L. KALINA et al.: EFFECT OF AMINO ALCOHOL ADMIXTURES ON ALKALI-ACTIVATED MATERIALS
349–353
EFFECT OF AMINO ALCOHOL ADMIXTURES ON
ALKALI-ACTIVATED MATERIALS
VPLIV AMINO-ALKOHOLNIH DODATKOV NA ALKALNO
AKTIVIRANE MATERIALE
Luká{ Kalina
*
, Vlastimil Bílek Jr., Eva Bartoní~ková
Brno University of Technology, Faculty of Chemistry, Purkyòova 118, 612 00 Brno, Czech Republic
Prejem rokopisa – received: 2019-07-15; sprejem za objavo – accepted for publication: 2020-01-29
doi:10.17222/mit.2019.150
One of the most important technological problems associated with alkali-activated materials (AAM) is large shrinkage. A
possible solution to decrease the extensive drying shrinkage of these materials is the use of shrinkage-reducing admixtures
(SRAs). The promising group of SRAs, from the perspective of using in AAMs, are amino alcohols. However, the efficiency of
reducing the drying shrinkage strongly depends on their chemical structure. Hence, the study is focused on the molecular
architecture of amino alcohol surfactants and its relation to the affected properties of alkali-activated blast-furnace slag systems.
Selected amino alcohols were tested in terms of the ability to reduce the surface tension of pore solution as well as to influence
the drying shrinkage, hydration mechanism and mechanical properties of AAMs. The study confirms that the length and
branching of the alkyl chain linked to the amino group play the key role in SRA efficiency. Amino alcohol surfactants with a
high-carbon alkyl chain decreased dramatically both the surface tension and the drying shrinkage, but simultaneously negatively
affected the process of alkali activation, resulting in a deterioration of the mechanical properties. Conversely, the addition of
0.5 w/ % of the surfactants with a low molecular weight, such as 2-(Methylamino)ethanol, showed a slight improvement of the
compressive strength after 7 d and 28 d, and at the same time reduced the drying shrinkage by 30 % compared to the reference
sample.
Keywords: amino alcohols, admixture, drying shrinkage, alkali-activated materials
Eden od najpomembnej{ih tehnolo{kih problemov, ki se nana{a na alkalno aktivirane materiale (AAM) je njihov skr~ek. Mo`na
re{itev za zmanj{anje znatnega kr~enja med su{enjem teh materialov je uporaba dodatkov (SRAs) za njegovo zmanj{anje.
Obetajo~a skupina SRA dodatkov s stali{~a njihove uporabe za AAM so amino-alkoholi. Vendar je u~inkovitost zmanj{anja
kr~enja med su{enjem mo~no odvisna od njihove kemijske strukture. Zato so se avtorji tega prispevka osredoto~ili na {tudij
arhitekture snovi (surfaktantov), ki aktivno vplivajo na povr{ino amino-alkoholov in njihovo povezavo z vzro~nimi lastnostmi
alkalno aktiviranih sistemov plav`nih `linder. Izbrane amino-alkohole so avtorji testirali glede na sposobnost zmanj{anja
povr{inske napetosti porozne (mehur~aste) raztopine, kakor tudi vpliv na kr~enje med su{enjem, hidracijske mehanizme in
mehanske lastnosti AAM. [tudija je potrdila da dolge in razvejane vezi alkalnih verig igrajo klju~no vlogo pri dodatkih, ki
u~inkovito zmanj{ujejo kr~enje. Amino-alkoholni surfaktanti z visoko vsebnostjo ogljiko-alkilnih vezi mo~no zmanj{ujejo tako
povr{insko napetost kot tudi kr~enje med su{enjem, ki pa `al isto~asno negativno vpliva na proces alkalne aktivacije, kar
posledi~no vodi do poslab{anja mehanskih lastnosti. Nasprotno temu pa dodatek 0,5 masnih % povr{insko aktivne snovi z
majhno molekularno maso kot je 2-(metilamino)etanol ka`e rahlo izbolj{anje tla~ne trdnosti po 7 in 28 dneh in isto~asno
zmanj{anje skr~ka med su{enjem za 30 % v primerjavi z referen~nimi vzorci.
Klju~ne besede: amino-alkoholi, me{anice, skr~ek po su{enju, alkalno aktivirani materiali
1 INTRODUCTION
From the general point of view, shrinkage-reducing
admixtures (SRAs) are organic surfactants that reduce
the surface tension of the pore solution of water films
that cover the solid surfaces in cementitious materials.
