2.6 Role of amorphous silica

To improve the properties of gypsum cement gypsum stone was proposed to be used as the active mineral additives and gypsum cement gypsum compositions of amorphous silica white carbon black.

The consumption of white carbon relative to the weight of Portland cement accounts for 7 against 35% for diatomaceous earth in the selection of the squad for GCPW. Such large differences in the consumption of additives used are determined by their different chemical activity. In particular, the solubility of fumed silica in 20% strength Koh solution for 3 h at 20°C is 94,44 against of 9.94% for the diatomaceous earth.

Different reactivity produces the various effects of diatomaceous earth and white carbon on the parameters of structure formation of the system. So, with the decrease in the content of semi-aquatic gypsum, the system does not reduce the plastic strength of the crystallization structure of the material, as is the case when applying diatomaceous earth. On the contrary, set at € rapid growth "'this strength, reaching maximum values when the content of 60-70% semi-aquatic gypsum by weight of the dispersed phase. With the same content of semi-aquatic gypsum in the system with increasing amounts of fumed silica up to 10% of the plastic strength of the structure material increases. The maximum growth rate observed under optimal maintenance of semi-aquatic gypsum.

With regard to diatomaceous earth such patterns of changes in plastic strength no. On the contrary, with a decrease in the content of gypsum binder, and with increasing content of diatomaceous earth plastic strength of crystallization of the structure is reduced. This indicates the need to clarify whether the optimal value of the additive (10% by weight of cement) and gypsum binder (60-70% of the total weight of the composition) only gypsum cement gypsum mixtures on a white soot or it is a more General pattern.

Increasing to 10-20% of the number of constituent active additives to cement the ultimate strength of the binder increased regardless of the additive introduced by changing the relative content of cement or semi-aquatic gypsum. Maximum strength gypsum cement gypsum stone is achieved when the content of 60-70% gypsum binder in the composition. Therefore, the ultimate strength characteristics of gypsum cement gypsum stone are correlated with parameters of structure formation.

Significant differences were also observed in the structures formed by the hardening of Portland cement mixed with gypsum binder. They are studied by the author and gypsum cement gypsum at a ratio of 1:2 by weight, providing a manifestation of the properties of the gypsum binder in the processes of structure formation of the system.

With the introduction of a specified quantity of gypsum binder in Portland cement has been a sharp decrease in the crystalline phase in the structure of stone with 50 to 35-37%. The main part of the crystalline phases comprise crystals of hydrated hair. A portion of these crystals and aggregates enveloped pelitomorphic substance, the occurrence of which is the result of interaction of gypsum with the products of cement hydration.

The filling material in this case partially loses its amorphous structure and acquires a uniform Micrograin structure, and its crystalline phase is amorphous.

Gypsum gypsum cement gypsum pastes in the presence of diatomaceous earth is accompanied by certain structural changes. With the introduction of 50% diatomaceous earth (to cement) content of the crystalline phase compared to the control samples has not changed, the crystals enveloped dirty brown amorphous diatomaceous earth.

The filling material mainly has an amorphous structure and only in some areas saves pelitomorphic structure. The porosity of the structure increases from 8-9 to 20%. Often have meandering cracks. The presence of calcium hydrosilicates at the age of 3 months not detected. When doubling additives diatomaceous earth is dramatically reduced relative content of the crystalline phase in the material structure. The contours of the crystals lose their shape.

When introduced into the system 10% of white carbon crystalline phase in the structure increases from 35 to 37% (for the sample without additive carbon white) up to 80%. Similarly, the cement structure of the system under study is also represented by calcium silicate hydrate in the form of scattered crystals, which are occasionally associated with amorphous silica, cementing in separate spots. However, in the described case pyrosilicate calcium forms incorrectly-angular concretion in size from 0.1 to 1.0 mm, inside which are deposited crystals of l'oreal.

In the crystalline phase structure only occasionally there are grains of gypsum. The filling material compared with gypsum cement gypsum sample without additive white carbon becomes more amorphous, but partially saves the crystal phase of colloidal dimensions. The pores in the material make up of 8% and have a rounded, less angular shape.

