CS241477B2 - Method of calcium hydroxide ca(oh)2 occurence limitation in hydraulic binder on base of portland cement clinker - Google Patents

Abstract

A hydraulic binder is obtained by mixing Portland cement clinker with hydrated alumina in such proportions that the Ca(OH)2 formed during the hydration of the Portland cement clinker combines completely with the alumina as it is formed.

Description

(54) A method of preventing the occurrence of calcium hydroxide Са (ОН) г in a Portland cement clinker hydraulic binder

2

The present invention relates to the treatment of Portland cement clinker to increase its resistance to the action of certain types of water and acids, as well as to increased durability in thermally stressed structures. The treatment is carried out according to the method according to the invention, in which aluminum hydroxide A1 (OH) ₃ is added to the Portland cement clinker in an amount of two moles to three moles of calcium hydroxide Ca (OH h) which separates during hydration from the Portland cement clinker; the binding of all the separated calcium hydroxide is achieved.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of preventing the occurrence of calcium hydroxide Ca (OH) 2 in an artificial Portland cement based binder during solidification and hardening occurring at ambient air temperature in the absence of added catalysts.

Conventional Portland cement types are known to release hydrated lime, calcium hydroxide Ca (OH) 2 during their hydration, so that they are unusable for some purposes, for example, they are unsuitable for cases where resistance to temperatures above 500 ° C is required. or resistance to pure water or to some acid types.

The release of hydrated lime results from the basic nature of Portland cement, the main component of which is expressed by the formula C3S, where C represents CaO and S represents SIO2. It is known that during hydration of C3S calcium hydroxide Ca (OH) 2 is released from cement clinker, and the course of hydration can be generally expressed by the equation

C3S + 3H → CSH + · 2 CH, where H = H ₂ O.

Furthermore, it is known that in the production of building materials, hydrated lime Ca. (OH) ₂ , separated during the hydration of cement, can be combined with additives. For example, on the basis of pozzolan, in order to form hydrated calcium silicate.

However, this reaction begins with a considerable delay after the start of hydration and is only applied in practice after 14 days hardening of the hydraulic binder mixture. These cements are generally known as pozzolanic cements, which are mainly used in conditions where resistance to pure water and acids is required.

If Portland cement is heated to about 400-500 ° C after hydration is complete, hydrated lime will change

Ca (OH) ₂ , separated during hydration, to quick lime CaO, which, when the temperature is reduced, for example when the furnace is stopped and the lining has cooled down, receives water from the ambient air and thereby significantly increases the volume of concrete and damages its structure.

The pozzolanic cements can be used as binders for refractory constructions, provided that the refractory concrete of this pozzolanic cement can be matured for several months in a humid environment or in a humid atmosphere so that the pozzolanic reaction can fully take place before exposure to concrete. This long technological break between the finishing of the lining and its usability is very disadvantageous and therefore a solution has been sought to eliminate the delay, which would also allow the use of conventional Portland cement for purposes for which it was not previously possible.

A solution to this problem has been found in a method of preventing the occurrence of hydrated lime Ca (OH) <2 in Portland cement clinker during solidification and curing of a mixture prepared from this cement at ambient temperature and in the absence of added catalysts. in that aluminum hydroxide Al (OH) ₃ is added to the Portland cement clinker in an amount of two moles to three moles of Ca (OH) 2 separable during solidification and curing of the mixture with the artificial Portland cement as a hydraulic binder.

In the process of the invention, aluminum hydroxide Al (OH) 3 is added to the mixture containing Portland cement clinker in an amount such that all hydrated lime Ca (OH) 2 binds at the time of its separation during hydration binder with aluminum hydroxide A1 (OH) ₃ and then hardened concrete does not contain any calcium hydroxide Ca (OH) 2 and therefore there can be no adverse effects as in the case of mild cements.

Aluminum hydroxide A1 (OH) ₃ can be added to the mixture with Portland cement clinker. a stage where it is best to ensure uniform mixing of the two components of the mixture. Therefore, it is preferred to add Al (OH) 3 aluminum hydroxide to the cement clinker after firing, and the two components can then be milled together. The reaction of calcium hydroxide · Ca (OH) 2 with aluminum hydroxide A1 (OH) ₃ or Al (OH) _n proceeds very rapidly if the mixture is formed with simultaneous grinding,. In particular grinding of Portland cement clinker and alumina-containing substances such as chemical aluminum hydroxide, crude bauxite or laterite. Co-milling of both components of the mixture can be omitted if the particles of both components are sufficiently small and pass through a 40 micron sieve.

