CN1277945A - Expansive cement and contact manufacturing method thereof - Google Patents

Abstract

The contact manufacture method of the expansive cement is that firstly the contact agent KAS is fired, then the silicate cement clinker, the semi-hydrated gypsum, the contact agent KAS and the mixed material are directly prepared according to the proportion and are ground into the expansive cement. The chemical mechanism is that in the plastic stage and within the elastic limit of the concrete, the aluminum-containing mineral in the expansive cement is quickly hydrated to generate ettringite under the action of the contact agent. Therefore, not only the damage of the set cement is not caused, but also the compactness of the set cement is increased, the defect of concrete shrinkage cracking is compensated, and the strength, the permeability resistance and the etching resistance of the concrete are improved. The invention has low production cost and good product performance. The expansion rate is easy to control.

Description

Expansive cement and contact manufacturing method thereof

The present invention relates to a special cement and its production method.

At present, the method for manufacturing silicate series expansive cement at home and abroad is to add 8-18% of expanding agent into general cement, wherein the main components of the expanding agent are CA and CA₂、C₄A₃S and CaSO₄According to the introduction of the book of "production and application of special cement" edited by the institute of building materials science of China, the expanded Portland cement produced by the method has the defects that the strength of ① expanded Portland cement is reduced by one grade compared with that of Portland cement, the sulfate erosion resistance of ② expanded Portland cement is poorer than that of Portland cement, and the manufacturing cost of ③ expanded Portland cement is higher than that of Portland cement by about 100 yuan per ton.

The invention aims to provide expansive cement and a contact manufacturing method thereof, which have the advantages of high strength, good sulfate erosion resistance and low manufacturing cost.

The purpose of the invention is realized as follows: the patent of 'special sulfate-resistant cement and production method thereof' with application number 96118342.X is improved by directly adding 0.3% of contact agent KAS, 7-14% of semi-hydrated gypsum and a proper amount of mixed material (one or two of slag, volcanic ash, fly ash and coal gangue) into general cement (portland cement, common cement, slag cement, volcanic ash cement and composite cement) clinker to prepare the expansive cement with high strength and high sulfate erosion resistance.

The theoretical basis and the mechanism of the chemical reaction of the present invention are as follows:

recent studies and experiments have demonstrated that: ettringite (also called high-sulfur calcium aluminate, molecular formula 3CaO. AI)₂O₃·3CaSO₄·30～32H₂O) has the characteristics of stability and expansibility, the crystal structure of ettringite is difficult to damage under various severe conditions of drying, moisture, high temperature, low temperature and the like, and the cooperation with other hydrolyzed minerals C-S-H in cement can enable the concrete to generate higher strength and expansibility. Therefore, the content of the ettringite in the cement mineral can be controlled to ensure that the concrete has expansion performance and self-stress, and the compactness of the concrete is increased, thereby increasing the strength, the permeability resistance and the sulfate erosion resistance of the concrete.

In order to avoid the damage to concrete caused by excessive expansion energy of ettringite, C must be added to the concrete in addition to controlling the amount of ettringite produced₃The expansion reaction of A converted into ettringite is controlled within the plastic stage and elastic limit strength of the concrete.

The principle of the invention is that the contact agent K is utilized in the plastic stage and the elastic limit strength of cement mortar (or concrete)₂O·AI₂O₃The cyclic contact effect makes C in cement mineral₃A、C₂AS、CAS₂CaO and CaSO₄The chemical reaction of generating fine ettringite is quickly finished by combination, and the process is combined with the sulfate leaching in the seawater etching processThe destructive reaction of etching "is similar. These fine ettringite crystals formed in the liquid phase are dispersed in the mortar and alternately and mutually overlapped to constitute the initial skeleton of the hardened mortar. At the same time, hydrated silicate (C-S-H) and hydrated aluminate (C-A-H) gel in the mortar are filled between the two, and the two are hardened to make the cement paste obtain initial strength, and then the hydration is continued to form hard cement stone.

As the concentration of CaO in the liquid phase is higher (PH is more than or equal to 12), when hydrated calcium sulphoaluminate in the form is generated, a part of calcium sulphoaluminate is gathered in a fine needle shape to surround the particle surface of the mortar, and the calcium sulphoaluminate is in a radiation state, has expansibility and generates stress. The fine needle-shaped calcium sulphoaluminate hydrate can fill gaps in cement slurry and destroy capillaries, and the stress of the fine needle-shaped calcium sulphoaluminate hydrate can be absorbed by the calcium silicate hydrate and the calcium aluminate hydrate which are generated simultaneously and are still in a plastic stage. Therefore, the expansion of the fine needle-shaped calcium sulphoaluminate not only has no destructive effect on the concrete, but also has the function of compacting slurry, compensates the defect of shrinkage and cracking of the concrete, increases the anti-permeability, anti-erosion performance and strength of the concrete, and prevents external water from permeating into the interior.

