Article
Influence of Pozzolanic Additives on the Structure
and Properties of Ultra-High-Performance Concrete
Jurgita Malaiškienė 1, *
and Ronaldas Jakubovskis 2
1
2
*
Laboratory of Composite Materials, Institute of Building Materials, Faculty of Civil Engineering, Vilnius
Gediminas Technical University, Sauletekio av. 11, 10223 Vilnius, Lithuania
Laboratory of Innovative Building Structures, Faculty of Civil Engineering, Vilnius Gediminas Technical
University, Sauletekio av. 11, 10223 Vilnius, Lithuania; ronaldas.jakubovskis@vilniustech.lt
Correspondence: jurgita.malaiskiene@vilniustech.lt
Abstract: The aim of this paper is to analyse the influence of the following different
supplementary cementitious materials (SCMs): milled quartz sand, microsilica, waste
metakaolin, milled window glass, and a binary additive made of one part waste metakaolin
and one part microsilica, on the properties of ultra-high-performance concrete, and choose
the best additive according to the physical, mechanical, and structural properties of concrete.
In all mixes except the control mix, 10% of the cement was replaced with pozzolanic
additives, and the changes in the physical, mechanical, and structural properties of the
concrete were analysed (density, compressive strength, water absorption, capillary water
absorption, degree of structural inhomogeneity, porosity, freeze–thaw resistance prediction
coefficient Kf values); X-ray diffraction analysis (XRD) and scanning electron microscopy
analysis (SEM) results were then interpreted. Concrete with microsilica and the binary
additive (microsilica + metakaolin) was found to have the highest compressive strength,
density, closed porosity, and structural homogeneity. Compared to the control sample,
these compositions have 50% lower open porosity and 24% higher closed porosity, resulting
from the effect of pozzolanic additives, with which the highest density and structural
homogeneity was achieved due to the different particle sizes of the additives used.
Academic Editors: Eddie Koenders
Keywords: high-performance concrete; pozzolanic additives; mechanical and durability
properties; cement hydration
and Andreas Lampropoulos
Received: 3 January 2025
Revised: 12 March 2025
Accepted: 14 March 2025
Published: 16 March 2025
Citation: Malaiškienė, J.;
Jakubovskis, R. Influence of
Pozzolanic Additives on the Structure
and Properties of Ultra-HighPerformance Concrete. Materials 2025,
18, 1304. https://doi.org/10.3390/
ma18061304
Copyright: © 2025 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license
(https://creativecommons.org/
licenses/by/4.0/).
Materials 2025, 18, 1304
1. Introduction
Advancements in concrete technology have allowed the creation of concrete mixtures
with compressive strengths, toughness, and ductility close to those of metallic materials [1]. Concretes with compressive strengths greater than 120 MPa are commonly called
ultra-high-performance concrete (UHPC) [2]; high-performance concrete usually refers to
concrete with compressive strength after 28 days above 70–80 MPa. In addition to high
compressive strength, UHPC features outstanding durability properties with regard to
water permeability, freeze–thaw resistance and carbonation rates almost ten times lower
compared to conventional concrete [3,4]. Both the extreme compressive strength and enhanced durability properties of UHPC result from high particle packing density and low
capillary porosity [5]. This makes UHPC applicable for slender and complex structural
elements, bridge girders, or thin cladding panels [6]. Nevertheless, practical applications
of UHPC are still scarce, mostly due to the relatively high cost of materials. The price of
commercially available UHPC mixes depends on the country, and ingredients can go up to
1500 EUR/m3 , compared to ordinary concrete at 50 to 200 EUR/m3 [7].
https://doi.org/10.3390/ma18061304
Materials 2025, 18, 1304
2 of 17
In addition to the high initial cost, UHPC mixes also have adverse environmental
impacts due to the enormous carbon footprint of their raw materials. The embedded CO2
emission of UHPC mixes ranges between 600 and 1200 kg/m3 . This emission rate is mostly
caused by the high amount of cement (700–1200 kg/m3 ) and silica fume (100–500 kg/m3 )
in the composition of UHPC [8,9]. In addition, natural sand and coarse aggregate (priced
around 15 EUR/m3 ) are generally replaced with finely ground quartz sand or quartz
powder (priced around 150 EUR/m3 ), which also contributes to the increased price of
UHPC.
Recently, researchers have shifted their attention to the development of more economical and less environmentally harmful UHPC mix designs, rather than achieving extremely
high compressive strengths (>200 MPa) [10–15]. In general, there are three main UHPC
cost and carbon footprint reduction strategies: (1) using sand and coarse aggregates from
natural gradation processes; (2) minimising the amount of silica fume; and (3) substituting
an amount of the high-grade Portland cement with supplementary cementitious materials
(SCMs).
Several independent studies [10–13,15,16] have reported that UHPC cost can be significantly reduced while compromising only 15–20% of its compressive strength by using sand
from natural gradation processes with relatively low amounts of silica fume. These findings
were adopted in the present study for the development of a cost-effective and efficient
UHPC mix. However, the use of SCMs in UHPC production is a much broader research
area that covers a wide variety of binders and mix design techniques [7,10]. Although
considerable effort has been put into studying the impact of different pozzolanic materials
on the performance of UHPC, there are still evident gaps in the research in this field.
The production of high-strength concretes (HPC) often involves the use of pozzolans
that promote the formation of calcium silicate hydrates (C-S-H and C-A-S-H). The most
common pozzolanic materials used are fly ash (FA) [2,17], silica fume (SF) [18], metakaolin
(MK) [19], and milled quartz sand (MQ), which, due to associated health hazards, should
be substituted with milled glass (MG) [20,21]. The addition of such mineral admixtures
makes concrete denser and reduces the amount of voids, resulting in better resistance to
sorption [22].
