WO1994025681A1

WO1994025681A1 - Method and apparatus for staged vibration of concrete

Info

Publication number: WO1994025681A1
Application number: PCT/GB1994/000859
Authority: WO
Inventors: Samuel Allen Face, Jr.
Original assignee: Williams, John, Francis
Priority date: 1993-04-30
Filing date: 1994-04-22
Publication date: 1994-11-10
Also published as: KR960702033A; DE69411269D1; DE69411269T2; EP0698153B1; CN1052281C; EP0698153A1; JPH08510302A; DK0698153T3; CA2161454A1; CN1124989A; ATE167716T1; ES2117271T3

Abstract

Introduction of vibration forces into plastic concrete structures, such as concrete slabs (M), decks and similar or related concrete structures controls the consolidation of the concrete mass. Vibrating apparatus (3) imparts controlled vibrations either onto the surface (1) or beneath the surface of the concrete mass in sequential stages. The number of stages, the amplitude and frequency of the vibrations, the physical orientation of the vibration producing apparatus (3), the time duration in each stage, and the thickness of each stage of vibration is variable depending upon the physical characteristics of the concrete mass, including the physical characteristics of the concrete being used, the thickness of the concrete slab and the specific materials incorporated into the concrete during formation of the concrete mass.

Description

Title: METHOD AND APPARATUS OF STAGED VIBRATION OF CONCRETE

The present invention generally relates to a method and apparatus for introducing vibrational energy into plastic concrete

structures which are generally oriented horizontally, (such as concrete slabs, decks, roadways and similar or related concrete structures), in successive stages or increments.

The term "Staged Vibration", as herein used means, subsequent to the pouring of a concrete mass, the introduction of vibrations into the concrete mass in such a manner that the lower portions of the mass are first consolidated, and the sequential

modification of the character of the vibrations so as to cause successively higher portions of the concrete mass to become consolidated, until all or nearly all of the concrete mass is consolidated into a single mass of uniform density.

Collateral with the consolidation of the concrete mass into a uniform density, "Staged Vibration" also produces a concrete structure whose final (exposed top) surface is uniform and which may be produced at a uniform rate. Essentially, the present invention is a method of placing concrete using staged vibration of the concrete by employing a vibration-producing apparatus which is in contact with a concrete mass, (either by submerged devices, or by devices in contact with the surface of the concrete mass, or both), in a staged, stepped or phased sequence. In the present invention vibrations are introduced to a concrete mass in sequential timed "stages", with the number of stages, the amplitude and frequency of the

vibrations, the time-duration of each stage, and the relative orientation of the vibration-producing devices each being variable, depending upon the physical characteristics of the concrete mass. The pertinent physical characteristics of the concrete mass include, but are not necessarily limited to: The physical characteristics of the concrete being used; the

thickness of the slab (or other structure) being placed; and the specific materials incorporated into the concrete during

formation of the concrete mass.

The determination of which variables to alter, the amount of alteration, and the implementation of the desired alterations are made and monitored by sensors and associated controls which determine the location "of the boundary layer between that portion of the concrete mass which has been satisfactorily consolidated by vibration and that portion which has not been satisfactorily consolidated. DESCRIPTION OF THE PRIOR ART

In constructing concrete structures, such as concrete slabs and the like, certain conventional procedures involve simply placing the concrete mass in a form and finishing the top surface in various well known manners and permitting the concrete to harden with no vibration whatsoever. Other procedures involve the use of vibrators placed temporarily into or upon the concrete mass at various locations, with the surface being finished by using various combinations of striking off the surface and/or

trowelling operations, including the use of hand trowels, powered rotary trowels and the like.

A problem with prior methods of placing concrete using vibrators is associated with the lack of control of the

vibrators. When any one section of a poured concrete slab is vibrated too much, it causes hard spots in the concrete slab approximately at the location of the contact with the vibrator.

In addition, over-vibration of the concrete can also cause aggregate separation in the vicinity of the vibrator. Aggregate separation and "hard spots" both results in a non-uniform and weakened final slab. For these reasons, prior concrete placing operations typically cautiously "under-vibrate" the concrete mass or may not vibrate the concrete mass at all.

Another known procedure involves the use of slip forms in which the concrete mass placed in the forms may or may not be vibrated by a continuously moving form into which, or in front of which, the concrete is poured and provided with a specific shape which is maintained after the form moves progressively, with the concrete then being finished using conventional procedures.

The principal purpose of vibrating plastic concrete in this context is to expeditiously consolidate the concrete mass to its maximum and at as nearly a uniform density as possible by encouraging and assisting the upward migration of water and air which would otherwise migrate slowly or not at all. Entrapment of air and water weakens the concrete and the slow migration of these materials extends the time required to place and finish the mass. Existing procedures for the application of vibrations to the concrete mass provide virtually no means to control or to modify the vibrational characteristics of the vibrators (other than by manually turning the vibrator off and on), and no means to control or modify the length of time the vibrators act upon the concrete mass in which the control means is based upon the degree of accomplishment of the end result desired. Therefore, the existing procedures produce a concrete mass in which the degree of consolidation varies from one location to the other and in which the time required for water to evaporate from the surface varies from one location to the other.

Another phenomenon associated with natural (i.e. non-vibrated) consolidation and curing of concrete is the entrapment of moisture inside of the curing mass. As poured, concrete mixtures commonly comprise an amount of water far exceeding the quantity which is actually necessary to effect proper curing and maximum strength of the concrete mass. The excess water is intentionally added to the concrete mixture in order to facilitate

transporting, pouring, forming, and finishing operations. If left stagnant (i.e. un-vibrated), pressure from the weight of the concrete mass initially slowly presses some of the excess water upward through the concrete mass, thus initially inducing migration of some of the excess water towards the surface of the slab and, at the same time, effecting the consolidation of the concrete mass near the bottom of the slab. As this concrete mass becomes dry, the concrete begins to cure, even while the concrete mass may not yet be optimally consolidated. This curing of the concrete mass retards the migration of the water towards the surface of the slab. At the same time, in many instances

(particularly when the slab is poured in sunlight, on a windy day of low humidity), water may evaporate so quickly from the top surface of the slab that the concrete at the top prematurely dries out and begins to cure. This results in the setting of the concrete at or near the surface of the slab, which further retards migration of excessive water from the concrete mass below to the surface. Ultimately, this phenomenon results in the entrapment of the moisture inside of the concrete slab. Over time the moisture bubbles dry out, leaving small air pockets throughout the solid concrete slab. Such air pockets reduce the final strength of the concrete slab.

