Method and device for producing a surface coating on a surface such as a road

The method comprises spreading a layer of bituminous binding material on the surface, spreading at least one layer of aggregates on the layer of binding material, and compacting the layer of aggregates in contact with the layer of binding material. The aggregates consist of loose chips covered with a mixture, which has a pasty consistency, of bitumen and of pulverulent material. The layer of binding material contains at least 11% of the total quantity of bitumen used in the coating. The operations of spreading the binding material and the aggregates and of compacting and surfacing the coating are performed in succession within a period of less than 5 seconds, the speed of advance of the site being at least ten meters per minute. An integral mobile device carrying a bitumen-spraying boom and a finishing table fixed to the rear part of the chassis makes it possible to produce a coating according to the invention using aggregates which are coated with bitumen produced by the device or transported thereby to the rear part of the chassis between the spraying boom and the finishing table.

BACKGROUND OF THE INVENTION 
The invention relates to a method and device for producing a surface 
coating consisting of aggregates and bitumen on a surface such as a road. 
Worn or damaged roads may be repaired by producing, on the surface of this 
road, a surface coating based on aggregates, such as loose chips and 
bitumen. 
The current technique for producing a surface coating includes spraying the 
road with a thick layer of bituminous binding material (for example a 
layer of 1.3 to 1.8 kg of bitumen per square meter of road). Then, loose 
chips, such as crushed rocks, are poured onto the binding material in a 
quantity which is excessive relative to the quantity required to just 
cover the road. Finally, compactors are used to ensure the best adhesion 
possible for the loose chips on the layer of bituminous binding material. 
It is necessary to pour, onto the layer of bituminous binding material, a 
quantity of loose chips which is greater than the quantity required to 
just cover the layer of binding material so that there is no exposed 
bituminous binding material remaining to adhere to the tires of vehicles. 
Those aggregates which do not adhere to the bitumen are thrown in all 
directions by vehicles travelling on the road and can cause the 
windscreens of other vehicles to shatter and paintwork to be chipped as 
well as, in urban areas, windows to be shattered. 
Moreover, the cost of the coating produced in this manner is increased by 
virtue of the fact that good-quality loose chips are wasted. 
This loss of loose chips just after the coating has been laid on the road 
constitutes what is known as operational rejection. 
There is also another type of rejection which is postponed until during the 
weeks following the laying of the coating and which consists of a 
progressive tearing away of the poorly adhered loose chips or of those 
loose chips which have adhered over too small a part of their surface. 
Finally, in the first period of cold weather following the laying of the 
coating, there will be a rejection known as first-winter rejection which 
occurs due to the fact that the aggregates which adhered satisfactorily 
when the binding material was still plastic are bound in a fragile manner 
and, when the first cold spell arrives become brittle. Travelling vehicles 
remove the small percentage of loose chips whose adhesion has not 
withstood the first cold spell. 
One year after laying of the coating, the loose chips which have withstood 
all the tests of the traffic under the various weather conditions 
experienced during the year are henceforth satisfactorily fixed and 
generally do not detach themselves further except when they are worn and 
when the adhesive binding material becomes too old. 
In order to withstand tearing away, the loose chips which are poured onto 
the binding material must have as large a surface as possible in contact 
with the adhesive binding material. Because the crushed loose chips do not 
have simple geometric shapes, such as the shape of a cube or the shape of 
a truncated pyramid, a point of a loose chip is often located opposite a 
face thereof. 
When the loose chips are disposed so as to have a point facing upwards, the 
corresponding disposition affords advantages in that the tires of vehicles 
grip well in wet weather. On the other hand, this leads to more rapid wear 
of the tires and to noise being produced due to the contact of the tires 
with the ridges or points of the loose chips. 
