SU52032A1 - The method of obtaining magnesia portland cement - Google Patents

Description

The main raw material for the manufacture of Portland cement is limestone and clay. The content of magnesia in the resulting finished product is allowed by an OST of no more than 5%, since a higher content acts destructively on concrete in the long term and limits its use of magnesia limestone in the cement due to its insignificant permissible content.

The proposed method consists in the fact that the magnesia content in Portland cement is adjusted to 10% by binding it to compounds that ensure full constancy of the volume in the finished product both in the first and in the subsequent service life of concrete made on magnesian portland cement. .

Raw materials for the production of Portland-Cement magnesia are calc-magnesia rocks that are found to contain MgO (over 8%) unsuitable for the production of ordinary Portland cement, light sand clay, suitable for the production of Portland cement, and for binding magnesium oxide in 4CaO. 2MdO. f.f) ,. ., at

the raw mix is added with pyrite butts containing the largest amount of ResO, and in the case of low content of AlsOg in the raw mix, rocks rich in the content of flUO :, (bauxite, alit, kaolin, etc.) are introduced into the raw mix.

The composition of the raw mix, depending on the percentage of MDO in it, varies within fairly wide limits, but the content of MDO per clinker is not allowed in the latter over 10%.

At present, the mineral composition of magnesian Portland cement has been studied in more detail, as a result of which it was found that alit (ZSaO. SiO.) Is the main mineral with an insignificant amount of dicalcium silicate, magnesium brownmillerite 4CaO. 2MdO. , ... Fe2O; 5 and in the allowed percentage (2-4%) of periclase (MDO free).

The mechanical strength of magnesian Portland cement fluctuates as it does for ordinary Portland cement.

The technological process of producing Portland-magnesia cement differs little from production.

conventional portland cement wet and dry in factories equipped with rotary kilns. The peculiarities of the production of Portland-magnesia cement should include the need for better homogenization of the raw mix, due to its more complex composition; In addition, clinker is calcined at a zone more distant from the furnace head than when conventional Portland cement clinker is fired. When calcining magnesian Portland cement clinker, the formation of Swara clinker in the kiln is not allowed, since this causes the decomposition of magnesium brownmillerite with release of free MgO.

When calculating the raw mix for the production of magnesian Portland cement, the authors proceeded from the assumption that the main compounds of magnesian Portland cement are 3-calcium silicate ZSaO. SiO, (alit), 2-calcium silicate 2CaOSiO, (whites) and brauimyllerite 4CaO. Haze The composition of the latter in the magnesium porous tland cement consists of 2 molecules of MdO, forming the following compound, its composition: 4CaO. 2MdO. . fe., o, In addition to these basic compounds, according to Bates research and the preliminary data of the authors of the present invention, MgO is bound in magnesian portland cement as MDO orthosilicate. Cao. SiO monticellite. In this case, according to Bates, the amount of monticellite (when the content of magnesia in cement is from 10 to 11%) is 9-10% if the content of RjOj in cement exceeds 10-11%. With a lower content of sesame oxides, the amount of monticellite, with a given content of MgO, is insignificant. Finally, in case the ratio

n i f

 0.64,

a compound is formed

2 Cao. MDO. Re.O.,

what if

fll.ps

- 0.64,

Fe., 0,

then an excess amount of AlaO is bound to MDO in the form of MDO. . For the calculation of the raw material mixture, it is commonly set to a certain degree of lime saturation. By this concept in magnesian portland cement is meant

Cao

Sn

2.8 510.2 + 2.2 flljO ;,

in case when calculating the received relation

fll, o ,.

equal to 0.64. FeoO.

When calculating the raw mix for Portland-Cement magnesia, it is important not only to saturate silica with lime to obtain the active part in the clinker, but it is also important to achieve the binding of a specific part of MgO as a compound with a normal hydration rate or not able to hydrate at all. Therefore, the calculation of magnesian Portland cement is based on the following compounds: the active part is alit ZSaO. SiO; the magnesian part — magnesium brownmillerite 4 CaO. 2MdO. . , for the formation of which, such an amount of iron cinders is introduced, which would ensure the binding of MDO in an amount of from 3.5 to 4% under the condition of clay-rich alumina.

A monticellite, which is adopted when the content of 10-11% MgO in the clinker is 10%, is not entered into the calculation formula; monticellite binds 2.5% MDO.

Free magnesia in clinker is allowed in an amount of total MgO in clinker can be allowed not more than 10%.

Calcination takes place in the far zone when operating on low-calorie fuel. The use of low-calorie fuel is of great importance and the use of local fuel in this method is favorably resolved.

In addition to the usual testing methods for cements, the authors introduced another additional accelerated method using an autoclave.

Autoclave testing of magnesian Portland cement was carried out as follows. Pellets are made according to OST, after 4 hours of boiling to identify free lime, and also to give them greater strength, the pellets enter the autoclave on special shelves with holes and are under pressure of water vapor.

Steam rise is up to 14 atm. within 2-254 hours Pressure 14 atm. held for 2 hours, after which the test ends.

Simultaneously with the pellets in the autoclave, Baunshinger prisms made of pure cement will prevent. Testing samples 1: 3 with cement was not performed, since under these conditions the effect of free MDO is detected only if it is in excess of 8%.

A sample which is passed through the test is recognized, which, after being removed from the autoclave, does not show any external changes (crack, net, warp). For Bauschinger prisms, a volume change of not more than 1.5% is allowed.

The release of magnesia Portland cement by the proposed method at the Podolsk Gostomzavod showed that no special manufacturing difficulties are encountered.

The use of this method significantly reduces the cost of developing quarries that have raw materials

dolomitic limestone interlayer, which leads to a significant reduction in the cost of the final cement product.

The method can be applied in all plants that work for raw materials that are clogged with interlayers or inclusions of dolomitic limestone and, as a result, have difficulties in developing quarries and building a production process.

The subject matter of the invention.

Claims (3)

1. A method for producing magnesian Portland cement, characterized in that dolomitic lime and clay are mixed with pyrite cinders or another material containing mainly Re., Oz for the purpose of binding magnesium oxide in clinker, and the resulting mixture is processed to obtain conventional cement in a way. 2. A method according to claim 1, wherein the charge composition is selected so that the total amount of magnesia in the clinker does not exceed 10%, and the amount of free oxides does not exceed 4-4.5%. 3. Acceptance of the method according to paragraphs. 1 and 2, characterized in that, when the content of alumina is insufficient, clay rich in alumina (bauxite, kaolin, etc.) is added to the mixture.