In prior concrete slab placing operations, de-watering techniques are used wherein the concrete mass is poured and formed into a structure having an upper surface, and the mass is then de-watered by applying a vacuum water extracting system over the wet concrete surface. Alternatively, the surface of the concrete mass is de-watered by placing absorbent material (such as burlap or the like) over the wet concrete surface, and then spreading a desiccant (such as dry cement) on the burlap. The surface is conventionally finished after the de-watering process has been completed, and the burlap or the vacuum water extraction system is removed. Existing concrete finishing procedures are labor intensive and require extensive use of skilled labor and

considerable time expenditure in properly carrying them out.

Efforts which have been made to automatically control mechanical finishing devices have been less than satisfactory due to the lack of uniformity of the physical characteristics of the concrete mass at the time the automatically controlled finishing devices are introduced to the mass, and due to the inability to control the physical characteristics of the concrete mass just prior to the finishing operation. Thus, human operators have been necessary to make decisions and adjustments to the finishing equipment. Adjustments generally must be made on a continuing basis for the entire time of the finishing operation since the variations in the character of the wetness or lack of

consolidation of the concrete surface are prevalent in the concrete surface immediately prior to and remain during the finishing operation and no mechanical element of the finishing operation has the capacity to moderate or reduce these variations either in number or intensity.

In highway construction, the surface is generally not required to be smoothly finished, with vibration and strike-off being all that is usually required. While this is essentially a machine operation, the end product (the concrete slab) is not uniform because the delivered materials forming the concrete mass are not uniform and the vibration and strike-off equipment do not adjust in any way to compensate for this lack of uniformity. Typically, highway concrete is de-watered only by gravity (and evaporation). Accordingly, water removal from highway slab is typically a slow, uneven and uncontrolled process. Water removal from highway slabs in the described a slow, uneven and uncontrolled manner results in uneven shrinkage of the slab as it cures, and

ultimately resulting in cracks and a weakened structure.

The following U.S. Patents relate to developments in the

introduction of vibration into a concrete mass by the use of vibrating devices that are immersed in or otherwise associated with the concrete mass: 2,015,217; 2,223,734; 2,269,109; 2 ,293 ,962 ; and 2 ,332 ,687 .

While the above patents relate to the vibration of a concrete mass, none of them suggests a staged or step-by-step vibration of a concrete slab, deck or the like in which each stage of the vibration introduced onto or into the concrete mass affects the mass of concrete to specific desired depths in the concrete mass; nor do any of them describe a means of determining the depth to which the concrete mass has been consolidated or should be vibrated.

SUMMARY OF THE INVENTION

Accordingly, it is a primary objective of the present invention to provide a method and apparatus for placing concrete slabs, or similar structures, by use of machine operations, in which the concrete is placed using staged vibration of the uncured, plastic concrete mass. It is another object of the present invention to provide a method and apparatus of placing concrete slabs of the character

described wherein, during each stage of vibration, water and air are caused to migrate upward through the uncured concrete mass, thus forming a definable, and substantially horizontal, boundary layer, below which boundary layer the concrete mass may be defined as being sufficiently consolidated, and above which boundary layer the concrete mass may be defined as not yet being sufficiently consolidated.

Another objective of the present invention is to provide a method and apparatus of placing concrete slabs, or similar structures, of the character described in which the uncured concrete mass is sequentially consolidated from the bottom upward toward the top surface, so as to effect a placed structure of substantially uniform density from the bottom to (or nearly to) the top, wherein the consolidation and integration of adjacent horizontal layers of the concrete mass is effected by a vibrator apparatus which advantageously imparts vibrations into the uncured concrete mass.

It is another object of the present invention to provide a method and apparatus for placing concrete slabs, or similar structures, of the character described, wherein the vibrational

characteristics of frequency, amplitude and time in contact with the uncured concrete mass are each monitored and controlled, so that the elevation of said substantially-horizontal boundary layer (between the sufficiently consolidated and the not-yet sufficiently consolidated concrete mass) may be closely regulated and adjusted by said apparatus. It is another objective of the present invention to provide a method and apparatus for placing concrete slabs having the character described, wherein the characteristics of said

vibrations advantageously imparted into the uncured concrete mass are controlled by sensors located in front of, under and/or behind the vibrator apparatus as it progresses across the concrete mass.

It is another object of the present invention to provide a method and apparatus for placing concrete slabs having the character described, wherein the sensors determine the elevation location of said boundary layer in front of, behind, and/or under the vibrator apparatus, relative to the elevation location of either the sub-base upon which the concrete mass is being placed or the top surface of the concrete mass.

Another objective of the present invention is to provide a method and apparatus of placing concrete slabs, or similar structures, by the use of machine operations in which the rate of hardening of the concrete mass is somewhat controlled by a plurality of "stages" (or series of vibrations of the concrete mass), with each "stage" affecting only a portion of the total thickness of the concrete mass. it is another object of the present invention to provide a method and apparatus for placing concrete slabs of the character described wherein the final "stage" of vibration produces a surface of the concrete mass which is substantially uniform as to wetness and other characteristics which are critical to the finishing process.

Another objective of the invention is to provide a method and apparatus of staged vibration of concrete in which variably controlled vibrations are introduced into or upon the concrete mass in successive stages so as to cause the elevation of said boundary layer, (or more specifically, the height of the

sufficiently-consolidated, relatively drier, uncured concrete mass) to rise at each "stage", with the number of vibration stages applied to a particular concrete mass being determined by the thickness of the mass and other physical characteristics thereof.

