DOUBLE LAYER DRAINING AND SOUND-ABSORBING WEARING COURSE, AND MEANS AND METHOD FOR ITS PREPARATION

Abstract: The present invention relates to a draining and sound-absorbing wearing course consisting of two layers having a different thickness, made up of modified bitumen and inert products having particular characteristics. This wearing course can be used for paving motor racing circuits highways, national and urban roads.

Description: DOUBLE LAYER DRAINING AND SOUND-ABSORBING WEARING COURSE, AND MEANS AND METHOD FOR ITS PREPARATION. The present invention relates to a double layer draining and sound-absorbing wearing course, its use in motor racing circuits and road paving, means and method for its preparation. The wearing courses used in motor racing circuits, highways, national and urban roads with heavy traffic require good mechanical properties, a high grip and sur- face regularity. These properties are traditionally obtained using "closed" wearing courses, i.e. with reduced content of residual voids. This solution however is of no help during rainfall. In fact, the rain stagnates on the surface with a consequent reduction in tyre grip (aquaplaning) also causing water spray which reduces the visibility. In order to solve these drawbacks, "open" wearing courses, also called draining pavements, were developed, whose use in road paving began on a wide scale towards the mid-eighties' and was applied to highways, national and urban roads . Draining pavements are mainly characterized by a high percentage of residual voids (>18%) obtained by adopting inert products with a discontinuous granu- lometric curve which ensures, with respect to a closed pavements, the following advantages: improvement in tyre grip on wet surfaces; decrease in water spray generated by tyres in the case of rain; - elimination of aquaplaning; reduction in the sound level outside the car owing to the absorption of acoustic energy; reduction in the luminous reflection at night. With respect to closed wearing courses, however, these pavements have a reduced structural resistance and a tendency towards rapid fouling, which blocks the voids and consequently reduces the draining capacity. The use of these draining pavements consequently does not seem to be very suitable for particular appli- cations, such as for example, the paving of motor racing circuits, on which there are greater problems of structural resistance and fouling. It has now been found that the drawbacks of the known art discussed above can be overcome by the use of an open wearing course consisting of two layers have different thicknesses and different granulometric curves of the stone aggregates (inert products). In particular, the use of modified bitumens having a reduced thermal susceptibility, high elasticity, high tack to inert products and good aging resistance, com- bined with this double-layered structure, allows the following advantages to be obtained: (a) an improved crushing strength with respect to the traditional draining pavements; (b) a reduction m the sound impact non only externally but, surprisingly, also inside the vehicle; (c) a draining capacity which decreases more slowly with time; (d) a lesser tendency towards fouling (pore blockage) . The upper layer, m fact, obtained with stone agglomerates having reduced dimensions, owing to its texture, acts as a sieve for the impurities present on the road surface. In this way the larger impurities are withheld on the surface without blocking the pores and can be mechanically removed by the passage of vehicles. The finer impurities penetrate through both layers and can be easily eliminated by rain water through the larger holes of the lower layer. In accordance with this, an objective of the pres- ent invention relates to a double layer draining and sound-absorbing wearing course made up of: (1) an upper layer having a thickness ranging from 2 to 5 cm consisting of a bituminous conglomerate which com ¬ prises : (a) a stone aggregate consisting of elements with dimensions ranging from 0.075 to 10 mm in a quantity ranging from 88 to 98% by weight; (b) a filler in a quantity ranging from 2 to 12% by weight; (c) a bituminous ligand having the characteristics indicated in table 2 in a quantity ranging from 3.5 to 5.5% by weight with respect to the sum of components (a) and (b) and (2) a lower layer having a thickness ranging from 2 to 7 cm consisting of a bituminous conglomerate which comprises : (a') a stone aggregate consisting of elements with dimensions ranging from 0.125 to 20 mm in a quantity ranging from 85 to 98% by weight; (b 1 ) a filler in a quantity ranging from 2 to 15% by weight; (c') a bituminous ligand having the characteristics indicated in table 2 in a quantity ranging from 3.5 to 5.5% by weight with respect to the sum of components (a' ) and (b 1 ) . The upper layer of the draining and sound-absorbing wearing course preferably has a thickness ranging from 2.5 to 4 cm and consists of: (a) a stone aggregate consisting of elements with dimensions ranging from 0.075 to 7.1 mm in a quantity