CC BY
5FORMATION OF CONCRETE PROPERTIES WHEN USING FILLED MICELLES OF SURFACE-
ACTIVE SUBSTANCES
Shyshkin A.
Doctor of technical sciences, Professor, Department of Technology of Building Products, Materials and Structures, National University, Kryvyi Rih, Ukraine
Abstract
Intensive methods of construction of buildings require the introduction of modern technologies that would ensure the dismantling of monolithic structures in a short time, increase the turnover of formwork, increase the efficiency of construction work in different temperature conditions of hardening, reduce the production cycle.
Keywords: powder, concrete, surface-active substances, strength
Introduction
Given the peculiarities of monolithic construction, when hardening of concrete occurs without use or with limited thermal exposure, it is mandatory for highspeed technology to introduce fast-setting binders to obtain high strength concrete in one or two days, to increase concrete strength at design age.
In addition, modern construction requires a number of engineering problems to maintain the efficiency and functionality of existing buildings, structures, road infrastructure, which is associated with increasing rates of physical depreciation of fixed assets [1, 2]. Therefore, there is a need to develop high-performance fast-setting building composites to ensure the commissioning of facilities in a short period of time and their reliable operation throughout the life cycle. Repair, restoration and reconstruction of existing construction sites, the restoration of operational functions of which is possible only in certain short periods of time (underpasses, pavements, facilities at airports and railways, hydraulic structures), requires the use of effective fast-setting materials.
The main directions of obtaining ultra-fast portland cements are based on providing the necessary chemical and mineralogical composition and structural features of clinker, cement dispersion, introduction of special crystallization seeds, mechano-chemical activation of cements with the introduction of superplasticiz-ers in the grinding process.
Therefore, the definition of the general principles of the mechanism of influence of micelles of surfactants (surfactants), including filled, on the structure and properties of concrete based on portland cement is relevant and has some scientific novelty.
Based on the above, the aim is to establish the mechanisms of influence of surfactant micelles on the structure and properties of concrete based on Portland cement in order to obtain fine-grained concrete.
Materials and research methods
Theoretical studies were performed by analyzing the conformity of previously defined processes of structure formation and properties of compositions based on Portland cement and water, structured using filled micelles of surfactants, according to the known laws of colloid chemistry and physicochemical mechanics of dispersed systems. As a theoretical basis for the development of these ideas used fundamental provisions: the theory of micellar catalysis [3,4], colloid
chemistry and physicochemical mechanics of dispersed systems [5], the effect of ultra-low doses [6], the theory of electroheterogeneous interactions in the hardening of cement binders [7].
Colloidal surfactants were used as modifiers of water structure. Determination of hydrogen, pH, electrical conductivity and strength of concrete was performed by standard methods.
The results of our own research and their discussion
It is known that effective water-reducing additives in Portland cement systems are polycarboxylate esters, the molecule of which consists of a main chain with carboxylate groups, negatively charged, and side chains, which are responsible for spatial repulsion. When the polycarboxylate interacts with the cement component, the surfactant density of the surfactant on the surface of the cement grain decreases, so part of the active centers of the polymer-free overlapping films remains, which provides water access to clinker minerals. It should be noted that the micelles of surfactants have the same properties [3], both conventional and filled [4], which also do not cover the entire surface of the cement grain and provide water access to clinker minerals.
If micelles formed on the basis of alkali metal are used in the manufacture of concrete, then calcium ions, which pass into the liquid phase in the primary acts of hydration of cement, promote the exchange reaction, which produces molecules of hydrophobic surfactants based on calcium and partially disappears micelles obtained on based on alkali metal. From now on, there will be two types of hydrophobic surfactant molecules in the system: alkali metal-based and calcium-based, ie two types of micelles (forward and reverse).
The results of determining the effect of the specified mixture of molecules (micelles), which are given in table. 1 show the positive effect of its application.
Table 1
The effect of surfactant mixture on the compressive strength of fine-grained concrete,
which was obtained using a surfactant mixture at the age of 28 days
Concentration of calcium oleate solution Relative strength of concrete,%, depending on the concentration of sodium oleate solution
0 10-3M 10-4M 10-5M
0 100 125 126 120
10-3M 109 140 145 146
10-4M 113 149 153 168
10-5M 118 148 148 156
Table 2 compares the strength of concrete obtained using a surfactant mixture with the strength of concrete obtained using only sodium oleate.