It is another object of the present invention to provide a method and apparatus for placing a concrete slab of the character described wherein the first vibrating "stage" causes the

formation of a layer of relatively drier, relatively stiffer, and relatively more consolidated concrete which extends from adjacent the sub-base of the concrete mass to a finite, definable

elevation above said sub-base; wherein the second vibration "stage", if required, causes the thickness of said layer of relatively drier, relatively stiffer, and relatively more consolidated concrete to increase, thereby moving the boundary layer upwards toward the surface of the concrete mass, and correspondingly decreasing the thickness of the relatively less dry, relatively less stiff, and relatively less consolidated concrete between the boundary layer and the surface of the concrete mass; and wherein additional successive "stages", if required, cause a further thickening of the layer of sufficiently consolidated concrete, until nearly the entire mass of concrete becomes essentially one consolidated, homogeneous mass. it is another object of the present invention to provide a method and apparatus of the character described in which the number of "stages" of vibration required to effect a single consolidated, homogeneous concrete mass is dependant upon the thickness and the physical characteristics of the slab being constructed, with thicker slabs generally requiring more "stages" of vibration than less thick slabs.

A further objective of the invention is to provide a method and apparatus of determining the location of the boundary layer between the relatively dry, firm, consolidated concrete in the lower portion of the concrete mass and the relatively wet, soft concrete in the upper portion of the concrete mass, so that the vibrational characteristics such as frequency, amplitude, and duration can be adjusted in order to cause the boundary layer to assume a uniform depth beneath the surface of the concrete mass. A further objective of the invention is to provide a method and apparatus of staged vibration of concrete in accordance with the preceding objectives in which the staged, stepped or phased vibration procedure described in the preceding objects results in migration of water to the surface of the concrete mass, and wherein the accumulated water on the surface of the concrete mass can be removed by mechanical means (such as by vacuuming), thus providing a uniform surface to the slab which enables surface-finishing operations to be advantageously performed automatically by machine.

Another object of the invention is to provide a method and apparatus of the character described which is operationally effective for use in any concrete slab of conventional thickness in various conditions, including interior slabs for buildings; slabs that may be either on grade or elevated; slabs for

highways, bridges, sidewalks and the like; and slabs either of single thickness or integrally or monolithically topped, thus enabling the unique method to be utilized with many concrete structures.

These together with other objectives and advantages which will become subsequently apparent reside in the details of

construction and operation as more fully hereinafter described and claimed, reference being made to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic sectional view of a concrete slab under construction immediately after the concrete mass has been poured;

Figure 2 is a schematic sectional view of the concrete slab of figure 1 shown a short time after the concrete mass has been poured;

Figure 3 is a schematic sectional view of the concrete slab of figure 1 shown during the first stage of vibration using the present invention;

Figure 4 is a schematic sectional view of the concrete slab of figure 1 shown immediately after the first stage of vibration using the present invention; Figure 5 is a schematic sectional view of the concrete slab of figure 1 shown during the second stage of vibration using the present invention;

Figure 6 is a schematic sectional view of the concrete slab of figure 1 shown during the final stage of vibration using the present invention; Figure 7 is a perspective view showing a plate vibrator apparatus used in the present invention;

Figure 8 is side elevation showing a mechanical probe used in a modification of the present invention;

Figure 9 is a side elevation showing a sled probe used in a modification of the present invention; Figure 10 is a perspective view of the apparatus of the present invention showing the vibrator apparatus supported from above;

Figure 11 is a side elevation of a modification of the vibrator apparatus of the present invention showing a submerged vibrating plate; and

Figure 12 is a side elevation of a modification of the present invention showing an adjustable vibrator structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 of the drawings illustrates a concrete mass (generally indicated "M" in the figures) which may be in the form of a slab as the concrete has been poured into a form (not shown) or the like from any suitable source onto a slab sub-base B. The concrete mass M typically includes aggregate, cement, water and other additives which may conventionally be employed in concrete slabs. When the concrete mass M is initially poured, as illustrated in Figure 1, the aggregate, cement, water and other materials incorporated into the concrete are typically randomly distributed throughout the thickness of the concrete mass M between the sub-base B and the exposed top surface 1 of the concrete slab. At the instant at which the concrete is mass M is first poured, virtually none of the concrete mass is sufficiently consolidated and dry enough for purposes of finishing the top surface 1 of the slab. Also, at the instant at which the concrete mass M is first poured, there typically exists variations in the moisture content and degree of consolidation (i.e. density) of the concrete mass M from one point to another over the entire volume of the concrete mass M. Such variation in consistency of poured concrete is not crucial to the operation of the present invention, but, as will be appreciated by those skilled in the art, is an inherent property of randomly mixed concrete.

Referring now to figure 2: After the concrete mass M has been poured onto the sub-base B into the form of a slab, the weight of the aggregates which comprise the concrete mass naturally push downward toward the sub-base B. The aggregates, being of relatively high density, begin to squeeze water and entrapped air out of the concrete mass M. Because there is more pressure near the bottom 2 of the slab than near the top 1 of the slab, more of the water and entrapped air is initially squeezed out of the concrete mass near the bottom of the slab than near the top of the slab, thus resulting in relatively more consolidated, relatively more firm and relatively drier concrete M1 near the bottom 2 of the slab, and relatively less consolidated,

relatively less firm and relatively less dry concrete M2 nearer the top 1 of the slab.

