Mixture for rapid hardening of portland cement and method of its application

and to improve strength. The invention can be used for the rapid curing of cementitious masses, cement-sand mortars and concretes intended for either seamless or prefabricated structures. ii There is a well-known mixture for obtaining fast-curing Portland cement (Finnish patent application 763462). The mixture contains calcium sulphate, calcium oxide and active dialuminium trioxide, which is used in the form of dialumin pentahydroxychloride, in weight ratios: AlgO 2 iCaSO 2: CaO = 1: 3.5-4.3: 1.3-1.8.

The disadvantage of this mixture is that it contains chlorine, but nevertheless, compared to, for example, the most commonly used curing accelerator mixture, i.e. calcium dichloride, the chlorine content is several times reduced. The presence of even this small amount of chlorine is likely to lead to restrictions on the use of this mixture for even more loose steel-reinforced concrete types / types.

It is also known · that there is a method using the same mixture (Bulgarian registration certificate No 21 932) and in which 4-8 parts by weight of the mixture '

58481I, ϊ mixed with water, initially adding active dialuminium trioxide in the form of dialumin pentahydroxychloride, and after diluting it, adding calcium, calcium sulfate and calcium oxide, followed by mixing all these components; mechanically and the mixture is mixed with 100 parts by weight of Portland cement with a strength of at least 35θ kg / cnT on the 28th day of the cement casting, .f

The disadvantage of this method is that, since the mixture is mixed with water, it can only be used for the production of cement masses, cement sand mortars and concretes in concrete mixing plants or on construction sites, making it suitable. * i machine must be installed for this purpose.j

When using the method according to the invention, the above-mentioned disadvantages can be eliminated, because the mixture prepared by that method can possibly be used for some special types of steel-reinforced concrete, thus extending * the range of use of the mixture.

The process according to the invention is characterized in that 100 parts by weight of Portland cement, water and 4-16 parts by weight of the mixture are mixed together. dialuminous pentahydroxychloride, calcium sulphate and calcium oxide in a weight ratio of iCaSO 4: CaO of 1: 3.5-4.3: 1.3-1.8, and 0.01-2 parts by weight of time: metal nitrite at a temperature not exceeding 90 ° C , after which the mixture thus attenuated is cured at a temperature of at most 100 ° C. A method is also provided in which said mixture and cement are mixed dry, preferably during the grinding of the cement, or said mixture is mixed into the cement with mixing water.

The temperature of the concrete mixture can be the same as the ambient temperature or it can be raised up to 9 ° C, but preferably to 30 ~ 50 ° C. The mixture thus obtained produces cementitious masses, cement-sand mortars and concretes, which are then left to cure at ambient temperature, or can be subjected to heat treatment up to 100 ° C, but preferably at 50-90 ° C.

The advantage of the present invention is that the new mixture neutralizes the effect of chlorine, thus extending its field of application also for some special types of steel-reinforced concrete. In addition, the addition of nitrite causes an increase in the strength of Portland cement.

Another advantage is that the mixing of the cement into the additive mixture can also be carried out dry, either in cement plants or when grinding cement.

A further substantial advantage is that by heating the cement, mortar or concrete mixtures or by their heat treatment after casting, the curing is further accelerated, which greatly helps to withstand the environmental impact and reaches a considerable speed of the casting cycle.

The invention is illustrated by the following examples:

Example 1

A batch containing 100 parts by weight of Portland cement, 2 parts by weight of dialuminium pentahydroxychloride and 0.22 parts by weight of sodium nitrite is metered in and the mixture is dissolved in mixing water. ·

To the solution thus obtained are successively added 4 parts by weight of gypsum containing 0.5 parts of water of crystallization and 2 parts by weight of slaked lime, the weight ratios being: Al 2 O 2: CaSO 4: CaO = 1: 3, 8: 1.6, and adding sand to the resulting mixture to form a cement-sand mortar having a cement / sand ratio of 1: 3 with a water / cement ratio of 0.5. The vibrator is used to make faces, measuring 4 x 4 x 16 cm. After removal from the mold, they are allowed to cure in water at 20 ° C up to the point where they stand. Edges without a sodium nitrite component are used as reference pieces, as well as those to which no additive mixture has been added at all. The experimental results (see Table 1) show that the sodium nitrite component of the mixture not only neutralizes the effect of chlorine, but also provides an additional increase in strength.

Example 2

A batch containing 100 parts by weight of Portland cement, 2 parts by weight of dialumin pentahydroxychloride and 0.22 parts by weight of sodium nitrite is dispensed.

They are then dissolved in stirring water. To the solution obtained is added successively 4

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ti

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1 part by weight of gypsum with 0.5 parts of water of crystallisation and 2 parts by weight of slaked lime (weight ratios: Al 2 O 3: CaSO 4: CaO = 1: 3.8: 1.6).