Table 2
The effect of surfactant mixture on the compressive strength of fine-grained concrete, which was obtained using _a surfactant mixture at the age of 28 days_
Concentration of calcium oleate solution Relative strength of concrete,%, depending on the concentration of sodium oleate solution
0 10-3M 10-4M 10-5M
0 100 125(100) 126(100) 120(100)
10-3M 109 112 115 122
10-4M 113 119 121 140
10-5M 118 118 117 130
Note. The value of the strength of concrete obtained without calcium oleate for each concentration of sodium oleate is taken as 100%
Table 3 compares the strength of concrete ob- ion and the other on a multivalent metal ion or the for-tained using a surfactant mixture with the strength of mation in the hydration of cement hydrophobic surfac-concrete obtained using only calcium oleate. tants based on polyvalent metal due to the rotation of
Experiments show that the use of a mixture of hy- the metal , leads to a significant increase in the strength drophobic surfactants for the manufacture of fine- of concrete. grained concrete, one of which is based on an alkaline
Table 3
The effect of surfactant mixture on the compressive strength of fine-grained concrete, which was obtained using
a surfactant mixture at the age of 28 days
Concentration of calcium oleate solution Relative strength of concrete,%, depending on the concentration of sodium oleate solution
0 10-3M 10-4M 10-5M
10-3M 109 (100) 128 133 134
10-4M 113(100) 132 135 145
10-5M 118(100) 125 125 132
Note. The value of the strength of concrete obtained without calcium oleate for each concentration of sodium oleate is taken as 100%
The presence of anionic surfactants in the system leads to an increase in the reaction rate primarily due to the electrostatic attraction of nucleophiles to the positively charged surface of the cement grain.
It is known that improving the quality of cement stone and concrete is possible through the use of ultrafine additives (removal ash, microsilica, metakaolin, carbon nanotubes and others) [8-16]. However, one of the disadvantages of ultrafine additives is considered to be the increased water consumption and ability to aggregate, as a result of which Portland cement systems lose mobility, which leads to the use of increased amounts of superplasticizers to provide a plasticizing effect. The positive effect of the complex organo-mineral additive is to reduce the duration of the plastic state of cement paste, respectively, intensify hydration and
strength of cement stone to create a high-density, mi-croporous, fine structure due to the formation of na-nosized hydrosilicate phases.
At the same time, such complex organo-mineral additives in accordance with the provisions of colloid chemistry and physicochemical mechanics of dispersed systems [5] are classified as filled micelles of surfactants (Fig. 1)..
Puc. 1. Scheme of filled micelles
The mechanism of micelle formation is in principle similar to the mechanism of surfactant adsorption at the water-air phase separation: the forces of interaction between strongly polar water molecules are much more intense than between water molecules and hydrocarbon radicals. Surfactant molecules seem to be dissolved in a "foreign" environment. For this reason, at low concentrations, molecules or surfactant ions are mainly pushed by water molecules to the surface, where they are adsorbed and oriented (according to their diphilic nature), and an adsorption equilibrium is established between the water phase and the surface. With a further increase in concentration, the surface layer becomes saturated, and the hydrophobic hydrocarbon radicals of the surfactant are pushed by water molecules into the micelles, ie into the liquid "pseudophase". The latter is separated from water by a hydrophilic shell of the polar groups of surfactants. Any process associated with the transition of hydrocarbon chains from the water phase to a phase close in polarity is energetically advantageous: the transfer of one group -CH2- from water to the micelle is accompanied by an energy gain of 1.08 kJ/mol, which is only slightly less work adsorption of the link -CH2- on the surface "liquid - gas". It should be noted that the formation of micelles occurs at much lower concentrations than the saturation of surfactant molecules of the surface layer "water - air". Therefore, the amount of adsorption is limited not by the degree of surface filling, but by the value of the critical concentration of micelle formation (CCM).
At the same time, in the presence of a fine component in the system, surfactant molecules at a concentration of much lower CCM are adsorbed on the surface of this component, forming an artificial filled micelle.
Puc. 2. Scheme
The actions of filled micelles, which were formed by anionic surfactants, were thoroughly studied in [1719], and the mechanism of their action when filled with carbon nanotubes was described in [8].
When used as a filler micelles of microsilica and other substances based on silica, the mechanism of action of such micelles is somewhat different. First of all, the micelle of anionic surfactant (for example, based on sodium ions) is adsorbed on the microsilica powder particles - micelle fillers. Sodium ions introduced into the dispersed system by colloidal surfactants have a destructive effect on silica, activating its surface. As a result of breaking the O - Si - O bonds, the surface of the silica is covered with active centers containing sodium ions.
Calcium ions - products of hydration of Portland cement minerals lead to the rotation of the micelle, which covers the particle of microsilica, and gain access to the surface of its particles. At the active centers formed and containing sodium ions, calcium ions are condensed by chemisorption - products of hydration of Portland cement minerals, ie they are fused with the reaction powder.
This is the exchange reaction of sodium ions from the active centers on the surface of the reaction powder and calcium. As a result of this process, calcium hydrosilicates are formed on the surface of the reaction powder particles, and colloidal surfactant micelles are returned to the system, which have fulfilled their role of catalyst. And this process is repeated (Fig. 2).
Cationic surfactants stabilize nanoparticles during their synthesis and interfere with agglomeration processes, which allows to obtain systems with a highly developed surface area. The growing interest in carbon nanotubes and the problem of their dispersion in solutions have led to the use of cationic surfactants for these purposes.
