Alena Vimmrová

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.

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.

A Method for Optimizing Lightweight-Gypsum Design Based on Sequential Measurements of Physical Parameters

Abstract A method for lightweight-gypsum material design using waste stone dust as the foaming agent is described. The main objective is to reach several physical properties which are inversely related in a certain way. Therefore, a linear optimization method is applied to handle this task systematically. The optimization process is based on sequential measurement of physical properties. The results are subsequently point-awarded according to a complex point criterion and new composition is proposed. After 17 trials the final mixture is obtained, having the bulk density equal to (586 ± 19) kg/m3 and compressive strength (1.10 ± 0.07) MPa. According to a detailed comparative analysis with reference gypsum, the newly developed material can be used as excellent thermally insulating interior plaster with the thermal conductivity of (0.082 ± 0.005) W/(m·K). In addition, its practical application can bring substantial economic and environmental benefits as the material contains 25 % of waste stone dust.

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.

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).

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.

Lightweight Gypsum Based Materials: Methods Of Preparation And Utilization

Although gypsum is one of the most environmentally friendly building binders, its use in the buildings is relatively limited and therefore the broadening of the gypsum product portfolio is desirable. One possibility is the development of the lightweight gypsum materials with better thermal insulation properties, attractive acoustic properties and also lower transportation costs. The lightweight gypsum materials can be used in a similar way as an aerated autoclaved concrete (AAC), whose energy consumption at production is several times higher. The main methods of the preparation of gypsum-based lightweight materials are described and compared. Gypsum can be lightened indirectly by the lightweight filler or directly. In the directly lightened materials, the pores are introduced into the gypsum material either by some chemical reaction producing gas or by the help of surface active substances. For the chemical lightening a large scale of waste products can be used. Lightening by the help of waste stone powder is described in detail. The materials with the properties comparable with the properties of AAC were prepared. Their bulk density was under 600 kg/m3, compressive strength was about 2 MPa and coefficient of thermal conductivity was under 0.2 W/m.K. Lightweight gypsum materials can be used as a thermal insulating blocks, for the lightweight gypsum boards, partitions blocks, lightweight fire-resistant plasters or thermal-insulating plasters.

Behavior of gypsum-based mortars with silica fume at high temperatures

The influence of high temperatures on the ternary and binary gypsum-based mortars is described. The gypsum-based mortar with ternary binder, composed from gypsum, hydrated lime and silica fume and mortar with binary binder, composed from gypsum and hydrated lime only were exposed to the temperatures from 50°C to 1000°C and their physical and mechanical properties were investigated. The comparison of ternary mortars and mortars without silica fume was carried out. The results were also compared with the results obtained from previous testing of gypsum-based pastes without sand. It was found, that gypsum-based mortars have better stability than gypsum-based materials without sand. Ternary materials have better volume stability than materials without pozzolan (about 5 % at 1000 °C).