SE448450B - PROCEDURE FOR THE PREPARATION OF AN ELFABLE HYDRAULIC BINDING AGENT - Google Patents

Description

448 450 2 is delayed because it does not begin until 15 days after curing. These cements are known as "pozzolanic cement" and are used in particular because of their stability to pure water and certain acids.

If, after hydration, ordinary Portland cement is exposed to a temperature in the range of 400-SOOOC, the calcium hydroxide Ca (OH) 2, which is released during the hydration, is converted to calcium oxide, which can then be rehydrated and cause swelling and destruction of structures.

Pozzolanic cement can be used as refractory binders provided that the refractory concrete obtained with these cements is stored in a humid atmosphere several months earlier in order for the pozzolanic reaction to be terminated before heating to a high temperature.

The invention relates to a process for producing a refractory hydraulic binder, which is substantially free of calcium hydroxide, by mixing an artificial Portland cement clinker, which tends to give rise to calcium hydroxide under standard conditions, with hydrated alumina, which is characterized by that the alumina is initially added in such amounts that noticeable formation of calcium hydroxide is prevented during the mixing operations and that curing is carried out mainly at ambient temperature. wherein the amount of hydrated alumina present initially is at least two moles of hydrated alumina, calculated as Al (OH) 3, per three moles of Ca (OH) 2 that may be formed during the hydration. It is advisable to collect the mixture. The reaction between Ca (OH) 2 and the hydrated alumina in the alumina-containing material is instantaneous if the mixture is obtained by collecting the Portland cement and an alumina-containing material (aluminous material), for example chemically hydrated alumina, crude bauxite and laterite . However, if the grain size distribution of the two constituents is 448 450 3 such that 90% of the material passes through a sieve with a mesh size of 40 μm, this aggregation can be excluded.

The binders of the invention are based on Portland cement and alumina, the alumina being hydrated alumina used in sufficient amounts to completely combine the nascent calcium hydroxide formed during the hydration of the binder with the hydrated alumina as it is formed. .

During the hydration of the binder of the invention, C35 gives rise to the release of calcium hydroxide, which when formed reacts with the hydrated alumina to form hydrated calcium aluminates of the type C3AH6 or C4AHn or silicon aluminates of hydrated (gelatinous type) CZASHB and hydrogranates.

This means that no traces of Ca (OH) 2 can be detected in the cement.

The present description discusses the use of new hydraulic binders, particularly in connection with refractory applications, but the invention is not limited to this use.

The advantages and features of the invention will be apparent from the following description and embodiments, which are intended to illustrate the invention without limiting its scope.

Experimentally, calcium hydroxide is easily determined by differential thermoanalysis (DTA), which shows an endothermic peak between 450 and 500 ° C.

Analysis of the products during hydration of the pure cement paste can be completed by examining X-ray diffraction diagrams. 448 450 Exemgel 1.

Binder obtained from a mixture with "Superblanc" <2 A binder is made from a mixture of 70% portland cement clinker designated Superblanc ® 2.7% gypsum 27.3% alumina trihydrate AH3 prepared by the Bayer process.

The grain size of these products is such that 90% of the material passes through a sieve with a mesh size of 40 .mu.m.

Superblanc ® is a Portland cement, which is essentially free of iron oxide and is traded in CIMENTS LAFARGE FRANCE, France.

If the development of the compound, pure cement paste is examined in comparison with the corresponding for Superblanrzc) only, it appears from Table I below that: for Superblancc) only: Cä (OH) 2 is present in large amounts after 1 day and 70-80 % of the possible amount of calcium hydroxide which can be formed by C35 hydration is present after 7 days, for the comparative cement according to Example 1: regardless of the time period, Ca (OH) 2 can not be detected.

According to this example, the alumina AH3 had been pre-ground in an AUREC Q? Type vibro mill for 30 minutes to give a partially amorphous product.

The pure cement paste was mixed with a water / cement ratio of 0.64 (V / C = 0.64). 448 450 s - * rábèii 71 :.

