Article

Ilmenite Mud Waste as an Additive for Frost

Resistance in Sustainable Concrete
Filip Chyliński * and Krzysztof Kuczyński
Instytut Techniki Budowlanej, 00-611 Warsaw, Poland; k.kuczynski@itb.pl
* Correspondence: f.chylinski@itb.pl; Tel.: +48-22-5796-438

Received: 22 May 2020; Accepted: 24 June 2020; Published: 28 June 2020

Abstract: Sustainable development leads to the production of building materials that are safer for
the environment. One of the ways to achieve sustainability in materials is the addition of industrial
wastes and by-products, especially to concrete. However, the addition of waste to concrete often
decreases its durability and the scope of aggression of the environment in which the concrete is used
has to be reduced. Making sustainable concrete, which is also durable in more aggressive
environments, is rather difficult. This article presents the results of tests performed on concrete
containing ilmenite mud waste from the production of titanium dioxide, which was exposed to frost
aggression with and without de-icing salts. The results have shown that a sustainable and frost
resistant concrete can be made. After 200 freeze–thaw cycles, the compressive strength of the tested
concretes decreased by less than 4%. Concretes were highly resistant for scaling and after 112 freeze–
thaw cycles in water with de-icing salt, the scaled mass was less than 0.02 kg/m2. The air void
distribution has also been analyzed. The results suited the requirements for frost resistance concrete
and were similar to those obtained for a reference concrete with fly ash. The examination of the
microstructure using scanning electron microscopy (SEM) has not shown any potential risks that
might affect the durability of concrete. Particles of waste were thoroughly combined in the binder
and some of its constituents seem to be an active part of the cement matrix. Long-term tests of
shrinkage (360 days) have not shown any excessive values that would differ from the reference
concrete with fly ash. The presented results have shown that sustainable concrete containing
ilmenite mud waste from the production of titanium dioxide might also be resistant to frost
aggression.

Keywords: ilmenite mud; waste; concrete; titanium dioxide; frost resistance

1. Introduction
According to the seventh point of the Basic Requirements for Construction Works CPR-EU
305/2011 published in March 2011, the European Union declares the “sustainable use of natural
sources” a priority [1,2]. Following this regulation, while encouraging development, the amount of
natural resources used in the production of building materials must decrease as the amount of used
by-products and industrial waste must increase. The second aspect of sustainable development is the
more effective use of natural sources by producing better materials using the same amounts of
constituents only improving their quality; for example, increasing the reactivity of the binder by
milling it to smaller particles [3,4]. A third way of making building materials more sustainable is by
using recycled building materials from demolitions [5]. Another aspect is that building materials and
whole constructions will be more sustainable if the time of usability is extended by more than the
typical 50 years, which is the lifetime of most concrete constructions [6].
Adding industrial wastes or by-products might decrease the durability of concrete. In many
cases, this is true and new material has to be dedicated to less aggressive environments. In this way,
at least some parts of waste are being valorized in order to use less natural sources [7]. If it is possible

Materials 2020, 13, 2904; doi:10.3390/ma13132904 www.mdpi.com/journal/materials

Materials 2020, 13, 2904 2 of 16

and safe to use industrial waste as an additive for concrete intended for more aggressive
environments, it would be easier to use larger amounts of it. One of the most aggressive occurrences
for concrete in moderate climates is frost attack. Concretes projected for such environments have to
contain larger amounts of cement, which makes them even less environmentally friendly materials.
That is why it is important to also use waste in these types of concretes as well.
The worldwide production of titanium dioxide in 2019 was estimated at 7.2 million tonnes [8].
TiO2 is mainly produced through two methods—sulphate and chloride. About 45% of the global
production is through the sulphate method, which generates varying amounts of different kinds of
by-products and waste. Each tonne of TiO2 produced by this method generates about 2.3 tonnes of
FeSO4·7H2O, 1.5 tonnes of FeSO4·H2O, 0.7 tonnes of red gypsum, and 0.35 tonnes of ilmenite mud
waste [9–11]. Iron sulphate is a by-product used mostly as a chromium (VI) reducing agent in the
production of cement clinker and as a flocculant in sewage treatment plants. Red gypsum is used in
the production of gypsum plasters [10–12]. There are only a few publications about the potential ways
of valorizing ilmenite mud waste [13–16], but even when they were successful they could not use
large amounts, keeping in mind that the world production of this waste is estimated at 1.1 million
tonnes annually [8,17,18].
This article aims to verify the theory that waste material, such as ilmenite mud, might be used
as an additive for concrete resistant against freeze–thaw corrosion. This would potentially valorise
this industrial waste more widely and make for more sustainable and, thus, greener concrete. Because
ilmenite mud waste contains some amounts of unleached TiO2 the concrete containing this waste
might also have a photocatalytic effect helping to reduce the NOx level in the air [19,20]. The waste
probably contains also some amount of nano silica particles which might affect the rheology of
cement paste [21,22]. There are two main ways of making a concrete resistant for frost attack. Both of
them require a relatively high amount of cement (above 320 kg/m3) and low water/cement ratio but
one of the way preferred by EN 206 standard [23] requires also entering air into the concrete mix. Air
voids prevent the structure of hardened concrete from being damaged by the increasing volume of
freezing water [24–28]. The other way of improving concrete’s resistance for frost attack is by making
its structure more compacted which prevents the concrete from being penetrated by water and
damaged by its freezing. This might be done by using even larger quantities of cement (above 380
kg/m3) and low water/cement ratio (0.30 or even less) and without using any air entering agents. This
way of protecting concrete from frost attack is more expensive and rather hard as shown in the results
of tests performed by Portland Cement Association [29] and others [30] because this type of concrete
has a high autogenous shrinkage and might have an early-age shrinkage cracking tendency [31]. This
type of frost resistance concrete is being used in the production of prefabricated concrete elements as
paving blocks and flags which are made using vibro-pressed technology [32–34].
This article presents a new way of valorising ilmenite mud waste as an additive to frost
resistance concrete. Previous articles [21,35] have shown that ilmenite mud waste might be a useful
material as an additive for typical low cost concretes with low compressive class and made from
common materials. This article presents the results of tests performed on higher compressive strength
classes, which are durable in more extreme environments including frost attack with de-icing salts.
The article presents the results of the following tests:
- properties of fresh concrete mixes
- compressive and flexural strength
- shrinkage
- frost resistance
- scaling
- air void analysis
- structure examination using scanning electron microscopy (SEM)
As a reference concrete the same concrete mix was prepared but in place of RMUD the same
amount of fly ash (FA) class A according to EN 450-1 standard [36], was added.
Materials 2020, 13, 2904 3 of 16