Why are the strength and sulfate erosion resistance of prior art expanded cements comparable to that of the same clinker and similar specific surface area compared? As the prior art adds 8-18% of expanding agent into clinker, the main components are CA and CA in the expanding agent in the process of hydration, hydrolysis and transformation into ettringite₂、C₄A₃S is involved in the conversion, and C in the clinker and the auxiliary materials₃A、C₂AS、CAS₂The conversion into ettringite is small, and the rest is large, especially C₃A is a substance which is extremely poor in resistance to sulfuric acid attack, and therefore the expansive cement produced by the prior art is inferior in sulfate attack resistance to general-purpose cement. In addition, since the total strength of the added expansive agent is lower than that of general-purpose cement, the expansive cement manufactured by the prior art is also lower than that of general-purpose cement.

On the contrary, theaddition of 0.3 percent of contact agent KAS in the clinker can promote C in the cement clinker₃A、C₂AS、CAS₂、CaSO₄Quickly react with CaO and transform into ettringite to makeC remaining in cement plants₃A、CaSO₄The expanded cement produced by the present invention has higher sulfuric acid etching resistance than general cement, and the same reason is that the expanded cement produced by the present invention has more ettringite formed in the cement stone and C₃A、CaSO₄And the residual amount of CaO is small, so that the strength is 0.5 to 1 mark higher than that of the general cement.

The chemical reaction of the invention is as follows:

in the liquid phase of the expanded cement mortar (or concrete), the minerals in the silicate clinker are hydrolyzed and hydrated to generate C-S-H, C₄AH₁₉、Ca(OH)₂And C₄(A·F)H₁₉(ii) a Soluble CaSO₄Dissolving in water quickly; contact agent KAI (SO)₄)₂Simultaneously dissolve in water and react with dissolved CaSO₄And Ca (OH)₂The ettringite and K (OH) are combined to generate the ettringite and the K (OH) can circularly promote the production of the ettringite. The chemical reaction formula is as follows:

1. hydrolysis and hydration reaction type

2. Reaction formula for generating ettringite under action of contact agent

Generated K₂O.Al₂O₃Then continuously reacting with CaSO in liquid phase₄And Ca (oH)₂Combined to generate ettringite 3CaO.Al₂O₃.3CaSO₄.(30-32)H₂O is generally abbreviated as C₃A.3CS.H32。

The mixture is circulated until CaSO in the liquid phase₄And Ca (OH)₂After the reaction is finished, K (OH) and CO in the atmosphere in the process of solidifying and drying the concrete₂Contact formation of K₂CO₃Until now.

In the liquid phase, the following reaction also directly produces ettringite AFt₁And AFt₂。

… … abbreviated AFT₁

… … abbreviated as AFt₂

The production steps of the invention are firstly to mix KAl (SO)₄)₂.12H₂Calcining and dehydrating the O at the temperature of 350-700 ℃ to obtain a contact agent KAl (SO)₄)₂[ abbreviated as KAS)]Then directly mixing the silicate cement clinker, the semi-hydrated gypsum, the contact agent KAS and the mixed material according to a certain proportion and grinding the mixture to obtain the cement clinker, the semi-hydrated gypsum, the contact agent KAS and the mixed material, wherein the difference is that the weight ratio of each component is as follows:

30 to 92.7 percent of Portland cement clinker

7 to 14 percent of semi-hydrated gypsum

Contact agent KAS 0.3%

The balance is one or two of slag, volcanic ash, fly ash and coal gangue, or the mixture is not used.

During the production process, common gypsum CaSO can also be added₄.2H₂Calcining O at 400-700 ℃ to obtain soluble CaSO₄To replace hemihydrate gypsum.

Table 1 in the drawings of the specification lists the physical properties (obtained by experiments) of several expansive cements produced according to the examples.

Several formulations of the present invention are specifically described below by way of examples.

Example one fabrication 525^#The shrinkage-free rapid hardening portland cement I is also called as pouring cement I.

Preparing raw materials according to the production steps to prepare a finished product, wherein the weight ratio of each component is as follows:

92.7 percent of Portland cement clinker and 7 percent of semi-hydrated gypsum

Contact agent KAS 0.3%

As can be seen from Table 1, the physical properties of the cement meet the standards defined in ZBQ 11009-88.

EXAMPLE two fabrication 525^#Non-shrinkage rapid hardening portland cement II is also called pouring cement II.

The production steps are as above, and the weight ratio of each component is as follows:

portland cement clinker 82.2% and semi-hydrated gypsum 7.5%

Contact agent KAS 0.3% slag 10%

As can be seen from Table 1, the physical properties of the cement meet the standards defined in ZBQ 11009-88.

EXAMPLE III manufacture 425^#And (3) micro-expansion anti-seepage cement I.

The production steps are as above, and the weight ratio of each component is as follows:

portland cement clinker 61.7% soluble CaSO₄9％

Contact agent KAS 0.3% slag 22%

7 percent of fly ash

EXAMPLE four manufacture 425^#Micro-expansionAnd (5) anti-seepage cement II.