X-ray diffraction tube intensities Material Time period C38 AH3a.Ca (OHl2.C3AH¿ C¿AHn Castable ld S - S - - Superblanc- 7 d fS - vS - - -slurge 28 d fS ~ VS - - Castable ld S VS ~ WW cement slurry 7 d fS S - SW according to example l 28 d fw S - SW according to the invention VS = very strong S = strong fS = relatively strong vw = very weak W = weak fW = relatively weak not determinable On the other hand, other phases occur, which are not specified in Table I according to Example 1, for example C2ASH8 (hydrated gelatin) and hydrogranates.

The results of DTA (after 1 day of storage at ZOOC and relative humidity (RE) = 95%, as shown in the drawing figure, give curve no. 2 for the cement according to example 1 and curve no. 1 for Superblant: É9 with coarse non- ground hydrated alumina.

This diagram shows that curve No. 2 for 24 hours of storage does not show a peak characteristic of Ca (OH) 2.

Example 2.

The cement is as given in Example 1 and is obtained according to the same method but using collection.

Examination of the cement with X-ray diffraction shows a partial amorphization of the alumina trihydrate, while Superblamcça is only slightly affected by this treatment.

After 4 days of storage of the pure cement paste, no 448 450 Ca (OH) 2 can be observed but hydrated calcium aluminates (C3AH6 - C4AHn) as well as hydrated gehlenite (CZASH8) are present. The hydration products are identical to the hydration products of the cement obtained from the mixture after prolonged grinding of each component.

These two examples show the possibility of reacting, under certain conditions, the calcium hydroxide released during the hydration of C35, a major constituent of Portland cement, with hydrated alumina.

Thus, a cement is obtained which, after hydration, contains only hydrated calcium silicates, hydrated calcium aluminates and hydrated calcium silicoaluminates.

The presence of Ca (OH) 2 and the avoidance of the consequent inconveniences thus enable the use of this type of cement, especially in the refractory range.

Example 3-32.

In the examples described below, three types of Portland clinker and different alumina-containing materials were examined.

Three types of tiles were used in the investigation: Tiles A: Tiles with a high content of C38 and C3A.

Tiles B: Tiles with a low content of C38 and C3A.

Tiles C: Tiles with a very low content of C3A.

These clinker materials had the following potential mineralogical compositions (based on their chemical analyzes): Alkali- C35 C25 C3A C4AF sulphate Free Total CaSO 4 ', CaO Clinker A 68 17.40 7.45 0.80 0.35 4.05 100 Clinker B 57 .5 21.60 7.20 9.80 1.60 0.65 100 Clinker C 66.3 15.35 0.50 14.50 0.40 1.55 100 448 450 Two types of bauxite were used: Bauxite A: Med low iron content Bauxite B: With high iron content which had the following compositions: sioz Tioz 141203 cao: ago so3 coz LoI Fe¿o3 Kzo. Nazo number of Bauxite A 0.70 3.90 60.90 0 O 0.05 0.05 30.85 3.45 0.05 0.05 100 Bauxite B 8.90 2.75 53.27 0 0 0.10 0.05 23.63 11.27 0.05 0.02 100 * Loss of annealing Of the different X-ray diffraction spectra and taking into account the content of aluminum and water, it is possible to calculate the proportions of trihydrate (AH3) and monohydrate (AH) in each bauxite and the percentages of the different phases are given in the following table: Table II.

AH3 Bayer Bauxite A _ Eauxite B AH3 100% 87.2% 61.9% AH - 4.7% 14.9% Pollution - 8.1% 23.2% Examples 3-5.

According to Examples 3-5, the clinker ratio is Blalumina oxide-containing material A 2: 1.

Example 3 after mixing without collection Example 4 after mixing and collecting 2 h Example 5 after mixing and collecting 6 h The collection was not carried out in the manner set out in Examples 1 and 2 in a vibro mill but in a conventional ball mill. The pure castable cement dispersions were stored at 20 ° C and 95% relative humidity.

At 20 ° C and 95% it is determined by differential thermal analysis and X-ray diffraction that the cement according to Example 3 (mixing without aggregation) still contains calcium hydroxide even after prolonged storage (3 months), while cement produced by aggregation no longer contains Ca ( 0H) 2 after 24 hours of storage.

Storage at 50 ° C and 95% relative humidity improves the reactivity of the mixture, as the Ca (OH) 2 present after 7 days at 20 ° C and 95% relative humidity disappears.

