An assessment of the service life of exterior renders of building structures using combined computational-experimental approach is presented in the paper. In the experimental part, durability of selected renders and concretes is determined in terms of their frost resistance. A diffusion-type model is used for the description of coupled heat and moisture transport aimed at the identification of the number of frost cycles in a real structure. The computational implementation of the model leads to a system of two non-linear partial differential equations with the moisture accumulation function as additional condition. In a practical application of the model, a concrete wall provided with exterior thermal insulation system and both exterior and interior renders is analyzed. The influence of different material composition of building envelope in the service life of exterior renders is analyzed to meet the main objective of the paper. Different types of concrete, thermal insulation materials and renders are under consideration. Conclusions on the most advantageous material composition with respect to the service life of exterior renders are drawn.
Computational modeling of coupled heat and moisture transport in porous building materials with hysteretic moisture transport and storage parameters in the conditions of difference climate is presented in the paper. A diffusion-type model is used for the description of coupled heat and moisture transport. An empirical procedure is chosen to describe the path between the transport and storage parameters corresponding to wetting and drying. In a practical example of computer simulation, a concrete wall provided with exterior thermal insulation is analyzed. Computational results reveal very significant differences in moisture and relative humidity profiles calculated using the model with hysteretic parameters and without hysteresis. As the differences are on dangerous side from the hygrothermal point of view, the application of hysteretic moisture transport and storage parameters in computational models can be considered as quite important for service life analyses of multi-layered systems of building materials.
A climatic database for computational service life assessments of historical buildings is presented. It is suitable for application in most current computational models of heat, moisture and salt transport. The included data were gathered from the authorized institute (CHMI) and the structure is expandable to other sources of weather observations, even in-situ measurements. Therefore, it can be used in designs aimed at the renovation of historical buildings on the territory of Czech Republic. The database is devised as an open system so that it can be extended in an arbitrary way, e.g., more sophisticated statistics or converting tool can be added. It also provides an easy-accessible and user-friendly interface for raw climatic data or long-time collected data important for service life assessments.
A combined experimental-computational approach is applied for the estimation of service life of innovative renovation renders. In the experimental part, the durability of two commercial renovation renders is determined in terms of their frost resistance, together with two newly developed renovation plasters that are supposed to be produced commercially in the near future. The computational part is aimed at the investigation of freeze-thaw cycles that may occur in surface layers of the plaster during its life time period. To achieve this, a diffusion type model of coupled heat and moisture transport is used. As a load-bearing structure several materials which are characteristic for historical buildings are chosen, namely ceramic brick, sandstone and arenaceous marl.
Computational simulation of salt transport and crystallization in limestone depending on the presence of crystallization inhibitor in the dissolved salt is presented. The diffusion-advection model is used for the basic description of coupled water and salt transport, taking into account both water movement due to the moisture gradient and diffusion and dispersion effects within the liquid phase due to the concentration gradient. Salt crystallization in the porous body is modelled using an equilibrium model, taking into account the effect of crystallization inhibition. The effect of salt bonding on the pore walls is taken into account as well. The results of numerical simulations using a well calibrated computational model give evidence that in the analyzed case the use of crystallization inhibitors leads to the slowing down of both water and salt transport.
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