Concrete construction depending on its type might be raised with or without reinforcement
which affects the properties of used concrete. There are also different types of reinforcements and
before using new waste materials in reinforced concrete the suitable tests needs to be performed
[37,38]. This article focuses on laboratory tests of concretes without any reinforcement.

2. Materials and Methods

Ilmenite mud is a waste created during the production of titanium dioxide by the sulphuric
method. The raw feed, containing mostly ilmenite and ilmenite slag, is leached by using concentrated
sulphuric acid. Part of the raw material is solubilized and processed further after filtration. Insoluble
parts remain, which are called ilmenite mud waste. This waste, classified as hazardous according to
European classification [38], is useful as an additive for concrete mostly for its high content of residue
sulphuric acid (about 14%). As a result, this waste is additionally rinsed with water and filtered in a
factory. After such modifications, the waste contains less than 1% of residual sulphuric acid, which
is further neutralized using calcium oxide in the laboratory. Neutralization is carried out until the pH
is slightly acidic (about 4–5) to avoid the initiation of pucolanic reaction, as shown in [39]. Next, the
neutralization material is dried in the oven at 105 °C until it reaches constant mass. Then, it is sieved
through a 0.50 mm sieve. Material prepared in this way is named RMUD (rinsed mud). The results
of previous tests have shown that heavy metals present in waste are immobilised in the cement binder
at a satisfactory level [40]. Also, the concentration of radioactive nuclides, as some authors have
suggested [9,13], is at a safe, low level.

2.1. RMUD, Fly Ash, and Cement

Tables 1 and 2 present the content of the main constituents received from XRF (X-ray
fluorescence) tests and the characteristics of RMUD, fly ash (FA), and Portland cement. The cement
used for the tests was CEM I 42.5R Portland cement according to the EN 197-1 standard [41].

Table 1. Concentration (%) of main constituents in RMUD, FA, and cement [42].

Element SiO2 TiO2 Fe2O3 MgO Al2O3 CaO Na2O MnO K2O P2O5 SO3 Cl
RMUD 35.07 33.05 9.65 7.26 5.53 3.09 1.10 0.53 0.26 0.01 0.98 –
FA 51.51 1.09 8.51 2.53 25.71 3.82 1.37 0.10 2.73 0.31 0.48 0.02
Cement 20.06 – 3.38 0.89 4.13 64.41 0.24 – 0.56 – 2.97 0.07

Table 2. Physio-mechanical characteristics of cement, RMUD, and FA [39].

Characteristic Value
Cement
Loss on ignition (%) 4.74
Insoluble residue (%) 0.89
Density (g/cm3) 3.05
Relevant surface (cm2/g) 4060
Compressive strength (MPa) acc. to EN 196-1 [43]: −
−2 days 29.2
−28 days 54.2
Bending strength (MPa) acc. to EN 196-1 [43]: −
−2 days 5.4
−28 days 7.9
RMUD
Loss on ignition (%) 2.70
Materials 2020, 13, 2904 4 of 16

Relevant surface (cm2/g) 8.390

Density (g/cm3) 3.15
FA
Loss on ignition (%) 1.43
Relevant surface (cm2/g) 4020
Pozzolanic activity (%) acc. to EN 450-1 [36]: −
−28 days 77.4
−90 days 93.3
Density (g/cm )3 2.20

2.2. Concrete
In order to prepare concrete which will be frost resistant, border parameters were taken from
the EN 206 standard [23]. According to this document, concrete that is durable for freeze–thaw cycles
in water with de-icing salts has to satisfy the requirements of XF4 and XD3 aggressive environments,
where XF is freeze/thaw attack with or without de-icing agents, and XD is corrosion induced by
chlorides other than seawater. The border parameters to fulfil these classes of expositions are:
- minimum cement content in the concrete mix: 340 kg/m3
- minimum strength class: C 35/45
- maximum water cement ratio (w/c): 0.45
- minimum air entered content: 4.0%
- frost resistant aggregates

As an aggregate, amphibolite grits fulfilling the requirement of frost resistant aggregates were
used. Figure 1 shows the sieving curve of the aggregate mix used in concretes. Border curves (green)
are recommended from Polish standard PN-B-06265 [44].

