Volume 4, Issue 5

The filling of the pores with paraffin is a known and effective method to establish a subsequent moisture barrier in walls. Paraffin is compatible with the building material and the environment. Is the material warm enough before, or while, the treatment takes place, the liquid paraffin fills the pores completely. The distribution of the paraffin in the building material will be controlled with the temperature around the penetration area. Experiments with different building materials take place in order to find the connection between the receptivity of different paraffins at different temperatures. The aim is, to find a appropriate paraffin for building up horizontal moisture barriers inside walls cross section.The absorption coefficient will be shown for different Paraffin's at different temperatures for brick and lime - sandstone. By the using a special paraffin it is possible to building up moisture barriers with higher effectiveness and security.

The precision of drilling resistance measurements depends to a different degree on the abrasive properties of the tested material due to the wear of the boring bit. The paper shows a formulation of model which may be able to eliminate the influences of wear by connecting a material's specific coefficient of abrasion with the square root of boring time. For the investigation of this coefficient by experimental means a special testing procedure and a technique of analysis have been developed.

In this contribution, a combined experimental and numerical study to assess the cracking resistance of cement-based materials subjected to desiccation is outlined. Experimentally, the tendency to hygral cracking is determined by means of mortar ring specimens exposed to drying atmosphere. A numerical model based on the nonlinear theory of diffusion and nonlinear fracture mechanics is developed. The relevant hygral and mechanical parameters and laws needed for the model have been determined by means of adequate experiments analyzed by inverse analyses. The hygro-mechanical behaviour of two different types of mortar is studied. Numerical results have been compared to experimental findings. Furthermore, a parametric study has been carried out with the aim to characterize the relevant material parameters influencing shrinkage cracking. It can be concluded that a combination of experimental and numerical methods can play a decisive role in optimizing mortars or concretes with respect to predefined and required material properties. In this way, the durability of concrete structures can be significantly enhanced.

Thermotropic materials as integrated part of „intelligent windows" based on polymer gel networks are developed. Systems change the transparency in dependence on temperature. These windows are able to protect buildings against superheating by sunshine. The aim of this work is the formation of a thermotropic material which operates like a heat filter. The effect is based on reproducible reversible phase transitions in the material. A decisive aspect is the adjustment of these transitions between the optical clear or opaque state of the windows, controled by the solar energy, to the perception of the human eye.

Concrete overlays are often used for the repair of damaged concrete surfaces. The material propreties of the concrete overlay are different from those of the substrate. Restraint of shrinkage and thermal strains result in tensile stresses. At the free boundaries of the system the tensile stresses reach a maximum value. If these values reach the adherence strength, strain softening and then delamination occur starting from the free boundaries. The adherence behaviour of such a repair layer depends on the surface roughness and could be characterized by the wedge splitting test by use of non-linear fracture mechanics. The surface roughness of the substrate could be determinated and correlated to the adherence behaviour of concrete repair layers.

The German Centre for Craftsmanship and Preservation of Historic Monuments performs intensive help oriented towards practical applications of a testing apparatus for non-destructive assessment of the condition of historical wooden structures. Possibilities and limits of a resistance drilling measuring apparatus are clearly demonstrated using as an example the Peace Church of the Holy Trinity at Swidnica, Poland, which is a monumental timber-framed building serving for a congregation of 7500. By means of the above mentioned apparatus, the task of assessing the condition of the completely faced and painted interior supporting structure was successfully solved. Damage inside the timber as well as structural changes, types of joints, species of timber, and the load transferring capability of the joints were determined. The restoration of the church dealing with these aspects is nearly completed. One can state that there were no "bad surprises " and the estimated expenditures could be maintained. This is an excellent result, especially in such a sensitive and cost-intensive area like the restoration ofhistoric monuments.