Aberle T., Pustovgar A.P. «Prevention of efflorescence formation on masonry structures of buildings and constructions»

Abstract

The article is concerned with effective methods to
prevent efflorescence on surface of masonry structures,
based on use of admixtures to masonry mortar that prevent
capillary transfer of water solutions of salts in engineering
structures.

Brick masonry is still widely used in civil engineering
thanks to its high fire proof ability, strength, corrosion
stability and, therefore, long life and high reliability
market offers a wide range of masonry materials that
are different in type and properties depending on their
applications. They differ one from another by durability
indicators, average density, water absorption and other
properties. Correct selection of masonry mortar is one of
crucial conditions for ensuring quality of masonry structures.

Majority of masonry materials are manufactured
with a use of advanced technologies so that they meet
requirements of Russian and European standards. However,
masonry structures consist not only of bricks and
blocks. It is a complicated structure, properties of which
depend on interaction of its structural elements, from
largest to submicro particles [2], if considered from the
point of view of structural mechanics. Main elements of
brick masonry are masonry material and mortar.

When structural units of buildings and constructions
are erected from natural and artificial rock materials,
masonry mortar binds elements of masonry with
a system of vertical and horizontal joints thus ensuring
integration of the overall construction.

Proper choice of masonry mortar for construction
works is one of crucial conditions for ensuring quality of
masonry constructions. In Russia, unfortunately, proper
attention to a choice of masonry mortar is rarely paid. As a rule, the best choice in construction sites is a simplest
sand and cement premix, and most frequently a mortar
is prepared in situ from sand, cement and water dosed
with buckets and shovels, without regard to a type or
purpose of masonry mortar. Results of such approach to
masonry works can be in most cases seen on the walls
of buildings and constructions in form of efflorescence,
mould and mycotic stains (Pic. 1). Formation of contrast
white coat, spots or streaks deteriorates the esthetic appearance
of a construction and further may cause erosion
and destruction of masonry structures.

Masonry structures usually serve under conditions
of precipitation, atmosphere pollution, temperature extremes,
formation of condensate water and, in some cases,
subterranean water that is transferred by capillary in
construction materials. Presence of capillary pores sized
from 10 nanometers to 100 microns in masonry materials
and mortar promotes transfer of water-solved salts
within a building structure. Crystallization of some salts
may cause destruction of materials’ construction, which
reduces their bearing capacity. Presence of salts with
high water absorbency causes notable humidification
of mason work, which, in its turn, deteriorates thermo
physical parameters of building envelope, and promotes
growth of mould and mycotic stains.

According to F. Fressel [3], harmful influence of
salts onto masonry structures depends on their solubility
and water absorbency (Table 1).

The worst part in this process is played by chlorides,
carbonates, sulphates and nitrates, especially by salts of
alkali and alkaline-earth metals. In most cases, formation
of efflorescence stems from presence of soluble
compounds in masonry mortar and materials. For example,
state standard GOST permits of presence of alkalies
in cement. Varied quantities of soluble salts may also
present in filling materials. Depending on quality of raw
materials and production technology, masonry materials
may contain soluble compounds as well. At tempering
masonry mortar with water, free alkalies of cement immediately transfer to a liquid state. Alkalies bonded by
silicates and aluminates transfer to solution as cement
is hydrating.

Pic. 1 Efflorescence on masonry structures

Table 1. Water absorbency of salts forming efflorescence

Contacting with atmospheric СО2, alkalies are carbonizing
with formation of efflorescence containing sodium
and potassium carbonates. Content of alkali’s at
an early stage of hydration may vary within wide limits
(from 5% to 45% of their total content) for cement by different
producers. Another source of carbonates formation
is Portlandite – a product of Portland cement hydration,
that forms calcium carbonate when contacting
with atmospheric СО2. Interaction of alkalis contained in
cement of masonry mortar with hazardous atmospheric
sulfur and nitrogen compounds, or with tempering water,
results in formation of sulphates and nitrates respectively.
Filling materials and tempering water for masonry
mortar are most frequently a source of chlorides.