Research results show that the compressive strength of concrete in which 20% of
the cement was replaced with milled window glass decreased during the first days of
hydration, and reached the strength of a control composition only after 28–56 days, while
at 91 days the compressive strength of the modified concrete even exceeded the strength of
the control composition by 5% [23–26]. According to the literature [27–29], SiO2 dissolves
rapidly, reacts with free portlandite (CH), and behaves like a pozzolan when the sizes of
milled glass particles are below 75 µm; the alkali silica reaction stops when the average
particle size is approx. 20 µm [30,31]. When coarse ground glass is used as a fine aggregate,
only a fraction of the glass particles dissolve, leading to the formation of silica gels in the
later stages of hydration. This gel tends to expand, and causes high internal stresses that
lead to concrete degradation [32]. Idir et al. [33] observed in their study that glass particles
of a size larger than 1 mm caused the formation of an alkali–silica reaction (ASR) gel. On
the other hand, smaller glass particles led to the generation of calcium-silicate-hydrate
(C-S-H) through pozzolanic reactions. Notably, when the particle size is slightly less than
1 mm, no formation of expansive ASR gel around the particles was observed. Smaller
glass particles contribute to improved bonding between the glass particles and the cement
paste [34,35]. The replacement of 50% quartz sand with milled glass makes it possible to
achieve an exceptionally dense microstructure in the UHPC that is safe from any expansion
resulting from ASR. The findings indicate that there is no formation of ASR products at the
Materials 2025, 18, 1304
3 of 17
particle level, and this absence is beneficial for the durability of UHPC, which has extremely
low permeability and effectively prevents the entry of alkali into the concrete structure [21].
Typically, MK is used as an additional cementitious material to improve the performance of cement-based materials [34–36]. This enhancement is commonly assessed by
various parameters such as compressive and flexural strength, water absorption, and
drying shrinkage [37]. MK improves the pore structure of cement-based materials by
reducing the presence of large detrimental pores and increasing the impermeability of the
concrete [38]. Incorporation of MK at cement replacement levels ranging from 0% to 20%
produces an observable improvement in compressive strength, splitting tensile strength,
modulus of elasticity, and flexural strength of concrete. This enhancement is attributed
to the pozzolanic reactivity of metakaolin due to the larger number of OH groups in the
crystal structure [39], which contributes to the formation of additional cementitious compounds, thus reinforcing the mechanical properties of concrete. However, a replacement
level higher than 20% seems to have an adverse impact on these key properties of concrete [40,41]. Several factors could contribute to this detrimental effect: a lower content of
cementitious materials replaced by supplementary additives may have a dilution effect,
leading to diminished strength in the concrete; a continuous increase in metakaolin content
may trigger excessive pozzolanic reactions, which can alter the balance of the concrete
mix, leading to deteriorated mechanical characteristics. The particle size distribution of
metakaolin becomes crucial at higher replacement levels. Excess fine particles can induce
issues, such as increased water demand or suboptimal particle packing, both of which can
compromise the properties of concrete [42].
SF, an SCM containing at least 85% silica and having ultrafine particles, not only
improves the strength, but also improves the durability of concrete. This improvement is
achieved through reduced porosity and enhanced quality of the transition zones within
the concrete [43–45]. Additionally, due to its ultrafine nature, SF has a significantly large
specific surface area. Consequently, it often requires a substantial dosage of superplasticizer
(SP) for effective dispersion of SF particles [46,47]. SF stands out as a prevalent SCM in
the production of UHPC. The large surface area of SF particles plays a crucial role not
only in filling the pores within the cement matrix, but also in contributing to the cement
hydration process [48,49]. However, the currently high cost of SF in many regions hinders
significant reductions being made in the initial cost of UHPC. In response, alternative
industrial by-products, including, but not limited to, FA, MK [50], and other SCMs, have
been proposed as partial substitutes for Portland cement (PC) in UHPC production [51].
In addition to the selection of appropriate raw materials in the design of the concrete
mix, it is of utmost importance to achieve a dense microstructure of concrete through an
effective particle packing method, both for fine and coarse particles. A dense microstructure
is the essential aspect that determines mechanical and durability properties of UHPC [52,53].
Given that SF is approximately 100 times finer than cement [54], there is a considerable size
disparity. MK, which is coarser than SF, is initially introduced to fill the gaps between the
cement particles. The voids between MK and cement particles are filled with a subsequent
addition of SF, which further reduces porosity and improves the overall microstructure of
the concrete. Conventionally, SF has been used independently to fill the voids between
cement particles with the aim of improving the workability and density, and of improving
the performance of mortar or concrete. However, this study suggests that incorporation of
SF along with an intermediate-size material such as MK is a more effective approach. The
combination of these additives gives more leverage to achieve a successive filling effect,
thus optimising the wet packing density and thereby maximising the overall efficiency of
the mixture [43,55]. Furthermore, the combined use of MK and SF in concrete can yield a
synergistic effect, which proves especially beneficial in the production of high-performance
Materials 2025, 18, 1304
4 of 17
concrete [56,57]. Silicate phases with low hydraulic reactivity found in blast furnace slag are
transformed through carbonation treatment into amorphous SiO2 and CaCO3 . These newly
formed compounds can then react with portlandite and alumina derived from metakaolin.
More specifically, the interaction between the produced CaCO3 and metakaolin results in
the formation of carbon aluminate phases and stabilises ettringite generated during cement
hydration. The consumption of CaCO3 further facilitates the pozzolanic reaction of the
newly formed amorphous SiO2 , leading to the production of more C-A-S-H gel. These
intricate reactions contribute to the refined microstructure with, ultimately, enhancement
of mechanical properties and the impermeability of the material [58].
The aim of this study is to analyse the effect of the following different SCMs: MG, MK,
MS, and MQ, and the synergistic effect of the use of a binary pozzolanic additive (MS and
MK) on the UHPC structure and properties. The binder replacement rate is kept constant at
10% because, according to the literature, this is the optimal amount of SCM for improving
the properties of concrete. The impact of pozzolanic additives is evaluated by examining
the hydration kinetics, mechanical and physical properties, and the microstructure of
concrete. It is important to compare the properties of UHPC with different pozzolanic
additives, especially waste materials, and to create a binary additive that contains waste
and can improve the properties of UHPC.
2. Materials and Methods
In this study, high-grade Portland cement CEM I 52.5 R (PC) and SCMs such as MQ,
MS, MK, and MG were used. The chemical compositions of PC and SCMs are presented in
Table 1, and the particle size distribution is presented in Table 2.
Table 1. Chemical composition of PC and SCMs (%).
Material SiO2
CaO
Al2 O3
Fe2 O3
Na2 O
MgO
SO3
K2 O
TiO2
Cl
ZnO
CO2
P2 O5
PC
MQ
MS
MK
MG
61.1
0.07
0.72
1.27
9.65
4.48
0.57
1.20
39.8
1.01
3.17
0.05
1.88
1.03
0.17
0.13
0.03
1.28
3.39
12.7
2.94
0.02
1.36
0.37
3.49
2.05
0.02
0.29
0.08
0.28
1.24
0.02
2.02
0.93
0.33
0.26
0.05
–
0.54
0.07
0.02
–
0.51
0.01
0.02
0.02
–
0.08
–
–
7.24
–
13.3
–
–
0.09
–
0.43
0.12
–
17.0
99.2
76.5
52.4
72.3
Table 2. Particle size distribution of PC and SCMs.