When loose chips are poured onto a layer of adhesive bituminous binding 
material, good and durable adhesion is produced only when the following 
conditions are fulfilled: 
the loose chips must not be dusty or contaminated with soil, and must be 
dry, which is rarely the case, and, similarly, the surface of the road 
must be clean and dry; 
the adhesive bituminous binding material must be sufficiently fluid to 
spread and moisten the loose chips, which requires the coating to be 
produced during a period of sufficiently hot weather. This limits the 
period during which surface coating can be laid to repair roads, in the 
geographical zone to which France belongs, to the five warmest months of 
the year, from May to September. 
The coating technique, implemented according to known methods, is thus 
risky, since it is sufficient for there to be excessive humidity, rain, a 
cold spell, for dirty loose chips to be used or for a road surface to be 
contaminated with soil, for the coating produced on the site to be of 
insufficient quality. 
Roads which have to be repaired usually have a defective longitudinal or 
transverse profile which is impossible to rectify using known techniques 
for producing surface coatings. In fact, by applying a layer of binding 
material on a deformed support and then fixing thereto a single layer of 
loose chips, the initial profile is retained in its general form. This 
also applies when two or more layers of loose chips are superposed in 
order to form the coating, the defects being reproduced in each of the 
successive layers. 
These defects are reflected in a lack of comfort when driving vehicles, in 
particular at the maximum speeds authorized on the road network. 
In addition to the above technique for producing coatings, roads are also 
repaired by depositing layers of bituminous coated products which are 
bound to the surface of the road by means of a layer of binding material 
of very small thickness, generally less than 10% of the total quantity of 
bitumen used. The coated material, which consists of a mixture of bitumen 
and aggregates of various particle sizes, has the form of a malleable mass 
which is spread and compacted on the layer of binding material. 
The covering obtained is generally very compact and smooth, and the absence 
of roughness leads to poor tire adhesion for this type of covering, 
particularly in wet weather. On the other hand, the spreading and 
compacting of a relatively homogeneous mass of malleable material on an 
uneven road generally makes it possible to compensate for the small 
defects in the roads profile when the covering is sufficiently thick. 
French Patent 2,550,248 discloses a mobile device for the cold production 
and spreading on site of bituminous coated products for surfacing roads. 
In particular, this machine can permit the production and spreading on 
site of bituminous concrete consisting of a material with a small particle 
size, such as sand, mixed with an emulsion of bitumen. 
This device, which can travel on a road at high speed and on site at low 
speed, by virtue of a dual transmission, has several possibilities for 
receiving or storing solid or liquid materials and for processing them. 
This integrated device, however, has never been set hitherto for producing 
coatings for repairing a road. 
SUMMARY OF THE INVENTION 
The aim of the invention is thus to propose a method for producing a 
surface coating consisting of aggregates and bitumen, on a surface such as 
a road. This method includes spreading a layer of bituminous binding 
material on the surface and at least one layer of aggregates on the layer 
of binding material and then compacting the layer of aggregates in contact 
with the layer of binding material. These spreading and compacting 
operations are performed in succession by a spreader travelling in a 
displacement direction corresponding to the direction of advance of the 
site, it being necessary for this method to make it possible to avoid the 
rejections of loose chips, whether these are operational rejections or 
postponed rejections, to reduce the traffic noise and the wear of the 
tires of vehicles travelling on the road, to increase the possibilities of 
producing the coating as a function of weather conditions, to 
substantially improve the quality of the covering produced and to make it 
possible to reprofile the road. 
To this end, the aggregates consist of loose chips covered with a mixture, 
which has a pasty consistency, of bitumen and of pulverulent material. The 
layer of binding material contains at least 11% of the total quantity of 
bitumen used for producing the coating. The operations of spreading the 
bituminous binding material, spreading the aggregates and compacting and 
surfacing the coating are performed one after the other within a period of 
less than 5 seconds, the speed of advance of the site being at least ten 
meters per minute. 
The invention also relates to a device which is similar in its general 
design to the device described in French Patent 2,550,248, but also 
comprises means which are adapted for producing a coating using the method 
according to the invention. 
