CC BY
9FORMATION OF CONCRETE PROPERTIES WITH STRUCTURED WATER
Shyshkina A.
Candidate of technical sciences, Associate Professor, Department of Technology of Building Products, Materials and Structures, National University, Kryvyi Rih, Ukraine
Abstract
The strength of fine-grained concrete was studied, for the production of which water was used, which was structured by adding non-electrolytes. It is determined that due to the structuring of water in its composition increased the content of protons, which accelerate the hydration reaction of cement minerals, as well as destroy the flocs of cement particles. The optimal amount of these substances, which are not electrolytes, allows you to control the rheological properties of concrete mixtures and modify the structure of cement stone so as to ensure the properties of concrete, which provide high operational reliability of structures. The aim of the study is to determine the effect of reaction powders used simultaneously with non-electrolytes on the strength of fine-grained concrete and the rate of its formation
Keywords: powder, concrete, surface-active substances, strength
Introduction
AS A result of development in the construction of tall and requirements for the construction and technical properties of new types of concrete production technologies of building products and structures that will determine is the current problem of building materials science.
In recent years, high-strength concretes have been intensively replicated, the method of obtaining them (reduction of water consumption, use of hyperplasticiz-ers) causes fair fear and caution [1,2]. At the same time, concretes were invented that have a high rate of formation and strength without reducing the amount of water and the use of hyperplasticizers [3,4].
But to date, many problems of the mechanism of hydration and hardening of cement are debatable and there are no clear answers to the questions that arise from these problems. The nature and physical essence of the induction period, the causes and mechanism of hydrolysis of calcium silicates, the "driving force" of the structure and formation of microbeton, its morphological structure, adaptability, etc. are not clear. Technological improvement, for example, is the complete conversion of cement grains into hydrated compounds that openly contradicts the experiment as second indicates the immutability of their size at any temperature and humidity conditions and terms of curing. (Moreover, the volume of grains even increases due to extrusion into the pore space of the surface highly porous amorphous hydrate). There is still a debatable way to transform plastic cement mass into stone (thoroughly soluble, topochemical or their symbol and lake). Although preference is given crystal and civilizational first "theory hardening", however, it has repeatedly been criticized and questioned an adequate reflection of the
process that actually takes place [5,6]. Therefore, determining the mechanism of influence of water structured by organic non-electrolytes on the structure and properties of concrete based on Portland cement is relevant and has some scientific novelty.
Accordingly, the purpose of the work is to establish mechanisms to water, structured organic electrolyte on the structure and properties of concrete based on Portland cement to obtain fine concrete.
Materials and research methods
Theoretical studies conducted by analyzing compliance processes previously determined the structure and properties of compositions on the basis of Portland cement and water, structured organic electrolyte, the known laws of colloid chemistry and physicochemical first mechanic and disperse systems. As a theoretical basis for the development of these ideas used the fundamental provisions: the formation of the surface of cement particles during grinding [7], the theory of micel-lar catalysis [8], colloid chemistry and physicochemical mechanics of disperse systems [9] effect of very small doses [10], theories of electroheterogeneous interactions in the hardening of cement binders [11,12].
Polyalcohol and hydrocarbons were used as modifiers of water structure. Index pH, electrical conductivity and strength of concrete were performed by standard methods.
The results of our own research and their discussion
According to [7], the grain of the solid after grinding consists of three parts (Fig. 1): the outer hyperamor-phized layer, 2-5 molecular diameters thick with a continuous decrease in density, the amorphous layer 5-15 ^m thick and the inner part, which remained intact.
Amorphous layer
Figure 1. The composition of cement grains after grinding
X-ray studies of the surface layers showed that their crystal lattice is strongly distorted, almost to the complete disappearance of the distant order in the arrangement of atoms. Such activated (amorphous) layers, according to [7], are characterized by abnormally high chemical activity and sorption capacity, as well as abnormally low diffusion resistance. Mechanically destroyed surface layers of cement particles interact intensively with molecules of the environment - water molecules that chemically bind to the activated substance of the surface layers of particles and penetrates deep into them. The diffusion rate in the plastic deformation-activated destructured layers of cement particles is several orders of magnitude higher than the diffusion rate in ordinary crystals and glass. This kind of absorption and interaction, both in intensity and by a mechanism not identical second physical second adsorption and classic second chemisorptions [7].
According to O Paschenko [13], the maximum thickness of the cement particles as ground undergoes hydration, is 15 micron meters, that practically corresponds to the thickness of amorphous and zovanoho layer and cement particles less than 30 microns completely amorphous and hydrated. In the fine fraction (020 ^m) - usually more C3S and C3A, and larger fractions are enriched with C3S and C4AF. As shown by numerous studies, the greatest influence on the strength of cement has a fraction of 5 to 30 microns. The fraction of 5-10 microns affects the strength at three and seven days of age, and the fraction of 10-30 microns - at one month of age and more. Cement fractions larger than 60 ^m are practically a ballast [15]. Research L Spi-nova and others. [15] it was also shown that cement particles up to 10 ^m in size when interacting with mixing water are completely hydrated, and larger particles are hydrated only on the surface.