Material
Average Particle Size (µm)
d10 (µm)
d50 (µm)
d90 (µm)
PC
MQ
MS
MK
MG
17.1
8.5
3.8
20.4
15.1
0.9
0.7
0.1
2.6
2.7
12.6
5.8
0.7
16.8
13.9
40.7
20.5
5.8
44.5
29.2
As fine aggregate was used, 0/4 mm fraction sand from a local quarry (Lithuania) was
used. Chemical admixtures such as superplasticizer based on modified polycarboxylates
(SP) and air displacers (ADs) were used.
The compositions of concrete mixtures and the W/B (water/binder ratio) are presented
in Table 3. Concrete samples were prepared from 6 different concrete mix compositions:
control HPC-1 without pozzolanic additives; HPC-2–HPC-5 with 10% of the cement replaced with different pozzolanic additives, such as MQ, MS, MK and MG; and HPC-6, with
a binary pozzolanic additive (5% of MS and 5% of MK). The amounts of other materials in
all compositions were the same.
Materials 2025, 18, 1304
5 of 17
Table 3. Compositions of concrete mixtures, kg/m3 , and W/B.
Designation
PC
NS
HPC-1
HPC-2
HPC-3
HPC-4
HPC-5
HPC-6
900
810
810
810
810
810
1400
1400
1400
1400
1400
1400
MQ
MS
MK
MG
90
90
90
90
45
45
SP
AD
W
W/B
20
20
20
20
20
20
2
2
2
2
2
2
196
196
196
196
196
196
0.22
0.22
0.22
0.22
0.22
0.22
The procedure for the preparation of the samples was as follows: cement, pozzolanic
additives, air displacer and sand were dry mixed in a Hobart mixer for 3 min; then, water
with a superplasticizer was added, and the mixture was mixed again for 6 min. After
mixing, 160 mm × 40 mm × 40 mm samples were moulded. After 24 h, the samples
were demoulded and stored in water at a temperature of 20 ± 2 ◦ C for the curing time
required for the tests (7 and 28 days). Three samples of each curing age were tested for
each property except for compressive strength, for which six samples were tested. These
tests were caried out according to EN 196-1 standard [59], but the mixing time, due to
superplasticizer efficiency was longer.
The particle size distribution of the materials was analysed using a laser diffraction
method (Cilas 1090, 3P Instruments GmbH & Co., Odelzhausen, Germany). Chemical
compositions of raw materials (Table 1) were determined using an X-ray fluorescence
spectrometer ZSX Primus IV (Rigaku, Tokyo, Japan) equipped with a Rh tube with an
anode voltage of 4 kV. Tablet-shaped samples with a diameter of 40 mm were prepared
and compressed with a hydraulic press at 200 kN.
The compressive strength was measured using a hydraulic press ALPHA3-3000S
(FORM+TEST Seidner&Co. GmbH, Riedlingen, Germany) according to EN 196-1 [59]. The
density of the specimens was measured according to EN 1015-10 [60]. The capillary water
absorption of the samples was measured according to EN 1015-18 [61] after 28 days of
curing, whereas the total water absorption and the degree of structural inhomogeneity
were measured according to the methodology described in [62].
The exothermic temperature of concrete mixtures was measured by recording the temperature rise in semi-adiabatic conditions for 36 h. The prepared concrete mixtures (Table 3)
were poured into 100 mm × 100 mm × 100 mm moulds, and a thermocouple in a glass pipe
was inserted in the middle of each sample to record the temperature increase. Thereafter,
the mould was immediately placed in a container insulated with polystyrene foam (thickness 50 mm, thermal conductivity coefficient 0.043 W/(mK)) from inside. The experiments
were carried out at (20 ± 1) ◦ C and the temperature was recorded, uninterrupted, until
the heat release from the samples considerably decreased. The temperatures of the raw
materials and the water used for the concrete mixtures were identical, i.e., (20 ± 1) ◦ C.
The microstructure of the concrete was observed by scanning electron microscopy
(SEM) in the secondary electron mode (SE) using a JEOL JSM-7600F device (Tokyo, Japan).
Images were obtained from gold-coated surface fractures of the hardened samples by
vacuum evaporation technique. The following microscope settings were used: 10 kV and
20 kV voltage; 7–10 mm distance to sample surface.
The XRD analysis was performed using a DRON-7 diffractometer with Cu-Kα
(λ = 0.1541837 nm). The following test parameters were used: 30 kV voltage; 12 mA current;
and a 2θ diffraction angle range from 4◦ to 60◦ , with an increment of 0.02◦ measured at
0.5 s.
Materials 2025, 18, 1304
6 of 17
3. Results
3.1. Temperature Monitoring Results
Materials 2025, 18, x FOR PEER REVIEW
7 of 20
Figure 1 and Table 4 show the temperature profiles of the concrete mixtures
during
the first 36 h after their preparation. The corresponding sets of the maximum temperature
and time to3.reach
it are presented in Table 4. The maximum temperatures of the concrete
Results
◦
mixtures are
similar
and range
3.1.quite
Temperature
Monitoring
Resultsfrom 55.0 C (HPC-4 mixture with 10% of MK) to
◦
58.6 C (mixture
HPC-1
additives),
with profiles
a difference
of approx.
Mixture
Figure
1 andwithout
Table 4 show
the temperature
of the concrete
mixtures6%.
during
HPC-2, where
10%
cement
was replaced
with MQ, showed
smallest
temperature
the first
36 of
h after
their preparation.
The corresponding
sets of thethe
maximum
temperature
timeCement
to reach ithydration
are presented
in Table
4. The maximum
of the concrete
variation ofand
1.7%.
was
accelerated
due to temperatures
the high specific
surface area
mixtures are quite similar and range from 55.0 °C (HPC-4 mixture with 10% of MK) to
of the pozzolanic additives MQ and MS, when their particles started to act as hydration
58.6 °C (mixture HPC-1 without additives), with a difference of approx. 6%. Mixture HPCcentres [63],2,and
probably
the highest
SiO2 with
content
in thesetheadditives.
Other additives
where
10% of cement
was replaced
MQ, showed
smallest temperature
varia- MK
and MG slightly
retard
cement
hydration.
The maximum
temperature
was
the
tion of 1.7%.
Cement
hydration
was accelerated
due to the high
specific surface
areareached
of the
MQ
andadditive.
