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26 CHEMICAL PROBLEMS 2020 no. 1 (18) ISSN 2221-8688
UDC 691.327:666.972.16
EFFECT OF COMPLEX MODIFIERS ON PROPERTIES OF CEMENT SYSTEMS
A.A. Guvalov, S.i. Abbasova
Azerbaijan University of Architecture and Construction 13, Ayna Sultanova str., AZ1143 Baku, Azerbaijan; e-mail: abbas-guvalov@mail. ru
Received 14.10.2019
Abstract: The management of the rheological properties of the cement systems and the kinetics of solidification by the use of specially designed complex modifiers has been proved. Modification of cement systems was made possible by the use of a complex modifier (CM) obtained as a result of the interaction of the hyperplasticizer GLENIUM 313 with liquid glass. The peculiarity of this method lies in the gel removal of the mineral component contained in the modifier. This complex modifier is used in conjunction with water when cement systems are solidified. It has been established that the application of CM in 1.0% of cement mass allows to reduce the amount of cement dough by 1.5 times, extends the retention period, and increases the strength of the solid on the first day by 2 times compared to the unchanged systems.
Keywords: complex modifier, cement systems, polycarboxylate, gel, liquid glass, hyperplasticizer, viscosity, strength.
DOI: 10.32737/2221-8688-2020-1-26-32
Introduction
Construction of complex structures is impossible without the use of new generation polyfunctional concrete with high construction and technical properties. Modifying cement systems for optimization of the concrete mixing process and remoteness during the construction of buildings on hot days of the year is one of the most important issues. At low or negative temperatures, it is necessary to shorten the hardening time so that concrete can quickly build up the strength of the brand. Therefore, the control over high-strength concrete retention and reinforcing modes is a pressing problem. In order to obtain a new generation of high-strength concrete, their structure must be modified by micro- and nanoparticles [1-4].
Modifiers play a special role in the structure of cement systems, including mineral, organic and organic-mineral [5, 6]. The application of micro and nanostructures close to the cement clinker minerals due to their crystallochemical structure allows obtaining high-density cement matrix. These particles regulate the hydration process of clinker minerals and provide the formation of
stable, high-strength dense cement stone, consisting of low-base calcium hydrocyclates in cement systems [7, 8]. It is well known that the most widely used effective mineral-active additive (MAA) is SiO2-based amorphous microsilica (d = 50 ^ 150 nm) and nanostructures (d = 5 ^ 10 nm) [9,10]. However, when they were incorporated into the cement composition, water content increased. This problem is solved by the addition of hyperplasticizers that reduce the water demand by 30-40% while preserving the rheological properties of cement dough [11,12]. According to modern concepts, the effect of hyperplasticizers on cement hydration and solidification involved complex physical and chemical processes. It revealed that the use of polycarboxylates is due to the electrostatic-steric mechanism induced by adsorption of organic matter molecules onto cement particles [6,12]. Polycarboxylate molecules formed a complex metastable complex with Ca2+ ions to provide low calcium-hydroxylate phases. During the interaction of polycarboxylate molecules with C3A, a new structure of hydrate compounds
CHEMICAL PROBLEMS 2020 no. 1 (18)
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was formed by the formation of stable member-mineral phases.The most effective complex modifier for cement stone modification is SiO2 nanoparticles and organic-mineral additives derived from hyperplasticizer. The widespread use of silicon-containing nanoparticles in concrete production is due to the complexity of the SiO2based nanopowders synthesis and their additon to cement systems. It matters from technological point of view that SiO2 is a gel in the complex modifier and its mixing with water strengthens cement systems. Hyperplasticizer, which is involved in the process of obtaining a complex modifier, has two functions: it stabilizes the growth of colloidal aggregates in the silicon and regulates the technological problem of uniform distribution of complex additives and regulates the rheological properties of cement system
development. It found that the incorporation of nanomodifying additives into the water-cement system increases the hydration of the cement several times [13,14]. It should be noted that the hydration rate in the cement systems with the modifier was added up to 75% of the daily room temperature at room temperature. However, the study into conditions of efficient nanomodification by identifying different functional carriers for transferring nanowires to cement systems is rather relevant. Also, the main focus of the current research is to identify the method of obtaining appropriate complex modifying additives for efficient transfer of SiO2 particles to cement systems and explore their effect on rheological properties, retention time and formation of cement stone in the initial phase of solidification.
Materials and research methods
During the studies, the samples were made from fixed water/Sem cement dough with 0.28. Portland cement CEM I 52,5N was used for preparation of cement stone samples in accordance with of AZS EN 197-1 requirements from the NORM cement plant. Experiments were carried out with the addition of cement stone and CM modified components. As a complex modifier, CM was synthesized on a 40% liquid glass with GLENIUM 313 (p = 1050 kg / m3, pH = 5.5) branded with BLAF based on polycarboxylate esters. During the preparation of fine-grained concrete, Bahramtapa tea sand (Mir = 2.1) and Guba crushed sand (Mir = 3.4) were used as fillers.The following characteristics of cement systems were revealed in the experiments: - Rheological characteristics of the cement dough are determined by its RV-8M rotation viscosity.
