Enclosing structures of a porous structure with polymeric reagents

. This article is devoted to the use of the polymer K-9 reagent in porous claydite-ash concrete and the design of its optimal composition according to the general design method of the optimal composition of the general theory of artificial building conglomerates (ISC). The data of experiments confirming the positive effect of the polymer reagent on increasing the durability, improving the moisture and heat engineering modes of porous concrete are presented.


Introduction
Increasing requirements for the level of thermal protection of building envelopes in a dry hot climate contributes to the intensive development and implementation of effective building envelopes with relatively low thermal conductivity coefficients and low water absorption into the practice of construction production.
In seismically active regions of Uzbekistan, in the production of external enclosing structures of buildings, as is known, it is necessary to use lightweight concrete, which must have a solid structure, which, at high heat-shielding performance, provides sufficient protection from atmospheric moisture, and reinforcement from corrosion.
Heat loss through lightweight concrete walls according to [1] is up to 30%.The problem of increasing the thermal properties of lightweight concrete of external walls is combined with the problem of creating lightweight concrete.
Such concrete can be obtained in an efficient way -by creating an optimally porous structure of the intergranular space, in other words, by porous binder.
At the same time, porous expanded clay concrete makes it possible to make up for the lack of scarce expanded clay sand, reduce the density and thermal conductivity of concrete, reduce the water demand and release moisture content of products, improve the cohesion and workability of the mixture and achieve a number of other advantages [2].
Porous claydite concrete with cement consumption equivalent to ordinary expanded clay concrete has almost equal strength.Porous concrete mix is less susceptible to water separation, since air bubbles seem to clog the channels through which water circulates.In this case, the intergranular space of expanded clay is filled with porous cement paste, consisting of small closed pores [3].
The aluminum powder commonly used for porosity has an undesirable tendency to float to the surface of the water film, forming a scaly coating.In order to evenly distribute the pigment powder in the binder mass and dissolve the oily film, additional substances are introduced.Therefore, it is much more expedient to use complex gas formers, which, being the initiators of gas swelling, at the same time contribute to a decrease in the average density of concrete while maintaining its required strength with the lowest consumption of aluminum powder.
The author has developed a complex blowing agent based on aluminum powder and K-9 polymer reagent (K-9 water-soluble polyfunctional acrylate additive based on nitron fiber production waste) in an amount of 0.002% by weight of the powder [4].Additive K-9, like all additives wetting agents of an ionic nature, envelops the particles of aluminum powder, evenly distributing them in the volume of the binder, preparing them for a joint spontaneous reaction.
On the basis of a complex blowing agent, a porous claydite-ash concrete was obtained, which is characterized by a decrease in the average density by 100-150 kg / m 3 .Replacing a part of expanded clay sand in expanded clay with ash (50% of the volume and complete 100% replacement), which has an amorphous structure and a bulk density lower than the bulk density of expanded clay sand leads to a decrease in thermal conductivity.

Method
When developing porous concrete according to the general method of designing the optimal composition of the general theory of artificial building conglomerates (ABC), the activity (R*) of cement-ash stone is determined initially (for given materials and established technological stages: mixing, compaction, hardening regime, etc.) optimal structure (Fig. 1) [5].

Compressive strength, MPa
Rcom,MPa Water-cement relations Curve A -envelope of cement binders with optimal structure; the curve with indices I, II, III, IV, V, VI correspond to the specific surface area (m 2 / kg) of the Portland cement binder, respectively, with a grinding time of 30 ', 45', 60 ', 90', 120 ', 180'.I -280 m 2 / kg; II -320 m 2 / kg; III -370 m 2 / kg; IV -400 m 2 / kg; V -450 m 2 / kg; VI -520 m 2 / kg /. (note: figures are taken from [3]).To design the compositions of porous claydite-ash concrete of classes B 5 and B 7.5 on the basis of a cement-ash binder of the optimal composition, the ash content in it is taken as 25% and K-9 additives in an amount of 0.002% with a grinding time of 45 minutes.The highest activity value R* = 77.6MPa was obtained at B* / B = 0.225.
The need to increase the binder activity was justified by the following reasons: R*calculated value included in the formula for the strength of conglomerates with an optimal structure: The amount of binder in the conglomerate depends on R*: the higher the R* value, the higher the W/C ratio the consumption of the binder decreases.In addition, according to the obligatory law of congruence, or the obligatory correspondence of properties, all strength, deformative and other qualitative indicators of a conglomerate are directly related to the same properties of a binder, and with optimal structures, their relationship is strictly natural.Therefore, it is necessary to have high-quality indicators of the properties of the binder and, in particular, strength.
To find the composition of porous concrete that meets the strength requirements Rreq, it is first necessary to determine the permissible degree of porosity of the cement-ash stone using aluminum powder.Since the real activity of the binder R* is much greater than Rreq of concrete, the cement stone can be porous to R_pores *, and the degree of permissible porosity of the binder in the structure of lightweight concrete is found from the condition that (R_pores*) / R_req = 2.0 -activity 3.5.Moreover, the higher the activity of the binder R*, the closer the degree of permissible porosity to 3.5.
For the experimental determination of the required amount of aluminum powder for porosity of the binder, samples were made from cement-ash dough with different contents of aluminum powder at a given W/W ratio.

