CA1048240A - Method of molding concrete - Google Patents

Abstract

ABSTRACT
The invention provides a method of and an apparatus for making a casting from a mass of dry particulate material and a liquid which co-acts with the dry material. It is particularly, though not exclusively, concerned with the production of concrete castings. In the method negative pressure is applied over a first portion of the surface of the dry particulate material, e.g. over one side of the material, and liquid is distributed over a second portion of that surface, e.g. over the opposite side of the dry material.
The negative pressure causes the particulate material to be compacted and draws the liquid into the particulate material.

Description

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ThLs invention relates to a method of producing concrete and other similar products.
As i~ well known, for a concrete product to be of good quality lt should be dense and void free, as strong as possible for a given cement content, have blemish-free and consistent surface colour and texture and be capable of productlon cleanly, consistently and economically.
It is in general the methods of mixing and proces3ing ; concrete materials which place distinct limitations on the forming and moulding techniques that can be employed, and this in turn markedly restricts the variety of finishes that can be achieved.
It ls an object of the invention to pro~ide a method of producing mechanically sound products of concrete, refrac-tory concrete, plaster or any similar material, rapidly, reliably and economically with a good quality finish for structural, decorative or other purposes.
According to the invention there is provided a method of molding concrete comprising subjecting a perfectly dry mass of particula~e material compr-lsing a mixture of cement and aggregate to subatmospheric pressure over a first portion of the surface of the mass while exposing a second portion of the surface of the mass to the atmosphere and distributing water over the second portion of the surface while continuing , the subatmospheric pressure, such that the entire mass is compacted and the water is drawn into and dispersed throughout the entire mass and such that the required water cGnten$ for binding the mass and activating the cement is provided to form a sound, strong integral, rigid concrete product.

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11l known tecllniqlles for ~he product1on of concrete castings, aggrega~-es are blended to ac.hleve a closely graded mix w~th cement. When adequate dispersion o the cement is attained water is introduced in sufficient quantity ;'. :

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: to nct-i.vate the cclllont an~ p:last.ici.se the mlxturc su~ficien-tly :for forl;lin~ purposes. (Tlle amount o:f water :intrc)duce~l to :
s~ic~se the mi~ will. vary according to the formin~
teCh r~ v~
employed alld ~ill va:ry consitlerably). It is ~
well established fact that concrete materials ~hlch contain ,,: ' .
as close to -the minimum amoun-t of watcr required to acti~ate ` the cement are best, but due to the n~ture Or the resulti.ng I l~ixture are e~tremely di.~ficult to ~orm a~d compact except ~ ~ under h.i~h press~re such as employed in a press.
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; o In contrast, in ~ ~orm of the present invention, aggrega-tes are closely blencled in ~ perfec-tly dry condition . ¦ and cemeIlt added and clispersed throughout the mix. ~he mix i I is then placed ancl levelle~ in a suitable mould ~hich has r` ~ means for applying a nega-tive pressure at its basa. The ¦ ~5 negative pressure is then app~ied, whereon the mixture i.s . I compacted to a solid ~oid-~reo mass which i~ only micro ` , scopically porous to air or wate.r. (I-t will be readily .~ appreciated that the degree o~ porosity will depend on the ~ineness o~ the closest screened material ingredient which . 20 will generally be the cemerlt). Water is then dispersed by .
¦- suitable means over the compacted mixture in suf~iclent . ~ .
, I quantity ~or it to be drawn into and through the material.
. ~ The result OI this action is to initially bind the material . ~ and activate the cement~ ~On completion the product is ~i 25 removed b~ sui-table means on to a pallet and allowed to ::1 . set.
The compaction e~ect on the mixture resulting : 1 ~rom the application of negative pressure leaves only room ; ~or the minimum water necessary to activate the cementS this , . . .
1 30 water only remaining in the mi~ture by capillary attraction '`'I , ,; ' .

