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Procedia Engineering 161 (2016) 1070 – 1075
World Multidisciplinary Civil Engineering-Architecture-Urban Planning Symposium 2016,
WMCAUS 2016
Influence of Hardening Accelerating Admixtures on Properties of
Cement with Ground Granulated Blast Furnace Slag
Jan PizoĔa,*, Patrycja Mieraa, Beata àaĨniewska-Piekarczyka
a
Silesian University of Technology, Akademicka 5 str. 44-100 Gliwice, Poland
Abstract
Ground granulated blast furnace slag (GGBFS) is a by-product of steel manufacturing process. As such it is commonly used in
concrete technology as component of blended cements or addition for concrete. Utilization of GGBFS conforms to idea of
sustainability. Unfortunately, slag may lead to delay of setting and hardening of concrete. It is undesirable effect for manufacturing
of precast elements or executing of concrete works during lower temperature period. Attempt to acceleration of hydration process
of such cements by hardening accelerating admixtures (ACC) was made. Paper shows results of compressive strength, hydration
heat and initial setting time examinations. Portland cement (CEM I 52,5R) and cement with addition of 35% of GGBFS (which
corresponds to normative range of CEM II/B-S) were tested. Tests have involved four accelerating admixtures with different
chemical base (calcium formate, C-S-H crystal seeds, calcium nitrate and trietanolamine). Initial setting time was measured by
Vicat apparatus. Compressive strength of mortars was measured after 12, 24, 48 hours and 7 and 28 days of curing in climatic
chamber. Hydration heat tests were conducted using isothermal calorimeter TAM AIR III during 72 hours after cement contact
with water. Tests were conducted in 20°C. Water-binder ratio of mortars for compressive strength tests and cement pastes for
hydration heat examinations was equal 0,5. Research had shown that all accelerators cause shortening of initial setting time by 40-
50% depending on admixtures chemical base. The most efficient was accelerator based on C-S-H crystal seeds. Increase of
hydration heat exhalation rate was observed. Summary hydration heat after 72 hours was greater in presence of hardening
accelerating admixtures. Those admixtures caused also the increase of early compressive strength of standard mortars. Higher
percentage growth of compressive strength was observed for cement with GGBFS addition. Calcium nitrate, calcium formate and
C-S-H crystal seeds based admixtures were the most efficient for Portland cement mortars and the latter for cement with GGBFS
addition.
©
© 2016
2016TheTheAuthors. Published
Authors. by Elsevier
Published Ltd. This
by Elsevier Ltd. is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer-review under responsibility of the organizing committee of WMCAUS 2016.
Peer-review under responsibility of the organizing committee of WMCAUS 2016
Keywords: hardening accelerating admixtures; slag; hydration heat; compressive strength; initial setting time;
1877-7058 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer-review under responsibility of the organizing committee of WMCAUS 2016
doi:10.1016/j.proeng.2016.08.850
Jan Pizoń et al. / Procedia Engineering 161 (2016) 1070 – 1075 1071
1. Introduction
Nowadays producers of precast elements as well as designers and executors of monolithic reinforced concrete
structures tend to shorten concrete curing time, necessary to demoulding and transport of elements or structure loading.
They take different actions for that purpose.
One of the methods to enhance compressive strength is using Portland cement [4]. However, producers more and
more often use cements with additives like ground granulated blast furnace slag (GGBFS).
Another method of increasing early concrete strength is using set and hardening accelerating admixtures. Their
action is to shorten the total setting time through accelerating hydration reaction connected with the increase of the
amount of hydration heat release. Unfortunately, the admixtures have some disadvantages. They can have adverse
influence on reinforcing steel corrosion (limitation of chloride content in accordance with standards) and concrete (e.g.
susceptibility to alkali-silica reaction) [3, 5, 6]. These threats may be limited by using cements with addition of GGBFS
[1, 2, 4].
To enhance early compressive strength of concrete, higher class cement can be used and water-cement ratio can be
lowered.
2. Experimental
2.1. Aim of experiments
The research aimed at determining the impact of the use of set and hardening accelerating admixtures on Portland
and slag cement properties. The scope of the research included the compressive strength tests of mortars in the time
limit from 12 hours to 28 days, the evolution of hydration heat in the first 72 hours, and the initial setting time of
cement pastes.
2.2. Materials
Portland cement (CEM I 52.5R) and slag cement with 35% of GGBFS were used. The chemical composition and
specific surfaces of cement and slag are presented in the table 1. In case of non-modified mortars fixed 0.5 water-
cement ratio was used.
Table 1. Chemical composition and specific surface of CEM I and GGBFS.
Constituent CEM I 52.5R GGBFS
Ignition losses 1.95 -
Unsolved parts 0.42 -
SiO2 20.54 37.35
Al2O3 5.14 7.30
Fe2O3 2.63 1.22
CaO 64.12 43.90
MgO 1.36 5.73
SO3 2.69 0.62
Na2O 0.17 -
K2O 0.81 -
Cl 0.06 0.03
Blaine surface [cm2/g] 4230 3870
Four types of hardening accelerating admixtures were used. They were added in the maximum amount
recommended by a manufacturer. The characteristics of the admixtures present table 2.