MS, when their
started
to actincreased
as hydration
centres
latest in thepozzolanic
samplesadditives
with the
MG
Theparticles
hydration
time
8.3%
(HPC-5)
[63], and probably the highest SiO2 content in these additives. Other additives MK and
because glass
particles dissolve more slowly in the alkaline solution and may retard the
MG slightly retard cement hydration. The maximum temperature was reached the latest
hydration processes
in the early stage. The authors [64,65] found that replacing part of
in the samples with the MG additive. The hydration time increased 8.3% (HPC-5) because
the cement glass
withparticles
MG lowered
and
the
dissolve the
morehydration
slowly in thetemperature
alkaline solution
andreduced
may retard
theamount
hydrationof heat
in the early
stage.and
The that
authors
foundsodium
that replacing
part was
of theinsufficient
cement
released dueprocesses
to the dilution
effect,
the[64,65]
dissolved
content
to
with MG lowered the hydration temperature and reduced the amount of heat released
accelerate the
bonding process or increase the early strength [66]. When the most hydrationdue to the dilution effect, and that the dissolved sodium content was insufficient to accelacceleratingerate
additive
MS and hydration-retarding additive MK are used in combination,
the bonding process or increase the early strength [66]. When the most hydrationthe maximum
temperature
reduced
by 2 ◦ C compared
thearecontrol
whereas
accelerating additiveisMS
and hydration-retarding
additivetoMK
used in sample,
combination,
the maximum
temperature
is reduced
2 °C compared to mixture.
the control Hence,
sample, whereas
the hydration
time is similar
to that
of theby
MK-containing
at this stage
hydration
is similar to
thatcoats
of the the
MK-containing
mixture.
at this
stage
of
of strength the
growth,
thetime
dissolving
MK
MS particles
andHence,
inhibits
the
hydrationstrength growth, the dissolving MK coats the MS particles and inhibits the hydration-acacceleratingcelerating
effect ofeffect
MS. of
Authors
[67] reported that low-quality metakaolin retards cement
MS. Authors [67] reported that low-quality metakaolin retards cement
hydration due
to
the
coating
of
cement
grains
bybyMK
the
formation
of ettringite,
hydration due to the coating of cement
grains
MKparticles,
particles, the
formation
of ettringite,
and theofdilution
of PC [63].
and the dilution
PC [63].
60
56
Temperature (oC)
52
HPC-1
HPC-2
HPC-3
HPC-4
HPC-5
HPC-6
48
44
40
36
32
28
24
1
3
5
7
9
11
13
15
17
19
21
23
25
27
29
31
33
35
Time, h
Figure 1. Temperature
as a function
of hydration
the hydrationtime
time of
of concrete.
Figure 1. Temperature
profile asprofile
a function
of the
concrete.
Table 4.temperature
Maximum temperature
to maximum
temperaturefor
foreach
each concrete
composiTable 4. Maximum
and the and
timethetotime
maximum
temperature
concrete
composition.
tion.
Parameter\CompositionHPC-1
HPC-2HPC-1
Parameter\Composition
58.6
Max temperature Max temperature (°C)
58.6
57.9 (−8.4
1.7%) *
Time (h)
(◦ C)
Time (h)
8.4
HPC-3
HPC-5
HPC-6
HPC-2
HPC-3 HPC-4HPC-4
HPC-5
HPC-6
57.9 (−1.7%)* 55.9 (−4.6%)* 55.0 (−6.1%)* 56.4 (−3.8%)* 56.6 (−3.4%)*
(−4.6%)8.0* (−4.8%)*
55.0 (−8.5
6.1%)
*
56.4
−3.8%) * 8.5 (+1.2%)*
56.6 (−3.4%) *
8.355.9
(−1.2%)*
(+1.2%)*
9.1 ((+8.3%)*
* Remark:
in parentheses
show
the difference
from
HPC-1 *composition
which *
8.3 (−1.2%)
* the numbers
8.0 (−4.8%)
*
8.5
(+1.2%)
*
9.1the
(+8.3%)
8.5 in
(+1.2%)
the pozzolanic additive was not used.
* Remark: the numbers in parentheses show the difference from the HPC-1 composition in which the pozzolanic
additive was not used.
3.2. Physical and Mechanical Properties
Samples HPC-1 and HPC-2 had the highest densities of 2410 kg/m3 and 2420 kg/m3 ,
respectively, both at 7 and 28 days, whereas the samples of other compositions had a
Materials 2025, 18, 1304
hough these compositions contained 10% less cement that the control sample. The explanation for such an increase in compressive strength is the large specific surface area and
pozzolanic activity of MS particles: a higher conversion of Ca(OH) 2 into C-S-H results in
a denser concrete structure. MK as a pozzolanic material contributes to the enhancement
7 of 17
of early-age strength and offers notable improvements in long-term strength. Research
[71] indicates that MK modifies the pore structure within cement paste, mortar, and concrete, significantly improving resistance to water transport
and diffusion of harmful ions.
3 (Figure 2). HPC-2 density increased, because
slightly
lower
density
of about
2360
This
enhanced
resistance
effectively
reduces
thekg/m
risk of degradation
of the matrix. ComMQ is with
generally
and additive
engages
only
in physical
positions
the MG inert
pozzolanic
had
the lowest
strengthinteractions
due to the poorduring
bond- cement hydration.
ing
of
smooth
glass
particles
and
the
cement
matrix
[72].
Furthermore,
the
reduction
These interactions include the dilution of cement grains, nucleationinof cement hydrates,
strength can be attributed not only to the decreased cement content but also to the retarand space-filling; however, MQ exhibits some reactivity at high pH values [68–70]. A slight
dation of cement hydration. Analysis of SEM results [73] indicates that the agglomeration
decrease in the density (2%) of other compositions could be caused by the lower density of
of ultrafine glass particles contributes to this decline by creating distinct porous zones
other pozzolanic
additives compared to the density of cement.
throughout
the material.
after 7 days
2500
after 28 days
Density (kg/m3)
2400
2300
2200
2100
2000
1900
1800
1700
1600
1500
HPC-1
HPC-2
HPC-3
HPC-4
HPC-5
HPC-6
Composition
Figure 2. The impact of additive type on density.
Figure 2. The impact of additive type on density.