Figure 1. Sieving curves of aggregate mixes used for concretes.

According to previous tests and optimization processes [45], the content of RMUD in concrete
should be 10.8% of the binder mass. As a reference concrete, the same mix was used but in place of
RMUD the fly ash (FA) has been added. Authors have chosen a reference concrete with fly ash instead
Materials 2020, 13, 2904 5 of 16

of the concrete with only Portland cement as a binder because previous tests have shown [21,40] that
the RMUD has a similar level of pozzolanic activity as fly ash.
The composition of concrete mixes is presented in Table 3.

Table 3. Composition of tested concretes

Constituent Quantity (kg/m3)

Portland cement CEM I 42.5R 350
RMUD or FA 42 (10.8% b.m.)1
Aggregate 0/2 (rinsed mining sand) 478
Aggregate 2/8 (crushed amphibolite) 511
Aggregate 8/16 (crushed amphibolite) 730
Water 176 (w/b = 0.45)
Air entraining admixture 1.37 (0.35% b.m.)1
Plasticising admixture 0.67 (0.17% b.m.)1
1 b.m.—binder mass (mass of cement + mass of RMUD)

The amount of 340 kg/m3 of cement was not enough or the water/binder ratio was too high to
fulfil the requirements of the strength class in EN 206 [23] for both of concretes. Increasing the
concrete’s compressive strength might be done by increasing the amount of cement or by reducing
the water/cement ratio in concrete an adding more of plasticising admixture. In these tests, the
compressive strength was increased by adding an additional 10 kg/m3 of cement (up to 350 kg/m3).

2.3. Properties of Fresh Mix

After mixing the concretes, the properties of the fresh mixes were tested as follows:
- consistency by slump loss method according to EN 12350-2 [46]
- density of fresh mix according to EN 12350-6 [47]
- air content by pressure method according to EN 12350-7 [48]

2.4. Compressive and Flexural Strengths

Mixed concretes were placed into 100 mm cubic and prismatic moulds with dimensions 100 ×
100 × 500 mm according to EN 12350-1 [49]. The following day, after demoulding, the samples were
cured in water at a temperature of 20 ± 2 °C according to EN 12390-2 [50] until the day of the test.
Compressive and flexural tests were performed after 28 and 90 days of curing according to the results
of previous tests, which have shown that RMUD is a pozzolanic reactive material increasing in
composite strength even after 28 days of curing [35,40].
Compressive strength was tested according to EN 12390-3 [51] and a flexural strength test was
performed according to EN 12390-5 [52]. The load was put on two points of the samples during the
tests.

2.5. Shrinkage
In order to check the stability of concrete over time in case there were any expansive reactions
in the binder, a shrinkage test was performed using Amsler’s method according to Polish standard
PN-B-06714-23 [53] which is similar to the new European standard EN 12390-16 [54]. Three prismatic
samples with dimensions 100 × 100 × 500 mm, made of the tested concrete, were measured after
demolding up to the 360th day. During the test, the samples were cured at a constant temperature
(20 ± 2 °C) and humidity (65 ± 5%) to avoid the influence of the environment on shrinkage.

2.6. Frost Resistance

Freeze–thaw tests were performed according to the PN-B-06265 Polish standard [44]. Twelve
100 mm cubic samples were prepared. After curing them for 90 days in water at a temperature of 20
Materials 2020, 13, 2904 6 of 16

± 2 °C, six of them were taken for freeze–thaw cycles and the rest were left in the water as reference
samples. A total of 200 freeze–thaw cycles were performed. Each cycle included a freezing stage to a
temperature of −18 ± 2 °C for at least four hours, and a thawing stage at a temperature of 18 ± 2 °C for
two to four hours. After completing the cycles, the samples were examined for any damage on their
surface. Next, a test of compressive strength was performed for all 12 concrete samples (including
the reference samples) for each type of concrete. According to PN-B-06265 [44], frost resistance
concrete in construction with a projected service life of 100 years in variable water levels or contact
with de-icing salts has to pass testing after 200 freeze–thaw cycles.

2.7. Scaling
The freeze–thaw resistance with de-icing salts (scaling) tests was performed according to PKN-
CEN/TS 12390-9 [55]. Four 150 mm cubic samples of concrete were cured in water at 20 ± 2 °C for 21
days. After that time, a 50 mm slice was cut from the middle of each, perpendicularly to the surface
of mashing. Cut slices were put back to the water until the 90th day of curing. On the 90th day,
samples were prepared as shown in Figure 2. On the exposed concrete surface, water with 3% NaCl
was poured and a temperature sensor was placed (the level of water was controlled throughout the
test). Samples were put into the freezing machine for 112 cycles. Each cycle included a freezing stage
to a temperature of −20 °C for two hours and a thawing stage at a temperature of up to 20 °C. One
full cycle lasted for 24 h. After 7, 14, 28, 42, 56, and 112 cycles, the samples were taken out and the
scaled material was collected from their surface. Then, the samples were put back to the freezing
machine with a new portion of the NaCl solution. The collected scaled material was rinsed with
water, filtered, dried in the oven and weighed.