1
The utilization of SRAs was introduced in 1983 in the
study by T. Sato,
2
where chemical admixtures based on
polyoxyalkylene glycol alkyl ether were used. Now-
adays, the SRAs are characteristic for their non-ionic
nature preventing the adsorption of the additive to the
hydration products. The typical chemical compounds
used for SRAs belong to the groups of mono-alcohols,
glycols, alkylether oxyalkylene glycols and polymeric
surfactants or their mutual combination, having a
synergic effect in enhancing the shrinkage reduction. The
vast majority of commercial SRAs are designed for
ordinary Portland cements (OPCs); therefore, their
efficiency in other inorganic binders may vary signi-
ficantly.
Alkali-activated materials (AAMs) represent a group
of inorganic materials characterized by a pore solution
with a high pH;
3
therefore, the molecular design of any
organic admixture plays a key role. The same applies to
SRAs. The searching for a suitable type of SRA de-
signed especially for AAMs turned out to be compli-
cated, despite the fact that shrinkage is one of the most
important technological problems related to many
alkali-activated systems. Until now, only several studies
have been focused on the organic admixtures affecting
the shrinkage of AAMs.
4
M. Palacios and F. Puertas
5
studied the effect of poly-
propylene glycol-based SRA on the shrinkage and other
properties of water-glass-activated slag (4 % Na
2
O). At a
Materiali in tehnologije / Materials and technology 54 (2020) 3, 349–353 349
UDK 620.1:661.725.844 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 54(3)349(2020)
*Corresponding author's e-mail:
kalina@fch.vut.cz (Luká{ Kalina)

relative humidity of 50 % the drying shrinkage of alkali-
activated slag mortars was reduced by approximately
7 % and 35 % for doses of SRA of1%a n d2% ,
respectively, while the shrinkage reduction at the relative
humidity of 99 % was considerably greater: about 50 %
and 75 % for the same doses. Also, C. Bilim et al.
6,7
used
SRA based on polypropylene glycol to mitigate the
shrinkage of alkali-activated slag mortars. Again, the
drying shrinkage as well as the shrinkage during the
moist curing was significantly reduced (up to about 40 %
after 180 days) for either liquid sodium silicate or solid
sodium metasilicate. The SRA based on polypropylene
glycols with different molecular weights was the subject
of an investigation by L. Kalina et al.
8
as well. The study
demonstrated that increasing the length of the polymeric
chain decreases the surface tension, but also fundament-
ally changes the pore size distribution, affecting the total
shrinkage of alkali-activated blast-furnace slag. The
effect of polyethylene glycols on the drying shrinkage of
water-glass-activated slag was studied by V. Bilek et al.
9
The results showed that the efficiency of the shrinkage
reduction increased with the increasing molecular weight
of the tested glycols.
It is evident that the research in this area was pri-
marily focused on the surfactants based on alkylene
glycols. Another alternative may be amino alcohols.
These surfactants provide an essential benefit in com-
parison with alkylene glycols. One of the important
properties regarding the SRA’s action is the dispersion of
used surfactants within the alkaline solution. Amino
alcohols show a high dispersibility range in the pore
solution because they contain hydrophilic groups, which
increase their hydrophile lipophile balance (HLB)
value.
10
Therefore, this study deals with the efficiency assess-
ment of amino alcohol-based SRAs in alkali-activated
blast-furnace slag systems. The molecular structure of
the used surfactants is evaluated in terms of affecting the
character and properties of the prepared alkali-activated
materials.
2 EXPERIMENTAL PART
2.1 Materials and sample preparation
Blast-furnace slag (BFS) with a Blaine fineness of
400 m
2
/kg and the chemical composition given in Table
1 was chosen as the primary aluminosilicate material for
the preparation of the alkali-activated samples. The XRD
analysis determined more than 90 % of amorphous phase
with the content of crystals such as melilite, calcite and
merwinite. Sodium water-glass with a silicate module of
1.98 was used as the alkaline activator. The Na
2
O/BFS
ratio was adjusted to 4 w/%. Amino alcohols with
different alkyl chains (summarized in Figure 1) were
added in the dosage of 0.5 w/% by mass of BFS.
