# Patent

## Title
Method for producing concrete parts and structure

## Abstract

A method for producing concrete parts and a structure includes (i) supplying a first concrete composition based on a quick binder containing Portland cement, curing accelerator system based on Al2O3, CaO lime and SO3 sulphates, a retardant system and a superplasticizer, (ii) adding a releaser system for forming a second concrete composition and pouring the second concrete composition into a concrete form. The use of a releaser system and the preparation of the first concrete composition are also disclosed.

## Background
TECHNICAL FIELD
The invention relates to a method for producing concrete parts and structures using quick binder compositions.
By quick binders for mortar or concrete is meant quick setting and hardening binders based on Portland cements, calcium aluminates and calcium sulfates. The concretes using such binders in their compositions, once implemented, adopt short-term high mechanical features after adding a component designated as releaser; they exhibit preferably a compression strength Rc of at least 1 MPa 2 hours after adding the releaser to a first composition. If the releaser is added no later than 2 hours once the first primary composition has been kneaded, the compression strength RC is at least 1 MPa after 4 hours, counted after the first composition has been kneaded.
These concretes are fluidic or self-compacting concretes with at least 1 hour workability keeping time before adding the releaser, and at least 1⁄2 hour after adding the releaser.
The workability of the fluidic concretes is measured by the Abrams cone slump height—or slump value—(according to the NF P 18-451 French standard, dated December 1981) and concrete is considered as fluidic when said slump is at least 15 cm, preferably at least 18 cm.
The workability of selfcompacting concretes (also designated as selfpositioning) is measured at generally on the basis of ‘slumpflow’, according to the operating mode described in “Specification and Guidelines for Self Compacting Concrete, EFNARC, February 2002, p 19-23”; the spread value is, generally, 650 mm minimum for selfcompacting concretes and 800 mm maximum.
In the case of mortars, consistency may be measured at generally on the basis of ‘slumpflow’, according to the operating mode described in “Specification and Guidelines for Self Compacting Concrete, EFNARC, February 2002, p 19-23”, using a 1⁄2 scale cone. Mortars will be considered as equivalent to fluidic concretes when the spread value is greater than 200 mm, selfpositioning above 300 mm.
The invention relates to concretes, and more particularly fluidic or selfcompacting concretes, intended for the production of parts and structures, regardless whether factory-prefabricated parts or structures built on sites, such as for example concrete shells, slabs, etc.
TECHNOLOGICAL BACKGROUND
FR-A-2810314 describes a quick binder for selfcompacting concrete containing Portland cement, the calcium aluminate, calcium sulfate, a curing accelerator, a retarder and a superplasticizer agent such as polyphosphonate polyox. In this document, it is stated that this binder enables to have a workability duration greater than 1 hour, to pump the concrete thanks to this selfcompacting formulation, while having high compression mechanical strengths as soon as 4 hours after completed kneading, including at temperatures ranging between 5 and 35° C. The applications described in this document are the emergency repair of structures, provisional timbering of tunnels, galleries or other similar structures.
This document FR-A-2810314 describes quick binder compositions for selfcompacting concretes which are realised by mixing all the components in a single step, wherein each composition leads to a given compromise between the workability keeping time and the rapid acquisition of the strength requested. Each modification of this compromise implies re-formulation of a new composition.
Document EP-A-0769482 describes binder compositions used for application of projected concretes; but the addition thereto of a curing accelerator component causes ultra quick hardening, without any workability keeping time after addition of the curing accelerator. This makes the implementation such compositions in all the factory and on-site applications impossible where concrete is poured in place.
There is the need however for a method for producing concrete parts and structures using quick binder-based concrete compositions, which would enable to dissociate the time period during which it is necessary to keep the workability of the composition from the end of the kneading to the time of pouring, for instance with ready-to-use concrete requiring a certain transport time before pouring, from the time period when quick hardening should be released so as to obtain minimum short-term strength, sufficient for instance for removing the concrete form.
SUMMARY OF THE INVENTION
The invention provides hence a method for producing concrete parts and structures, including the following steps:
(i) supplying a first concrete composition based on a quick binder containing:

    
    