At the surface 1 of the concrete slab there develops a finishing zone 7 which preferably is no more than 1/4 inch thick. In the finishing zone 7 migrated water may collect throughout the placing operation. Also, finishing operations (which will be described in more detail later) may be used which effect a relatively higher concentration of "fines" and "superfines", and a relatively lower concentration of aggregates in the finishing zone 7 than in the rest of the concrete mass M. Between the relatively more consolidated, relatively more firm and relatively drier concrete M1 near the bottom 2 of the slab and the relatively less consolidated, relatively less firm and relatively less dry concrete M2 nearer the top 1 of the slab, is a boundary layer L. For purposes of understanding the present disclosure, the boundary layer L may be interpreted as

representing the line (or zone) below which the concrete mass M1 is sufficiently consolidated, firm and dry to effect the desired concrete curing rate and properties, and immediately above which line the concrete mass M2 is not sufficiently consolidated, firm and dry to effect the desired concrete curing rate and

properties. Further, it should be understood that the boundary layer L represents a line (or zone) through the concrete mass M wherein the concrete mass at all points along the boundary layer L is of substantially similar, consolidation, firmness and dryness. In practice the boundary layer L may be either a very narrow line (for example as exists after a plastic concrete mass is vibrated) or a zone having a measurable vertical width (for example as exists at the instant a concrete slab is initially poured). As will be appreciated by those skilled in the art, because of the inconsistencies inherent in the mixing and pouring of concrete, the boundary layer L which naturally occurs in a newly poured slab is notoriously uneven, as illustrated in figure 2. The unevenness of the boundary layer L may vary due to uneven concentrations of aggregate, or pockets of water, etc. in the poured concrete mass M. It will further be appreciated by those skilled in the art that the curing rate (and, therefore, the strength and consistency) of the concrete mass M will normally vary depending upon the depth of the boundary layer L below the top surface 1 of the slab. More specifically, in a given vertical segment of the concrete slab, the greater the depth below the surface 1 to the bottom of the insufficiently

consolidated, insufficiently firm and insufficiently dry concrete mass M2, the longer the curing time for that particular vertical segment of the concrete slab.

Referring now to figure 3: A vibrator apparatus 3 capable of introducing vibrations into the concrete mass M moves across the top surface 1 of the slab in the forward direction (indicated by arrow 4 in the figures). As the vibrator apparatus 3 is

activated, it introduces vibrations into the concrete mass M beneath the vibrator apparatus, which causes water and air entrapped inside of the concrete mass M to migrate upwards towards the top surface 1 of the slab. As the water and air migrate upward due to the vibrations, the depth of the relatively more consolidated, relatively more firm and relatively drier concrete M1 near the bottom 2 of the slab rises, and, correspondingly the elevation of the boundary layer La rises. As illustrated in figure 3, the boundary layer L ahead of the vibrator apparatus 3 remains substantially unchanged (i.e. uneven and at a relatively lower elevation). It has been found that, due to internal friction within the concrete mass M as well as the geometric diffusion of the vibrational energy, the farther away from the vibrator apparatus, the less the vibrations are felt and the less the effect of the vibrator apparatus.

Accordingly, the vibrations more profoundly affect the concrete mass beneath the vibrator apparatus 3 than concrete mass distant to the vibrator apparatus 3. By advantageously adjusting the frequency of the vibration, the amplitude of the vibration, and/or the duration of the vibration (i.e. by varying the forward speed of. the vibrator apparatus 3) so as to selectively effect the consolidation of the concrete mass, the depth of the boundary layer La beneath the vibrator apparatus 3 can be correspondingly adjusted. Sensors 5 in communication with the vibrator apparatus 3 monitor the instantaneous depth of the boundary layer L beneath the vibrator apparatus 3. In operation the sensors 5 provide feedback data to a processing unit 6 which determines the depth and profile of the boundary layer L and which adjusts the frequency of the vibration, the amplitude of the vibration, and/or the duration of the vibration (i.e. by varying the forward speed of the vibrator apparatus 3) as necessary to effect the desired profile of the boundary layer La. Figure 4 illustrates the condition of the concrete slab after the vibrator apparatus has completed a first pass or first "stage" of vibration of the concrete mass M. As contrasted with the characteristic of the slab prior to the first stage (as

illustrated in figure 2), the volume of the sufficiently

consolidated, sufficiently firm and sufficiently dry concrete mass M1 is greater, and the profile of the boundary layer La is more flat, after the first stage of vibration is completed (as illustrated in figure 4).

Referring now to figure 5: After the boundary layer La has been raised and somewhat evened out by the first pass or "stage" of vibration, the vibrator apparatus 3 may then be used for a second pass or "stage" of vibration, as shown in figure 5, to further raise the boundary layer Lb. As will be appreciated by those skilled in the art, by introducing controlled vibrations into the concrete mass M in the manner described above, the consolidation and drying of the concrete mass M is expedited relative to that which would naturally occur from stagnant settling of the concrete mass. In addition to more rapidly consolidating and drying the concrete mass M, the structural integrity of the slab is improved. The structural integrity of the slab is improved by use of the present invention due to the improved consistency of consolidation, (represented by the substantially horizontal orientation of the boundary layer Lb), and due to the expedited migration (and subsequent removal) of water from the concrete mass which advantageously results in less entrapped water and air pockets in the concrete slab.

Referring now to figure 6: In the preferred embodiment of the invention, upon completion of a final "stage" of vibration or a final pass of the vibrator apparatus across the surface 1 of the concrete slab, the depth of the sufficiently consolidated, sufficiently firm and sufficiently dry concrete M1 extends from the bottom of the slab 2 to (or nearly to) the finishing zone 7 at top surface of the concrete slab 1. Typically, the water which had migrated toward the top of the slab 1 may accumulate in the finishing zone 7, and may subsequently simply evaporate, run off the slab due to gravity, be pushed off the slab by the vibrator apparatus 3, be vacuumed, or otherwise removed.

It may be appreciated from an understanding of the foregoing that by using a method and apparatus of placing concrete in accordance with the disclosed invention, the boundary layer L, (or more specifically the top of the sufficiently consolidated, firm and dry concrete mass M1), is evenly brought up towards the top surface of the concrete slab 1. Because the boundary layer L, (or more specifically the top of the sufficiently consolidated, firm and dry concrete mass M1, is evenly brought up towards the top surface of the concrete slab 1), the entire top of the slab 1 (or more specifically, the finishing zone 7) becomes in condition for finishing operations at substantially the same time. In the preferred embodiment of the invention, the boundary layer L is so evenly brought upwards toward the top surface of the concrete slab 1 that the depth of the boundary layer Lc does not vary by more than 1 inch after completion of the final stage of

vibration.

