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Procedia Engineering 196 (2017) 97 – 104
Creative Construction Conference 2017, CCC 2017, 19-22 June 2017, Primosten, Croatia
Properties of underwater concretes containing large amount of fly
ashes
Elżbieta Horszczaruk*, Piotr Brzozowski
West Pomeranian University of Technology Szczecin, Department of Civil Engineering and Architecture, Al. Piastow 50, 70-311 Szczecin,
Poland
Abstract
The results of the testing of the underwater concretes, containing fly ashes from circulating fluidized bed combustion (CFBC) of
the black coal, are presented in the paper. The concrete mixes were designed in such a way that the content of the binder was 400
kg/m3 and water to binder ratio w/b was equal to 0.48. Five mixes are prepared with the content of fly ashes: 0, 20, 30, 40 and 50
per cent of the cement mass, respectively. The consistence of the mixes was controlled by adding the suitable amounts of
superplasticizer. The content of AWA admixture was constant for all mixes and equal to 1% of the binder mass. The following
properties were tested for the concrete mixes: slump-flow, viscosity using V-funnel and passing ability using L-box. The wash-out
losses were also determined. All tests of the concrete mixes were carried out immediately after mixing the components and after
60 minute after mixing. For the hardened underwater concretes, the following properties were determined: compressive strength
after 7, 28 and 56 days of curing as well as the depth of water penetration under pressure and water mass absorbability. The best
composition, regarding to the properties of the mix and hardened concrete, appeared that with 30% of the fly ashes.
©2017
2017Published
The Authors.
Published
by Elsevier
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by Elsevier
Ltd. This
is an openLtd.
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(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer-review under responsibility of the scientific committee of the Creative Construction Conference 2017.
Peer-review under responsibility of the scientific committee of the Creative Construction Conference 2017
Keywords: circulating fluidized bed combustion, fly ashes: underwater concrete, mechanical properties;
1. Introduction
Fly ashes, as the by-products of coal combustion, are important and valuable raw materials for the building materials
industry, particularly for the producers of cement and concrete. This is reflected in the valid standards, which give
* Corresponding author. Tel.: +48-91-449-4900; fax:+ 48-91-449-4369
E-mail address: elzbieta.horszczaruk@zut.edu.pl
1877-7058 © 2017 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 scientific committee of the Creative Construction Conference 2017
doi:10.1016/j.proeng.2017.07.178
98
Elżbieta Horszczaruk and Piotr Brzozowski / Procedia Engineering 196 (2017) 97 – 104
precise requirements for the fly ash used as an addition to cement (PN-EN 197-1:2012) or concrete (PN-EN 4501:2012).
As a consequence of the strict requirements referring to the emission of CO2, SO3 and NOx, introduced by European
Union, the growing number of combustion systems with fluidized beds is installed in the Polish energy plants as a part
of their modernization. Therefore, the amount of the conventional siliceous fly ashes, produced by the Polish energy
industry, is decreasing. There are more than 300 circulating fluidized bed combustion (CFBC) systems working over
the Europe, including 14 in Poland. The volume of unused wastes from the fluidized beds is growing recently, and
according to the data by Central Statistical Office is about 0.8 mln ton annually [1].
The fly ashes from the fluidized beds are the mixture of the products of ash removal from the exhausts and the
residues of the sorbent. Thus, they often contain high amount of SO3 and CaO and show high loss on ignition [2,3],
and do not meet the rigorous requirements of European Standards for the mineral additions to cement and concrete.
For this reason they are often considered unuseful for traditional technologies of cement production. According to the
requirements of the standard PN-EN 197-1, the fly ashes from fluidized bed combustion may be used in the cement
production in the amount up to 5%, as the secondary mineral addition.
The interest in use of the fly ash from the fluidized beds to the production of building materials, including cement
composites, has rapidly grew. Because of the strict requirements referring to SO3 content, it can be used in the
production of concrete as a substitute of the natural aggregate, usually the sand. The fly ashes from CFBC are utilized
for stabilizing the soil substrate and as a basis for the road construction, as well as in the manufacturing of the roller
compacted concrete for the roads and hydraulic structures [4-6]. The technologies of using the CFBC ashes for the
production of the autoclaved aerated concrete were also developed [7].
The subject of the authors’ research was determination of the impact of CFBC ashes on the properties of underwater
concrete mixes and on the basic properties of the hardened underwater concretes (UWC), including their development
over time. The CFBC ashes were used in tests as the substitute of cement, in the amount from 20 to 50% of the binder
mass. The rheological properties of the mixes are important when designing UWC; considering the technology of the
underwater concreting, the UWC are usually designed as almost self-compacting concretes. Therefore, the authors
have determined the rheological properties and wash-out loss of the mixes containing CFBC ashes.
