Abstract:
The invention relates to an accelerator used for setting and hardening and a method for accelerating and hardening hydraulic binding agents using said accelerator. The principal components of said accelerator are nitrates, aminoalcohols, hydroxycarboxylic acids and polyalcohols. The hardening acceleration is not connected with a rapid loss in processability, which is common in other accelerated systems.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims the priority of the European patent application no. 01 114 736.0 that was filed on Jun. 22, 2001, and the entire disclosure contained therein is herewith included in the present by way of reference.  
         BACKGROUND  
         [0002]    1. Field of the Invention  
           [0003]    The subject-matter of the present invention comprises an admixture and a method for accelerating the setting and hardening of hydraulic binding agents, in particular for the manufacture of prefabricated elements and the acceleration of the hardening process of concrete produced at the job site; especially preferred is that of self-compacting concrete (SCC).  
           [0004]    2. Description of the Related Art  
           [0005]    Many substances are already known in the art that accelerate the setting and hardening of concrete. The most commonly used substances include nitrates, formates, thiocyanates, nitrites, mono-, di- and triethanolamine, strongly alkaline reacting substances such as alkali hydroxides, alkali carbonates, alkali silicates, alkali aluminates and alkali earth chlorides.  
           [0006]    The strongly alkaline reacting substances cause undesired annoyances for the workers handling them.  
           [0007]    Viewed in terms of concrete technology, strongly alkaline setting accelerators reduce the final strength and enlarge shrinkage which may lead to the formation of tears, thereby compromising the durability of the structure.  
           [0008]    Chloride-containing setting accelerators are generally undesired at job sites because they may cause corrosion of both the reinforcement steel bars in the concrete as well as the construction equipment.  
           [0009]    It is furthermore known that chloride-containing setting accelerators massively reduce the stability of the chemicals, primarily the sulfate stability of the cement as well as long-term strength.  
           [0010]    Nitrates have been known in the art for a long time as antifreeze agents, i.e., they effect a setting acceleration at low temperatures. At room temperatures, however, the effectiveness of nitrates is insignificant (refer, e.g., U.S. Pat. No. 4,337,094 (Tokan)).  
           [0011]    Calcium formate has already been described as a hardening accelerator for Portland cement in DE 2 611 419; but its effectiveness is considerably below that of CaCl 2 . In addition, its solubility in water is too poor.  
           [0012]    Ca(NO 2 ) 2  (refer to SU 563 392) is a very good setting accelerator; however, using it at the necessary concentrations in Europe is inconceivable because it is highly toxic.  
           [0013]    The combination of a thiocyanate and an alkanolamine increases, as U.S. Pat. No. 4,373,956 (Rosskopf) teaches, both the hardening speed and the compressive strength of cement-containing products.  
           [0014]    Various organic setting accelerators have been described, but only a few are important in the marketplace. Correspondingly, mono-, di- and triethanolamine in combination with nitrates have an accelerating effect with regard to the setting of concrete at low temperatures.  
           [0015]    A combination of triethanolamine together with aluminum sulfate increases, in accordance with U.S. Pat. No. 3,782,991 (Burge), the early strength of construction materials.  
           [0016]    The suitability of α-hydroxycarboxyl compounds as a setting accelerator for Portland cement is disclosed in U.S. Pat. No. 4,264,367 (Schutz).  
           [0017]    U.S. Pat. No. 4,473,405 (Gerber) describes an accelerator comprised of a nitrate, an alkanolamine and a thiocyanate; combinations of alkanolamine, nitrate, thiocyanate and carboxylic acids are disclosed in EP 0 670 292.  
           [0018]    The corrosion-inhibiting effectiveness of alkanolamines with regard to steel is known, e.g., from U.S. Pat. No. 4,726,914.  
           [0019]    All of the customarily used accelerators and/or the accelerators described above have one or several disadvantages: they are only active at low temperatures but not at room temperature, they increase the early strength but reduce the final strength in comparison to a corresponding sample not containing the admixture, they abbreviate the time the concrete can be worked with, or they are toxic or corrosive.  
           [0020]    EP 0 554 046 A1 describes the use of low-molecular glycols in conjunction with calcium nitrate and calcium nitrite as setting accelerators. But EP 0 554 046 A1 does not give any indications as to the corresponding effectiveness as a hardening accelerator, i.e., as to an accelerated hardening process.  
           [0021]    The object of the present invention consisted therefore in providing a setting and hardening accelerator that will supply, primarily in combination with superplasticizers, high early and final strengths of hydraulic binding agents or of mixtures containing hydraulic binding agents, in particular of concrete and mortar, without shortening the processing time that the product can be work with.  
         SUMMARY  
         [0022]    Surprisingly, it has been found that it is possible using a combination of four components which are specifically:  
           [0023]    (1) at least one inorganic nitrate, in particular at last one alkaline and/or alkaline earth and/or aluminum nitrate,  
           [0024]    (2) at least one alkanolamine,  
           [0025]    (3) at least one carboxylic acid, in particular at least one C1-C6 hydroxycarboxylic acid, and  
           [0026]    (4) at least one polyol, in particular at least one C2-C6 polyol to produce accelerators meeting the above referenced requirements.  
           [0027]    Further technical advantages of the accelerators according to the invention are the absence of chloride and nitrite as well as the fact that the mixtures have no corrosive effect relative to steel rebars, not least of all thanks to the admixture of an alkanolamine.  