Results and their discussion
Kinetics of solidification of cement dough was determined through measuring the plastic strength when measuring cone-shaped plasticity of the Moscow State University MV Lomonosov [15]. Impact of CM on the strength of cement stone was evaluated based on the results obtained during the determination of the strength of compression after 1, 3, 28 days of 2x2x2 cm solid samples under normal conditions. Determination of durability was made on the AUTO 105/250 CEMENT COMPRESSION and FLEXURAL MACHINE. Effect of CM on properties of small concrete was made in 10x10x10cm samples of solid state under normal conditions.
CM was obtained by shaking the polycarboxylate solution with a diluted 1: 3 water bottles. Vibration was carried out until the ambient pH = 7.5. When the hyperplasticizer solution was neutralized with a liquid glass solution by continuous stirring at 300C, colloidal aggregates of SiO2 form and stabilized by carboxylate molecules.
Application of CM in the same Water/Sem ratio in all variants allowed to reduce the content of cement paste by 1.6-2 times as compared to the unchanged benchmark system and at the same time increase the strength of cement stone (Table 1). The largest reduction of cement dough was observed when the modifier was used in 1.2%
of cement mass. This was due to the large constituents is 0.073%, 0.082% and 0.10% amount of superplasticizer in the system. The cement by mass. content of SiO2 gel in the 2nd, 3rd and 4th
Table 1. Rheological and strength characteristics of cement systems
№ Additive quantitiy Viscosity of cement paste, SPZ Cement stone strength, MPa
1 day 3 days 28 days
1 Non-additive 8.25 7.2 21.8 49.6
2 0.8% CM 5.12 28.8 35.3 70.2
3 1.0% CM 4.84 29.2 41.3 82.6
4 1.2% CM 4.12 28.5 38.7 76.4
Changing the amount of bride does not have a sharp impact on the cement paste itself. A sharp decrease in the cement paste content was due to the effect of the hyperplasticizer. Based on the results obtained, it can be concluded that the use of this supplement allows regulating the rheological characteristics of cement paste and contributes to their application in obtaining high-flow 1,4
concrete mixes. It revealed that the Pm kinetic curve of plastic strength of cement systems changed in the course of the CM use (Fig. 1). In this case, the regularity of capture kinetics was determined by the amount of CM. In the CM systems with 0.8% and 1.0% mass of cement mass, the effect of increasing the plastic strength after 5 and 8 hours after mixing with water was revealed.
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14
The value of Pm = 0.02 MPa which corresponded to the beginning of the retention period in non-additive cement samples, was obtained 160 minutes after water mixing with cement, that is, after the standard starting time of catching. When using CM in the mass of 0.8-1.0%, the plastic strength value of 0.02 MPa was achieved 4-5 hours after mixing the water with cement. Plastic strength value of 0.08 MPa corresponding to the end of the
setting period was 6 hours in the supplementary samples and 8-10 hours with 0.8-1.0% CM added. Thus, the addition of CM increased the setting period of the cement test. As a result, rheological characteristics of the modified cement systems proved more stable than unmodified systems.
Rising strength of cement stone during the CM use was proved. First of all, the acceleration of strength of cement stone was
determined (Table 1). Application of complex additives in all quantities provides that the three-day cement stone gains 50% of the 28-day strength. Note that the modified systems gained strength up to 28.8-32.2 MPa per day and up to 33.3-38.3 MPa in three-dayshardness. Value of strength in nonadditive systems was 7.2 MPa per day and 21.8 MPa per 3 days. At the same time there was rise in the price of the strength limit to 70.2-82.6 MPa, as opposed to 49.6 MPa for non-additive systems. The highest strength is observed when the amount of additive is used
in the amount of 1.0% of cement mass. This difference is explained by the modifying effect of the additive on the dispersive and morphological composition of new compounds of cement stone.This is where the modified structure has a higher resistance to collapse.
Electronic microscopy shows micropores between newly formed composite. In the newly formed compositions, large crystals of high-base hydrocyclates (size 10-15 p,m) and large plates of ettringite were observed (Fig. 2a).
Figure 2. Microstructure of cement stone, 1000X magnification a - cement stone non-additives; b - cement stone with 1.0% CM added
The structure of the cement stone attached to the CM mainly composed of low-grade hydrocyclates (sizes 10-15 p,m) (Fig.2.b).
