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Properties of the Phase Components of the Modified Cement System TEKA. COMMISSION OF MOTORIZATION AND ENERGETICS IN AGRICULTURE – 2013, Vol. 13, No.4, 218-224 Properties of the phase components of the modified cement system Dmytro Rudenko Volodymyr Dahl East-Ukrainian National University, Molodizhny bl., 20ɚ, Lugansk, 91034, Ukraine, e-mail: [email protected] Received September 18.2013: accepted October 09.2013 S u m m a r y : The article presents the results of the properties. The simplest way of intensification study of the influence of modification on the clinker of hydration process and optimization of mono minerals structure formation. A research of synthesized and modified mineral systems resistance to cement systems structure formation is a usage the weathering (carbonation, varying conditions), as of polyfunctional admixtures [5, 11, 16, 19, well as to the aggressive solutions exposure was 23]. Such additives, intensifying hydration conducted. process, having an effect on the hydration K e y w o r d s : cement system, modification, mono products morphology and their structure minerals, resistance. formation process, can’t be composed of one component [15, 27, 28, 30]. Obviously, such INTRODUCTION additives must form a complex with polyfunctional properties. At the same time, There are many ways of purposeful organic plasticizers, widely used at building control of structure formation of the concrete industry enterprises, require an addition with mixtures’ cement systems at different stages of special mineral components, chemically hardening [1, 3, 6]. The most rational way is a interacting with clinker minerals. Thus, it’s structure adjustment through the introduction necessary to choose a complex composition of modifiers. Modification of cement systems modifier with polyfunctional effect on the by various chemically-active components structuring cement system. An optimizing intentionally changes hardening and structure effect of the complex modifier becomes formation processes, provides the apparent on the crystallochemical level of improvement of the technological properties of structure formation. Consequently, the material [2, 4, 7-9]. However, modification crystallochemical optimization of the cement has an ambiguous impact on the properties of systems structure formation may be performed mono minerals of the cement system [12, 13, by a special complex, based on modern non- 21, 22, 26]. deficit and effective components [10, 17, 18]. Modification means creation of favorable Nowadays there are many ways of conditions for the clinker minerals chemical modification of binding systems, most of them interaction and further formation of the based on the turbulent mixing of components. concrete cement matrix with specified At the turbulent motion material particles PROPERTIES OF THE PHASE COMPONENTS OF THE MODIFIED CEMENT SYSTEM 219 move randomly both in the direction of current RESEARCH DATA and transversely to it. The particles interpenetrate from one layer to another, the Study of the property change of the number of their encounters increase [14, 19, phase components of the modified cement 20, 24]. system during six months carbonation shows Usually abroad turbulent mixing is used that the bending strength of both, hydrated for the preparation of injection compositions, calcium silicate (tobermorite group) and as they help to raise the stability of concrete xonotlite, diminishes, whereas on the contrary mixtures. the strength of the highly basic hydrated In the authors’ opinion, turbulent mixing calcium silicate significantly increases (Table leads to the deflocculation of a cement-water 1). In this conditions low-basic hydrosilicates, suspension, as a result saturation of suspension especially tobermorite group, despite their with colloid particles increase, the paste higher density, carbonate much faster and becomes more stable, bleeding reduces. As a change more intensively in comparison with result of turbulent mixing, cement paste the less dense highly basic hydrated calcium viscosity decreases to a certain point in time, silicate. when the mixture temperature rise due to the Table 1. Operating abilities of modified monomineral exothermal reaction of clinker minerals systems hydration starts acting back and the mixture Bending resistance, MPa thickens. The optimal duration of mixing, after Phase when paste viscosity decreases with the after after alternate components simultaneous reduce of bleeding, is in a certain synthesis carbonation wetting and drying relationship to a water-cement ratio [10, 17, C–S–H(I) 8,0 9,3 8,6 18, 25]. Xonotlite 14,3 11,6 10,2 The authors [18, 23] are of opinion that ɋ2SH(A) 4,5 5,9 6,6 turbulent treatment leads to an increase of the C2SH(C) 2,8 4,8 5,4 C3AH6 4,4 6,2 5,6 cement specific surface area due to the grinding of fine fraction. However, the results C3ASH4 3,9 5,7 6,3 Degree of of the research conducted by authors [10, 29, Bending resistance, MPa Freeze- shrinkage thaw 30] showed that specific surface area remains in 5% in 2,5% after resistance, unchanged. Hence, contradictoriness of solution of solution of carbonation, cycles opinions is indicative of insufficient Na2SO4 MgSO4 % knowledge of binding systems modification. 