Band 4, Heft 2

The following article would like to acquaint the reader with the research project, entitled „Preservation of North German Terracotta, as exemplified by the castles of Schwerin, Gadebusch and Basedow". This paper gives an overview of the way and the main subjects of our work which is to be dealt with through inter-disciplinary cooperation and contains results of the chemical investigations, in particular ceramic tests and protective material tests. The aim is to identify both the causes and the development of the various types of damage to terracotta, both where their cause is environmental and where it lies in the manufacturing process. The following stage is the problem of on-site conservation. The term „conservation " here does not refer only to the protective material complex but basicaly also to some materials and techniques necessary for conservation, for example adhesive mortars (to fill blistered areas), battering mortars (to secure the transitional areas of intact surfaces and de tio rated surfaces) and technics of desalination. At the same time, attention is directed to the fact that the material classification „building terracotta" includes a very wide range of characteristic properties, so that one cannot speak of terracotta as such.

As there are no certificated qualification for the fire resistance period of halftimbered walls different walls with and without claddings were tested. The tests were carried out in a small fire chamber and are based on DIN 4102. On the basis of the tests the dependence of the building elements and materials according tofire were revealed. It was obvious that careful sealings mainly in the area of joints could reduce the passage of fire and thereby the failure of the whole construction. Good sealings are clay and other insulating mortars that are used for infillings. Good sealing materials are further plaster and/or insulating plaster layers just as panel kind materials like gypsum and fire prevention boards. The present results are not able to replace a test according to DIN 4102 Τ 2/3 but they can be helpful for a judgement of an individual expert's opinion.

In order to seal structural elements which are in contact with soil at a later stage, external and internal sealing has been the usual practice for years. It is the aim of this contritution to point out the possibility of sealing by means of area injection in a structural element and veil injection in the soil. Both methods can be applied under water pressure. In particular, the requirement frequently formulated by representatives of service for the protection of monuments to seal a structure at a later stage without modifying the surface of historical structural elements is taken into consideration. Measures are discussed which may be applied if the serviceability of a new structure is jeopardized by water infiltration. Restoration methods, restoration planning and the necessary apparatus are described. In addition, the injection materials to be used are indicated depending on the water pressure.

The following article will describe the procedure of quality control of a car park repair with synthetic resin coating. Basic prerequisites for the realisation of the quality control are exact knowledge of the condition of the building, the assessment of possible repair variants, the necessary know-how in product application as well as the definition of the limits to be observed. The example shows that frequently the quality of the work carried out is improved in the process of construction up to a satisfactory level. Due to constant quality control, faults were discovered in time. Quality control has proved to be successful provided that all parties involved are behind this concept and are prepared to carry through the quality requirements defined.

The risk for corrosion is substantially increased in carbonated concrete. Recently, methods for realcalization of carbonated structural concrete elements have been proposed and applied. A stable pH-value higher than 10 is aimed to be achieved by impregnation with aqueous solutions of alcali carbonates. Analyses of impregnated concrete elements in practice has shown, however, that the pH-value of the pore solution drops to values below 10 despite an apparently sufficient alcali content. Results described in this contribution are used to develop a hypothesis in order to explain the time-dependent decrease ofpH-value. It is concluded that the composition of the pore solution and the chemical equilibrium is changed in the presence of dissolved sulfates. Under these conditions, a comparatively high content of alcali carbonates is not sufficient any more to ascertain a pH-value higher than 10. The chemical mechanisms suggested here are used to interprete observations in practical cases. The complex interactions of dissolved ions in the pore solution of concrete has hardly been taken into account up to now. For this reason, the application of realcalization as discussed in this contribution cannot be recommended so far