GB2063240A - Hydraulic binders based on Portland cement clinkers - 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

SPECIFICATION Novel hydraulic binders based on Portland cement clinkers and their process of obtention The present invention is related to novel hydraulic binders based on Portland cement clinkers which, after hydration, are free of hydrated or calcium hydroxide Ca(OH)2. In fact, it relates to a process by which these binders can be obtained, as well as to certain applications of them.

It is well known that on hydration Portland cement liberates hydrated lime Ca(OH)2 which renders the cement unsuitable for certain uses, which require, among other things, a refactory character at a temperature higher than about 5000 C, or stability with respect to pure water and/or certain acids.

In fact, the formation of hydrated lime results from the nature of the cement the principal constituent of which is expressed by the formula C3S (C where C = CaO; S = SiO2). Thus, it is well known that during the hydratation process of C3S hydrated lime is produced.

The nature of this hydration may be expressed schematically by the reaction: C3S + 3H e CSH + 2CH (H = H20).

Moreover, it is known that in the construction materials industry it is possible to combine the lime which appears during the hydration with additives such as pozzolanes in order to form hydrated calcium silicates. This reaction is delayed since it does not start until 1 5 days after hardening. These cements are known by the term "pozzolanic cements" and are especially used for their stability with respect to pure waters and certain acids.

After hydration, if ordinary Portland cement is subjected to a temperature in the range of 400 to 5000 C, the hydrated lime Ca(OH)2 liberated during the course of the hydration, is transformed into calcium oxide which may subsequently rehydrate and provoke swelling and deterioration.

The pozzolanic cements may be used as refractory binders on condition that the refractory concretes obtained from these cements several months previously are stored in a humid atmosphere in order that the pouzzolanic reaction may be complete before bringing them to a high temperature.

The present invention is based on the surprising and unexpected observation that it is possible, under certain conditions, to use these Portland cements in unusual applications.

The present invention relates to a process for the production of binders obtained from a mixture of Portland cement and hydrated alumina, the latter used in a quantity sufficient for the hydrated lime which is formed during the hydration of the binder to combine completely with the hydrated alumina as its formation proceeds. This means that Ca(OH)2 is never present, even after a long time has elapsed.

Preferably the mixture is co-ground. The reaction between Ca(OH)2 and the hydrated alumina of the aluminous material is instantaneous if the mixture is obtained by grinding together the Portland cement and an aluminous material, such as chemical hydrated alumina, raw bauxites and laterites. If, however, the granulometry of each of the constituents is such that 90% of the material passes through a 40 ,u sieve, such co-grinding may be ommitted.

The binders according to the present invention are based on Portland cement and alumina, which alumina consists of hydrated alumina used in sufficient quantities for the nascent lime hydrate produced during the hydration of the binder to combine completely with the hydrated alumina as fast as it is formed.

In fact, during the hydration of the binder according to the invention, the C3S gives rise to the liberation of the lime which, as it is formed, reacts with the hydrated alumina to form hydrated calcium aluminates of C3AH6 or C4AHn type or silico-aluminates of hydrated(gehlenite type) C2ASH8 and hydrogarnets.

This means, therefore, that no trace of Ca(OH)2 is detectable in the cement.

In this specification, the use of these novel hydraulic binders is more specially examined in the framework of refactory applications although the invention is in no way limited to such applications.

The advantages and characteristics of the invention will become apparent from the following nonlimiting examples.

On the experimental level, slaked lime is easy to detect through differential thermal analysis (DTA) showing an endothermic peak between 450 and 5000 C.

Analysis of the products of the hydration of the neat cement paste may be completed by examination of the X-ray diffraction diagrams.

EXAMPLE 1 binder obtained by mixture from "Superblanc" (Reg. Trade Mark) a binder is prepared from a mixture of 70 % Portland cement clinker known as "Superblanc" 2.7% gypsum 27.3% aluninium trihydrate AH3 produced by the Bayer process the granulometry of these products being such that 90% of the material passes through a 40 u sieve.

"Superblanc" a Portland cement, substantially free of iron oxide sold by the company CIMENTS LAFARGE FRANCE.

