On magnetite concentrate grains with respect to their use in concrete
Abstract
Magnetic iron oxide grains and/or micrograins embedded into concrete are suggested for pH-protection of concrete. To this aim a phenomenological formula for the change in pH of the water solution after contacting iron oxides was derived. It has a broader meaning because it refers to all materials for which surface electric potential varies with pH of the contacting solution. It may be used to design a suitable composition of the mortar. In addition, the important property of magnetite concentrate grains that they may increase compressive strength of the mortar is shown. In the study, all the mortar under consideration was made from Portland cement CEM I 42.5 R, natural aggregate - quartz sand fraction 0-2 mm and magnetic material was magnetite concentrate supplied by Magnetite-Grochow Sp. z o. o.
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Introduction
Placement of the magnetic iron oxide grains, micrograins as well as nanograins in mortars causes emergence of a new type of material which is expected to be promising in the construction for use with the following objectives:
1. Materials for electromagnetic shielding, e.g. magnetic materials for absorption and shielding of electromagnetic radiofrequency radiation [1, 2], design of heavyweight concrete containing iron oxides which is suggested for radiation shielding of nuclear reactors [3],
2. design of materials for acoustic shielding [4] and thermal protection (also as pigments in paints),
3. chemical protection against acidic environment [5, 6], protection of concrete against waste water [7]
4. protective barrier against organic pollution (magnetic micrograins and nanograins),
5. Increase of compressive strength of concrete [3].
In this study, two objectives have been chosen for a discussion, the ability of magnetic grains to increase of compressive strength of concrete and their role with respect to chemical protection of mortars. It is well known that stability of mortar made from Portland cement strongly depends on pH and the best for it is the value of around of pH 11 [8]. Long-term exposition to acid rain, salt, carbonation [6] (generation of carbonic acid in the pores of concrete after its reaction with atmospheric CO2) or contacting low pH wastewater decreases pH and cement degradates - it stops to keep the quartz sand and other possible components of concrete together. At the same time, the iron containing wastes generated by metallic industry is steadily increasing and some forms of the waste could be successfully used in building materials to improve their properties both mechanical and chemical [7]. Recycling of such waste materials is environmentally friendly and inexpensive way to deal with them. In this study, the magnetic material which was used in mortars is magnetite concentrate supplied by Magnetite-Grochow Sp. z o. o. in Poland. Different sources of magnetite could be used equally, also the natural magnetite resources.
Conclusion
It has been shown that inexpensive magnetite concentrate if added to mortar can increase its compressive strength as well as it can be considered as a material protecting the porous concrete from the long-term impact of acidic/alkalinite environment. The phenomenological formula which determines the change in pH value of water solutions in the pores of concrete by magnetite applies to all Nerstian materials, not only to the magnetite concentrate under consideration. Therefore it has great importance for the design of mortar composition also with respect to the discussion on new cements for 21st century [15].