US2093970A - Plastic concrete transportation system and method - Google Patents

Description

P 1937- c. l. LONGENECKITR 2,093,970

PLASTIC CONCRETE TRANSPORTATION SYSTEM AND METHOD Filed NOV. 24, 1953 g: ll i w a g Q gay. A

Concrete Patented Sept. 21, 1937 UNlTED STATES PATENT OFFIQE PLASTIC CONCRETE TRANSPORTATION SYSTEM AND METHOD Application November 24, 1933, Serial No. 699,633

'7 Claims.

This invention relates to the transportation of plastic concrete mixtures, and has for its principal object the provision of a system and method for facilitating the transfer in closed conduits and without segregation, of such mixtures from a higher to a lower level, as in the construction of tunnels, sewers, and other underground conduits.

Concrete, as defined by the American Concrete Institute, is a mixture in which a paste of Portland cement and water binds fine and coarse materials, known as aggregates into a rock-like mass as the paste hardens through the chemical action of the cement and the water. It is well known to those skilled in the art that in order to produce the best concrete for any given purpose, the various constituents, but more especially the cement and water, should be accurately proportioned; they should be thoroughly mixed to provide each piece and particle of the aggregates with a complete coating of the cement-and-water paste; and the coarse aggregates should be fairly evenly distributed throughout the mixture. The coarse aggregates, however, because of their greater size and weight, have a marked tendency, particularly in the thinner or wetter mixes, to settle to the bottom if allowed to remain quiescent for any considerable length of time, with the finer aggregates and cement-and-water paste floating on top. This is termed segregation, and is studiously avoided wherever possible, as the hardened mass resulting from a segregated mix is of non-uniform texture and strength.

Segregation will also occur if the plastic mixture be dropped free an appreciable distance, apparently due in a measure, to the greater elasticity or resilience of the larger aggregates, which causes them to bound out of the mixture when striking or landing. The finer aggregates are driven into a compact mass with an accumulation of the coarse aggregates at the sides or on top thereof. If the concrete falls into a pipe or a form, it is thus deposited in distinct layers of fine aggregate and coarse aggregate.

In the construction of underground conduits such as tunnels, sewers and the like it is frequently desirable that the concrete be mixed at the surface and transported for placement to the lower level at which the conduit is being constructed. This has heretofore been accomplished in pipe lines with some measure of success, using compressed air or other fluid under pressure as a means for moving the mixture, and more recently the mechanical concrete pumps of the type shown in the U. S. Patent No. 2,017,975, granted October 22, 1935, to Jacobus C. Kooyman have been similarly employed with materially greater success. The horizontal tunnel bore is driven in the usual manner and vertical shafts which are sunk every so often are employed as openings through which the pipe line may be extended from the x surface to the tunnel bore. At the bottom of such vertical shafts the pipe line may be extended horizontally in either direction up to the maximum distance to which the particular pressure means being employed will successfully operate.

Where the horizontal tunnel bores are comparatively near the surface no unusual difficulties are encountered in operating such systems. However, when the bores are further below the surface, say 15 feet or more, it has been found that in starting a pumping operation, the first portion of concrete to descend through the vertical pipe line, segregates as above explained. Such segregation tends to form separated compact masses of coarse aggregates and line aggregates, which are unpumpable because of a deficiency in cement and finer aggregates in the coarse aggregate mass, which are necessary to hold the coarse aggregate in suspension, and to also act in a measure asa lubricant between the coarse aggregate and the pipe. Not only is such segregated concrete undesirable from the standpoint of non-uniformity in texture and strength of the resulting product, but it also introduces difliculty into the further movement of the mix through the pipe, since it is extremely difficult and in many cases utterly impossible to move a concrete mass in which the coarse aggregates are not uniformly distributed throughout the mixture. In other words, the segregated coarse aggregates at the bottom of the vertical pipe section act as a plug or dam in the pipe and because of the stowing property of plastic concrete mixtures, now well recognized, it is often found impossible, with any degree of pressure, either fluid or mechanical, which it is practical to attain, to start the mixture moving through the lower horizontal section of the pipe. Stowing will also result from comparatively slight constrictions of, or obstructions in, the line, as well as from sharp changes in the;

direction of travel of the mixture, all as is now well known.