2. Materials and mix proportions
The investigation of the effect of CFBC ashes on the properties of underwater concretes was conducted on the
concretes containing the fly ash from the fluidized beds as the substitute of the cement in the amount: 0, 20, 30, 40
and 50% of the cement mass. The ashes from the combustion of the black coal were used; their chemical composition
is presented in the table 1. All mixes contained: Portland cement CEM I 42.5 R, river sand and fractioned gravel with
the maximum grain size 16 mm, stabilizing admixture for the underwater concretes, containing polysaccharides, and
superplasticizer containing naphthalene sulfonates. The content of the superplasticizer was increased together with
growing amount of the fly ashes in the concrete mix for keeping the value of the slump-flow above 400 mm. Constant
amount of the stabilizing admixture – 4 kg/m3 – was added into all UWC mixes. The composition of the concrete
mixes is presented in the table 2. Below is an example which the authors may find useful.
Table 1. Chemical composition of CFBC ash.
Content of the component [mass %]
LOI
SiO2
Al2O3
Fe2O3
CaO
MgO
Na2O
K2O
SO3
TiO2
P2O5
10.31
39.06
21.01
5.55
10.74
1.87
0.54
1.98
6.83
0.80
0.64
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Elżbieta Horszczaruk and Piotr Brzozowski / Procedia Engineering 196 (2017) 97 – 104
Table 2. Mix proportion of concretes, kg/m3.
Unit weight [ kg/m3]
Component
Cement CEM I 42.5 R
CFBC ashes
C0
C20
C30
C40
C50
400
320
280
240
200
200
0
80
120
160
192
192
192
192
192
River sand 0/2
593.1
593.1
593.1
593.1
593.1
Gravel 2/8
341.5
341.5
341.5
341.5
341.5
Gravel 8/16
768.4
768.4
768.4
768.4
768.4
Superplasticizer
8
10
12
14
16
AWA
4
4
4
4
4
Water
3. Scope of tests and methods used
3.1. Testing of UWC mixes
All mixes were designed as almost self-compacting concretes (ASCC). For the confirmation of the required values
of the particular properties, the following tests were performed on the designed mixes:
x determination of flowability by slump-flow (according to PN-EN 12350-8:2012),
x determination of viscosity using V-funnel (according to PN-EN 12350-9:2012),
x determination of passing ability through the reinforcement using L-box (according to PN-EN 12350-10:2012),
x determination of wash-out loss of the mixes according to the Instruction CRD-C 61-98A [8].
All tests of the mixes were performed immediately after mixing of the components and after 60 minutes from the
mixing of the components.
3.2. Testing of hardened concretes
Compressive strength of UWC were determined using the cubic specimens of 150 mm. After demoulding, the
specimens were stored in the containers with water at the constant temperature 20 qC+/-2qC until testing. The tests were
conducted after 7, 28 and 56 days of curing, according to the standard PN-EN 12390-3.
Additionally, the determination of the depth of water penetration under pressure was carried out for all concretes,
according to the standard PN-EN 12390-8:2011. The results for every type of concrete were obtained from three cubic
specimens of 100 mm. After demoulding, the specimens were stored in the containers with water at the constant
temperature 20qC+/-2qC until testing.
4. Results and discussion
4.1. Properties of UWC mixes
Underwater concretes are often transported over long distances, so their rheological properties should be stable
over time. According to the literature [9,10], rheological properties of UWC mixes are most often determined after 60
minutes from the mixing of the components. There are no uniform standard recommendations referring to the
rheological parameters, which should be demonstrated by UWC mixes. According to the Japanese requirements [11],
the slump-flow of UWC mixes should be in the range 450 to 500 mm. According to the standard DIN 1045-2, this
value should be at least 400 mm. The results of tests of slump-flow for the concrete mixes with various contents of
CFBC ashes are presented in the Fig. 1. All mixes with CFBC ashes had the slump-flow above 400 mm after 1 hour
from the mixing of the components. In spite of increasing content of superplasticizer, the significant growth of the
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Elżbieta Horszczaruk and Piotr Brzozowski / Procedia Engineering 196 (2017) 97 – 104
amount of CFBC ashes in the concrete mix causes worsening of its consistence. For obtaining of the slump-flow above
30% there was necessary to increase the superplasticizer content by 50% regarding to the reference mix (C0), and in
the case of the mix with 50% content of CFBC ashes the necessary amount of superplasticizer increased by 100%.
Fig. 1. Slump-flow of the tested concrete mixes as the function of CFBC ashes content.
