US3493644A - Process for continuously casting concrete members - Google Patents

Description

Feb. 3, 1970 S. H. OWEN PROCESS FOR CONTINUOUSLY l'CASTING CONCRETE MEMBERS Filed March 24, 1967 in@ xxolxbb "um danken .But .023:39 tu 1 x S Bubba .Engl mb m ESS Shulbe/ l Gwen INVENTOR.

United States Patent C 3,493,644 PROCESS FR CUNTINUUSLY CASTING CONCRETE MEMBERS Shubel H. Owen, McMillan Township, Marathon County, Wis., assignor to Dycon, Inc., a corporation of Wisconsin Filed Mar. 24, 1967, Ser. No. 625,661 Int. Cl. B28b 3/20 U.S. Cl. 264-148 5 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a process for continuously casting concrete members and more particularly to a process for rapidly and continuously casting high strength concrete members.

Numerous processes have been devised heretofore for the casing of concrete members wherein a cementitious mixture is continuously cast onto a moving surface and conveyed through a curing kiln to raise the temperature of the formed member so as to accelerate the curing thereof. In addition, it has been proposed heretofore to cast concrete members by use of a cementitious slurry which is heated subsequent to mixing and prior to casting. However, such prior proposals are not generally carried forth in a manner whereby undesirable stresses in the concrete member formed are avoided.

It is therefore an object of the present invention to provide an improved process for continuously casting concrete members generally devoid of a loss of strength in the final product caused by expansion or contraction before sufficient strength is attained to resist such strains.

Another object of the present invention is to provide an improved process for continuously casting concrete members in a significantly shorter period of time than generally possible heretofore whereby attendant economies of manufacture may be realized.

A further object of the present invention is to provide an improved process for continuously casting concrete members wherein the relatively non-reactive components of the cementitious slurry are heated to a relatively high temperature prior to admixture with the reactive cementitious component of the slurry, which hot slurry is then formed and cured at a substantially constant temperature, approximating that of the initial hot slurry, to avoid loss of strength caused by thermal expansion or contraction before suliicient concrete strength is attained to resist the strains.

Still another object of the present invention is to provide an improved process for continuously casting concrete members of a reinforced or non-reinforced type in approximately three to four hours so as to produce concrete members capable of being handled without structural failure while avoiding the unduly time consuming and thus costly handling times encountered with processes proposed heretofore.

Further objects and advantages of the invention will become apparent from the discussion which follows, reference `being had to the accompanying drawing forming a part hereof, and in which:

3,493,644 Patented Feb. 3, 1970 ice FIGURE l is a schematic flow diagram of an exemplary mode of carrying forth the process of the present invention to continuously produce a concrete member; and

FIGURE 2 is a perspe-ctive view of an exemplary form of a concrete member produced by the process of the present invention.

Brieiiy, the present invention provides an improved process for rapidly producing reinforced and non-reinforced high strength concrete members by introducing the heat energy required to elevate the members to a design curing temperature by adding the heat required to the relatively non-reactive or inert ingredients, i.e. the aggregates, and water before the reactive component of the cementitious mixture, i.e. the cement is admixed with the non-reactive components. The aggregates may be heated rapidly to a temperature slightly a-bove the desired design curing temperature by high pressure, high temperature steam applied directly to the aggregates while they are under agitation in a mixing machine. This heating can take place in one to iive minutes, depending upon the kind of aggregate, the size of the aggregate particles, the temperature of the steam, the amount of agitation, etc. Since the cement is not in the aggregate-water mixture during the heating process, no chemical reaction will take place. The cement, in a dry state and at normal ambient temperature, i.e. unheated, is then introduced to the hot aggregate water mixture and the combined aggregate-water-cement mixture thoroughly blended for a short period of time to produce the hot cementitious slurry having a temperature corresponding to the design curing temperature. Thus, it will be apparent that inasmuch as the aggregate-water portion of the slurry comprises the greatest portion of the total slurry the unheated cement added thereto will be heated instantaneously to the design curing temperature, which substantially coincides to the temperature of the hot slurry as indicated hereinabove, by the aggregate-water-mixture before the initial set of the concrete takes place. Therefore, since the concrete may be manipulated and formed without harm before it takes on its initial set if performed rapidly the concrete may then be formed and surface finished in a continuous manner followed by curing approximately four hours at the desired mix temperature. It will thus be apparent that once the concrete has been mixed, it is maintained at substantially the same temperature for the entire four hours to avoid a loss of strength caused by thermal expansion or contraction before suiiicient concrete strength is attained to resist such strains.

