Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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-
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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.
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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.
-- 4 --
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~
5 -
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~
-- 8 -
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
- 10 --
~or three hours. The skid resistance value at the end of the
six hour test was termed the polished s$one value (PSV),
TABLE 1
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
TABLE 2
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~
-- 11 --
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