7,6 6,7 54 2,4 12,9 9,6 47 0,93 An ambiguous impact of different modifiers 4,4 2,5 275 0,52 on clinker mono minerals should also be taken 3,6 2,7 154 0,34 into account, as in bulk this may have a Fractures in Fractures in - 0,21 17 days 26 days negative impact on the processes of structure Fractures in Fractures in - 0,12 formation of the concrete cement matrix. 46 days 57 days PURPOSE The reason of it is a big specific surface area of C–S–H(I), which accelerates its The purpose of the work is a research of interaction with carbonic acid gas and leads to synthesized and modified mineral systems a fast oversaturation and occurrence of a big resistance to the weathering (carbonation, number of nuclei. A lot of small defective varying conditions), as well as to the crystals emerge as a result. Besides, the aggressive solutions exposure. significant carbonation speed of low-basic hydrated calcium silicate (tobermorite group) can be explained by its layer structure. Access of moisture-dissolved carbon acid gas inside the hydrated calcium silicate 220 DMYTRO RUDENKO takes place together with hygroscopic water observed in the process of carbonation of when a water molecule penetrates along the calcium hydrosilicate, besides the chemical layered crystal cleavage surface. The processes listed above. The intensity of stress carbonation speed of hydrated calcium silicate and its tension seem to raise with the increase to a great extent depends on the humidity of of carbonation speed. environment. At the same time, ions of ɋɚ2+ in Study of changes of the hydrated calcium hydrosilicate, being a center of water molecule aluminate and calcium hydrogarnet properties persorption according to the two types of a showed that when artificially carbonated the bond (silicon-oxygen radicals and Ɉɇ- ions) in hydrated calcium aluminate strength increases a crystal cell, take carbon acid gas much in a greater degree than calcium hydrogarnet - easier. If ɋɈ2 is replaced according to Ɉɇ strength. Judging by the amount of the bonds, then ɋɚɋɈ3 forms instead of combined ɋɈ2 this corresponds to a significant hydrosilicate, and if the replacement takes degree of carbonation of hydrated calcium place according to the silicon-oxygen radicals aluminate in comparison with calcium bond, then scawtite forms. It should be hydrogarnet. In the conditions of alternate mentioned that in the usual terms replacement wetting and drying during 50 cycles the of ɋɈ2 takes place according to the ionic bond strength of tobermorite group and xonotlite - Ɉɇ . decreases and the strength of C2SH(A) and It is established that modified concrete C2SH(C) increases, but in a lesser degree than strength and deformability change differently at carbonation (Table 1). In these conditions depending on the concentration of carbon the strength of hydrated calcium aluminate dioxide in the atmosphere. In the first case, almost doesn’t change and the strength of when the concentration of ɋɈ2 is weak, i.e. the calcium hydrogarnet increases slightly. Along oversaturation of the solution is not too big, with this an imperceptible shrinkage is calcite crystallizes calmly and its crystals are observed. larger. Calcite crystals grow due to the joining The layered structure and water of atoms near the active centers, calcite has contained in the structure of hydrated calcium better structural properties (less defect and silicate (tobermorite group) are able to change dislocation cluster). depending on the effect of environment. If we In the second case, when the ɋɈ2 consider a layered crystal of tobermorite as concentration is strong and the oversaturation compiled packages connected along the basal is significant and even exceeds a critical value, planes of the elementary crystallites than calcite crystallization takes place in a abrupt change of desorption curves is due to spontaneous formation of nuclei, small crystals exudation of hygroscopic water from the of the same size form for a certain period of interplanar spacing. At the same time a unit time. Therefore, to improve the structure and cell ɫ parameter changes from 27 to 24,6. 10-10 m properties of the crystals of calcite, which is [5, 12, 15]. one of the products of hydrated calcium Properties of hygroscopic water in silicate carbonation, it’s necessary to reduce hydrated calcium silicate with layered oversaturation, i.e. to reduce the concentration structure depend on H2O/SiO2 ratio. When the of the carbonized environment. ratio value is less than one then molecules of The strength of the carbonated calcium hygroscopic water are not included in the hydrosilicate is determined by the degree of structure of the crystal lattice and have a crystallization and the size of crystals. In the mobility of liquid water and so the water is process of carbonation of a less crystallized inconstant due to the environment factors C–S–H(I) a large amount of loose calcium variations [6, 22].
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