ranging from 90 to 95% by weight; (b) a filler in a quantity ranging from 5 to 10% by weight; (c) a bituminous ligand having the characteristics indicated in table 2 in a quantity ranging from 4 to 5% by weight with respect to the sum of components (a) and (b) . The lower layer of the draining and sound-absorbing wearing course preferably has a thickness ranging from 3 to 7 cm and consists of: (a 1 ) a stone aggregate consisting of elements with dimensions ranging from 0.125 to 15 mm in a quantity ranging from 90 to 95% by weight; (b 1 ) a filler in a quantity ranging from 5 to 10% by weight; (c') a bituminous ligand having the characteristics indicated in table 2 in a quantity ranging from 4 to 5% by weight with respect to the sum of components (a 1 ) and (b') . The stone aggregates which can be used consist of healthy, hard granular elements, in a non-flattened, elongated or lenticular form, clean and without foreign matter, according to regulation C.N.R. 139/1992. These aggregates typically have the characteristics indicated in table 1. Table 1 The fillers are those conventionally used for the production of conglomerates. They are generally powders with a particle size of less than 0.125 mm. Examples of fillers suitable for the purpose of the present invention comprise calcium carbonate and cement. The bituminous ligand is selected from modified bi- tumens having the characteristics indicated in table 2. Table 2 A modified bitumen having a softening point of over 80°C and an elastic flow at 25°C higher than 80%, is preferably used. Particularly preferred is a modified bitumen containing SBS (styrene-butadiene-styrene) polymers obtained, for example, as described in U.S. patent 5,756,563, or, for example of the type sold by AGIP PETROLI S.p.A. under the trade-name of ELIFLEX ® . Some of the characteristics of the pavements of the present invention are indicated in table 3. Table 3 The sound-absorbency characteristics, determined by means of sound level measurements, not only indicate a decrease in noise outside the vehicle, but also a reduction thereof inside the vehicle of over 3 decibel. The bituminous conglomerate, which forms a further objective of the present invention, is prepared under heating in a suitable plant by putting the stone aggregate, the bitumen and filler in contact with each other in the appropriate quantities . The temperature and mixing time are generally selected in relation to the materials and climatic conditions during the laying. In any case, the mixing conditions are selected so as to obtain a conglomerate having an adequate laying temperature to allow effective roll- ing . The pavement of the present invention is prepared by: (i) the laying of a first lower layer having a thickness ranging from 2 to 7 cm and consisting of a bitumi- nous conglomerate which comprises: (a 1 ) a stone aggregate consisting of elements with dimensions ranging from 0.125 to 20 mm in a quantity ranging from 85 to 98% by weight; (b') a filler in a quantity ranging from 2 to 15% by weight; (c 1 ) a bituminous ligand having the characteristics indicated in table 2 in a quantity ranging from 3.5 to 5.5% by weight with respect to the sum of components (a' ) and (b* ) ; and (ii) the curing of this first layer; and (iii) the laying on said first layer of a second upper layer having a thickness ranging from 2 to 5 cm consisting of a bituminous conglomerate which comprises: (a) a stone aggregate consisting of elements with di- mensions ranging from 0.075 to 10 mm in a quantity ranging from 88 to 98% by weight; (b) a filler in a quantity ranging from 2 to 12% by weight; (c) a bituminous ligand having the characteristics in- dicated in table 2 in a quantity ranging from 3.5 to 5.5% by weight with respect to the sum of components (a) and (b) . In practice, before proceeding with the laying of the conglomerate, all the usual operations are effected for its preparation, consisting in milling the damaged layer, profiling and cleaning. A water-proofing membrane is then laid on top of the base layer to protect it from the infiltration of rain water. This membrane consists of modified bitumen, pref- erably a bitumen identical to that used for the preparation of the conglomerates, suitably saturated with grit or filler. The bituminous conglomerate is then laid on top of this membrane to obtain a first lower layer having the characteristics described above. After laying the lower draining layer, it is advisable to allow a curing time of not less than two days before proceeding with the laying of the upper layer. The bituminous conglomerate is laid using slightly staggered vibratory finishers in parallel thus avoiding, or in any case reducing, longitudinal joints. These should be particularly treated (flanking and compaction) to avoid stagnation of rain or reduction in the draining capacity. The rolling is carried out using the conventional techniques . The draining and sound-absorbing wearing course of the present invention is particularly suitable for the paving of motor racing cirsuits and heavy traffic roads.