Compressive strength (MPa)
The highest compressive strength (Figure 3) was recorded in sample HPC-3 with
10% of the cement being replaced with MS, and sample HPC-6 containing the binary
pozzolanic additive (5% of cement replaced with MS and 5% with MK). At 28 days, the
compressive strength of HPC-3 increased 8.6%, and the strength of HPC-6 increased 2.3%
although these compositions contained 10% less cement that the control sample. The
explanation for such an increase in compressive strength is the large specific surface area
and pozzolanic activity of MS particles: a higher conversion of Ca(OH)2 into C-S-H results
in a denser concrete structure. MK as a pozzolanic material contributes to the enhancement
of early-age strength and offers notable improvements in long-term strength. Research [71]
indicates that MK modifies the pore structure within cement paste, mortar, and concrete,
significantly improving resistance to water transport and diffusion of harmful ions. This
enhanced resistance effectively reduces the risk of degradation of the matrix. Compositions
with the MG pozzolanic additive had the lowest strength due to the poor bonding of
smooth glass particles and the cement matrix [72]. Furthermore, the reduction in strength
can be attributed not only to the decreased cement content but also to the retardation of
cement hydration. Analysis of SEM results [73] indicates that the agglomeration of ultrafine
Materials 2025, 18, x FOR PEER REVIEW
9 ofzones
20
glass particles contributes to this decline by creating distinct porous
throughout the
material.
140
after 7 days
after 28 days
120
100
80
60
40
20
0
HPC-1
HPC-2
HPC-3
HPC-4
HPC-5
HPC-6
Composition
Figure 3. The impact of additive type on compressive strength.
Figure 3. The impact of additive type on compressive strength.
3.3. Microstructure Analysis
SEM tests (Figure 4) confirmed the formation of a very dense structure in samples
HPC-3 and HPC-6 (Figure 4b and Figure 4c, respectively). Samples of HPC-3 have a very
dense structure, MS particles with a very smooth surface are uniformly distributed, and
they are well bonded with the cement matrix. In HPC-6 concrete, the surface of MS particles is covered with new hydrates, the growth of which is induced by the reactivity of MK,
Composition
Materials 2025, 18, 1304
Figure 3. The impact of additive type on compressive strength.
8 of 17
3.3. Microstructure Analysis
3.3. Microstructure Analysis
SEM tests (Figure 4) confirmed the formation of a very dense structure in samples
SEM tests
(Figure
4) confirmed
the formation
very dense
in samples
HPC-3 and HPC-6 (Figure
4b and
Figure
4c, respectively).
Samplesof
ofaHPC-3
have astructure
very
HPC-3
and HPC-6
4b and 4c,
respectively).
Samples
of HPC-3and
have a very dense
dense structure,
MS particles
with(Figures
a very smooth
surface
are uniformly
distributed,
structure,
MS
particles
with
a
very
smooth
surface
are
uniformly
distributed,
and they
they are well bonded with the cement matrix. In HPC-6 concrete, the surface of MS partiare well
with
cement
matrix.
In HPC-6byconcrete,
the surface
cles is covered with
newbonded
hydrates,
thethe
growth
of which
is induced
the reactivity
of MK,of MS particles
is
covered
with
new
hydrates,
the
growth
of
which
is
induced
by
the reactivity of MK,
which bonds well and reacts with the cement matrix. The degree of MK particle reaction
which
bondswhere
well and
with were
the cement
matrix. The
degree of MK
particle reaction
was higher in the
samples
bothreacts
additives
used together
in comparison
with
was
higher
in
the
samples
where
both
additives
were
used
together
in
comparison
with
sample HPC-4 modified by metakaolin alone (Figure 4f). The structures of control samples
by metakaolin
4f).visibly
The structures
of control samples
of HPC-1 weresample
slightlyHPC-4
more modified
porous, with
more poresalone
with(Figure
ettringite
distributed
of
HPC-1
were
slightly
more
porous,
with
more
pores
with
ettringite
visibly
distributed
across the entire surface area (Figure 4a). The structures of HPC-5 samples containing MG
across
the
surface
areapaper
(Figure
4a).
The
of HPC-5
samples
containing
were more porous
and,
asentire
mentioned
in the
[68],
most
of structures
the pores formed
near
the
MG
were
more
porous
and,
as
mentioned
in
the
paper
[68],
most
of
the
pores
formed
glass particle (Figure 4d). Concrete samples HPC-2 and HPC-4 had very similar compresnear
the
glass
particle
(Figure
4d).
Concrete
samples
HPC-2
and
HPC-4
had
very
similar
sive strengths, but their microstructures were different. Samples of HPC-2 revealed the
compressive
strengths,
their microstructures
were different.
formation of rather
large (10–50
μm) but
air voids
around the aggregate
grains, Samples
whereas of
noHPC-2 revealed
the
formation
of
rather
large
(10–50
µm)
air
voids
around
the
aggregate
such air voids were observed in other samples. No ettringite was observed in these airgrains, whereas
no such
air voids
observed
in other
samples.
Noofettringite
wasMK
observed in these
voids, which was
different
from were
the control
sample
HPC-1.
Samples
HPC-4 with
air
voids,
which
was
different
from
the
control
sample
HPC-1.
Samples
additive had a more plate-shaped microstructure. As waste MK from expanded glassof HPC-4 with
MK additive
more
microstructure.
As wastewith
MK diamfrom expanded glass
granule manufacturing
was had
useda in
thisplate-shaped
study, numerous
fine glass granules
granule
manufacturing
was
used
in
this
study,
numerous
fine
glass
granules
eters from 100 to 200 μm, mostly with closed porosity, and which were firmly bonded with diameters
from
100 were
to 200observed
µm, mostly
with closed
porosity,
and
which
firmlyabbonded with the
with the cement
matrix
in concrete
HPC-4
(Figure
4f).
Thesewere
granules
cement
matrix
were
observed
in
concrete
HPC-4
(Figure
4f).
These
granules
sorbed part of water added to the mixture and therefore reduced the porosity of the ce- absorbed part
ment matrix. of water added to the mixture and therefore reduced the porosity of the cement matrix.
s 2025, 18, x FOR PEER REVIEW
10 of 20
(a)
(b)
Figure 4. Cont.
Materials 2025, 18, 1304
9 of 17
(b)
(c)
(d)
s 2025, 18, x FOR PEER REVIEW
11 of 20
(e)
(f)
Figure 4. SEM images
concrete:
(×3000 and(a)
×5000),
(b)(×
HPC-3
(×3000
and ×20,000),
Figureof4.HPC
SEM
images(a)
ofHPC-1
HPC concrete:
HPC-1
3000 and
×5000),
(b) HPC-3 (×3000 and
(c) HPC-6 (×3000×and
×10,000),
(d) HPC-5
(×3000
×10,000),
HPC-2
(×3000
and
×25), (f) (e)
HPC20,000),
(c) HPC-6
(×3000
and and
×10,000),
(d) (e)
HPC-5
(×3000
and
×10,000),
HPC-2 (×3000 and
×25),
(f) HPC-4 (×
3000 and
×250) (E—ettringite;
A—fine
aggregate;
EGG—expanded glass granule).