        60 to 95% Portland cement;
        5 to 40% curing accelerator system based on Al2O3 alumina, CaO lime and S03 sulfate; wherein sulfates may be, for instance, metallic, alkaline, alkaline-earth sulfates, organic sulfates, or mixtures; preferably, the curing accelerator system will be based on calcium aluminate and calcium sulfate;
        a retarder system; and
        a superplasticizer containing a polyphosphonate polyox type polymer, or a mixture of polymers of the type polyphosphonate polyox and polycarboxylate polyox;
    
    


then
(ii) adding a releaser system to form a second concrete composition; and
(iii) pouring this second concrete composition in a concrete form.
According to an embodiment, the step (i) is a wet mixing step wherein the first primary composition is prepared and which contains the following steps:
(a) a concrete composition is prepared containing, on the base of the quick binder:

    
    
        60 to 95% Portland cement;
        the retarder system; and
        a superplasticizer containing a polyphosphonate polyox type polymer, or a mixture of polymers of the type polyphosphonate polyox and polycarboxylate polyox;
    
    


then
(b) adding, on the base of the quick binder:

    
    
        5 to 40% curing accelerator system based on Al2O3 alumina, CaO lime and SO3 sulfate; wherein sulfates may be, for instance, metallic, alkaline, alkaline-earth sulfates, organic sulfates, or mixtures; preferably, the curing accelerator system will be based on calcium aluminate and calcium sulfate.
    
    


According to an embodiment, the method includes the following steps:

    
    
        (i) supplying by wet mixing in a ready-mix plant a first concrete composition based on a quick binder;
        then
        (ii) adding a releaser system; and
        (iii) pouring the concrete immediately after the releaser system addition step (ii).
    
    


The step (ii) may be implemented in a truck-mixer.
The step (iii) consisting in pouring the second concrete composition in a concrete form may be conducted with a second concrete composition exhibiting (a) a slump test value ranging from 15 to 24 cm, preferably from 18 to 22 cm or (b) a slump test value ranging from 580 to 750 mm, preferably from 650 to 750 mm.
According to an embodiment, the second concrete composition exhibits a compression mechanical strength Rc of at least 1 MPa 2 hours after the step (ii); if the releaser is added no later than 2 hours after the step (i), the compression mechanical strength Rc is at least 1 MPa 4 hours after the step (i).
According to an embodiment, the first concrete composition has a workability keeping time of at least 1 hour after the step (i) for wet mixing.
According to an embodiment, the second concrete composition has a workability keeping time of at least 30 minutes after the step (ii) for wet mixing.
The invention also relates to the use of a releaser system by addition to a first quick concrete composition in a method of preparation of concrete objects as defined in the present invention.
The invention also relates to the preparation of a first quick concrete composition intended for being added a releaser system for a method of preparation of concrete parts and structures, such as defined in the present invention.
The invention thus enables to produce a base concrete with a long workability keeping time to which it suffices to add as appropriate, for instance just before pouring, another component releasing quick hardening and enabling short-term mechanical strength. It is thus possible from a solely basic concrete composition to reach the different compromises requested in terms of workability keeping time/quick acquisition of strengths. The invention thus offers a polyvalent solution which applies to the cements described in the European standard EN 197-1.


DESCRIPTION OF EMBODIMENTS OF THE INVENTION
The invention is now explained more in detail in the following description.
The invention is based upon the postponed addition of a releaser system to a first concrete composition, before the implementation thereof.
The binder involved in the composition of fresh concrete contains:

    
    
        60 to 95% Portland cement;
        5 to 40% in weight of an curing accelerator system based on Al2O3 alumina, CaO lime and SO3 sulfate; wherein the sulfates may be, for instance, metallic, alkaline, alkaline-earth sulfates, organic sulfates, or mixtures; preferably, the curing accelerator system is based on calcium aluminate and calcium sulfate;
        a retarder system; and
        a superplasticizer containing a polyphosphonate polyox type polymer, or a mixture of polymers of the type polyphosphonate polyox and polycarboxylate polyox.
    
