In situ assessment of the stone conservation state by its water absorbing behaviour : a hands-on methodology

This paper describes the use of the water absorbing behaviour (WAB) for assessment of the conservation state of stone in situ. A test methodology, consisting of a combination of techniques for in situ measurement of the WAB, was applied in a case study on Lede stone, a sandy limestone, used in a medieval facade in Ghent, Belgium. The methods used were the contact sponge method (CSM), the Karsten tube (KT) and the droplet method (DM). Additionally, the residual hardness of the stone was measured by Schmidt hammer (SH). After careful selection of representative measuring points, a qualitative analysis of the stone’s condition could be made, based on its WAB, residual hardness, reference data from laboratory experiments and thorough visual observations. From this analysis it could be concluded that CSM, KT and SH generated coherent and compatible results; that DM could indicate superficial alterations which were not necessarily representative for the subsuperficial WAB and that this methodology could give an insight on the conservation state, beyond visual observations, when combined with reference data

Validation of in situ applicable measuring techniques for analysis of the water adsorption by stone

As the water adsorbing behaviour (WAB) of stone is a key factor for most degradation processes, its analysis is a decisive aspect when monitoring deterioration and past conservation treatments, or when selecting a proper conservation treatment. In this study the performance of various non-destructive methods for measuring the WAB are compared, with the focus on the effect of the variable factors of the methods caused by their specific design. The methods under study are the contact-sponge method (CSM), the Karsten tube (KT) and the Mirowski pipe (MIR). Their performance is compared with the standardized capillary rise method (CR) and the results are analysed in relation to the open porosity of different lithotypes. Furthermore the effect of practical encumbrances which could limit the application of these methods was valuated. It was found that KT and CSM have complementary fields of investigation, where CSM is capable of measuring the initial water uptake of less porous materials with a high precision, while KT was found commodious for measuring longer contact times for more porous lithotypes. MIR showed too many discommodities, leading to unreliable results. To adequately compare the results of the different methods, the size of the contact area appears to be the most influential factor, whereas the contact material and pressure on the surface do not indicate a significant influence on the results. The study of these factors is currently being extended by visualization of the water adsorption process via X-ray and neutron radiography in combination with physico-mathematical models describing the WAB

Comparison of non-destructive techniques for analysis of the water absorbing behavior of stone

Existing non-destructive techniques for analysis of the water absorbing behavior of stone material have a different nature. This leads to discrepancies in practical application and measuring area, resulting in difficulties when comparing results of different methods. The present study focuses on the comparison of different non-destructive methods in terms of practical application, influence of variable factors and accuracy in relation to the open porosity and the capillary rise measurements. The comparison was based on repetitive measurements and X-ray and neutron radiography of the water absorption by lithotypes with a varying open porosity. The methods under study are the Karsten tube (KT), the contact sponge method (CSM) and the Mirowski pipe (MIR). It can be concluded that KT and CSM have complementary fields of investigation, whereas MIR produces unreliable results due to practical discommodities. The most significant variable factor influencing the measurements is the surface of the contact area. A study of analytical models describing the capillary water absorption as reference for interpretation of results of the different methods is currently ongoing

Monitoring frost susceptibility of limestone facies

Limestones are among the most frequently used building stones worldwide. Their frost susceptibility has been assessed in many ways, but due to the large amount of existing limestone types and the natural stone heterogeneity, laboratory testing of the freeze-thaw resistance remains a necessary testing method to predict their behavior when used as a building stone. In this research, the frost susceptibility of some frequently used French building stones from the Oolithe Blanche Formation is assessed indirectly and directly in several ways by laboratory testing. The selected stones have similar components (ooids and bioclasts) but differ in dolomite content and thus porosity distribution, resulting in dissimilar water transport properties. The results of experimental freeze-thaw cycles are coupled to the water absorption by capillarity and the saturation coefficient through water imbibition. Mechanical properties as flexural strength provide additional information. Experiments with neutron radiography and X-ray microtomography allow to visualize the water absorption pathways inside the stones. X-ray allows to visualize and quantify the changes in pore structure and the damage propagation