CA1139974A - Surface treatment - Google Patents

Abstract

Abstract:

Surface Treatment A method and apparatus suitable for treating a surface, e.g. that of a road, which comprises at least one aggregate (8) in a binder matrix (9). The invention resides in applying fine abrasive particles (11) each having a mean diameter of up to 500 microns so that they will be bonded only to those portions of aggregate (8) in the binder matrix (9) which will be directly exposed to wear. The method is applicable to new or old surfaces and also to runways, pavements and sports surfaces.

Description

t~L

SURFACE TREATMENT

This invention relates to a method and apparatus suitable for treating a surface, e.g. that o~ a road, and to the novel treated surface produced thereby.

~n conventlonal road sur~ace conætructions at least one aggregate is combined in a blnder matrix and applied where required by suitable means The friction level i.e. skid-resistance of the resulting road surfare gensrally tak0s thefollowing path: a) inltially th0re ls a high level of ~riction provlded by the fine aggregates ("~ines") used in the mix. These are worn away by the action o~ traffic, leaving a thin fllm of binder covering the aggregate sur~ace b) this binder film masks the microtexture of the aggregate and thus re~ults in a low level of friction~
c:) once this binder film has worn away, the microtexture of the aggregate is exposed and the friction level rlses d) further traffic actlon polishes the aggregate, i.e.
removes the microtexture, thereby causing the ~riction level to fall until eventually it will reach a stage where its friction level is too low for ~afety.

There are thus two stages at which the frictlon level can fall below a safe level i.e. ~b)" when the fines have been worn away but the thin film of binder is still pres6nt, and "d)" when the exposed aggregate has been polished to a low microte~tural level by the action of tra~ic. Incidentally, the time ta~en for a particular road surface to reach these stages is dependent upon a number of ~actors including the type of aggregate and bi~der, the volume c3f traffic, the speed at which traf~ic travels on the road (at higher speeds a higher friction level is required for safety), the frequency of rain (wet sur~aces require a higher frictlon level for safety)and the geometry of the site.

There are two traditional solutions to this problem. The first is to apply to the road surface a layer of hot bitumen-

- 2 coat~cl aggrega~e particles ~ usually 14 to 19 mm in slze~

having ~irst ~pra~y-coated the road ur~ace with a tack coat o~ bitumen. Thi~ solutlon, known as sur~ace dre~slng, restore~ bo~h mlcrotexture and n~crotexture but the resultlng ~urface will ~ollow the path outllned above with its two attendant disadvantageou~ stage~ "b" and 7~d~o Furthermore the adequate retention of the aggreg~te particle~ can be a problem; they will o~ten have no mechanlcal irlterlQck with the underlying surface and wlll therefoxe only be held by the binder ~ilm. The ~orces applied to these large aggregate particle~ by the action o~ traf~ic will o~ten be ~u~icient to dislodge them ~rom the sur~ace, resulting in con~iderable damage to pa~sing tra~ic u~ually in the ~orm o.~ chlpped paintwork and broken windscreens.
The ~econd solution to the problem ls to combine aggregate partlcle~ i~ an epoxy resin binder and app~y thls ~o the entlre ~ur~ace. Again, thl~ improves both microte~ture and macrotexture. The dlsadvantage o~ this ~ystem 1~ the high co~t lnvolved.

The preeent invention alm~ to overcome these di~advatltage~
by providing a relatiYely cheap and simple method o~ improving the micro~extural character o~ aggregate particles.ln a binder matxix. The lnvention 1s parSicularly use~ul both in the early li~e o~ a road ~ur~ace (problem ~tage "b)" ~nd when the road sur~ace has been exposed to tra.~icking ~or a ti.me ~problem ~tage "d)".

~ccording to o~e aspect o~ the present inventlon, a composite suitable ~or use as the sllrface o~ a road, runway, pavement9 spor-ts sur~ace or the like comprlses at: least one aggregate in a binder matrix bonded to particles 9 chaxacterised i~ that the particles are ~ine abrasive particles each havlng a mean diameter o~ up to 500 mlcrons and said particles are bonded s~bstanti~lly only to those portions o~ aggregate in the binder matrix which will be direc~ly exposed to wear.

- 3 -Accordlng to a ~urthsr aspect of the present inventiQn a mel;hod sul~able :eor traating ~he sur~ace of a road9 runway pavement~ sports sur~ace or the like comprisir.tg at least one aggregate in a binder matrix is characterised in that fine abrasive particles each having a mea~ diameter o~ up to 500 microns are applied to the sur~ace so that said particles will be held substantially only by those portions o~ the sur~ace which will be directly exposed to w a.r.

