be 1.08 m
3
( 1.1 m
3
). A typical den-
sity of mortar varies from 2400 kg m
–3
to 2900 kg m
–3
.
Since PCMs are a relatively low-density phase in mortar
composites, they somewhat lower the final mortar den-
sity. Thus, for additional calculations, we may consider
the mortar (plaster) density to be  2300 kg m
–3
, result-
ing in a final mass of 2500 kg of used mortar for plas-
tering. The latter further suggests that the latent-heat
storage capacities of mortars A 0.46-5, B 0.46-10 and C
0.53-5 are calculated as 6.74 kWh, 12.99 kWh and
6.53 kWh, respectively, if the hypothetical room is plas-
tered. Such relatively high values might substantially re-
duce the energy consumption for the cooling and heating
of buildings as well as increase the thermal comfort for
residents. Finally, the use of mortars with PCM addition
can aid in constructing buildings that are more energy ef-
ficient and environmentally friendly.
29
4 CONCLUSIONS
The study described the development of some func-
tional properties of mortar mixtures with various addi-
tions of a PCM based on encapsulated paraffin wax. All
the mortar composites with the PCM addition exhibited
gradually increasing flexural and compressive strengths
within 28 d of curing time. The composite (C 0.53-5)
with a w/c ratio of 0.53 reached the highest value. Its
flexural and compressive strengths after 28 d of harden-
ing were 82 % and 95 %, respectively, compared to the
reference mixture. The elastic modulus of the mortar
composites with the PCM addition after 20 h of harden-
ing reached between 60 % and 70 % of the reference
value. The freeze-thaw tests suggested that relatively low
PCM additions (5  /%) negligibly affected the freeze-
thaw durability, while an addition of 10  /% made mor-
tar completely inappropriate to use in extreme weather
conditions. The SEM-EDS microstructural analysis
showed that the PCM capsules were undamaged and uni-
formly distributed in the mortar matrix. Thermo-analyti-
cal cycling tests showed repeatable melting/solidification
of the PCM, indicating a high potential of mortars with
PCM additions for developing energy-efficient building
materials. A closer examination of the DSC results re-
vealed that the melting/solidification enthalpy for sam-
ples A 0.46-5, B 0.46-10, and C 0.53-5 were 9.7 J g
–1
,
18.7 J g
–1
, and 9.4 J g
–1
, respectively. Assuming that
these composites were installed in a room of average di-
mensions, they could result in up to 20 % savings in
heating/cooling energy consumption throughout the year.
Overall, the results of this study are an important step to-
ward the development and use of mortar mixtures with
PCM additions as a viable approach to improving the
thermal performance and structural integrity of building
materials.
Acknowledgment
The authors would like to acknowledge financial sup-
port of Slovenian Research Agency through research
programmes P1-0175 and P2-0185 and The Centre for
Research Infrastructure at the Faculty of Chemistry and
Chemical Technology (IC UL FCCT).
P. [TUKOVNIK et al.: CEMENT COMPOSITES WITH THE ADDITION OF PHASE-CHANGE MATERIALS AS ...
Materiali in tehnologije / Materials and technology 58 (2024) 3, 379–386 385
Table 4: Peak temperatures and calculated latent heat capacities of various mortar samples as obtained from the DCS measurements
Step
Sample
1
st
cooling 1
st
heating 2
nd
cooling 2
nd
heating
Tpeak
/°C  H/Jg
–1
T
peak
/°C  H/Jg
–1
T
peak
/°C  H/Jg
–1
T
peak
/°C  H/Jg
–1
Ref not detected not detected not detected not detected
PCM 14.6 –58.2 29.4 183.0 22–17.5 –184.1 29.5 187.0
A 0.46-5 17.8 –2.4 28.5 9.7 22.5–18 –9.7 28.5 9.8
B 0.46-10 14.9 –4.9 29.2 18.6 23–18 –18.9 29.2 18.4
C 0.53-5 15.3 –2.6 28.6 9.6 23.5–18 –9.3 28.6 9.3

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