Martin Boháč

Hydraulic Binder from Hazardous Waste

Since asbestos has been classified as a hazardous chemical, it is desirable to propose a practical and safe procedure for the disposal of asbestos-cement products, or even better to re-use them. In this work, the temperature conditions of degradation of samples of various types of asbestos and products containing asbestos were examined. Samples were burnt at different temperatures and monitored by XRD, DTA, light and electron microscopy. By evaluation of changes at different burning temperatures, the previous findings on the decomposition of asbestos minerals have been confirmed. It has been found that the burning of asbestos cement materials alone or with the addition of limestone at the temperature above 1100 °C leads to the decomposition of hazardous asbestos and, with or without the addition of a setting regulator, hydraulic binder is formed with technological parameters suitable for the building industry.

Non-Destructive and Destructive Monitoring Methods of Fibre Concrete Homogeneity

Design, preparation and testing of fibre-cement composites are a task of wide range of research workplaces and universities in our country and abroad. However, a question on homogeneity of all cement matrix components and mainly optimal dispersion of fibre reinforcement in a mixture has not been yet solved sufficiently. Within testing of properties of such designed composites there is usually a realized fact, that variability of these properties is distinctive mainly for the reason of uneven dispersion of commonly used fibres in a whole matrix volume. Elimination of this phenomenon could be achieved by means of a design of the optimal homogenization process of dry mixture components with fibre reinforcement. The aim of research works was to find suitable homogenization techniques, design of mixing process and optimal dosing of individual components. By means of these actions it is possible to achieve the best dispersion of selected fibre types, both metal and non-metal, in fine-grained cementitious matrixes, which is subsequently verified in hardened composites at first by non-destructive and then by destructive methods. Four different fibre-cement mixtures were chosen as representatives for commonly used reinforcement in fibre-cement composites and test specimens with a thickness of 40 mm were prepared using processes suitable for the specific fibre reinforcement. At the first stage non-destructive testing by means of ultrasound waves was carried out at first on a compact test slab with dimensions 500 x 500 x 40 mm and subsequently on individual test specimens with dimensions 250 x 40 x 40 mm, cut from the test slab according to a designed pattern. At the second stage destructive testing of test specimens was performed, mainly evaluation of flexural strength with 4-point bending and subsequently preparation of thin sections from the failure area for observation by means of polarizing microscopy. A purpose of all these research works is finding of correlation between testing by means of destructive and non-destructive methods.

The Effect of Particle Size Distribution of Lime on Properties of the Autoclaved Calcium Hydrosilicate Materials

This investigation was made to examine how the particle size of lime influence the properties of calcium hydrosilicate materials. Quicklime was sorted in three fractions: 0-1 mm, 1-11.2 mm and 11.2.-22.4 mm. Slaked lime putties were prepared in the laboratory by mixing lime fractions and deionized water under vigorous stirring. The C/H ratio was 1:8. The lime putties were mixed with finely ground sand with the C/S ratio equal to 0.85. The hydrosilicate materials were prepared under hydrothermal conditions: temperature 205 °C, pressure 16 bar. This work focuses on lime putty rheological behaviour and on composition and properties of lime hydrosilicates. It was found that hydrated particles of fractionated lime form smaller aggregates than standard lime. Plasticity increases with the increasing size of fraction. When separate fractions are used, 11.3 Å tobermorite crystallization is slower.

The Role of Temperature on Hydration of Binary System of Metakaolin/Portland Cement

The role of temperature of metakaolin/Portland cement binary system was studied by isothermal calorimetry. Sample with 50 % of metakaolin replacement were monitored at 30 °C, 40 °C, 50 °C and 60 °C. Structural and chemical characterization of hardened pastes was obtained by scanning electron and Raman microscopy. Paper deals with kinetics of main exothermal reactions during early hydration of the system. Activation energies were calculated for processes related to each exothermic peak. The nature of hydration products at different temperatures was revealed by microstructural studies.

Application of Sol-Gel Method to Investigate the Influence of P2O5 on the Course of Reactions in CaO-SiO2 System

The effect of P2O5 addition on the calcium silicate phase equilibrium during the sol-gel synthesis of dicalcium silicate was investigated using Scanning electron microscope and X-ray diffraction. It is established that phosphorous oxide can form solid solution with dicalcium silicate, but its causes the formation of phosphatic calcium silicate phases such as Ca14.92 (PO4)2.35(SiO4)5.65 and 5CaO.SiO2.P2O5 also. Local analysis has demonstrated the presence of calcium phosphate epicenters containing silicon oxide and calcium silicate zones with minimum content of phosphorous oxide and intermediary areas of various phosphatic calcium silicates. The formation of two distinct islets of calcium silicate and calcium phosphate is due to the affinity between acid oxides (SiO2, P2O5) and basic one (CaO) during sol-gel process. Then, the formation of various phosphatic calcium silicates result from the diffusion of P2O5 towards calcium silicate and that of SiO2 towards calcium phosphate.

Rheological and Calorimetric Characterization of the Role of CaCl2 on Portland Cement Early Hydration

Paper describes a new way how to characterize early hydration and setting of Portland cement pastes with various dosages of setting accelerator CaCl2. The aim was not to characterize the role of well-known setting accelerator CaCl2 but to correlate rheology and calorimetry in view of early hydration of Portland cement. Characterization was based on measurements on rotational rheometer, isothermal calorimeter and semiadiabatic calorimeter. The courses of calorimetric exotherms in time were correlated to the development of the phase angle obtained by rheological oscillation tests. Heat flow peaks can be successfully correlated to rheological processes described by change of storage and elastic moduli up to the time that corresponds to the start of the setting which was found to be the limit for rheological tests. The start of the setting on calorimetric curve belongs to the onset point of the main silicate peak during acceleration period of hydration. The value of phase angle decreases as the setting cement paste changes from liquid to solid-like. Times of low values of phase angle ~ 2.5 (°) can be related to times of onset points of main peak for every dosage of setting accelerator.

Evaluation of P{sub 2}O{sub 5} distribution inside the main clinker minerals by the application of EPMA method

The formation of Portland clinker phases has taken place in thermodynamically non-equilibrium state between macro-oxides CaO, SiO{sub 2}, Al{sub 2}O{sub 3}, Fe{sub 2}O{sub 3} and MgO from raw meal and P{sub 2}O{sub 5} from bone meal. The paper deals with the study of clinker minerals as solid solutions with P{sub 2}O{sub 5} during the clinkerization of raw mixture containing bone meal (BM). The ash of BM has contributed as a raw material to the formation of different clinker phases. Electron probe microanalysis (EPMA) method was used to determine the preferential distribution of P{sub 2}O{sub 5} inside calcium silicate phases and its influence upon C{sub 2}S/C{sub 3}S ratio. Basing on these results, composition of solid solution of C{sub 2}S and C{sub 3}S was established.