2.2 Preparation and physical-mechanical testing of
samples
Alkali-activated BFS mortars were prepared as
follows. The sand-to-BFS ratio was 3:1 using three
different fractions of siliceous sand specified according
to the EN-196-1 standard and the water-to-BFS ratio was
adjusted to 0.50. The mixing and curing processes were
carried out at laboratory temperature (25 °C). Mortar
samples with the dimensions of (40 × 40 × 160) mm
were cast and further cured under a defined relative
humidity (50 %) and then subjected to compressive
strength measurements using the strength tester Beton-
system Desttest 3310 after 1, 7 and 28 d. The same
process of preparation was applied for (25 × 25 × 285)
mm samples. These species were subjected to the shrink-
age measurements based on ASTM C596 (25 °C;
RH = 50 %). The dynamic surface tension of synthetic
pore solutions with 128
different amino alcohol admixtures was measured by
the tensiometer BPA-800P (KSV Instruments company)
using the maximum-bubble-pressure method. The
synthetic pore solution was prepared based on the
chemical composition of the real pore solution obtained
24 hours after mixing and determined by ICP-OES. It
L. KALINA et al.: EFFECT OF AMINO ALCOHOL ADMIXTURES ON ALKALI-ACTIVATED MATERIALS
350 Materiali in tehnologije / Materials and technology 54 (2020) 3, 349–353
Table 1: Chemical compositions of blast furnace slag by XRF analysis
Raw material
Chemical composition / w/%
SiO2 Al2O3 CaO MgO SO3 Na2OK
2OT i O 2 MnO Fe
2O3
blast furnace slag 34.7 9.1 41.1 10.5 1.4 0.4 0.9 1.0 0.6 0.3
Figure 1: Molecular structure of used amino ethanol surfactants
(MAE: 2-(Methylamino)ethanol; EAE: 2-(Ethylamino)ethanol; PAE:
2-(Propylamino)ethanol; IPAE: 2-(Isopropylamino)ethanol; BAE:
2-(Butylamino)ethanol; TBAE: 2-(tert-Butylamino)ethanol)

means the same time as the drying shrinkage
measurement was started.
2.3 Isothermal calorimetry
The evolution of hydration heat was monitored using
the TAM Air isothermal microcalorimeter (TA instru-
ments). The measurements of heat evolution were
performed at a constant surrounding temperature of
25 °C. When the thermal equilibrium was achieved, the
BFS and alkaline activator with a specific SRA were
mixed together by injecting the solution into the 15-mL
vial and stirring it for 3 min. The samples were made of
alkali-activated paste without the standard sand;
however, with the same water/BFS and Na
2
O/BFS mass
ratios that were used for the preparation process of the
mortars. The heat evolution was recorded as the heat
flow immediately after mixing.
2.4 Microstructure characterization
Microstructure characterization was performed using
scanning electron microscopy (Zeiss EVO LS 10) in
secondary-electron mode. The working distance during
the observation was 9.5 mm and the accelerating voltage
was set to 10 kV. All the samples were sputtered with
gold before the measurements.
2.5 Mercury-intrusion porosimetry
The total porosity of the samples was determined
with a mercury porosimeter (Poremaster Quantachrome
Instruments). The working pressure range was from 0.14
MPa to 231 MPa, which covered a pore diameter range
from 0.007 μm to 10 μm. The measurements were per-
formed with the following conditions: Hg surface tension
was 0.480 N/m, Hg contact angle was 140° and scan
mode was chosen to average from 11 points. The
intrusion data were normalized by sample weight and
volume.
3 RESULTS AND DISCUSSION
The mechanism of action of SRA was introduced in
the study of Sato et al.
2
in 1983. They suggested that the
decrease of the surface tension of a cement pore solution
tends to reduce the shrinkage due to the elimination of
capillary forces. Therefore, the effect of quantity and
molecular structure of the used amino alcohols on the
surface tension of pore solution were tested. Figure 2
shows that the surface tension decreases with both a
large amount of surfactant and the presence of long or
branched alkyl substituents. Moreover, the surface-
tension measurement provides information about the
effective bulk concentration of surface-active admixtures
in AAM. In terms of a good ability to decrease the
L. KALINA et al.: EFFECT OF AMINO ALCOHOL ADMIXTURES ON ALKALI-ACTIVATED MATERIALS
Materiali in tehnologije / Materials and technology 54 (2020) 3, 349–353 351
Figure 4: Effect of amino alcohols (0.5 % by weight of BFS) on the
total heat evolution
Figure 2: Effect of amino alcohols on the surface tension of the pore
solution
Figure 3: Effect of amino alcohols (0.5 % by weight of BFS) on the
drying shrinkage

surface tension, the addition of 0.5 w/% by mass of BFS
was used for the preparation of the mortar samples.
