Band 6, Heft 2

In the field of conservation of monumental buildings actually a standard methodology is lacking, with which it is possible to determine with the same sensitivity and reliability the "stone hardness" both at the superficial surface and at larger depths (few centimetres), both in laboratory and in situ. The use of the drilling resistance to determine the stone hardness is a very recent application and few working outdoor devices exist. The objective of this work is to validate a new and improved system to assess the drilling resistance of stones. The DFMS is portable and a quasi non-destructive device for direct determination of the "cohesion" of stone materials through the determination of their drilling resistance. The best operational features of the prototype have been established together with the assessment of the sensitivity and reliability of the system.

The degradation of monumental stones is the result of the interaction between the material and environmental factors, such as water, heat, atmospheric pollutants and living organisms. This interaction starts at the stone surface, progresses inwards and may reach several millimetres in depth. The common decay processes may lead to significant losses of the strength properties of the outermost layer of some stone materials which results in erosion, cohesionless appearance and disintegration. At present there is no method to measure stone hardness, both at the superficial surface and at larger depths (few centimetres), with the same sensitivity and reliability, which can be used both in laboratory and in situ. The aim of this paper is to present the application of a new methodology for measuring the Drilling Resistance (DR) of natural stones, by the use of the new portable system (DFMS) that can operate in the laboratory and in situ. The results obtained so far show that this new method is highly promising for in situ evaluation of the mechanical properties in order to assess the consolidating treatment applied for the conservation of monuments.

Geo-electrical relative difference mapping is presented as a non-destructive evaluation technique for ancient masonry. The method allows to visualise the internal structure and condition of the masonry. The decision on the necessity and on the type and degree of consolidation or strengthening of the masonry wall can be based on the information, obtained from the mapping. The paper deals with the arrangement of the original measurements to make them suitable for engineering evaluation. Firstly a numerical model is presented to filter out the influence of geometrical boundary conditions: they distort the measurements, but are of no interest for the evaluation. Secondly the maps are calibrated, to eliminate the influence of measuring configuration, and moisture content. The calibration methods are presented, and applied on the resistivity measurements, executed at the restoration project of the building "Duke's Mills" (13th Century) at Aarschot (B).

The author analyzes the different behavior of structures and monuments under restoration works with different types and levels of technical interventions from the safeguard to their strengthening. The article also deals with the concept of seismic protection following the new strategies of the modern seismic engineering and with the new technologies for reducing the seismic risk. Various examples are presented in the text.

Subject of this paper is the development of a method for the identification of the type of cement present in a hardened concrete or mortar. The method is based on the dehydration of the cement paste and the identification of the phases present after the dehydration. Considering clinker phases and real cements, the following possibilities for the identification of cements were worked out: • differentiation between Portland cements and cements containing additions by the identification of the mineral phases which are typical for the type of the addition • differentiation between ordinary and sulphate resistant Portland cements by the identification of the Ye'elimite phase after a dehydration at a temperature of 1100° C • determination of the characteristic compressive strength of Portland cements by the evaluation of the Alite-content. For an identification at least two dehydration temperatures have to be considered. The first temperature range is at about 1100 to 1200°C. It is important for the identification of the aluminates and ferrites. Temperatures from about 1400 to 1450°C are needed for the dehydration of the silicates. Because of the appearence of melting phases at temperatures above 1200°C, the Alite-content will be determined indirectly by the determination of the Belite-content and the content of free lime after a dehydration at 1100°C. At this temperature the free lime is considered to represent the difference in calcium oxide between the Alite and the Belite.