Table III.

Storage Example Time period C38 AH3 Ca (OH) 2 C3AH6 C4AHn 24 h SSS - - 3 7 d fS S VS - - 3 WS vS - - o C 24 _ ss - fw w% _ F_ 4 7 fs fs - fw w 95 R 3 W fS - fW W 24 ssg - fw w 7 fS fW - fW W 3 W fW - fW W 24 SSS - - 3 7 fS fW - fW W 3 WW - fW W o 50 C 24 ss - fw w 4 7 fW fW - fW W 95% RF 3 W W _ fw W 24 S S - fW W 7 fW fW - fW W 3 W W - fW W As in examples 1 and 2, C ASH (hydrated whole) and hydrogranates are detected. w 448 450 Examples 6-8.

In these examples, clinker B and bauxite B were used in a ratio of 2: 1.

Example 6 after mixing without collection Example 7 after mixing and collecting 2 h Example 8 after mixing and collecting 6 h The pure cement paste was stored at 20 ° C and 95% R.F. (rela-: iv degree of humidity) resp. via so ° c and 95% Raa.

In Examples 6-8 it was found that as in previous examples the reaction Ca (OH) 2-AHn is instantaneous in all cases when the cement is produced by collection.

This reaction is accelerated as the temperature increases.

Examples 9-27.

Further experiments were carried out with other compositions, whereby the nature of the material and the quantity ratio of clinker / alumina material were modified¿ Example Alumina- Clinker- Front- Clinker-containing material filler position AA 57/43 9-27 BB 67/33 Collection C 77/23 Det the total number of combinations is 3 x 2 x 3 = 18 compositions of this type (examples 9-27).

Analysis of the pure cement paste obtained in each of Examples 9-27 after the hydration time of 24 hours shows the absence of calcium hydroxide both by X-ray diffraction and differential thermoanalysis. It will be apparent to those skilled in the art that it is convenient to adjust the amount of alumina-containing material to the amount of calcium hydroxide which can be expected to be formed by hydrating the Portland cement taking into account the impurities contained in the two materials.

The properties of the pure cement paste according to the invention are such that after hydration it never contains Ca (OH) 2, which makes it possible to use these binders for applications in which the presence of calcium hydroxide is unsuitable.

Example 28. a) Burning stability.

A mixture is prepared from 67% clinker and 33% chemical AH produced by the Bayer process. The mixture is collected for 3 2 hours. After hydration for 24 hours at 20 ° C and 95% R.F. the pure cement paste is dried at 110 ° C and then heated to 300-500-800-110-250 ° C for 6 hours and finally cooled in the oven.

'Treatment temperature Mineral phase 2o ° c 11o ° c 3oo ° c 5oo ° c soo ° c 11oo ° c 12so ° c c3s. sswwwww A113 vs vs - - - - - cammz - - _ - _ - _ cao - - - - - - - c3AH6 sss - - - - 04mm W - - - - - - czAs - - - - wss Cl2A7 - - SS - VS S: m2 - - - - - vs w cA -'- - - - - vw. ice The intensity of the pure cement paste after heat treatment.

It turns out that regardless of the firing temperature of the 448,450 ll of pure cement paste, the binder defined according to the example will never release lime which is rehydrated and can therefore be used as a refractory binder. b) Moisture stability.

From the cement defined in Example 28 a), cubes measuring 10 cm were made of fire clay concrete, which were then treated according to a heat treatment cycle given in the table. Compared to a reference cement sample, cubes made from an activated cement base remained intact, while cubes of comparative cement cement showed cracks. activated cement comparative test 6 h - SOOOC no cracking no cracking h in humid no cracking no cracking conditions sh - 8oo ° c no cracking cracking day in humid no cracking cracking conditions 6 h - 110 ° C no cracking cracking day in damp cracking 'no cracking conditions _ _ Examples 29-31.

According to Examples 29-31, the properties of a composite cement consisting of clinker C and bauxite B were examined with conventional tests for refractory purposes, ie. by determining: the mechanical properties after heating linear dimensional change after firing refractory under load (temperatures).

