Bituminous mixtures for roads with very high performances, method for producing said mixtures and their application on roads

The bituminous mixtures for roads consist in a granular composition basically containing hard rock aggregate and a binder composed of very hard bitumens and possible additives and used in an amount corresponding to a corrected richness modulus .kappa. within the range of 3.8 to 4.5 in accordance with the relation: ##EQU1## .SIGMA.=conventional specific surface-area of the aggregate=0.25 G+2.3 S+12s+135f, in m.sup.2 /kg with the proportions by weight PA1 G representing the percentage of particles larger than 6 mm PA1 S representing the percentage of particles ranging from 6 to 0.315 mm PA1 s representing the percentage of particles ranging from 0.315 to 0.08 mm PA1 f representing the percentage of particles smaller than 0.08 mm PA1 K=corrected richness modulus PA1 .alpha.=corrective coefficient intended to take into account the mass per unit volume of the aggregate, .alpha. being equal to 2.65/mass per unit volume of the aggregate.

This invention relates to bituminous mixtures for roads with very high 
performances, a method for producing said mixtures and their application 
of roads. 
In all countries, road regulations allow running of vehicles with heavy 
axles, even if the limit-weight is higher or lower according to countries. 
The existence of such loads makes it necessary to use bituminous mixtures 
having a high creep resistance on roadways with a heavy dense traffic. It 
is essential to ensure a sufficient working life. This involves the use of 
an important amount of bituminous mixture. 
However, due to various limitations, it is sometimes necessary to apply or 
lay a bituminous mixture of a thickness much lower than the conventional 
bituminous mixture thickness indispensable to obtain the required working 
life. 
The characteristics for a bituminous mixture showing, at a reduced 
thickness, the same effect as a conventional bituminous mixture of normal 
thickness should be improved in two fields: 
the flexure modulus which has to be increased; 
the capacity of deformation under repeated loads which has to be augmented. 
The purpose of the present invention is to provide bituminouds mixtures for 
roads with very high performances adapted to meet the above-stated 
requirements both in the field of creep resistance and the fields of 
modulus and of fatigue strength. 
It is well known that the composition of bituminous mixtures for roads 
involves three main parameters, viz.: 
the aggregate volume AV 
the binder volume BV 
the void volume v. 
In the report of the XVIth Road World Congress, September 16-21, 1979, Wien 
(Austria), the following was specified: 
the bituminous mixtures which have the best resistance to rutting are those 
whereof the compression modulus sensitivity to temperature is as low as 
possible; 
this requirement may notably be met by the use of hard bitumens, the search 
of a high ratio between the aggregate content per volume and the binder 
content per volume (AV/BV) and of a low void percentage (v); 
the bituminous mixtures having resistance to rutting and meeting the 
above-stated requirement (high AV/BV, low v, hard bitumen), if laid to a 
suitable thickness, will also resist to fatigue cracking. As concerns 
fatigue, however, it is advisable to avoid the use of bitumens having 
excessive hardness (either naturally or due to ageing) which could render 
the compositions liable to cracking of thermal origin; 
besides the bitumen characteristics, the two composition parameters 
governing the fatigue phenomenon and the creep phenomenon are the AV/BV 
ratio and the void percentage v. The simultaneous obtention of a high 
AV/BV ratio and of a low void percentage v is governed by the 
particle-size, the aggregate shape and the compacting efficiency; 
any mixture having a high AV/BV ratio, but a high void percentage v, may be 
resistant to rutting but poor as regards cracking and overall durability. 
On the other hand, the researches effected by the applicant led to the 
following conclusions: 
the mixtures characterized by a low binder content, such as required to 
have a high AV/BV ratio, have a rigidity modulus of high value and a high 
creep resistance; 
such mixtures have a resistance to fatigue all the more low as their 
rigidity modulus is higher. 
The applicant thus found that researches directed along the generally 
received line of opinion could not lead to the provision of bituminous 
mixtures with high performances. 
Deviating from the teachings of the prior art, the applicant took up an 
unexpected line and found out, quite surprisingly, that the use of a very 
hard bitumen involves no drawback as concerns cracking, contrarily to the 
present knowledge, provided that a large amount of binder is used. 
According to the invention, there was thus provided both unexpected and 
valuable results by using very hard bitumens in very large amounts, this 
leading to relatively low values of AV/BV. 
From the present state of the art, it could not be anticipated that such 
bituminous mixtures, having a composition different from that recommended, 
would be satisfactory. 