           [0028]    The accelerator according to the invention, which is also called an admixture, is especially suitable for accelerating the setting and the hardening of hydraulic binding agents, in particular for the manufacture of prefabricated elements, and for accelerating the hardening process of concrete produced at the job site; especially preferred in this context is self-compacting concrete (SCC). In the first instance, it is possible to shorten the usual hardening acceleration by way of heat (electric or oil heater without steam) or even eliminate it altogether. In the second instance, it is possible to shorten the timeframe for dismantling the formwork for concrete, or it is possible to continue with the concrete placement even at low temperatures. Applications also result from the manufacture of quickly setting cement and mortar mixtures especially for fixing prefabricated parts or for pouring molded parts.  
           [0029]    One subject-matter of the present invention is therefore a setting and hardening accelerator for hydraulic binding agents comprised of or containing an accelerating composition that is comprised of the following components and/or of the acid/base reaction products of these components:  
           [0030]    (1) at least one inorganic nitrate,  
           [0031]    (2) at least one alkanolamine,  
           [0032]    (3) at least one carboxylic acid and  
           [0033]    (4) at least one polyol.  
           [0034]    A further subject-matter of the present invention is a method for accelerating the setting and hardening of a hydraulic binding agent such as cement; in its pure form or as an admixture with latent hydraulic binding agents, usually by adding 0.2 to 5.0 weight % of the accelerator according to the invention relative to the weight of the binding agent. The accelerator according to the invention can be applied as a powder, dispersed or dissolved in water and/or in combination with one or several other concrete admixtures, such as water-reducing admixtures, superplasticizers, liquefiers, silica slurries and/or dispersing agents. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0035]    The setting and hardening accelerators for hydraulic binding agents according to the invention are comprised of or contain at least one inorganic nitrate, which is preferably an alkaline, alkaline earth or aluminum nitrate or mixtures thereof.  
         [0036]    A preferred alkanolamine component is comprised of propanolamines and/or ethanolamines, in particular mono-, di- or trialkanolamines as well as alkylalkanolamines, preferably alkylalkanolamines with C1-C3-alkylene. Examples of preferred alkanolamines are monoethanolamine, diethanolamine, triethanolamine, N-methyl-diethanolamine, triisopropanolamine and mixtures thereof.  
         [0037]    A preferred carboxylic acid component is comprised of carboxylic acids selected from the group of unsubstituted carboxylic acids, in particular C1-C6 carboxylic acids, α-hydroxycarboxylic acids, polyhydroxycarboxylic acids, α-aminocarboxylic acids and mixtures thereof. Especially preferred are α-hydroxycarboxylic acids, polyhydroxycarboxylic acids and α-aminocarboxylic acids with 1 to 6 C-atoms, as well as, if necessary, aryl-substituted C1-C6 α-hydroxymonocarboxylic acids. Examples of suitable and preferred acids are α-hydroxymonocarboxylic acids, such as lactic acid and an amygdalic acid.  
         [0038]    In another preferred embodied example the alkanolamine is used as a salt of an organic carboxylic acid; and preferably the carboxylic acid is one of the above referred to carboxylic acids.  
         [0039]    Usable for the manufacture of the accelerator are an alkanolamine as a salt of an acid or an alkanolamine as a salt of different acids or different alkanolamines as a salt of the same acid or different alkanolamines as salts of different acids.  
         [0040]    The one polyol is preferably a C2-C6 polyol. 1,2,3-propanetriol is an especially preferred polyol.  
         [0041]    The accelerator usually contains the nitrate component in quantities of 10-58 weight %, the alkanolamine component in quantities of 1-20 weight %, the carboxylic acid component in quantities of 1-15 weight % and the polyol component in quantities of 0-20 weight %. Preferably, the accelerator contains the nitrate component in quantities of 15-50 weight %, the alkanolamine component in quantities of 5-20 weight %, the carboxylic acid component in quantities of 2-12 weight % and the polyol component in quantities of 2-15 weight %.  
         [0042]    The accelerator is customarily added to the hydraulic binding agent, in particular cement, in the quantity of 0.2-5.0 weight % relative to the weight of the hydraulic binding agent, preferably in the quantity of 0.2-3.5 weight %.  
         [0043]    A further subject-matter of the present invention relates to a method for accelerating the setting and hardening of a hydraulic binding agent, such as cement, in its pure form or as a mixture with latent hydraulic binding agents such as fly ash, blast furnace slag, pozzolans, burnt oil shale ash or silica fume as well as mortar and concrete manufactured from the former by adding 0.2 to 5.0 weight % of the accelerator according to the invention relative to the weight of the binding agent.  
         [0044]    The accelerators according to the invention can be used in the form of a powder, dispersed or dissolved in water and/or in combination with one or several other concrete admixtures, such as water-reducing admixtures, superplasticizers, liquefiers, silica slurries and/or dispersing agents.  
         [0045]    Admixing occurs usually in solid or liquid form directly into the mixing water and to the cement, to the dry mixture or to the finished concrete or mortar mixture.  
         [0046]    But a setting or hardening accelerator in powered form can also be applied as a premix in hydraulic binding agents or in dry mortar and concrete; for example, it can be added in with the binding agent at the time of the manufacture of the binding agent at the factory.  
         [0047]    In preferred embodied examples the accelerator is added to the dry or binding agent or to the binding agent mixed with water, to mortar or concrete at the factory, at the job site, in the mixing vat, in the feeding pump or directly into the mixture via a static mixer with a powder dosing device or a liquid dosing device.  
         [0048]    The following examples are intended to explain the invention in more detail, however, without being in any way restrictive as to its content.  
       EXAMPLES 1 TO 4  
       [0049]    Utilizing mortar tests, the influence of the individual components and partial mixtures of the accelerator according to the invention is demonstrated.  
         [0050]    The testing mixture for examples 1 to 4 is made up as follows:  
                                                       Portland cement CEM I   1.000 kg           Sand 0-5 mm   3.000 kg           Water   0.395 kg           Polycarboxylate superplasticizer   0.010 kg           Component(s) of the accelerator   0.015 kg                      
 