According to yet another aspect of the present invention, all apparatus ~or treating the sur~ace of at leas~ one aggregate ill a binder rnatrix is characterised in that it comprises means for applying a binder to the surface and in tandem therewith means for applying to the resulting binder-coated surface fine abrasive particles each having a mean diameter o~ up to 500 microrts.

Aggregate mat.erials ~uitable for u3e as the fine abraslve material are those derived fr~m aggregate~ having a maximum aggregate crushing value as specifled in BS 812:197S o~ not more than 300 .Materials derived other than ~rom aggregatesl e.g. metal~3, mucst be of ar.t equal perYormance to this e.g. havlng a hardness o~ at least 1 and pre~erably at least 2 on the ~oh scale Oe hardness.
~5 Preferably at least 50% by weight of the ~ine particles ~ach have a mean diameter in the ra~lge 50 to 250 ~lcrons, Examples ~ suitable materials includs crushed naturally occurring gritstones e.g. "Gil~ach", "Craig-yr-Hess" and "Millstone grit~9 artificial aggregates~ e.g, cr ~hed calcined bauxite 9 slags and emeries.

Where an aggregate/binder matr1x is to be coated according to the present invention and uncoated aggregate par~icles are exposed to the surface lt will be necessary ~o apply a fresh coating of the same or a differellt binder to the surface to which the fine particles will adhere.

Th~ is a lso a ~olution to the problem of coa tlI~s an a~grega~s/
binder matrlx whare the binder læ ln the solid~ tack-Iree s tate e . g . in the case o~ a road sur~ace which is not newly laidO An alternative approach to this lalt;ter o~eratiorl i~
5 to soIten the e~isting binder tt) a tacky s tate beIore applyi3lg the fine particles.

Examples of aggregate/blnder ma trice~ the sur~aces OI which may he treated according to the pre~ent inveIltion lnclude 10 road, pavements 9 runways 9 ~ports sur~aces and the like.
The present invention can be used bot;h to restore a worn or old sur:~ace and to provide a top-coat Ior a newly laid ~urIace ~ Thi~ ca~ be dor~e by coating onl.y th~ uppermos ~
portions wi.~h binder Qe it ig only whare there i~ binder 15 t;hat ~he ~ e particles wlll remalrl. The appa.ratus OI ~he pres~nt lnven~ion can be u~ed to achieve ~his result by de~ignîxlg t;he means ~ r applying i;he binder ~o thQt; it i3 oxlly appliHd to ~he uppermost aggregatH surface~ and/or by ensuring th~t the blnder i~ su~iciently vlscnu3 not to ~low over the entlre sur~ace and has su~flcient tack to hold the ~ine particles applied thereto. This pre~erred method o~ treatment is intended to improve the micro-~exture~ . roughn~s, o~ the lndlvidual aggregate particle~.
ThH ~brasive material can be applied in dry form ox in a binder. q'he proport~ on of binder mus ~ be su~ficlen~ly great to hold the ~brasive particles ~o eaeh o~her but not so great a~ tQ mask the microtext.ure o~ ~he abraslve pa.rticles. I~ deslred ~urther dry abrasive particles may be du~ted on~o the resulting sur~ace.

Preferably at least 160 g/m o~ dry flne abrasive ma terial is applied to the underlying substrate. Where the abrasive material is applied as a paste iIl a binder, e.g.
50/50 by waightg pre~erably at least 250 g/m2 is applied to give aIl average fllm thickness of 0.14 mm.

~39~

By way of example only, two embodlments of the method of the present lnvention, both of whlch relate to the top-coating of a newly laid road surface but which equally apply to $op-coating a new runway9 pavement~ sports surface ox the like, are as follows:

(i) After a road surface comprising aggregate particles ln a blnder ma~rix has been laid and whila the binder (whlch may ba o~ eOg~ bltumen or a specialised surface dressing type such as rubberised bitumen or epoxy^bitumen) is still warm9 fine particles are applied dryy warmed and in excessO
The excess material may be left to be dispersed nat~rally or removed9 eOg. by suction9 where the cost of the material warrallts it and/or i~ there is a possibility that the drainage channels either between the indlvidual aggregate particles in the road ~urface or within the body of a porous road surface become blockecl by excess material (ii) After the road surface comprlsing aggreg~ate par~icles i~ a binder matrix has baen laid, a film oi' a di~ferent binder is applied to the road suri'ace. Fine particles are then applied to the surface and the excess material can be dealt with as described in (1). This process allows two different types of binder to be used if deslred so that the properties of each can be selected to suit the require-ments of different layers o~ the road structure.

The binder to which the ~ine material adheres may be selected from e.g~ bitumen9 tar9 epoxy-bitumen9 bitumen-polymer blend or an epoxy resin.