The results of testing of viscosity of UWC mixes, determined by measurement of time of flowing of the mixes
through the V-funnel, are presented in the Fig. 2. According to [11], the recommended time of flowing for the UWC
mixes in such a test should be not more than 20 s. The significant increase of the viscosity of the mixes has been
observed with growing content of CFBC ashes, immediately after mixing of the components as well as after 60
minutes from the mixing. For achieving the required viscosity, the amount of the used superplasticizer should be
increased. The content of fly ashes higher than 30% seems to be unprofitable due to the necessity of use of large
amount of superplasticizer.
Fig. 2. Time of passing of the concrete mixes through the V-funnel.
Elżbieta Horszczaruk and Piotr Brzozowski / Procedia Engineering 196 (2017) 97 – 104
The ability of concrete mixes to passing through the reinforcement was evaluated using L-box equipment.
According to the requirements for SCC mixes, the passing ability ratio PL should be at least 0.8. The results of tests
of passing ability of the concrete mixes using L-box are presented in the Fig. 3. Immediately after mixing of the
components, only the reference mix without CFBC ashes (C0) achieved the required value of PL > 0.8. Because of
mixing of the components with low speed (approx. 1 rpm) for 60 minutes until the second measurement, the activity
of the ashes increased significantly, which resulted in the improvement of the rheological properties. The concrete
mixes containing 30 and 40% of CFBC ashes obtained the PL values higher than 0.8, while the reference mix (C0)
after 60 min. from the mixing of the components has seized in the L-box (PL=0.0).
Fig. 3. The passing of UWC mixes through the reinforcement (L-box).
The mechanical properties of UWC containing CFBC ashes in the natural circumstances are to large extent affected
by the conditions of concreting, i.e. water temperature, velocity of the flowing water and depth of placing of the
concrete mix. Therefore, the aforementioned investigation of the concrete mixes properties has been complemented
with the tests of wash-out loss by the American method [8]. The tests results are presented in the Fig. 4.
Fig. 4. Wash-out loss of the samples determined according to CRD-C61-89A.
101
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Elżbieta Horszczaruk and Piotr Brzozowski / Procedia Engineering 196 (2017) 97 – 104
According to the requirements of US Army Corps of Engineers [9], the wash-out loss for the ordinary concrete
should be not higher than 12% of the mass of the tested sample, and for SCC – 8% of the mass of the sample. The
increase of the content of CFBC ashes in the concrete mixes, tested immediately after mixing of the components,
caused already in the case of addition of 20% of CFBC ashes a twofold increase of the wash-out loss. After 60 min.
from the mixing of the components, the wash-out loss for the concrete mixes containing CFBC ashes decreased
significantly and did not exceed 8% for any of them. This improvement can be explained by the activation of the
binding properties of the ashes.
4.2. Properties of hardened concretes
The results of tests of compressive strength of UWC are presented in the Fig 5.
Fig. 5. Results of tests of compressive strength of the concretes containing various amounts of CFBC ashes.
The addition of CFCB ashes caused decreasing of compressive strength of the tested concretes after 7 and 28 days.
However, in the case of CFBC ashes content up to 30%, the compressive strength of the tested concretes (C10, C20
and C30) after 56 days was slightly lower than that of the reference concrete (C0). This phenomenon has been
confirmed by the researches described in [12-15]. After 90 days, the strength of the concrete with addition of CFBC
ashes can be even higher than that of the unmodified concrete [14, 15].
The results of tests of water penetration under pressure are presented in the Fig. 6. The addition of CFBC ashes
caused increase of the tightness of the tested concretes. All tested concretes showed very good tightness, as the depth
of water penetration under pressure did not exceed 30 mm.
Analysing the obtained tests results, the optimum amount of CFBC ashes as the substitute of cement in underwater
concretes seems to be 30%. Such content of the ashes allows to achieve the tight concrete mix, with the strength
properties close to the reference mix. However, considering that not all rheological parameters of the concrete mix
C30 were optimal from the point of view of concreting technique (e.g. too high viscosity), the correction of its
composition should be done, including the increase of superplasticizer content for achieving the proper viscosity of
the concrete mix.
Elżbieta Horszczaruk and Piotr Brzozowski / Procedia Engineering 196 (2017) 97 – 104
103
Fig. 6. Water penetration under pressure for the tested concretes.