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therelo, ~lle n~gal;ive l~:r-~r.sllre hav:ing dra~n a].l cxcess water ~llrougll an~1 out o:f th~ mixturcD
q'}l~ r~si~ o5 ~)l^o~ C~ v~lri~d l~y t~ rcldin~ 0 -the Inixture used to any required specifica~ion within a range ~hich is dependent on th~ aggrega-te being used in striot relationsilip to poro~ity~
Some examples of the invention will nol~ be described in more detail ~ith reference to the accompanying dral~:ings7 ~herein: `
Figure 1 is a perspective diagramlllatic view of an apparatus ~or carrying out the process of $he invention ` manually, Figure 2 is an exploded perspective view of a ~lodification of the device of Figure 19 ~igure 3 is a perspeet:ive view of an appara$us for carrying out the invention substantially automa-tically, Figure 4 is a side elevation of the apparatus of Figure 3, Figure 5 is a plan vie~ of the apparatus o~ Figure 3, - Figure 6 is a side elevation of a portion of the apparatus of Figure 3 showing parts of two moulds of the lower run of the mould train, and part of the means for driving the moul~ train, ~ `
Figure 7 is a diagrammatic side elevation showing a carrier ~or removing castings from the apparatus, 25 Figure 8 is a diagrammatic side elevation showing part of the means for distributing negative and positive pressure to the moulds, - Figure ~ is an end elevation corresponding to ~igure 8 and, - 30 ~igure 10 sho~s in plan view a detail o~ a means for delivering material into the moulds.
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F:Lgllre 1 showx an open top mou Id 1 hav:illg a b~s~ 2 w:it~ a m~sh 3 :Eor~ d o:f ~ire, pla~tics or other suita~le material placed over tlle base, The mesh derines with the bnse an array of channels. AJ.ternati.vely the mesh could be omi.-tted and -the base 2 provide~ with two sets of channels running at 90 to each other to ~orm an lntcr-connecting array of channels~ A. bore 4 is provided :In the base and this bore is connected by a pipe 5 a~d a branch pipe 6 to a ~acuum cylinder (not shown) malntained at between 20 i~l.Hg, and 28 in.I-~g. Between the cylinder and the mani-fold is a v~lve 7 for closing off the mould Erom the vacuum cylinder. The bore is also connected by the pipe 5 , I and a br~nch pipe 8 to a pressure cylinder (no-t shown) via ¦ a second valve 9 Eor closing of:E the mou].d ~rom the pressure ¦ 15 cylinder.
¦ Port].and cement (1 part) and closely graded granite (4 parts) are mixed together in a dry conditio~
~or a period su~ficient to ef~ect a fully blended mix. A
second mix is made up as above, ~ut consisti~g of white Portland cement (20 parts), colour pigment (1 part) and ., ~
- closely graded granite (~0 parts~, The two mixes are then j placed in separate dry storage containers or hoppers. It ~ will of course be appreci~ted that these mixtures are given I , by uay o~ example only.
~5 ` A wetted wet strength ~ilter paper allowing only the passage of air and watcr is arranged in the bottom of ~ -the mould so de~ining an array o~ passages below i~, (The ~ilter paper has been omitted ~rom the Figure to allow the . mesh 3 to be see~ he valve 7 i.s opened a~d the ~ilter 30 paper is dra~ tightly to the mould bottom configuration.

