Efflorescence Phenomenon on Concrete Structures

Abstract

Since the introduction of modern pigmented concrete products in the early 1950's, coloured concrete products have opened new possibilities in the field of building and landscape design and ironically to a new visible phenomenon called efflorescence. Unfortunately, despite careful selection of raw materials and conscientious compliance with the production parameters, colour changes of the finished products are always the enemy. In many cases, these colour irregularities often described as fading is attributed to calcium carbonate efflorescence. One might question how efflorescence can still occurs after presumably, manufactu6rers have done everything right such as utilized quality materials, had a good mix design, exceeded strength requirements and met production schedule. By studying in depth the mechanism of efflorescence one might answer this mind-boggling question. Although, a great deal of work has been done in investigating the phenomenon of efflorescence and agreement has been reached to a large extent by researchers worldwide on the mechanism behind the formation of efflorescence, there is still no effective methods that can be used by concrete manufacturers to prevent the formation of efflorescence on finished concrete products. This paper has the purpose of providing some direction for future work to mitigate this phenomenon.

Full text

Efflorescence Phenomenon on Concrete Structures
NORSUZAILINA Mohamed Sutan
1, a
and SININ Hamdan
2
(1,2)
Department of Civil Engineering,Faculty of Engineering, Universiti
Malaysia Sarawak,94300 Kota Samarahan,Sarawak, Malaysia
a
msnorsuzailina@feng.unimas.my
Keywords: Efflorescence, concrete, calcium carbonate, calcium hydroxide, aesthetics
Abstract. Since the introduction of modern pigmented concrete products in the early 1950’s,
coloured concrete products have opened new possibilities in the field of building and landscape
design and ironically to a new visible phenomenon called efflorescence. Unfortunately, despite
careful selection of raw materials and conscientious compliance with the production parameters,
colour changes of the finished products are always the enemy. In many cases, these colour
irregularities often described as fading is attributed to calcium carbonate efflorescence. One might
question how efflorescence can still occurs after presumably, manufacturers have done everything
right such as utilized quality materials, had a good mix design, exceeded strength requirements and
met production schedule. By studying in depth the mechanism of efflorescence one might answer this
mind-boggling question. Although, a great deal of work has been done in investigating the
phenomenon of efflorescence and agreement has been reached to a large extent by researchers
worldwide on the mechanism behind the formation of efflorescence, there is still no effective
methods that can be used by concrete manufacturers to prevent the formation of efflorescence on
finished concrete products. This paper has the purpose of providing some direction for future work to
mitigate this phenomenon.
Introduction
In the past, when architects and designers mentioned concrete, people rarely got excited. It
usually meant a dull, grey, visually unappealing appearance. Since the introduction of modern
pigmented concrete products in the early 1950’s, coloured concrete products have opened new
possibilities in the field of building and landscape design. Today, concrete can be cast into a variety
of finishes and colours offering architects and the construction industry a material that is both
practical and aesthetically pleasing. The currently available inorganic colour pigments, for example
iron oxide pigments, are lightfast and weather-stable[1]. The strong colour they impart to concrete
will stand up to decades of rough wear and tear.
Unfortunately, despite careful selection of raw materials and conscientious compliance with
the production parameters, colour changes of the finished products are always the enemy. In many
cases, these colour irregularities often described as fading is attributed to calcium carbonate
efflorescence. It is important to point out that the pigments used to colour concrete have no influence
on the development of efflorescence [2].
Efflorescence, which used to be ignored due to its relatively harmless effect structurally, has
suddenly become a big and costly problem to the manufacturer, the pigment and the concrete
producers. The primary efflorescence as opposed to secondary efflorescence is creating more
problems since it occurs immediately after production since the manufacturer usually has to bear the
cost of unsatisfied customers. By studying in depth the mechanism of efflorescence we might
understand this phenomenon better. Although, a great deal of work has been done in investigating the
phenomenon of efflorescence and agreement has been reached to a large extent by researchers
worldwide on the mechanism behind the formation of efflorescence, there is still no effective
methods that can be used by concrete manufacturers to prevent the formation of efflorescence on
finished concrete products.
Advanced Materials Research Vol. 626 (2013) pp 747-750
Online available since 2012/Dec/27 at www.scientific.net
© (2013) Trans Tech Publications, Switzerland
doi:10.4028/www.scientific.net/AMR.626.747
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,
www.ttp.net. (ID: 49.50.236.211, Universiti Malaysia Sarawak, Sarawak, Malaysia-02/11/14,02:58:23)

