Regulation of the properties of constraction gypsum by the admixtures

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KARAKALPAK RESEARCH INSTITUTE OF NATURAL SCIENCES, KARAKALPAK BRANCH

ACADEMY OF SCIENCES OF THE REPUBLIC OF UZBEKISTAN, NUKUS

Regulation of the properties of constraction gypsum by the admixtures

Turemuratov Sharibay Naurizbayevich - PhD in Chemistry, Senior scientific researcher

Akhmedov Ulug Karimovich - Doctor of chemical sciences, Professor

Republic of Uzbekistan

Abstract

Influence the nature of fine-disperse micro fillers on the kinetic of isolation and localization of a hydrate, the degree of its crystallization and formation of contacts between the particles of the systems, including various modifications of gypsum (semi hydrous, soluble and unsoluble anhydrites) was established.

New admixtures on the base of industrial wastes for inhibition of setting and increasing of cons traction gypsum durability were investigated. It has been proposed to use these fillers as carriers of electrolytes or surfactants in order to increase water-resistance and harde. Keywords: regulation, processes, structure, the mineral, gypsum, marble, a kaolin, montmorillonite, hydration, coagulation, condensation, crystallization, astringent.

Аннотация

РЕГУЛИРОВАНИЕ СВОЙСТВ СТРОИТЕЛЬНОГО ГИПСА С ПОМОЩЬЮ ДОБАВОК

Туремуратов Ш.Н.1, Ахмедов У.К.2 (Республика Узбекистан)

Туремуратов Шарибай Науризбаевич - кандидат химических наук, старший научный сотрудник, заведующий лабораторией, лаборатория химии;

Ахмедов Улуг Каримович - доктор химических наук, профессор,

Каракалпакский научно-исследовательский институт естественных наук, Каракалпакское отделение,

Академия наук Республики Узбекистан, г. Нукус, Республика Узбекистан

Влияние природы мелкодисперсных микронаполнителей на кинетику выделения и локализации гидрата, степень его кристаллизации и образование контактов между частицами систем, включая различные модификации гипса (полуводные, растворимые и нерастворимые ангидриты).

Исследованы новые примеси на основе промышленных отходов для регулирования затвердевания и повышения прочности нерастворимого гипса. Было предложено использовать эти наполнители в качестве носителей электролитов или поверхностно-активных веществ для повышения водостойкости и прочности. Ключевые слова: регулирование, процессы, структура, минерал, гипс, мрамор, каолин, монтмориллонит, уравнение, коагуляция, конденсация, кристаллизация, вяжущее.

Introduction

Semi hydrated-gypsum-based products having a series of positive properties (quick hardening, low specific mass at a sufficiently high strength, good surface structure), have certain restrictions when being used in construction due to their short-term setting and low water resistance. Anhydrite binders, on the contrary, require the introduction of activating additives facilitating hardening [1-3].

The vast printed-matter analysis dedicated to the investigation of plaster binders makes it possible to conclude that, though the mechanism of action of propertyregulating additives to plaster binders has been elucidated in general, but in spite of it the scientifically-based choice of efficient additives for their various types is practically absent particularly in case of complex additives comprising mineral fillers and surface- active substances or electrolytes.

Experimental

In this report, in order to approximate to the creation of such fundamentals, the role of various additives in the dependence - “properties of hydration hardening structures-phase composition of initial plaster binder” for dihydrous gypsum and its dehydration products - semi hydrated gypsum, soluble and insoluble anhydrites. In such a way, the objects of investigation were four modifications of calcium sulphate differing by the structure of crystal lattice, dispersion and capabilities and kinetics of hydration structure formation.