The effect of amino alcohol SRA on the reduction of
the drying shrinkage is clear from Figure 3. It can be
seen that the surfactants with a long alkyl chain bonded
to the amino group tended to decrease the drying
shrinkage. Branched chains of substituents also play an
important role. It is evident that 2-(tert-Butylamino)alco-
hol has a higher ability to reduce the drying shrinkage
compared to 2-(Butylamino)alcohol. However, we can
see that the surface-tension measurement does not fully
correlate with the drying shrinkage evolution. Therefore,
the fundamental question arises. Are these two para-
meters directly dependent on each other? The answer can
be suggested by the monitoring of the hydration process.
The measurement of the total heat evolution (Figure 4)
during the alkaline activation clearly indicates the
negative effect of the SRA content, especially during the
early ages of the hydration process. This is also con-
firmed by the development of compressive strengths
(Figure 5). The results from the isothermal calorimetry
also show that amino alcohols with a low molecular
weight such as 2-(Methylamino)alcohol exhibit almost
the same total heat evolution as the reference sample
without any admixture after 7 d.
It is well known that the total heat evolution is
directly related to the binder phase’s formation. CASH
(calcium-aluminium-silicate-hydrate) gel is the main
hydration product in the systems based on the alkaline
activation of BFS, which was confirmed by several
studies.
11
The amount of formed CASH gel strongly
influences the porosity of the a AAM. The materials with
higher content of CSH or CASH gels create denser
structures with small pores. Such systems contain mainly
pores with a diameter lower than 10 nm, which greatly
affects the magnitude of the drying shrinkage.
12
Since
alkali-activated BFS without SRA has a typical structure,
as mentioned above, one would expect the shrinkage
strain to be larger than in a material with a coarser
microstructure, such as in the case of AAM with TBAE
(Figure 6). A similar relationship between the adverse
effect of the SRA on the AAM hydration resulting in a
lower amount of CASH and a more porous micro-
structure was also observed in previous studies
8,13
where
L. KALINA et al.: EFFECT OF AMINO ALCOHOL ADMIXTURES ON ALKALI-ACTIVATED MATERIALS
352 Materiali in tehnologije / Materials and technology 54 (2020) 3, 349–353
Figure 7: Total porosity measurement of alkali-activated blast-furnace
slag with and without amino alcohol admixtures (0.5 % by weight of
BFS) after 7 d
Figure 5: Effect of amino alcohols (0.5 % by weight of BFS) on the
compressive-strength development
Figure 6: Microstructure of alkali-activated blast-furnace slag without
(top) and with 2-(tert-Butylamino)alcohol (bottom) after 7 d

SRAs-based glycols were used. The changes in total
porosity were confirmed by mercury-intrusion porosi-
metry (Figure 7). The samples with the addition of SRA
had a significantly higher porosity compared to the
reference sample after 7 d. The direct relationship
between drying-shrinkage development and the porosity
of samples caused by the addition of specific amino
alcohol surfactants was clearly observed.
4 CONCLUSIONS
The results suggest that the extent of the drying
shrinkage of AAM is mainly controlled by the porosity
of the formed structure. In other words, by the quantity
of created binder phase, rather than by the decrease of
surface tension of the pore solution. Despite the
non-ionic character of the used amino alcohol
surfactants, the adsorption on the BFS particles, causing
the reduction of their solubility in an alkaline
environment could be assumed. Promising results
indicate the usage of 2-(Methylamino)alcohol. This
surface-active admixture in the amount of 0.5 w/% by
mass of BFS did not negatively influence the mechanical
properties after 7 d and 28 d and reduced the drying
shrinkage by 30 % compared to the reference sample.
Acknowledgement
This outcome has been achieved with the financial
support by the project: GA17-03670S, “Development of
shrinkage reducing agents designed for alkali activated
systems,” with financial support from the Czech science
foundation.
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L. KALINA et al.: EFFECT OF AMINO ALCOHOL ADMIXTURES ON ALKALI-ACTIVATED MATERIALS
Materiali in tehnologije / Materials and technology 54 (2020) 3, 349–353 353