A preferred embodiment of the present inveIItiorl will nowbe described by way of example only with reference to the accompanying drawings in which:
~igure 1 is a simplified representation of a machine for applying binder and flne particles to a new or old road ~ 6 --or similar surface;
Figure II is a section of the resulti~g treated surface, and ~igure XII is a sectional view of the uppermost portion of a single aggregats particle in the treated surfaGe shown in Figure II.

Referring now to Figure I, the machine 1, which may or may not be self-propelled7 includes a binder reservoir (not shown provided with means for heating the binder to its working temperature 9 means (not shown) for controlling the flow rate of the binder and, in communication with the binder reservoir, a spreader bar 2 provided with an outlet 2b for applying binder to the uppermost surface of the road 3. In tandem with ~.he binder applicator is dusting means 4 for applying fine abrasive material to the coated road surface. The dusting means may simply be (as shown) a tapered outlet 4 for the fine material in the reservoir 5. The outlet is usually provided with closure means (not shown) which would come into operation when the machine is not in use and means ~not shown) for controlling the ~low rate of the material. Suction means 7 may be provided to remove the excess fine material from the road surface and to tran~sfer it back into the reservoir.
In use9 the machine 1 is moved over the road surface to be treated9 binder is applied to the uppermost portion of the surface by means of the spreader bar 2 and immediately followin~ thls, fine material is dusted in excess from the tapered outlet 4 onto the binder-coated road surface. The viscosity of the binder is selected so that it is sufficiently viscous not to flow over the entire road surface but has sufficient tack to hold the fine particles.
If excess fine material is to be removed, suction is applied through the suc-tion means 7 and the excess material is thereby returned to the reservoir 5.

_ 7 _ As shown in Figures II and IIIg the product o~ the method and apparatus descrlbed wlth re~erence to Figure I is a road sur~ace comprising particles 8 coated with binder 9 and provided with a n~w coating o~ binder 10 on the uppermo~t portions 7 adhered to which are ~ine particles 11.

The invention is further illustrated by the ~ollowing Examples in which the materials referred to are as -follows:

Resin - Epoxy resin/hardener Bitumen - A 100 penetration graderesidual bitumen Calcined bauxite - Crushed calcined bauxite of particle seive size from 100 to 200 ~1 B.S.
Thermoplastic rubber - An additive compatible with bitumen.
The testing procedure adopted for each sample was that described ~or polished stone value (PSV) contained in BS 812:1075. Each sample consists of a single layer o~
35 to 50 polished aggregate particles packed as closely as possible and covering a~ area o~ 90.6 x 44.5 mm, set in a thin resin mortar so that the aggregate surfaces were exposed.
The samples were sub;ected to a polishing ac`tion to simulate that which would occur in a road ~surface and then the residual -~rictional resistance was measured using a pendulum skid-tester. Samples tested in ~his way were then used as described in the E~amples and the ~inal "road sur~ace" was tested in the same way to gauge the effect of the abrasive material applied.

EXAMPLE I
Two samples o~ each of seven dif-ferent aggregates - blast furnace slag, wimmis9 Morraine, Basalt, Diabaseg Enderby and LD - were heated in an oven and -then the uppermGst surfaces were coated with a film of bi-tumen. Calcined bauxite was applied in excess and rolled into the bitumen ~ilm. As shown by the results summarised in Table 1, the mean skid resistance rose ~rom 47 (uncoated) ~o 94 a-fter coating and fell to 58 ~ 3~

durlng the six hour test. The skid rcsistance measured for each sample was found to be independent of the substrate.

E~AMPLE II
A paste consisting of about 50% by welght resin/50% by weigbt calcined bauxite was applied as a relatively thick coating to the uppermost surfaces of various types o~
aggregate. Dry bauxite particles were then dusted over the coatings. The uncoated aggregates had PSV's in the range 44 10 to 79 with a mea~ of 61. Twelve samples were tested in all.
Table 2 summarises the mean skid resistances of the coated samples. The standard deviation o~ the result was only 3. 97 thus indicating that the result was independent of the aggregates used in the substrates.
XAMPLE III
Four dlf~erent methods of producing a total o:E 1~ samples were employed:
(i) ~ thin re~in film was appli~ed to the uppermost surface of each of four aggregate samples.

(ii) A paste of resin and bau~ite particles was applied as a thin coating to the uppermost surface of each of four samples, (iii) Two samples were prepared as in (ii), but using Bridport pebble as the aggregate substrate. Bridport pebble - presents a very smooth sur~ace and therefore hindered any interlock with the surface treatment.
(iv) Two samples were made by a two stage process~ Firstly, a bitumen film was applied to the uppermost surface of the aggregate and the sample was heated and then dusted with bauxite particles. An epoxy resin/bauxite paste was applied to this after the sample had been cooled.