The bituminous mixtures according to the present invention have: 
a very high rigidity modulus; 
a very high capacity of deformation under alternating loads; 
a very high creep resistance. 
These are the characteristics sought for bituminous mixtures with very high 
performances. 
According to the present invention, the bituminous mixtures for roads with 
very high performances having resistance to rutting and to cracking are 
characterized in that they consist in a granular composition basically 
containing hard rock aggregate and a binder composed of very hard bitumens 
and of possible additives and used in an amount corresponding to a 
corrected richness modulus K ranging from 3.8 to 4.5 in accordance with 
the relation: 
##EQU2## 
where .SIGMA.=conventional specific surface-area of the aggregate=0.25 
G+2.3 S+12 s+135f, in square meters per kilogram (m.sup.2 /kg) with the 
proportions by weight: 
G representing the percentage of particles larger than 6 mm 
S representing the percentage of particles ranging from 6 to 0.315 mm 
s representing the percentage of particles ranging from 0.315 to 0.08 mm 
f representing the percentage of particles smaller than 0.08 mm 
K=correct richness modulus 
.alpha.=corrective coefficient intended to take into account the mass per 
unit volume of the aggregate, .alpha. being equal to 2.65/mass per unit 
volume of the aggregate. 
It should be noted that, according to the present invention, use may be 
made of aggregates of various natures. The most suitable aggregates are 
porphyries, calcareous rocks and the like. 
Various specific characteristics, taken singly or in combination, of the 
bituminous mixtures of the present invention are recited hereunder: 
the granular composition includes 10/20, 6/10, 2/6 gravels, a 0/2 sand and 
a calcareous filler mixed in the following amounts: 
Gravels: 10/20 mm mesh size 35 to 45% 
6/10 mm mesh size 10 to 20% 
2/6 mm mesh size 10 to 15% 
Sand: 0/2 mm mesh size 25 to 35% 
Filler: 0 to 5% 
the thus formed mixture being a 0/20 (2% refuse on a 20 mm-mesh screen); 
the binder has a ball and ring temperature of 70.degree. to 90.degree. C., 
a penetrability at 25.degree. C. of 5 to 20, a PFEIFFER penetration index 
&gt;1 and an embedding temperature of the order of 175.degree. C.; 
the modulus of rigidity is within the range from 160,000 to 240,000 bars 
(16 to 24.times.10.sup.9 pascals); 
the capacity of deformation under alternating loads is in the range from 
200 to 300 .mu.D (.mu.D=microdeformations); 
the creep resistance is in the range from 1 to 6 mm after 100,000 cycles in 
the L.C.P.C. rutting test effected at 50.degree. C. on plates having a 10 
cm thickness; (L.C.P.C.: Laboratoire Central des Ponts et Chaussees 
Official French Organization) 
the possible additive added to the binder is usually a sequenced copolymer 
of styrene-butadienestyrene or of ethylene-vinyl acetate. 
The present invention also relates to a method for producing such 
bituminous mixtures, consisting in heating the aggregate mixture to a 
temperature of about 160.degree.-190.degree. C. and incorporating in said 
aggregate the binder at a temperature ranging from 170.degree. to 
200.degree. C., then kneading the mixture during 20 to 60 seconds. 
According to further features of the present invention, the aggregate is 
wholly dry and heated, its water content being lower than 0.5%. 
The method of the invention further consists in incorporating the possible 
additive directly in the mixture or previously in the binder prior to 
kneading and incorporation of the binder in the aggregate. 
Said possible additive is usually a sequenced copolymer of 
styrene-butadiene-styrene or of ethylene-vinyl acetate. 
The present invention also relates to the application on roads of such 
bituminous mixtures to a thickness of about 8 to 20 cm, more usually 
ranging from 10 to 15 cm. 
The adjustment of the bituminous mixtures according to the invention is 
completely different from the prior art techniques. Said adjustment 
involves the following steps: 
for a given granular composition and a given binder, applicant determines 
the maximum binder content which will afford good creep resistance; 
for the same granular composition, a similar determination is made with 
binders of increasing hardness or of increasing polymer content. 
As a result of such searches, a good creep resistance was found for a 
binder amount corresponding to a corrected richness module ranging from 
3.8 to 4.5.

The following examples are given to illustrate the present invention by no 
way of limitation. 
EXAMPLE 1 
A. Aggregate 
The aggregate used was 10/20, 6/10, 2/6 gravels, a 0/2 sand and a 
calcareous filler. The gravels and sand originated from the quarry of La 
Meillerrie-Tillay in Vendee (France). The filler is a calcareous filler of 
current use in granular formulations. 