    


Preferably, the binder contains:

    
    
        70 to 85% Portland cement;
        10 to 25% in weight of a curing accelerator system based on calcium aluminate and calcium sulfate.
    
    


Portland cement is conventional and complies with the families described in the European standard EN 197-1.
Advantageously, Portland cement is a quick cement (so-called R type), preferably crushed to a fineness of at least 4000 cm2/g. The cement may be HIS type (High Initial Strength). For instance, 52.5 N or R CEM1, 32.5, 32.5 R, 42.5 or 42.5 R type CEM2 cement may be used. The ratio of soluble alkalines will be preferably lower than 1% in weight expressed in Na2O equivalent. The invention applies to the cements described in the European standard EN 197-1.
The amount of Portland cement is generally, relative to the weight of the binder, from 60 to 95%%, preferably from 70 to 85%, typically approximately 80%.
The curing accelerator system is based on Al2O3 alumina, CaO lime and SO3 sulfate.
Its composition is generally as follows, in weight:
















Al2O3 alumina:
35 to 50%



CaO lime:
10 to 50%



Sulfate (expressed in SO3):
 5 to 30%










Preferably, the curing accelerator system will be based on calcium aluminate and calcium sulfate.
The calcium aluminate liable to be used in the invention includes CA and/or C3A and/or C12A7 mineralogical phases.
The calcium sulfate may be in any suitable form, i.e. semi-hydrate, dihydrate, anhydrite (II or III), etc. Anhydrite will be used for instance.
The mass ratio between the calcium aluminate and the calcium sulfate ranges generally between 1:4 and 4:1, preferably between 1:2 and 2:1.
The amount of the curing accelerator system depends on the operating temperature of the concrete, the exact implementation method, the level of strengths to aim for, etc. It is generally 5 to 40% and preferably 15 to 25%, typically approximately 20% relative to the weight of the quick binder.
The retarder system may be any conventional system. In particular it may be of carboxylic type, in the form of carboxylic acid, in particular citric, tartaric, gluconic acid or similar, or of boric type or in the form of the corresponding salts. Optionally another mineral additive providing or using calcium may also be used; sodium, potassium, lithium, strontium or barium carbonates or fluorides may be mentioned, as well as calcium complexing agents such as EDTA.
The amount of the retarder system depends on the workability keeping time requested, the operating temperature of the concrete, the exact implementation method, the level of strengths to aim for, etc. The quantities are generally, relative to the cumulated weight of the Portland cement and of the curing accelerator system, 0.05 to 5% and preferably 0.1 to 1%, typically approximately 0.3 to 0.45%.
The superplasticizer contains a polyphosphonate polyox corresponding to the compound described in FR-A-2810314 and FR-A-2696736 as well FR-A-2689895, documents to which it is referred explicitly for a detailed description. For instance, polyphosphonate polyox may be formed of a water-soluble or water-dispersible organic compound, comprising at least one amino-di(alkylene-phosphonic) moiety and at least one polyoxyalkylated chain or at least one of its salts.
It may also contain a mixture of polymers such as polyphosphonate polyox and in particular polycarboxylate polyox. Polycarboxylate polyox type superplasticizers are generally known, and it may be referred to the description of patents US20030127026 (U.S. Pat. No. 6,858,074) and US20040149174.
The amount of the superplasticizer is generally, relative to the cumulated weight of the Portland cement and of the curing accelerator system, 0.5 to 5% and preferably 1 to 3%, typically approximately 2 to 2.5%.
The concrete containing this superplasticizer may be of fluid or selfcompacting consistency.
The releaser may be selected among the group consisting of:

    
    
        aqueous suspension containing (i) at least one calcium aluminate, (ii) from 0.5 to 4%, preferably from 0.6 to 2.3%, in weight relative to the total weight of the calcium aluminate(s), of a setting inhibitor of the aluminous cements, and (iii) at least one settling-preventing agent; such a suspension is described in FR-A-2849440, of Lafarge Aluminates, to which it is referred for further information;
        a transition alumina; such a transition alumina is available for instance as RHOXIMAT SA 502 from Rhodia company;
        an alumina hydroxide gel; such an alumina hydroxide gel is available, for instance, as GECEDRAL BZ 111 from Degussa company;
        a mixture thereof.
    