The present invention not only expedites the consolidation and drying of the relatively deep pockets of moist and unconsolidated concrete by applying vibrational energy directly above such areas, but it also restricts the premature drying and hardening of relatively shallow areas of moist and unconsolidated concrete by reducing the vibrational energy imparted into such shallow areas. It may be appreciated by those skilled in the art that if constant vibrational forces were equally imparted into all areas of a heterogenous concrete mass, the boundary layer would approach the surface of the slab earlier in some areas than in other areas, thus having the undesirable effect of causing "hard spots" in the concrete mass. Hard spots in concrete typically cause uneven curing, cause cracking of the slab, increase the difficulty of finishing operations, virtually precludes the use of automatic finishing equipment, and significantly reduce the structural strength of the slab. By adjusting the vibrational energy imparted into various areas of the concrete mass M so as to evenly bring the boundary layer L towards the surface of the slab 1, a concrete slab made with the method and apparatus of the present invention has fewer (or no) hard spots, is more easily finished, has fewer cracks, and is structurally more strong than concrete slabs produced using either uncontrolled vibrations or using no vibrational input.

A vacuum water removal system (not shown) may be provided comprising a vacuuming device which employs a rolling or track-like device attached to the vibrating apparatus. Such a vacuuming device preferably includes a means of imposing a vacuum within a rolling cylinder, the exterior surface of the cylinder being porous and composed of a material through which water, but not the other materials composing concrete, could freely pass. The exterior surface of the vacuum enclosing cylinder is kept clear of accumulated materials by a scraper which is in contact with the surface at some time during each rotation of the cylinder. The vacuum is applied to the porous surface only when that surface is in contact with the surface of the concrete mass. The surface speed of the rolling cylinder is preferably made to match the speed of the vibrator apparatus relative to the surface of the concrete mass.

It will be appreciated from an understanding of the above disclosure that a concrete slab placed in accordance with the method and apparatus of the present invention produces a top surface 1, and finishing zone 7, of uniform physical character over the entire area of the slab. Furthermore, because of the consistency of the physical character of the entire area of the surface of the slab, finishing operations may be performed automatically by machine. Thus, this method and apparatus for placing concrete by staged vibration uniquely produces a uniform surface condition which allows the finishing of the top surface to be performed automatically by machine without the problemswhich typically hinder prior automatic finishing efforts in concrete slabs placed by prior methods and apparatuses. The disclosed staged vibration method and apparatus for placing concrete is effective due to the reaction of concrete to

vibration. During vibration, the water, air and certain finer and lighter materials migrate upward, with the materials' migration being affected by the characteristics of the vibration including the amplitude, frequency and duration of the vibration. The characteristics of the vibration are adjusted in the present invention to consolidate the relatively less consolidated, relatively less firm and relatively less dry concrete M2 near the top 1 of the slab at a controlled rate.

In addition to controlling the profile of the boundary layer La and Lb by adjustments to the frequency, amplitude and duration of the vibration, the effect of the vibration is also dependent upon the shape, orientation and configuration of a surface (or surfaces) of the vibrator apparatus 3 which is in contact with the concrete mass M and which imparts the vibrations to the concrete. Using this invention, when a horizontally placed concrete mass M is deposited on a prepared surface (i.e. sub-base B),

consolidation of the concrete mass M occurs in stages to bring water to the surface for removal in a manner that finishing operations, if necessary, (or curing, if no finishing operations are required), may immediately follow behind the concrete placing operations at a uniform rate.

Because the consolidation of the concrete mass M is expedited, and because the slab is of substantially uniform consolidation and dryness from the top of the sub-base B to the bottom of the finishing zone 7, using the method and apparatus in accordance with the present invention a concrete slab can be placed without using wire mesh (which is commonly imbedded inside of concrete slabs so as to reduce the undesirable affects of uneven drying and curing rates between the top and bottom of the slabs).

The vibration produces an boundary layer La and Lb between the relatively consolidated and relatively unconsolidated portions of the mass M1 and M2, respectively, with the boundary layer preferably being maintained as nearly as possible at a uniform depth below the top surface 1 of the slab.

The vibrator apparatus used in the preferred embodiment of this invention differs from prior vibrators by including a structure(i.e. sensors 5) which enables the location of the boundary layer L relative to the surface of the slab 1 to be determined with an associated feedback control system (i.e. processor unit 6).

Sensors 5 may be mounted on or adjacent to the vibrator apparatus 3. The sensors 5 sense the depth of the boundary layer L, La or Lb, and, through suitable feedback data processing equipment (i.e. processor unit 6), the controllable features of the vibrator apparatus 3 are adjusted as necessary to leave behind a boundary layer La and Lb at a substantially uniform depth below the top surface 1 of the slab. The sensors 5 may be advantageously positioned to determine the vertical location of the boundary layer L, La and Lb at locations in front of, behind or directly beneath the vibrator. The sensors 5 are preferably mounted in a manner such that the vibrations will not adversely affect performance of the sensors Further, the sensors 5 are preferably provided in sufficient numbers and at sufficient locations to sense the location of the boundary layer L at as many sites relative to the vibrator apparatus 3 as may be necessary to produce the desired location and profile of the boundary layer La and Lb.

The characteristics of the vibrator apparatus 3 which are controlled include the frequency, amplitude and focus or

direction of vibrating energy. In addition the forward speed of the entire vibrator apparatus 3 may be controlled. The vibrator apparatus 3 may comprise means for adjusting the character of the vibrations to enable vibrations to be focused to a particular depth either by independent adjustment of individual vibrators or by adjustment of a plurality of vibrators in concert with each other, thus providing additional control of the depth of the consolidation of the concrete by the vibrator apparatus. One type of vibrator apparatus that can be used is a plate vibrator 3a (as shown in figure 7) having either one or a plurality of moving pistons or rotating eccentric vibrators 8 mounted thereon, with each vibrator 8 being individually

controlled by its own sensor 5a and processor unit 6a (or by a single multifunctional processor unit, not shown) which reads the conditions in front of the plate 9. As the vibrators 8 vibrate, the unbalanced dynamic forces of the vibrators 8 are imposed upon the plate 9, which transmits the forces directly into the concrete mass M as vibrations. Additional sensors 5b may be mounted behind the plate vibrator 3a in order to sense the results of the vibration. The plate vibrator 3a can be pulled or moved by a winch which moves at a speed that is also controlled by the sensor's (5) data.