The binder treated by the process of the invention comprises essentially technical Portland cement clinker and alumina consisting of aluminum hydroxide (Al) (0H) _n , which is present in the binder in sufficient quantity to prevent free separation of hydrated lime during hydration. all bound by aluminum hydroxide.

In the hydration of the binder treated according to the process of the invention, the C3S binder base component transfers to the hydrated lime mixture, which is bound immediately after separation and is reacted with aluminum hydroxide Ai (OH) _n to form calcium aluminate type C ₃ AH _c or C / AH _n , or on silica aluminate of the hydrating gehlenite type C2ASH8 and hydrogranate. After complete hydration, no calcium hydroxide Ca (OH) ₂ is present in the Portland cement.

The Portland cement clinker hydraulic binder treated in this manner according to the invention can be used for a variety of purposes, some of which are set forth in the description below, particularly for those concrete mixtures where high strength of hardened concrete is required. However, in addition to the examples, a number of other applications are possible.

The treatment of the cement according to the invention as well as the course of the reactions in carrying out the process are explained by means of examples and also by a drawing in which a graphical representation of the results of the thermodifferential analysis (TDA) is shown. This analysis can detect the presence of hydrated lime in the binder, as the occurrence of lime results in an increase in the endothermic peak to between 450 ° C and 500 ° C.

Analysis of the results of the cementitious mortar hydration process can be performed by evaluating the X-ray diffraction curves.

Example 1

The binder was prepared by mixing artificial Portland cement clinker Superblanc with ingredients, the blends containing by weight% artificial Portland clinker with the trade name "Superblanc",

2.7% · gypsum,

The 27.3% aluminum hydroxide (AH ₃ ) produced by the Bayer process, the particle size of these components being selected such that they all passed through a 40 micron sieve.

“Superblanc” is an artificial Portland cement manufactured by CIMENTS LAFARGE FRANCE and is characterized primarily by the fact that it contains no iron oxide.

Examining the behavior of the mortar prepared from this mixed cement compared to the mortar containing only "Superblanc", the results are shown in Table I:

mortar containing "Superblanc" alone, after one day a significant amount of Ca (OH) ₂ occurred, whereas after seven days there was 70 to 80% free, hydration of C ₃ S releasable lime, and mixed cement according to Example 1:

In this embodiment, the aluminum oxide is first crushed with an AUREC crusher for 30 minutes, so that the material is partially amorphous.

The cement m-alta is then formed by adding water in an amount such that the water to cement ratio is 0.64.

Table I

X-ray diffraction peaks

C ₃ S AH ₃ Ca (OH) ₂ C ₃ AH ₆ c ₄ ah, cement 1 day F _ F - - malta se 7 days mF - tF - - Superblancem 28 days mF - tF - - cement 1 day F tF - F F mortar according to 7 days mF F - F F of Example 1 28 days F mF - F F tF = very high F = high mF = medium high mf = medium f = small tf = = very small

In addition, other stages not yet evident from the table of Example 1 are formed in this process, such as the formation of Ca ₂ ASH ₈ (gehlenite hydrate) and garnet hydrate.

The results of differential thermal analysis of DTA (after one day hardening at 20 degrees Celsius and 95% RH), which are indicated in the drawing, corresponding to the n ° 2 curve for the cement of Example 1, the n ° 1 curve corresponding to Superblanc with unground aluminum hydroxide .

From this graphical representation, it can be seen that the n ° 2 curve does not contain any peak for daytime hardening to indicate the presence of Ca (OH) ₂ .

Example 2

The cement used corresponds to the cement used in Example 1, but was additionally subjected to simultaneous grinding under the same conditions.

X-ray diffraction testing of the cement revealed partial amorphous aluminum trihydrate, while "Superblanc" was not significantly affected by this treatment.

In the cement mortar, consisting only of a mixture of cement and water, no Ca (OH) ₂ appeared after four days, but hydrated calcium aluminate (C ₃ AH ₆ - C ₄ AH _n ) and gehlenite hydrate (C ₂ AH ₈ ) appeared . The hydration products correspond to similar hydration products obtained from the mixture by finely grinding each of the components of the mixture.

Both examples tyíoi thus explained the possibility that under certain conditions the slaked lime formed during the hydration of the main components of Portland cement, in particular C ₃ S, react with the aluminum hydroxide.

Thereby, it is possible to obtain a cement which, after hydration, contains only hydraulic aluminum silicate and hydraulic calcium silicate aluminate.

The absence of Ca (OH) ₂ and overcoming the deficiencies resulting from the presence of Ca (OH) ₂ make it possible to use this type of cement for a variety of purposes, and in particular in the field of refractory building materials.

Examples 3 to 32

The following examples, which are shown in turn, involve the application of three types of Portland cement and different types of aluminate materials.