The resulting mixture is used to make concrete by adding aggregates in the following proportions: cement / concrete aggregates =

O

1: 4.5, with a Portland cement of 410 kg / 1 n: and a water / cement ratio of 0.42.

The concrete admixtures are preheated so that, after their preparation, the temperature of the admixture is 36 ° C with a forced-action concrete mixer.

Under the same conditions, a concrete mixture is prepared which does not contain an admixture mixture but which otherwise has the same composition.

Under the same preheating conditions, the temperature of the concrete mix rises to 32 ° C, because without the admixture, the hydration and cracking of the cement take place more slowly.

Cubes, 15 x 15 x 15 cm in size, are formed from each concrete mix by vibrating. The experimental results obtained in the tests performed with these cubes are shown in Table 2.

To show the effect of preheating the concrete mix, the same table also shows the test results for concrete with a cement / filler ratio of 1: 6.5 and a Portland cement of 300 kg / 1 m and a water / cement ratio of 0.56 without preheating the starting materials at a mixture temperature of 20 ° C.

An admixture mixture is added to the second batch with the mixing water (the composition of the admixture is the same as that of the preheated concrete), while no admixture is added to the second batch at all. The formation of cubes takes place in the same way as with preheated concrete.

From the results obtained, it can be seen that heating the concrete mix results in hard ♦, I “58481;

additional and significant acceleration of the production process, ie within 4 hours:. 2. .... .t achieves a strength of 1.53 kg / cm m, This makes it possible to remove the concrete from the mold in less than 4 hours, thus guaranteeing a double casting cycle per shift. >;

f

Example 3L. . .p

A batch containing 100 parts by weight of Portland cement and 1 part by weight of dialuminium pentahydroxychloride is metered in, and the mixture is then dissolved in mixing water, after which h parts by weight of gypsum containing 0.5 l of crystalline water and 2 parts by weight of slaked lime are added. The resulting mixture is mixed with cement.

ti sand mortar with the following ratios: portland cement / sand = 1: 3 and j water / cement ratio = 0.5. [

The mixture thus obtained is formed into triangles, in size, by means of a vibrating device; 4 x 4 x 16 cm. Some of these faces are air cured at 20 ° C after removal from the mold until the test tests are performed. Another part of the same facets is subjected immediately after casting with its molds to a heat treatment at 50 ° C for 6 hours, ·. after which the molds are removed. Half of the facets are tested immediately, while^rthe other half is allowed to cure in air, after which they are also tested. |

For comparison, cement mixtures containing admixture in parallel ¹The same cement-sand mortar is also produced, but without the additive mixture, * the test results obtained with these are shown in Table 3. They clearly show a considerable acceleration of the curing process as a result of the heat treatment of the cement-sand mortar after casting.

Example 4,

A batch containing 100 parts by weight of Portland cement, 2 parts by weight of dialumin pentahydroxychloride, 4 parts by weight of gypsum with 0.5 crystals is dispensed. . . . * water, and 2 parts by weight of slaked lime, and the mixture is mixed dry with cement until a homogeneous mixture is obtained. A cement-sand mortar is then prepared with · the following ratios: portland-cement / sand = 1: 3 and a water / cement ratio of “0.5. '

From this mixture, edges of size 4 x 16 cm are formed by means of a vibrating table, which, after removal of the mold, are cured under water at 20 ° C. _t^!i

For comparison, a cement-sand mortar is prepared in the same way without: the admixture mixture and is shaped, the test values ​​obtained from this are shown in Table 4.

These clearly show that even when the admixture mixture and cement are dried, _rna the curing process is significantly accelerated - while the strength is considerably;

i increases.4 .t

Example 5;

A batch containing 100 parts by weight of Portland cement and one part by weight of dialuminium pentahydroxychloride is metered in, the mixture is then dissolved in the mixing mixture, followed by successive additions of 4 parts by weight of semi-hydrate gypsum and 2 parts by weight of slaked lime. With the mixture thus obtained, more cement-sand-mortar is prepared. !

'i ⁵58481

Re-form faces 4 x 4 κ 16 cm as described above. They are removed from the molds and cured under water at 20 ° C until the test time. The test results are shown in Table 5 · They clearly show। • k that when the mixture is fed together with the mixing water, the hardening of the cement accelerates considerably at the same time as the strength more than doubles first!

After 2i and after 28 days the strength, i.e. the quality, increases from 350 kg / cm to I 450 kg / cm².ί

Table 1

Compressive strength of cement-sand mortar 1: 3 with a cement ratio of 0,5f with and without the addition of sodium nitrite to the complex mixture | f

<td>Compound</td><td>1 day kg / cm²</td><td> %</td><td>3 days kg / cm²</td><td> %</td><td>28 days kg / cm²</td><td> %</td><td>1 h. il ί</td>

<td>♦ PC</td><td> 73,8</td><td> 100</td><td> —</td><td> —</td><td> 422,9</td><td> 100</td><td></td>

<td>PC * without adding nitrite to the mixture</td><td> 160,1</td><td> 216,9</td><td> —</td><td> —</td><td> 466,0</td><td> 100,2</td><td> 1</td>

<td>PC</td><td> 83,7</td><td> 100,0</td><td> 213,4·</td><td> 100,0</td><td> 417,6</td><td> 100,0</td><td>fi</td>

<td>PC by adding nitrite to the mixture</td><td> 183,8</td><td> 219,6</td><td> 330,9</td><td> 155,1</td><td> 478,5</td><td> 114,6</td><td> 1</td>

Note: PC * is for portland cement that has been stored for a long time before use compared to PC.