4 (×3000 and ×250)
(E—ettringite;
A—fine
aggregate;
EGG—expanded
glass
granule).
3.4. Water Absorption and Sorbtivity
Concrete samples HPC-3 and HPC-6 with MS had the lowest water absorption rates,
as their structures had the highest density. Water absorption of the MS-containing samples reduced by about 50%, from 1.32% to 0.71% (Figure 5), compared to the HPC-1. Traditionally, MS has been used to improve workability, packing density, and the perfor-
(f)
Figure 4. SEM images of HPC concrete: (a) HPC-1 (×3000 and ×5000), (b) HPC-3 (×3000 and ×20,000),
Materials 2025, 18, 1304
(c) HPC-6 (×3000 and ×10,000), (d) HPC-5 (×3000 and ×10,000), (e) HPC-2 (×3000 and ×25), (f) HPC-
10 of 17
4 (×3000 and ×250) (E—ettringite; A—fine aggregate; EGG—expanded glass granule).
Water absorption ( %)
3.4. Water Absorption and Sorbtivity
3.4. Water Absorption and Sorbtivity
Concrete samples HPC-3 and HPC-6 with MS had the lowest water absorption rates,
Concrete samples HPC-3 and HPC-6 with MS had the lowest water absorption rates, as
as their structures had the highest density. Water absorption of the MS-containing samtheir structures had the highest density. Water absorption of the MS-containing samples reples reduced by about 50%, from 1.32% to 0.71% (Figure 5), compared to the HPC-1. Traduced by about 50%, from 1.32% to 0.71% (Figure 5), compared to the HPC-1. Traditionally,
ditionally, MS has been used to improve workability, packing density, and the perforMS has been used to improve workability, packing density, and the performance of concrete
mance of concrete by filling voids between cement particles. However, the proposed apby filling voids between cement particles. However, the proposed approach strategically
proach strategically combines the effects of MK and MS, with the aim of a more comprecombines the effects of MK and MS, with the aim of a more comprehensive improvement
hensive
improvement
of the concrete
microstructure.
MK,MS,
which
is coarser to
than
MS, isfill
of the concrete
microstructure.
MK, which
is coarser than
is introduced
initially
introduced
to
initially
fill
the
voids
between
the
cement
particles.
The
addition
of
MS
helps
the voids between the cement particles. The addition of MS helps to fill the voids between
toMK
fill the
between
MK[52–54].
and cement
particles
[52–54].
HPC-2MQ
samples
containing
MQ
andvoids
cement
particles
HPC-2
samples
containing
had the
highest water
had
the
highest
water
absorption
rate,
which
was
6%
higher
than
the
absorption
of
absorption rate, which was 6% higher than the absorption of the control sample. the
SEM
control
images numerous
(Figure 4f)voids
revealed
with 50–100
diameters
apimagessample.
(FigureSEM
4f) revealed
withnumerous
diameters voids
of approx.
µm of
around
prox.
50–100 μmin
around
the aggregates in these samples.
the aggregates
these samples.
1.6
HPC1
HPC2
HPC3
HPC4
HPC5
HPC6
2400
2800
1.4
1.2
1
0.8
0.6
0.4
0.2
0
400
800
1200
1600
2000
Duration (min)
Figure
The
impact
additive
type
water
absorption
rate.
Figure
5.5.
The
impact
ofof
additive
type
onon
water
absorption
rate.
Capillary water absorption
(g/cm2)
The MS-modified samples HPC-3 and HPC-6 had the lowest capillary water absorption
The MS-modified samples HPC-3 and HPC-6 had the lowest capillary water absorp(Figure 6), clearly indicating the difference in the number of open capillaries. In 120 min,
tion (Figure 6), clearly indicating the difference in the number of open capillaries. In 120
the capillary water absorption in these samples reduced by about 30% compared to the
min, the capillary water absorption in these samples reduced by about 30% compared to
control sample (HPC-1). This means that MS, either added alone or in combination with
the control sample (HPC-1). This means that MS, either added alone or in combination
metakaolin,
has a strong pozzolanic effect, causing faster and more copious formation12ofof 20
Materials 2025, 18,with
x FOR PEER
REVIEW has a strong pozzolanic effect, causing faster and more copious formetakaolin,
C-S-H, which fills, to a certain extent, open pores and capillaries. The highest capillary
mation of C-S-H, which fills, to a certain extent, open pores and capillaries. The highest
water absorption was recorded in HPC-2 samples with the addition of milled quartz sand
capillary water absorption was recorded in HPC-2 samples with the addition of milled
due to the highest
open
porosity
of these
samples
(Figure
It should
be 7).
noted
that be
quartz sand
due
to the highest
open
porosity
of these7).samples
(Figure
It should
HPC-6 samples
containing
binarycontaining
additive the
hadbinary
the lowest
capillary
noted
that HPC-6the
samples
additive
had the water
lowest absorption
capillary water
absorption
forabsorption
30 min, andrate
thenreached
the absorption
reached
that of HPC-3 samples.
for 30 min, and
then the
that ofrate
HPC-3
samples.
0.035
HPC1
HPC2
20
40
HPC3
HPC4
HPC5
HPC6
0.03
0.025
0.02
0.015
0.01
0.005
0
10
30
50
60
70
80
90
100
110
120
Duration (min)
Figure 6. The impact of additive type on capillary water absorption.
Figure 6. The impact of additive type on capillary water absorption.
3.5. Pore Structure and Resistance to Freeze–Thaw Cycles
The predicted resistance to freeze–thaw cycles was evaluated according to the Kf coefficient calculated applying the methodology described in [74,75]. Briefly, the porosity
Materials 2025, 18, 1304
porosity results. HPC-4 samples with the addition of metakaolin waste also fit into the
lowest total porosity, because metakaolin improves the pore structure of cement-based
materials by reducing the appearance of harmful large pores and improving impermea11 of 17
bility [38].
8
Porosity (%)
7
Pg
7.3
6.9
6.3
6.3
6.0
Po
Pc
6.0
6
4.7
5
3.8
3.2
4
4.0
3.9
3.4
3
2.0
1.7
2
4.3
3.9
2.4
1.7
1
0
HPC-1
HPC-2
HPC-3
HPC-4
HPC-5
HPC-6
Composition
Figure 7. The impact of the additive type on porosity.
