Vladimír Živica

Relationship between pore structure and permeability of hardened cement mortars: On the choice of effective pore structure parameter

An experimental study has been performed with the aim of quantifying pore structures systems of cement mortars and correlating them with water permeability. A new pore structure parameter has been found to predict the permeabilities of mortars with an acceptable accuracy. A reasonably close correlation was found between the structural parameter and the permeability if the relevant pore size range was incorporated into the functional equation which expresses the relation between the pore structure and permeability.

Silica fume-basic blast furnace slag systems activated by an alkali silica fume activator

This paper deals with the results of research on binder systems based on the use of silica fume. The data obtained show that the optimal proportion of blast furnace slag and alkali activator prepared from silica fume permits the obtaining of interesting materials from the point of view of their technical properties as well as from the possibility of utilizing industrial wastes. The composite developed is hydraulic. It is possible to state that these kinds of binding systems have shown promise of future use.

High effective silica fume alkali activator

Growing demands on the engineering properties of cement based materials and the urgency to decrease unsuitable ecologic impact of Portland cement manufacturing represent significant motivation for the development of new cement corresponding to these aspects. One category represents prospective alkali activated cements. A significant factor influencing their properties is alkali activator used. In this paper we present a new high effective alkali activator prepared from silica fume and its effectiveness. According to the results obtained this activator seems to be more effective than currently used activators like natrium hydroxide, natrium carbonate, and water glass.

Properties of blended sulfoaluminate belite cement

Abstract The subject of the study was the possibility of the blending of sulfoaluminate belite (SAB) cement by means of various pozzolanas. The results obtained show that it was possible effectively to modify the properties of SAB cement by means of granulated blast furnace slag, fly ash, and silica fume, and the properties of materials based on these blends. Interesting properties from practical viewpoints of these materials was their compressive strength. As it is very well known, this is by the blending used to decrease. From a viewpoint of the acceptable compressive strength decrease, for SAB cement blends well-found portions of pozzolana with the values of approximately 5–15% seem to be optimal. This range was significantly lower than well-found portions of pozzolanas with values of approximately 20–40% for Ordinary Portland Cement (OPC) blends. The main cause was the fact that unique sources of calcium hydroxide needed for pozzolanic reaction in SAB was only β–C2S compared to OPC having two sources of calcium hydroxide — the hydration of C3S and β–C2S. Therefore, the amount of calcium hydroxide for the pozzolanic reaction in the SAB cement blends was significantly lower. That was why the lower portions of pozzolanas in SAB cement blends were suitable.

SIGNIFICANCE OF THE AMBIENT TEMPERATURE AND THE STEEL MATERIAL IN THE PROCESS OF CONCRETE REINFORCEMENT CORROSION

Abstract According to the results obtained, the ambient temperature and the steel material of concrete reinforcement represent significant factors of its corrosion rate and corrosion sensitivity under chloride induced corrosion. It has been found that the increase in ambient temperature up to 40 °C accelerates the corrosion rate significantly. The increase over the value of 40 °C has an opposite effect resulting in the corrosion rate slowing down. The possible causes of the effect are analysed. Three types of steel material, differing in their chemical composition, structure and mechanical properties, showed significantly different corrosion sensitivity. Of the studied steel materials, the steel showing the presence of inclusions and the highest values of yield point and tensile strength and the lowest value of ductility manifested the highest corrosion sensitivity. Therefore, the given characteristics seem to be symptomatic of the level of sensitivity of the material of steel opposite the chloride induced corrosion.

UTILISATION OF ELECTRICAL RESISTANCE METHOD FOR THE EVALUATION OF THE STATE OF STEEL REINFORCEMENT IN CONCRETE AND THE RATE OF ITS CORROSION

Abstract In this paper, the applications of an electrical resistance method for monitoring of the state of steel reinforcement in concrete and its rate have been described. The following possibilities of the method were shown: an estimation of quantitative data on corroding steel reinforcement, including the values of a cross-sectional decrease, the depth of the corroded layer, the mass loss of steel material due to corrosion; the possibility of the mathematical modelling of the dependence of the rate of steel reinforcement on important factors like ambient relative humidity, concentration of chloride in embedding concrete and others; and obtaining quantitative data on corroding steel reinforcement by means of a potentiodynamic method through the results of the electrical resistance method and the related mathematical relationship.

Alkali - Silicate admixture for cement composites incorporating pozzolan or blast furnace slag

Abstract This research was devoted to the study of the influence of the developed alkali-silicate admixture (AS admixture) on mortar properties. The obtained results shown, that the admixture significantly increased the strength of the mortars made from portland cement (PC) and silica fume (SF) or blast furnace slag (SL). For example after 24 h hardening of mortar (30% SF + 70% PC), with the admixture, reached value of compression strength 18,7 MPa opposite to the value of 5,6 MPa of control mortar (100% PC). The same accelerating effect of AS admixture was observed also with mortar incorporating slag and with slag mortar (100% SL). Further results shown, that the mortars with AS admixture had an increased content of hydration products and substantially more dense pore structure than mortars of the same composition, but without the admixture.

Experimental principles in the research of chemical resistance of cement based materials

Abstract The object of this paper is to set out the principles which should be taken when researching the chemical resistance of cement-based materials under particular experimental conditions. The chemical resistance of cement-based materials is a result of a complex interaction between cement-based material and aggressive medium. Therefore, the applicated methodology must take into consideration: (1) the main aggressivity factors of the medium and the chemical resistance of both partners of the interaction; and (2) complex observation of the changes in the properties of the attacked material caused by the interaction. The description of the experimental methodology considerating these principles is given. Examples of its application are given including the development of a new mathematical model of the deterioration of cement-based material and corrosion of steel reinforcement.

The behaviour of cement composite under compression load at sulphate attack

Abstract In the paper the influence of a compression load on sulphate corrosion rate of mortar is studied. It is shown that the applied compression load up to level of 60% from compression strength value of the given mortar significantly slows down this rate. This inhibition effect by decrease of content of bound SO3 and destructive phases, as ettringite and gypsum in attacked material is connected. A relatively high - quality pore structure of attacked mortar was the further result of mentioned inhibition effect. The reasons of the effect are analysed and discussed and the quantitative relationships between studied corrosion rate factors are given.

Sulfate resistance of the cement materials based on the modified silica fume

Abstract The object of the study was the influence of chemically modified silica fume (MSF) on the sulfate resistance of cement-based materials. MSF is a liquid product prepared from a suspension of silica fume and a water solution of a reactant under the defined composition of suspension, defined ambient temperature and time of procedure. MSF is added into mortar or concrete mixtures instead of water in the quantities needed for the desired consistency. The results obtained at the application of MSF shows a significant increase of sulfate resistance of materials based on Portland cement slag blends and slag binder. This positive effect represents a further beneficial potential of MSF that has already been shown as an effective hardening accelerator together with its ability to increase the acidic resistance of materials based on Portland cement slag blends and slag binder.