The results of the research showed that when organic non-electrolytes are added to water (in experiments of polyalcohol and hydrocarbons) it changes its properties: the temperature decreases, the electrical
conductivity increases and the pH decreases. This indicates that the water is structured and acquires acidic properties, ie a negative charge. It should be noted that the sum of the volumes of water and organic non-electrolyte does not coincide with the volume of the solution of non-electrolyte in water. This means that organic non-electrolytes are located in the cavities of water clathrates, which leads, at a certain concentration, to stabilization of the volume, and a decrease in temperature indicates a decrease in the amplitude of oscillations of water molecules, ie to its stabilization. At a certain concentration of organic non-electrolytes in water, a continuous fractal network is formed, which provides free movement of protons.
Based on the above, the theoretical model of the initial phase of the interaction of cement with structured water can be represented as follows.
As is known [11], on the surface of Portland cement particles in an aqueous medium, regions with a negative surface charge (regions containing C3S, C2S) and regions with a positive surface charge (regions containing C3A, C4AF) are formed. According to [11,12], after mixing with water, between it and the oppositely charged areas of the cement particles there are forces of electrostatic attraction. Therefore, water molecules, which due to structuring under the influence of non-electrolytes are negatively charged, are grouped near the active centers C3A, C4AF, positively charged, and seek to compensate for the thickness of the solvate shell potential of their surface. There is a similarity to the classical electric layer with the nucleus of the micelle -cement grain (floccule) and water solvate shell. The latter is a layer of liquid, part of which in the zone of contact with the active centers of the cement surface is oriented in its force field, forming a "cluster" of tightly spaced polarized water molecules. In this case, the difference between the system "cement core - solvate shell water" is that groups of water molecules are formed not only at active centers on the surface of the solid phase of cement particles [11,12], but also in the depth of their
hyperamorphized layer. Over time, these water molecules create forces that exceed the binding energy within the volume of the solid phase. Thus, by definition, D Mendeleev, provides the necessary and sufficient condition for the dissolution of the latter.
The difference between the system "cement particle - non-electrolyte-structured water", which is studied, is that when its components collide, water molecules (respectively, protons) are actively absorbed by the hyperamorphized layer of cement particles.
Hydrogen ions (ie protons) penetrating the hyper-amorphized layer and the amorphized layer of the cement particle have an abnormally high mobility -3.26 • 10-5 m/s at an electric field strength of 1 V/cm and high penetrating power, as their size several orders of magnitude smaller than the size of the crystal lattice of cement clinker minerals and bind strongly to electronegative oxygen atoms and form hydroxylions. In addition, protons enter into ion exchange reactions with cations (Ca2+^2H+, etc.). As a result, aquacomplexes [Ca (H2O)6]2+ and primary molecules of Ca(OH)2 are formed along with hydroxyls, the size of which can be compared with the size of the crystal lattice of basic minerals. Due to this, the destruction of the surface layer of cement particles with the formation of nanodis-persed hydrated particles with a size of 5-10 nm.
On the surface of cement grains, an electric layer of not flattened (with evenly spaced Helmholtz layer of charges) configuration is formed, but in the form of locally dispersed polymolecular water clusters. Explosion-like destruction of Ca-O bonds in the structure of calcium silicates, hydrogen and chemical bonds of adsorbed clusters, the appearance of active particles (Ca2+, (SiO4)4-, H3O+, OH-, etc.), their transient interaction and is the cause of the appearance on the surface of cement grains amorphous hydrate product.
Hydration of cement minerals is accompanied by hydrolysis, first of all, of the aluminate and then of the silicate component of clinker, with a predominant release of calcium ions into the liquid medium. Hydrolysis "residues" (SiO4)4- remain in the solid phase, bind to highly reactive decay products of water molecules.
Since protons from water molecules on the surface migrate into the original crystal, fixing on the acceptor with the formation of stable OH- particles, in the opposite direction is the movement of calcium atoms and, to a lesser extent, silicon out into the solution through the hydration products. When C3S is hydrated, the topo-chemical reaction of protonation of unsaturated oxygen atoms in the C3S structure is first carried out.
In the process of hardening of cement stone, its pores are penetrated by needle crystals of etringite, which acts as a center of crystallization for other hydrate compounds formed, as well as crystals of port-landite (application of 0.0002% hydrocarbon solution). the introduction of hydrocarbons or alcohol in small concentrations (0.0002 - 0.0004%) leads to the formation of evenly distributed pores in the cement stone, which migrate the formed portlandite and etringite. as a result, the structure of cement stone with a high content of high-strength low-base calcium hydrosilicates is formed, which leads to an increase in the strength of
cement stone almost 2 times after a year of hardening in air and humid conditions..
Acceleration of the hydration process and subsequent curing process leads to a more uniform crystallization of tumors, their subsequent collective recrystal-lization, which provides a more homogeneous matrix, which has increased density and strength.
At the same time there is an involuntary disaggre-gation of cement flocs, which under the influence of structured water develops due to the repulsive (wedging effect) of thin films of liquid when wetting the surface of the contacting cement particles. As a result, in the mouth of such "cracks" films of liquid are formed, which pass into monolayers of oriented water molecules, there is an effort of mutual repulsion of the same charged surfaces and the destruction of flocs.