B. Characteristics of aggregate 
Samples were taken from the quarry existing stocks for a preliminary study. 
The identification tests made on these samples gave the results shown in 
table 1 hereunder. 
The 0/2 sand contained 16% of fines. Its equivalent of sand, viz. 49, is 
markedly higher than the minimum specified for the sands containing more 
than 15% of filler for the construction of roadways courses, viz. 35. 
The granulous texture of the faces is a favorable factor for resistance to 
rutting. 
The Los Angeles coefficient has a value lower than 11. The gravels have a 
hardness meeting the specifications for rolling layers, including the case 
of the heaviest and most dense traffics. 
The four granular fractions were wholly crushed. 
The aggregate was mixed with the following proportions: 
10/20 mm mesh size gravel=35 to 45% 
6/10 mm mesh size gravel=10 to 20% 
2/6 mm mesh size gravel=10 to 15% 
0/2 mm mesh size sand=25 to 35% 
filler=0 to 5%. 
The thus formed mixture is a 0/20=2% refuse on a 20 mm-mesh screen. Its 
particle-size distribution is shown in the table hereunder. 
______________________________________ 
Percentage of particles 
Screen mesh size in mm 
clearing the screens 
______________________________________ 
20 98 
12.5 73 
10 62 
4.0 42 
2.0 32 
1.0 22 
0.500 16 
0.200 11 
0.080 8.4 
______________________________________ 
EXAMPLE 2 
Binder 
The binder used was formulated from direct distillation bitumens and from 
additive. It was specially prepared for the production of gravel-bitumen 
with very high performances. 
The characteristics of the special bitumen are compared, in table 2, with 
those of three reference road bitumens covering the overall range of 
conventional road bitumens. 
TABLE 1 
__________________________________________________________________________ 
10/20 6/10 2/6 
0/2 
SPECIFICATIONS 
FILLER 
__________________________________________________________________________ 
Nature microdiorite 
L.A. dependent on the 
calcareous 
traffic classes as de- 
fined in the Catalogue de 
"Structures - types 
de chaussees" 
Specific weight of particles 
2.91 2.9 
(1977 edition) 
-- 
Percentage of particles 
insolubles in hydrochloric 
acid 100 T1 to T3 
T0 .congruent.0 
LOS ANGELES coefficient (L.A.) 
6 to 11 &lt;30 &lt;25 -- 
Shape coefficient of the 
-- -- S.E. dependent on 
-- 
gravels the percentage of 
filler in the 
0/2 fraction 
Angularity entirely crushed -- 
Face texture granulous &lt;12% 12 to 
&gt;15% 
-- 
15% 
Sand equivalent (S.E.) as 
measured on the sand itself 
-- 49 &gt;45 &gt;40 &gt;35 -- 
__________________________________________________________________________ 
TABLE 2 
______________________________________ 
Bitumen Reference bitumens 
Binders of the invention 
20/30 60/70 180/220 
______________________________________ 
Ball and ring 
temperature 
70 to 90.degree. C. 
52-65.degree. C. 
43-56.degree. C. 
39-48.degree. C. 
Penetrability 
at 25.degree. C. 
5 to 20 18 64 200 
PFEIFFER 
penetration 
index &gt;1 -0.3 -0.3 -0.5 
Embedding 
temperature 
175.degree. C. 
170.degree. C. 
145.degree. C. 
130.degree. C. 
______________________________________ 
The ball and ring temperature, higher than that of the 20/30, indicates 
that the special binder will retain more consistency than the 20/30 at a 
high temperature (60.degree. C.), this rendering the road bituminous 
mixture free from creep-deformation. 
The embedding temperature of the special binder is of 175.degree. C., i.e. 
slightly higher than the embedding temperature of a 20/30 bitumen. 
EXAMPLE 3 
Behaviour tests 
The following tests were effected: 
determination of the characteristics which the embedded product in position 
will exhibit immediately and checking of the water behaviour of the 
embedded products (expanded DURIEZ test according to the procedures of 
June, 1979, of the Laboratoire Central des Ponts et Chaussees L.C.P.C.), 
determination of the characteristics which the embedded product in position 
will exhibit after a prescribed time (Marshall test) according to the 
procedures of December, 1972, of the Laboratoire Central des Ponts et 
Chaussees), 
checking of the rutting behaviour; 
determination of the purely tensile properties. 