The device may be used either for the cold production of covered 
aggregates, for spreading them on site, for spreading the layer of binding 
material and for surfacing the covering, or, alternatively, for receiving 
and spreading hot-produced aggregates, spreading the binding material and 
surfacing the covering. 
In order to make the invention understandable, a description will now be 
given, by way of non-limiting examples and with reference to the appended 
figures, of several embodiments of the method according to the invention 
and of the corresponding device for implementation thereof.

DETAILED DESCRIPTION OF THE INVENTION 
In FIGS. 1 and 2, the mobile machine of the invention is, in general, 
similar to the device which is the subject of French Patent 2,550,248. 
FIG. 1 shows the device of the invention in its working position on site, 
and the tipper (or pouring) section of a truck as it supplies loose chips 
into a hopper of this device. 
The device comprises a chassis 1 resting on four sets of wheels 2a, 2b, 2c, 
2d. The axles of the sets 2c and 2d are driven by means of drive axles 
which are operatively connected to a drive unit having a motor 5 
associated with a gear box 6. The drive unit makes it possible to move the 
machine both on the road and on site, and is described in detail in French 
Patent 2,550,248. 
The machine moves over the ground 7 of the site, consisting of the upper 
surface of a road on which a layer of coating 8 is produced using the 
method according to the invention. 
The chassis 1 carries a control cab 10 whose width is less than half the 
width of the chassis and which occupies a position which is offset towards 
one of the lateral sides of the chassis. A bucket elevator 12, inserted 
between the two side members of the chassis 1, is located in a position 
which is adjacent to the cab 10 and centrally located relative to the 
chassis. A receiving hopper 14 is located at the front of the machine just 
above the ground 7, and is fixed to the ends of the side members of the 
chassis 1 and communicates with the lower end of the bucket elevator 12. 
The bucket elevator 12 and receiving hopper 14 together define an 
automatic feeding mechanism for the machine. 
The bucket elevator 12 comprises a housing 17 and a set of buckets carried 
by two chains 18 which ascend towards the rear of the machine, such that 
they form an angle of about 60.degree. with the plane of the chassis 1. 
An upper part of the chassis 17 communicates, via its discharge opening 19, 
with the upper part of a hopper 20 for storing granular materials, such as 
loose chips. 
Obviously, the bucket elevator could be replaced by an elevator of another 
type. 
As can be seen in FIGS. 1 and 2, the hopper 20 occupies most of the length 
of the machine and a substantial part of its width, at least in its upper 
part. A device, known as a bar leveller, for distributing the loose chips 
makes it possible to spread the loose chips over the entire length and 
over the entire width of the storage hopper 20, and is located above the 
hopper 20 over its entire length. 
The bar leveller 31 consists of one or two endless chains trained about end 
pinions or pulleys and carrying transverse bars 23. The path of the bars 
of the leveller is very slightly tilted upwards, from front to rear. 
Instead of a bar leveller, a screw leveller can be used. 
The bucket elevator 12 and the bar leveller 31 are driven, in order to 
transport the loose chips 27, by hydraulic or electric motors by way of 
reduction gears (not shown). 
A tipper (or pouring) section 28 of a truck, which is adapted to supply 
loose chips to the machine, is shown in FIG. 1 in its operative position 
for pouring chips into the receiving hopper 14. The chassis of the truck 
can be connected via a coupling device 29 to the machine, and the rear 
gate of the tipper section can be connected to a pivoting hook 30. In this 
manner, the loose chips 27 are poured in a perfectly controlled manner 
into the receiving hopper 14 and are then transported by the bucket 
conveyor 18 to the upper part of the hopper 20 where the bar leveller 31 
spreads the loose chips over the entire surface of the hopper 20, which 
has a large cross-section. 