5. Summary
The results of tests of the series of underwater concretes containing various amounts of CFBC ashes are presented
in the paper with suggestion that the fly ashes from the fluidized bed combustion can be used in the technology of
underwater concretes. It is possible to control the rheological properties of UWC mixes, if CFBC ashes substitute up
to 30% of the cement mass. The increase of the content of CFBC ashes causes a downfall of 28-day compressive
strength of the concrete, however, after 56 days the concrete with 30% content of CFBC ashes achieve the strength
close to the reference concrete. Delaying of hydration of the concrete mixes containing CFBC ashes is an additional
advantage in the case of massive structures.
When higher amounts of CFBC ashes were used, the significant drop of the strength was observed even after 56
days. This was a result of insufficient amount of superplasticizer. On technological and economic grounds, the addition
of CFBC ashes in the amount higher than 30% requires introduction of large amount of superplasticizer. However,
this still does not guarantee the obtaining of good mechanical parameters due to the weaker binding ability of the
ashes, which in this case makes the modification of the concrete mixes unprofitable.
Acknowledgements
This research was funded by the National Centre for Research and Development within SEFIRCAOM
2/KONNECT/2016 (KONNECT Joint Call).
References
[1] A. Uliasz-Bocheńczyk, M. Mazurkiewicz, E. Mokrzycki, Fly ash from energy production – a waste, byproduct and raw material, Mineral
Resources Management Vol. 31 Iss. 4 (2015) 139–150.
[2] X. Fu, Q. Li, J. Zhai, G. Sheng, F. Li, The physical–chemical characterization of mechanically-treated CFBC fly ash, Cement and Concrete
Composites Vol. 30 Iss. 3 (2008) 220–226.
[3] E. Horszczaruk, Influence of addition of fluidal fly ashes on the mechanical properties of underwater concretes, Journal of Building Chemistry
Vol. 1 Iss. 1 (2016) 26-30.
[4] J. Havlica, J. Brandstetr, I. Odler, Possibilities of utilizing solid residues from pressured fluidized bed coal combustion (PFBC) for the production
of blended cements, Cement and Concrete Research Vol. 28 Iss. 2 (1998) 299–307.
[5] N. Ghafoori, Y. Cai, Laboratory-made roller compacted concretes containing dry bottom ash: Part I – mechanical properties, ACI Materials
Journal Vol. 95 Iss. 2 (1998) 121–130.
104
Elżbieta Horszczaruk and Piotr Brzozowski / Procedia Engineering 196 (2017) 97 – 104
[6] M. Chi, R. Huang, Effect of circulating fluidized bed combustion ash on the properties of roller compacted concrete, Cement & Concrete
Composites Vol. 45 (2014) 148–156.
[7] V. Cerny, R. Drochytka, Utilization of FBC ash in autoclaved aerated concrete technology, International Journal of Materials Vol. 1 (2014) 7983.
[8] CRD C61-89A. Test method for determining the resistance of freshly-mixed concrete to washing out in water, US Army Experiment Station,
Handbook for Concrete, Vicksburg, Mississippi, 1989, pp. 3.
[9] S.X. Yao, D.E. Berner, B.C. Gewerick, Assessment of underwater concrete technologies for in-the wet construction of navigation structures,
U.S. Army Corps of Engineers Publication, ERDC Technical Report INP-Sl-1, 1999.
[10] M. Sonebi, A.K. Tamimi, P.J.M. Bartos, Application of factorial models to predict the effect of antiwashout admixture, superplasticizer and
cement on slump, flow time and washout resistance of underwater concrete, Materials and Structures Vol. 33 Iss. 5 (2000) 317–323.
[11] Japan Society of Civil Engineers, Recommendations for design and construction of anti-washout underwater concrete, Concrete Library of
JSCE Vol. 19 (1992).
[12] T.R. Naik, S.S. Singh, M.M. Hossain, Properties of high performance concrete systems incorporating large amounts of high-lime fly ash,
Construction and Buildings Materials Vol. 9 Iss. 4 (1995) 195-204.
[13] K.H. Khayat, M. El Gattoui, C. Nmai, Effect of silica fume and flay ash replacement on stability and strength of fluid concrete containing
anti-washout admixture, Superplasticizers and Other Chemical Admixtures in Concrete 5th International CANMET/ACI Conference, Special
Publication Vol. 173, ACI, Farmington Hills, 1997, 695-718.
[14] A.H. Memon, S.S. Radinb, M.F.M. Zainc, J-F. Trottiera, Effect of mineral and chemical admixtures on high-strength concrete in seawater,
Cement and Concrete Research Vol. 32 Iss. 3 (2002) 373–377.
[15] P. Gao, X. Lu, H. Lin, X. Li, J. Hou, Effect of fly ash on the properties of environmentally friendly dam concrete, Fuel Vol. 86 Iss. 7-8 (2007)
1208-1211.