If the evolution of the composite neat cement paste is examined in comparison with that of the "Superblanc" alone, it appears from TABLE I below that: - for the "Superblanc" alone: Ca(OH)2 is present in large quantities after 1 day and 7080% of the available lime able to be formed by the C3S hydratation is present after 7 days; - for the composite cement, object of EXAMPLE 1: whatever lapse of time, Ca(OH)2 is never detected.

In this example, AH3 alumina had previously been ground in a vibro-mill of the AUREC 8 type for 30 minutes, leading to a partially amorphous product.

The neat cement paste was mixed at a water/cement ratio of 0.64 (W/C = 0.64) TABLE I X diffraction peaks intensi:ies

Material Lapse of Time #C3S AH, Ca(OH)2 #C3AH6 t::AHe Castable Superblanc 1 d S - S - - 7 d fS - vS - | - Slurry 28 d fS - vS - Castable 1 d S vS - W W Cement Slurry 7 d fS S - S W Example 1 28 d fW S - S W Present Invention vS - very strong S- strong fS - fairly strong vW- very weak W- weak fW= fairly weak - - not detectable On the other hand, other phases occur which are not cited in TABLE I of EXAMPLE 1, such as C2ASHB (hydrated gehlenite) and hydrogarnets.

The results of DTA (after 1 day storage at 200C and R.H (relative humidity = 95%) recorded on the annexed drawing lead to curve nO 2 for the cement of EXAMPLE 1 and curve nO 1 for the Superblanc #R with coarse non-ground hydrated alumina.

This diagram shows that the curve nO 2 for 24 hours storage does not present a peak characteristic of Ca(OH)2.

EXAMPLE 2.

The cement is such as that defined in EXAMPLE 1 and is obtained according to the same method although submitted to co-grinding.

Examination of the cement by X diffraction shows a partial amorphisation of the trihydrate alumina while the Superblanc O is only slightly affected by this treatment.

In the neat cement paste after 4 days storage no Ca(OH)2 is observed but hydrated calcium aluminates (C3AH6-C4AHn) as well as hydrated gehlenite (C2ASH8) are present. In fact, the hydration products are identical to those of the cement obtained from the mixture after prolonged grinding of each of the constituents.

These two examples reveal the possibility of causing to react, under certain conditions, the hydrated lime liberated during the hydration of C3S, the principal constituent of Portland cement, with the hydrated alumina.

Thus a cement is obtained which, after hydration only contains hydrated calcium silicates, hydrated calcium aluminates and hydrated calcium silico-aluminates. The absence of Ca(OH)2 and the overcoming of the consequent drawbacks which result therefrom permit the use of this type of cement in refractory field.

EXAMPLES 3 to 32 In the examples which are described below three types of Portland clinker and different aluminous materials are examined.

The operation proceeds with three types of clinker: Clinker A: clinker having a high C3S and C3A content; Clinker B: clinker having a low C3S and C3A content; Clinker C: clinker having a very low C3A content having the following potential mineralogical compositions (calculated from their chemical analysis):

alkalin sulphonate free C35 C2S C3A C4AF CaSO4 CaO TOTAL 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 Two types of bauxite, among others, are used: - Bauxite A: low iron content - Bauxite B: high iron content having the following compositions;

SiO2 TiO2 Al2O3 CaO MgO SO3 CO2 L.O.I." Fe2O3 K2O Na2O Total Bauxite A 0,70 3,90 80,90 0 0 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 on ignition From the various X-ray diffraction spectra and taking into account the aluminium and water content, it is possible to calculate the proportions of trihydrate (AH3) and monohydrate (AH) in each bauxite; the percentage of the different phases is given in the following table.

TABLE II

AH3 Bayer Bauxite A Bauxite B AH3 100% 87.2% 61.9% AH - 4.7% 14.9% impurities - 8.1% 23.2% EXAMPLES 3 to 5 In Examples 3 to 5, the clinker B/aluminous material A ratio is 2:1.