Among the most important practically significant properties of supramolecular systems based on cationic surfactants should be noted their ability to act as nano-reactors, allowing to regulate the speed and mechanism of chemical processes, as well as their anticorrosive properties.
The presence of cationic surfactants in the system leads to an increase in the reaction rate primarily due to
the electrostatic attraction of nucleophiles to the positively charged surface of the cement grain.
Conclusions
1. The so-called "mineral-organic additives", which are now widely offered for use in concrete technology, are filled micelles of colloidal surfactants and their action is subject to known mechanisms of micellar catalysis, which increases the rate of formation and strength at compression, frost resistance and water resistance of concrete.
2. Application of theories of electroheterogeneous interactions in hardening of cement binders, theories of ultralow concentrations and micellar catalysis allows to
present a theoretical model of the initial phase of interaction of cement with water, which contains micelles of colloidal surfactants.
3. The basis of the processes occurring in the system "cement - water - micro (nano) component - micelles of colloidal surfactants" are adsorption and thermodynamic processes at the interface between the components of the phases that are introduced into the system of cement that hardens.
4. Simultaneous use of micelles of different types (forward and reverse) leads to an increase in concrete strength by 40-68%, frost resistance by 40 cycles of freezing and thawing, water resistance by 2 marks.
REFERENCES:
1. Dvorkin LY, Dvorkin OL, Dorofeev VS, Mishutin. AV 2012. Hydraulic and road concrete. Odessa (ZHC). 216 p. (in Russian)
2. Mishutin AV, Smolyanets VV, Krovyakov SA 2014. The prospect of using hard pavements for city streets and the highway "North - South" in Odessa. Problems of urban development.. 1. pp. 104-111. (in Russian)
3. Bukanova EF Colloid chemistry of surfactants. 2006. Part 1. Micelle formation in surfactant solutions. Moscow (MITXT). 80 p. (in Russian)
4. Berezin IV Martinek K., Yatsimirsky AK 1973 Physicochemical bases of micellar catalysis. Successes in chemistry. XLII, 10. pp. 1729-1756. (in Russian)
5. Friedrichsberg DA 1984 Colloid chemistry course. L. (Chemistry). 368 p.
6. Burlakova E.B. 1994 The effect of ultrasmall doses. Bulletin of the Russian Academy of Sciences, 64, 5, p. 425 - 431
7. Plugin AN 1985 Electroheterogeneous mechanism of structure formation of cement-water systems. Thesis. report VI Respubl. conference. on physi-cochemistry and technology of production and application of washing liquids, dispersed systems and grouting solutions. Kiev (IKXXB) AS UCCP. I. p. 127. (in Russian)
8. Plugin A. et al 2020 Nanomodified cement composites for thin walled architectural structures To cite this article: IOP Conf. Ser.: Mater. Sci. Eng. 907 012030
9. Pukharenko Yu.V., Aubakirova IU, Staroverov VD 2009 Efficiency of activation of mixing water by carbon nanoparticles. Engineering and construction magazine. 1.pp. 40-45. (in Russian)
10. Dvorkin LY, Lushnikova NV, Runova RF, Troyan VV 2007 Metakaolin in mortars and concretes. Kyiv (KNUBA). 216 p. (in Russian)
11. Kirakevich II, Marushchak UD, Sanitsky MA, Stechyshyn MS 2012 Self-compacting concretes with a rapid increase in strength. Bulletin of Lviv Polytechnic National University.737. pp. 153-158. (in Russian)
12. Sanitsky MA, Sobol HS, Markiv TE 2010 Modified composite cements. Lviv (BLP). 132 p. (in Russian)
13. Lagier F., Kurtis K. E. 2007 Influence of Portland cement composition on early age reactions with metakaolin. Cement and Concrete Research. 37. pp. 1411-1417.
14. Diamond S., Sahu S. 2006 Densified silica fume : particle size and dispersion in concrete. Materials and Structures. 39. 9. pp. 849-859.
15. Korpa A., Kowald T., Trettin R. 2008 Hydration behavior, structure and morphology of hydration phases in advanced cement-based systems containing micro and nanoscale pozzolanic additives. Cement and Concrete Research. 38. 7. pp. 955-962. (in Russian)
16. Zdeb T. 2007 Aktywnosc pucolanowa m^czek kwarcowych jako skladnika betonow z proszkami reaktywnymi. Cement Wapno Beton. 1. pp. 34-39
17. Shishkina, A., Shishkin, A. 2020Application of the easy concentration effect in concrete technology IOP Conference Series: Materials Science and Engineering, 907(1), 012038.
18. Shishkina, A., Nastich, O., Romanenko, K., Oliinyk, S. 2019 The aerated concrete based on an integrated foam concentrate containing iron compounds EEJET, 4(6-100), pp. 48-53
19. Shishkin, A., Shishkina, A. 2018 Study of the effect of micellar catalysis on the strength of alkaline reactive powder concrete EEJET, 3(6-93), pp. 4651