    


The amount of the releaser depends on the temperature of the concrete, the amount of the curing accelerator system used, the level of initial strength requested. It is added, relative to the cumulated weight of the Portland cement and of the curing accelerator system, generally in an amount of 1 to 10% and preferably 2 to 5%, typically approximately 2.5 to 3.5%.
The compounds of the final concrete composition may be introduced for instance in the following order:

    
    
        according to a first embodiment, the Portland cement and the curing accelerator system, the retarder and the superplasticizer are wet mixed, then the releaser is added after a given time;
        in a second embodiment, the cement and the superplasticizer are wet mixed, then the curing accelerator system and the retarder are added after a given time; then the releaser is added after a given time.
    
    


The first embodiment will be preferred, since the different constituents (cement, superplasticizer, curing accelerator, retarder) may also be added at the ready-mix plant, while the releaser may be added at the truck-mixer before leaving or on the road, on the building site, just before pouring the concrete.
According to the first embodiment, the releaser may be added as soon as 10 minutes after kneading the other constituents, preferably as soon as 60 minutes after kneading the other constituents (cement wet mixing in step (i)), and no later than 8 hours after.
The releaser may also be added immediately before the concrete pouring operation (the step (ii) is implemented immediately before the step (iii) for pouring concrete), and this regardless of the time elapsed from the wet mixing step in the ready-mix plant, “immediately” should be understood as ranging between 5 and 15 minutes before starting the pouring operation.
According to the second embodiment, the curing accelerator and the retarder may be added 10 to 90 minutes, preferably 10 to 45 minutes after the wet mixing step. The releaser may be added as soon as 10 minutes after kneading the other constituents.
The releaser may also be added, as above, immediately before the pouring operation, and this regardless of the time elapsed from the first addition of the curing accelerator and of the retarder. As above, the releaser may hence be added immediately before the concrete pouring operation, “immediately” should be understood as ranging between 5 and 15 minutes before starting the pouring operation.
Regardless of the embodiment, the releaser is not added, generally, more than 8 hours counted from the wet mixing step of Portland cement.
Generally speaking, the effective water/dry binder weight ratio is generally comprised between 0.35 and 0.50.
The final composition contains generally conventional aggregates (sands, grits, and/or gravels). Preferably, the constituents of the final composition have a size smaller than or equal to 20 mm. The composition may thus be pumped easily.
The aggregate/binder dry weight ratio is generally comprised between 4 and 5.
The concrete compositions according to the invention are easy to be implemented. They have a suitable rheology, involving preferably a workability duration (after wet mixing) of one hour minimum and one hour and a half to two hours maximum and very quick hardening.
Keeping the workability is characterised in particular:

    
    
        either by keeping the Abrams cone concrete slump value corresponding to the typical value of a fluidic concrete of at least 15 cm
        or, in the case of a selfcompacting concrete, by keeping the slump flow value corresponding to the typical value of a selfcompacting concrete of at least 650 mm,
        or, in the case of a mortar, by keeping the slump flow value corresponding to a value of at least 200 mm.
    
    


The invention provides hence a concrete composition which may exhibit a compression strength of at least 1 MPa 2 hours after adding the releaser to a first composition. When the releaser is added no later than 2 hours once the first composition has been kneaded, the compression mechanical strength Rc is at least 1 MPa 4 hours, counted from the end of the kneading of the first composition. It is measured on 16 cm×32 cm cylindrical test pieces.
Both these workability holding and short-term high strength properties enable in particular to produce a precursor concrete composition in a ready-mix plant and for instance to transport said composition to a building site via a truck-mixer, wherein the composition hardens rapidly once implemented, after adding the releaser. In this example the curing accelerator system is preferably added in the ready-mix plant. These qualities of the binder also enable to pump it mechanically thanks to its fluidity and to pour or pump it into a form while obtaining quick hardening.
The invention concerns more particularly a quick binder for fluidic or selfcompacting concretes, easily pumpable or pourable, being positioned in the forms without any vibrations, in the case of the selfcompacting concretes. The invention is useful for the manufacture of concrete parts and structures, regardless they are factory prefabricated parts, or structures built on sites, such as for example concrete shells, slabs, etc., at external temperatures ranging in particular between −5° C. and 30° C., in particular smaller than 10° C.
EXAMPLES
The following examples illustrate the invention without being limited thereto.
Example 1
A first mortar composition is prepared (in g for 1 litre mortar):
