Figure 7. The impact of the additive type on porosity.
3.5. Pore Structure and Resistance to Freeze–Thaw Cycles
The predicted resistance to freeze–thaw cycles was evaluated according to the Kf
coefficient calculated applying the methodology described in [74,75]. Briefly, the porosity
parameters of concrete were determined by measuring the total, open (Po), and closed (Pc)
porosities. These porosity values were then used to predict resistance to freeze–thaw cycles
and to calculate the coefficient Kf from the following equation [74,75]:
Kf = Pc/(Po·0.09)
(1)
Figure 7 illustrates the results for total porosity (Pg), open porosity (Po), and closed
porosity (Pc). Samples HPC-3 and HPC-6 had the lowest open porosity, which, compared to
the control sample, decreased by 50%, while the closed porosities increased approximately
24% and 13%, respectively. Samples HPC-6 demonstrated the best total and open porosity
Materials 2025, 18, x FOR PEER REVIEW
13 of 20
results. HPC-4 samples with the addition of metakaolin waste also fit into the lowest total
porosity, because metakaolin improves the pore structure of cement-based materials by
reducing the appearance of harmful large pores and improving impermeability [38].
Figure
8 shows
thethe
values
of the
freeze–thaw
resistance
prediction
coefficient
calcuFigure
8 shows
values
of the
freeze–thaw
resistance
prediction
coefficient
calculated
from
the
open
and
closed
porosity
values
given
in
Figure
7.
lated from the open and closed porosity values given in Figure 7.
35
31.0
28.5
Kf (units)
30
22.8
25
18.3
20
15
13.1
12.8
HPC-1
HPC-2
10
5
0
HPC-3
HPC-4
HPC-5
HPC-6
Composition
Figure 8. Freeze–thaw resistance prediction coefficient values.
Figure 8. Freeze–thaw resistance prediction coefficient values.
The maximum Kf value used in the prediction method presented in the literaThe maximum Kf value used in the prediction method presented in the literature
ture [74,75] only goes up to 12, because conventional concrete is the most frequently
[74,75] only goes up to 12, because conventional concrete is the most frequently studied.
studied. The highest Kf values were recorded in HPC-3, HPC-4, and HPC-6 compositions
The highest Kf values were recorded in HPC-3, HPC-4, and HPC-6 compositions containcontaining MS and MK. The greatest positive change in the Kf coefficient is observed with
ing MS and MK. The greatest positive change in the Kf coefficient is observed with the
increase in closed porosity. MS and MK additives acting independently and, especially,
in combination promote cement hydration, and C-S-H and C-A-S-H formation, due to the
very small particles of different sizes as well as the pozzolanic activity of these additives.
Gradually, the pores are filled to a certain extent by new crystal hydrates. According to
Materials 2025, 18, 1304
12 of 17
the increase in closed porosity. MS and MK additives acting independently and, especially,
in combination promote cement hydration, and C-S-H and C-A-S-H formation, due to the
very small particles of different sizes as well as the pozzolanic activity of these additives.
Gradually, the pores are filled to a certain extent by new crystal hydrates. According to
other scientific works [76,77], after 3 days of hydration, water penetrates the capillary
pores of the initially formed C-S-H and reaches the particle surfaces. During this time, a
significant amount of calcium hydroxide is generated as a reaction by-product. The outer
hydration products gradually fill the pores between the particles, resulting in a denser
structure. Between 3 and 27 days of hydration, the amount of C-S-H increases significantly
and a large volume of inner hydration products form within the pores, further enhancing
the dense structure of the material. The lowest HPC-2 values could be explained by hydrated products being encapsulated in cement particles covered with MQ, which is not as
active as MS and MK. This layer [77] acts as a diffusion barrier, reducing the availability
of water and reactants to non-hydrated particles, thereby slowing the overall hydration
reaction of the paste, and the hydration products are insufficient to completely fill the
voids. This results in the formation of additional voids, contributing to an increase in pore
diameter and cumulative pore volume, thereby impacting the microstructural integrity
of the material [77]. According to the curve provided in the literature sources referred
to above, the concrete tested in ourstudy could resist more than 1000 freeze–thaw cycles;
therefore, only the Kf values directly related to the improved freeze–thaw resistance of
concrete are given for the comparison of compositions.
The degree of structural inhomogeneity enables the evaluation of the structural inhomogeneity of effective capillaries by their equivalent length, and this is calculated from
Equation (2) [62]:
N = (Hmax − Hmin )/Hmin
(2)
where Hmax and Hmin are the rates of the capillary wetting front (after 10 min and 120 min),
in mm.
Materials 2025, 18, x FOR PEER REVIEW
14 of 20
The determined degree of structural inhomogeneity (Figure 9) showed that compositions HPC-3 and HPC-6 had the most homogeneous structures. The density and structural
homogeneity
of these concrete
samples
resulted
from
the most
hydrationhydraprocess
structural homogeneity
of these
concrete
samples
resulted
fromintensive
the most intensive
being
andbeing
the formation
the
greatest amount
of fine amount
amorphous
phases
of C-S-H
tion used,
process
used, and of
the
formation
of the greatest
of fine
amorphous
and
C-A-S-H,
which
affects
micro- and
macro-properties
of concrete such
phases
of C-S-H
andsignificantly
C-A-S-H, which
significantly
affects
micro- and macro-properties
ofas
concrete
such
as strength
and
durability
Theof
highest
degree
of structural inhomogestrength
and
durability
[78].
The
highest[78].
degree
structural
inhomogeneity
was found
wasHPC-1
found due
in sample
due identified
to the ettringite
identified
in the
pores, and
havin neity
sample
to theHPC-1
ettringite
in the
pores, and
it having
theithighest
ing the highest
portlandite
content (Figure 10).
portlandite
content
(Figure 10).
Degree of structural
inhomogeneity (units)
1
10 min
120 min
0.8
0.6
0.4
0.2
0
HPC1
HPC2
HPC3
HPC4
HPC5
HPC6
Composition
Figure 9. The impact of additive type on the degree of structural inhomogeneity.
Figure 9. The impact of additive type on the degree of structural inhomogeneity.
3.6. Results of X-Ray Analysis
X-ray diffraction analysis of concrete (Figure 10) revealed the same minerals, namely
ettringite, quartz, portlandite, calcite, feldspars, dolomite, alite, and belite, existing in all
concrete samples irrespective of the pozzolanic additive used.