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~ Th~ r~ lr~l thicl~n~ss Or th~ second~ eolour~(l mix is ', sprinlclecl into thc mould and is immcdiately compacted by the pres~llre tlif-~erent;ial create~l ~y the ~uction of air i.IltO t~le V~CllUm cylind~r.
The fir~t, Imcoloured mix is now placed ln the mould and also co~np~cted by th~ above mentioned pressure di~-~ercntLal. '~he top surf'ace o~ the compactecl mix is now levelled ~ith the top surface edges o~ th~ mould and rolled smooth, The a~r flo~ rate throu~h the eo]npacted mix " 10 is lo~ as the cavlta~ion and air passages wi-thin the Inix havc bcen reduced to a size equal to that remain:Lng between ' ~
' the smallest closelvv compacted particlesO The ob~ect of ~' rolling the top surface smooth is to overcome the rapld i~ fall off o~ the compactin~ ef-feGt at the sur~ace due -to the reduction o~ the pressure differential, A quantity o~
water greater than 0035 of the cement content is now sprayed , , or floocled over the sur~ace of the concrete mix and is carrled b~ suction into a~d through the IlliX~ and excess ' , uater is carried out of the mix~ The rapidity o:~ thi~
'~ 20 sequence will be determined by the degree of vacuum and the ' resultant density o-~ the mix being proce~sed. ~en the ~ater has been dispersed through the mix, ~hich takes approximately , 30 seconds per 1" thickness for a dense mix, the mi~ is ,, .
~ vir,tually impervious to air or waterO
,' 25 After the water has ~een dispersed through the ~,'' mix, the negative pressure is allowed to continue to act ~'- for a shor-t time to remove any excess water from the mix, : - ~
The mould is now inverted on to a pallet, ~,~, the valve 7 closed the valve 9 opened to apply a pressure ~;;
', ~0 between 5 and 100 p. 9 .i. dependin~ on the casting size~
thiGkness and rapidity o~ e~ection required, , ~ , "" , , ., '.
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t~ assist in ~v~n reLease o~ ~he casting ~rom the mould.
The ~iltex paper can now ~e rcmoved from the casting OI' leCt on tlle produot for suri'ace protcctio~ up to time oY
sale or use, The method clescribed above can be m~dified to produce a patterned eE~ect on -th~ ~inished casl;ing~ For this pl1rpose a mask :is placecl over the ~ilter paper prior to the introduction o~ the coloured mix When the coloured n r~ ~sk~d mix is sprinkled in, there~ore, it on:ly Ialls on the-~N~rx~
area Or the -filter paper. rrhe màsk is then removed and a portion o~ tlle uncoloured mix sprinkled in to ¢over the ¦ areas o~ the ~ilter paper which were origi~ally masked. The rest o~ the uncoloured mix is then introduced. rrhe negative ~¦ pressure applied to the ~ilter paper retains the coloured mix in the areas where it was originally applied and prevenis the pattern bein~ disturbed when the uncoloured mix is introduced.
A further modi~ication, illustrated in Figure 2 ~ ~ makes it possible to produce a~ embossed e-f~ect on the ~inished casting. For this purpose a plate 10 is placed under the ~ilter paper 11 which plate has portiolls12 cut ~way to leave a pattern identical to that o~ a mi~sk 13 placed above the -~ilter paper. When the negative pressure is applied the ~ilter paper 11 con~orms to the shape o~ the , 25 plate 10 thus resulting in a greater $hickness in the ! finished casting in areas where the coloured mix is present and so ca~sing those areas to be embossed.
Figure 3 shows a machine which pc-rmits substantially automatic operation.
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! ac - ~ 7 z~o Tlle mac~l:ine con~l)r:i~cs a plura:Lity o~ moulds 20 pivotally connocted to one ~nol.hcr by pi~ots 22 to for~ an endless continuously Inoving tru:in ~:ith parallcl upper ~nd ~.ower horizontal runs. q'he ul1ders:ide o~ each mould has a longitudin~lly e~tending racls 2~ (see ~:i.gure 6) which enables th~ train o~ moukl -to 'be driYen by t~o toothed pinions 26 ~only one o~ whiell is shown) which enguge the ~lpper and lowcr runs re.specti.vely, The two pini.ons are driven by .
the same motor 27.
Negat:ive pre.ssure is distributed to all the moulds.
This is done by means o:~ a vacllum source connected to the ~ :
moulds by n1eans of two l'le~ible pipes 28 and 29 (see especially Figures 8 and 9) which are connected rcspectively to two o~ the moulds. Negative pressure is dis-tributed to the other moulds via ~urther pipes ~not shown) which '~
comlect together adjacen.t rnoulds. As the mould train , moves, the pipes are each alternately wound on to and off ' from a reel 30 in anti~phase to one ano-ther. In the '~. position illustrated the pipe 29 is almos-t i'ully wound on, ;,: 20 and the pipe 28 is almost ~ully ~ound of-~, 'Within one of the pipes 28 and,29 is a.~urther pipe (not ~isible) for istributing positive pressure to all the moulds~
Application of po.sitive and negative pressure to the ~ -'; individual moulds is controlled by a valve meohanism moun-ted ~ ~.
on the rear of each mould. Normally this allows negative ~, ~
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pressure to be applied~ and the negative pressure is only ..
'~ released and positive pressure applied when the valve operating ~lechanism 31 engages a rail 32 in the region where the blocks are to be ejected ~rom the moulds~ In .
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: practice -the lln(lerside of the ra:il i.s so shaped that the ne~at:i.ve pre.ss~rc is relcase(I ju~st before I;ho positive prcssure :Ls applied.
A main hopper 33 :L`or delivel^:ing unco:loured mix is positior1ed above the upper run O:e the mould -traln and matericll i.s i~ed from the hopper 33 into a delivery portion 33', '~he portlon 33' is d:i.viclcd :into ar1 upstream section 31~ and a down~tream section 36 (-the terms ~upstreaml' and "downstream" referring to the direction o:~ travel of the upper run of the mould train) and a devi.ce 38 i9 positioned adjacent the oul;let end of the upstream section 34 ~or sprinkling the mi~ on to a mould passing ber1ea-th the rnain hopper. In the em~ndi.ment illustrated this de~ice comprises a rod 39 carrying an elongate plate 40 e~rtending transversely o~ the direction of mould travel and ha~ing scal.loped edges 42. A motor driven cam 44 is provided .~or reciprocating the rod in a direction parallel to i.ts length. The outlet from the downstream section ~6 of the main hopper has no such sprin1~ling device and the mix discharges directly from that section in-to a mould passing beneath the hopper, An additional fixed hoFper (not shown) ~or the coloured mix is posi.tioned upstream of the main hopper and feeds mix into a container 48 (see especially Fig. lO) to maintain ;, :. the le~el of mix in that container approximately at a 2~ constant desired heigl1tO The container 48 is moun-ted to travel from an upstream location to a do~nstream location immediatel~J ~pstream of the main hopper and b~ck again.
~ ~ The contciiner has a ~iFe mesh base 50 and an array .: :