Accordingly, it will be readily apparent that the present process for continuously casting concrete members is a constant temperature process in which no significant heat transfer takes place to or from the product after the unheated cement is introduced to the hot aggregate-water mix until the cured concrete member discharges from a curing chamber, as a continuous ribbon, approximately four hours after admixture of the hot slurry.

Thus it will be seen that since the concrete member is maintained at a substantially uniform high temperature throughout the entire body thereof after mixing and forming each and every portion of the concrete member, i.e., interior and exterior, cures at substantially the same rate. Thus no time is lost in slowly heating a relatively cold substantially unset member to the necessary temperature to accelerate the cure thereof. Thus, the product of the present invention is of substantially uniform strength throughout and characterized by a higher strength in a shorter period of time than possible by processes proposed heretofore. While the drawings, merely for purposes of illustration, show the continuous casting of a non-reinforced member such as might be utilized for a oor decking, it will be appreciated that the prOCFSS of the present invention is not restricted to the forming of concrete members of any particular configuration and is thus applicable to the forming of cored as well as solid members of various shapes and configurations of either reinforced or non-reinforced nature.

Inasmuch as the specific cementitious slurry formulations utilized do not comprise the salient feature of this invention it is not considered necessary to set forth such formulations. However, it will be appreciated that standard methods of mix formulation, such as set forth in the Portland Cement Association Bulletin on the Design and `Control of Concrete Mixtures is applicable to the practice of the present invention. Numerous mixtures of Portland cement, water, aggregate and the like may be utilized to produce an acceptable concrete member in accordance with the practice of the present invention.

Although not critical, it shall be appreciated that in any continuous casting processes set forth herein the consistency of the hot cementitious slurry should preferably comprise a slurry having a slump of about two inches normally determined by the ASTM Slump Test for consistency of Portland 4Cement-Concrete. The factors effecting slump are water-cement ratio, aggregate gradation, and time. At normal ambient temperatures, after the concrete has been mixed, it starts to hydrate removing free water from the mix and in the process becoming stiffer (i.e., of lower slump). At elevated temperatures, such as set forth in the practice of the present invention, the physical process of hydration is the same except that the time element is much shorter to produce the same reduction in slump. Other factors being equal, a given water-cement ratio and aggregate gradation will produce the same slump initially at 70 F. or at 180 F., provided that the mixture is formed before the slump changes appreciably. Therefore, it will be appreciated that no significant difference in mix formulation is normally required for elevated temperature casting, such as in the case of the present invention, than is required for normal temperature casting.

With the foregoing in mind it will be seen from FIG- URE 1 that a plurality of storage bins indicated generally at feed suitable amounts of aggregate to a Weighted batcher 12 in amounts consistent with the formulation of the cement slurry to be formed. The aggregate mixture is then collected in a holding hopper 14 and an appropriate amount of water is added thereto which water is preferably in a temperature range of approximately 180 F. to 200 F. High temperature-high pressure steam may then be injected into the holding hopper 14 to raise the temperature of the entire batch assembled therein to the requisite temperature, i.e., 180 F. to 200 F., for example, which it will be appreciated hereinafter comprises an exemplary design curing temperature. Alternatively, it will be appreciated that the aggregate may be heated in a substantially dry state by the introduction of super heated steam followed by the addition of an appropriate amount of hot or cold water as long as the temperature of the relatively inert aggregate-water mixture is raised to a temperature corresponding to the design curing temperature or slightly higher prior to the transfer of the hot aggregate-water mixture to a mixing vessel 16 wherein an appropriate amount of dry cement, normally at ambient temperature, is added thereto and admixed intimately therewith for approximately one minute. It will also be appreciated that inasmuch as the cement component of the cementitious slurry normally comprises a small proportion of the total batch, and particularly when the temperature of the aggregate-Water mixture is slightly above the design curing temperature the cementitious slurry formed in mixer 16 will be understood to conform to the design curing temperature. While the foregoing is illustrative of a batch mixing precedure it will nevertheless be appreciated that the several manipulative Steps of mixing the hot cementitious slurry used in the practice .of the present invention could be carried forth in a continuous manner, however, for purposes of illustration it will be understood that the batch mixing procedure disclosed herein provides a continuous supply of hot cementitious slurry to a forming machine indicated at 18. It will also be appreciated from the foregoing that the heating of the aggregate-water mixture prior to mixing of the completed formulation is a significant aspect of the process of the present invention.