Definition of Efflorescence
The dictionary definition, which is relevant to this research, is powdery deposit on a surface.
This term is frequently used to describe whitish deposits or stains on building materials. Let us see the
definition of efflorescence in the point of view of engineers. Terminology (ACI 116R-90) defines
efflorescence as “ a deposit of salts, usually white, formed on a surface, the substance having emerged
in solution from within either concrete or masonry and subsequently been precipitated by
evaporation”. The British Standard Glossary, BS6110: Subsection 1.3.7:1991 defines efflorescence
as “crystalline deposit of soluble salts on a surface that results from the migration and evaporation of
water”[3].
Elaboration on definition
Efflorescence is a crystalline deposit which leach from the concrete or mortar as soluble
calcium hydroxides and within a short period of time will combine with the atmospheric carbon
dioxide to form insoluble calcium carbonates, usually white, grey or black depending on the region
and the amount of moisture. Efflorescence begins to appear on the surfaces of concrete, masonry or
brick and as it accumulates its forms a very hard dense surface very similar to how a stalactite forms
in a cave except on a flat surface.
The mechanisms behind the occurrence of efflorescence can be described in only a few words,
as the cement sets or hardened, free calcium hydroxide is formed which is soluble in water even if
only to a slight extent. Consequently, it can migrate to the concrete surface either after already being
dissolved in the mixing water of the fresh concrete, or through the hardened concrete when exposed
to the effects of rain or dew. Having reached the surface of the concrete, the calcium hydroxide reacts
with carbon dioxide in the air to form water-insoluble calcium carbonate. Efflorescence occurring
during the hardening of the concrete will be referred to as primary efflorescence (lime bloom), and
that resulting from the weathering of the hardened concrete being referred to as secondary
efflorescence (lime weeping) [4, 5]. Equation 1 represents the chemical reactions of efflorescence.
Ca (OH)
2
+ CO
2
→ CaCO
3
+ H
2
O evaporates =Efflorescence (1)
According to Deichnel [6], surplus water which is not physically or chemically bound in the
hardened cement paste can make its way by diffusion through the capillary pore systems of the
concrete and it thus carry calcium hydroxide along with it. It is found out later that it is not the water
in the concrete that migrate or diffuse to the surface and entrains the calcium hydroxide; rather, the
calcium hydroxide diffuses up through the water-filled capillary system of the concrete to the surface,
where it reacts in accordance with the above equation.
The precipitation of the calcium carbonate reduces the calcium hydroxide concentration, thus
creating a concentration difference in relation to the interior of the capillary system. New Ca (OH)
2
is
supplied to the surface. This means that Ca(OH)
2
will continually diffuse from the deeper concrete
layers to the surface pores as long as there exist a concentration gradient [7].
If enough air has access to the surface of the concrete while setting, the capillary pores will
gradually be blocked with calcium carbonate within about 8 hours and the whole process of primary
efflorescence comes to a halt. If the surface of the concrete is covered with a film of condensation, the
calcium hydroxide can spread over its entire area and react to form a layer of calcium carbonate that is
insoluble in water. Primary efflorescence will be more severe than when no water film is present on
the surface of the concrete and calcium carbonate is only found at the capillary mouths. This shows
that calcium carbonate is the substance responsible for efflorescence and on the other hand, it blocks
the capillary mouths and halts the process of efflorescence. It was also proven that it is solely the
presence of carbon dioxide during hardening governs the time taken to seal the surface of concrete[8].
748 Advanced Materials Engineering and Technology