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of mov~lble scraper b:Lncl~s 51 posLt,iolled adjacl3nt the baseO
An ecocntric mech~nism 52 is provided to l:eciprocate -the scrnper -bl ad~s wherl rcq~li red, as ~lescribed below, -- I'ositiorled below -the base 50 is a pat;tern defining plate ~not visible ) which h;ls portions cut ~ y.
In opcration t;he ma{:hine, a Iil ter paper is ` , placed in each mould, ~`or example by hand, jllS t before it reaches the hopper Ior the colou-red mix. Alternatively the filter paper could be insertefl by sui-~,able mechanical means. As the mould wi th the fil~;er paper therein reaches, the container ~8 in its upstream position the container begins to be dri~ren alon~ synchronously l~i th the mould and ~i ,,ust above it. The container then moves down inl;o the mould and the ecce~itric ~echanism 52 begins to reciprocate the blades 51 thereby displacing coloured mi~ through the ~1ire mesh and thence through the cu t away portions o:E the pattern deEining plate. Coloured mi~ is thus deposited on the ~ ?
~ilter paper at the base o~ the mould in a pattern deIined by the said plate, As the container 48 reaches its downstream position it rises ~rom the mould and travels 1- .
bacl~ to its ups tream position under the :in~luence of a counter ~;
eight 49 connected to the container by wires ~9 ' . This operation ~ s repeated at a rate sùch -that coloured mix is deposited in all the moulds be~ore they reach the main hopper 3 The coloured mix is retained in the mould by the negative pressure a~plied to tlle bottom o E the mould. As ~l~ the mould passes beneath the hopper 33 a quantity OI un--' coloured mix ~or a second colourea mi~) is sprinl{led into ' ~

':~ . , ' ' - ~ ac - 10 -, it from ~ c u~)sl;rc.. l11 section 3'1, ~ni1 sllEficient ~l1rther l~nCOlOllrC`~I IlliX ~or second coloured mi~)~ to ~ill the nouL(1 :is t1~c1~ di~char~e~ di1~ctLy into the moul~ -from the dow11stream sec-tion 36 a~1d rolled level ~ith the mould edges by means o~ a roller 60. Water is then spr~yed on to the top sur-eace o~ the n1ollld through a spray head 61~. Alt,ernatively water coulc1 be ~looded on to the top surface o~ the mould through a ~ilter clol;h conveyor with a sur~ace speed equal to th~ travel speed of the mould.
~he water is d1~a~n into the mix as described earl:ier9 and excess wat,er is drawn through the mixer and recycled.
At an appropriate point along the lo~er mould run the ~ negative pressurc is released and replaced by positive L pressure to dischar~e the cnsting ~rom the mould on to a mould-carrier 66 having a pallet 67 th~reon ~see ~igure i 7), The carrier 66 is guided on i~clined guides 68 and ~ moves downward with the casting thereon until the pallet r rests on a pair o~' chains 70 which move intermitten-tly ~ ~ and carry the pallet and its casting to an unloading point.
The carrier 66 then moves upwardly o~ the guicles 68 carrying a fre~h pallet 67 on which to collect the ne~t , casting.
; It has been ~ound that the re~uired water content can be at-tained by means o~' the invention irrespective o~
the amount o~ excess water applied by virtue o~ the retentive nature o~ the ce~ent mi~ture. It has been ~ound that patterned multi-coloured ~acings show no signs o~ colour migration ~nd retain an excellent delineation.

