Moisture impact on building rocks - the laboratory and in situ investigations

1. water diffusion capillary transport Rain Frost rb 24,8 Ground water 24,6 End of heating Temperature [°C] 24,4 Start of heating Tm 24,2 R 24,0 23,8 Base line 23,6 0 100 200 300 400 500 Time [sec] capillary transport integral moisture local moisture gradually saturation Mechanism sustaining a constant water level Moisture impact on building rocks -the laboratory andin situ investigations FIDRÍKOVÁ D., KUBIČÁR Ľ. Institute of Physics SAS, Bratislava, Slovakia The work was supported by the project APVV LPP–0442–09 Goal:Rocks are influenced by moisture that in combination with temperature, hydrological conditions, climatic conditions, etc. leads to changes of physical and chemical properties. These changes can be observed in the laboratory, where different conditions can be simulated in which the rocks can be found. This work is focused on water transport and moisture determination in various sandstones observed in laboratory conditions and also directly in environment. Porosity affects transport properties of rocks. Experiments are focused on the mechanism distributing the water in sandstones with different porosities. Measurements were carried out by thermal conductivity sensors (Hot-ball sensor) which measure local temperature and local thermal conductivity. The sensor in connection with the RTM device is used for monitoring of the moisture in various sandstones with different porosity. For in situ measurements a moisture sensor is constructed. The sensor is made of the original stone in a form of the cylinder (diameter and length around 20 mm) in which thermal conductivity sensor is placed. The moisture sensor must be calibrated for dry and water saturated state, and then it is inserted into the original site to start monitoring of the impact of surrounding weather conditions on the rock. Meteorological data are correlated to the measured data. Results from water transport and change of moisture in sandstones at various monitoring conditions are presented. Moisture impact to building rocks: Principle of Hot-ball method:A heat source in the form of ball delivers constant heat flux for t > 0 to the medium and simultaneously the ball surface temperature is measured. Heat flux is in the form of a step-wise function. The stabilized value of temperature Tm is measure and from the parameters of the temperature response the thermophysical parameters can be calculated, according to the model used. Temperature function: • Moistureaffects the life of building materials and reduced the weathering resistance, so it´s very important to determine of water content in a material in dependence on surrounding conditions Initial and boundary conditions: q = const, t>0, r = rb approximation • Moisture goes into the material: • by capillary transport • by water diffusion • freezing the wall Working relation: t→ ∞ , T = Tm at r = rb Working regime: steady state Thermal conductivity sensor (Hot-ball sensor) The laboratory monitoring of moisture In situ monitoring of moisture in St. JacobChurch in Levoča, Slovakia • CONCLUSIONS: • Hot-ball sensor (thermal conductivity sensor) allows investigation of processes • running in pores that depend on various conditions • The structure of porous materials the most affects moisture transport in • samples • Moisture monitoring in porous stones gives a information about • deterioration of building and other industrial objects • Change of material stability in laboratory by cycles freezing-thawing, • moisture-drying can be studied • By cycles of temperature and humidity we are able to simulate behaviour of • material in laboratory devices • By means of above described cycles we are able to predict behavior in • material during day-night, summer-winter and in dry-wet enviroment • Hot-Ball method is advantageous for continuous monitoring changes of • moisture in rock massive and in historical monuments and for other • applications (monitoring of concrete setting, monitoring of polymerization, • monitoring of structure transformation in pores, material ageing) • Other monitoring by Hot-ball probe: • Spis Castle • St. Martin's Cathedral in Bratislava, Slovakia • Pravčicka gate in Czech republic