Three basic types of clinkers are used:

clinker A: clinker having a high content of C ₃ S and C ₃ A;

clinker B: a clinker having a low C ₃ S and C 2 A content;

clinker C: clinker with very low C ₃ A content.

These clinkers have the following potential mineralogical composition, calculated from their chemical analysis:

alkaline sulfonate free

C ^ AF CaSO _Zj CaO total

C ₃ SC ₂ S

C ₃ A

clinker 68 17.4 7.75 0.8 0.35 4.05 100 ALIGN! clinker В 57.5 21.6 7.20 9.8 1.60 0.65 100 ALIGN! clinker C 66.3 15.35 0.50 14.50 0.40 1.55 100 ALIGN! Next are two types are used bauxite: bauxite B: high in iron, which bauxite A: p low iron content, have the following composition: SiO ₂ TiO ₂ Al ₂ O _{; i} CaO MgO _{SO; 1} CO ₂ losses Fe _{2 O:!} K ₂ O Na ₂ 0 Total bauxite A 0.7 3.9 60.9 0 0 0.05 0.05 30.85 3.45 0.05 0.05 100 ALIGN! bauxit В 8.9 2.7 53.3 0 0 0.1 0.05 23.63 11.3 0.05 0.02 100 ALIGN!

losses are understood as combustion losses

From the various X-ray diffraction spectra and the alumina and water content values for each bauxite type are possible. calculate the content of trihydrate (AH ₃ ) and monohydrate (АН), the percentages for the various stages of the process being given in Table II below:

Table II

AH ₃ Bayer bauxite A bauxite В

AH ₃ 100%

АН - impurities -

Examples 3 to 5

In Examples 3-5, the ratio of clinker V to aluminate material is 2: 1.

Example 3 after mixing without simultaneous grinding.

Example 4 after mixing and simultaneous grinding for 2 hours.

Example 5 after mixing and co-milling for 6 hours.

Co-milling was not carried out, as in Examples 1 and 2, by vibratory mills, but by conventional ball mills.

Pure cement slurry was stored at 20 ° C and 95% relative humidity.

87.2% 61.9%

4.7% 14.9%

8.1% 23.2%

When stored under these conditions, i.e. at 20 ° C and 95 ° C relative humidity, it was found by differential thermal analysis and X-ray analysis that the cement of Example 3 containing a mixture that was not milled concurrently contained after prolonged storage for example, after three months, slaked lime Ca (OH) ₂ , while cements prepared by simultaneous grinding of the components, no more slaked lime Ca (OH) ₂ is present after twenty-four hours.

Storage at 50 ° C and 95% RH improves the reaction capability of the mixture because the Ca [OH] ₂ still present in the mixture after seven days when stored at 20 ° C and 95% RH , completely disappeared.

Table III

Save Example time c3s AH ₃ Ca (OH) ₂ C3AH6 C ₄ AH _n 24 hours F F F - 3 7 days mF F tF - - Noc: 18 ° C 2 min F F tF - - 95% rel. 4 24 hours F F - mf F humidity 7 days mF mF - mf F 2 min F mF - mf F 24 hours F F - mf F 5 7 days mF mf - mf F 2 min F mf - mf F 24 hours F F F - - 3 7 days mf mf - mf F Deň: 32 ° C 2 min J F - · mf F 95% rel. 24 hours F F - mf F humidity 4 7 days mf mf - mf F 2 min F F - mf F 24 hours Л F - mf F 5 7 days mf mf - mf F 2 min F F - mf F

Similar to Examples 1 and 2, the presence of C2ASH8 (hydrated gehlen-itj and hydrated garnet) was also found in these cases.

In Table III, tF = very high content,

F - high content, mF - medium content, mf = medium content, f = low content and tf - very low content.

Examples 6 to 8

In these examples, a 2: 1 mixture of clinker B and bauxite B was used.

Example 6, after mixing, they are not simultaneously sown,

Example 7 After mixing, grinding is carried out for two hours.

Example 8 After mixing, grinding is carried out for six hours.

The cement slurries were stored at 20 ° C and 95% RH and at 50 ° C and 95% RH in each example.

In Examples 6 to 8, it was observed, similar to ¹ in the previous examples, that the reaction of Ca (OH) ₂ - AH _n occurred immediately when the cement mixture was prepared while grinding both components.

This reaction is accelerated as the ambient temperature rises.

Examples 9 to 27

In these examples mixtures of different compositions containing different materials and different ratios of cement clinker to aluminate material were investigated for the same purpose.

Examples 9 to 27

Example clinker aluminate material clinker / filler preparation AND AND .57 / 43 together 9 to 27 (B) (B) 67/33 grinding C 77/23

Taken together, the combinations of 3x2x3 = = 18 different cases contained in Examples 9 to 27.