1072 Jan Pizoń et al. / Procedia Engineering 161 (2016) 1070 – 1075
Table 2. Admixture characteristics.
Symbol Characteristics Dosage range [% c.m.] Dry mass [%]
CF Calcium formate based hardening accelerating admixture 0.2 – 5.0 50
CSH CSH crystal seeds based hardening accelerating admixture 2.0 – 4.0 20
CN Calcium nitrate based hardening accelerating admixture 1.0 – 3.0 <5
TEA Trietanolamine based hardening accelerating admixture 1.0 – 2.0 <5
2.3. Methods
The compressive strength tests were conducted according to the standard EN 196-1:2006. The hydration heat tests
were conducted using isothermal calorimeter TAM AIR III during 72 hours after cement contact with water. The
initial setting time was measured by Vicat apparatus. The temperature of ingredients used to prepare mortars and of
the environment was constant 20±1°C. The samples cured in stable conditions in climatic chamber in temperature of
20±1°C and relative humidity of 60%.
3. Results and discussions
The results of the tests of compressive strength of mortars prepared with Portland cement and slag cement with 35%
of GGBFS are presented in figure 1. In case of accelerating admixtures aided mortars, we can see the general tendency
of compressive strength enhancement in comparison to non-modified mortars.
In case of compressive strength, it was noticed that after 12 hours all kinds of admixtures, besides the one based
on trietanolamine, increase compressive strength of Portland cement mortars. The use of admixture based on CSH
crystal seeds brings the best effects. With these admixtures the mortars show higher compressive strength in
comparison to reference mortar by about 100%.
Fig. 1. Compressive strength of CEM I mortars.
All admixtures used in the tests cause the increase of compressive strength. However, there are definitely lower
increments than in the case of 12-hour compressive strength. The admixtures based on calcium nitrate and CSH crystal
seeds are the most effective. Whereas the ones based on TEA and calcium formate are less effective. The percentage
Jan Pizoń et al. / Procedia Engineering 161 (2016) 1070 – 1075 1073
increment of compressive strength after 24 hours is bigger for slag cement mortars. The beneficial influence of
admixtures for Portland cement mortars disappears after longer time.
Fig. 2. Hydration heat evolution during first 72 hours’ graph of CEM I pastes (initial setting time marked).
Fig. 3. Cumulative hydration heats up to 72 hours of CEM I pastes.
The hydration heat tests after 12 hours proved that all kinds of admixtures, apart from the one based on TEA,
accelerate setting of Portland cement paste (fig. 2). The admixture based on TEA in CEM I paste shows the features
of the set retarding admixture through the whole period of hardening. For pastes with CSH crystal seeds and calcium
formate based admixtures the dormant period evidently shortens. It is proved by measurement of the initial setting
time, which for paste with CSH crystal seeds based admixture is 90 min. and for paste without it is 160 min. (fig. 2).
1074 Jan Pizoń et al. / Procedia Engineering 161 (2016) 1070 – 1075
The pastes with CEM I and admixtures based on CSH crystal seeds and calcium formate exhale the biggest amount
of hydration heat up to 44 hours. Whereas after 44 hours of hydration CEM I paste with CSH crystal seeds and TEA
exhale the biggest amount of hydration heat (fig. 3).
Fig. 4. Hydration heat evolution during first 72 hours’ graph of CEM II pastes (initial setting time marked).
Fig. 5. Cumulative hydration heats up to 72 hours of CEM II pastes.
For the pastes of cement with addition of GGBFS, admixtures cause the increase of 48-hour compressive strength
(the biggest increase for calcium nitrate). The exception is TEA. After 7 and 28 days of curing the higher compressive
strength of accelerating admixtures aided mortars is also noticed.
Jan Pizoń et al. / Procedia Engineering 161 (2016) 1070 – 1075 1075
The tests of hydration heat of pastes with CEM I and GGBFS after 12 h, as well as the pastes with CEM I, showed
that all kinds of admixtures, besides TEA, accelerate setting (fig. 4). Admixture based on TEA in paste with cement
with slag addition also shows the features of set retarding admixture through the whole hardening period. The test of
the initial setting time also showed set accelerating for the pastes modified with CSH, CN, CF admixtures (fig. 4).
The paste of cement with GGBFS and admixture based on calcium formate exhales the biggest amount of hydration
heat up to 48 hours. Whereas after 48 hours of hydration slag cement pastes modified with calcium formate and
trietanolamine exhale the biggest amount of heat (fig. 5).
4. Conclusions
The accelerating admixtures show the greatest effectives in the first 12 hours of curing. In case of mortars with
addition of GGBFS, the evident increase of compressive strength is seen between 2nd and 7th day.
The examined accelerating admixtures increase the amount of hydration heat exhale in 72 hours.
The admixture modified mortars with CEM I and addition of GGBFS show better compressive strength after 7 and
28 days in comparison to non-modified mortar.
On the basis of the results presented in figure 1 you can see that hardening accelerating admixtures work more
effectively together with cement with addition of GGBFS than with Portland cement.
Acknowledgements
The authors would like to thank Ms Paulina Jaworska for cooperation and English corrections of manuscript.
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