Although it can normally be expected that the capillary pores be sealed by calcium carbonate
once the concrete has set, secondary efflorescence may occur later when the concrete is exposed to
weathering. It occurs for approximately as long as the concrete continues to display significant
increase in hardness during the course of weathering. The drying out of the concrete at the surface is
one of the reasons for its occurrence. The second cause is if the concrete is poorly compacted to start
with, water such as rain or dew can penetrate the surface of the material that can dissolve soluble
calcium salts in an essentially patchy manner. In the case of low-density, porous concrete, there is no
distinction between primary and secondary efflorescence since the mechanism of their formation is
virtually identical. [7]
Factors contribute to efflorescence
Concrete does not have to have particularly low permeability for all fields of application but in
the case of decorative concrete such as concrete paving blocks, where efflorescence does tend to
occur, the concrete should also basically have low permeability. If it does not, there may be a variety
of reasons:[5,6,9,10,11].Of these factors, it can be concluded that the most important ones leading to
efflorescence are generally considered mix proportion, insufficient curing, poor compaction of the
concrete, and atmospheric conditions that cause a rapid drying out of the concrete.
Existing test procedures on efflorescence
There exists no standard test for efflorescence on concrete due to difficulty predicting if and
when it will appear precisely. Furthermore, efflorescence is essentially a qualitative phenomenon so
that it is not possible to devise a test method that would give a numerical answer. The reason for this
is that the extent of efflorescence in any given structure depends on number of factors that were
mentioned before that cannot always be established or quantified. There is a standard efflorescence
test for brick and structural clay that is ASTM Standard Test Method C67-00, which provides for a
visual comparison between bricks that had been in contact with water and those kept dry; looking at
the bricks from a distance of 3m, an observer classifies the bricks as “effloresced” or “ not
effloresced”, however this test is not intended to be used on concrete[12].
Conclusion
Based on this review, further research is needed to resolve the following issues: The contradictory
hypotheses on how capillary sizes influence efflorescence; How alkalis, which are not themselves
constituents of the efflorescence deposits and which reduce the solubility of Calcium Carbonate,
could promote efflorescence; To what extend do additives such as pozzolans, fly ash can reduce
efflorescence.
Acknowledgements
This research work reported in this paper has been funded by the Ministry of Higher education,
Malaysia and University Malaysia Sarawak under the project FRGS/03(07)/839/2012(79).The study
was conducted at the Concrete Laboratory, Department of Civil Engineering, University Malaysia
Sarawak, and the authors would like to thank the technicians in the laboratory for their contributions
in the experimental works. The authors would like to extend their gratitude to the Mr Ibrahim Yakub
for his editorial and valuable insight on this review.
Advanced Materials Research Vol. 626 749

References
[1] P. Crouchore, "Color: A force in construction," Concrete International, vol. 7, 1985.
[2] J. Nasvik, "Diagnosing problems with decorative concrete," 2003.
[3] A. Neville, "Efflorescence-surface blemish of internal problem? Part 1: The knowledge."
Concrete International, vol. 24, 2002.
[4] J. Bensted, "Efflorescence-prevention is better than cure," Concrete, vol. 34, pp. 40-41, 2000.
[5] P. Kresse, "Coloured concrete and its enemy: efflorescence," Chemistry and Industry, pp.
93-95, 1989.
[6] T. Deichnel, "Efflorescence-origins, causes, counter-measures." Betonwerk+Fertigteil-
Technik, vol. 48, pp. 590-597, 1982.
[7] P. Kresse, "Efflorescence-Mechanism of Occurrence and Possibilities of Prevention,"
Betonwerk+Fertigteil-Technik, vol. 53, pp. 160-168, 1987.
[8] P. Kresse, "Efflorescence and its prevention," Betonwerk+Fertigteil-Technik, vol. 57, pp.
84-88, 1991.
[9] P. Kresse, "Studies of the phenomenon of efflorescence on concrete and asbestos cement,"
Betonwerk+Fertigteil-Technik, vol. 49, pp. 560-568, 1983.
[10] J. Bensted, "Efflorescence- a visual problem on buildings," Construction Repair, vol. 8, pp.
47-49, 1994.
[11] A. Neville, Properties of Concrete, 4 ed: Prentice Hall, 2000.
[12] A. Neville, "Efflorescence-surface blemish of internal problem? Part 2: Situation in practice,"
Concrete International, vol. 24, 2002.
750 Advanced Materials Engineering and Technology

Advanced Materials Engineering and Technology
10.4028/www.scientific.net/AMR.626
Efflorescence Phenomenon on Concrete Structures
10.4028/www.scientific.net/AMR.626.747