Analysis and analysis of the cement slurry obtained from all of these Examples 9 to 27 revealed that after 24 hours of hydration, both differential thermal analysis and X-ray diffraction showed that slaked lime was not present in the mass.

For the expert it is clear that it is necessary to adapt the amount of aluminous material amount of slaked lime ¹ generated during the hydration of cement portlandského-, taking into account the impurities occurring in both materials.

An essential feature of the mixed cementitious mortar prepared according to the invention is that the mortar does not contain Ca (OH) 2 in any time interval after hydration, and consequently can only be used as a heat-resistant binder, and in addition it can be used in all cases where the presence of slaked lime is undesirable to maintain, for example, resistance to pure water or certain acids.

Example 28

and] heat resistance

Mixture. is prepared from 67% clinker A and 33 why, chemical AH3, produced. Bayer process. The mixture was then milled for two hours.

After 24 hours hydration at 2 ° C and 95% relative humidity, the cement slurry was dried in an oven at 110 ° C and then gradually heated to 300, 500, 800, 1100 and 1250 ° C for six hours. and then finally cooled.

Intensity. individual stages of heat treatment of pure cement slurry:

mineralogical phase 20 ° C 110 ° C 300 ° C 500 ° C 800 ° C 1100 ° C 1250 ° C

C3S FF

AH3 tFtF

Ca (OHh - ~

CaO ——

C3AH6 FF

СзАН _п f—

C2AS —— ^C 12 ^A 7 ——

CA2 -CA—

It has been found that irrespective of the firing temperature of the pure cementitious slurry of the binder according to the invention, there was no release of quicklime which could hydrate again, so that the binders can be used as a refractory binder without any difficulty.

(b) moisture resistance:

f f f f

F - - - - _ f F F F F - tF F - - - tF F - - - tf mf la vyrobena šamotocementová cube o edge length 10 cm that was by-

following tables exposed to heat treatment.

Compared to a similar cement sample, the cement binder cube of the present invention remained intact, while the cement comparative cube popraskaa.

From cement shown in example 28 byactivated cement comparative sample hours - 500 ° C hours in humid - air hours - 800- ° C days in humid environment hours - 110 ° C days in humid environment without cracks without cracks without cracks without cracks without cracks without cracks without cracks cube with cracks cube with cracks cube with cracks

Examples 29 to 31

In these examples, the behavior of the mixed cement, composed of clinker C and bauxite B, is investigated by tests which are used for routine testing of refractory products, and in particular in particular:

- mechanical properties after heating;

- subsequent change of sample size;

- shrinkage under temperature and load conditions.

The limit temperature for use of the mixture lies between 1 250 ° C and 1 300 ° C, since up to these temperatures the dimensional changes still fall within the limits set by the Syndicat des Fabricant de Produits Réfractaires Européens, ie less than or equal to + 1.5%.

In general, the heat resistance of cement depends on the ratio of cement-clinker to aluminate components and also on the purity of the components, especially the content of iron oxide.

Examples 2 9 to 3 1

Properties of refractory concrete containing 500 kg of cement per 1 m ^{3 of} concrete, with binder components being milled simultaneously for two hours

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The rheological properties of the cement can be adjusted by the addition of anhydrous or hydrated calcium sulfate or additives, in particular plasticizers, liquefying agents or water reduction agents.

Example 32

The mixed cement formed by co-milling of cement clinker B and bauxite B 'for two hours has a workability when mixed with quartz sand for mortar:

after 3 min.169 s after 30 min.268 s

Addition of 0.1% (0.1 / 1000) sodium gluconate gives the following values:

after 3 min.14 s after 30 min.34 s

Workability was measured with a Mania: bilimeter L. C. L. of Etablissements Perrier in Monrouge, France as described in "Mode Opératoire BF M-1", published by · Dunod 1973.

It has thus been found that the binder according to the invention can further improve its properties by adding further additives used in concrete practice. The type of additives selected depends essentially on the nature and fineness of the hydraulic binder materials of the invention.

However, the invention is not limited to the examples given, the binder may be further varied within the scope of the invention.

Claims (1)

OBJECT OF THE INVENTION A method for preventing the occurrence of calcium hydroxide Ca (OH) 2 in a Portland binder based on Portland cement clinker during solidification and hardening occurring at ambient air temperature and in the absence of added catalysts, characterized in that the artificial Portland cement clinker Al (OH) -3 is added in an amount of two moles to three moles of calcium hydroxide Ca (OH) ₂ , separable according to stoichiometric laws, of the artificial Portland cement clinker during its setting and setting.