It is the primary object of the present invention to overcome this difliculty in a simple and efficient manner and with this and other objects in view which will appear as the description proceeds, the invention consists in the novel details of construction and combinations of parts constituting the apparatus and in the novel steps and combinations of steps constituting the method all;

as will be more fully hereinafter described, and particularly pointed out in the appended claims.

Referring to the accompanying drawing forming a part of this specification:-

Figure 1 is a diagrammatic sectional elevational view of a concrete placement system employing a mechanical concrete pump of the type above mentioned for transferring plastic concrete mixture from an upper level to a lower horizontal bore in which a tunnel or other similar conduit is being constructed; and

Figure 2 is a fragmentary diagrammatic sectional view illustrating a slightly modified way of carrying out the general method.

In the drawing 5 indicates a lower horizontal bore which is connected by a vertical shaft 6 with the upper level I, here indicated as being the ground level. Within the bore 5 a suitable form 8 has been erected around which plastic con crete 9 has been placed in order to form the desired conduit.

At the upper or ground level there is shown a mechanical concrete pump ID of the Kooyman type, the outlet of which is connected by a horizontal pipe section I I and vertical pipe section I2 to the lower horizontal pipe section I3 which may be extended in either direction from the vertical portion I2 of the pipe line as the work progresses, to discharge at the proper point relative to the form 8.

Heretofore, when operating sucha system the plastic mixture was forced by the pressure means such as II] through the horizontal pipe section I I without any difliculty or segregation, but when it reached the vertical section I2 it would fall under the action of gravity faster than the pump would supply it to the section II, with the result that the heavier and coarser aggregates would separate from the remaining constituentsand would collect at the bend or elbow M which connects the vertical section I2 with the lower horizontal section I3. When the pump had supplied sufficient mixture to completely fill the vertical section I2 it was then found in many instances to be impossible to force the mixture further, due to the packing or stowing of the segregated mixture, or if by any chance the mixture could be forced through the lower horizontal pipe section I3, that portion which had first filled the vertical section I2 was of such a character that it would result in a concrete of non-uniform texture and strength, and wherepossible, it was necessary to remix the concrete in order to secure uniform texture and strength, otherwise, official inspectors caused it to be discarded.

In order to obviate these diificulties, under the present invention there is provided at a suitable point in the lower horizontal pipe section I3 a control valve I5 which is preferably of the adjustably loaded type, and which is capable of yieldingly restraining or holding a fluid, such for example as water, which may be introduced into the pipe line above the said valve, such fluid being designated at H. The valve I5 may be arranged to permit escape of such fluid through the remaining portion of the pipe line I3 which lies beyond the valve, or a separate discharge line I8 may be provided for conducting the fluid back to the upper level, where a tank or reservoir '22 may be provided to receive it, and upon demand return it to the pipe line for a succeeding operation. A suitable shut-off valve I9 capable of controlling the flow of the concrete mixture is also preferably provided in the lower horizontal pipe section I3 as shown in the drawing.

In operating the system in accordance with the present method, the spring or other loading device of the valve I5 is so adjusted that the valve will remain closed against the normal pressure of the fluid I'I when the latter is introduced into the pipe line up at least to the upper horizontal level so as to completely fill the vertical section I2 of the line. This section being thus filled with fluid, a separating element in the form of a free piston or go-devil 2B is introduced into the line and this is followed by the plastic concrete mixture. The function of the piston or go-devil is to maintain the stream of plastic mixture separated from the stream or column of liquid in order that the mixture will not be thinned-out and also in order that the heavier constituents of the mixture may not sink through the fluid and become segregated as in the prior practice. When the pipe line has been thus prepared further operation of the pump in forcing the concrete mixture into the upper horizontal section I I in the line will create a pressure in excess of that for which the valve I5 is loaded so that the fluid I! will escape past the said valve I5 and be discharged either through the right hand portion of the pipe section I3 or through the fluid discharge line I8 if the latter be provided. When all the fluid has been forced out past the valve I5 the pump Iii is temporarily stopped, the valve I9 is closed in order to hold the vertical column of mixture which now completely fills the pipe section I 3, and the valve I5 is either removed entirely from the pipe line or it is adjusted to fully open position in which it will not interfere with the passage of plastic mixture. is also removed, and the valve I 9 is then again opened and the pumping operation resumed with the result that no difliculty is experienced in getting the mixture to flow through the line and the first part of the mixture need not be discarded because it has become segregated.