Materials 2025, 18, x FOR PEER REVIEW
Materials 2025, 18, 1304
15 of 20
13 of 17
Q
Q
E
P
4
8
12
16
HPC-1
CE E
20
HPC-2
24
FF
C
28
HPC-3
D B
A P
32
Q
C
CD Q
EQ
36
40
HPC-4
44
HPC-5
Q P C
Q
PD
48
52
Q
C
P
56
60
HPC-6
Figure 10. X-ray diffraction patterns of the concrete.
Figure 10. X-ray diffraction patterns of the concrete.
3.6. Results of X-Ray Analysis
The
lowest
portlandite
peaks
recorded
in10)
samples
HPC-3,
HPC-4,
and HPC-6,
X-ray
diffraction
analysis
of were
concrete
(Figure
revealed
the same
minerals,
namely
whereas
sample
HPC-1,
without
pozzolanic
additives,
had
the
highest
portlandite
peak.
ettringite, quartz, portlandite, calcite, feldspars, dolomite, alite, and belite, existing
in all
Compositions
with
MK
showed
more
intensive
calcite
peaks.
In
particular,
the
interaction
concrete samples irrespective of the pozzolanic additive used.
between
the
CaCOportlandite
3 produced peaks
and the
metakaolin
in the
development
of carbon
The
lowest
were
recordedresults
in samples
HPC-3,
HPC-4, and
HPC-6,
aluminate
phases,
stabilising
the
ettringite
formed
during
cement
hydration
[58].
whereas sample HPC-1, without pozzolanic additives, had the highest portlandite peak.
Compositions with MK showed more intensive calcite peaks. In particular, the interaction
4.between
Conclusions
the CaCO3 produced and the metakaolin results in the development of carbon
aluminate
phases,
stabilising the
ettringite formedquartz
duringsand,
cement
hydration [58].
The effects
of pozzolanic
additives—milled
microsilica,
waste metakaolin, milled window glass, and a binary pozzolanic additive (microsilica and waste
4. Conclusions
metakaolin)—on
the properties of ultra-high-performance concrete were analysed. The
The
effects
ofsummarised
pozzolanic additives—milled
quartz sand, microsilica, waste metakaolin,
analysis
results
are
below:
window having
glass, and
additive
and waste
metakaolin)—
• milled
Microsilica,
thea binary
highestpozzolanic
pozzolanic
activity(microsilica
and the largest
specific
surface
on area,
the properties
of
ultra-high-performance
concrete
were
analysed.
The
analysis
results
accelerates hydration the most, whereas milled glass inhibits hydration due
to
arethe
summarised
below:
slower dissolution of the particles and insufficient content of dissolved sodium.
• Metakaolin,
Microsilica,added
having
highest
pozzolanic
activity and
largest
specific surface
as athe
waste
product
from expanded
glassthe
granule
manufacturing,
area,
accelerates
hydration
the
most,
whereas
milled
glass
inhibits
hydration
due to
also inhibits hydration.
slower
dissolution
of the
particles
and insufficient
content
of dissolved
sodium.
•
Inthe
spite
of the
insignificant
drop
in density
(up to 2%),
the highest
compressive
Metakaolin,
added
as
a
waste
product
from
expanded
glass
granule
manufacturing,
strength was recorded in the samples containing microsilica and the binary additive.
inhibits
Atalso
28 days,
thehydration.
compressive strength of modified samples in comparison with the
• control
In spite
of
the
insignificant
drop
density
(up
2%), the
compressive
sample
increased
by 8.6%
andin2.3%
due to
thetodensity
andhighest
the homogeneous
strengthofwas
recorded
in the
samples
containing
microsilica
and the
binary
additive.
structure
concrete.
These
samples
had
the lowest
total porosity
and
the highest
At
28
days,
the
compressive
strength
of
modified
samples
in
comparison
with
the
closed porosity due to the high pozzolanic activity of microsilica. The freeze–thaw
control sample
increased
by 8.6%
and 2.3%
the
density
the
homogeneous
resistance
prediction
coefficient
Kf value
was due
alsoto
the
highest
inand
these
compositions.
Materials 2025, 18, 1304
14 of 17
•
•
•
structure of concrete. These samples had the lowest total porosity and the highest
closed porosity due to the high pozzolanic activity of microsilica. The freeze–thaw
resistance prediction coefficient Kf value was also the highest in these compositions.
A high Kf value was also observed in the samples with the binary additive and with
metakaolin used alone.
XRD analysis showed that all compositions of concrete contained the same minerals;
however, the lowest intensity of portlandite peaks was observed in the samples
containing microsilica, metakaolin, and the binary additive metakaolin + microsilica.
The use of the binary pozzolanic additive is recommended, primarily because
metakaolin is a waste product that inhibits the formation of harmful pores in concrete,
improves durability, and, above all, reduces the cost of concrete. Microsilica enhances
the performance of concrete by accelerating cement hydration and also filling the
voids between cement particles.
This research demonstrates the benefits of using binary pozzolanic additive, which
consists of waste metakaolin and microsilica, to optimise the durability of UHPC by
analysing the physical and mechanical properties, and the microstructure, of concrete.
Research should be continued by replacing a larger amount of cement with SCMs,
in order to test the economic and ecological efficiency for the environment, while
conducting durability tests under different environmental conditions.
Author Contributions: Conceptualization, J.M. and R.J.; methodology, J.M.; software, R.J.; validation,
J.M. and R.J; formal analysis, J.M.; investigation, J.M. and R.J.; resources, J.M. and R.J.; data curation,
J.M.; writing—original draft preparation, J.M. and R.J.; writing—review and editing, J.M. and R.J.;
visualisation, J.M.; supervision, J.M.; project administration, J.M. and R.J.; funding acquisition, J.M.
All authors have read and agreed to the published version of the manuscript.
Funding: The equipment and infrastructure of Civil Engineering Scientific Research Center of Vilnius
Gediminas Technical University was employed for investigations. This research was supported by
the centre of excellence project “Civil Engineering Research Centre” (Grant No. S-A-UEI-23-5).
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: All results are presented in the article.
Conflicts of Interest: The authors declare no conflicts of interest.
Abbreviations
The following abbreviations are used in this manuscript:
UHPC
C-S-H
C-A-S-H
SCM
MS
MK
MQ
MG
Ultra-high-performance concrete
Calcium silicate hydrates
Calcium aluminium silicate hydrate
Supplementary cementitious materials
Microsilica
Metakaolin
Milled quartz sand
Milled glass
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