BRJ – Volume 58, Number 3, 2010

Editorial . . . . . . . . . . . . . 137–138

Ľubomír Bágeľ, Martin T. Palou:
Cement composites under hydrothermal load. Effect of prolonged autoclaving on the pore
structure alterations . . . . 139–156

Martin T. Palou, Vladimír Živica, Marta Kullifayová:
Thermal and microstructure analysis of fibre reinforced binder composites cured in autoclave. . 157–173

Vladimír Živica:
Sulphate attack – possible danger for cementing material in the boreholes . . . . . . . . . . . . . . . 175–185

Vladimír Živica, Ľubomír, Bágeľ, Marta Kullifayová:
High strength alkali-activated slag paste . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187–197

Abstracts

Cement composites under hydrothermal load
Effect of prolonged autoclaving on the pore structure alterations

Ľubomír Bágeľ, Martin T. Palou

Cement-based materials are dominantly used for cementing the oil, gas and geothermal wells. In any case, durability of the cement-based materials placed into the wells is of considerable importance. Thus many formulations have been suggested for these targets, however, studies which have been presented on the pore structure alteration as the demonstration of material degradation under severe hydrothermal conditions are still missing. Samples of three different mixtures on the binding systems of OPC /HAC /SF and HAC /sodium polyphosphate HAC /sodium phosphate/SF were autoclaved under hydrothermal conditions (pressure of 20 bar) for the duration from 24 to 168 hours to study the effect of curing time on the alteration of the pore structure and density. Compressive strength was also reviewed in connection with the pastes porosity. It was turned up that the time of autoclaving plays a crucial role in the objective assessment of the durability of the composites as candidates for geothermal applications.

Keywords: geothermal cement, hydrothermal curing, autoclave, pressure, pore structure, mercury intrusion porosimetry (MIP), density

Thermal and microstructure analysis of fibre reinforced binder composites cured in autoclave

Martin T. Palou, Vladimír Živica, Marta Kullifayová

Four fiber-reinforced cement composites were prepared and cured in autoclave up to 7 days at 20 bars. Thermal analysis method was used to identify different temperature ranges of thermal decomposition of cured samples and to characterize the nature of hydrate products. Also, fractured surface and surface microstructure were investigated by means of SEM . Two kinds of products are formed. The first ones consists of ordinary hydration products like CSH , CSAH , CAH and calcium carbonate as a product of carbonation. The second ones are the products chemically bound like in ceramics as hydroxyapatite and gibbsite. These two hydroceramic products formed under hydrothermal conditions act also as binder and could be useful as geothermal cement binders.

Keywords: geothermy, autoclave, hydrate products, hydroceramics, thermal analysis, microstructure

Sulphate attack – possible danger for cementing material in the boreholes

Vladimír Živica

The results of the study on the sulphate resistance of the slag cement activated by sodium hydroxide and a new silica fume activator and its comparison with ordinary Portland cement are the subject of the paper. An excellent sulphate resistance of alkali activated slag cement has been found, especially when silica fume activator was used. The slag cements seem to be promising binder for the cementing materials assigned to a boreholes application not only for their high sulphate resistance but also for their high acidic resistance. In the borehole waters a common presence of acidic and sulphate species is very frequent and the danger of combined attack of the cementing materials is relevant. Therefore, the resistance of cementing material to the both kinds of aggressiveness against cement is very important.

Keywords: slag, alkali activation, sulphate attack, sodium hydroxide, silica fume Activator

High strength alkali-activated slag paste

Vladimír Živica, Ľubomír, Bágeľ, Marta Kullifayová

In the paper the results of the study on the co-effect of a very low liquid/solid (l/s) ratio and pressure compaction at alkali-activated slag paste are presented. A significant compressive strength increase effect has been found, reaching 215 % or 150 MPa respectively. It has been found that this positive effect was based on a significant modification of the pore structure. The dense structure with a higher degree of its homogeneity, based on the formation of the finer hydration products was a consequence. The studied approach seems to be a very prospective way for the preparation of slag composite materials as an alternative for the replacement of the ceramic, metal or organic materials in some areas.

Keywords: slag, alkali activation, pressure compaction, compressive strength, pore structure