Claims: CLAIMS 1. A double layer draining and sound-absorbing wearing course consisting of: (1) an upper layer having a thickness ranging from 2 to 5 cm consisting of a bituminous conglomerate which comprises: (a) a stone aggregate consisting of elements with dimensions ranging from 0.075 to 10 mm in a quantity ranging from 88 to 98% by weight; (b) a filler in a quantity ranging from 2 to 12% by weight; (c) a bituminous ligand having the characteristics indicated in table 2 in a quantity ranging from 3.5 to 5.5% by weight with respect to the sum of compo- nents (a) and (b) and (2) a lower layer having a thickness ranging from 2 to 7 cm consisting of a bituminous conglomerate which comprises: (a 1 ) a stone aggregate consisting of elements with dimensions ranging from 0.125 to 20 mm in a quantity ranging from 85 to 98% by weight; (b') a filler in a quantity ranging from 2 to 15% by weight; (c') a bituminous ligand having the characteristics indicated in table 2 in a quantity ranging from 3.5 to 5.5% by weight with respect to the sum of components (a' ) and (b 1 ) . 2. The wearing course according to claim 1, wherein the upper layer has a thickness ranging from 2.5 to 4 cm and consists of: (a) a stone aggregate consisting of elements with dimensions ranging from 0.075 to 7.1 mm in a quantity of 90 to 95% by weight; (b) a filler in a quantity ranging from 5 to 10% by weight; (c) a bituminous ligand having the characteristics indicated in table 2 in a quantity ranging from 4 to 5% by weight with respect to the sum of components (a) and (b) . 3. The wearing course according to claim 1, wherein the lower layer has a thickness ranging from 3 to 7 cm and consists of: (a) a stone aggregate consisting of elements with dimensions ranging from 0.125 to 15 mm in a quan- tity of 90 to 95% by weight; (b) a filler in a quantity ranging from 5 to 10% by weight; (c) a bituminous ligand having the characteristics indicated in table 2 in a quantity ranging from 4 to 5% by weight with respect to the sum of compo- nents (a) and (b) . 4. The wearing course according to claim 1, wherein the stone aggregates consist of healthy.. hard granular elements, in a non-flattened, elongated or lenticular form, clean and without foreign matter. 5. The wearing course according to claim 1, wherein the filler is selected from calcium carbonate and cement . 6. The wearing course according to claim 1, wherein the bituminous ligand is a modified bitumen containing styrene-butadiene-styrene polymers. 7. The wearing course according to claim 1, wherein the lower layer is coupled with a water-proofing membrane consisting of modified bitumen saturated with grit or filler. 8. The wearing course according to claims 1 to 7 , useful for the paving of motor racing circuits, highways, national and urban roads. 9. A bituminous conglomerate which comprises: (a) a stone aggregate consisting of elements with dimensions ranging from 0.07 to 20 mm in a quantity ranging from 85 to 98% by weight; (b) a filler in a quantity ranging from 2 to 15% by weight; (c) a bituminous ligand having the characteristics indicated in table 2 in a quantity ranging from 3.5 to 5.5% by weight with respect to the sum of components (a) and (b) . 10. The bituminous conglomerate according to claim 9, useful for the preparation of the upper and lower layer of the draining and sound-absorbing wearing course according to claim 1. 11. A method for the preparation of the double-layered draining and sound-absorbing wearing course which comprises: (i) the laying of a first lower layer having a thickness ranging from 2 to 7 cm and consisting of a bituminous conglomerate which comprises: (a 1 ) a stone aggregate consisting of elements with dimensions ranging from 0.125 to 20 mm in a quantity ranging from 85 to 98% by weight; (b') a filler in a quantity ranging from 2 to 15% by weight; (c') a bituminous ligand having the characteristics indicated in table 2 in a quantity ranging from 3.5 to 5.5% by weight with respect to the sum of components (a') and (b'); and (ii) the curing of this first layer; and (iii) the laying on said first layer of a second upper layer having a thickness ranging from 2 to 5 cm consisting of a bituminous conglomerate which comprises : (a) a stone aggregate consisting of elements with dimensions ranging from 0.075 to 10 mm in a quan- tity ranging from 88 to 98% by weight; (b) a filler in a quantity ranging from 2 to 12% by weight; (c) a bituminous ligand having the characteristics indicated in table 2 in a quantity ranging from 3.5 to 5.5% by weight with respect to the sum of components (a) and (b) . 12. The method according to claim 11, wherein the lower layer has a thickness ranging from 3 to 7 cm and consists of: (a 1 ) a stone aggregate consisting of elements with dimensions ranging from 0.125 to 15 mm in a quantity ranging from 90 to 95% by weight; (b') a filler in a quantity ranging from 5 to 10% by weight; (c') a bituminous ligand having the characteristics indicated in table 2 in a quantity ranging from 4 to 5% by weight with respect to the sum of components (a' ) and (b' ) . 13. The method according to claim 11, wherein the upper layer has a thickness ranging from 2.5 to 4 cm and consists of : (a) a stone aggregate consisting of elements with dimensions ranging from 0.075 to 7.1 mm in a quantity ranging from 90 to 95% by weight; (b) a filler in a quantity ranging from 5 to 10% by weight; (c) a bituminous ligand having the characteristics indicated in table 2 in a quantity ranging from 4 to 5% by weight with respect to the sum of compo- nents (a) and (b) . 14. The method according to claim 11, wherein the lower layer is laid on a water-proofing membrane consisting of modified bitumen saturated with grit or filler.

Inventors: D ELIA LUIGI, DA VIA MAURO, DIANI ELIO, ITALIA PAOLO, DA VIA, MAURO, D'ELIA, LUIGI, DIANI, ELIO, ITALIA, PAOLO
Applicants: AGIP PETROLI, DA VIA MAURO, DIANI ELIO, ELIA LUIGI D, ENICHEM SPA, ITALIA PAOLO, AGIP PETROLI S.P.A., DA VIA, MAURO, D'ELIA, LUIGI, DIANI, ELIO, ENICHEM S.P.A., ITALIA, PAOLO
Application year: 2000
Main classification: E01C7
IPC codes: E01C7, E01C11