Figure 2. A concrete sample prepared for freeze–thaw cycles.

2.8. Air Void Characteristics

The appropriate pore structure in concrete is one of the main aspects of frost resistance concretes
[56,57]. Air pore distribution tests were performed according to EN 480-11 [58]. These tests are
required by the EN 934-2 standard [59] for air-entraining admixtures. Two 150 mm cubic samples of
concrete were cured in water for 14 days after demoulding. Then, from the middle of each, a 10 mm
slice was cut perpendicularly to the surface of mashing with a surface size of 100 × 150 mm. The
surface of each slice was polished and contrasted after drying. Figure 3 presents how a sample
prepared for testing looked like.
Materials 2020, 13, 2904 7 of 16

Figure 3. Concrete sample prepared for air pore distribution tests.

Each sample was scanned five times using the Rapid Air 457 automatic air void analysis system.

2.9. Scanning Microscopy

Structure observations were made using a scanning electron microscope (SEM) produced by
Zeiss, model Sigma 500 VP(Carl Zeiss Microscopy GmbH, Köln, Germany). Secondary electron (SE)
and backscattered electron (BSE) images were collected. Phase compositions and mapping were
analysed using the EDS detector model Oxford Ultim Max 40 (Oxford Instruments, High Wycombe,
UK).
Samples of concrete for microscopic examination were prepared from 90-day-old concrete. First,
smaller pieces (20 mm × 20 mm × 5 mm) were cut from the inside of the 100 mm cubic samples. Next,
these were dried in the oven at a temperature of 40 °C and put into epoxy resin under vacuum for
better filling of the air voids. The final step of preparing the samples was polishing their surface. The
samples were gold evaporated before examining them under the microscope. Structure observations
were examined only for the RMUD concrete.

3. Results and Discussion

3.1. Properties of Fresh Mix

Table 4 presents the properties of concrete fresh mixes. The same amount of plasticising
admixture was added to both of concretes to reach a proper consistency for moulding the samples
(S2–S3 consistency class acc. to EN 206). The air content in both concretes was higher than 4% which
suits the border requirements.

Table 4. Properties of concrete mix

Property RMUD Concrete FA Concrete

Slump loss (mm)
110 ± 10(S3) 1 80 ± 10(S2) 1
(consistency class acc. to EN 206)
Density of concrete mix (kg/m3) 2,340 ± 20 2390 ± 20
Air content (%) 5.4 ± 0.5 4.8 ± 0.5
1 class of consistency according to EN 206.

3.2. Compressive and Flexural Strengths

Table 5 presents the results of the compressive and flexural strength tests of concrete containing
RMUD and concrete containing FA. Both samples of concretes reached the projected strength class
Materials 2020, 13, 2904 8 of 16

(C35/45) after 90 days of curing. The strength class was calculated according to EN 206, as per the
initial production tests [23].

Table 5. Compressive strength of concretes

Average Compressive Standard Deviation (MPa) Compressive Strength

Concrete
Strength (MPa) (Coefficient of Variation) Class acc. to EN 206
RMUD 28
36.2 ± 2.0 2.1 (0.06) C25/30
days
RMUD 90
51.2 ± 2.0 1.7 (0.03) C35/45
days
FA 28 days 35.7 ± 2.0 2.3 (0.06) C25/30
FA 90 days 49.5 ± 2.0 0.7 (0.01) C35/45
Average Flexural
− − −
Strength (MPa)
RMUD 28
6.6 ± 0.3 0.2 (0.03) −
days
RMUD 90
7.0 ± 0.3 0.1 (0.02) −
days
FA 28 days 6.3 ± 0.3 0.3 (0.04) −
FA 90 days 6.9 ± 0.3 0.4 (0.06) −

The results show that the values of both compressive strengths increase between the 28th and
90th day of curing by about 40% for both tested concrete samples. The flexural strength increased to
about 6% and 9% for RMUD and FA concrete, respectively. Relatively high increases were observed
for compressive strength relating to flexural strength that might be caused by the effect of compacting
the microstructure of concretes by the pozzolanic reaction products which increases the compressive
strength, but it affects less on the cohesive binding. If cement (CEM I) was the only active constituent
in concrete, the compressive strength would remain almost constant after the 28th day [60,61]. This
observation proves that RMUD just like fly ash is an active material and plays a role in increasing the
strength of concrete. This theory has also been proven in previous tests [35,40].

3.3. Shrinkage
Figure 4 present the results of shrinkage tests. After 120 days, both concretes had almost stopped
shrinking, including the uncertainties of the performed test (± 0.03 mm/m). No expansion of the
samples was observed at any time. The reached value of about 0.5 mm/m and almost the same for
both types of concretes is typical for concretes containing these amounts of cement [35,62].
Materials 2020, 13, 2904 9 of 16

Figure 4. Results of shrinkage tests.

3.4. Frost Resistance

After the freezing cycles were completed, concrete samples were weighed and their surfaces
were examined for cracks or any other damage. Six of the samples from each of concretes prepared
for freeze cycles were weighed before and after the freeze cycles were completed. All 12 samples for
each type of concrete (six having undergone freeze cycles and six references) were tested for
compressive strength. The results of the freeze–thaw tests are presented in Table 6.

