Additive composition for bituminous conglomerates with high mechanical performances

Abstract

Additive composition compositions intended to be mixed into bituminous conglomerates for road paving, comprising containing a thermoplastic polymer, a polymeric compound selected from the group consisting of polyvinylbutyral (PVB), polyethylacrylate (PEA) polymethylacrylate (PMA), polybutylacrilate (PBA), lignin and mixtures thereof, and graphene are disclosed. preferably wherein The graphene is contained in a quantity between 0.005 and 1% by weight based on the total weight of the composition. A bituminous conglomerate suitable for making a road paving, containing comprising aggregates, filler, bitumen and said the additive is also disclosed.

Claims

1. An additive composition intended to be mixed into a bituminous conglomerate for road paving and suitable for improving the mechanical properties of bituminous conglomerate, comprising a thermoplastic polymer, polyvinylbutyral, and graphene, wherein the thermoplastic polymer is a polyolefin or a mixture of polyolefins.

2. Additive composition according to claim 1, wherein the thermoplastic polymer is a recycled material.

3. Additive composition according to claim 1, wherein the polyvinylbutyral is a recycled polyvinylbutyral.

4. Additive composition according to claim 1, wherein the graphene is recycled graphene.

5. Additive composition according to claim 1 wherein the graphene is contained in the additive composition in a quantity between 0.005 and 1%, by weight based on the total weight of the composition.

6. Additive composition according to claim 1, wherein the thermoplastic polymer is contained in the additive composition in a quantity between 45 and 95% by weight based on the total weight of the composition.

7. Additive composition according to claim 1, wherein the polyvinylbutyral is contained in the additive composition in a quantity between 5 and 55% by weight based on the total weight of the composition.

8. Additive composition according to claim 1, consisting of the following components, expressed in percentage by weight based on the total weight of the composition: thermoplastic material 50-95; polyvinylbutyral 5-50; and graphene 0.005-1.

9. Additive composition according to claim 1, being in granular form or in form of chips, or in powder form.

10. Bituminous conglomerate suitable for making a road paving with improved mechanical properties, comprising aggregates, filler, bitumen and the additive composition according to claim 1, wherein the additive composition is contained in the bituminous conglomerate in a quantity between 0.09 and 15%, by weight based on the total weight of the bitumen.

11. A process for producing a bituminous conglomerate suitable for making a road paving with high mechanical performances, comprising the step of adding to said aggregates, under stirring and at a temperature between 130 C. and 200 C., the additive composition according to claim 1, bitumen and a filler.

12. Additive composition according to claim 1, wherein the thermoplastic polymer is selected from the group consisting of polyethylene, polypropylene and mixtures thereof.

13. Additive composition according to claim 12, wherein the thermoplastic polymer is a mixture of polyethylene and polypropylene comprising a quantity of polyethylene between 25 and 75% by weight based on the total weight of the mixture.

14. Additive composition according to claim 5, wherein the graphene is contained in the additive composition in a quantity between 0.005 and 0.15% by weight based on the total weight of the composition.

15. Additive composition according to claim 14, wherein the graphene is contained in the additive composition in a quantity between 0.01 and 0.1% by weight based on the total weight of the composition.

16. Additive composition according to claim 6, wherein the thermoplastic polymer is contained in the additive composition in a quantity between 50 and 90% by weight based on the total weight of the composition.

17. Additive composition according to claim 7, wherein the polyvinylbutyral is contained in the additive composition in a quantity between 10 and 50% by weight based on the total weight of the composition.

Description

DETAILED DESCRIPTION

(1) Hereinafter are some examples of additive compositions according to the present invention, which have been prepared and tested with favorable results in relation to their effect of increasing the mechanical performances in the production of bituminous conglomerate. Finally, a comparative example follows, wherein a possible additive composition is shown, not comprising graphene and not according to the present invention.

Example 1

(2) TABLE-US-00003 Mixture of polyethylene and polypropylene (70:30) 49.995% polyvinylbutyral 49.995% virgin graphene 0.01%

Example 2

(3) TABLE-US-00004 Mixture of polyethylene and polypropylene (50:50) 49.95% polyvinylbutyral 49.95% virgin graphene 0.1%

Example 3

(4) TABLE-US-00005 Mixture of polyethylene and polypropylene (60:40) 49.95% polyvinylbutyral 49.95% recycled graphene 0.1%

Example 4

(5) TABLE-US-00006 Mixture of polyethylene and polypropylene (30:70) 74.995% polyvinylbutyral 24.995% virgin graphene 0.01%

Example 5

(6) TABLE-US-00007 Mixture of polyethylene and polypropylene (50:50) 74.95% polyvinylbutyral 24.95% virgin graphene 0.1%

Example 6

(7) TABLE-US-00008 Mixture of polyethylene and polypropylene (70:30) 79.995% polyvinylbutyral 19.995% virgin graphene 0.01%

Example 7

(8) TABLE-US-00009 Mixture of polyethylene and polypropylene (40:60) 79.95% polyvinylbutyral 19.95% virgin graphene 0.1%

Example 8

(9) TABLE-US-00010 Mixture of polyethylene and polypropylene (70:30) 89.995% polyvinylbutyral 9.995% virgin graphene 0.01%

Example 9

(10) TABLE-US-00011 Mixture of polyethylene and polypropylene (70:30) 89.95% polyvinylbutyral 9.95% virgin graphene 0.1%

Example 10

(11) TABLE-US-00012 Mixture of polyethylene and polypropylene (60:40) 89.5% polyvinylbutyral 9.5% virgin graphene 1%

Example 11

(12) TABLE-US-00013 Mixture of polyethylene and polypropylene (70:30) 89.990% polyvinylbutyral 9.995% virgin graphene 0.005%

Example 12 (Reference Example not According to the Invention)

(13) TABLE-US-00014 Mixture of polyethylene and polypropylene (70:30) 90.00% polyvinylbutyral 10.00%

(14) The compositions of Examples 1-11 were prepared by grinding separately the mixture of polyethylene and polypropylene, the polyvinylbutyral and the graphene, and by mixing then the grinded components inside a mixer, obtaining a homogeneous mixture with particles having an average diameter of 2 mm.