The sensor 5 may rely on mechanical probes, submerged sleds or skis, or acoustic characteristics, penetrating radar or similar technology for determining the depth of the boundary layer.

Typically, mechanical sensors are less expensive than more sophisticated probes.

Several alternative arrangements are suitable for supporting the vibrator apparatus above or on the top surface of the concrete slab 1, including, but not limited to the following: support from concrete forms; support from support arms mounted upon various types of peripheral equipment; support from skis riding on tracks; support from skis or sleds submerged in the concrete mass and riding on the boundary layer L between the top and bottom concrete portions M2 and M1, respectively; or the vibrator apparatus 3 may be supported by any means which will allow the vibrator apparatus 3 to move in a manner to produce the desired staged vibration.

One type of sensor which may be used in the present invention is a mechanical probe 5c, as illustrated in figure 8. A piston 11 is pivotally connected to a pivot arm 12, with the bottom of the pivot arm being provided with a flat plate 13 which comprises the sensing surface of the probe 5c. The flat plate 13 determines the location of the boundary layer L between the relatively more consolidated, relatively more firm and relatively drier concrete M1 near the bottom 2 of the slab and relatively less

consolidated, relatively less firm and relatively less dry concrete M2 near the top 1 of the slab. The force required to push the flat plate 13 downward to the location of the boundary layer L is measured. Calibration of the force indicative of the boundary layer L may preferably be based on a determination of the force required to push against a sufficiently consolidated, sufficiently firm and sufficiently dry concrete mass, and this data preferably forms the basis of the feedback control system. An alternative sensor which may be used with the present

invention is a sled probe 5d, as illustrated in figure 9. The sled 14 is mounted on a pivoting support arm 15 extending from the beam 16. The sled has a substantially flat bottom surface 14a that is dragged along by the forward moving beam 16. The force required to keep the sled 14 at the correct penetration into the boundary layer L is determined and forms the reference point for the feedback control system.

It will be appreciated that the by employing staged vibration in accordance with the above described invention, a system is provided that induces water from the concrete mass to the surface of the slab in such a way that drying of the surface advances at a uniform rate. Those skilled in the art will appreciate that such uniform rate of drying of the slab is an essential first step toward the facilitation of automatic or robotic finishing of concrete slabs.

In addition, this enables concrete placement to be completed much faster than prior methods of concrete placement, depending on temperature and weather conditions.

As will be appreciated from a review of the above disclosure, the present invention provides a method and apparatus for placing concrete slabs which eliminates the need for various additives (such as drying agents, accelerators, plasticizers, etc); which results in more uniform slab density; which has a flatter finished surface, less shrinkage, less curling and fewer cracks; and which requires the use of less manpower, than is typically necessary with prior concrete placing methods and apparatuses. This disclosed method and apparatus for placing concrete slabs can be used in conjunction with common form systems or laser screeding.

The vibrating apparatus 3 may ride on reinforcing bars, on an independent base, on metal forms (as illustrated in figure 10), or other supporting means.

While the preferred embodiment of the invention comprises a vibrating apparatus 3 which applies vibrational forces directly to the surface 1 of the concrete slab (for example, by plate 9 of plate vibrator 3a, as shown in figure 7), in cases where the concrete mass M is particularly thick it may be desirable to impose the vibrational forces directly to the concrete mass M at a finite distance below the surface 1 of the concrete slab.

Figure 11 illustrates a modified vibrator apparatus 3b which is capable of applying vibrations directly to the concrete mass M beneath the surface 1 of the concrete slab. The modified vibrator apparatus 3b is provided with wheels 18 which ride upon rail(s) 19. A vibrating arm 20 is pivotally connected to an eccentric drive motor 21 on one end, and attached to a tamping rod 22 which extends below the surface 1 of the concrete slab at its opposite end. A substantially horizontally oriented

vibrating plate 23 is attached to the bottom of the tamping rod 22. When the eccentric drive motor 21 is activated, the

vibrating plate 23 vibrates, thereby applying vibrational forces directly to the concrete mass M beneath the surface 1 of the concrete slab.

It will be appreciated from and understanding of the above disclosure that, regardless of whether the vibrational forces are applied directly to the surface 1 of the concrete slab (as illustrated in figures 3, 5, 6 and 7) or directly to the concrete mass M beneath the surface 1 of the concrete slab (as illustrated in figure 11), the disclosed method and apparatus of applying vibrations to the concrete mass M must occur while the concrete mass M is plastic (i.e. while the concrete mass M is uncured). In the preferred embodiment of the invention, the final finished concrete surface of the slab is related dimensionally to a reference device or system. Such a reference system may comprise either the fixed rails (such as rails 19 in figure 11) or fixed forms (such as metal form 17 in figure 10), or a laser system in fixed relationship to the sub-base B (not shown), or similar means.

A modified vibrating apparatus 3c is illustrated in figure 12. The vibrating apparatus 3c shown in figure 12 comprises a flexible structure 30 which moves vertically and/or horizontally relative to the surface upon which it rests, the structure typically being supported by wheels 81 which roll upon the sub-base B, or by skids (not shown) which rest upon the structural steel or formwork 31 of the installation. The vertical locations of the sensors 5 and the vibrating surface 32 (or surfaces) relative to the structure 30 are preferably fixed. The entire structure 30 adjusts vertically in response to data supplied to the processor unit 6 by an optical sensor 40 or other instrument which detects the vertical location of the reference device or system relative (for example the formwork 31) to the structure 30, maintaining a predetermined vertical relationship with that device or system.

The processor unit 6 receives data from the sensors 5 regarding the elevation of the boundary layer L, as well as data pertaining to the relative elevation of the reference device (i.e. formwork 31) from the optical sensor 40, and adjusts the vibrating

characteristics of the vibrating apparatus 3c, the forward speed of the structure 30 and the relative locations of the vibrating surface(s) 32 so as to produce a boundary layer L which is asnearly parallel to the desired surface 1 of the concrete slab as possible.