* Example 3 after mixture without co-grinding * Example 4 after mixture and co-grinding for 2 h * Example 5 after mixture and co-grinding for 6 h The co-grinding was not carried out as in EXAMPLES 1 and 2 in a vibro-mill but in a conventional ball-mill.

The pure castable cement slurries were stored at 200C and 95% R.H.

It is observed at 200C and 95% by DTA and XR that the cement of EXAMPLE 3 (mixture without co-grinding) still contains the hydrate lime even after a long storage period (3 months) while the cements which were made by co-grinding no longer contain Ca(OH)2 after 24 hours storage.

Storage at 500C and 95% R.H. improves the reactivity of the mixture since the Ca(OH)2 present after 7 days at 200C and 95% R.H. disappears.

TABLE Ill

Time Storage Example lapse C3S AH3 Ca(OH)2 C3AH6 C4AHn 24 h S S S - | - 3 7 d fS S vS - 3 W S vS - 20 C 24 S S - fW W 4 7 fS fS - fW W 3 W fS - fW W & BR< 24 S S - fW W 95% R.H. 5 7 fS fW - fW W 3 W fW - fW W 24 S | S S - - 3 7 fS fW - fW W 3 W W - fw W 24 S- S - fW W 50 C 4 7 fW fW - fW W 3 W W - fW W & BR< 24 S S - fW W 95% R.H. 5 7 fW fW - fW W 3 W W - fW. W As in Examples 1 and 2, C ASH (hydrated gehlenite) and hydrogarnets are detected.

EXAMPLES 6 to 8 In these examples, clinker B and bauxite B were used in a 2:1 ratio.

* #Example 6 after mixture without co-grinding * Example 7 | after mixture and co-grinding for 2 h * Example 8 after mixture and grinding for 6 h The neat cement paste was stored respectively at 200C and 95% R.H. and at 500C and 95% R.H.

In Examples 6 to 8, it was observed that as for the preceeding examples the Ca(OH)2-AHn reaction is immediate whenever the cement is prepared by co-grinding.

This reaction is accelerated when the temperature is increased.

EXAMPLE 9 to 27 Further tests were carried out on other compositions, the nature of the material and the clinker/aluminous material ratio of which were modified.

EXAMPLES 9 to 27

aluminous clinkar/ n * example clinkar material filler preparation A A 57/43 9 - 27 B B 67/33 co-grinding C 77/23 The total of the combinations represents 3 x 2 x 3 = 18 cases of this type (thus Examples 9 to 27).

The analysis of the neat cement paste obtained from each of these examples 9 to 27 after a hydratation time of 24 hours, shows the absence of hydrated lime both by X-ray diffraction and DTA.

It is obvious to a man skilled in the art that it is advisable to adjust the quantity of aluminous material to the hydrated lime liable to be formed by hydratation of the Portland cement, taking into account the impurities present in both materials.

In fact, the characteristic of the neat cement paste according to the invention is that after hydration it never contains Ca(OH)2, therefore enabling the use of these binders in applications where the presence of Ca(OH)2 is disadvantageous.

EXAMPLE 28 a) fire stability A mixture is prepared from 67% clinker and 33% chemical AH3 produced from the Bayer process.

The mixture is then co-ground during 2 hours. After hydration for 24 hours at 200C and 95% R.H. the neat cement paste is dried at 1 1 OOC then heated to 300--5000-8000-1 100--12500C for 6 hours and finally cooled in the oven.

treatment temperature mineralogical phase 20 C 110 C 300 C 500 C 800 1100 C 1250 C C3S S S W W W W W AH3 vS vS - | - | - | - | - Ca(OH)2 - - - - - - CaO - - - - - - C3AH6 S S S - | - | - | - C4AHn W - - - - - C2AS - - - - W S S C12A7 - - S S - vS S CA2 - - - - - vS W CA - - - - - vW fS

Intensity of the neat cement paste after heat treatment * To conclude, it is observed that whatever the firing temperature of the neat cement paste, the binder defined in this example never liberates lime liable to be rehydrated and thus it may be used as a refractory binder.

b) humidity stability From the cement defined in Example 28, a, 10 cm cubes of fire clay concrete were prepared, then treated according to a thermic cycle as shown n the table below. Compared to a reference cement sample, the cubes made from an activated cement base remained intact while the cubes of the reference sample cement present cracks.

