Volume 5, Issue 3

Water repellents are widely used in Iceland on structures of concrete for the purpose of protecting cracks against water and for reducing the moisture content of the concrete, often as priming imprégnants under paint coatings. The climate is wet, freeze-thaw cycles are frequent and exterior concrete has suffered serious damages in general. A number of experiments involving the various kinds of application of repellents has been carried out, including both laboratory testing and tests in real house situations. The results show the water repellents to be very effective in protecting commonly occurring relatively narrow cracks, but not to be very effective at all in the lowering of the moisture content of concrete exposed to the climate of south-west Iceland.

Fluorinated acrylics are used as oil and water repellent finishes for papers, textiles and leather. Those polymers are available in different forms: water emulsions, aqueous solutions, organic solutions. It seemed to be interesting to test one of these products as an alternative for the impregnation of construction materials. In this paper, we study the efficiency of one specific fluorinated acrylic resin, presented in aqueous solution, produced by Elf-Atochem under the trade name ,,FORAPERLEx 321". Our work will describe the product and give some information about its effectiveness. It will be shown that water absorption decrease without change in permeability to water vapour of the treated samples. In order to have a better understanding of the capability of this product, some experiments have been made with a silicone-based product widely used.

Service life and lifetime of a concrete structure are not only depending on mechanical but also on chemical loads. Therefore precautions are often taken into account already in the planning- or construction phase. Certain protective measures such as water repellent treatment need preliminary tests on the finished concrete surface, in order to be applied in an optimal way . The present paper describes the preliminary tests performed on three tunnels of the second section of the Swiss National Highway N5 (Grenchen - Zuchwil) in the area of Solothurn. For the construction of the three tunnels different qualities of concrete and different types of form work were used. Furthermore the selected sections of the tunnels differ also from age and environmental conditions. A new two-chamber measuring cell developped at the Institute for Building Materials of ΕΤΗ-Zurich was applied to determine the capillary suction capacity of selected tunnel sections. Values measured on concrete elements in practice with this new cell are much more reliable than those measured with the traditional Karsten-cell.

By means of laboratory experiments it is shown that the penetration depth of a treatment of concrete with Silane depends strongly on the duration of suction and on the moisture content of the concrete. The necessary duration of suction can be estimated for any required penetration depth.

In several discussions, but also on the sites, the following thesis can often be heard: "Hydrophobic agents cause damage on stone surfaces!" or "Water repellent properties vanish in a few years!" In spite of this we know that great efforts have been done in research and development of water repellent agents in the past 20 years. So we can choose today between a great amount of different products for nearly every type of application. A lot of damage still occurs. This paper describes the typical destructions from some examples out of 15 years of practical experience and gives an explanation for the origin of the damage. In almost every case there are 2 main factors responsible for the damage: Caused by the lack of essential preliminary examinations on the building, there is no sufficient knowledge about facts and dates concerning the building materials. On the other side application is an important factor, and there is only a very small progress to be seen during the past decades. Mistakes in application lead in a very short time to a great amount of damage - and this may be the main reason for the general "bad reputation" of water repellent agents. Last not least, the architects, civil engineers and the building owners carry a certain responsibility too, especially for the lack of information on these complex topics and the lack of control during application.