This results in the hopper 20 being filled in a perfectly balanced manner 
despite its great length and width. The use of a bucket conveyor with a 
sharp slope makes it possible to lift the materials to a great height, 
despite the small size of the elevator, in the longitudinal direction of 
the machine. 
Although remaining within regulations applying to the road, the machine may 
be supplied with chips automatically and comprises a considerable 
loose-chip storage capacity. As indicated in Patent 2,550,248, this hopper 
can have a capacity of 10m.sup.3. 
A conveyor belt 34 is disposed under the hopper 20 and removes and 
measures, in terms of volume, the loose chips in the hopper 20 which are 
conveyed by the conveyor 34 to above an inlet opening of a mixer 35 into 
which the loose chips fall. Rollers which drive the conveyor 34 are driven 
in rotation by a hydraulic motor (not shown). 
Pulverulent material, contained in a storage hopper 36, is also poured in a 
measured quantity into the opening of the mixer 35. The pulverulent 
material may consist of stone powder or fine sand and may be poured in a 
measured quantity into the mixer 35 simultaneously with the loose chips 
27. 
As shown in FIG. 2, the device comprises two lateral reservoirs 43 and 44 
located on either side of the storage hopper 20. The reservoirs 43 and 44 
are adapted to contain bituminous emulsions which may be different or 
identical. 
A boom 40 for spraying bituminous binding material, consisting of the 
emulsion contained in one of the reservoirs 43 and 44, is fixed on the 
lower part of the chassis 1 under the mixer 35 and at the rear of the set 
of wheels 2d. 
The emulsion contained in the second reservoir is adapted to be fed into 
the mixer 35. The mixer 35 then mixes the loose chips coming from the 
storage hopper 20 with the pulverulent material coming from the hopper 36 
and the bituminous emulsion conveyed to the mixer 35 from one of the 
reservoirs 43 and 44. 
The quantities of loose chips, pulverulent material and bituminous emulsion 
are measured so that aggregates are produced in the mixer 35 which consist 
of the loose chips covered with bitumen mixed with the pulverulent 
material in a proportion such that the aggregate has a pasty consistency. 
In this aggregate, the proportion of bitumen relative to solid materials is 
less than 6% and the resulting product is in the form of aggregates which 
are distinct from one another and not in the form of a pasty mass, as in 
the case of the production of a bituminous coated product. 
Such aggregates, consisting of loose chips covered with bitumen and mixed 
with a pulverulent material, may hereinafter be called dressed aggregates 
in order to distinguish them clearly from bituminous coated products which 
form an amorphous mass consisting of a mixture of the bitumen, aggregates, 
one or more sands and a pulverulent material, the aggregates being 
completely bound together by the bitumen, the pulverulent material and the 
sand which fill all the gaps between the aggregates. 
The dressed aggregates are poured onto the surface 7 of the road through 
the discharge opening of the mixer 35 upstream of a spreading and 
distributing device 41. 
A heating and vibrating surfacing table 42 is fixed in an articulated 
manner to the rear end 1a of the chassis 1, immediately behind the device 
41 for distributing the dressed aggregates 45 cold-produced in the mixer 
35. 
The table 42, of a type which is well-known to road work specialists, 
compacts and surfaces the aggregates in order to form the layer of coating 
8 at the rear of the machine which moves in the direction and the sense of 
the arrow 46 (FIG. 1), this direction corresponding to the longitudinal 
direction of the site or road. 
The layer of coating 8 is produced in the manner which will be described 
hereinbelow. 
The boom 40 fed with bituminous emulsion from one of the lateral reservoirs 
of the mobile machine dispenses a layer of bituminous emulsion of constant 
thickness, by virtue of a set of spraying nozzles uniformly spaced in the 
direction of the boom 40 corresponding to the transverse direction of the 
machine, over the entire width of the road or of the carriageway. 
It should be noted that the bituminous emulsion is dispensed at the rear of 
the last set of wheels 2d, so that the machine producing the coating never 
rolls over the layer of emulsion which has just been spread on the surface 
7 of the road. 