activated cement reference sample 6 h - 500 C no cracking no cracking 5 h in humid conditions no cracking no cracking 6 h - 800 C no cracking crackings 5 days in humid conditions no cracking crackings 6 h - 110 C no cracking crackings 5 days in humid conditions no cracking crackings EXAMPLE 29 to 31 In Examples 29 to 31 the behaviour of a composite cement constituted from Clinker C and bauxite B is examined by conventional tests for refractory purposes, i.e. by determination of:: - the mechanical properties after heating - the linear change after firing - refractiveness under load (temperatures).

The service temperature limit is in the range 1 2500C-1 3000 C, since @9 to 31 @ kg cement by m of concrete-cement co-ground 2 hours

Cement composition refractiveness under load 20 C 800 C 1100 C 1250 C linear (temperature) Clinker/ Example Lapse charge Clinker Bauxite Bauxite No. W/C of time F* C** F C F C F C 1250 C 1% 2% 5% 10% 1 d 15 35 15 120 15 120 57/43 29 0,44 2 d 25 100 22 165 7 d 48 215 30 175 1 d 18 80 19 150 C B 67/33 30 0,44 2 d 33 125 26 185 103 500 - 0,3 1175 1235 1275 1300 7 d 57 250 40 335 33 195 1 d 16 80 19 150 77/23 31 0,44 2 d 29 110 24 160 148 765 - 1,45 1195 1220 1250 1275 7 d 56 335 37 320 31 195 * F = Bending in kg/cm ** C = Compression in kg/cm the linear change after firing lies within the ERP recommendations* ( < + 1.5%).

As a general rule, the refractarity of the cement will depend on the clinker/aluminous material ratio and the purity of the constituents (iron oxide content).

The rheology of the cement may be modified by complementary addition of anhydrous or hydrated calcium sulphates or additives such as plasticizers, fluidizers, water reducers.

EXAMPLE 32 A cement realized by co-grinding clinker B and bauxite B for 2 hours has a workability when used as a mortar with silica sand (W/C = 0.5) after settling of 3 mn 169s - after settling of 30 mn 268 s After addition of 0.1% (0.1/1 000) sodium gluconate, this changes to: after settling of 3 mn 14s -after settling of 30 mn 34 s The workability was measured by a flow technique with the apparatus known as "Maniabilimetre L.C.L." sold by Etablissements Perrier in Montrouge, France according to the method described in the "Mode Opératoire B F M-1" " edited by the French Publishers Dunod 1973.

It is thus observed that the binders according to the present invention are liable to have added auxiliary agents used currently in cement techniques. The nature of these auxiliary agents will depend essentially on the nature and the fineness of the materials constituting the novel hydraulic binder.

Of course, the present invention is in no way limited to the embodiments shown and represented, it has many variations within the reach of a man skilled in the art, according to the applications envisaged and without departing from the spirit of the invention.

Thus, the duration of the co-grinding indicated in various examples does not constitute a lower limit; but simply an experimental indication.

It is obvious in the case of industrial use that the construction of the mill as well as its operating parameters could be adapted to render optimum efficiency.

By time lapse is meant in the present description curing or hardening time.

Claims (6)

1. Process to obtain a hydraulic binder, characterized in that Portland cement clinker is mixed 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.

2. Process according to dlaim 1, characterized in that the hydrated alumina and the Portland cement clinker are ground together.

3. Process according to claims 1 or 2, characterized in that the hydrated alumina is alumina trihydrate.

4. Process according to claim 3, characterized in that the alumina trihydrate is a constituent of a natural bauxite or a laterite.

5. Process according to one of the claims 1 to 4, characterized in that one or more additives such as fluidizers, plasticizers, water reducers or calcium sulphate are added.

6. A hydraulic binder based on Portland cement clinker and alumina, characterized in that the alumina is hydrated alumina and is used in sufficient quantity that the Ca(OH)2 which forms during the hydration of the Portland cement clinker combines completely with the hydrated alumina as it is formed.