CA1138903A

CA1138903A - Hydraulic binders based on portland cement clinkers and their process of obtention

Info

Publication number: CA1138903A
Application number: CA000364866A
Authority: CA
Inventors: Alain Mathieu
Original assignee: LAFARGE AND LAFARGE FONDU INTERNATIONAL
Current assignee: LAFARGE AND LAFARGE FONDU INTERNATIONAL
Priority date: 1979-11-19
Filing date: 1980-11-18
Publication date: 1983-01-04
Also published as: FR2470103B1; NL8006298A; GR71925B; GB2063240B; DE3041652C2; IE802388L; CS782980A2; JPS56145140A; BR8007555A; OA06655A; CS241477B2; SE448450B; ES496952A0; DE3041652A1; AU6415180A; SE8008088L; ES8205187A1; BE886239A; ZA806783B; LU81915A1

Abstract

ABSTRACT OF THE DISCLOSURE

The present invention is related to novel hydraulic binders based on Portland cement clinkers which, after hydration, are free of hydrated lime or calcium hydroxide Ca(OH)2.
It relates to a process for the obtention 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.

Description

3~

The present invention is related to novel hydraulic binders based on Portland cement clinkers which, after hydra~ion, are free of hydr-lime or calcium hydroxide Ca(OH)2 . In fact, it relates to a proc-ess for the obter,tion of these binders as well as to certain of their applications.
It is well known that Portland cement during the course of its hy-dratation liberates hydrated lime Ca(OH)2 which renders the cements un-suitable for certain uses, requiring , among other things, a refractory character at a temperature higher than about 500C, or a stability with respect to pure water and/or certain acids.
In fact, the formation of hydrated lime results from the nature itself of the cements whose principal constituent is expressed by the formula C3S (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 -~ CSH + 2cH
(H - H2O) Moreover, it is known that in the construction materials industry it is possible to combine the lime which appears during the hydration with additive substances such as pozzolanes in order to form hydr-ated ca'lcium silicates. This reaction is delayed since it does not start until 15 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.

. ~

1~.3~ 3 After hydration, if ordinary Portland cement is subjected to a temperature in the range of 400 to 500C, the hydrated lime Ca(OH)2 liberated during the course of the hydration, is trans-formed into calcium oxide which, may subsequently rehydrate and provoke swelling and deterioration of structures.

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 atmos-phere in order that the pouzzolanic reaction may be complete beforebringing them to a high temperature.
The present invention is based on the surprising and unexpected observation that it is possible, in defined conditions, to use these Portland cements in unusual applications.
The present invention relates to a process for the obtention of binders obtained from a mixture of Portland cement and hydrated al-umina, the latter used in a quantity sufficient for the lime hydrate which is formed during the hydration oF the binder to combine completely with the hydrated alumina as its formation proceeds.
This means that the presence of Ca(OH)2is never observed regardless of the lapse of time.
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 co-grinding of the Portland cement and an aluminous material, such as chemical 1~ 38~3 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~ s;eve , such co-grinding may be omm;tted.
The binders according to the present invention are based on Portland cement and alumina, which alum~na cons;sts of hydrated alum;na used in sufficient quantities for the nascent lime hyd-rate produced during the hydration of the binder to combine completely w;th 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 CLIAHn type or silico-aluminates of hydrated(gehlenite type) C2ASH8 and hydrogarnets.
This means, therefore, that no trace of Ca (OH) 2 i s detectable in the cement.
In the present description, the use of novel hydraulic binders is more especially examined in the framework of refractory applications althouth the invention may in no way be considered as being limited to this application.
The advantages and characteristics of the invention will become apparent whilst reading the following description and examples given by way of illustration but without limiting the scope of said invention.
On the experimental level, slaked lime is easy to detect through d;fferentialthermal analys;s(DTA) showing an endothermic peak between 450 and 500 C.

1~3~3 Analysis of the products of the hydration of the neat cement paste may be completed by examination of the X- ray diff-f~action diagrams..

_ _ _ _ _ _ _ _ _ b;nder obtained by mixture from Superblanc a binder is prepared from a mixture of 70 % Portland cement clinker calle~ Superblanc

2.7% gypsum . 27.3% trihydrate alumina AH3 produced by the sayer process the granulometry of these products being such that 90% of the material passes through a ~0~ sieve.
Superblanc ~ a Portland cement, substantially free of iron oxide sold by the com~any CIilENTS LAFARGE FR~NCE.

