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Hydrophobic Impregnation of Concrete Structures: Effects on Concrete Properties
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Design and Bridges.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Hydrophobic impregnations often referred to as 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 becomes hydrophobic and thereby water droplets are stopped from entering, still allowing water vapour to pass through. This change can reduce chloride ingress and stop heavy rain from penetrating through the surface layer.

This thesis presents results concerning how the properties of concrete are affected by a hydrophobic impregnation. Moisture transport and fixation in the surface layer of the concrete are studied as well as the secondary effects of more practical use such as the effect on chloride ingress, water absorption and humidity level. It also presents results on how the penetration depth and concentration of the water repellent agent (i) depend on a number of parameters, and (ii) affect the outcome of the treatment. Water repellent treatments on a number of different concrete structures in Stockholm, ranging from tunnel to high-rice building, are evaluated as well.

The three most important factors for the penetration of any water repellent agent into concrete are time, porosity and degree of saturation. A semi-empirical equation is derived that gives an idea on how much these factors affect the efficient penetration depth of the water repellent agent. The depth and concentration have a major effect on the performance of the treatment.

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. 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. A hypothesis is presented which suggests that the RH inside the concrete at the time of the treatment affects not only the depth and concentration but also in which range of pore radii the water repellent agent is present and active.

The durability of hydrophobic impregnations can be divided into surface effects and in depth effects. The first is sensitive to the environmental and mechanical loadings and normally disappears within a year while the later can be long lasting if a sufficient depth is reached.

Hydrophobic impregnations are not the answer to all problems in concrete related to moisture, but if correctly used it can prolong the service life of the structure which will lead to savings of natural resources and thus both economical and environmental savings for the community.

Abstract [sv]

Vattenavvisande impregneringsmedel, som i dagsläget till största del består av alkylalkoxysilaner, används ofta på betong för att förlänga livslängden på konstruktionen. Detta syfte uppnås genom att armeringen skyddas mot klorider eller att fukthalten inuti betongen sänks. När betongen impregneras ändras ytskiktets fuktmekaniska egenskaper från hydrofila till hydrofoba vilket gör att vattendroppar kan stoppas medan vattenånga tillåts passera. Dessa förändrade egenskaper kan medföra att kloridinträngningen minskar och att kraftiga regn inte tränger genom det impregnerade skiktet.

Denna avhandling presenterar resultat om hur betongen påverkas av en vattenavvisande impregnering. Fukttransport och fuktfixering i betongens ytskikt har undersökts men även sekundära effekter som kloridinträngning, vattenabsorption och förändring i fuktinnehåll vilka alla är av större praktisk nytta. Avhandlingen presenterar också resultat om vilka faktorer som påverkar impregneringens inträngningsdjup och koncentration samt vilken betydelse dessa har för funktionen. För att utvärdera impregneringars effekt i olika miljöer har ett stort antal objekt i Stockholm undersökts, innefattande olika konstruktioner från en tunnel till höghus.

Impregneringens inträngningsdjup och koncentration har en avgörande betydelse för dess funktion. De tre viktigaste faktorerna för alla impregneringsmedels inträngning i betong är tid, porositet och fuktnivå. En semiempirisk ekvation har tagits fram där det framgår hur dessa tre faktorer påverkar det slutliga inträngningsdjupet för impregneringen.

Till skillnad från obehandlad betong är transportkoefficienten för en impregnerad betong nästan oberoende av den relativa fuktigheten (RF) i omgivningen. Vid höga RF, där största delen av fukttransporten i obehandlad betong sker på grund av kapillärkrafter, är ångtransporten fortfarande den dominerande transportmekanismen i impregnerad betong.

Fuktfixeringen i betong påverkas av en impregnering och effekten är störst vid höga RF. Det är dock tydligt att en viss mängd fukt finns inuti den impregnerade betongen. Detta kan förklaras med att största delen av kapillärporerna påverkas av impregneringen medan gelporerna förblir obehandlade. Resultaten indikerar också att fuktnivån vid impregneringstillfället avgör vilken del av porsystemet som kan behandlas och inte bara koncentrationen och inträngningsdjupet.

Långtidsegenskaperna hos impregneringen kan delas upp i yt- och djupeffekt. Effekten på ytan avtar normalt sett inom ett år på grund av damm och partiklar, UV-ljus, slitage mm. Djupeffekten påverkas däremot inte av dessa faktorer och kan finnas kvar i decennier.

Vattenavvisande impregneringar är inte lösningen på alla fuktrelaterade problem i betong, men om de används på rätt sätt så kan det förlänga livslängden på många konstruktioner. Detta leder till ett bättre hushållande med naturresurser och därmed både ekonomiska och miljömässiga besparingar för samhället.