The operating temperature limit is in the range 1250-1300 ° C, as the dimensional change after firing is within the ERP recommendations (S in 1.5%). 12 WNN NNONN NNmNN mm Q N mNNNomNNoNNN mNNNmN.N | m @> N «NowN NN ONN NN u N« «.o NN NN \ NN om fl NN ON NN w N mm fi Nmmmm o« omN Nm v N ooNNmNNNmNNN NNNN N_o «oem NoNmNN NN mNN NN Ü N« «_o om NN \ > N m U om fi NN NN NN UN NNN om NNN NN NN mw fi NN UQN NN w N 44.0 NN NN \ Nm ONN m fi WN NN u N Ned Nm NN NN un fi ww 0 mum UN 440 * N | m @ wMw u \> Nwm \ Hwmm @ Mm u al xømm HWX = NNM løcw | @Hwm zäwxm NWO f n wwwmwmmwwm | MMW uoomNN uoooNNuoooN uooN DE FR SS al mømaoxuøwemu 448 450 A H fifl SM DÜUCÜEUO _m: ouøn E Mmm vcwëwo mx oom wwam flfi wnwcc fl ^ EE mxov mcouwnnæm fi onwu f w mo: ummmxmcmmm, m .fl mlmm fi wmšmxm <| ~ 448 450 13 As a general rule, the refractory strength of the cement depends on the ratio of clinker / alumina-containing material and the degree of purity of the constituents (iron oxide content).

The rheological properties of the cement can be modified by supplementary addition of anhydrous or hydrated calcium sulphate or such additives as plasticizers, fluidizing agents, water reducing agents.

Example 32.

A cement was prepared by collecting clinker B and bauxite B for 2 hours and exhibits a workability time when used as mortar with silica sand (V / C = 0.5) after deposition (settling) 3 minutes - 169 s after deposition (settling) 30 minutes - 268 s.

After addition of 0.1% (0.1 / 1000) sodium gluconate this changes to: after deposition 3 minutes - 14 s after deposition 30 minutes - 34 s.

Workability was measured by a moving technique using the device known as "Maniabilimetre LCL", which is marketed by Etablissements Perrier in Montrouge, France, according to the method described in "Mode Opëratoire BF Ml", published by Dunod 1973 ( French Publishers Dunod).

It thus appears that binders according to the invention can be added to the additives which are generally used in the cement technique. The nature of these additives essentially depends on the nature and degree of fineness of the materials that form the new hydraulic binder.

Of course, the invention is in no way limited to the embodiments shown, but can be varied in a variety of ways as will be apparent to those skilled in the art without departing from the spirit of the invention. 448 450 14 Thus, the collection times given in different examples do not constitute a lower limit but only examples in the experiments. In industrial use, the construction of the grinder ~ ï as well as its operating parameters can be adjusted so that an optimal effect is obtained.

Curing time refers to time for curing or curing.

Claims (6)

PATENT REQUIREMENTS 1. A process for producing a refractory hydraulic binder which is substantially free of calcium hydroxide by mixing an artificial Portland cement clinker which tends to give rise to calcium hydroxide under standard conditions, with hydrated alumina, e.g. characterized in that the alumina is initially added in such amounts that appreciable formation of calcium hydroxide is prevented during the mixing operations and that curing is carried out mainly at ambient temperature, the amount of hydrated alumina present initially being at least two moles of hydrated alumina, calculated as Al (OH) 3, per three moles of Ca (OH) 2 which may be formed during the hydration. 2. A process according to claim 1, characterized in that the hydrated alumina is selected from the group consisting of natural bauxite, laterite and mixtures thereof. 3. A process according to claim 1 or 2, characterized in that the hydrated alumina is alumina trihydrate. 4. A method according to claim 2, characterized in that the hydrated alumina is atomized hydrated alumina, of which 90% can pass through a screen with a mesh size of 40 μm. 5. A process according to any one of claims 1 to 4, characterized in that an additive selected from the group E consisting of fluidizing agent, elastic improving agent, water reducing agent, calcium sulphate or mixtures thereof is added to the elaphase hydraulic binder. medlet. 1 I z -____, ______ ___- J 448 450 6. A method according to any one of claims 1-5, characterized in that 90% of Portland cement clinker can pass through a screen with a mesh size of 40 μm.