With increasing content of carbon white double crystal phase in the material structure practically does not increase, but it includes much more calcium silicate hydrate. The number then increases to 15%. These pores having a size of from 0.03 to 0.8 mm, sometimes connected by a winding cracks.

Thus, the introduction of gypsum cement gypsum composition of amorphous silica more effectively than in less active mineral additives like diatomaceous earth. To achieve the optimal structure of stone with a maximum strength of consumption of white soot should be 10%, and for the necessary stability of this structure 15% by weight of Portland cement (which corresponds to a SiO₂/C₃A≥4.8 V).

2.7 Pre-hydration of the cement component of the composition

Activation gypsum cement gypsum cement component of the composition can be achieved by pre-hydration of cement in the absence of the hemihydrate of calcium sulfate. In such conditions it is possible to partially eliminate the negative impact that the hemihydrate of calcium sulfate on the hydration of aluminate and silicate phases of Portland cement clinker.

Pre-hydration of the Portland cement at a/T = 0.2 to 0.5 and a temperature of 20-140°C for 0.5-8 h,after which h formed in su-spengiu to enter the gypsum binder. Due to the activation of Portland cement in the specified mode, the strength characteristics of gypsum cement gypsum compositions, ceteris paribus, significantly improve. However, pre-hydration creates more favourable conditions for the formation of gypsum cement gypsum stone, but is lost to a certain degree of hydraulic activity of cement. Therefore, pre-hydration of Portland cement for 8 h at 80°C accompanied by a decrease in the tensile strength and elastic modulus of the formed stone is almost 2 times.

Based on the concept of the role of competing interactions of the components in the hydration process of hardening of mineral binders, studied the effect of the input components in the mixture to conditions for the formation of gypsum cement gypsum stone.

Short-term pre-hydration of the cement component in isolation does not provide a positive result. However, in combination with other physico-chemical factors such hydration is essential to improve the hardening of gypsum cement gypsum systems. It is necessary to emphasize the protective and dispersing effects of surfactants, the intensity of which increases if prevented hydrolysis of the products of hydration of Portland cement monomineralic under the influence of the activeadditives.

2.8 Pre-sulfation of the cement component of the composition

An effective way to eliminate the negative interaction posled¬stvy alyuminatnoi and sulfate phases can be partial movement of process of interaction of sta¬dii hardening gypsum cement binder in his stage polu¬cheniya. In the case of wet grinding of Portland cement with 15% gypsum sulphate formed stone is greatly improved.

Of particular note is a method for producing GTSPV where gypsum cement composition is prepared in pots for cooking gypsum binder. The digester is introduced gip¬sovuyu tripoli flour and ground, the mixture is heated to 80-100 ° C and introduced into a saturated solution of sodium chloride (calcium or potassium) at a rate of 0.1-0.3% solids by weight of the mixture. This mixture is heated to a temperature of 120-125 ° C and then fed ko¬tel predetermined amount of Portland cement, and the mixture is heated to a temperature ensuring prevrasche¬nie gypsum calcium sulfate hemihydrate.

The proposed method simplifies the production technology of gypsum cement binder and improves its quality mainly due to the increase odnorod¬nosti mixture. Furthermore, in the process mode, it is also alyuminatnoi phase hydration of Portland cement to water vapor to form a highly basic environment hydroaluminates S4AN13-type calcium hydroxide required for forming four-calcium hydroaluminate, cleaved from tricalcium silicate hydratable than po¬slednego activation is achieved.

The method of sulfation, provides a new rapid-sulfated cement (BSC) This astringent Obra-is generated from the gypsum-containing raw materials and Portland cement, combined in certain proportions. Technological cycle BSC poluche¬niya includes selective hydration of the aluminate phases of Portland cement clinker, calcium gidrosulfoalyumi¬natov synthesis, dehydration of gypsum to calcium sulfate hemihydrate and activation of tricalcium silicate portlandtse¬mentnogo clinker.

The process of obtaining BSC comes down to finding the mode in which the required degree gid¬ratatsii aluminate phase synthesis and calcium gidrosulfoalyuminatov achieved in a time not exceeding prodolzhi¬telnost induction period of hydration of tricalcium silicate.