The calculation of specific surface by the data of isotherms of sorption-desorption of vapours of water has shown that it changes extremely depending on heat treatment temperature-sharply (60-80 times) increasing at hydration up to semi hydrate and soluble anhydrite and 4 times only-to insoluble anhydrite CaSO4-2H2O CaSO4-0,5H2O CaSO4, 3000C CaSO4, 7000C

Ssp, m2/g 3,5 250 180 13,6

Natural mineral substances of various genesis and composition-quarts sand containing 99,2% of SiO 2 , marble 99,9% of CaCO3, kaolinite, montmorillonite and loess loam. All they were reduced to fragments up to a complete passage through a 0,01 mm2 mesh screen, but differed sharply by specific surface (m2/g): quartz-3.33, marble-4.04, loam-18.30, kaolin- 33.60 and montmorillonite-42.0. In such a manner, the choice of initial binders and finedispersed fillers (aggregates) allows to trace the role of the nature of an aggregate at early stages of structure formation on the example of systems with one and the same structureforming phase, but different genetics of its isolation.

Differing from mineral aggregates introduced into gypsums suspensions in great quantities (up to 10-30%) we studied the effect of small (0.3-3.0%) dosages of inorganic electrolytes with one-name cation (calcium hydroxide), anion (aluminum sulphate) and their blends as well as some surface-active substances based on industrial wastes-modified lignosulphates (MIS), cellulose-production still fluid (SF), cottontar (CT) and gas- condensate-based additives(GC).

Discussions

The analysis of the results of measurement of plastic strength change kinetics in the pastes of various gypsum modifications and results obtained from mathematical processing of regression equations has shown that by the ability of activization of initial structure formation in dispersions the mineral additives studied are arranged in a line corresponding to the reduction of Ssp : quarts marble loess loam kaolin montmorillonite; for suspensions of insoluble anhydrite this line is reverse [4]. microfiller hydrate crystallization gypsum

An aggregate functioning as substrate for the isolation of new formations from the oversaturated solution releases from it the initial particles and intensifies their solution that is visually illustrated by the results of the kinetics of change of the composition of liquid phase and specific conductance of diluted suspensions containing gypsum and aggregate in optimal ratios. In mixes with all high-dispersed aggregates by 1 - 5 minutes already the values of specific conductance noticeably exceed them for purely gypsum suspension, the maximum indices correspond to the mixes with montmorillonite [5].

In concentrated pastes of CaSO4-0,5H2O, especially at lower water-solid ratios, the strength during the first 5 min 10-30 times exceeds the strength of the paste without an aggregate; correspondingly according to the data of derivatographic analysis the increase of hydration rate was confirmed by that moment. By 60 minutes, regardless of the kind of aggregate the semihydrous gypsum had been hydrated completely in all mixes.

The most informative in the analysis of the contact zone: substrate-new formations proved to be a method of scanning electronic microscopy of the chips from the surface of a gypseous stone. From the photograph on a can see that at introduction of finely dispersed quarts the structure consolidation occurs, its porosity lowers and the number of contacts between particles increases, the needle crystals of the new formations lay the surface of the glassy particles of quartz. The dihydrous gypsum does not crystallize on the surface of calcite particles, all new formations are mostly localized in the volume; in the mixes with kaolin the new formations are very fine and badly crystallized; with montmorillonite the hydrate crystallization is noticeably improved, but the contact zone is filled at the growth of crystals from the volume, but not from the surface of the clayey particle. The most close contact of the hydrate-substrate is observed on the grains of quartz. The influence of the kind of substrate is most contrastly seen in a system with a slowly hydrating insoluble anhydrite.

When studying the influence of water-solid ratio upon the character of the change of plastic strength of the CaSO4 insoluble dispersions it was noted that in spite of the most coagulative character of the structure during the first time the Pm -B/T dependence is directly opposite to that for a CaSO4-2H2O system - it is such as for other rapidly hydrating modifications of calcium sulfate-the increase of B/T from 0,30 to 0,50 leads to a three-fold lowering of the paste strength. The micro aggregates do not cause changes in the character of such dependence, but during the first day and night of hardening is distinctly seen the activating effect of clayey minerals in particular upon the degree of anhydrite hydration; so in the mixes with 10-30% of these aggregates the degree of anhydrate hydration in an hour constituted 12-13% against 3,4% in their absence. However, no direct link with the strength of the structures appearing at it exists-there was not noticed any case of sharp strength increment by that time; a noticeable increase of the stone strength in the presence of aggregates takes place by 7 days and nights only, at approximately the same degree of hydration compared with the control.

