Coating processes – Spraying – Inorganic coating material
Reexamination Certificate
2000-08-11
2002-10-15
Beck, Shrive P. (Department: 1762)
Coating processes
Spraying
Inorganic coating material
Reexamination Certificate
active
06465048
ABSTRACT:
BACKGROUND OF INVENTION
(a) Field of the Invention
This invention refers to an improved method in the domain of the shotcrete technology, using a microstructure, the shotcrete being composed by a perfect chemically stable mineral mixed with cement, aggregates and water, placed in position by projection preferably pneumatic.
Particularly, this invention is about adding barium sulphate, specifically barite, in the shotcrete technology, aiming to improve the feeding, the mixing, the transportation and the projection, as well as the resulting improved products, namely grouts, coatings, mortars concretes, embankments, etc.
(b) Description of the Prior Art
It is well known that placing mortars and concretes by projection began in the USA by the beginning of this century. The projection was done using a special machine called “Cement Gun”. The shotcrete technology, as far as we know, was applied first in Romania, in 1905 for a concrete dam, protected by a 8 cm shotcrete casing.
Sixty years later, in 1965, the dam was verified and it was found out that on the upstream side it was well preserved but on the downstream it presented distortions and fissures. This work proved the durability of shotcrete, the distortions being due to normal aging after 60 years especially considering the equipment used by that time.
The shotcrete technology has been drastically improved during the last 90 years, mostly after the second world war, concerning the equipment, the components, the environmental problems, the hygiene and the work security, the professional illnesses and the workers training; but still progress has to be made.
Shotcrete is though a concrete placed in position by projection usually a pneumatic one, at high speed, with or without previous pumping. Compared to standard concrete, cast and vibrated, this concept of projection at high speed offers specific advantages and disadvantages, and consequently, a specificity of uses. Thus the speed and the power of projection make it easier to get a more compact product, denser, more impervious and less porous, with a better cohesiveness and better adherence to the surfaces to be placed on, indifferent to their regular or not regular shape, texture or hardness. Among others, this pneumatic projection concept assures the mixed components transportation from the mixer to the surfaces to be covered by hoses and that up to 600 meters distance with the dry process. It allows operating in very exiguous spaces, eliminates forms, allows vertical or horizontal (ceiling or floor) projections. It serves also in getting a better anticorrosive protection, especially on metal reinforcements, and as fireproof protection. In spite of all these many important advantages, it faces a lot of difficulties and limitations which were the subject for science and industry to solve since many years. Depending on the kind of mixing process, dry or wet, the main disadvantages are: abrasion and blocking of the mixing equipment and of the hoses; irregular quality of the mixing operation and segregation during transportation and projection; long, difficult and often imperfect cleaning of the equipment after use; very important need of controlling and adjusting the degree of humidity inside and outside the equipment during mixing and transportation to avoid the early and unwanted setting of cement; need to use setting retarders or superplasticizers in the wet process; generation of dust especially in the dry process during feeding, transportation and projection, negatively affecting the pulmonary health of the “nozzleman”, the visibility and the adherence to the receiving surfaces; rebounds and ricochets during projection, causing waste of materials, risks of injuries for the “nozzleman”, sand pockets and voids in the projected product; a jerkily projection, with blocking ups and lashings, causing risks of injuries for the “nozzleman” and also variation in the quality, homogeneity and uniformity of the final product; difficulty for the “nozzleman” to maintain a perfect control over the water-cement ratio during projection in the dry process which is an essential factor for the quality of the product; expertise and adequate experience of the “nozzleman” as the main factor; generation of static electricity mostly in the dry process.
Many innovations have been suggested in the past years to correct those disadvantages, or to improve the performance of the shotcrete technology, namely by using set accelerators or retarders, air entertaining agents, latex, water reducers or superplasticizers. Nevertheless, the more components there are, the more difficult it is to control the long term durability due to the problems of compatibility of admixtures-additives, cements, or aggregates used. More, one must keep in mind that shotcrete is often used in unknown environments, or in environments that will become unknown or uncontrolled with time.
It is well known from previous works (U.S. Pat. No. 4,931,098), to improve shotcrete projection by using silica fume with less than 90% SiO
2
in the starting mixture. It is usual to use 5-30% silica fume weight to the weight of bubbling solution and this is 8-10% to the weight of cement. Silica fume is used because one can get a more impervious product in the short run and a satisfactory quantity of rebounds. Also one may notice that silica fume is on a long term a source of professional illnesses and its use neither eliminated nor minimized the alkaline reactions or the appearance of fissures or micro fissures of expansion or contraction in the long run. More, the “nozzlemen” as well as the environmentalists are more reserved in using and working with this product in shotcrete technology.
One of the applicants, engineer Toma already applied the shotcrete technology in 1943 in Romania, in a coal mine. The work place was situated in a zone with methane gas (CH
4
) emanation and the work consisted in stopping the gas migration and silting the place. More, a patent concerning a shotcrete machine sold in Romania and Morocco as “Torcreting machine type Toma” was delivered to him as author (patent number 51,166/Jun. 27 1966). He also got another Romanian patent as a co-author (patent number 50,548/Mar. 14 1966) for a device to shoot a mix of concrete. This device used a pneumatic engine and was used to protect the feeble strength rocks 15 minutes after rocks dislocation. Another patent (51,338/Oct. 20 1967) was delivered to him as author of a method of consolidating the underground excavation of feeble strength rocks with shotcrete. The method consisted of making helical canals in the rocky walls on different angles.
On the other hand it is known that the use of barite in the standard concrete mixtures was studied for a long time. The goal was to get a heavy concrete, impervious to X-rays and Gamma-rays. But these studies were done on concrete made by pouring and vibrating ways and they did not come to eliminate the gravimetric segregation (resulting in less compactness and imperviousness).
Therefore the inventors think that their efforts must, as much as possible, look for “sustainable development” as expressed in the “Rio Convention”.
The invention has, as a goal, the minimal use of chemically constituted components which might interact chemically and/or act chemically with the environment, in short, medium, or long term.
SUMMARY OF INVENTION
The disadvantages of the prior art are highly eliminated by providing an invention which is directed to a method which comprises preparing a water-hydratable-cement base projection mix, and pneumatically projecting the mix at high speed and ambient temperature directly against a surface under conditions such that the mix forms a layer which adheres to the surface and which holds well in place without having to use forms or closed or non closed molds, wherein the mix necessarily comprises barite, which is compatible with all organic and inorganic components, the mix requiring no addition of calcium sulphate in free state, nor any addition of silica fume in free state.
Preferably, the projection mixture is a groutin
Rolland Pierre
Toma Ileana
Toma Ioan
Beck Shrive P.
Fuller Eric B
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