Sulfate-free and alkali-free setting and hardening accelerator

Details Sulfate-free and alkali-free setting and hardening accelerator Sulfate-free and alkali-free setting and hardening accelerator

2001-06-18

2003-04-01

Marcantoni, Paul (Department: 1755)

Compositions: coating or plastic

Coating or plastic compositions

Inorganic settable ingredient containing

C106S819000, C106S823000

Reexamination Certificate

active

06540826

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the priority of European patent application no. 00 113 019.4, filed Jun. 21, 2000, the disclosure of which is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
The present invention relates to a sulfate-free and alkali-free or alkaline metal-free, respectively, and chloride-free accelerator as well as a method for setting and hardening of a hydraulic binder.
Examples for binders the setting and hardening of which occurs faster due to the addition of an accelerator of the present invention are for example cement or hydraulic lime, and examples for mixtures comprising such binders are mortar and concrete.
Applications for the inventive accelerator and the inventing method are the production of pre-fabricated elements and the acceleration of concrete produced at the construction site. In the first case, the usual acceleration of the hardening by heating (by means of electro ovens or oil ovens or steam) can be shortened or even entirely eliminated. In the second case, the time needed until the mold encasing the concrete can be removed, can be shortened, or the application of concrete can be continued also at lower temperatures. Further applications are in the production of fast setting cement and mortar mixtures, in particular for fixing pre-fabricated parts, casted parts etc.
A specific field of application is spraying mortar and spraying concrete. Such mortars and concretes serve the production of building constructions in underground and surface engineering as well as for the extension and lining of underground, natural or artificially constructed cavities, such as adits, tunnels or mines, for which the concrete must meet the static requirements as well as being water-tight. They also serve the consolidation of excavations, embankments, loose rock faces etc.
Already many substances are known that accelerate the setting and hardening of concrete. The most often used are i.a. strongly alkaline reacting substances such as alkali hydroxides, alkali carbonates, alkali silicates, alkali aluminates and alkaline earth chlorides.
Substances with strongly alkaline properties are undesired due to the health risks they can cause when persons are handling such substances. Burning of the skin of the worker, harmful effects on the respiratory system, especially the lungs, and irritation of the eyes and etching of the cornea can occur.
In view of concrete technology, strongly alkaline setting accelerators reduce the final strength, they cause larger shrinkage, what may result in crack formation and therefore strongly reduces the long time quality, in particular the resistance to sulfate of the concrete.
An important factor that affects the long time stability of concrete constructions is the later formation of Ettringit (furtheron referred to as Delayed Ettringit Formation (DEF)). By the formation of ettringit in the cured cement system, the structure of the building or construction, respectively, expands such that cracks or flakings occur.
In literature many documents concerning the DEF can be found that unambiguously show that an additional sulfate source significantly furthers the later formation of ettringit.
The commercially available accelerators comprise 15-25% sulfate and therefore are a not neglectable source for sulfate.
Further, in several standards, limitations for the sulfate content of concrete systems is prescribed (e.g. the Austrian standard [guideline Shotcrete] requires a maximal total sulfate content of 4.5% by mass SO
3
[sum of accelerator and cements]).
The setting accelerator according to the present invention does not comprise any sulfate, thus hinders a supplementation of the concrete with sulfates and such does not add to the DEF.
Accelerators for the setting of hydraulic binders on the basis of amorphous aluminum hydroxide are already known from EP-A 0 026 262, in particular claims
1
and
11
to
13
, as well as from chemical abstracts volume 86, number 18, May 1977, page 300, 126087c.
According to EP-A 0 026 262, page 2, last paragraph, the particle size of the amorphous aluminum hydroxide is in particular in the range of 4.8 and 5.4 &mgr;m.
Also a swellable cellulose product and further additives can be comprised in such a hardening accelerator, see EP-A-0 026 262, in particular claims
8
to
10
and the examples.
From DE-A 2 548 687, in particular patent claim and page 15, the addition of aluminum sulfate and nitrates to setting accelerators on the basis of aluminates and aluminum oxide are known.
From FR-A 2 471 955, in particular claims
1
to
6
, the use of formats and nitrates in accelerators are known.
EP 0 076 927 describes a method for the acceleration of the setting by addition of amorphous aluminum hydroxide and at least one water-soluble sulfate and/or nitrate and/or formiate.
EP 181 739 A1 describes the use of calcium sulfoaluminate and a mixture of calcium aluminates that together with alkali metals or alkaline earth metals and addition of 250% water result in a curable slurry.
JP 63 206 341 A2 discloses an accelerator comprising calcined alunite, calcium sulfoaluminate, sodium aluminate and sodium carbonate.
JP 58 190 849 A2 describes a mixture of calcium sulfoaluminate, calcium sulfate hemihydrate and calcium hydroxide for the preparation of fast setting, sprayable coatings.
SU 697 427 mentions a fast setting cement obtained by addition of calcium aluminate, calcium sulfoaluminate, calcium oxide, ferrite, silicate and gypsum.
JP 54 026 817 mentions the accelerated curing of gypsum by addition of calcium sulfoaluminate.
JP 53 099 228 describes an accelerator for grouting mortar based on calcium sulfoaluminate and calcium fluoroaluminate and water reducing agents.
In DE-OS 2 163 604 accelerators on the basis of calcium fluoroaluminate are mentioned.
From JP 01 290 543 A2 mixtures of calcium sulfoaluminate with calcium sulfate and lithium carbonate are known as accelerators for low temperature applications.
SU 1 350 136 A1 describes clinker with fast setting achieved by addition of barium sulfate, calcium aluminate and calcium sulfoaluminate.
WO 97/36839 describes the use of lithium silicate and/or lithium aluminate and/or aluminum salts.
WO 98/18740 comprises a method for the production of a setting and hardening accelerator for hydraulic binders. The product that according to claim
1
necessarily comprises of 5 components shows strong turbidity, high viscosity and a low storage stability. This can lead to plug up of the spray nozzles. At the construction site, upon dosing of the product, in particular at low temperatures, the high viscosity causes problems. A dilution of the product is not possible since thereby part of the basic salts are precipitated. The low pH-value leads to corrosion at dosing and spraying apparatuses.
U.S. Pat. No. 5,772,753 describes an accelerator on the basis of aluminum hydroxide with an organic anion. The production from an alkali aluminate solution comprises a very sumptuary washing procedure and mostly leads to insoluble aluminum compounds.
BRIEF DESCRIPTION OF THE INVENTION
Hence, it is a general object of the invention to provide a sulfate-free and alkali-free or alkali metal-free, respectively, and chloride-free setting and hardening accelerator by which a very fast setting can be achieved.
Now, in order to implement these and still further objects of the invention, which will become more readily apparent as the description proceeds, the accelerator for the setting and hardening of a binder or a mixture comprising a binder is manifested by the features that said accelerator comprises at least one water-soluble fluoride comprising aluminum salt, and optionally a complexing agent (the term complexing agent as it is used in the scope of the present invention means substances that improve the setting procedure and the stabilization) and/or amines, whereby said amines act as stabilizers in order to prevent a precipitation of aluminum hydroxide. Preferably the pH-value of an accelerator of the present inventi

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