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Impregnation of concrete structures: transportation and fixation of moisture in water repellent treated concrete
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges (name changed 20110630).
2006 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Water repellent agents, today mainly consisting of alkylalkoxysilanes, are often used on concrete to prolong the service life of the structure. This is accomplished by protecting the reinforcement bars from chlorides or by changing the moisture content inside. When the concrete is treated with a water repellent agent the properties of the surface layer turn from hydrophilic to hydrophobic and thereby water droplets are stopped from entering, still allowing water vapour to pass through. This property change can reduce chloride ingression and stop heavy rain from penetrating through the surface layer.

This thesis presents results concerning how the moisture transport and fixation in the surface layer of the concrete is affected by a water repellent treatment. It also presents an investigation in which the effective penetration depth and the factors that influence it are studied. The methods used covers uni-dimensional transport of moisture using the so called cup method, measurements on moisture fixation using climate boxes with saturated salt solutions, penetration depth by cracking samples and spraying water on them, and field tests in a harsh tunnel environment.

The moisture diffusion coefficient for a water repellent treated concrete is close to constant and not nearly as dependent on the relative humidity (RH) as for untreated concrete. Unlike untreated concrete, where capillary suction plays an important role for the moisture transport at high RH, the vapour transport is the dominant transport mechanism even at high RH for water repellent treated concrete.

The moisture fixation is affected by a water repellent treatment and the effect is clearest at high moisture levels. There is, however, a certain amount of moisture present in a concrete treated with a water repellent agent. It can also be seen that the main reason for this is that the capillary porosity is affected by the treatment to a relatively high degree while the gel porosity to a large extent remains unaffected.

The three most important factors for the penetration of any water repellent agent into concrete is time, porosity and degree of saturation. An empirical equation is derived that gives an idea on how much these factors affect the efficient penetration depth of the water repellent agent.

Measures prolonging the service life of a concrete structure will lead to savings of natural resources and thus both economical and environmental savings for the community. The aim with the PhD-project is to develop explanation models to the promising results that have been obtained from the empirical research during the last decade and by doing this also create a better knowledge about when and how to apply a water repellent agent in order to benefit as much as possible from the product. The results presented in this Lisenciate thesis will be used as input in these models in the planned second phase of this project.

Place, publisher, year, edition, pages
Stockholm: KTH , 2006. , x, 38 p.
Series
Trita-BKN. Bulletin, ISSN 1103-4270 ; 84
National Category
Building Technologies
Identifiers
URN: urn:nbn:se:kth:diva-4160OAI: oai:DiVA.org:kth-4160DiVA: diva2:10982
Presentation
2006-10-13, Sal L1, KTH, Drottning Kristinas väg 30, Stockholm, 13:10
Opponent
Supervisors
Note
QC 20101117Available from: 2006-10-25 Created: 2006-10-25 Last updated: 2012-02-21Bibliographically approved
List of papers
1. Impregnation of concrete structures - introduction to a PhD-project
Open this publication in new window or tab >>Impregnation of concrete structures - introduction to a PhD-project
2005 (English)In:  Proceedings Hydrophobe IV: water repellent treatment of building materials, Freiburg, Switzerland: Aedification Publishers , 2005, 59-68 p.Conference paper, Published paper (Refereed)
Abstract [en]

Moisture is the source of most damage in concrete bridges, such as frost damage and reinforcement corrosion. Experiments and field investigations show that impregnation with silanes and siloxanes provide good protection against moisture for at least eight to ten years. But most of the research only verifies this without providing a reason for the positive results. This project analyses how common impregnation substances work in concrete. Additionally, the authors develop models in order to explain these effects. As a first step, it is important to obtain reliable data on how the moisture diffusion coefficient is affected by hydrophobic treatments. Some of the factors investigated are how the water-cement ratio and the impregnation depth will influence moisture transport. One of the goals is to create a computer model to predict the moisture and chloride content over time when the geometry, the material properties of the concrete structure and the environmental conditions are known.