Table 6. Results of freeze–thaw tests (200 cycles)

Average Standard Deviation Average

Standard Deviation
Samples Compressive (Coefficient of Compressive
(Coefficient of Variation)
Strength (MPa) Variation) Strength (MPa)
– RMUD concrete FA concrete
Reference samples 56.8 0.96 (0.02) 59.6 1.59 (0.03)
Samples after freeze–
54.7 1.19 (0.02) 56.5 1.91 (0.03)
thaw cycles
− Loss of compressive strength after 200 cycles of freeze–thaw (%)
− 3.7 5.2
− Loss of mass after 200 cycles of freeze–thaw (%)
− 0.1 0.03 (0.37) 0.1 0.04 (0.38)

According to the PN-B-06265 Polish standard, the requirements for frost resistance concrete are
as follows [44]:
- no visible damage on the surface of any tested sample
- change of mass in any sample after the freezing cycles cannot be more than 5.0% of the initial
mass
- average loss of compressive strength of samples after freezing cannot be higher than 20%
compared to the average of the reference samples
The results of frost resistance tests presented in Table 6 have shown that both of the tested
concretes suit the above requirements and that they are durable in freeze–thaw environments. After
200 freeze–thaw cycles, there were no cracks on the surface of any specimen nor any other visible
damage. Loss of compressive strength of the tested concrete was very low 3.7% and 5.2% for RMUD
and FA concrete respectively. The change of mass for both concretes was 0.1%, which is a very good
result. This shows that the material should be durable in a frost environment for its projected service
life of, at least, 100 years and so is the reference concrete.
Materials 2020, 13, 2904 10 of 16

3.5. Scaling
The results of freeze–thaw resistance with de-icing salts (scaling) are presented in Figure 5.

Figure 5. Scaling of tested concrete.

After 112 cycles of freeze–thaw, the mass of scaled material from both types of the tested
concretes was less than 0.02 kg/m2, which is a very low value compared to the requirements given in
EN 1338 [32], according to which the upper layer of concrete paving blocks should not have more
than 1.0 kg/m2 of the scaled material after 56 freeze–thaw cycles. The recorded values prove that the
tested concrete containing RMUD is also durable in a freeze–thaw environment with de-icing agents,
such as NaCl, and it is as good as the reference concrete containing fly ash.

3.6. Air Void Characteristics

Figure 6, presents an example of pictures collected and analyzed by the automatic air void
analysis system software. The results are presented in Table 7.

Figure 6. Scanning line of automatic air void analysis system.

Materials 2020, 13, 2904 11 of 16

Table 7. Results of the air pore distribution test

Standard
Deviation
Characteristics Average Standard Deviation (Coefficient of Variation) Average
(Coefficient
of Variation)
− RMUD Concrete FA Concrete
Spacing
152.9 9.1 (0.1) 151.7 15.0 (0.1)
factor l (µm)
Air content
2.77 0.33 (0.12) 3.51 0.65 (0.18)
(%)
Micro air
content A300 1.19 0.14 (0.11) 1.64 0.42 (0.26)
(%)

The values of air content obtained in this test are lower than the values received from tests on
the fresh mix. This is caused by the fact that an air void analysis does not take into account very large
pores (of a few millimeters and above), which does not increase the frost resistance of concrete. The
most important air voids, which affect the frost resistance of concrete, are those with a diameter of
300 µm and below. The total air content in those pores (A300) above 1% is an appropriate value for
frost resistance concretes. The main result from the air void characteristic test is the value of the
spacing factor, which is related to the maximum distance of any point in the cement paste from the
periphery of an air void. This shows the distribution of air voids in the cement matrix. According to
the requirements for air-entraining admixtures given in EN 934-2 [59], the spacing factor should not
exceed 200 µm and, according to ASTM C 457 [63], not exceed 230 µm. The values obtained from the
tests are presented in Table 7. Both tested types of concretes fulfil both of these requirements.
According to the above, both tested concretes should be freeze–thaw resistant.

3.7. Scanning Microscopy

In the RMUD concrete sample, leached grains of ilmenite and rutile were spotted. Additionally,
particles of almost unreacted plagioclases and pyroxenes, whose surfaces were leached by alkalis
from the cement, were observed. Some of the siliceous particles were highly reacted. Siliceous glass
phase with trace contents of magnesium, aluminium, sodium, calcium, and titanium was also
observed. As relics of clinker, the CA and C4AF phases were mostly observed. Magnesium ions which
might form the expansive phases were forming the orthopyroxene grains do not affect the durability
of the cement matrix. No undesirable reactions which might affect the durability of concrete were
spotted.
Figure 7 presents an SEM/BSE image of a leached ilmenite grain and a clinker grain (identified
by the EDS analysis). The area between the clinker and the ilmenite grain has been examined for the
migration of ions between the ilmenite grain and the CSH phase surrounding the clinker grain.
Materials 2020, 13, 2904 12 of 16

Figure 7. BSE image of concrete.

Figure 8 presents the area of CSH phase between the clinker and ilmenite grain. EDS mapping
shows the diffusion of titanium and iron ions from ilmenite grain into the CSH phase and calcium
ions in the opposite direction—from the CSH phase into ilmenite grain. This shows that leached
ilmenite grains from RMUD are reactive in the cement matrix and they are an active part of the binder
in concrete.
Materials 2020, 13, 2904 13 of 16

Figure 8. Migration of ions between the C-S-H phase and ilmenite.