The hot cementitious slurry, at the design curing temperature is discharged from the mixer 16 into a suitable conventional slip forming machine 18 which continuously forms compacts, screeds, oats, etc., the cementitious slurry so as to form a continuous concrete member 20 which is preferably, although not necessarily deposited on a continuous belt 22 supported by a steel plate Z4 such as lubricated by a suitable amount of Water between the plate 24 and belt 22. The hot cementitious slurry is maintained at the design curing temperature in its passage through the forming machine 18 by utilization of suitable insulating means or auxiliary heating means thereabont. The concrete at this elevated temperature will change from a plastic to a generally non-plastic state in the time it takes it to pass through the forming machine, i.e., 2 to 7 minutes, and therefore it will be appreciated that the ribbon of concrete 20 exiting from the forming machine 18 will be self-supporting on the belt. Although not specically illustrated herein it will be understood, as discussed heretofore, and as may be seen in U.S, Patent No. 3,055,073 to Gerwick, reinforcing members may be fed into the forming machine 18 so as to be slip cast with the concrete ribbon 20 exiting therefrom.

The continuously cast concrete ribbon 20, which is as indicated hereinabove self-sustaining, is introduced in'o a suitable curing kiln, also of conventional construction wherein the concrete member 20 is maintained at substantially the design curing temperature by a suitable heating means such as indicated at 26, -for example. The humidity within the kiln 25 is maintained at a relatively high percentage by a recirculating spray means indicated generally at 28 including a pump drawing heated water from a sump in the base of the kiln and delivering it to a plurality of spray headers in the upper portion of the kiln 25 so as to prevent drying out of the surface of the concrete member or slab 20 through its travel through the kiln 25. As indicated heretofore under normal circumstances a given portion of the concrete member 20 will take approximately three to four hours to travel from the discharge outlet of the forming machine 18 to the discharge outlet of the kiln 25 at which time it will be understood the concrete member 20 has been cured suiciently, so as to be self-sustaining and capable of being handled so that it may be severed into appropriate lengths such as by travelling cutoff saw indicated generally at 30 prior to being stacked in a storage area or the like.

From the foregoing it will be seen that the apparatus utilized in the practice of the present invention comprises conventional components and that accordingly any suitable apparatus may be utilized which is capable of carrying forth the several manipulative steps comprising the inventive process of the present invention. The foregoing is considered as illustrative only of the principles of the invention.

What is claimed as new is as follows:

1. A process for forming a concrete member which comprises the steps of (a) mixing the aggregate and water components of a cementitious composition in a manner so as to raise the temperature of these components to an elevated temperature approximating a predetermined curing temperature of a concrete member to be formed therefrom;

(b) adding the Portland cement component of the cementitious composition to the heated components whereby a hot cementitious slurry having a temperature approximating the curing temperature is prepared;

(c) subjecting the hot cementitious slurry, prior to the onset of initial set, to a forming means within which the hot cementitious slurry is confined for a period of time and at a temperature approximating the curing temperature suiicient to develop the initial set of the slurry whereby the concrete member will be generally self-sustaining on a supporting surface; and

(d) curing the initially set concrete member at the predetermined curing temperature whereby a selfsustaining relatively high strength concrete member is formed.

2. A process for continuously forming a concrete member which comprises the steps of:

(a) mixing the aggregate and water components of a cementitious composition in a manner so as to raise the temperature of these components to an elevated temperature approximately 180 F. to 200 F. corresponding to a desired curing temperature;

(b) adding the Portland cement component of the. cementitious composition to the heated components whereby a cementitious slurry at approximately 180 F. to 200 F. is prepared;

(c) subjecting the hot cementitious slurry, prior to the onset of initial set, to a continuous forming means within which the hot cementitious slurry is confined for a period of time at approximately 180 6 F. to 200 F. sucient to develop the initial set of the slurry whereby the concrete `member will -be generally self-sustaining on a supporting surface; and (d) curing the initially set concrete member at approximately 180 F. to 200 F. whereby a self-sustaining relatively high'strength concrete member is formed. 3. The process of claim 2 including the step of: (e) severing the concrete member into segments. 4. The process of claim 2 wherein step (d) is carried forth in approximately three to four hours.

5. The process of claim 2 wherein step (c) is carried forth in approximately two to seven minutes.

References Cited UNITED STATES PATENTS 1,102,851 7/1914 Avram 106-120 1,442,764 1/192'3 Fox 25-14 2,540,354 2/1951 Selden 264--333 3,055,073 9/1962 Gerwick 2.64-145 FOREIGN PATENTS 538,893 4/ 1957 Canada.

ROBERT F. WHITE, Primary Examiner K. J. HOVET, Assistant Examiner U.S. Cl. X.R.

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