Place, publisher, year, edition, pages
Freiburg, Switzerland: Aedification Publishers, 2005
Keyword
Hydrophobization, Concrete, Model, Mathematic model
National Category
Building Technologies
Identifiers
urn:nbn:se:kth:diva-6300 (URN)3-931681-81-5 (ISBN)
Conference
4th International Conference on Water Repellent Treatment of Building Materials, Stockholm, Sweden, April 12-13 2005
Note
QC 20101117Available from: 2006-10-25 Created: 2006-10-25 Last updated: 2010-11-17Bibliographically approved
2. Moisture transport in impregnated concrete: Moisture Diffusion Coefficient, Modelling, Measurements and Verification
Open this publication in new window or tab >>Moisture transport in impregnated concrete: Moisture Diffusion Coefficient, Modelling, Measurements and Verification
2006 (English)In: Journal on Restoration of Buildings and Monuments, ISSN 1864-7022, Vol. 12, no 1, 13-24 p.Article in journal (Refereed) Published
Abstract [en]

In order to understand the mechanisms of water repellents it is important to have reliable data on how the moisture diffusion coefficient is affected by a hydrophobic treatment. The results from the experiment described below will be used as input data in a project aiming to create a computer model for simulations of moisture and material transport in impregnated concrete structures. Two types of concrete with wo /c = 0.8 and 0.45 have been investigated by means of the cup-method to determine the moisture diffusion coefficient. Half of the specimens have been completely impregnated with trietoxy(isooctyl)silane by capillary suction and the other half were left untreated. This silane is one of the most common used water repellents on the Swedish market. Four different saturated salt solutions are used to create a relative humidity (RH) between 85 % and 97 % inside the cups while the surrounding environment is kept at 50 % RH. Three cups for each situation, two cups with pure water and four cups for verification give a total of 54 cups. The weight of the cups has been monitored weekly until a constant weight loss per unit time is obtained. With the use of Kirchhoff's potential in the calculations, the cup method is an efficient way of measuring the moisture diffusion coefficient. The moisture diffusion coefficient for treated concrete is found to be close to constant and less influenced by the RH compared to untreated concrete. Further, the results have shown that the transport of water vapour is highly reduced after a water repellent treatment. The accuracy of the method is verified at conditions of low humidity and a one dimensional steady state flow.

Keyword
Water repellent treatment, Moisture diffusion coefficient, Cup-method, Kirchhoff’s potential
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-6301 (URN)
Note

QC20100714

Available from: 2006-10-25 Created: 2006-10-25 Last updated: 2017-04-18Bibliographically approved
3. Moisture fixation in concrete treated with a water repellent agent
Open this publication in new window or tab >>Moisture fixation in concrete treated with a water repellent agent
(English)In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873Article in journal (Other academic) Submitted
National Category
Building Technologies
Identifiers
urn:nbn:se:kth:diva-6302 (URN)
Note
QS 20120327Available from: 2006-10-25 Created: 2006-10-25 Last updated: 2012-03-27Bibliographically approved
4. Penetration depth for water repellent agents on concrete as a function of humidity, porosity and time
Open this publication in new window or tab >>Penetration depth for water repellent agents on concrete as a function of humidity, porosity and time
2006 (English)In: Restoration of Buildings and Monuments, ISSN 1864-7022, Vol. 12, no 1, 3-16 p.Article in journal (Refereed) Published
Abstract [en]

Water repellent agents are used on concrete to change the conditions for moisture transport and fixation and thereby protect the concrete and the reinforcement bars from, e.g., chlorides, frost damage and alkali silica reactions. The most frequently discussed topic regarding water repellent treatments is the penetration depth of the agent. What is required and what is needed to achieve it? The effective penetration depth of a water repellent agent is defined as the distance from the surface to the sharp line between dry and wet concrete after it has been sprayed with water. During the past decade several papers have been published where factors having a major influence on the penetration depth for different water repellent agents have been investigated. The conclusions that can be drawn from these papers are that the three most important factors are time, porosity and degree of saturation. The time referred to is the duration of contact between the water repellent agent and the concrete surface. The porosity and degree of saturation refer to the concrete pore system and the amount of moisture inside the concrete at the time of the impregnation. There is, however, a lack of investigations quantifying the influence of these factors. This paper presents an empirical equation that gives an idea on how much these factors affect the efficient penetration depth of the water repellent agent. The equation is based on 300 new tests described and analysed in the paper. It is clear that the polymerisation rate of the water repellent agent affects the penetration depth. A fast reaction has the effect of slowing down the penetration.

Keyword
water repellent agents, peneration depth, concrete
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-6303 (URN)
Note

QC20100714

Available from: 2006-10-25 Created: 2006-10-25 Last updated: 2014-04-14Bibliographically approved

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