While the foregoing describes the use of the apparatus and method of the present invention in placing a horizontal concrete slab of substantially constant thickness using a single pour of concrete, it should be understood that the application of this method and apparatus to the placing of slabs having substantially flat inclined top surfaces, and to the placing of slabs on top of uneven or inclined sub-bases are within the scope of the present invention. In addition, the described method and apparatus also has application to the placing of concrete slabs which have integrally bonded toppings, wherein a second pour of concrete (i.e. topping) may be introduced on top of a first concrete pour. In the placing of a concrete slab having an integrally bonded topping, the second concrete pour is preferably made after

initial series of staged vibrations have been introduced to the first-poured concrete in accordance with the present invention, but before the boundary layer reaches too close to the top of the first-poured concrete mass. The foregoing is considered as illustrative only of the

principles of the invention. Many other variations are possible, for example:

A single vibrator apparatus 3 may be provided with both surface-vibrating plates (as illustrated in figure 7) and with submerged vibrating plates (as illustrated in figure 11);

A single vibrator apparatus 3 may be provided with either a single sensor 5 or with multiple sensors 5;

The Vibrating Surface 9 or 23 may comprise a flat plate of any shape which is either in contact with the surface of the concrete mass or is submerged therein; The vibrating surface 9 or 23 may comprises a plate having a single face in contact with the surface of the concrete mass, or may comprise an object of any shape which is submerged within the concrete mass; When multiple vibrating surfaces 9 or 23 are used in a single vibrating apparatus 3, they may be constructed in such a way as to permit independent adjustment relative to each other; The vibrator apparatus 3 may be of any type, provided the characteristics of either amplitude, frequency, or duration of vibration, or any combination thereof, can be controlled over the ranges which are necessary^ for the proper control of the concrete consolidation;

The vibrator apparatus 3 may be either electric, hydraulic or air powered;

When a piston type sensor 5c is employed, the sensing plate 13 may be either a flat or curved surface, and the piston may be either electric, mechanical, air, or hydraulic powered; When a sled or ski type sensor 5d is employed, the probe can be either electric, mechanical, air or hydraulic powered;

Ultrasonic, acoustic or ground penetrating radar or other similar electronic systems may be employed as sensors 5;

The vibrating apparatus 3 may be supported by wheels on the sub-grade, formwork or screeds; or it may be supported directly by and slide upon the formwork or screeds; and

The reference device or system may be any device or system which can provide the vibrator apparatus with a means of determining the vertical location of the desired surface of the concrete slab; Such a reference device or system may comprise either a taut string, a laser beam, a wooden or metal form or a pipe screed or any other device or system which can provide similar information.

Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and, accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention. Accordingly, the scope of the invention should be determined not by the embodiment illustrated, but by the appended claims and their legal equivalents.

Claims

1. A method of placing concrete comprising the following steps: depositing a plastic concrete mass to form a concrete structure, said concrete structure having a bottom surface and a

substantially flat top surface; introducing into said concrete structure a first series of vibrations; said first series of vibrations causing a first segment of said plastic concrete mass to become relatively more dense than a second segment of said plastic concrete mass; wherein said first segment of said plastic concrete mass extends vertically from said bottom surface of said concrete structure to a manipulatable definable boundary layer, said manipulatable definable boundary layer being below an elevation of said top surface of said concrete structure; and wherein said second segment of said plastic concrete mass extends vertically from said manipulatable

definable boundary layer to said top surface of said concrete structure; and wherein said first series of vibrations causes said manipulatable definable boundary layer to become located at a first position, said first position being between said first segment of said plastic concrete mass and said second segment of said plastic concrete mass.

2. The method according to claim 1 further comprising: introducing into said concrete structure a second series of vibrations subsequent to said first series of vibrations; wherein said second series of vibrations causes said manipulatable definable boundary layer to become located at a second position, said second position being higher than said first position.

3. The method according to claim 2 further comprising: determining a location of said first position of said

manipulatable definable boundary layer; and controlling a physical characteristic of said second series of vibrations so as to cause said manipulatable definable boundary layer to be more closely parallel to said top surface of said concrete structure at said second position than at said first position.

4. The method according to claim 3 wherein said step of

introducing said first series of vibrations into said concrete structure comprises vibrating a first tamping member; wherein said first tamping member is in direct contact with said plastic concrete mass; and wherein said first tamping member is vertically above said manipulatable definable boundary layer; and further comprising horizontally moving said first tamping member concurrently with said step of introducing into said concrete structure said second series of vibrations; and wherein said controlled physical characteristic of said second series of vibrations comprises frequency, amplitude or duration;

and wherein said step of determining a location of said first position of said manipulatable definable boundary layer comprises generating feedback data;

and wherein said step of controlling a physical characteristic of said second series of vibrations so as to cause said

manipulatable definable boundary layer to be more closely parallel to said top surface of said concrete structure at said second position than at said first position comprises the steps of processing said feedback data and adjusting said physical characteristic of said second series of vibrations in response to said feedback data;

and wherein said step of determining a location of said first position of said manipulatable definable boundary layer, and said step of processing said feedback data, and said step of adjusting said physical characteristic of said second series of vibrations are each accomplished concurrently with said steps of

horizontally moving said first tamping member.

5. The method according to claim 4 wherein said first tampingmember is at immersed within said second segment of said plastic concrete mass.

6. An apparatus for placing a plastic concrete mass forming a concrete structure, said concrete structure having a bottom surface and a substantially flat top surface having an area within a definable perimeter, comprising: means for introducing into a concrete structure a first series of vibrations, wherein said first series of vibrations causes a first segment of said plastic concrete mass to become relatively more dense than a second segment of said plastic concrete mass; said first segment of said plastic concrete mass extending vertically from said bottom surface of said concrete structure to a manipulatable definable boundary layer below an elevation of said top surface of said concrete structure; and said second segment of said plastic concrete mass extending vertically from said manipulatable definable boundary layer to said top surface of said concrete structure; and wherein said first series of vibrations causes said

manipulatable definable boundary layer to become located at a first elevation such that said first segment of said plastic concrete mass is below said first position and said second segment of said plastic concrete mass is above said first position .