Place, publisher, year, edition, pages
Stockholm: KTH , 2010. , xii, 45 p.
Series
Trita-BKN. Bulletin, ISSN 1103-4270 ; 104
Keyword [en]
hydrophobic impregnation, silane, siloxane, concrete, surface treatment, water repellent agent, building protection
Keyword [sv]
impregnering, betong, silan, siloxan, ytbehandling
National Category
Civil Engineering
Identifiers
URN: urn:nbn:se:kth:diva-12179OAI: oai:DiVA.org:kth-12179DiVA: diva2:305538
Public defence
2010-04-16, Sal D2, Lindstedtsvägen 5, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC20100715Available from: 2010-03-30 Created: 2010-03-24 Last updated: 2010-07-15Bibliographically approved
List of papers
1. 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
2. Penetration profiles of Water Repellent Agents in Concrete as a function of Time: Determined with FTIR-Spectrometer
Open this publication in new window or tab >>Penetration profiles of Water Repellent Agents in Concrete as a function of Time: Determined with FTIR-Spectrometer
2010 (English)In: Int. journal Nordic Concrete Research, Vol. 41, no 1, 51-60 p.Article in journal (Other academic) Published
Keyword
silane, water repellent agent, FTIR-spectrometer, penetration profile
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-12236 (URN)
Note
QC 20100714. Updated from submitted to published.Available from: 2010-03-30 Created: 2010-03-30 Last updated: 2012-02-09Bibliographically approved
3. Water Repellent Treatments: The importance of reaching a sufficient penetration depth
Open this publication in new window or tab >>Water Repellent Treatments: The importance of reaching a sufficient penetration depth
2010 (English)In: CONSEC’10, Merida, Mexico, 2010Conference paper, Published paper (Refereed)
Identifiers
urn:nbn:se:kth:diva-12237 (URN)
Note
QC20100714Available from: 2010-03-30 Created: 2010-03-30 Last updated: 2010-07-14Bibliographically approved
4. 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
5. Moisture Fixation in Water Repellent Treated Concrete
Open this publication in new window or tab >>Moisture Fixation in Water Repellent Treated Concrete
(English)Article in journal (Other academic) Submitted
Identifiers
urn:nbn:se:kth:diva-12304 (URN)
Note
QS 20120327Available from: 2010-04-07 Created: 2010-04-07 Last updated: 2012-03-27Bibliographically approved
6. Sorption Isotherms of Water Repellent Treated Concrete
Open this publication in new window or tab >>Sorption Isotherms of Water Repellent Treated Concrete
2008 (English)In: Proceedings, Hydrophobe V, 2008, 261-271 p.Conference paper, Published paper (Refereed)
Keyword
sorption isotherms, moisture fixation, water repellent treatment, silanes
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-12238 (URN)
Conference
5th International Conference on Water Repellent Treatment of Building Materials
Note
QC 20110211Available from: 2010-03-30 Created: 2010-03-30 Last updated: 2011-02-11Bibliographically approved
7. Preventing Chloride Ingress in Concrete with Water Repellent Treatments
Open this publication in new window or tab >>Preventing Chloride Ingress in Concrete with Water Repellent Treatments
2010 (English)In: CONSEC’10, 2010Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-12239 (URN)
Note
QC20100715Available from: 2010-03-30 Created: 2010-03-30 Last updated: 2010-07-15Bibliographically approved
8. Decreasing Humidity in Concrete Facades after Water Repellent Treatment
Open this publication in new window or tab >>Decreasing Humidity in Concrete Facades after Water Repellent Treatment
2008 (English)In: Hydrophobe V, 2008, 379-386 p.Conference paper, Published paper (Refereed)
Identifiers
urn:nbn:se:kth:diva-12240 (URN)
Conference
5th International Conference on Water Repellent Treatment of Building Materials
Note
QC20100715Available from: 2010-03-30 Created: 2010-03-30 Last updated: 2010-07-15Bibliographically approved
9. Long Term Performance of Water Repellent Treatment: Water Absorption Tests of Field Objects in Stockholm
Open this publication in new window or tab >>Long Term Performance of Water Repellent Treatment: Water Absorption Tests of Field Objects in Stockholm
2008 (English)In: International Journal on Restoration of Buildings and Monuments, ISSN 0947-4498, Vol. 14, no 1, 39-47 p.Article in journal (Refereed) Published
Keyword
Water repellent agents, Water absorption, Long term performance, Concrete
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-12241 (URN)
Note
QC20100715Available from: 2010-03-30 Created: 2010-03-30 Last updated: 2010-07-15Bibliographically approved

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