There exists a mistaken opinion, that salt can be
soaked out of masonry work after erection of masonry
structure, and that this option may eliminate a risk of
efflorescence formation for ever. Unfortunately, all
methods of fighting efflorescence that exist today, can
give a temporary effect only and can be applied only until
a certain concentration of salts in building structure is reached. For instance, use of various cleaning fluids
provides only a short-term effect. As a rule, efflorescence
appears on a surface in some time. Apart from
this, fighting efflorescence in already built masonry
constructions is quite expensive. Taking into account its
short-time effect, costs for repair and maintenance of
buildings and constructions are growing. Thus, prevention
of efflorescence formation at a stage of construction
is the most effective.

Pic. 2 Mechanism of CaCO3 formation in masonry mortars

Carbonates are the most wide spread efflorescence
on surface of masonry constructions. We will consider
a mechanism of efflorescence formation and possible
measures to prevent it using example of carbonates. As
mentioned above, efflorescence is a result of migration
of dissolved salts through a porous structure of material
to its surface, where salts are precipitated after water
evaporation. Mechanism of CaCO3 formation in masonry
mortars based on Portland cement can be described as
follows (Pic. 2).

Calcium hydroxide (Portlandite) – a product of
Portland cement hydration, which is dissolved in water
films adsorbed along pores of material forming ions Ca2+
and OH–. At that, atmospheric CO2 diffuses into pores of material, dissolves in the same water films and partly
forms carbonic acid (H2CO3). Carbonic acid and calcium
hydroxide undergo a neutralization reaction forming
hardly soluble CaCO3 (Pic. 3). This reaction is frequently
called carbonization of lime (calcium hydroxide). Speed
of efflorescence formation is considerably influenced
by temperature, humidity, concentration of CO2 in atmosphere,
as well as by wind rose in a given location.
Most frequently efflorescence appears in autumn or
spring, and in regions with variable humidity during a
day, when speed migration of salts to a surface and fast
evaporation of water from a surface are stimulated.

Pic. 3 Masonry mortar with efflorescence CaCO3

Considering sources and mechanism of efflorescence
formation, methods to prevent it can be developed.
There are several methods to prevent efflorescence:

ƒƒ* encapsulation of masonry constructions surface;

ƒƒ* creation of conditions to stop migration of water to
a surface of masonry structures;

ƒƒ* use of active mineral admixtures binding calcium
hydroxide (Portlandite) at a stage of its formation,
and also use of complex admixtures eliminating
main sources of efflorescence formation in masonry
mortar.

Encapsulation method consists in creation of watertight
covering on a surface of masonry. This method
is effective, but it cannot be applied for enclosure, plus
it is expensive. Cut-off of water migration to a surface
of masonry is provided by volumetric waterproofing of
masonry mortar, or by blockading capillary pores with
micro-particles. In this case, formation of efflorescence
can be weakened or fully eliminated for a certain period
of time due to reduction of capillary activity at volumetric
waterproofing. Capillary pores can be blocked with
fine fillers, for example microsilica, meta-caoline, or superfine
carbonate fillers added to masonry mortar.

Binding calcium hydroxide (Portlandite) at a stage
of its formation is based on application of active mineral
additives with high pozzolane activity in composition
of masonry mortar. Calcium hydroxide reacts with
pozzolane taken in excess amount and thus reaction
with atmospheric carbon dioxide is prevented. The following
materials can be taken as a puzzolane additive:
tripoli powder, gaize, diatomit, microsilica and other. A
patent [4] for method of preventing formation of efflorescence,
based on binding calcium hydroxide with a
system of mixed binding materials was issued in 2000.
While a main active substance reacting with Ca(OH)2
is amorphous SiO2, when pozzolane additives are used,
the patented system reaches the effect on account of use
of aluminate’s cements and calcium sulphates together
with Portland cement, which enables to ensure a direct
formation of masonry mortar mineral structure.

Presence of complex additives that eliminate main
sources of efflorescence formation, in composition of
masonry mortar is quite a new and promising method.
Research results [1] prove high effect of their application.
Peculiar character of work of those additives is based on combination of all main principles of fighting
efflorescence. Complex approach realized in the effect
provided by the additives enables to prevent formation
of efflorescence of practically all types of salts.

