Global invertibility theorems and their applications - a variational approach

This book is concerned with deriving abstract tools which are applicable in solving integro-differential equations posed in a Banach space setting. Our approach relies on deriving conditions which guarantee that certain mapping acting between two Banach spaces is a diffeomorphim thereby obtaining that if this mapping is a solution operator to some equation then this very equation has a unique solution which in fact is well posed in the sense of Hadamard.(...

numerical model of the alkali silica reaction development with external source of alkalis

Abstract Experimental research, in which mortars prepared with reactive aggregates have been exposed to different conditions, has been performed. The samples have been stored in water or 1 M NaOH water solution at 80 °C. Based on the observed strains, ASR extent has been calculated. Mathematical model of combined action of hygro-thermal, chemical and mechanical phenomena has been developed to analyze evolution of the ASR reaction. It is based on mechanics of multiphase porous media. Development of the ASR depends on the alkali content. Diffusion of alkalis from the cement paste to the aggregate grains is considered. Both external alkali sources and alkali binding by the formed ASR gel are taken into account. The proposed mathematical model has been validated by comparison with the experimental results

Effect of Internal Hydrophobization on the Properties of Porous, Cementitious Materials

Water is one of the main factors affecting the durability of porous materials and it is one of the most common causes of their degradation. Physical phenomena such as freezing or salt crystallization, as well as the development of fungi and moulds, are caused by the presence of moisture. In wet material thermal conductivity coefficient increases and the heat loss begins to rise. Hydrophobization is one of the protecting methods of porous materials against water. Two different type of water-repellent agents were used for the internal hydrophobization. The first of them is an aqueous emulsion of silane: triethoxy(octyl)silane (OTES) and the second one is also an aqueous emulsion but the matrix is poly(dimethylsiloxane) (PDMS). The paper focuses on the use of organosilicon water repellents. The main purpose of this paper is to determinate the possibility of use organosilicon agents as admixtures to internal hydrophobization. We compared results obtained for two different silicon-based admixtures. We investigated influence of both water-repellents on basic characteristics such as: absorbability, capillary water absorption and mechanical properties of cement mortar as well as heat of hydration of cement paste

Ice-induced Damage of Cement Based Composites – Experimental and Numerical Study

AbstractThe paper considers water solidification in porous materials. Mathematical model describing heat and water transport in deformable porous materials considering the kinetics of water phase change was proposed. The crystallization pressure was determine using the volume averaged Everett's equation. The ice-induced destruction of concrete was modeled by means of the delayed damage approach. The numerical code was developed using finite element, finite difference and Newton-Raphson methods

Stochastic Finite Element Method for Modelling Heat Transfer in the Building Envelope

Improving the energy efficiency of the buildings is one of the most effective and fastest ways of reduction of the carbon dioxide emission. However, in the assessment of the energy demand of the buildings, numerous factors are uncertain, i.e. layer thickness, material parameters, climatic conditions, etc. In the present study, mathematical model was developed for analyzing temperature distribution and heat flux in the wall with thermal conductivity of insulation as a random parameter. The results obtained employing a stochastic perturbation technique were compared against the results of the Monte Carlo simulation. Stochastic perturbation technique has been implemented using the tenth order Taylor series expansion. The direct differential method was used to determine the values of Taylor’s coefficient. The obtained results indicate good accordance of the stochastic perturbation technique with the Monte Carlo method. Afterwards, the expected value of the heat flux and its variance were studied for the reference year for a city in the Central Europe. Two cases of the external wall were investigated, in which the thermal insulation was localized either on the internal or the external side of the wall. Performed analyses serve as a good method for assessing the reliability of results obtained using standard, deterministic approach

The influence of type of cement on the degradation of microstructure and transport properties of cement mortars exposed to frost induced damage

The purpose of the study is to understand how the cyclic water freezing (0, 25, 50, 75, 100 and 150 freeze-thaw cycles) impacts microstructure and transport properties of cement-based materials. Tests were conducted on cement mortars with different water/cement ratios (w/c=0.45 and 0.40) and on two types of cement (CEM I and CEM III) without air-entraining admixtures. The changes of pore size distribution and open porosity were investigated by means of mercury intrusion porosimetry. Additionally, the relationship between intrinsic permeability and the water absorption coefficient of cement mortar samples was analysed. The water absorption coefficient and gas permeability were determined using capillary absorption test and the modified RILEMCembureau method. The evolution of transport coefficients with growing number of freeze-thaw cycles were determined on the same sample. It was also established that change of pore structure (a decrease of small pore volume 100nm) induces an increase of water transport parameters such as permeability and water absorption coefficient. The higher gas permeability corresponds to the higher internal damage. In particular, it is associated with the change of cement mortar microstructure, which indicates damage of narrow channels in the pore structure of cement mortars

Thermal analysis of water confined in fully and partially saturated cement paste

The main object of the presented research is to apply thermal analysis in order to investigate microstructure of hardened cement paste. The test is conducted by means of differential scanning calorimetry on samples stored in various relative humidity levels as well as the fully saturated ones. The obtained results describe water solidification beginning at several different temperatures, which implies complex nature of cement paste microstructure. The recorded thermograms consist of two main peaks, which clearly indicate the division into capillary and gel pores. Additionally, the thermodynamic properties of actual pore solution confined in cement matrix are investigated. The obtained results indicate ions present in the liquid strongly affects its phase transition temperature as well as amount of ice formed during such the phase change

Influence of the Thermal Conductivity and Ambient Temperature Uncertainty on the Heat Losses through the External Wall

Numerous parameters assumed in the calculations of the buildings’ energy demand are uncertain. Therefore, calculations should be accompanied by determination of propagation of such uncertainties in the mathematical model. In the article, the influence of uncertainty of thermal conductivity and ambient temperature has been studied by means of the generalized perturbation stochastic finite element method and compared against the Monte Carlo results, indicating good accordance. Expected value and variance of heat flux on the internal side of the wall have been investigated. The perturbation stochastic finite element method is much more efficient than the Monte Carlo method for the analysed problem. The largest variance of temperature is noted in the node between the constructive layer and insulation

Internal hydrophobization of cementitious materials by using of organosilicon compounds

The low resistance to harmful acting of water confined in porous, cement-based materials is a negative feature. As the consequence of porous structure these materials have not sufficient resistance as some physical and chemical detrimental factors. The objective of this paper was to evaluate the impact of organosilicon admixture based on silane and siloxane on physical properties of cement mortar. Internal hydrophobization can significantly improve the durability of a cement materials. At this paper the results of mechanical strength, absorbability and capillary water absorption of internally hydrophobized cement mortar are presented. In addition, a contact angle test was used to assess the changes in wetting angle of cement paste