Eva Navrátilová

Application of a-SiO2 Rich Additives in Cement Paste

The effect of a-SiO2 of various origin on the properties of cement paste with incorporated different silica containing materials is experimentally studied in the paper. For the applied a-SiO2 materials, basic physical and chemical properties are accessed, together with their chemical composition. Amount of amorphous phase of SiO2 in particular siliceous materials is determined using XRD analysis. Matrix density, bulk density, total open porosity, compressive and bending strength are measured for all developed pastes with incorporated a-SiO2 containing materials, together with initial and final setting time of fresh mixtures. The obtained data give evidence on a high and fast reaction activity of tested siliceous materials which results in a significant improvement of porosity and mechanical strength of a-SiO2 modified cement pastes.

Effect of the preparation of lime putties on their properties

In the study of lime as the basic component of historical mortars and plasters, four lime putties prepared from various kinds of lime of various granulometry and by various ways of preparation were evaluated. The rheological properties and micro-morphologic changes, growing of calcite crystals, and rate of carbonation were monitored. The lime putty prepared from lump lime achieves the best rheological properties, yield stress 214.7 Pa and plastic viscosity 2.6 Pa·s. The suitability of this lime putty was checked by testing the development of calcium hydroxide and calcite crystals using scanning electron microscopy and environmental scanning electron microscopy. The disordered crystals of calcium hydroxide exhibit better carbonation resulting in the large crystals of calcite; therefore, the mortar prepared from the lump lime has the highest flexural strength and compressive strength 0.8/2.5 MPa, its carbonation is the fastest and exhibits the longest durability. Also, thanks to the micro-morphological characterization of samples in their native state by means of environmental scanning electron microscopy, the new way of lime putty preparation by mixing was proven. The preparation consists in the mechanical crash of the lime particles immediately after hydration. This enables the properties of putty prepared from lump lime to be nearly reached.

Study of Morphological Changes of The Lime Putties During Maturing by SEM/ESEM

The lime putty belonged in the past to the traditional materials with a wide application in the construction. It used to be prepared from a stone lime and it featured with good workability, plasticity, and durability. The traditional preparation of the lime putty was replaced by the modern chemicaltechnological processes. The lime putty is essential for the restoration of the historic plaster, wall painting, sgraffito etc. Lime putty is obtained by hydration of calcined limestone in an excess of water according to the following equation [1, 2, 3, 4]: CaO + H2O → Ca(OH)2 + 65 kJ·mol-1.

Dynamical In Situ Study of Morphological Changes of Bentonite in ESEM

The bentonite has a variety of industrial applications. It is used as a stabilizing and suspending agent, an adsorbent and clarifying agent, a buffer material for barriers in geological disposal facilities for radioactive waste, liners for remediation of contaminated soils and ponds. Characterization of the morphological changes of the bentonite during the process of swelling and shrinkage is very important for these applications [1-3]. The environmental scanning electron microscope (ESEM) allows observation under the water vapour pressure from units to thousands of Pa and at a selected temperature from -20 ° C to 1500 ° C. Moreover, these samples do not have to be treated, namely dried and covered with the conductive metal layer [1, 4]. ESEM is also very effective for in-situ investigation of bentonites, which can be realised under dynamically changing relative humidity (RH).

Characterization of Burnt Clays by X-ray Diffraction Analysis, Chemical Analysis and Environmental Scanning Electron Microscopy

Clays are mixtures of clay minerals (kaolinite, illite, montmorillonite and others) that are hydrated aluminosilicates from the chemical point of view. The clays also contain quartz, calcite, feldspars, micas, anatase and sulfides. The clay minerals are crystalline substances with a layered structure in which layers of SiO4 tetrahedrons and AlO6 octahedrons alternate [1]. Heat treatment (600 to 900 ° C) leads to dehydroxylation of clay minerals and the creation of the amorphous phases which are reactive and the calcined clays obtain pozzolanic activity [2-4]. The pozzolanic activity is an ability of pozzolans (silicate or aluminosilicate substances which themselves possess no binding ability) to react in the presence of water at normal temperature with calcium hydroxide to form hydration products. It can be determined as the amount of calcium oxide which is consumed in the reaction with pozzolan and by the reaction kinetics of the reaction [2, 5, 6]. The pozzolanic activity of the burnt clays is dependent on the content of amorphous phase. The pozzolanic activity increases with increasing amorphous phase content in the burnt clays. It significantly enhances the strength of modified lime mortars [7].

Reactivity of Brick Powder in Lime Mortars

The article deals with the assessment of three brick powders. Their properties are evaluated on the basis of their pozzolanic activity, specific surface area and amorphous area. The brick powders were used in amounts of 20 and 40% as a substitute for binder in lime mortars. The influence of the powders on the properties of the modified plasters in a hardened state was evaluated via the determination of strength characteristics. It was found that not all brick powders are suitable for use in modified lime mortars.