The rate of corrosion of concrete reinforcement and possibilities of its mathematical modelling

The paper describes a method for the mathematical modelling of steel reinforcement corrosion rate. This method is based exclusively on experimental results and expression of the influence of significant corrosion factors in the form of functional relations. The method takes into account the reality of the effects of corrosion factors, their contigency and complexity, and various circumstances occurring in practice. It represents one way towards the development of methods for the prediction of service life of reinforced concrete and structures.     

Possibility of improvement of potentiodynamic method for monitoring corrosion rate of steel reinforcement in concrete

Quantitative data on corroding steel reinforcement in reinforced concrete structures are undoubtedly very useful for evaluation of their service life and timely repairs. The method of electrode potential measurement is a convenient and simple test for this purpose, but it provides no quantitative data on corrosion rate and only information regarding active or passive state of steel reinforcement can be obtained. We show here the possibility of obtaining quantitative data on degree of corrosion of steel reinforcement by a potentiodynamic method. The developed method is based on experimentally estimated mathematical relation between the results of potentiodynamic method and degree of corrosion of steel reinforcement. It is possible to calculate the degree of corrosion of steel reinforcement using this mathematical relation and the measured values of current density by the potentiodynamic method.     

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

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.     

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.     

Significance and influence of the ambient temperature as a rate factor of steel reinforcement corrosion

The rate of corrosion of reinforcement being an electrochemical process, undoubtedly is dependent even on the level of the ambient temperature. Therefore, the ambient temperature seems to be an important factor of the corrosion rate and the durability of the reinforced concrete structures in aggressive environment. The present data on the influence and significance of the ambient temperature in the process of corrosion of reinforcement of the reinforced structures are surprisingly limited and poor. It seems that it is supposed to be a simple increase of corrosion rate when the ambient temperature is increased. The lack of information was a motivation for the present study. It was aimed at the experimental research of the influence of the increase of the ambient temperature on the rate of chloride induced corrosion of steel reinforcement. The results obtained show that the influence of the studied factor is more complex showing an acceleration effect till a temperature of 40°C diversified by the inhibition effects with further increase of the ambient temperature.     

Influence of<Emphasis Type="Italic">w/c</Emphasis> ratio on rate of chloride induced corrosion of steel reinforcement and its dependence on ambient temperature

The permeability of the embedding cement material for the rate of chloride induced corrosion when the ambient temperature is increased has found a dominant position. The importance of the given permeability in the process is based on the fact that it represents a factor conditioning the possibility of the escaping of the unambiguous reaction partners, oxygen and water vapour, from the system embedding cement material— steel, as the ambient temperature is increased. The resulting effect is a slowing down of the corrosion rate when the w/c ratio over the value 0.6 and the ambient temperature over the value 40†C are increased. Due to the similarity of the chemism of the corrosion process of steel reinforcement, independent of the action of aggressive species, the found relationships are generally valid, e.g. for the corrosion due to carbonation.     

Hardening and properties of cement-based materials incorporating heavy metal oxides

The subject of the study was the influence of oxides PbO, ZrO₂ and Cr₂O₃ immobilized in cement matrix. The obtained results show the positive effect of the present oxides in hydrating cement on compressive strength development and the quality of the formating pore structure of the resulting material. A surprising effect showing the paralysis of the positive effect of heavy metal oxide admixture has been shown by the increasing of the added quantity of PbO (from 1 to 4%) and the used w/c ratio (0·7 instead of 0·4). The increase of the quantity overcoming the optimum of the reaction product of the interaction between hydrating cement and PbO added for the cause of the paralysis is supposed. The explanation of the adverse effect and the identification of the reaction product in question needs more detailed study.     

Dependence of efficiency of pressure compaction on the cement type used

The results of the study on the properties of the pastes, with w/c ratio 0.20–0.10, compacted in the fresh state by the pressures between 27 and 82 MPa are given. The comparison of their properties with those found at the reference non-pressured cement pastes prepared with w/c ratio 0.30 showed the significantly increased compressive strength. Two effects were the cause: the significant decrease of the initial porosity due to the extremely low w/c ratios and the mechanical compaction of the fresh pastes. It has been found a significant increase of the effectiveness of the pressuring by the cement quality decrease. The long-term development of the properties of the pressured cement pastes is similar to the non-pressured cement pastes. At the conservation of the properties differences in the benefit of the pressured materials.     

Electrochemical activity of heavy metal oxides in the process of chloride induced corrosion of steel reinforcement

The influence of heavy metal oxides on the chloride induced corrosion of steel reinforcement in concrete was studied. Significant inhibition and stimulation of chloride induced corrosion have been observed. Basicity and acidity of the relevant metal ions, and their ability to form complexes are considered as the main factors of the observed effects.