Precise numerical examples will be given hereinbelow in respect of the 
quantities of bitumen deposited on the surface of the road by the boom 40 
for distributing binding material. Generally, these quantities are 
approximately two to three times smaller than the quantities dispensed 
during production of a conventional coating using dry loose chips and 
three times greater than the quantity dispensed to produce the adhesion of 
a layer of bituminous coated products on the surface of a road. 
The dressed aggregates emerging from the mixer 35 are dispensed onto the 
surface 7 of the road where they are spread in a first stage by the 
spreading and distributing device which preferably comprises an endless 
screw device 41. 
The vibrating and heating table 42 or finishing table compacts and surfaces 
the dressed aggregates which have just been dispensed onto the layer of 
bituminous binding material. 
The boom 40 for spraying the binding material, the zone in which the 
dressed aggregates 45 are dispensed, and the finishing table 42 are 
disposed close together, one after the other, at the rear part of the 
machine for producing the coating, which moves in the direction of the 
arrow 46. 
The distance between the boom 40 and the rear part of the finishing table 
42 is such that, bearing in mind the speed of the machine corresponding to 
the speed of advance of the site, there are never more than five seconds 
between the spreading of the bituminous binding material on the surface 7 
of the road and the completion of compacting and surfacing of the coating 
on the corresponding part of the road. 
The three operations of spreading the binding material, spreading the 
dressed aggregates, and compacting are thus performed in under five 
seconds on any part of the road. 
Moreover, the speed of advance of the site, which corresponds to the speed 
of the machine in the direction of the arrow 46, is always greater than a 
value which is approximately equal to ten meters per minute, it being 
possible for this speed of advance to be of the order of twenty to 
twenty-five meters per minute. 
This speed, which is much higher than the speed of advance of a finisher, 
in the case of the production of a layer of covering consisting of the 
prior art bituminous coated products, makes it possible to obtain a 
particularly good surfacing quality and a very effective reprofiling of 
the road during repair. 
This advantage is obviously in addition to those advantages connected with 
the increase in productivity of the installation. 
The road is reprofiled by virtue of the formation of a coating which 
comprises a different number of superposed layers of loose chips according 
to the zones of this road which may comprise profile defects which are 
reflected in hollows of a considerable depth. 
In fact, the surfacing performed by the finishing table makes it possible 
to obtain a layer of coating whose upper surface is perfectly planar, 
because the hollows in the road are filled by a number of layers of 
superposed dressed aggregates which is sufficient to compensate for the 
level of the upper surface of the layer of coating. The aggregates in the 
successive layers bear directly on one another, which makes it possible to 
produce a material for filling those cavities which cannot be pressed out. 
The dressed aggregates are covered with a pasty layer which is both 
adhesive and lubricating, and are placed, without difficulty, on the 
surface of the road or on a lower layer of aggregates by sliding which is 
enhanced by the dressing layer. The speed of displacement, which is 
greater than ten meters per minute, of the finishing table makes it 
possible to enhance the displacement and placing of the layers of 
aggregates. 
Compacting the aggregates affords an efficient adhesion and binding of 
these aggregates on the layer of binding material spread over the surface 
of the road. 
The dressed aggregates coated with a pasty and adhesive layer based on 
bitumen are immediately fixed, one on top of the other, at the time of 
compacting, so well that any operational rejection is prevented. Moreover, 
compacting is greatly facilitated by the fact that the loose chips are 
coated with a lubricating bituminous layer. It is thus possible to use the 
road for vehicular traffic very soon after the production of the coating. 
The coating obtained makes it possible to reduce the vehicle traffic noise 
as the surface roughness of the loose chips no longer exists and as the 
cavities between the loose chips absorb the sound waves. 
These characteristics, together with the excellent profiling of the road, 
permit a substantial increase in comfort for motorists. 
