In-situ characterization of efflorescence and other saline compounds in walls José Miguel Rodrigues Tuna Extended Abstract INTEGRATED MASTERS IN CIVIL ENGINEERING Supervisors: Doutora Inês dos Santos Flores Barbosa Colen Doutor Jorge Manuel Caliço Lopes de Brito Lisbon, October 2011
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In-situ characterization of efflorescence and other
saline compounds in walls
José Miguel Rodrigues Tuna
Extended Abstract
INTEGRATED MASTERS IN CIVIL ENGINEERING
Supervisors: Doutora Inês dos Santos Flores Barbosa Colen
Doutor Jorge Manuel Caliço Lopes de Brito
Lisbon, October 2011
In-situ characterization of efflorescence and other compounds in saline walls
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1. Introduction
The presence of soluble minerals (salt) is one of the most common anomalies on buildings.
When disregarded, they can produce a negative impact, either esthetical, on the living
conditions or, in the worst case scenario, in the structural performance.
The rehabilitation of walls affected by the presence of salt is frequently problematic. Experience
indicates that interventions only have a temporary effect, as the symptoms of the phenomenon
often reappear after some time.
This thesis aims to improve the understanding of the efflorescence phenomena, as well as
contributing to enrich the knowledge about inspection methodologies used in this type of
anomalies and other saline compounds.
A diagnosis methodology suitable for the various studied cases was defined. The utilization of
different techniques is also considered, in order to increase the quality of the results.
These techniques can be divided in three groups: sensorial analysis, which uses the human
body senses, in-situ assessment techniques, and laboratorial tests. The applicability of the
techniques used and their sensitivity to various factors involved are also studied.
Another goal that this thesis aims to achieve is the association of different types of
efflorescence with the corresponding causes, which may lead to more efficient inspections and
rehabilitation methodologies.
2. Efflorescence characterization
There are two distinct groups of anomalies due to the presence of salt: efflorescences and
subflorescences. The first group is usually related to the constant presence of humidity and
esthetic problems on the walls (Rodrigues and Gonçalves, 2005).
The subflorescences originate peeling and detachment of plaster fragments, leading to its
rupture. In some cases, where the anomaly reached an advanced stage, and especially in old
buildings, the degradation leads to structural problems. This fact is due to the construction
process and materials used in it: these buildings are usually erected by solid walls of great
thickness, with porous and hydrophilic materials that enable the rise of capillarity water from the
ground. In most of the cases these two types of phenomena occur simultaneously (Gonçalves
and Rodrigues, 2005).
The degradation process associated with subflorescences is often related to the increase and
decrease of salt´s volume within the pores. This increase is due to the stages of hydration /
dehydration and crystallization / re-crystallization of those minerals.
There are several types of mechanisms that enable the development of efflorescences.
According to the authors’ experience, the presence of a specific type of salt is related to its
origin. It is, therefore, easier to determine the efflorescence’s origin and immediately act on the
Extend Abstract
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source of contamination, instead of resorting to more accurate methods.
3. Experimental work’s methodology
Experimental tests were carried out in 10 different case studies. The diagnosis methodology
proposed in the beginning of the thesis was adapted to the cases throughout the work, when
necessary (Figure 1).
The referred methodology consists of distinct stages.
Initially, an assessment of the building’s general properties is performed: type of utilization,
number of floors (elevated and underground) and type of structure. Then, the building’s
configuration in plan is sketch, as well as its orientation. It is also important to register the
building’s distance from the sea, the environment to which it is exposed, the type of soil, the
presence of vegetation and the groundwater level near the building.
To understand the evolution of the anomalies associated with the efflorescence phenomenon, it
is necessary to inquire the users of these divisions, in order to establish whether the
efflorescence’s size increases or decreases depending on the weather, and when its presence
was detected for the first time.