The production steps are as above, and the weight ratio of each component is as follows:

30% soluble CaSO of silicate cement clinker₄12％

Contact agent KAS 0.3% slag 50.7%

7 percent of fly ash

EXAMPLE five fabrication 425^#Micro-expansive sulfate-resistant cement I.

The production steps are as above, and the weight ratio of each component is as follows:

portland cement clinker 87.7% soluble CaSO₄7％

Contact agent KAS 0.3% slag 5%

EXAMPLE sixthly manufacture 425^#Micro-expansive sulfate-resistant cement II.

The production steps are as above, and the weight ratio of each component is as follows:

77.2% soluble CaSO of silicate cement clinker₄7.5％

Contact agent KAS 0.3% and slag 15%

Example seven a micro-expansive leak-proof cement III was manufactured.

The production steps are as above, and the weight ratio of each component is as follows:

65% of silicate cement clinker and 14% of semi-hydrated gypsum

Contact agent KAS 0.3% slag 13.7%

Volcanic ash 7%

Example eight a poured cement III was made.

The production steps are the same as above, and the weight ratio of each component is as follows:

portland cement clinker 88.2% and semi-hydrated gypsum 7%

Contact agent KAS 0.3% slag 4.5%

As can be seen from Table 1, the cement prepared by the method has higher strength and sulfate leaching resistance compared with the general portland cement under the conditions of the same clinker and basically similar fineness and specific surface area.

The content of ettringite after hydration of the cement prepared by the invention is 10-28%. From XRD analysis ofsample hydration 3d, 7d and 28 d: ca (OH) in cement stone₂Very small content of CaSO₄.2H₂The content of O is less than that of the corresponding type of cement.

Hemihydrate gypsum has been thought in the past to be responsible for the rapid and false setting of cement. Practice has shown that when the amount of the hemihydrate gypsum is more than 3%, the setting time can be completely normal. In addition, the addition of 0.3% of the contact agent KAS only corresponds to a 0.1% increase in K in the cement₂O, alkali concentration reaction caused by excessive alkali content is avoided.

In a word, the micro-expansion anti-seepage cement, the pouring cement and the micro-expansion sulfate-resistant cement manufactured by the invention have the advantages of low production cost, good product performance and easy control of expansion rate, and can be produced in numerous mechanical vertical kiln cement plants in China.

Claims (10)

1. A contact manufacturing method of expansive cement comprises the steps of first contacting KAI (SO)₄)₂.12H₂Calcining and dehydrating the O at the temperature of 350-700 ℃ to obtain a contact agent KAS, and then preparing the portland cement clinker, the semi-hydrated gypsum, the contact agent KAS and the mixed material in proportion and grinding the mixture to obtain the cement, wherein the contact agent KAS comprises the following components in percentage by weight:

30 to 92.7 percent of Portland cement clinker

7-14% of semi-hydrated gypsum

Contact agent KAS 0.3%

The balance is one or two of mixed materials, namely slag, volcanic ash, fly ash and coal gangue.

2. The contact manufacturing method of expansive cement according to claim 1, wherein the soluble CaSO calcined at 400-700 ℃ with ordinary gypsum is used₄Instead of hemihydrate stoneAnd (6) making paste.

3. The expansion cement is characterized by comprising the following components in percentage by weight:

30 to 92.7 percent of Portland cement clinker

7-14% of semi-hydrated gypsum

Contact agent KAS 0.3%

The balance is one or two of mixed materials, namely slag, volcanic ash, fly ash and coal gangue.

4. Expansive cement according to claim 3, characterized in that it is prepared with soluble CaSO₄Instead of hemihydrate gypsum.

5. The expanded cement according to claim 3, wherein the constituents are, by weight, 92.7% of portland cement clinker, 7% of hemihydrate gypsum, and 0.3% of KAS as a contact agent.

6. The expansive cement according to claim 3, wherein the components are 82.2% by weight of portland cement clinker, 7.5% by weight of hemihydrate gypsum, 0.3% by weight of KAS as a contact agent, and 10% by weight of slag.

7. An expanded cement according to claim 3 or 4, wherein the constituents are, by weight, 61.7% Portland cement clinker and soluble CaSO₄9 percent of contact agent KAS0.3 percent, 22 percent of slag and 7 percent of fly ash.

8. An expanded cement according to claim 3 or 4, characterized in that the weight of each componentThe quantity ratio is 30 percent of Portland cement clinker and soluble CaSO₄12 percent, 0.3 percent of contact agent KAS, 50.7 percent of slag and 7 percent of coal gangue.

9. An expanded cement according to claim 3 or 4, wherein the constituents are, by weight, 87.7% Portland cement clinker and soluble CaSO₄7%, contact agent KAS 0.3%, and slag 5%.

10. An expanded cement according to claim 3 or 4, wherein the weight ratio of the components is 77.2% Portland cement clinker and soluble CaSO₄7.5 percent, 0.3 percent of contact agent KAS and 15 percent of slag.

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