CEM 1 52.5 cement
517 g



0/4 sand
1327 g 



BL 200 filler
129 g



SECAR 51, from Lafarge Aluminates
54.8 g 



Anhydrite
34.2 g 



OPTIMA 175 superplasticizer from CHRYSO: in
1.2%



weight relative to the weight of the




CEM 1 + SECAR 51 cement




Citric acid:
 2.3 g



Total water
267 g










(The OPTIMA 175 superplasticizer has a 30% dry extract, measured according to EN 480-8 standard).
Four mixtures of fresh mortar are realised successively according to this first composition.
A second composition is then prepared by adding the releaser at each wet mixing operation, following a given interval, counted from the end of the kneading, in an amount of 14.7 g.
The releaser is an aqueous suspension having the following composition, in % weight:
















Water
38.36%



Boric acid
2.13%



CP10 plasticizer
0.39%



Aluminous cement
58.81%



Xanthan gum
0.16%



K 35R biocide
0.15%










The CP plasticizer is a product marketed by BASF. The K 35R biocide is a product marketed by PROGIVEM.
For each mortar, the spread obtained during flow test will be measured in mm after 15, 30, 60, 90 minutes counted from the end of the kneading of the first composition.
The test pieces intended for measuring compression mechanical strengths Rc are made immediately after adding the releaser.
The deadline for measuring the mechanical strength after 4 hours and 5 hours and a half is counted after the end of the kneading operation of the first composition.
The RC 2 is measured 2 hours after adding the releaser.
The temperature of the tests is 15° C.
The results obtained are as follows:















TABLE 1





Releaser
15
30
60
90
120





addition
mn
mn
mn
mn
mn
2 hour
4 hour
5H30


deadline
flow
flow
flow
flow
flow
Rc
Rc
Rc























30 mn
300
330
315
210
N.M*
1.5
4
12


60 mn
300
300
285
250
150
1.3
2
11


90 mn
300
300
290
250
200
1.1
1.5
8.5





N.M*: stiff mortar; flow non-measurable.






These results put in evidence that:

    
    
        regardless of the deadline at which the releaser is added, the mortars remain fluidic/selfpositioning 30 minutes to a minimum after adding the releaser,
        in spite of this long workability keeping time, the short-term mechanical strength acquired is at least 1 MPa 2 hours after adding the releaser, in all cases at least 1 MPa 4 hours, counted from the end of the kneading of the first composition.
    
    


Example 2
A first mortar composition is prepared (in g for 1 litre mortar):
















CEM 1 52.5 N cement
507 g



0/4 sand
1327 g 



BL 200 filler
129 g



SECAR 51, from Lafarge Aluminates
63.7 g 



Anhydrite
39.8 g 



OPTIMA 175 superplasticizer from CHRYSO: relative
1.2%



to the weight of the cement CEM 1 + SECAR 51




Citric acid:
 2.3 g



Total water
267 g










Four mixtures of fresh mortar are realised successively, according to this composition.
A second composition is then prepared by adding the releaser, which is that of the example 1, after 60 minutes, counted from the end of the kneading of the first composition.
The spreads obtained during flow test are measured in mm after 15, 90, 120, minutes, counted from the end of the kneading of the first composition.
The test pieces intended for measuring compression mechanical strengths Rc are performed immediately as soon as the releaser has been kneaded.
The deadline for measuring the mechanical strength after 4 hours, 5 hours and a half and 24 hours is counted after the end of the kneading operation of the first composition.
The RC 2 is measured 2 hours after adding the releaser.
The temperature of the tests is 18° C.
The results obtained are as follows:














TABLE 2





Added
15
90



5 hour



amount of
mn
mn
120 mn
2 hour
4 hour
30 MPa
24 hour


releaser
flow
flow
flow
Rc
MPa Rc
Rc
MPa Rc























0

220
140
60
0.3
1
10
15.5


8.2
g
220
165
60
1
2.5
11
15.5


16.3
g
220
200
75
1.7
5
11
15


22
g
220
220
90
1.5
4
10
14









These results put in evidence the influence of the amount of releaser on the workability keeping time and on the minimal amount which enables to reach the compromise between the workability keeping time and the mechanical strength.
Example 3
A first series of tests is performed at 5° C.
Three first fluidic concrete compositions B1, B2, B3 are prepared having the following compositions for 1 m3:

















CEM 1 52.5 cement
294
kg



Le Vernet 0/4 sand
750
kg



4/14 mm granulate
1050
kg



Filler
100
kg



SECAR 51:
60.3
kg



Anhydrite:
37.7
kg



Citric acid:
1.36
Kg



Optima 175
5.00
kg for B1




6.53
kg for B2




6.83
kg for B3



Total water
175
litres










These concretes are realised, each with a different CEM 1 52.5 cement, having the following features:














TABLE 3





Con-









crete
CEM1
C3S
C2S
C3A
C4AF
Soluble
Soluble


ref.
cement
%
%
%
%
K %
Na %






















B1
Le Havre
61.4
12.1
10.2
5.2
0.21
0.11


B2
La Couronne
58.0
14.3
7.6
8.4
0.71
0.05


B3
Val
58.5
15.4
0.4
14.5
0.62
0.09



d'Azergues









The second concrete compositions are then prepared by adding the releaser which is that of example 1; it is inserted 1 hour after kneading all the previous constituents.
The amount for each concrete is 9 kg/m3.
For each concrete, the slump obtained with the Abrams cone will be measured in cm after 15, 90 and 120 counted from the end of the kneading of the first composition, and the test pieces intended for measuring the compression mechanical strengths Rc will be prepared immediately after adding the releaser.
The deadline for measuring the mechanical strength 4 hours, 5 hours and a half and 24 hours is counted from the end of the kneading of the first composition.
The RC 2 is measured 2 hours after adding the releaser.
The results obtained are as follows;














TABLE 4






15
90



5 hour



Concrete
mn
mn
120 mn
2 hour
4 hour
30 MPa
24 hour


ref
flow
flow
flow
Rc
MPa Rc
Rc
MPa Rc






















B1
24
23
21
1
2
12
17


B2
24
22
22
1.5
3.5
15.5
22


B3
24
22
22
1.1
2
14
23









A second series of tests is performed at 20° C.
Four first fluidic concrete compositions B4, B5, B6, B7 are prepared having the following compositions for 1 m3.

















CEM 1 52.5 cement
294
kg



Le Vernet 0/4 sand
750
kg



4/14 mm granulate
1050
kg



Filler
100
kg



SECAR 51
27.44
kg



Anhydrite
17.18
kg



Citric acid
1.46
kg



Optima 175
4.77
kg for B4




5.70
kg for B5




5.60
kg for B6




7.24
kg for B7



Total water
175
litres










These concretes are realised, each with a different CEM 1 52.5 cement, having the following features (the three first are those mentioned in Table 4):














TABLE 5





Con-









crete

C3S
C2S
C3A
C4AF
Soluble
Soluble


ref.
CEM1 cement
%
%
%
%
K %
Na %






















B4
Le Havre
61.4
12.1
10.2
5.2
0.21
0.11


B5
La Couronne
58.0
14.3
7.6
8.4
0.71
0.05


B6
Val d'Azergues
58.5
15.4
0.4
14.5
0.62
0.09


B7
Saint Pierre LC
54.8
16.6
7.3
9.1
0.62
0.10









The second concrete compositions are then prepared by adding the releaser which is that of example 1; it is inserted within 1 hour after kneading all the previous constituents.
The amount for each concrete is 9 kg/m3.
For each concrete, the slump obtained with the Abrams cone will be measured in cm after 15, 90 and 120 counted from the end of the kneading of the first composition, and the test pieces intended for measuring the compression mechanical strengths Rc will be prepared immediately after adding the releaser.
The deadline for measuring the mechanical strength 4 hours, 5 hours and a half and 24 hours is counted from the end of the kneading of the first composition.
The RC 2 is measured 2 hours after adding the releaser.
The results obtained are as follows:














TABLE 6





Con-





5 hour



crete
15 mn
90 mn
120 mn
2 hour
4 hour
30 MPa
24 hour


ref
slump
slump
slump
Rc
MPa Rc
Rc
MPa Rc






















B1
24
24
13
1.7
4
8
10


B2
23
24
12
4
7
11
12


B3
24
22
21
2.7
6
10
12


B4
19
20
20
2.5
5
9
12









These two series of tests put in evidence that:

    
    
        at 5° C. and 20° C., the concretes obtained remain fluidic at least 30 minutes counted from the end of the kneading with the releaser;
        a mechanical strength acquired of at least 1 MPa is obtained 2 hours after adding the releaser, in all cases of at least 1 MPa 4 hours counted from the end of the kneading of the first composition;
        these features are obtained with cements having quite different mineralogical compositions and soluble alkaline contents; this demonstrates the polyvalence of the system.
    
    


Example 4
Tests were conducted with different CEM 2 cements from LAFARGE, i.e.:
Ref C1-CEM 2/A-S 52.5 N La Malle
Ref C2-CEM 2/B-M (S-LL) 42.5 Le Teil
Ref C3-CEM 2/B-LL 32.5R Val d'Azergues
Ref C4-CEM 2/B-LL 42.5N Val d'Azergues
Ref C5-CEM 2/B-LL 32.5R Le Havre
With each concrete, different first mortar compositions each including (in g for 1 litre mortar) the following components:
















CEM 2 cement
512 g



St Bonnet 0/4 sand
1327 g 



BL 200 filler
129 g



Total water
267 g







Two series of tests are performed at 20° C.






For each series the first compositions are complemented with the other components as defined in Table 7 (in g for 1 litre mortar).











TABLE 7





Ref CEM 2
SECAR 51
Anhydrite
Citric acid
Optima 175















First series of tests











C1
57.8
36.2
2.4
16.13


C2
57.8
36.2
2.4
14.23


C3
57.8
36.2
2.4
14.80


C4
57.8
36.2
2.4
15.20







Second series of tests











C2
35.7
22.3
2.11
10.43


C3
35.7
22.3
2.11
12.33


C5
35.7
22.3
2.11
12.33









The second mortar compositions are then prepared by adding the releaser which is that of example 1; it is inserted within 1 hour after kneading all the constituents of the first compositions.
The amount for each mortar is 14.7 g.
For each mortar, the spread obtained during flow test will be measured in mm after 15, 60, 90, 120 minutes counted from the end of the kneading of the first composition and as of the end of the kneading of the second composition, the test pieces intended for measuring the compression mechanical strengths Rc will be prepared.
The deadline for measuring the mechanical strength after 4 hours and 5 hours and a half is counted after the end of the kneading operation of the first composition.
The RC 2 is measured 2 hours after adding the releaser.
The results obtained are as follows:















TABLE 8







15
60
90
120
2

5 hour



CEM2
mn
mn
mn
mn
hour
4 hour
30 MPa



ref.
flow
flow
flow
flow
Rc
MPa Rc
RC























First
C1
330
320
295
260
1
2.4
10.4


series
C2
365
285
285
215
2
3.5
3.8


of tests
C3
330
300
135
NM
6
13.8
19.5



C4
305
235
225
225
5
10.7
18.7


Second
C2
340
275
265
140
2.3
4.8
11.3


series
C3
300
295
225
145
1.5
3.8
6.3


of tests
C5
330
265
200
195
0.7
1.8
4.3









These results put in evidence that the requirements imposed by the different CEM 2 cements used are met.