The next step consists of a sensorial analysis of the anomaly, where all of its aspects are
described and several photos of the phenomenon and its localization are taken. It is important
to visualize the anomaly and its surroundings first, and then register the type of coating, the
substrate and the area of the wall where the efflorescence is located. The color, size, flavour,
texture, wall’s humidity, and in some cases, the smell, are properties that should also be
registered.
Two or three different samples of the affected areas should be collected, using independent
laboratorial tagged bags. The samples are afterwards analyzed with the field kit and colorimetric
strips. These tests measure the concentration of chloride, nitrate and sulfate ions present in the
different samples, providing the results in milligrams of ion per liter (mg/L). If these tests
manage to determine the types of efflorescence and the causes for its appearance, a report is
prepared and an intervention methodology is proposed.
The last step of the diagnosis methodology consists of the execution of laboratorial tests that
present high reliability, when necessary, despite their elevated costs when compared to the in-
situ techniques.
Parallel to the experimental work, standard solutions with the desired concentration of chloride,
nitrate and sulfate ions were prepared, in order to assess the quality of the results of the tests
performed with the field kit and the colorimetric strips. These solutions were produced using salt
samples, which were afterwards dissolved in pure water, resulting in solutions with known
concentrations. Six solutions were prepared (two for each type of ion) with different
concentrations.
In-situ characterization of efflorescence and other compounds in saline walls
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Figure 1 – Flowchart illustrating the diagnosis methodology applied on the efflorescence’s assessment
In-situ analysis:
colorimetric strips
field kit
Sample collection
New analysis
Conclusion about the type of efflorescence
Yes No
Report and intervention
proposal
Sensorial analysis:
sight
touch
smell
taste
hearing
Choose the place to
inspect
Record all the information about the
anomaly, including its evolution and
possible causes identified by the user
Photographic record
Laboratorial Techniques:
XRD
XRF (confirms in-situ
analysis results)
FTIR (if XRD is not possible)
Conclusion about the type of efflorescence
Yes
No
Report
Extend Abstract
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4. Results
The experimental tests enabled the gathering of enough information on the use of the various
techniques proposed in the diagnosis methodology, thus helping to deepen the existing
knowledge in this area. In several case studies, in addition to the sensorial analysis of
anomalies, 17 different samples were collected. The total of walls analyzed presented obvious
signs of degradation associated with the presence of salts. During the assessment based on the
in-situ techniques (using the field kit and colorimetric strips), 116 samples were analyzed.
Laboratorial tests were performed on another 35 samples, adding to a total of 151 analyses.
4.1. Case study example
This case study is located in Torres Novas, on a multi-storey building of two floors (Figure 2).
The anomaly is located on the first floor, next to a window (Figure 3).
Figure 2 – Exterior photograph of the building (the anomaly is identified by the red circumference)
Figure 3 – Interior Photograph of the Anomaly
Being built around the 1960’s, the structure had to suffer some repairs to ensure a desirable
service performance. The initial structure featured thick stone walls, which proved to be very
porous and permeable.
According to the owner, the building was subjected to some repairs in 2002. Approximately 3
years after this intervention, the presence of efflorescence was noticed. This anomaly was only
visible in one of the interior walls, which indicates that it is a localized anomaly.
During the repair of the building, the walls’ thickness was reduced, and some openings were
created to build windows. This situation may have enabled the beginning of the phenomenon.
After the detection of the anomaly, an inspection form was completed with the owner’s help,
where the general condition of the building and the anomaly itself were carefully examined.
Several pictures were taken and two samples were collected: one picture featuring the fluffy
efflorescence (Figure 4) and the other illustrating the plaster affected by the presence of salts
(Figure 5).
A sensorial analysis was carried out on site, where a characteristic smell was not detected. It
was verified that the efflorescence had a fluffy texture and white color. This aspect is enhanced
by the fact that the salt was on its hydrated phase, which implies bigger volume. The presence
In-situ characterization of efflorescence and other compounds in saline walls
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of moisture was not detected by touching, although, given the rotten of the skirting board, it was
reasonable to assume the existence of moisture where the anomaly was first detected.