One of the current trends in the production of new building materials and in civil engineering as a whole is the effective use of building materials with high-quality functional properties, which leads to the ever-increasing requirements for the quality of these materials. Particularly in modern, low-energy and passive buildings, the emphasis is put on their thermal technical properties.
An important parameter monitored in connection to the energy performance of currently being built and already existing buildings is the thermal insulating capacity of the building materials used. This is often lowered due to the presence of moisture inside the construction. Moisture can get into buildings in different ways, most often in the form of storm water or rising damp, but also through the diffusion of water vapour or condensation. The content of moisture in building materials and rate of the spread of moisture in building structures are important criteria which are used in thermal and technical calculations as input parameters and which predict possible degradation of both the material used and the structure as a whole.
The coefficient of capillary conductivity for different materials can be found e.g. in tables, where it is often stated in empirical values, mostly with considerable imprecision. The parameters of building materials can also be found using a gravimetric method, which is a destructive method, however. Moreover, it provides only a limited amount of necessary data and is affected by the imprecision of measurement results caused by handling the measured sample.
Doc. Jan Škramlik and his research team at the BUT Faculty of Civil Engineering have managed to develop a new and more exact method of measuring the moisture parameters of building materials using a new device which enables these important characteristics of building materials to be effectively monitored and measured.
The apparatus for measuring the moisture parameters of porous building materials (see Fig. 1) uses for its task electromagnetic microwave radiation and enables precise, repeatable and human error-free determination of the capillary conductivity coefficient and its relation to the mass moisture of various materials. Just the determined capillary conductivity coefficient is a significant characteristic which predicts the rate of the spreading of water in the capillary system of the building material, and stands up as the basic parameter.
Fig. 1: Newly assembled measuring apparatus
Relé pro spínání záření - Relay for radiation switching, závitová tyč - thread pole, vodicí lišty - guiderails, váha - scales, rám váhy - scales frame, závěs vzorku - sample hanger, uchycení vzorku - sample fixation, měřený vzorek - measured sample, motor - engine, vlnovody - waveguides, nádoba - vessel, voda - water
The device solves the issue of how to receive input data for the numerical evaluation of moisture parameters based on experimentally measuring the spread of moisture of a particular material sample. The advantage of this method of measurement is that it is not destructive for the sample and repeated measurements can be made in different phases of moistening in a non-stationary state, with an option to programme the course of measurement in order to determine the capillary conductivity coefficient. Measurement outputs are recorded using a PC and are processed by a specially designed computer programme. For detecting moisture contained in a sample of the monitored material an electromagnetic microwave radiation is used. The measurement output is a graphic distribution of moisture in 3 dimensions and the functional relation of the capillary conductivity coefficient to the mass moisture (see the title figure - Depiction of the resulting matrix for a three-dimensional image of the spread of moisture in the monitored material sample based on single measurements).
The non-destructive method used by this newly invented device enables the acquisition of any frequency of particular outputs (in profiles of a material sample approx. every 3 mm), while at the same time it eliminates the imprecision of measurement results caused by handling the sample. Measurement results are continually scanned and saved electronically without human error, so it is also possible to use an integral method to determine the capillary conductivity coefficient, a method which is based on the use of several moistening curves for one monitored material sample.
The objective for measuring using the reported device is to discover, by the non-destructive method of the moistening curve, and then determine, according to the known laws of physics, the moisture gradient, the capillary conductivity coefficient and evaluate its functional dependence on the moisture contained in one and the same material sample at various time intervals from the beginning of moistening.
The multifunctionality of the presented device is expressed in part by the fact that its use is not limited to the field of porous building materials for civil engineering. As pointed out by Doc. Škramlik, the device inventor, the measuring apparatus can be also used in geological surveys for detecting and describing the spread of moisture in soil layers. The uniqueness of the measuring apparatus invented by Doc. Škramlik is now protected for BUT by being registered as a utility model at the Industrial Property Office in Prague. The Czech and international patent is also pending. Doc. Škramlik’s further aim is to press for the inclusion of this newly invented way of measuring moisture parameters within the standard principles of practical use in civil engineering by incorporating it into directives, regulations, and standards.
Doc. Ing. Jan Škramlik, Ph.D. has been working at the Faculty of Civil Engineering, Brno University of Technology, since 1989 as a lecturer in the Institute of Building Structures, where he specializes in designing new buildings as well as their rehabilitation and reconstruction. He is also Deputy Head of the Institute of Building Structures. In his experiments, Doc. Škramlik engages in basic research to describe liquid moisture transport in the materials of building structures.