       Example 1  
       [0051]    Effect of an alkanolamine by itself and in combination with a hydroxycarboxylic acid relative to the 28-day compressive strength.  
                                                       Compressive           Admixture   Strength 28 Days                           Blank test (without accelerator)   45 MPa           Alkanolamine   52 MPa           Alkanolamine + hydroxycarboxylic acid   59 MPa                      
 
       Example 2  
       [0052]    Example to explain the influence of two alkanolamines that can be used as part of an accelerator according to the invention.  
                                                       Compressive           Admixture   Strength 1 Day                           Blank test (without accelerator)   24 MPa           Diethanolamine + lactic acid   26 MPa           N-methyldiethanolamine + lactic acid   32 MPa                      
 
       Example 3  
       [0053]    Example to represent the effect of a nitrate that can be used as part of the accelerator according to the invention. Test temperature 10° C.  
                                                                     Compressive Strength                    Admixture   1 Day   2 Days                       Blank test (without accelerator)   6.4 MPa   21 MPa           Calcium nitrate   9.0 MPa   24 MPa           Aluminum nitrate   18.0 MPa    30 MPa                      
 
       Example 4  
       [0054]    Example to explain the effect of polyol.  
                                                       Compressive           Admixture   Strength 18 h                           Blank test (without accelerator)    4.8 MPa           Alkanolamine + lactic acid   19.8 MPa           Alkanolamine + lactic acid + propanetriol   24.2 MPa                      
 
       EXAMPLES 5 TO 7  
       [0055]    The following examples 5 to 7 demonstrate the effect of the individual components in conjunction with a polycarboxylate superplasticizer as well as two accelerators according to the invention relative to the ease of working with them (spreading rate 0-60 minutes after mixing), the setting times and relative to the 20-hour compressive strength.  
                                             Concrete Test Mixture:                                    Portland cement CEM I   7.500 kg           Rock meal   1.500 kg           Sand 0-1.2 mm   9.500 kg           Sand 1.2-4 mm   8.000 kg           Sand 4-8 mm   4.500 kg           Gravel 8-16 mm   9.500 kg           Gravel 16-32 mm   17.000 kg                       
 
         [0056]    Test cubes with the dimensions of 12×12×12 cm were produced from these concrete mixtures and used to determine the compressive strength values.  
         [0057]    The following accelerators according to the invention were used for the test mixtures:  
                                                       Accelerator   1   2                           Alkanolamine lactate   12%    9%           Inorganic nitrate   40%   47%           Propanetriol   10%    5%           Water   38%   39%                      
 