The resul ts of these tests are summarised in Table 3 .

- 9 ~ -EXAMPLE IV
A series of fourteen samples were made:

(i) Three samples were produced by applying binder to the uppermost aggregate surface and then dus tiIlg this with ~auxite partlcles. Thermoplastic rubber had been incorporated into the 100 penetration bitumen binder, in an amount equivalent to 10 parts by weight per 100 parts bitumen.

(.ii) The binder used in (i) was used to make a paste with bauxite particles and this was then applied to the uppermost aggregate surface and then dusted with excess dry bauxite particles. Three samples were made in this way.

(iii) A paste was made from bauxite particles and a binder consisting of 95 parts bitumen/5 par ~ carbon black bitumen additive. This was then applied as a thin film which was subsequently dusted with dry bauxite particles. Three samples were made in this way.
(iv) A paste was made from bauxite particles and a binder consisting of 40 parts bitumen/60 parts epoxy resin. This was then applied as a thin film which was subsequently dus$ed with dry bauxite particles. Three samples were made in this way.

(v) A paste was made from bauxite particles and bitumen.
This was then applied as a thin film which was subsequently ~usted with dry bauxite particles, Two samples were made in this wayO

~11 of these samples were subjected to polishing and measurement of the.ir frictional properties according to BS 8120 The samples were removed at differen-t stages of the test and their skid resistance measured9 The standard test consisted of polishing the samples under wet application of a coarse abrasive for three hours 9 followed by fine polishing ~or three hours. The skid resistance value at the end of the six hour test was termed the polished s$one value (PSV), Results o~ Example I

Method of coating : Thin coating of bitum2n/bauxite paste ~ollowed by dusting with ex~ess bauxite particles Number of samples : 12.
10 Mean Skid Resistance Values :Prior to coating 47 After c0ating 93-9 After ~ hour coarse polish 76.7 After 1 hour coarse polish 70.9 15 After 1~ hour coarse polish 66.7 After 2~ hour coarse polish 68.4 A:eter 3 hour coarse polish 58.8 A:Eter 4 hour pollsh ~3 coarse + 1 fine) 55.6 ~fter 5 hour polish (3 coarse + 2 ~ine) 54.8 ~fter 6 hour polish (3 coarse ~ 3 fine) 58.7 Resul-ts of Example II
5 Method o~ coating : Thick co,ating of epoxy resin/bauxite paste followed by dusting with excess bauxite particles.
Numbe~ of samples : 12.
Mean Skid Resistance Values _ _ .
30 Prior to coating 61.1 After coating 92.8 After 3 hour coarse and 4 hour fine 68.7 polishing Mean Wei~ht,s of Coatin~ Applied and Lost 35 Mean weight of coating applied per sample 6.60 grams Mearl weight of coating lost per sample after 0.42 grams 6 hours polishing Ai . ~ 3~

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Claims (10)

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

1. A composite suitable for use as the surface of a road, runway, pavement, sports surface or the like, comprises at least one aggregate in a binder matrixe wherein substantially only those portions which will be directly exposed to wear are bonded to fine abrasive particles each having a mean diameter of up to 500 microns.

2. A composite according to Claim 1 wherein the aggregate/
binder matrix is bonded to the fine abrasive particles by means of an interlayer of an identical or different binder.

3 A composite according to Claim 1 wherein at least 50% by weight of the fine abrasive particles each have a mean diameter in the range 50 to 250 microns.

4. A composite according to Claim 11 2 or 3 wherein the abrasive particles constitute a coating of at least 160 g/m2.

5. A composite according to Claim 1, 2 or 3 wherein the Line abrasive particles comprise at least one aggregate having a maximum aggregate crushing value as specified in BS 812 : 1975 of not more than 30.

6. A method suitable for treating the surface of a road, runway, pavement, sports surface or the like comprising at least one aggregate in a binder matrix, by applying fine abrasive particles having a mean diameter of up to 500 microns so that said particles will be held substantially only by those portions of the surface which will he directly exposed to wear.

7. A method according to Claim 6 wherein an identical or different binder is applied substantially only to those portions of the surface which will be directly exposed to wear and then -the abrasive particles are applied in dry form.

8. A method according to Claim 6 wherein the abrasive particles are combined with a binder to form a paste which is then applied substantially only to those portions of the surface which will be directly exposed to wear.

9. A method according to Claim 8 wherein the paste is applied in an amount of at least 250 g/m2.

10. A method according to Claim 8 or 9 wherein the average film thickness resulting from the paste is at least 0,14 mm.