Research of porosity of a cement stone with a zeolite containing filler and a superplastic stificator

This research paper discusses the influence of the zeolitecontaining filler of the Beltau deposit and the polycarboxylate superplasticizer on the formation of the porosity of the cement stone. The results of experiments to establish the effect of zeolite-containing filler and plasticizing additive on pore size distribution are graphically presented. The data obtained confirm the feasibility of using this type of filler in concrete.

Currently, there is no generally accepted method for dividing the pores of capillaryporous bodies by size. However, it can still be noted that this issue was most fully developed by M.M. Dubinin [2,3]. The international organization IUPAK provides for the division of pores by size into micropores (less than 2 nm), mesopores (2-50 nm), and macropores (more than 50 nm).
The complete data on the influence of certain categories of pores on the properties of cement stone are presented in Table 1.
The classification shows that physical and mechanical parameters (strength and deformability), contraction deformations (shrinkage), special properties (water resistance, frost resistance, etc.) are largely determined by the emerging pore structure of the cement stone.
A large number of works are devoted to the formation of the structure of a cement stone in unfilled systems [3]. As for the filled ones, the influence of industrial waste and manmade products on the formation of the structure of cement stone has been studied to a certain extent. In this regard, it is of certain scientific interest to study the issues of structure formation of cement compositions modified with an active mineral additive of a certain dispersion from zeolite-containing rocks. This article shows the results of studies of the effect of zeolite-containing (ZCR) filler (natrolite) and superplasticizer on the formation of the pore structure of a cement stone.
The ZCFC of the Beltau deposit (Central Kizilkum) with a specific surface SP-11А 3400 cm 2 /g. The chemical composition of ZCR.
The surfactant used was a polycarboxylate superplasticizer (SP) POLIMIX from ARMENT CONSTRUCTION CHEMICALS.
The water-reducing effect of SP is 30%, the optimal dosage is 0.8% of the binder mass. The porosity characterization of the cement stone was determined using a Thermo Scientific Pascal 240 mercury porosimeter (Italy). For the experiment, samples of 20x20x20 mm in size were made and immersed in a CD3 dilatometer to form a vacuum on the evacuator. After the formation of a vacuum, the dilatometer was filled with mercury and immersed in the autoclave compartment of the porosimeter to obtain porograms. Porograms were calculated automatically using the SOLID EVO software, and the following characteristics were determined: specific pore volume (mm 3 / g), relative pore volume (mm 3 / g), and total porosity (%).
During the experiments, four types of compositions were made: The mixing of the binder components was carried out separately -first, the filler from ZCR ground to a specific surface of 3400 cm 2 / g and cement were mixed with part of the mixing water, and then with the rest of the water and the additive. The cement-bonded particle board filler consumption is assumed constant and equal to 30% of the cement mass, and the SP dosage is 0.8%.

Results and Discussion
According to the shape, the pores in the cement stone are divided into closed (pores are rounded and isolated from other pores), channel-forming (pores are open at both ends and can be straight, worm-shaped and loop-shaped), and dead-end (open only at one end and can, has straight, worm-like, loop-shaped configuration). By origin, the pores in the cement stone are subdivided into the air, sedimentation (capillary, sedimentation), and contraction pores. Air pores are formed as a result of technological factors, sedimentation as a result of external and internal water separation. With external water separation, part of the mixing water goes out, forming a system of communicating capillaries, and the rest accumulates in the contact zones and contributes to the formation of sedimentation pores.
Contraction pores are formed due to the manifestation of contraction of the "cementwater" system during hardening of the cement stone. There is an assumption [3][4][5][6][7] that the contraction pores have sizes characteristic of capillaries. Of undoubted interest are studies on the formation of the structure of multicomponent systems "cement-mineral-additivesuperplasticizer." The characteristics of the study of pore parameters are shown in Fig. 1, 2. Based on the processing of the experimental results shown in Fig. 1, 2, the characteristics of the pore structure of the studied samples were obtained (Table 3.). Analysis of these tables shows that compositions № 3, 4 differ from the control ones: with the introduction of a finely ground additive, insignificant changes in porosity are observed. The porosity of composition № 2 is reduced by 14.95%, the specific and relative volume by 21.53% relative to the control. The introduction of the filler helps to reduce the pore size in the region of 4.8682-0.1846 microns, which, according to the classification [2], [3][4][5][6][7][8][9][10], affect strength, frost resistance, and water resistance. In our opinion, a decrease in porosity in such systems occurs due to the formation of low-basic neoplasms due to interactions arising with the participation of active silica and alumina with calcium hydroxides. In composition № 3, there is a significant decrease in porosity by 32.16%. Specific and relative pore volumes are reduced by 39.45%. In our opinion, this is due to the waterreducing ability of the SP. As a result, capillary porosity decreases, and a denser structure of the cement stone is formed.
Based on the classification [3], we can also conclude that pores less than 10 nm do not affect the mechanical properties. Dangerous pores that reduce strength, frost resistance, permeability, etc., are larger than 10 nm. Further, we carried out studies of the influence of individual pore categories in terms of size on the strength and durability of the cement stone ( Figure 3). The best performance is observed in the composition № 4: the porosity of the cement stone decreases relative to the control by 50.5%. Due to a significant decrease in porosity, composition № 4 has the highest strength index. The reason for the change in the pore structure is, apparently, the transformation of Ca(OH) 2 into ow-base compounds due to interaction with active silica and a decrease in the amount of mixing water.  Figure 3 it can be seen that the dangerous porosity of composition № 1 is 16.663%. With the introduction of SCR microfiller, the dangerous porosity of the composition № 2 is reduced by 33.17% and is 11,135. The introduction of SP in the composition № 3 reduces the number of dangerous pores in the cement stone by 43.52%. In composition № 4, the dangerous porosity is reduced by 66.95% and reaches 5.507%.
Based on the classification [3], we propose to divide the capillary pores of the cement stone into the following three groups: 1. Macrocapillaries -15-0.5 microns (affect strength, permeability, frost resistance); 2. Mesocapillaries -50-10 nm (affect strength, permeability, and shrinkage at high humidity); 3. Microcapillaries -10-2.5 nm (affect shrinkage). To establish the presence of capillary pores formed due to hardening of the multicomponent system cement + ZCR + SP, studies were carried out to determine the quantitative content of such pores in the developed composite (figure 4). Comparing the pore structure of a cement stone with different content of modifying additives showed that the most favorable in reducing the macro-, meso-and microcapillaries increasing the strength of the cement stone is composition № 4.

Conclusions
The research results obtained can be summarized as follows: -introduction into the mixture of a finely ground filler made from ZCR helps to reduce the porosity of the cement stone by 2.622%; -introduction of SP into the mixture provides a significant increase in stone density and a decrease in porosity (by 5.638%); -as a result of using a filler from ZCR + SP it helps to reduce the porosity by 8, 854% (50% in relation to the control).
The results obtained indicate the positive effect of the composition based on finely ground ZCR and CP based on polycarboxylate ethers on the formation of the required parameters of concrete properties and contributes to the creation of the necessary conditions for a deeper flow of hydration processes in the system "cement + water + CP + ZCR"