No loose chips are thrown up, and the drawbacks associated therewith are 
thus eliminated. 
Even though it has very good rolling qualities, the coating obtained using 
the process according to the invention provides good adhesion for 
vehicles, even in wet weather, as it has roughness and surface cavities. 
FIG. 3 shows an alternative embodiment of the device described hereinabove 
and shown in FIGS. 1 and 2. 
The device shown in FIG. 3, whose general structure is similar to that of 
the mobile device described in French Patent 2,550,248, is intended to be 
used for producing a coating according to the invention of dressed 
aggregates produced by hot mixing of dried and heated loose chips, bitumen 
and pulverulent material in an installation performed by other than the 
machine which produces the coating. 
The dressed aggregates can be produced, for example, in a conventional 
hot-coating drum and then transported to the site by dump trucks which are 
fixed to the front of the coating machine at the hopper 14 in order to 
pour the hot dressed aggregates into this hopper from the pouring section 
28' of the truck. This operation is performed in the same manner as the 
pouring of the loose chips 27 in the embodiment of FIG. 1. 
The dressed aggregates 50 poured into the hopper 14 carried upwardly by a 
bar conveyor 12' and then poured into the central hopper 20 at the 
discharge end of the conveyor 12'. 
A rung conveyor 34' transports the hot dressed aggregates to the rear of 
the machine where the aggregates 50 are dispensed onto the surface 7 of 
the road. 
As in the case of the device shown in FIGS. 1 and 2, the central hopper 20 
may comprise a bar leveller or a screw leveller similar to the leveller 31 
in order to increase the storage capacity of the hopper 20. 
It is not necessary for the machine shown in FIG. 3 to include a mixer 
since the dressed aggregates are hot-produced in a different machine. 
The hopper 36 for storing pulverulent material in the first embodiment is 
replaced, in this second embodiment, by a tank 51 intended to contain the 
bituminous binding material which may consist of an emulsion. 
The device shown in FIG. 3 includes lateral reservoirs similar to the 
reservoirs 43 and 44 of the device shown in FIGS. 1 and 2. These 
reservoirs, and the tank 51, can contain bituminous binding material, such 
as an emulsion, intended to be spread over the surface 7 of the road, 
using a variable width spreading boom 52 fixed to the chassis 1 of the 
machine at the rear of the rear set of wheels 2d. The machine's capacity 
for storing bituminous binding material is thus greatly increased and, 
moreover, only one type of emulsion is required to produce the layer for 
catching the dressed aggregates. 
In a machine which has a chassis width of 2.50 m, a height of 4 m and a 
length of 11 m, and which is constructed in accordance with this 
embodiment of the invention, a 15-ton aggregate reserve can be disposed in 
the central hopper and a 12-ton binding material reserve can be stored in 
the lateral reservoirs and in the rear tank 51. 
This makes the machine very independent, enabling it to operate normally 
even when the supply from the trucks is irregular. 
Under normal operating conditions, the tanks of binding material in 
emulsion need to be resupplied only once during the day's work on the 
site. 
As in the machine shown in FIGS. 1 and 2, the rear part 1a of the chassis 1 
of the machine shown in FIG. 3 carries a vibrating and heating finishing 
table 42. The table 42 is mounted in an articulated manner on the chassis 
by means of a three point hitch. 
The boom 52 for spreading the binding material and the finishing table 42 
are located on the rear part of the chassis 1 so that no more than 5 
seconds elapses between the spreading of the binding material on the 
surface 7 of the road by the boom 52 and the end of compacting and 
surfacing performed by the finishing table 42, bearing in mind the speed 
of advance of the machine. 
The hot dressed aggregates 50 are poured out at a point located between the 
spreading boom 52 and the finisher 42, and slightly in front of an 
endless-screw distribution device 41. 
