Mårten Janz

Long term performance of water repellent treatment : water absorption tests of field objects in Stockholm

In Sweden and many other countries the chloride ingress from deicing salts and seawater often sets the limit of service life for an exposed structure. 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 reinforced concrete from chloride ingress and/or by changing the moisture content inside. Several investigations and field experiments show a significant decrease in water absorption between samples treated with a water repellent agent and untreated samples. These experiments are in most cases carried out just a few weeks or months after the treatment but what happens after a few years? Should the treatment be repeated or is one single treatment enough? The water uptake of 27 different concrete structures treated with water repellents in Stockholm were tested by Nyman and Leon seven years ago to see if the water repellent effect was still there a few years after the treatment. It was the case in most of the structures but since no measurements were done right after the treatment it is not possible to say if there is an aging effect or not. In December 2006 new cores were drilled at the same places and the same testing procedure was repeated. The results indicate that most of the treatments are still functioning well.

Penetration Depth for Water Repellent Agents in Concrete as a Function of Humidity, Porosity and Time / Eindringtiefe von Hydrophobierungsmitteln in Beton in Abhängigkeit des Feuchtigkeitsgehaltes, der Porosität und der Zeit

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.

Feuchtigkeitstransport in hydrophobiertem Beton - Wasserdampfdiffusionskoeffizient, Modellieren, Messungen und Validieren / Moisture Transport in Impregnated Concrete - Moisture Diffusion Coefficient, Modelling, Measurements and Verification

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 th ...