A 1: 3 cement filler (50% sand and 50% crushed sand) was prepared to study the effect of CM on properties of fine concrete. The amount of supplement was 0.8-1.0% of the cement mass in the solution. At the same time, the concentration of SiO2 gel at the given ratio of the complex modifier was 0.0730.1%. Results of the experiment are shown in Fig. 3.
It can be seen that CM raises the compression strength of fine-grained concrete from 49.25 MPa to 70.49 MPa. In the early stages of reinforcement, the strength of the modified samples rose by 50-55% as compared to non-additive samples, and by 43% in 28 days. As can be seen from the
results, the nanomodifier provides a faster accumulation of strength in the initial stages of solidification. This was due to the interaction of SiO2 gel with the Portlandite formed during the hydration of clinker. Samples with additives of complex modifiers gain up to 3 days of labeling strength without additional samples.
Thus, it was experimentally proved that the use of polycarboxylate either and synthesized CM based on liquid glass can significantly reduce the cement paste viscosity. At the same time, the optimal use of CM provides the stability of rheological characteristics of the modified cement systems more than twice as compared to the unmodified systems. The use of complex modifying additives in the amount of 1.0% of cement mass contributed to the production of
high-viscous concrete mixes (which maintains the flow for, at least, 3 hours).
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Figure 3. The influence of CM on the compressive strength of fine-grained concrete
It should be noted that due to the accelerated formation of concrete structure at early stages of reinforcement, the shortening of the reinforcing period makes it particularly efficient for monolithic structures. Thus,
improvement of comfort placement of concrete mixes in monolithic structures, their transportation to long distances and reduction of labeling efficiency are important issues.
Reference
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3. Singh L.P., Agarwal S.K., Bhattacharyya S.K. Preparation of silica nanoparticles and its beneficial role in cementitious materials. Nanomaterials, nanotechnology. 2011, vol. 1, no. 1, pp. 44-51.
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KOMPLEKSMODÍFÍKATORLARIN SEMENTSÍSTEMLORÍNÍN
xassoloríno tosírí
A.A. Quvalov, S.i. Abbasova
Azdrbaycan Memarliq vd ln§aat Universiteti Az 1148, Baki, Ayna Sultanova kûç.13 tel. : +994 50 350 29 88; e-mail: abbas-guvalov@mail.ru
Xüsusi hazirlanmiç kompleks modifikatorlarin tdtbiqi ild sement sistemldrinin reoloji xüsusiyydtldrinin vd bdrkimd kinetikasinin idard olunmasi sübut edilmiçdir. Sement sistemhrinin modifikasiyasi GLENlUM 313 hiperplastikld^diricisinin maye ild qarqiliqli tdsiri ndticdsindd alinmuç kompleks modifikatorun (KM) istifaddsi ild aparilmiçdir. Bu üsulun özündmdxsuslugu modifikatorun tdrkibind daxil olan mineral hissdciyin gel halinda alinmasi ild baglidir. Bu kompleks modifikator sement sistemldrinin bdrkimdsi zamani su ild birlikdd istifadd olunur. Müdyydn edilmiçdir ki, sementin kütldsinin 1.0 %-i miqdarinda KM tdtbiqi sement xdmirinin özlülüyünü 1.5 ddfd azaltmaga imkan verir, tutma müdddtini uzadir, bdrkimdnin ilk günündd möhkdmliyi modifikasiya olunmamiç sistemldrld müqayisddd 2 ddfd artirir. Açar sözlsr: kompleks modifikator, sement sistemldri, polikarboksilat, gel, maye §ü§d, hiperplastikld^dirici, özlülük, möhkdmlik.
ВЛИЯНИЕ КОМПЛЕКСНЫХ МОДИФИКАТОРОВ НА СВОЙСТВА ЦЕМЕНТНЫХ СИСТЕМ
А.А. Гувалов, С.И. Аббасова
Азербайджанский Университет Архитектуры и Строительства, AZ1143 , Баку ул. А. Султановой, 13 тел .: +994 50 350 29 88; e-mail: abbas-guvalov@mail. ru
Доказано управление реологическими свойствами цементных систем и кинетикой затвердевания с использованием специально разработанных сложных модификаторов. Модификация цементных систем стала возможной благодаря применению комплексного модификатора (КМ), полученного в результате взаимодействия гиперпластификатора GLENIUM 313 с жидким стеклом. Особенность этого метода заключается в том, что минеральный
компонент, который содержится в модификаторе, получается в виде геля. Этот комплексный модификатор используется вместе с водой при затвердевании цементных систем. Установлено, что применение КМ в количестве 1.0% от массы цемента позволяет
уменьшить вязкость цементного теста в 1.5 раза, увеличивает время схватывания и повышает прочность цементного камня в первый день в 2 раза по сравнению с немодифицированными системами.
Ключевые слова: комплексный модификатор, цементные системы, поликарбоксилат, гель, жидкое стекло, гиперпластификатор, вязкость, прочность.