The dressed aggregates are at a temperature which is generally greater than 
120.degree. C. and which may be in the region of 150.degree. C. when they 
are spread over the layer of bituminous binding material dispensed by the 
boom 52 over the surface 7 of the road. 
As with the machine shown in FIGS. 1 and 2, the speed of advance of the 
machine shown in FIG. 3, in the direction and the sense of the arrow 46, 
must be greater than ten meters per minute in order to obtain a perfectly 
surfaced layer of coating 8 providing an effective reprofiling of the 
road. 
In the coating method according to the invention which is utilized with the 
device shown in FIG. 3, the advantages are at least equivalent to the 
advantages obtained when implementing the method by making use of the 
machine shown in FIGS. 1 and 2. 
The quantity of bitumen contained in the layer of binding material spread 
over the road before the spreading of the dressed aggregates is slightly 
less than the quantity of bitumen poured over the road in order to produce 
the adhesion of dry loose chips in the prior art, and can, in fact, be two 
to four times less. 
The dressed aggregates are covered with a relatively thick and pasty layer 
consisting of bitumen and pulverulent material. 2 to 6% of bitumen and, as 
pulverulent material, either 4 to 5% by weight of stone powder or 10 to 
20% of fine sand is incorporated with the loose chips. 
The function of the stone powder or the sand is only to make the fluid 
bitumen pasty and to thicken the adhesive layer so that the loose chips 
adhere together in a thicker layer. 
This is a very important idea, since the bitumen-coated loose chips are 
surrounded only by a thin film of hot bitumen, which is thus very fluid 
and which has a tendency to flow. 
The stone powder (or the fine sand) is added only to make the bitumen, 
which is too fluid, pasty and to thicken the layer of binding material, 
which is much too thin to guarantee durable binding between the particles. 
The thickening agent added is thus added for a dual purpose: 
it is a thickener in the geometric sense of the word; and 
it is a thickener in the sense that it increases the consistency. 
By way of the example, the composition of a surface coating according to 
the prior art, comprising two superposed layers (two-layer coating) and 
the composition of a coating according to the invention will be given 
hereinbelow. 
The surface coating according to the prior art comprises a first layer of 
bitumen emulsion spread at the rate of 1.1 kg/m.sup.2, that is to say 0.8 
kg of pure bitumen per square meter. 
A first layer of loose chips with a large particle size is spread over the 
layer of emulsion. This first layer comprises 7 kg of large loos chips per 
square meter. 
A second layer of emulsion is spread over this first layer of loose chips 
at the rate of 1.5 kg of emulsion per square meter, that is to say 1 kg of 
pure bitumen per square meter. 
A second layer of loose chips with a fine particle size is spread over this 
second layer of emulsion at the rate of 8 kg of fine loose chips per 
square meter. 
The coating according to the prior art undergoes compacting, after which a 
relatively large proportion of loose chips are not sufficiently bound to 
the surface of the road by the bituminous binding material, such that 
these loose chips risk being thrown up when vehicles pass by. 
The coating method according to the invention, given by way of example, 
consists in spreading a layer of bitumen emulsion over the surface of the 
road at the rate of 0.95 kg of emulsion per square meter, i.e. 0.60 kg of 
pure bitumen per square meter. 
A layer of dressed loose chips is spread over this layer of emulsion at the 
rate of 22 kg of dressed loose chips per square meter. The dressed loose 
chips are dispensed onto the layer of bituminous binding material 
immediately after it is applied and the layer of dressed loose chips is 
actually compacted and smoothed immediately after the spreading of the 
dressed loose chips. 
The quantity of bitumen covering the dressed loose chips is 1.4 kg per 
square meter of coating. The bitumen covering the dressed aggregates is 
thickened by being mixed with 5 to 6 kg of fine sand or 1 to 2 kg of stone 
powder per square meter of coating. 
The total quantity of bitumen relative to the solid materials is thus in 
the region of 5%, which represents approximately the upper limit of the 
proportion of bitumen spread on the loose chips for forming the dressed 
aggregates according to the invention. 
