Reactions pozzolanic materials 


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Reactions pozzolanic materials



The pozzolanic reaction - Chemical interaction of powdered silicate and aluminosilicate compounds with calcium hydroxide or lime in the presence of moisture.

Pozzolan - Light Ash porous volcanic tuff, used as an additive for the production of pozzolan cement and hydraulic lime.

For conventional low-calcium fly ash was noted that the pozzolanic reaction began after 11 days after hydration at 20 ° C; found perceptible effect reaction at a compression test through 28 days. In another consideration, where 30% by weight of concrete has been substituted for a low-calcium fly ash, growth did not work reliability mixtures tested by ASTM S109 after 1, 3 and 7 days. But then there was a significant effect of Putz-tsolanovoy response to a fortress in 28 days. After 90 days the fortress of concrete mixtures with fly ash was of the same order as the original Portland. When using vysokokaltsievoy fly ash was observed a significant increase in reliability after 3 days and after 7 days, the fortress was equal reliability verification solution.

Briefly permissible to note the following. While highly pozzolans begin to participate in increasing the reliability of the start almost immediately after the hydration of Portland cement, low-calcium fly ash is not pozzolanic activity indicates noticeable affecting the castle before 2-weeks after the start of the hydration. Vysokokaltsievaya fly ash is beginning to show its hydraulic activity in more earliest time - within 3 days after hydration.

The presence of hydroxyl ions, sulfate and calcium in the solution sufficiently rapidly inhibits hydration vysokokaltsievoy fly ash, and the process is stopped due to the influx of these ions by hydration of fly ash itself.

solid concrete consistency, having in its composition 504 kg / m3 of Portland cement, 59 kg / m3 of low-calcium fly ash and the additive, reducing water demand (vodovyazhuschee ratio is equal to 0.33) were developed for the Water Tower Place and River Plaza in Chicago. They showed a fortress under compression of about 70 MPa after 50 days. In Texas similar reliability were obtained in cement consistencies having only 400 kg / m3 portland cement 100 kg / m3 vysokokaltsievoy fly ash (ASTM, class C) and the additive that lowers the water demand (vodovyazhuschee ratio is 0.33).

Level (8 points)

Slowing solidification

n the previous chapters we have already shown, what is the role of calcium sulfate cement hydration and, therefore, its processability. The importance of this has not been recognized in the last century to the advent and widespread use of rotary kilns. Previously, when using the shaft furnace prepared coarse clinker cements that were not enough active and hardened properly, even without the addition of gypsum when grinding. The increasing fineness of cement grinding has caused an increase in its activity, which required the use of regulators setting time almost all cement. Many researchers countless attempts regulyatorovaniya timing setting [147] were taken. The effect of almost all the additives, hardening regulators, greatly depends on the chemical and mineralogical composition of clinker used, by its fineness. Proven in practice methods of regulation setting can only be achieved by introducing CaSO4 · 2H2O. The use of CaSO4 · 2H2O as a regulator, in addition to achievable hydration delay also speaks about the availability in the price. Therefore, since 1930 the plaster is considered as an integral part of the cement. The amount contained in the cement clinker tricalcium aluminate has a significant impact for initial reactivity and curing rate of cement. Fineness C3A plays a significant role. sulphate carrier must be optimal for a given amount of C3A and reactivity for achieving a favorable curing rate and subsequent strength. The cement sulfate as a carrier can be used easily soluble alkaline sulfates, calcium sulfate hemihydrate, natural anhydrite and dihydrate. Figure 56 shows the behavior of different calcium sulphate solution. Since the rate of dissolution of various sulphate, available as a solution in various concentrations of sulfate, which leads to different results retardation.

Structure of a cement stone

The hardened cement stone represents a microscopic heterogeneous system consisting of crystalline aggregates and gelatinous masses represented by particles of colloidal size. The heterogeneity of the cement stone structure is enhanced by the fact that it contains clinker unreacted portion of grains which time content decreases. By analogy with conventional concrete cement stone such heterogeneous system. VN Jung called "microconcrete".

Significantly affect the structure of the cement stone and gypsum hydraulic additives, as their grain structure varied, and new products are formed as a result of reaction with components of cement clinker rock. Rationally choosing the mineralogical composition of clinker and cement composition with the desired content of the individual clinker minerals, giving the hardening cement paste the crystal aggregates, the gel structural component, it is possible to influence the structure and physicomechanical properties of the cement stone and concrete in the desired direction.

The difference in the physical and mechanical properties of crystalline and colloidal gel-like substances is one reason why the influence of the mineralogical composition of the clinker to some of the main construction properties of cement: deformability, resistance to alternating freezing and thawing, wetting and drying. This allows the rational selection by the mineralogical composition of the clinker to regulate the properties of portland cement and receive, the quality of satisfying the specific operating conditions.

On the concrete structure has a significant influence of the porosity of the cement stone, associated with the initial water content in the concrete mixture and air entrainment during its preparation. To obtain a workable concrete mixture it is administered 2-3 times more water than is chemically bonded during cement hardening. The amount of water react chemically with the cement, under favorable conditions, curing is 15-20% by weight of cement, to obtain a workable mixture of 40-60% of the water required. Thus, most of the mixing water is in the free state and in the hardened rock forms a plurality of fine pores. Therefore always seek to apply concrete mixtures with a minimum content of water in order to obtain the most dense structure of cement stone, which also increases its durability and resistance to frost.