It is preferred to employ water as the fluid which is used to fill the vertical section I2 of the pipe line because of the cleaning and lubricating properties it possesses, which facilitate the initial passage of the plastic mixture through the pipe line, as is disclosed in the co-pending application filed jointly by Charles F. Ball and myself entitled Method of cleaning and preparing conduits for the handling of plastic concrete mixtures, filed November 24, 1932, Ser. No. 699,632. Under some circumstances, however, other fluids may be employed and in some cases where the character of the underground work is such that no free water be permitted in the tunnel, the fluid used to retard the concrete may be the air contained in the pipe line or compressed air may be introduced into the pipe line to build up sufficient pressure to retard the head of concrete as it descends the vertical pipe. Likewise, although the invention is particularly adapted for use in connection with pressure systems it may in some instances find application in cases where the concrete is being lowered solely by gravitational action.

In Fig. 2 there is diagrammatically illustrated a slight modification of the method in which a combination of liquid and gaseous restraining media is employed. The lower portion of the line I2I3 may be filled with a compressible fluid, such as air, at or above normal atmospheric pressure, and this is separated from the water or other non-compressible fluid I! by a second free piston or go-devil 23. The action is substantially identical with that above described, but this The go-devil 20 combination may be preferable under certain conditions.

It is obvious that those skilled in the art may vary the precise details of construction and ar- 5 rangement of parts constituting the apparatus,

as well as the precise steps constituting the method, without departing from the spirit of the invention, and therefore it is not Wished to be limited to the above disclosure except as may be required by the claims.

What I claim is:

1. The method of preventing segregation of the constituents of a plastic concrete mixture when moving it in a confined stream from a higher to a lower level, which comprises confining a body of fluid in advance of said mixture; maintaining said fluid and mixture separated from one another during the downward movement; and causing the fluid to escape gradually as the mixture is moved forwardly.

2. The method of preventing segregation of the constituents of a plastic concrete mixture when moving it under pressure in a confined stream from a higher to a lower level, which comprises confining a stream of liquid in advance of said mixture; maintaining said streams separated from one another; and causing the liquid to escape under restraint as the mixture is moved forwardly.

3. The method of preventing segregation of the constituents of a plastic concrete mixture when pumping it in a solid confined stream from a higher to a lower level, which comprises retarding the movement of the head of the stream 3 through the imposition of a partially restrained mobile medium in advance thereof, whereby the said head is prevented from moving faster under the influence of gravity than mixture is supplied to the rear end of the stream, and the 40 continuity and cross sectional area of the latter are continuously maintained.

4. The method of preventing segregation of the constituents of a stream of plastic concrete mixture when moving under pressure through an unobstructed conduit from a higher to a lower level, which consists in confining a mobile medium in advance of said stream; and controlling the escape of said medium so as to maintain a substantially uniform rate of movement through- 5 out the entire length of the stream.

5. In a system for transferring plastic concrete mixtures from a higher to a lower level without segregation of their constituents, and without stowing, an unobstructed conduit ex- 10 tending from said higher to said lower level; means for supplying the mixture to the conduit at the higher level; and fluid-pressure controlled means arranged to travel with and restrain the head of the mixture stream to prevent its moving 15 from said higher to said lower level under the influence of gravity faster than the mixture is supplied to said conduit, said means imposing said restraint without constriction or obstruction thereof which would produce stowing. 0

6. In a system for transferring plastic concrete mixtures from a higher to a lower level without segregation of their constituents, a conduit extending from said higher to said lower level; means for supplying the mixture to said conduit 25 under pressure at the higher level; and means for confining a body of fluid in said conduit ahead of said mixture, said means being arranged to permit said fluid to escape under restraint as the mixture is forced into the conduit.

7. In a system for transferring plastic concrete mixtures from a higher to a lower level without segregation of their constituents, a conduit extending from said higher to said lower level; means for supplying the mixture to said conduit under pressure at the higher level; means at the lower level for confining a body of fluid in said conduit ahead of said mixture, said means being arranged to permit said fluid to escape under restraint as the mixture is forced into the 40 conduit at the higher level; and means for maintaining the mixture separated from the fluid.

CHARLES .I. LONGENECKER.

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