The table given hereinbelow shows the various quantities of materials used 
to produce the coating according to the prior art and according to the 
present invention. 
______________________________________ 
Coating according 
to the prior art 
Coating according 
(two-layer) 
to the invention 
______________________________________ 
Total quantity 
1.8 kg/m.sup.2 
2.00 kg/m.sup.2 
of bitumen 
Quantity of 
1.8 kg/m.sup.2 
0.60 kg/m.sup.2 
bitumen spread 
over the ground 
Quantity of 
0 1.4 kg/m.sup.2 
bitumen used to 
dress the 
aggregates 
Total thickness 
15 mm at any 10 to 40 mm depending 
of the covering 
point on the defects of the 
old support 
Total quantity 
17 kg of large 
22 kg of medium-sized 
of loose chips 
loose chips + 
loose chips 
used (per m.sup.2) 
8 kg of small 
loose chips = 
25 kg 
Other additives 
if appropriate, 
an obligatory 5 to 
adhesion additive 
6 kg of fine sand or 
at the loose 1 to 2 kg of stone 
chips/binding 
powder in order to 
material interface 
thicken the bitumen 
Total quantity 
25 kg 23 to 28 kg 
of solid 
material of 
mineral origin 
______________________________________ 
Obviously, these values are only indicative and the invention may be 
implemented by using quantities of materials or relative proportions of 
these materials which are different from those which have been indicated 
in the example given hereinabove. 
The quantity of bituminous binding material used to produce the dressed 
aggregates from loose chips may be a good deal less than the quantity 
indicated hereinabove which corresponds substantially to the upper limit 
for implementation of the invention. However, the quantity of bitumen used 
for dressing the aggregates must be sufficient to avoid any rejection and 
any ejection of loose chips after production of the coating. 
The quantity of bitumen used for dressing the loose chips must represent at 
least 11% of the total quantity of bituminous binding material used per 
square meter of finished coating. 
In other words, the bitumen contained in the bituminous binding material 
spread over the surface of the road before spreading of the dressed 
aggregates may represent up to 89% of the total quantity of bitumen. 
Moreover, in order to produce satisfactory binding with the road, the 
quantity of bitumen contained in the binding material must not be less 
than 11% of the total quantity of bitumen used per square meter of 
coating. The aggregates may thus contain up to 89% of the total quantity 
of bitumen used. 
Currently, the quantity of bitumen contained in the binding material is 
greater than 20% of the total quantity of bitumen used. This quantity of 
bitumen in the binding material is preferably in the region of 30% of the 
total quantity of bitumen used. 
The proportion of bitumen relative to the weight of solid materials, that 
is to say the weight of loose chips and of pulverulent material, is 
generally between 2 and 6%. 
Obviously, the method according to the invention may be implemented by 
making use of a bituminous binding material other than an emulsion and, 
for example, by making use of the bitumen incorporated in a solvent or, 
alternatively, of hot liquid bitumen. 
The method according to the invention can be implemented regardless of the 
particle size of the loose chips used to form the coating, within the 
limit of the particle sizes usually used to produce coatings according to 
the prior art. 
Instead of crushed rock loose chips, use may advantageously be made of 
crushed products from the demolition of old bituminous road layers, these 
recycled products generally being known as millings. In this case, in 
addition to the advantage which consists in using a product which normally 
has to be stored or removed, material is saved both in respect of the 
loose chips and bitumen used in the method according to the invention. In 
fact, the layer of solid bitumen which remains fixed to the milling to 
form the pasty coating for the aggregates. 
The method according to the invention may be implemented by making use of 
machines which are slightly different from those which have been 
described. The totally integrated design of these machines for producing 
and laying a coating makes it possible, however, to implement the 
invention under optimum conditions, avoiding any error in adjustment of 
the parameters required for producing a coating of satisfactory quality.