Technology
Experimental results.Aluminum powder was introduced into the binder in the form of a water-aluminum suspension.In water with a temperature of up to 800, the additive K-9 (0.002% of the powder weight) was dissolved, then aluminum powder (by weight) was poured into the solution and the suspension was stirred for 2 minutes.
After molding, curing, hardening according to the accepted mode and testing of the samples, graphical dependencies were built -curves 1, 2, 3, 4 in Fig. 3. Curves 1.4 express the dependence R of the cement-ash stone (without the addition of K-9) on the content of aluminum powder for concrete of classes B5 and B 7.5, respectively; on curves 2,3 -the same dependence, but for cement-ash stone with chemical additive K-9.
The data presented confirm the assumption that the K-9 additive is an initiator of gas swelling.This is due to the fact that the PAK-3 aluminum powder used for porization has the ability to float on the surface of a water or oil film, forming a scaly cover.
The floatation of pigment powders, which is a negative quality, is associated with the lamellar shape of particles, the presence of fatty acid molecules on their surface and the products of their interaction with the oxide surface of the metal -aluminum stearates.The K-9 additive, like all additives -wetting agents of an ionic nature, envelops the particles of aluminum powder, evenly distributing them in the volume of the binder, prepares them for a joint spontaneous reaction.That is, a kind of complex blowing agent is obtained, which provides a decrease in the average density while maintaining Rtr / pore at the lowest consumption of aluminum powder.The effect of the K-9 additive on the gas-forming ability of aluminum powder was studied by the kinetics of gas evolution and swelling of the cement-ash dough using the device in Fig. 2. Figure -3 shows the outgassing curves.The porous mixture had the same temperature -40 0 C, swelling rate and gas evolution time.The results obtained show that the K-9 additive enhances the gas-generating ability of aluminum powder and allows it to be saved.

Discussion of results
According to the research results, it has been established that to obtain a porous cement-ash binder for concrete of B5 classes (Rreq of concrete is 6.75 MPa) and for B 7.5 (Rreq of concrete is 9.0 MPa), the degree of permissible porosity can be taken equal to 3, 5, since R* = 77.6MPa (there is a large difference between R* and Rreq of concrete).In this case, the activity of the porous binder is equal to Rtr / pore = 35.0MPa [1][2][3][4][5][6][7].
It was determined that for the porosity of the binder containing the K-9 additive to obtain Rtr / pore = 35.0MPa for class B5 concrete at a given average density of 900-1050 kg/m 3 , it is necessary to introduce aluminum powder in an amount of 520-540 g/m 3 according to the indicated average density.To obtain a porous binder with K-9 for class B 7.5 concrete at a given average density of 1050-1100 kg / m 3 , respectively, 500-400 g / m 3 of aluminum powder were required [5][6][7][8][9][10][11][12].
For the porosity of the binder without the addition of K-9, the consumption of aluminum powder was obtained for concrete of class B 5 and an average density of 900-1050 kg / m 3 , respectively, 580-540 g / m 3 , and for concrete of class B 7.5 and an average density of 1050-1100 kg / m 3 , respectively 550-500 g / m 3 .

Compressive strength, MPa
Rcom,MPa Amount of aluminum powder, kg / m 3 Fig. 4. Dependence of the strength of the porous binder on the amount of blowing agent: 1-cement-ash stone without K-9 additive (for concrete with an average density of 900-1050 kg/m 3 ); 2 -the same with 0.002% K-9; 3-cement-ash stone with 0.002% K-9 9 (for concrete with an average density of 1050-1100 kg / m 3 ); 4 -the same without K-9.
In the general case, in order to find the required content of aluminum powder at a given average density, it is necessary along the ordinate axis, as can be seen from Fig. 4, to postpone the value of Rtr / pore, translate it to the corresponding curve (1,2,3,4) and along the abscissa axis will find the required required content of aluminum powder in the cement-ash stone.

Conclusion
On the basis of a complex blowing agent, a porous claydite-ash concrete was obtained, which is characterized by a decrease in the average density by 100-150 kg/m 3 .
No weight loss was observed in concrete.The magnitude of the shrinkage deformations of heat-insulating concrete on the developed complex gas generator is in the range (50-75) .10-5m.
A necessary indicator for predicting and studying the thermophysical properties of concrete of external walls during operation are the characteristics of mass transfer.The moisture characteristics of lightweight concrete are determined on a special moisture meter, which is based on the capacitive method, based on the fact that cellular concretes, as capillary-porous bodies, are good dielectrics with a dielectric constant of 1-6.
For water, this value is 8.According to the readings of the device in accordance with the schedule for determining the moisture content, the fixed value of the moisture content of the product is set.In the case of obtaining high values of moisture content, its decrease should be corrected by reducing the initial moisture content of concrete and adopting a hardening regime that would combine two interrelated phenomena -heat-moisture hardening and drying of the material [7][8][9][10][11][12][13][14][15].
Thus, the use of the K-9 polymer reagent in porous claydite-ash concrete of the outer walls improves their moisture and thermal conditions, increases durability, saves fuel and energy resources, and also improves sanitary and hygienic conditions in the room.

Fig. 1 .
Fig. 1.Dependence of the ultimate compressive strength of cement stone on the water-cement ratio at different specific surface areas of the Portland cement binder.