4. Conclusions
Upon analysis of the results of the performed tests and comparing them to the results of the
reference concrete, the following conclusions have been drawn:
• RMUD waste is an active constituent increasing the compressive strength of concrete between
the 28th and 90th day of curing by 40% as was the fly ash in the reference concrete.
• During 360 days of measuring the shrinkage of concrete, no measurements were noted that
might suggest that any highly expansive or increasing shrinkage reactions are taking place. The
recorded values were almost the same as for the reference FA concrete, which is promising for
the durability of concrete.
• Examination of the microstructure of concrete did not show any areas that would suggest
reactions that might affect the durability of concrete. Most RMUD particles, as partly leached
ilmenite grains and silicon dioxide, were well bounded in the cement matrix. Magnesium ions
present in RMUD are constituents of orthopyroxenes and should not affect the durability of
cement composites.
• The tested RMUD concrete was highly resistant to freeze–thaw in water and also in water with
de-icing salts. The parameters of air void distribution were also satisfactory, which predicts that
concrete containing RMUD might be durable in a frost environment for a projected period of
100 years. The results of frost resistance tests were at the same level as for the reference FA
concrete. This proves the hypothesis of this article, namely that sustainable concrete containing
ilmenite mud waste might also be frost resistant.

Author Contributions: Conceptualisation, F.C. and K.K.; Investigation, F.C. and K.K.; Methodology, F.C. and
K.K.; Project administration, F.C.; Resources, F.C.; Writing—original draft preparation, F.C.; Visualisation, F.C.;
Writing—review and editing, F.C.; Supervision, F.C. All authors have read and agreed to the published version
of the manuscript.

Funding: This research received no external funding.

Materials 2020, 13, 2904 14 of 16

Conflicts of Interest: The authors declare no conflict of interest.

References
1. European Commission. Regulation (EU) No 305/2011 of the European Parlament and of the Council.Off. J.
Eur. Union 2011, 88, 5–43.
2. Michałowski, B.; Marcinek, M.; Tomaszewska, J.; Czernik, S.; Piasecki, M.; Geryło, R.; Michalak, J. Influence
of rendering type on the environmental characteristics of expanded polystyrene-based external thermal
insulation composite system. Buildings 2020, 10, 47.
3. Jankovic, A.; Valery, W.; Davis, E.Cement grinding optimisation. Miner. Eng. 2004, 17, 1075–1081
4. Dvorkin, L.; Zhitkovsky, V.; Sonebi, M.; Marchuk, V.; Stepasiuk, Y. Improving Concrete and Mortar Using
Modified Ash and Slag Cements; CRC Press Taylor & Francis Group (Boca Raton, FL. US); 2020.
5. Struble, L.; Godfrey, J. How Sustainable Is Concrete? International Workshop on Sustainable Development
and Concrete Technology, Beijing, China, 20–21 May 2014.
6. Czarnecki, L.; van Gemert, D. Innovation in construction materials engineering versus sustainable
development. Bull. Pol. Acad. Sci. Tech. Sci. 2017, 65, 765–771.
7. Czarnecki, L. Would recycled plastics be a driving force in concrete technology? J. Zhejiang Univ. 2019, 20,
384–388.
8. Titanium Dioxide (TiO2) Market 2019 Global Industry Analysis By Key Players, Share, Revenue, Trends,
Organizations Size, Growth, Opportunities, And Regional Forecast To 2025.” Available Online:
https://www.grandviewresearch.com/industry-analysis/titanium-dioxide-industry.
9. Bolívar, J.P.; Gázquez, M.J.; Pérez-Moreno, S.M.; Tenorio, R.G.; Vaca, F. Valorization of NORM waste from
titanium dioxide industry through commercial products. In Proceedings of the 4th EAN NORM Workshop
on Transportation of NORM, NORM Measurements and Strategies, Buildings Materials, Hasselt, Belgium,
29 November–1 December, 2010.
10. Gázquez, M.J.; Bolívar, J.P.; Vaca, F.; Lozano, R.L.; Barneto, A.G. Valorization of two industrial wastes from
titanium industry as fire resistance building materials. In Proceedings of the 3rd International CEMEPE
and SECOTOX Conference Skiathos island, Greece, 19–21 June, 2011.
11. Gázquez, M.J.; Mantero, J.; Bolívar, J.P.; García-Tenorio, R.; Galán, F. Characterization and valorisation of
NORM wastes; application to the TiO2 production industry. In Proceedings of the 1st Spanish National
Conference on Advances in Materials Recycling and Eco—Energy, Madrid, Spain, 12–13 November, 2009.
12. Vondruska, M.; Bednarik, V.; Sild, M. Stabilization/solidification of waste ferrous sulphate from titanium
dioxide production by fluidized bed combustion product Waste Manag. 2001, 21, 11–16.
13. García-Díaz, I.; Gázquez, M.J.; Bolivar, J.P.; López, F.A. Characterization and Valorization of Norm Wastes
for Construction Materials. Manag. Hazard. Wastes 2016, 13, 13–37.
14. Contreras, M.; Gázquez, M.J.; García-Díaz, I.; Alguacil, F.J.; López, F.A.; Bolívar, J.P. Valorisation of waste
ilmenite mud in the manufacture of sulphur polymer cement J. Environ. Manag. 2013, 128, 625–630
15. Contreras, M.; Martin, M.; Gazquez, M.; Romero, M.; Bolívar, J. Manufacture of Ceramic Bodies by Using
a Mud Waste from the TiO2 Pigment Industry. Key Eng. Mater. 2015, 663, 75–85.
16. Llanes, M.C.; González, M.J.G.; Moreno, S.P.; Raya, J.P.B. Recovery of ilmenite mud as an additive in
commercial Portland cements. Environ. Sci. Pollut. Res. 2018, 25, 24695–24703.
17. Sahu, K.K.; Alex, T.C.; Mishra, D.; Agrawal, A. An overview on the production of pigment grade titania
from titania-rich slag. Waste Manag. Res. 2006, 24, 74–79.
18. Middlemas, S.; Fang, Z.Z.; Fan, P. A new method for production of titanium dioxide pigment.
Hydrometallgy 2013, 131, 107–113.
19. Xu, M.; Bao, Y.; Wu, K.; Xia, T.; Clack, H.L.; Shi, H.; Li, V.C. Influence of TiO2 incorporation methods on
NOx abatement in Engineered Cementitious Composites. Constr. Build. Mater. 2019, 221, 375–383.
20. Xu, M.; Clack, H.; Xia, T.; Bao, Y.; Wu, K.; Shi, H.; Li, V.C. Effect of TiO2 and fly ash on photocatalytic NOx
abatement of engineered cementitious composites. Constr. Build. Mater. 2020, 236, 117559.
21. Bobrowicz, J.; Chylinski, F. Comparison of pozzolanic activity of ilmenite MUD waste to other pozzolans
used as an additive for concrete production. J. Therm. Anal. Calorim. no. 0123456789, 2020,.
https://doi.org/10.1007/s10973-020-09740-6
22. Khayat, K.H.; Meng, W.; Vallurupalli, K.; Teng, L. Rheological properties of ultra-high-performance
concrete—An overview. Cem. Concr. Res. 2019, 124, 105828.
23. CEN. EN 206+A1:2016-12 Concrete—Specification, Performance, Production and Conformity; European
Materials 2020, 13, 2904 15 of 16