If the evolution of the compos;te 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(Ot1) 2 is present in large quantities after 1 day and 70-80% 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 the time lapse, Ca(OH)2 is never detected.
In this example, AH3 alumina had previously been ground in a 25 vibro-mill of the AUREC ~ type for 30 minutes, leading to a 1~3~ 3 partial1y amorphous product.
The neat cement paste was mixed at a water/cement ratio of 0.64 (W/C = 0.64) TAsLE I
x diffraction peaks intensities __ _ __ __ __ _ __ .
MATERIAL LAPSE OF TIM C35 P~13 Ca(OH)2 C3AH6 C4AHn ~ _ cAsTAsL~ 1 d s _ S _ _ supERsLANc 7 d fS _ vs _ _ SLURRY 28 d fS _ vS _ _ CASTABLE 1 d S vS _ W W
CEMENT SLURRY 7 d fS S _ S W
Ex~MPLE 1 28 d fW S _ S W
PRESENT INVENTION _ _ _______ ________ _ ______Y , vS = very strong S = strong fS = fairly strong vW = very weak w = weak fW = fairly weak - = not detect-able On the other hand, other phases occur which are not cited in TAsLE I
of EXAMPLE 1, such as C2ASHg (hydrated gehlenite)and hydrogarnets.
The results of DTA (after 1 day storage at 20C and R.H(relative humidity = 95%) recorded on the annexed drawing lead to curve n 2 for the cement of EXAMPLE 1 and curve n 1 for the Superblanc ~ with coarse non-ground hydrated alumina.
This diagram shows that the curve n 2 for 24 hours storage does not present a peak characteristic of Ca(OH)2.
EXAMPIE_2 The cement is such as that defined in EXAMPLE1 and is obtained according to the same method although submitted to co-grlnding Examination of the cement by X diffraction shows a partial amorph-isation of the trihydrate alumina while the Superblanc ~ 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 pro-ducts are identical to those of the cement obtained from the mixtureafter prolonged grinding of each of the constituents.
These two examples reveal the possibility of causing to react, under certain conditions, thehydratelime liberated during the hydration of C3S, 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 thus enable the use of this type of cement and especially in the refractory field.
EXAMPLES 3 to 32 ________________ In the examples which are described here-under three types of Portland clinker and different aluminous material are examined.
Operation proceeds with three types of clinkers :
. Clinker A : clinksr 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 havina the followlna Dotenf.ial mineraloaical comwsitions (calculated from their chemical analysis):

------~ ------------alkalin free C3SC2sC3A C4 AF sulpho- CaO TOTAL
_ clinker A 68 17.40 7.45 0.80 0.35 4.05 100 _ clinker B 57.521.60 7.20 9.80 1.60 0.65 100 clinker C 66 315 35 O.SO 14 SO 0 40 1.55 100 Two types of bauxite, among others, are used :
- Bauxite A : low iron content - Bauxite B : high i ron content having the following compositions;
_ . I ,____ ~ _ . _ _ S;O ~ TiO2 AL203 CaOMgO SO3 CO2 L-O.I Fe203 K20 Na20 TotaL
_ . _ _ BauxiteA 0,70 3,90 60,9G O O 0,05 0,05 30,85 3,45 0,05 O,OS 100 l _ _ . _ ~auxiteB 8,90 2,75 53,27 O O 0,10 0,05 23,6~ 11,2~ 0,05 0,02 100 * loss on ignition From the different X diffraction spectra and -taking into account the aluminium and water content, it is possible to calculate the proportions of trihydrate ~AH3) and monohydrate (AH) i n each bauxite; the percentage of the different phases is given in the following table TABLE II
AH~ Bayer Bauxite A Bauxite B
AH3 100% 87.2% 61.9%
_ AH _ 4.7% 14.9%
_ .
impurities _ 8.1% 23.2%

. ` 1~3~ 3 EXAMPLES 3 to 5 ____ __________ In Examples 3 to 59 the clinker B/aluminous material A ratio is 2:1.
__.
* Example 3 after ~ixture ~ithout co-grinding * Example 4 after mixture and co-grinding for 2 h . _ _ _ . __ * Example 5 after mixture and co-grinding for 6 h __ ,. l The co-grinding was not carried out as ;n EXAMPLES 1 and 2 in a vibro-mill but . in a conventional ball-mill.
The pure castable cement slurries were stored at 20C and g5% R.H.
It is observed at 20C and 95% by DTA and XR that the cement of EXAMPLE 3 (mixture without co-grinding) still contains thehvdratelime even after a long storage period (3 months) while the cements wh;ch were made by co-grinding no longer contain Ca(OH)2 after 24 hours storage.
Storage at 50C and 95% R.H. improves the reactivity of the mixture since the Ca(OH)2 present after 7 days at 20C and 95% R.H.
disappears. -- ~~~-~