To check effect from application of different approaches
to prevention of efflorescence in masonry
constructions, comparative tests of samples of masonry
mortars were carried out. Tests were executed under a
procedure of constant watering of a sample beginning
from the first stage of hardening. Compositions of samples
used in the experiment are shown in the Table 2. After
preparation, samples have been cured at 20°C and humidity
of 55% during 24 hours, and then have been watered
at temperature 5°C during 28 days. This enabled to
simulate influence provided by precipitations onto masonry
constructions at a temperature which is the most
favorable for formation of efflorescence. Visual control
of surfaces of masonry mortar took place every day, to
find if any salts appeared on a surface. Three different
approaches to prevention of efflorescence formation,
and five samples of masonry mortar were tested:

ƒƒ* sample 1 – control sample of masonry mortar;

ƒƒ* sample 2 – masonry mortar with complex additive
«Elotex ERA 100»;

ƒƒ* sample 3 – masonry mortar with microsilica additive;

ƒƒ* sample 4 – masonry mortar with meta-caoline additive;

ƒƒ* sample 5 – masonry mortar volumetrically waterproofed
with silanes .

Quantity of cement being a main source of calcium
hydroxide (Portlandite) in a hardening masonry mortar
was taken constant for all the samples. Introduction of
additives was carried out on account of reducing the
content of high-silica sand. As results of the experiment
show (Pic. 4) formation of efflorescence on a surface
of controlling sample begins on the second day of
hardening. It becomes stronger by the 14th day, then
intensity of efflorescence formation goes down and stabilizes by the 28th day. There was no efflorescence on
a surface of the sample with complex additive «Elotex
ERA 100» during the whole period of tests. Efflorescence
appeared on samples with additives of microsilica and
meta-caoline on the 1st and the 2nd days of hardening
then getting stabilization on the 7th day. However, local
formation of efflorescence continued up to the 14th day.
Minor efflorescence on surface of samples volumetrically
waterproofed with silanes were seen at the early
stage of hardening, but later, during the whole period of
hardening, no efflorescence was observed.

Table 2. Compositions for tests

Pic. 4 Recovery surface of masonry mortar after experimental research: 1 – control sample of masonry mortar 2 – masonry mortar with complex additive «Elotex ERA 100» 3 – masonry mortar with microsilica additive 4 – masonry mortar with meta-caoline additive 5 – masonry mortar volumetrically waterproofed with silanes

It should be noted that influence of the experiment
temperature onto effect of microsilica and meta-caoline
additives in composition of samples in the most probable.
This is why application of additive of such type is
reasonable at average daily temperature above 18 °С.
Satisfactory results were shown by volumetric waterproofing
with silanes excluding the beginning stage of
hardening. It can be also connected with the influence of
temperature onto cement hydration.

The best result was observed when a complex additive
«Elotex ERA 100» was used. Absence of efflorescence
during the whole testing period proves effect of
its application even at minimum temperature of atmosphere.
The experimental tests have shown that different
methods to prevent formation of efflorescence were
effective. Priority should be put onto additives with
complex effect which eliminate formation of efflorescence
on all stages of masonry mortar hardening.

Bibliography

1. Аберле Т. Образование, механизм и пути пре-
дотвращения / Т. Аберле, Р. Цюрбригген, А. Келлер //
Современные технологии сухих строительных смесей,
М., 2006. С. 25–30.

2. Комохов П. Г. Структурная механика кирпич-
ной кладки. Совершенствование методов армирования
кирпичной кладки / П. Г. Комохов, Ю. А. Беленцов //
Строительные материалы. 2004. № 1.

3. Фрессель Ф. Ремонт влажных и поврежденных
солями строительных сооружений / Ф. Фрессель. М.:
Пейнт-Медиа, 2006.

4. Pat. WO 01/72658, 2000. Non-Efflorescing
Cementitious Bodies / A. G. Constantinou et al.


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