Hydrated parts of cement have a negative surface charge, so the presence of structured water, which has a negative charge, prevents their coagulation. Subsequently, protons are adsorbed on the surface of the oxygen nodes of the crystal lattices of hydrated C3A by the formation of hydrogen sorption bond with the oxygen atom:
It is also possible the interaction of the acidic proton with the oxygen atom of the oxygen node hydrated
C4AF:
and this atom with a hydrogen atom of water:
and the hydrogen bonds between oxygen atoms and hydrogen atoms of water molecules with hydrogen hydroxyl node hydrateds C2S and C3S:
If the spatial second orientation of the molecules near the oxygen the crystal lattice silicate, aluminate or ferrite acidic protons appear at a distance to be adsorbed and centers oxygen units or happen their migration (diffusion) in the surface layer for oxygen units and subsequent adsorption, they vacancies can be occupied by hydrogen atoms of water molecules with the formation of a "new" structure close to the polymer.
Thus, increasing to a certain limit the concentration of protons in the system "cement - water" increases the strength of cement stone. The increase in the concentration of protons in the structuring of water by organic non-electrolytes, which are introduced in ultra-low concentrations (up to 0.0005%), leads to an increase in concrete strength at an early age (2 days) by
an average of 60-83%, and later more) - 35-40%. Frost resistance of concrete is 200-300 cycles of freezing and thawing, water resistance corresponds to brand W6.
Conclusions:
- the use of organic non-electrolytes for water structuring leads to increased compressive strength, frost resistance and water resistance of fine-grained concrete
- the application of theories of electroheterogene-ous interactions in the hardening of cement binders, the formation of the surface of cement particles during grinding, theories of ultra-low concentrations and mi-cellar catalysis allows us to present a theoretical model of the initial phase of interaction of cement with structured water.
- the basis of the processes that occur in the system "cement - non-electrolyte-structured water" are acidic protons, which are introduced into the system when structuring water with organic non-electrolytes.
- a certain concentration of non-electrolytes in water (0.0002-0.0005% by weight of cement) provides the optimal number of protons in it, which leads to an increase in the strength of concrete at an early age (2 days) by an average of 60-83%, and in later (28 days or more) - 35-40%, frost resistance for 50 cycles of freezing and thawing, water resistance for 2-4 brands.
REFERENCES:
1. Usherov-Marshak AV, Zlatkovsky OA, Per-shina LA, Tsiak M. 2003. On the evaluation of compatibility of chemical additives with cements in concrete technology. Construction materials. 4. p. 11-15 (in Russian)
2. Babkov VV, Polak AF, Komokhov PG 1988 Aspects of durability of cement stone. Cement, 3, pp. 14-16 (in Russian)
3. Shishkina A. Shishkin A., Application of the easy concentration effect in concrete technology. IOP Conference Series: Materials Science and Engineering, 2020, 907(1), 012038
4. Shishkin, A., Shishkina, A 2018 Study of the effect of micellar catalysis on the strength of alkaline
reactive powder concrete. Eastern-European Journal of Enterprise Technologies, 3 (6/93), pp. 46-51
5. Gladkikh Yu.P., Zavrazhina VI 2005 On condensation in nature in the hardening of inorganic binders. Bulletin of BSTU.V.G. Shukhova, 10, pp. 5961. (in Russian)
6. Usherov-Marshak O.V. 2008 On the levels of development of concrete management and concrete technology. Proceedings of the International Congress Science and Innovation in Construction SIB-2008, vol. 1, book.2. Voronezh: VGASU, pp. 569-573.
7. Khodakov GS 1972 Fine grinding of building materials. (Moscow: ASV) p 198. (in Russian)
8. Berezin IV, Martinek K., Yatsimirsky AK 1973 Physicochemical bases of micellar catalysis. Successes in chemistry. Issue 10.. Volume XLU. pp.17291756. (in Russian)
9. Friedrichsberg DA 1984 Colloid chemistry course. L.: Khimiya,. p. 368. (in Russian)
10. Burlakova EB 1994 The effect of ultra-small doses. Bulletin of the Russian Academy of Sciences, Volume 64, 5, pp. 425-431(in Russian)
11. Plugin AN 1985 Electroheterogeneous mechanism of structure formation of cement-water systems. Abstracts. report VI Republic. confer. on physical chemistry and technology for the production and use of flushing fluids, dispersed systems and grouting solutions. Kiev: IKHHV AN USSR. Part IC 127. (in Russian)
12. Andrii Plugin et al 2020 Nanomodified cement composites for thin walled architectural structures. To cite this article: IOP Conf. Ser.: Mater. Sci. Eng. 907 012030
13. Pashchenko AA, Serbia VP, Starchevskaya EA 1975 Binding materials. (K.: Higher school), p. 444. (in Russian)
14. Shpynova LG, Chikh VI, Sanitsky MA. 1981 Physico-chemical bases of formation of structure of a cement stone. (Leo: Higher school). p. 160. (in Russian)