7. The apparatus according to claim 6 further comprising: means for introducing into said concrete structure a second series of vibrations subsequent to said first series of

vibrations; wherein said second series of vibrations causes said manipulatable definable boundary layer to become located at a second elevation, said second elevation of said manipulatable definable boundary layer being higher than said first

elevation.

8. The apparatus according to claim 7 further comprising: means for determining a location of said first elevation of said manipulatable definable boundary layer; and means for controlling a physical characteristic of said second series of vibrations to cause said manipulatable definable boundary layer to be more closely parallel to said top surface of said concrete structure at said second elevation than at said first elevation.

9. The apparatus according to claim 8 wherein said means for introducing said first series of vibrations into said concrete structure and said means for introducing said second series of vibrations into said concrete structure comprise a tamping member; wherein said tamping member is in direct contact with said plastic concrete mass; and wherein said tamping member is vertically disposed above said manipulatable definable boundary layer; and further comprising means for horizontally moving said tamping member concurrently with introducing into said concrete structure said second series of vibrations; and wherein said means for determining a location of said first position of said manipulatable definable boundary layer comprises means for generating feedback data; and wherein said means for controlling a physical characteristic of said second series of vibrations comprises means for

concurrently processing said feedback data while horizontally moving said tamping member relative to said concrete structure, and means for concurrently adjusting said physical characteristic of said second series of vibrations in response to said feedback data while horizontally moving said tamping member relative to said concrete structure.

10. The method according to claim 3, wherein said manipulatable definable boundary layer is continuous between two spaced points beneath said perimeter of said area of said top surface, and wherein said means for controlling a physical characteristic of said second series of vibrations to cause said manipulatable definable boundary layer to be more closely parallel to said top surface of said concrete structure at said second elevation than at said first elevation limits the maximum difference between a depth below said top surface to said first point and a depth below said top surface to said second point to less than one inch.

11. A method of placing concrete comprising the following steps: depositing an initially substantially homogeneous plastic concrete mass to form a concrete structure, said concrete structure having a bottom surface and a substantially flat top surface. introducing into said concrete structure a first series of vibrations; said first series of vibrations causing a first segment of said initially substantially homogeneous plastic concrete mass to become relatively more dense than a second segment of said initially substantially homogeneous plastic concrete mass; wherein said first segment of said initially substantially homogeneous plastic concrete mass extends

vertically from said bottom surface of said concrete structure to a manipulatable definable boundary layer, said manipulatable definable boundary layer being below an elevation of said top surface of said concrete structure; and wherein said second segment of said initially substantially homogeneous plastic concrete mass extends

vertically from said manipulatable definable boundary layer to said top surface of said concrete structure; and wherein said first series of vibrations causes said manipulatable definable boundary layer to become located at a first position, said first position being between said first segment of said initially substantially homogeneous plasticconcrete mass and said second segment of said plastic concrete mass; and further comprising introducing into said concrete structure a second series of vibrations subsequent to said first series of vibrations; wherein said second series of vibrations causes said manipulatable definable boundary layer to become located at a second position, said second position being higher than said first position; and determining a location of said first position of said manipulatable definable boundary layer; and controlling a physical characteristic of said second series of, vibrations so as to cause said manipulatable definable boundary layer to be more closely parallel to said top surface of said concrete structure at said second position than at said first position.

12. A method of placing concrete comprising the following steps: depositing an initially substantially homogeneous plastic concrete mass to form a concrete structure, said concrete structure having a bottom surface and a substantially flat top surface having a definable area within a first perimeter; introducing into said concrete structure a first series of vibrations; said first series of vibrations causing the formation of a manipulatable definable boundary layer within said plastic concrete mass, said manipulatable definable boundary layer having a finite thickness as measured perpendicular to the plane of said substantially flat top surface; wherein said manipulatable definable boundary layer is continuous within a boundary layer perimeter defined by a vertical projection of said first perimeter on said manipulatable definable boundary layer; and wherein said boundary layer perimeter and said finite thickness describe a first volume, said first volume inscribing a boundary layer concrete mass segment; and wherein the firmness of said boundary layer concrete mass segment is constant throughout said first volume; said first series of vibrations further causing a first segment of said plastic concrete mass located between said manipulatable definable boundary layer and said bottom surface of said concrete structure to become relatively more dense than a second segment of said plastic concrete mass located between said manipulatable definable boundary layer and said top surface of said concrete structure; and said first series of vibrations further causing said manipulatable definable boundary layer to be disposed at a first average elevation; and further comprising introducing into said concrete structure a second series of vibrations subsequent to said first series of vibrations, said .second series of vibrations causing said manipulatable definable boundary layer to be disposed at a second average elevation; wherein said second average elevation is higher than said first average elevation; and wherein said step of introducing said first series of vibrations into said concrete structure comprises vibrating a tamping member, and said step of introducing said second series of vibrations into said concrete structure comprises vibrating said tamping member;

wherein said tamping member is disposed vertically above said manipulatable definable boundary layer;

and wherein said first tamping member is in contact with said second segment of said plastic concrete mass; and further comprising horizontally moving said tamping member relative to said concrete structure concurrently with said step of introducing into said concrete structure said second series of vibrations; and, after said step of introducing said first series of

vibrations into said concrete structure and concurrently with said step of horizontally moving said first tamping member relative to said concrete structure, determining a depth of said manipulatable definable boundary layer beneath said top surface; and generating feedback data during said step of determining said depth of said manipulatable definable boundary layer beneath said top surface; processing said feedback data concurrently with said step of horizontally moving said first tamping member relative to said concrete structure; and adjusting a physical characteristic of said second series of vibrations, concurrently with said step of horizontally moving said first tamping member, in response to said feedback data so as to cause said manipulatable definable boundary layer to be more closely parallel to said top surface of said concrete structure after said step of introducing said second series of vibrations into said concrete structure than before said step of introducing said second series of vibrations into said concrete structure; wherein said controlled physical characteristic of said second series of vibrations comprises frequency, amplitude or duration.