FR2471955A1 - Acceleration of cement setting and hardening - by adding reducing agent - Google Patents

Abstract

Setting and hardening of cement is accelerated by adding a reducing agent (I) such as a sulphite (pref. a bisulphite) and/or an aldehyde. (I) is pref. an HCHO/NaHSO3 adduct (Ia), but can also be NaHSO3, HCHO or glyoxal. (I) is pref. added in an amt. of 0.5-5wt.%, based on the wt. of cement, pref. together with one or more alkali(ne earth) metal formates and/or nitrates. Additive compsns. pref. contain 5-40 (esp. 10)wt.% (I), 2-20wt.% formate and 10-90wt.% nitrate, esp. in the form of an aq. soln. prepd. by dissolving the formate, nitrate and (I) successively in hot (80 deg. C) water and cooling to ambient temp. The process provides reduced setting and hardening times without impairing the physico-mechanical properties of the cement and without using potentially corrosive chloride additives.

Description

 The present invention essentially relates to a method for accelerating the setting and hardening including cement, a composition for implementation and a method for preparing said composition.

 The cements are generally characterized by 28-day standardized mortar strengths.

It is therefore desirable for the fabricator to add a setting and hardening accelerating agent to bring setting and hardening time to more industrially acceptable values for relatively rapid fabrication of structures such as buildings.

 The current setting accelerators are either chlorinated accelerators, most of them calcium chloride solutions whose use is regulated because of the dangers due to the risks of corrosion that may appear in reinforced concrete; or non-chlorinated accelerators generally based on alkali or alkaline earth salts of compounds such as formate, nitrate whose effectiveness is often discussed.

 The present invention therefore aims to provide a solution to accelerate the setting and hardening including cement avoiding the use of chlorinated accelerators while obtaining undeniable effectiveness over the duration of setting and hardening. Preferably, this solution must make it possible to keep at least the physicomechanical properties of the cement while being of particularly simple design.

 This solution consists, according to the present invention, in a process for accelerating the setting and the hardening, in particular of the cement, while maintaining at least its physicomechanical properties, including the incorporation of an accelerating agent for setting and hardening, and characterized in that it comprises incorporating as accelerating agent setting and hardening of at least one reducing compound such as a sulfite, preferably a bisulfite, and / or an aldehyde, in amounts sufficient to achieve the desired effect of acceleration setting and hardening. Advantageously, the above-mentioned sulphite is constituted by sodium bisulfite.

 According to another characteristic of this process, the aforementioned aldehyde is chosen from formaldehyde, glyoxal, or their homologs.

 Preferably, the reducing compound having the best efficiency of setting acceleration and hardening is sodium formaldehyde bisulfite.

 According to yet another characteristic of this process, from 0.5 to 5% by weight of the cement of the setting and hardening accelerator mentioned above is incorporated.

In addition, according to another characteristic of the process according to the present invention, the aforementioned setting and hardening accelerating agent comprises, in combination with the abovementioned reducing compound, such as the abovementioned sulfite and / or the above-mentioned alkali metal aldehyde and / or an alkaline earth metal of formate and / or nitrate, said combination making it possible to obtain a particularly unexpected synergistic effect.

 The subject of the present invention is also an accelerator setting and hardening additive composition, in particular cement, which comprises at least one reducing agent such as a sulphite, preferably a bisulfite and / or an aldehyde. Advantageously, this composition comprises from 5 to 40%, preferably 10% by weight, relative to the dry materials, of sulfite and / or aldehyde above, preferably in the form of an aqueous solution.

According to yet another characteristic of this composition, it comprises the following constituents in percentage by weight relative to the dry materials
Sulphite and / or aldehyde 5-40
Formiate 2-20
Nitrate 10--90
The subject of the present invention is also a method for preparing the composition comprising the formate and / or the nitrate according to which the formate and then the nitrate (if any) are dissolved in water at approximately 800 ° C. with stirring. finally sulphite and / or formaldehyde; then the solution obtained is cooled to ambient temperature.

 Other objects, features and advantages of the present invention will become more apparent in light of the following explanatory description made with reference to the following example of a presently preferred embodiment of the present invention merely given as a illustration and in no way limit its scope.

 Example.

An accelerating and setting accelerating additive composition, especially cement, comprising the following constituents is prepared
Calcium formate 7%
40% calcium nitrate
Bisulfite formaldehyde Na 10%
Water the rest is 43%.

 This composition is manufactured in the form of a solution by dissolving, according to the method of the present invention, calcium formate in water at around 800 ° C. with stirring, and then the calcium nitrate is dissolved and finally the calcium nitrate is dissolved. bisulfite formaldehyde.

The resulting solution is then cooled to room temperature.

This solution has the following characteristics
Tests have been made from this composition according to the present invention with regard to setting time and mechanical characteristics as follows
a) setting time
The tests focused on two grades of referenced cement
-CPA 55 de Guerville (French cement)
HTS 55 from Theil (Lafarge)
The measurement of the setting time was carried out on standardized mortar at the normal use dose N = 196 and 3N = 3% having the following composition
- standardized sand (AFNOR P 15 403) 1350 g
- cement 450 g
- water 225 g
For blank measurements, the water / cement ratio = 0.5.