Table 2

<td>Compressive strength of concrete by preheating and</td><td>preheated concrete mix ^?i</td>

<td>Compound 4 hours</td><td>i 10 hours 1 day 28 days'</td>

<td>kg / cm²</td><td>p 2 2 * % kg / cm% kg / cm% kg / cm% '</td>

Preheating concrete mix;

I I. —— UI I ¹ I IM .. I ..WI

PC-410 kg / m³; !

W / C = 0.42; without mixture I

<td>t = 32 ° C</td><td> 43</td><td> 100,0</td><td> - - 265</td><td> 100,0 485</td><td> 100 1</td>

<td>PC-410 kg / m³; W / C ratio with addition of mixture; t ° = 36 ° C</td><td> = 0,42; 153</td><td> 355,8</td><td> - - 340</td><td> 128,3 571</td><td>ί 117.7 ·</td>

f.!

Table 2 (continued)

Preheating of Iina concrete mix · 4 hours 10 hours 1 day 28 days 9 9 9 9 kgx / cm% kg; / cm% kg / cm% kg. / crn _%

PC-300 kg / m³;

W / C ratio = 0.56;

without mixture;

t ° = 20 ° C - - 15 100.0 115 100.0 393100.0

PC-300 kg / m³; .'

W / C ratio = 0.56; adding the mixture t ° = 20 ° C - - 21 140.0 199 173.0 423107.6

W / C = water / cement

Table 3

Cement-sand mortar 1: 3 compressive strength with a water / cement ratio of 0.5, with or without heat treatment after formation.

<td colspan="2" rowspan="2">Compound</td><td rowspan="2">6 hours 2 kg. / cm</td><td rowspan="2"> %</td><td rowspan="2">8 hours 0 kg. / cm%</td><td colspan="2">16 hours</td><td colspan="2">28 days</td>

<td>7 kg / cm</td><td> %</td><td>9 kg. / cm</td><td> ' %</td>

<td>Curing PC</td><td>in the air</td><td>At 20 ° C</td><td> —</td><td> 7,1 100</td><td> 61,7</td><td> 100</td><td> 296,5</td><td> 100</td>

<td colspan="2">PC by adding the mixture</td><td> -</td><td> -</td><td> 20,0 281,7</td><td> 135,3</td><td> 219,3</td><td> 367,1</td><td> 123,4</td>

<td>Curing PC</td><td>50 ° C</td><td colspan="3">in heat treatment: 130.6 100.0 - -</td><td> *·</td><td> -</td><td> 296,8</td><td> 100</td>

<td>PC mix</td><td colspan="8"></td>

<td>adding</td><td></td><td> 173,9</td><td> 133,2</td><td> - -</td><td> -</td><td> -</td><td> 361,9</td><td> 121,9</td>

. . 7 . 58481

Table 4

1: 3 compressive strength of senent sand mortar with a water / cement ratio of 0.5 with and without the addition of a mixture, mixed dry with portland cement · '

<td>Compound</td><td>1 day 2 kg / cm</td><td> %</td><td>3 days kg / cm?</td><td> %</td><td>28 days kg / cm^? %</td><td>i</td>

<td>PC PC by adding the mixture</td><td> 84,1 187,7</td><td> 100,0 223,2</td><td> 200,7 362,3</td><td> 100,0 180,5</td><td> 423,6 100,0 527,0 124,4</td><td>1 l · '·</td>

<td></td><td></td><td>Table 5</td><td></td><td></td><td></td><td>f i</td>

<td colspan="5">Cement-sand mortar 1: 3 compressive strength in water / cement ratio</td><td>being 0.5,</td><td> 1 .</td>

adding and not adding the mixture when fed with mixing water

<td rowspan="2">Compound</td><td colspan="2">1 day</td><td colspan="2">3 days</td><td colspan="2">28 days</td>

<td>,, 2 kg / cm</td><td> %</td><td>2 kg. / cm</td><td> %</td><td>. / 2 kg, / cm</td><td> %</td>

<td>PC</td><td> 88,9</td><td> 100,0</td><td> 238,0</td><td> 100,0</td><td> 411,4</td><td> 100,0</td>

<td>PC by adding the mixture</td><td> 187,7</td><td> 211,0</td><td> 346,2</td><td> 145,5</td><td> 497,1</td><td> 121,0</td>