The structure of the cement stone, namely the presence of pores and a gel-like substance, makes its propensity to humid deformation: when wet it swells and shrinks upon drying. The alternating compressive and tensile stresses caused by changes in ambient humidity, loosen the cement stone structure and reduce the strength of concrete. The degree of deformation depends on the humidity ratio of the gel-like and crystalline phases in the cement stone: with an increase in resistance of the last stone in such an environment (called vozduhostoykostyu) increases. Unlike pozzolanic Portland cement ordinary portland cement discussed further characterized by high air resistance

Building lime

In the production of building materials and as raw material for processing of some surfaces is widely used lime. Lime produced by calcination in special furnaces equipped with a temperature of 1000 to 1200 degrees carbonate rocks. Thermally treated lime takes the form of irregularly shaped pieces that are in the process of further use is subject to various processing.

Chemical composition formula and lime

For lime production does not apply any chemical catalysts, the main condition for its receipt, only the respective thermal regime. This is produced in the manufacturing process is completely natural material, it permitted content of impurities of small lime clay.

Limestone, CaCO3 formula has, as is predominantly calcium. In the process of temperature influence the carbon dioxide is released and produced raw materials has the formula CaO.

Razgashennaya lime can be in several states:

• fluff or a fine powder obtained by mixing lime with water, the pieces, and the moisture percentage should be from 60 to 70%.

• lime dough - a starting material compound with water, it takes about 3.5 times greater. As a result of such cancellation, a dense mass that is used in various fields.

• If lumps dissolve lime with water in the ratio of 1:10, it is possible to obtain lime milk. This slaked lime used for whitewashing the interior of buildings, facades, household outbuildings.

• When slaked lime for a long time is not used, the process is reversed, ie, the solution absorbs carbon dioxide and hardens. On sale you can often meet lime - hydrated lime or lumpy.

Technical properties

For the production of quicklime and quicklime special requirements regulated by the state standard (GOST 9179-77):

1) In the production of lime is used only carbonate rocks and some mineral supplements. The amount of additives should not exceed the amount specified in the standards for certain varieties of lime.

2) Quicklime divided into three classes and should not contain additives, powdery additives available in two varieties, slaked may or may not have additives, and is distributed in two classes.

3) calcium lime is calcium the main component, MgO percentage should not exceed 5.

4) Dolomitizirovanayaya lime contains up to 20% MgO

5) Dolomite 40% MgO.

6) In the hydraulic may include silica, iron oxide, a small amount of clay.

lime properties are defined primenyamymi during firing rocks and by the manufacturing process. As a result of the heat treatment furnace limestone out solid pieces quicklime depends on the color additives present, shade whiter than the higher grade material. Dolomitic lime and hydraulic grayish ottenok.Pri have contact with water releases carbon dioxide and lime becomes liquid, the concentration of which depends on the amount of water. Depending on the process and the firing temperature can be obtained by varying the strength of lime - firmly deification, intermediate variant and softly deified.

Stamps and some types of lime

Lime and divided by grades and primary raw materials used.

View and lime and the main brand is defined by its scope:

• Construction of lime produced from calcium and magnesium species. Apply lime building for administration as a plasticizer in the concrete mixtures, solutions. Building lime comes in lumps, in the form melkoypushonki or lime putty.

• Hydraulic lime - calcine limestone containing from 6 to 20% clay impurities. This kind of use of lime for the production of concrete of low marks, as a par with high strength, it has a low ductility. Hydraulic lime is often used in the construction of buildings, operation of which involves finding in a moist environment.

• lump lime is a semi-finished product used for the manufacture of powdered raw materials or solutions. The lumps of lime stored in closed warehouses, protected from humidity. Lump lime is marketed for the preparation of solutions for whitewashing.

• Gardening lime needed for the enrichment of acidic soils. In acidic soils minimum calcium content, which leads to poor growth and development of plants. Introduction of hydrated and quick lime in the soil is carried out in the spring or autumn, and preferably during the rainy season, so the limestone is more soluble. Do not make use of lime along with other fertilizers, and during operation is required to protect the eyes and hands.

• sodium (soda) limestone - porous white mass, which is a mixture of sodium hydroxide and hydrated lime. Soda lime is used as an absorber of carbon dioxide and moisture from the air. It is used in chemical laboratories for the production of gas masks, diving equipment. In medicine, used as a sorbent for anesthesia devices and hyperbaric chambers.

• Bleach is obtained in the course of a complex combination of free chlorine and calcium hydroxide. Bleach has strong disinfectant properties, previously used in its pure form in health care facilities. Today, chlorine is used for disinfection of latrines, cesspools, for the production of solutions for disinfection. Bleach has and bleaching properties.

 

Production and manufacturing technology

Lime production generally consists of two phases:

1) Quarry limestone and other rocks used. For the production of lime Komkova can use and waste production, using limestone for other purposes.

2) Roasting prepared rocks.

Limestone is mined in open pit quarries using explosives. Selective mining of rocks allows you to prepare the raw material, uniform in its density and chemical composition, which affects the quality of lime produced in the future.

Firing limestone - the main stage of the process of manufacturing an air lime. Depending on the impurities content and use different temperature conditions. All technological conditions must be met, as the limestone burned leads to low quality characteristics of the material. Dead burned lime is poorly soluble in water, has a high density and a negative impact on concrete solutions.

Calcination of the starting material is carried out in different furnaces. Widely used shaft furnaces, they are characterized by a continuous cycle of operation, efficiency, ease of management. Rotary kilns myagkoobozhennuyu allow to obtain the highest quality lime.

Developed and used by installation allows for the firing of the material in a fluidized bed or in suspension. Such systems make good use of the firing of the smallest fractions of rocks, but they have low efficiency.



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