Committee for Standardization: Brussels, Belgium, 2016.

24. Wilburn, F. Handbook of Thermal Analysis of Construction Materials. Thermochim. Acta 2003, 406, 249.
25. Zhou, Y. Research of the Frost Resistance Durability of Concrete Material Road Engineering. In Proceedings
of the 2016 International Conference on Education, Management, Computer and Society, Shenyang, China,
1–3 January, 2016.
26. Pigeon, M.; Marchand, J.; Pleau, R. Frost resistant concrete. Constr. Build. Mater. 1996, 10, 339–348.
27. Czarnecki, L.; et al. Research of the Frost Resistance Durability of Concrete Material Road Engineering.
Bull. Pol. Acad. Sci. Tech. Sci. 2016, 65, 1328–1331.
28. Zhou, M.; Liu, Z.; Chen, X. Frost Durability and Strength of Concrete Prepared with Crushed Sand of
Different Characteristics. Adv. Mater. Sci. Eng. 2016, 2016, 2580542.
29. Pinto, R.C.A.; Hover, K.C. Freeze-thaw durability of high-strength concrete. In Research & Development
Bulletin; PCA: Skokie, IL, USA, 2001.
30. Glinicki, M.A.; Jaskulski, R.; Dąbrowski, M. Design principles and testing of internal frost resistance of
concrete for road structures—critical review. Roads Bridges 2016, 15, 21–43.
31. Czarnecki, L.; et al. Frost resistance of concrete in bridges constructions. Build. Technol. Archit. 2015, 69, 66–
69. (In Polish)
32. CEN. EN 1338:2003/AC:2006 Concrete Paving Blocks—Requirements and Test Method; European Committee
for Standardization: Brussels, Belgium, 2006.
33. CEN. EN 1339:2003 Concrete Paving Flags—Requirements and Test Methods; European Committee for
Standardization: Brussels, Belgium, 2003.
34. CEN. EN 1340:2003/AC:2006 Concrete Kerb Units—Requirements and Test Methods; European Committee for
Standardization: Brussels, Belgium, 2006.
35. Chyliński, F.; Kuczyński, K.; Lukowski, P. Application of ilmenite mud waste as an addition to concrete.
Materials (Basel) 2020, 13, 866.
36. CEN. EN 450-1:2012 Fly Ash for Concrete—Part. 1: Definition, Specifications and Conformity Criteria; European
Committee for Standardization: Brussels, Belgium, 2012.
37. Foraboschi, P. Masonry does not limit itself to only one structural material: Interlocked masonry versus
cohesive masonry. J. Build. Eng. 2019, 26, 100831.
38. Foraboschi, P. Predictive multiscale model of delayed debonding for concrete members with adhesively
bonded external reinforcement. Compos. Mech. Comput. Appl. 2012, 3, 307–329.
39. Wahlström, M.; Laine-Ylijoki, J.; Wik, O.; Oberender, A.; Hjelmar, O. Hazardous Waste Classification; Norden:
Denmark, Copenhagen, 2016.
40. Bobrowicz, J.; Chyliński, F. The influence of ilmenite mud waste on the hydration process of Portland
cement J. Therm. Anal. Calorim. 2016, 126, 493–498
41. Chyliński, F.; Łukowski, P. Management of hazardous waste from the production of titanium dioxide as a
substitute for part of cement in cement composites. Mater. Bud. 2016, 530 18–20. (In Polish)
42. CEN. EN 197-1:2012 Cement—Part. 1: Composition, Specifications and Conformity Criteria for Common Cements;
European Committee for Standardization: Brussels, Belgium, 2012.
43. CEN. EN 196-1:2016-07 Methods of Testing Cement—Part. 1: Determination of Strength; European Committee
for Standardization: Brussels, Belgium, 2016.
44. PN-B-06265:2018-10/Ap1:2019-05 Concrete—Specification, Performance, Production And Conformity—National
Annex to PN-EN 206+A1:2016-12; Polish Committee for Standardization, Warsaw, Poland, 2019. (In Polish)
45. Chyliński, F.; Łukowski, P. Zastosowanie modelu materiałowego do optymalizacji składu zaprawy
cementowej z dodatkiem odpadu z produkcji bieli tytanowej. Przegląd Bud. 2017, 10, 1–13.
46. CEN. EN 12350-2:2011—Testing Fresh Concrete—Part. 2: Slump Test; European Committee for
Standardization: Brussels, Belgium, 2011.
47. CEN. EN 12350-6:2019-08—Testing Fresh Concrete—Part. 6: Density; European Committee for
Standardization: Brussels, Belgium, 2019.
48. CEN. EN 12350-7:2019-08 Testing Fresh Concrete—Part. 7: Air content—Pressure Methods; European
Committee for Standardization: Brussels, Belgium, 2019.
49. CEN. EN 12350-1:2019-07—Testing Fresh Concrete—Part. 1: Sampling European Committee for
Standardization: Brussels, Belgium, 2019.
50. CEN. EN 12390-2:2019-07— Testing Hardened Concrete—Part. 2: Making and Curing Specimens for Strength
Tests; European Committee for Standardization: Brussels, Belgium, 2019.
Materials 2020, 13, 2904 16 of 16