Issuing from the results obtained, it is possible to recommend the silica-containing aggregates in quantities up to 15% as an anhydrite binder hardening activator. We have tested in this respect with a positive effect the natural and dehydrated silica-affected alunite which can be considered as a mix of mineral aggregate (fine dispersed quarts and silica) and potash alum.

Summarizing the results obtained at the investigation of the systems: calcium sulfate-mineral aggregate-water, one can arrive at a conclusion that to obtain a maximum effect from the presence of mixes in a system, a micro aggregate should be combined with the activators of hardening, or with surface-active substances and electrolytes (poly electrolytes) for construction gypsum depending on the modification of calcium sulfate and a preset property.

A special series of experiments with SAS has shown that out of the investigated- aggregates the GC and SF in the concentrations of 0,1-0,5% and CT -1-3% of the mass of semihydrous gypsum noticeably increase the water resistance of gypsum stone in the humidair conditions of hardening.

The introduction into a gypseous dispersion of individual additives with a cation or an anion of the same rame produces a small effect on the water resistance of the gypseous stone. At same time a complex additive of calcium hydroxide and aluminum sulfate intended for the formation in the system of calcium hydrosulfoaluminate increases the strength and water resistance noticeably. A positive result has been obtained also in the use of fine dispersed aggregates-quarts and calcite modified with SF and lime (or containing its ashes), MIS modified in a special way as an additive to construction gypsum.

Issuing from a comparative analysis and established relarities of the structure formation and hardening in suspensions of various modifications of gypsum, an approach to the regulation of properties of the structures of hardening of natural-clayey gypsum-based binders has been suggested:

for products of heat treatment of natural clayey gypsum (ganch) up to 2000C in which the hydration structure comes into existence as the result of hydration of semihydrous gypsum (the clayey portion does not change)-additives changing the solubility of semihydrous and dihydrous modifications of calcium sulfate;

for products of high-temperature kilning which harden on the base of insoluble anhydrite for which, differing from semihydrate, the stresses do not play a considerable role, but the achievement of maximum strength is limited by a very slow formation of the hydrate-additive intensifying the solubility of the structure forming phase.

Combinations of low and high-kilned ganch binders providing high strength and water resistance in optimal ratios have been suggested.

Conclusions

In such a manner, the regularities established for model systems of various modifications of calcium sulfate with additives of various origin can serve as a basis for a directed choice of the regulators of properties of gypsum-containing binders differing by the composition of non-sulfate part.

References / Список литературы

1. Turemuratov Sh.N., Nurymbetov B.Ch. Synthes and research of lime-ware knitting on the basis of marl in Ak-Zharsky place. //Science and education of Southern Kazahstana. Shymkent, 2000. № 11. S. 223-225.

2. Rebinder P.A. Structurization processes in disperse systems / in the collection: The Physical and chemical mechanics of soils and building materials. Tashkent: the FAN, 1966. S. 9-25.

3. Segalova E.E., Rebinder P.A. Occurrence crystallizet structures твердения in the conditions of development of their durability. In кн.: New in chemistry and technology of cement. M: Gosstroyizdat, 1982.

4. Turemuratov Sh.N., Asamatdinov М., Nurymbetov B. The of role of mineral consistence in the course of hydration and structurization in modeling systems CaSO4III - H20.//Bulletin КГУ, 2009. № 1. S. 26-28.

5. Turemuratov Sh.N., Asamatdinov М., Nurymbetov B.Ch. The of role of mineral consistence in the course of hydration and structurization in modelling systems CaSO4II - Н2О. // Bulletin КГУ, 2009. № 2. S. 21-23.

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