It should be noted that the measurements on the adjuvanted mortar are made with the same plasticity and the new water / cement ratio and the reduction of entrained water are noted.

The preparation of the mortar was carried out according to standard P 15 411
The measurement of the start and end time of setting was carried out with the Vicat needle according to the standard P 15 431.

 The results regarding setting time are listed in the following Table I and are indicated in hours and minutes.

 Table I.

Dosages: Control N = 1% N = 3%
Product Temperatures Start End Start End Start End
CPA 55 20 C 4H30 5H30 2H45 4H00 1H40 2H40
5 C 6H10 8H00 4H10 5H30 2H10 3H20
HTS 55 2O0C 5H45 6H10 3H30 4H20 1H10 2H05
SOC 8H00 10H20 5H00 7H10 1H30 2H40
At dose N and 3N, Table II below gives for each cement studied the water / cement ratio (E / C) used and the reduction of water caused:
Table II.

Cement Dose E / C Reduction of water
CPA 55 1% 0.5
3% 0.5
HTS 55 1% 0.48 5%
3% 0.45 10%
The plasticity that has been measured at the impact table is constant and equal to 105 mm.

Regarding setting times, the current regulations require that the start of setting compared to the control is at least 1 hour before for temperatures of 50C and 200C. We can see from
Table I above that the setting accelerator according to the present invention meets this requirement almost twice.

 With regard to the end of setting relative to the control, the standard requires from 1 h 30 to 6 h before for a temperature of 50C and from 1 h 30 to 3 h 30 before for a temperature of 200C. It can also be seen from Table I that the setting accelerator according to the present invention fully satisfies this standard.

b) mechanical strengths
The mechanical strengths on standardized mortar were measured at constant plasticity. The results of compression and bending expressed in relative values relative to the control represent the average of six tests of rupture in compression and three in flexion ~ made on specimen 4 x 4 x 16 normalized. As for measuring the setting time, an experiment was carried out with 1% incorporation of the aforementioned composition according to the present invention and incorporation at 3% by weight relative to the weight of cement.

 The relative values of the results obtained are listed in Table III below.

 The relative values mentioned in Table III below are all given in relation to the values corresponding to the control, the specimens of which were stored at 200 ° C. Therefore, the values given at 50C represent the results of the tests on specimens according to the invention stored at 50C relative to the values of the control, the specimens of which were stored at 200C.

Table III

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It can be deduced that the setting accelerator additive composition and curing according to the present invention allows at least to maintain the mechanical properties of the cement and therefore largely meets the standards in force.

Of course, the invention is in no way limited to the embodiment described which has been given only as an example. In this regard, it should be pointed out that other aldehydes than those mentioned above can be used, but it is preferred to use current products which are more available on the market and among these it is preferred to use, of course, formaldehyde, glyoxal or mixtures thereof, as indicated above.
Likewise, other sulfites than those mentioned above can be used. Finally, the use of sulfites and / or aldehydes can be combined with others. known components having a setting acceleration effect. According to the present invention a combination with formate and / or nitrate has been indicated since a particularly unexpected synergistic effect has been observed.

 Ain, the present invention comprises all the means constituting technical equivalents of the means described, as well as their combinations, if they are carried out according to its spirit and implemented in the context of the following claims.

Claims (9)

 A method for accelerating the setting and hardening of cement, while maintaining at least its physicomechanical properties, including the incorporation of an accelerating agent hardening and setting, characterized in that it comprises the incorporation as agent accelerator for setting and hardening at least one reducing compound such as a sulfite, preferably a bisulfite, and / or an aldehyde, in amounts sufficient to achieve the desired effect of setting acceleration and hardening.  2. Process according to claim 1, characterized in that the above-mentioned sulphite is sodium bisulphite  3. Method according to claim 1 or 2, characterized in that the aldehyde is chosen from formaldehyde, glyoxal, or their homologs.  4. Method according to one of the preceding claims, characterized in that sodium formaldehyde bisulfite is incorporated as reducing agent.  5. Method according to one of the preceding claims, characterized in that incorporates from 0.5 to 5% by weight of setting accelerator and hardening above relative to the weight of cement.  6. Method according to one of the preceding claims, characterized in that it comprises in combination with the above-mentioned reducing compound, such as the above-mentioned sulphite and / or aldehyde, an alkali and / or alkaline earth salt of formate and / or nitrate  7. Accelerator additive composition setting and hardening including cement, for carrying out the process according to one of claims 1 to 6, characterized in that it comprises at least one reducing agent such as a sulfite, preferably bisulfite and / or an aldehyde.  e. Composition according to Claim 7, characterized in that it comprises from 5 to 40%, preferably 10% by weight, relative to the sulphite and / or aldehyde solids mentioned above, advantageously in the form of an aqueous solution.  9. Composition according to claim 7 or 8, characterized in that it comprises the following constituents in percentage by weight relative to the dry materials.  sulfite and / or aldehyde 5-40  formate 2-20  nitrate 10-90  10. A process for preparing the composition according to claim 9, characterized in that dissolved in bed at about 80 C with stirring formate then nitrate and finally sulfite and / or formaldehyde; then the solution obtained is cooled to ambient temperature.