       Example 5  
       [0058]    Concrete tests at 15° C.; water/cement ratio 0.41 constant:  
                                                                                                                                                   Spreading   Compressive                       Rate   Strength   Setting time           Concentration   Dosage   [cm]   [MPa]   [h]            Admixture   [%]   [%]   0′   30′   60′   20 h   Beginning   End                    Polycarboxylate   22   1.0   55   55   55   13.0   10.5   25.0       Superplasticizer       Polycarboxylate   22   1.0   56   52   54   17.7   10   25.0       Propanetriol   100   0.04       Polycarboxylate   22   1.0   53   51   53   20.4   10   23.0       Methydiethanolamine   100   0.03       Polycarboxylate   22   1.0   54   54   56   18.0   9.9   23.3       Aluminumnitrate  x 9H2O   100   0.14       Polycarboxylate   22   1.0       Accelerator 1 according   100   0.3   54   45   48   26.1   8.6   22.0       to the invention       Polycarboxylate   22   1.0   53   45   49   22.5   9.5   22.0       Propanetriol   100   0.08       Polycarboxylate   22   1.0   56   52   54   21.5   10   23.0       Methydiethanolamine   100   0.06       Polycarboxylate   22   1.0   54   54   57   21.2   9.8   23.0       Aluminumnitrate  x 9H2O   100   0.28       Polycarboxylate   22   1.0       Accelerator 1 according   100   0.60   45   34   33   28.0   7.5   18.0       to the invention       Polycarboxylate   22   1.0   53   41   48   23.8   9.5   23.0       Propanetriol   100   0.11       Polycarboxylate   22   1.0   53   46   48   24.9   10   23.0       Methydiethanolamine   100   0.10       Polycarboxylate   22   1.0   48   50   50   25.2   8.9   20.4       Aluminumnitrate  x 9H2O   100   0.42       Polycarboxylate   22   1.0       Accelerator 1 according   100   0.90   43   31   32   31.9   7.5   17.0       to the invention                  
 
       Example 6  
       [0059]    Concrete tests at 10° C.; water/cement ratio 0.44 constant:  
                                                                                                                                                   Spreading   Compressive                       Rate   Strength   Setting Time           Concentration   Dosage   [cm]   [MPa]   [h]            Admixture   [%]   [%]   0′   30′   60′   20 h   Beginning   End                    Polycarboxylate   36   0.3   54   49   46   3.2   8   30.2       Superplasticizer       Polycarboxylate   36   0.3       Accelerator 1 according   100   0.42   53   37   35   5.7   8.6   24.6       to the invention       Polycarboxylate   36   0.3       Accelerator 2 according   100   0.54   54   39   38   7.6   8.1   22.0       to the invention       Polycarboxylate   36   0.4   61   58   61   3.7   8.3   26.8       Superplasticizer       Polycarboxylate   36   0.4       Accelerator 1 according   100   0.36   62   49   47   7.8   8.0   21.0       to the invention       Polycarboxylate   36   0.4       Accelerator 2 according   100   0.50   62   43   44   11.2   8.0   20.0       to the invention       Polycarboxylate   36   0.5   52   52   51   3.7   8.4   27.0       Superplasticizer       Polycarboxylate   36   0.6       Accelerator 1 according   100   0.40   49   47   46   7.7   7.9   20.1       to the invention       Polycarboxylate   36   0.6       Accelerator 2 according   100   0.68   51   50   45   13.2   7.2   18.3       to the invention                  
 
       Example 7  
       [0060]    This example demonstrates the difference between an accelerator according to the invention in comparison with a commercially available, calcium-nitrate-based accelerator and calcium chloride. The tests were run at a temperature of 10° C. The concrete was plastified with 1% polycarboxylate superplasticizer.  
                                                                         Water/   Compressive           Cement   Strength            Admixture   G/G   Ratio   1 Day   2 Days               Blank test (without accelerator)   —   0.460   10.5 MPa   26.7 MPa       Commercially available calcium-nitrate-based   1.0%   0.470   11.3 MPa   26.0 MPa       accelerator       Calcium chloride 30%-solution   6.0%   0.480   12.7 MPa   22.1 MPa       Accelerator 1 according to the invention   1.5%   0.460   30.6 MPa   35.1 MPa       Accelerator 2 according to the invention   1.5%   0.460   31.3 MPa   37.8 MPa                  
 
         [0061]    While the present application has described preferred embodiments of the invention, clearly, it should be noted that the invention is not limited to these practical examples and can be realized in other ways within the scope of the following claims.