Magdaléna Doleželová

Temperature resistance of the ternary gypsum-based binder with microsilica

The influence of high temperatures on the ternary gypsum materials with microsilica is described in the paper. The ternary samples, prepared from gypsum, lime and microsilica and samples without pozzolan admixture were exposed to temperatures from 50 °C to 1000 °C and their mechanical properties were investigated. The visual comparison and the comparison of mechanical properties of ternary samples and samples without microsilica were carried out. The mixtures with microsilica resisted better to the high temperatures than the samples without microsilica, although the resistance of both materials against the high temperature was not very good.

Evaluation of Fine Aggregate Surface and Fracture Surface by Confocal Microscope

The gypsum mortars with different types of aggregate were studied. The surface roughness of fine aggregates and the fracture surface roughness were evaluated by a confocal laser scanning microscopy. Four gypsum mortars and one gypsum paste were tested. The results from the confocal laser scanning microscopy (CLSM) are compared with the pictures of grain surface taken by a scanning electron microscopy (SEM) and both methods seem to be appropriate for surface evaluation. The influence of the surface aggregate roughness on some gypsum mortar properties is demonstrated.

Influence of weather-affected material characteristics on appearance of freeze/thaw cycles in building envelopes

The possible appearance of freeze/thaw cycles in external wall made of selected building material is assessed within this paper. Main objective of the presented research is to investigate the influence of weather-affected material characteristics on that phenomenon. For this sake, the samples were exposed to long-term weathering while the material characteristics were determined in the beginning of the experiment and then after two and three years. The comparative simulations of coupled heat and moisture transport inside the wall when exposed to dynamic climatic conditions were subsequently performed using reference and weather affected data. The results revealed that hygric parameters of the material, in particular, got worse which led also to deterioration of hygrothermal performance of the studied construction. The time of wetness under the external surface was twice as high when weather-affected data had been assumed. The number of possible freeze/thaw cycles was higher as well.

Moisture influence on compressive strength of ternary gypsum-based binders

The environmental influence on the ternary gypsum-based binders is described in the paper. The ternary mixtures were composed from gypsum, lime and pozzolan. The crushed ceramic, microsilica and granulated blast slag were selected as representatives of pozzolan. Changes of compressive strength were investigated according to the method of storing and treatment before the test. Samples with microsilica have the best results of compressive strength from all tested mixtures when stored in the water and tested in moist state.

Porosity of the Ternary Gypsum-Based Binders with Different Types of Pozzolan

Ternary gypsum-binders with different types of pozzolan were stored in the water and in the air. Brick powder, microsilica and blast slag were used as a pozzolan admixture. The quantity of the pozzolan in the mixture was determined from the amount of the amorphous phase in the pozzolan. Mixtures with pozzolans do not lose strength when stored in the water. Porosimetry shows that the product of the pozzolanic reaction started to develop.

Moisture Resistance and Durability of the Ternary Gypsum-Based Binders

The moisture resistance of the ternary gypsum-based materials with metakaolin was investigated. Materials with metakaolin have lower porosity and higher strength than gypsum-lime binder without metakaolin. While material without metakaolin lost compressive strength in the wet environment, the strength of the ternary binders increased. Therefore it can be concluded that the gypsum – lime mixtures with the metakaolin can be used in the environment with higher humidity, e.g. in the exterior.

Porous Structure and Hygric Properties of Concrete for Radioactive Waste Repositories

The paper presents the evaluation of the influence of supplementary materials on the porous structure and hygric properties of concrete for waste repositories. The used supplementary materials were natural zeolite, brick dust and metashale. Studied parameters were basic physical properties, distribution curves of pores obtained by mercury intrusion porosimetry and water absorption coefficient. Obtained results revealed worse behaviour of natural zeolite compared to brick dust and metashale, as there was significant rise in open porosities when higher amount of the material was added as well as rise in absorption coefficient.

Microstructure and Pore Systems Development of Ternary Gypsum-Based Mortars

Paper deals with ternary gypsum-based mortars with higher resistance against water, prepared from gypsum, hydrated lime, several pozzolans (crushed ceramic, silica fume, granulated blast slag) and sand. The samples were stored in the water and the pore systems development in time was studied by mercury intrusion porosimetry. The change of pore structure in samples with pozzolans were observed, the size of pores shifted to the smaller pores during tested period. The elementary composition and microstructure of all materials were also studied by scanning electron microscopy (SEM).

Time evolution of pore system in lime - Pozzolana composites

The lime – pozzolana mortars and plasters are used in restoration works on building cultural heritage but these materials are also following the trend of energy – efficient solutions in civil engineering. Porosity and pore size distribution is one of crucial parameters influencing engineering properties of porous materials. The pore size distribution of lime based system is changing in time due to chemical processes occurring in the material. The present paper describes time evolution of pore system in lime – pozzolana composites; the obtained results are useful in prediction of performance of lime – pozzolana systems in building structures.The lime – pozzolana mortars and plasters are used in restoration works on building cultural heritage but these materials are also following the trend of energy – efficient solutions in civil engineering. Porosity and pore size distribution is one of crucial parameters influencing engineering properties of porous materials. The pore size distribution of lime based system is changing in time due to chemical processes occurring in the material. The present paper describes time evolution of pore system in lime – pozzolana composites; the obtained results are useful in prediction of performance of lime – pozzolana systems in building structures.

Optimization of the gypsum-based materials by the sequential simplex method

The application of the sequential simplex optimization method for the design of gypsum based materials is described. The principles of simplex method are explained and several examples of the method usage for the optimization of lightweight gypsum and ternary gypsum based materials are given. By this method lightweight gypsum based materials with desired properties and ternary gypsum based material with higher strength (16 MPa) were successfully developed. Simplex method is a useful tool for optimizing of gypsum based materials, but the objective of the optimization has to be formulated appropriately.