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Tho inventioll has mally ol;her advant~lges. One is that it is not n~ce~sary to use vibr~tioll. Another is that sinco all the Ini~ing is c~rriecl out on dry mi~tur~s cleaning And maintcnallce Qf mixing equipment is s:impli~ied and wcar on the equipment is rcduced compared to known methods~ which involve mixing ~et mate1ials~ Furthermore 7 t.he inven tion avoids the disadvanta~e inherent in ~no~n ,` methods that any mi}~ which is not usecl ~airly shortly a~ter being produced cannot be'kept eor subsequent use~ In 1~ the present inventlon, in contrast, any dry mix which is not used when produced can be stored~ i:E necessary, for engthy periods lultil required.
One application of the invention is to llash set mixes The idea o-~ ~ ash set mixes is well ~nown in the industry and has been generally condemned as bacl practice. In known methods concrete mixes are prepared and w~-ter added during mixing and with rapid set mixes -~
M~k~
;-~ containing say Portland cement and cement Fond~ or quiek~setting plaster o~ paris blended with e~foliate mica, hydration can be well advanced prior to placing the mix in the mould. Movemen-t o~ the cement particles during this stage o~ crystallisation impalres bond due stre~lgth?lto the crystal ~ormation being broken. ~sing a ~lash set mi~ in the method of this invention this problem can be overcome since there is no slgni~icant movement of the placed mix after the addition o~ water.

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Il (les:irc~l one or bo tll surl`accs O:e tlle cas-ting prodllce~l co~ c trea tecl :in l~nol~n mamler to give a te~ red or exposed aggre~a t;e :finish, Although tlle al~ove descri.pt.ion ha~ boen mai.nly ~r:ith rcîerence to the malcing o:t' concre te produc ts the invenl;io ~s app:l icable to o ther produc ts :~'ormed :~rom a particu].a te materia:l and a 1 :i.quid .

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Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of molding concrete comprising subjecting a perfectly dry mass of particulate material comprising a mixture of cement and aggregate to subatmospheric pressure over a first portion of the surface of the mass while exposing a second portion of the surface of the mass to the atmosphere and distributing water over the second portion of the surface while continuing the subatmospheric pressure, such that the entire mass is compacted and the water is drawn into and dis-persed throughout the entire mass and such that the required water content for binding the mass and activating the cement is provided to form a sound, strong integral, rigid concrete product.

2. A method as claimed in claim 1, wherein the mixture is a flash set mix.

3. A method as claimed in claim 1, wherein the dry par-ticulate material is placed on a filter medium in a tray having a base provided with means for applying a negative or positive pressure selectively thereto, the water is flooded over the upper surface of the particulate material, negative pressure being applied to the base to draw the water into the particulate material, and positive pressure is then applied to the base to enable the casting thus formed to be released from the tray.

4. A method as claimed in claim 3, wherein the filter medium is a filter paper.

5. A method as claimed in claim 4, wherein a mesh is located between the base and the filter paper to define channels with the base, thereby to distribute negative or positive pressure over the base.

6. The method of claim 4 comprising forming the mass of particulate material of two distinct portions; initially forming a first colored portion of material and subsequently forming a second portion of material, the second portion not being of the same color as the first colored portion.

7. The method of claim 6 comprising distributing the first colored portion onto the filter paper in a predetermined pattern, while subjecting the filter paper to subatmospheric pressure, by masking predetermined portions of the filter paper, whereby the predetermined pattern matches the unmasked portions of the filter paper

8. The method of claim 7 comprising, in addition, initially placing a masking plate beneath the filter paper having predetermined openings therethrough such that the filter paper is drawn out through the cut-outs through the plate by the sub-atmospheric pressure, whereby the first colored portion enters the drawn out portions of the filter paper and is thereby molded as an embossment with respect to the second portion of material.