## Claims

1. A method for making concrete parts and structures, comprising:
(i) supplying a first concrete composition based on a quick setting and hardening binder containing:
60 to 95% Portland cement;
5 to 40% curing accelerator comprising Al2O3 alumina, lime and sulfate;
a retarder; and
a superplasticizer polymer selected from the group consisting of polyphosphonate polyox, and polycarboxylate polyox, or mixture thereof,;

then
(ii) adding a releaser to form a second concrete composition selected from the group consisting of:
aqueous suspension containing:
(i) at least one calcium aluminate,
(ii) from 0.5 to 4% in weight relative to the total weight of the calcium aluminate(s), of a setting inhibitor of the aluminous cements, and
(iii) at least one settling-preventing agent;

a transition alumina;
an alumina hydroxide gel;
a mixture thereof; and

(iii) pouring this second concrete composition in a concrete form.

2. The method according to claim 1, wherein the curing accelerator contains, in weight:
















Al2O3 alumina:
35 to 50%



lime:
10 to 50%



Sulfate:
  5 to 30%.

3. The method according to claim 1, wherein the curing accelerator comprises calcium aluminate and calcium sulfate.

4. The method according to claim 1, wherein the sulfate is selected from the group consisting of metallic, alkaline, alkaline-earth sulfates, the organic sulfates or the mixtures thereof.

5. The method according to claim 1, wherein the step (i) is a wet mixing step wherein the first primary composition is prepared and which contains the following steps :
(a) a concrete composition is prepared containing:
Portland cement;
the retarder; and
the superplasticizer;

then
(b) adding, on the
curing accelerator.

6. The method according to claim 1, wherein the step (ii) is implemented at least 10 minutes but no later than 8 hours after wet mixing of the step (i).

7. The method according to claim 1, wherein the step (ii) is implemented immediately before the concrete pouring step (iii).

8. The method according to claim 1, including the following steps:
(i) supplying by wet mixing in a ready-mix plant a first concrete composition based on a quick setting and hardening binder;
then
(ii) adding a releaser; and
(iii) pouring the concrete immediately after the releaser addition step (ii).

9. The method according to claim 7, wherein the step (ii) is implemented in a truck-mixer.

10. The method according to claim 1, wherein the step (iii) comprising pouring the second concrete composition in a concrete form is conducted with a second concrete composition exhibiting a slump test value ranging between 15 and 24 cm.

11. The method according to claim 1, wherein the step (iii) comprising pouring the second concrete composition in a concrete form is conducted with a second concrete composition exhibiting a slumpflow value ranging between 580 and 750 mm.

12. The method according to claim 1, wherein the concrete parts and structures are concrete shells or concrete slabs.

13. The method according to claim 1, wherein the first concrete composition contains:
70 to 85% Portland cement;
15 to 25% curing accelerator;
the retarder; and
the superplasticizer.

14. The method according to claim 1, wherein the Portland cement is a cement complying with the EN 197-1 standard.

15. The method according to claim 1, wherein the curing accelerator comprises calcium aluminate and calcium sulfate in semi-hydrate, dihydrate or anhydrite form.

16. The method according to claim 1, wherein the calcium aluminate used includes at least one of CA, C3A and C12A7 phases.

17. The method according to claim 3, wherein the mass ratio between the calcium aluminate and the calcium sulfate ranges between 1:4 and 4:1.

18. The method according to claim 1, wherein the retarder is carboxylic or boric acid or its salts.

19. The method according to claim 1, wherein the amount of the retarder, in weight relative to the cumulated weight of the Portland cement and of the curing accelerator, ranges between 0.05 and 5%.

20. The method according to claim 1, wherein the amount of the superplasticizer, in weight relative to the cumulated weight of the Portland cement and of the curing accelerator, ranges between 0.5 and 5%.

21. The method according to claim 1, wherein the amount of the releaser, in weight relative to the cumulated weight of the Portland cement and of the curing accelerator, is 1 to 10%%.

22. The method according to claim 1, wherein the second concrete composition exhibits a compression mechanical strength of at least 1 MPa, 2 hours after the step (ii).

23. The method according to claim 1, wherein the second concrete composition exhibits a compression mechanical strength of at least 1 MPa, 4 hours after the step (i).

24. The method according to claim 1, wherein the first concrete composition has a workability keeping time of at least 1 hour after step (i).

25. The method according to claim 1, wherein the second concrete composition has a workability keeping time of at least 30 minutes after step (ii).