51. CEN. EN 12390-3:2019-07— Testing Hardened Concrete—Part. 3: Compressive strength of Test Specimens;
European Committee for Standardization: Brussels, Belgium, 2019.
52. CEN. EN 12390-5:2019-08—Testing Hardened Concrete—Part. 5: Flexural Strength of Test Specimens; European
Committee for Standardization: Brussels, Belgium, 2019.
53. PN-B-06714-23:1984 Mineral. Aggregates—Testing—Determination of Volume Changes by Amsler Method.
Polish Committee for Standardization, Warsaw, Poland, 1984. (In Polish)
54. CEN. EN 12390-16:2020-03 Testing Hardened Concrete—Part. 16: Determination of the shrinkage of concrete;
European Committee for Standardization: Brussels, Belgium, 2020.
55. CEN. PKN-CEN/TS 12390-9:2017-07 Testing Hardened Concrete—Part. 9: Freeze-Thaw Resistance with De-Icing
Salts—Scaling; European Committee for Standardization: Brussels, Belgium, 2017.
56. Grubeša, I.N.; Markovic, B.; Vracevic, M.; Tunkiewicz, M.; Szenti, I.; Kukovecz, Á. Pore structure as a
response to the freeze/thaw resistance of mortars. Materials 2019, 12, 3196.
57. Wang, Y.; Ueda, T.; Gong, F.; Zhang, D.; Wang, Z. Experimental Examination of Electrical Characteristics
for Portland Cement Mortar Frost Damage Evaluation. Materials 2020, 13, 1258.
58. CEN. EN 480-11:2006 Admixtures for Concrete, Mortar and Grout—Test. Methods—Part. 11: Determination of
Air Void Characteristics in Hardened Concrete; European Committee for Standardization: Brussels, Belgium,
2006.
59. CEN. PN-EN 934-2+A1:2012 Admixtures for Concrete, Mortar And Grout—Part. 2: Concrete Admixtures—
Definitions, Requirements, Conformity, Marking and Labelling; European Committee for Standardization:
Brussels, Belgium, 2012.
60. Gołaszewski, J.; Ponikiewski, T.; Cygan, T. Influence of Type of Superpalsticizers on Workability and
Compressive Strength. Int. J. Adv. Eng. Technol. 2010, 17, 37–44.
61. Gołaszewski, J.; Ponikiewski, T.; Cygan, G. Influence of Temperature on Workability and Compressive
Strength of Ordinary Concrete with High Calcium Fly Ash. Trans. VŠB Tech. Univ. Ostrava Civ. Eng. Ser.
2017, 17, 37–44.
62. Jiang, F.; Mao, Z.; Deng, M.; Li, D. Deformation and compressive strength of steel fiber reinforced MgO
concrete. Materials 2019, 12, 3617.
63. ASTM. ASTM C457—98 Standard Test. Method for Microscopical Determination of Parameters of the Air-Void
System in Hardened Concrete; American Society for Testing and Materials: Washington, DC, USA, 1998.

© 2020 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 (http://creativecommons.org/licenses/by/4.0/).