~3~3~3 TABLE III
_ _ _ _ _ _ _ _ _ _ , ... Time _______ __~______ ~ __~_____ __~_____ Storage Example lapse C3S AH3 Ca(OH~2 C3AH6 C4AHn _ 24 h 5 S S _

3 7 d W S vS _ 20C 24 S S _ fW W

4 7 fS fS _ fW W
& 3 W fS _ fW W
24 S S _ fW W
95%R.H 5 7 fS fW _ fW W
3 W fW _ fW W
____N____ . I . ._. 24 S ' S S _~ _ 3 7 fS fW _ fW W
3 W W _ fW ~ W
o 24 S S _ fW -W
50 C 4 7 fW fW _ fW W
~ _ 3 W W _ fW W
95%R.H. 5 247 fW fW _ fW . W
. . 3 W W _ fW W

15 As in Examples 1 and 2, C ASH ( hydrated gehlenite) and hydrogannets 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 ~

The neat cement paste was stored respectively at 20C and 95%R.H
and at 50C and 95% R.H.

~3~3 In Examples 6 to 8, it was observed that as for the preceedillg exam-p7es the Ca~OH)2-A~n reaction is immediate whenever the cement is prepared by co-grinding.
This reaction is accelerated when the temperature is in-creased.
EXAMPLE 9 to 27 _______________ Furthertests 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 -- a Lumi no~ls ~;~
n exampleclinker A 57/43 preparation 9 ~ 1B _ 67/33 ~ ~ r i n~ ~ ~9 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 diffraction and DTA.
It is obvious for 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 never contain Ca(OH)2, therefore enabling the use of these binders in apPlications where the presence of lime hydrate is ill-advised.

_ _ _ _ _ _ _ _ _ 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 20C and 95% R.H.
the neat cement paste is dried at 110C then heated to 300-500-800-1100-1250C for 6 hours and finally cooled in the oven.
__~ _ mineralogical treatment temperature phase 20C110C 300C500C 800 1100C 1250c _ _ _ AH3 vS vS _ _ _ _ C ~OH) 2 _ _ _ _ C4AHn W _ _ _ _ _ c2AS _ _ _ _ w S S
~, _ _ S S _ vS S

Intensity of the neat cement paste_ after heat tre_tment *

1~3~Q3 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 in 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.
~ tivated cement ~_ 6 h - 500C no cracking no cracking

5 h in humid conditions no cracking no cracking

6 h - 800C no cracking crackings 15 5 days in humid conditions no cracking crack;ngs 6h - 110C no crack;ng crackings 5 days in humid conditions no cracking crackings - ,....................... _ EXAMPLE 29_to 31 In Examples 2~to 31 the behaviour of a composite cement constituted 20 from Clinker C and bauxite B is examined ~y conventional tests for refractory purposes, i.e. by determination of :
- the mechanical properties after heat;ng - the linear change after firing - refractiveness under load (temperatl~res).

The service temperature limit ls in the range 1250C-1300C, since 1~3~

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~3~ 3 the linear chanqe after firing lies within the E~P
recommendations* (< + 1.5%).
As a general rule, the refractarity of tbe cement will depend on the clinker/aluminous material ratio and the purity of the constituents (iron oxide content).
The rheology ofthe cement may be modified by complementary addition of anhydrous or hydrated calcium sulphates or additives such as plasticizers~
fluidizers, water reducers.
EXAMP~E 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 ................... 169 s - after settling of 30 mn .................. 268 s After addition of 0.1% (0.1/1000) sodium gluconate, this changes to :
- after settling of 3 mn ................... 14 s - 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 Mont-rouge, France according tothe method described in the "Mode Opératoire B F M-l" 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 embodi-ments shown and represented, it has many variations within the reach ;3~1~3 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.
S It is obvious in the case of indus,tr,ial use that the constr-uction of the m;ll 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

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Process for the obtention of a hydraulic binder, characterized in that Portland clinker is mixed with hydrated alumina in sufficient quantity that the lime hydrate formed during the hydration of the Portland clinker combines completely as it is formed with the alumina.

2. Process according to claim 1, characterized in that the hydrated alumina and the Portland clinker are co-ground.

3. Process according to claim 1, characterized in that the hydrated alumina is a trihydrate alumina.

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

5. Process according to one of the claims 1 to 3, characterized in that additives selected from fluidizers, plasticizers, water reducers, calcium sulphate, and mixtures thereof are used.

6. As a novel industrial product, a Portland cement clinker based hydraulic binder and alumina, characterized in that the alumina is hydrated alumina used in sufficient quantity that the lime hydrate which forms during the hydration of the cement combines completely at the time of its formation with the hydrated alumina.