The general characteristics are the following: 
percentage of retained binder (P) . . . 6% 
theoretical density (TD) . . . 2.66 
##EQU3## 
corrected richness module: 
##EQU4## 
1-Duriez tests 
(a) Characteristics of the "EXPANDED DURIEZ" type samples 
Behaviour tests were effected on the "Expanded Duriez" samples to show that 
the bituminous mixtures according to the invention are satisfactory. 
The prepared mixtures were kneaded during about one minute. 
The samples were prepared by being held under a 18-metric ton load for 5 
minutes, then removed from the mold 24 hours after their preparation. They 
were then classed so as to form three series having the same average 
density. Their characteristics are the following: 
______________________________________ 
Hydrostatic apparent density (Da) 
2.25 
Void percentage (V) 4% 
Compacity (C) 96% 
Filling coefficient (FC) 
77% 
______________________________________ 
(b) Immersion-compression 
The first series of 3 samples was crushed after being held in air for 7 
days subsequent to removal from the mold. 
The maximum breaking stress under simple compression, as expressed per unit 
of cross-sectional area of the sample, at 18.degree. C. and 1 mm/s after a 
standing period of 8 days in air, Rc, amounts to 220 bars. 
The second series of 3 samples was immerged, after being degassed, during 7 
days, then removed from the water. 
The samples were crushed, then their water content was determined. The 
measurements gave the following results: 
the maximum breaking stress under simple compression, as expressed per unit 
of cross-sectional of the sample, at 18.degree. C. and 1 mm/s, after a 
standing period of 24 hours in air plus seven days in water (R'c) amounts 
to 221 bars. 
the water content at time of crushing after immersion is 0.4%. 
the immersion-compression reduction coefficient ic=R'c/Rc=1. 
2. Diametral compression 
Another series of 3 samples was held 8 days in air, then crushed under 
diametral compression at 18.degree. C. and 1 mm/s; the maximum stress 
under diametral compression Rt amounts to 55 bars. 
The bituminous mixtures of the invention are excellent as regards their 
resistance under simple compression and diametral compression, as well as 
their water behaviour. 
3. Marshall tests 
The tests effected under standardized conditions gave the following 
results: 
______________________________________ 
Number of impacts 50 100 
Hydrostatic apparent density 
2.54 2.57 
Compacity (c) 95.5% 96.6% 
Voids (V) 4.5% 3.4% 
Stability (daN) 2900 3100 
______________________________________ 
4. Rutting test 
Resistance to rutting was examined under traffic action simulation by means 
of a rutting device on laboratory-made plates of 500.times.180.times.100 
mm. 
(a) Characteristics of the samples 
The tests were effected on two 10-cm plates which were compacted in an 
attempt to reach 100% compacity. The characteristics of the plates are as 
follows: 
______________________________________ 
thickness (cm) 10 
geometrical apparent density 
2.55 
relative compacity with respect 
to DURIEZ density 102% 
Percentage of geometrical voids 
4% 
______________________________________ 
(b) Test conditions 
The test were made by applying a 500 daN load through a wheel having its 
tire inflated at 6 bars and driven in a reciprocating translation motion 
at a frequency of 1 Hz during 100,000 cycles (200,000 passes) at 
50.degree. C. in accordance with the test standards for bituminous 
mixtures intended to form basic layers. 
______________________________________ 
Inflation pressure 6 bars 
Applied load 500 daN 
Skidding angle 0.degree. 
Motion frequency 1 Hz 
Temperature 50.degree. C. 
______________________________________ 
(c) Measurement of the rut depth 
The rut depth was measured by comparing with the initial outline subsequent 
outlines drawn along three profiles by means of a cross-contour 
micro-tracer, after subjection of each sample to: 
1,500 cycles or 3,000 wheel passes 
6,000 cycles or 12,000 wheel passes 
25,000 cycles or 50,000 wheel passes 
100,000 cycles or 200,000 wheel passes 
The results obtained are expressed in mm in the table hereunder: 
______________________________________ 
Sinking in mm with respect to 
Number of cycles 
the initial contour 
______________________________________ 
400 1.2 
1,500 1.8 
6,000 2.8 
25,000 3.7 
100,000 4.4 
______________________________________ 
The quite limited depth of the rut, viz. 4.4 mm at 50.degree. C., evidences 
a remarkable behaviour of the bituminous mixtures according to the 
invention, even if the applied bituminous mixture is thin. 
The invention is not limited to the embodiments described in details and 
various modifications may be brought thereto within the scope of the 
following claims.