(15) The composition of Example 12 was prepared in the same way, starting only from mixture of polyethylene and polypropylene and from polyvinylbutyral.

Example 13

(16) Using the composition according to Example 8, eighteen briquettes of bituminous conglomerate with a diameter of 100 mm and a thickness of about 25 mm, containing such composition according to the proportions of the ingredients indicated in the following Table 2 (Conglomerate A), were prepared in the laboratory. Also eighteen briquettes of bituminous conglomerate with the same composition but comprising the additive composition according to Example 12 (Conglomerate B), and eighteen briquettes of bituminous conglomerate not comprising the additive composition according to Example 8, nor the composition according to Example 12 (Conglomerate C), as well as nine panels of bituminous conglomerate, three for each type of conglomerate A, B and C.

(17) TABLE-US-00015 TABLE 2 Bituminous Bituminous conglomerate conglomerate Bituminous A, containing B, containing conglomerate the composition the composition C, without of Example 8 of Example 12 any additive Materials Parts by weight Parts by weight Parts by weight Inerts grit 12/20 25 25 25 Inerts grit 6/12 35 35 35 Inerts grit 3/6 10 10 10 Sand 0/4 25 25 25 Filler (CaCO.sub.3) 5 5 5 Bitumen 70/100 4.5 4.5 4.5 Additive 0.27 0.27 0 composition Total 104.77 104.77 104.5

(18) The bituminous conglomerate is prepared in the laboratory by means of the procedure that follows, using devices which simulate, in function, machinery on higher scale, usually used in plants for the production of bituminous conglomerate: selecting a granulometric curve, depending on the road paving which is desired to be made with the bituminous conglomerate currently under preparation; selecting aggregates according to the above-mentioned granulometric curve, in the present case the aggregates according to Table 2, and bringing the aggregates to a temperature of 170-180 C. inside a mixer; adding an appropriate quantity of additive composition, in the present case the additive composition according to Example 8 in the quantity expressed in Table 2, then mixing for 40-60 seconds so as to obtain a blend; adding to the blend an appropriate quantity of bitumen, in the present case the quantity expressed in Table 2, then mixing for at least 20-30 seconds; adding to the blend an appropriate quantity of filler, in the present case the quantity expressed in Table 2, then mixing for at least 5 minutes (as provided by the normative law EN 12697-35), obtaining a homogeneous blend of bituminous conglomerate.

(19) In particular, the blend is maintained at a temperature between 170 and 180 C. during all the steps of processing thereof.

(20) In case of the bituminous conglomerate B, instead of the composition of Example 8 according to the invention, the composition of Example 12 not according to the invention (which is graphene-free) is added. In the case of the bituminous conglomerate C, after the step of heating the aggregates, a step of adding bitumen to them directly follows.

(21) The blend of bituminous conglomerate obtained thereby is then discharged from the mixer, dosed in a quantity equal to about 1210 g in containers and subsequently it is conditioned in oven at a temperature of 150 C. for about 3 hours (to simulate the transportation conditions).

(22) The bituminous conglomerate obtained thereby, after the step of oven conditioning, is then inserted inside a template. Then, in order to obtain a voids percentage of about 2.5%, a compaction by means of gyratory compactor is performed (alternatively to the gyratory compactor it is possible to use any other type of compactor suitable for the purpose, for example a Marshall compactor):

(23) TABLE-US-00016 Load pressure: 600 kPa; Gyratory angle: 1.25; Limit density: 2400 kg/m.sup.3.

(24) 18 briquettes were made for each type of bituminous conglomerate for performing the mechanical tests, simultaneously three panels of 50 cm70 cm size were formed, one for each type of bituminous conglomerate.

(25) The eighteen briquettes of conglomerate A, the eighteen briquettes of conglomerate B and the eighteen briquettes of conglomerate C, as well as the panels of conglomerate A, the panels of conglomerate B and the panels of conglomerate C have been finally placed in climatic chambers for the appropriate conditioning for performing the mechanical tests.

Example 14 (Determination of the Tensile Strength)

(26) Six briquettes of conglomerate A, six briquettes of conglomerate B and six briquettes of conglomerate C were used to perform a tensile strength test.

(27) Each briquette was respectively housed in a mechanical press of the designated test basket, then a tensile strength test was performed according to the methodology UNI EN 12697-23.

(28) The mechanical characterization occurred with the Indirect Tensile Strength (ITS). The ITS simulates the maximum stress generated by vehicle passage which can be tolerated by the road pavement.

(29) The results of the individual tests are shown in Table 3, which follows.

(30) TABLE-US-00017 TABLE 3 Mixture ITS (MPa) Conglomerate A 1.71 Conglomerate B 1.57 Conglomerate C 1.07 Mixture (comparison) Percent change (%) A vs. B +8.9 A vs. C +59.8 B vs C. +46.7

(31) From the data reported in Table 3 it is possible to note that the additive composition according to the present invention allows to increase the Indirect Tensile Strength by about 60% in a bituminous conglomerate made with it (conglomerate A) if compared with a traditional bituminous conglomerate with bitumen as such (conglomerate C), and by 9% if compared to a bituminous conglomerate comprising an additive composition substantially identical regarding polyethylene/propylene and PVB contents but which is graphene-free (conglomerate B). An increase of the Indirect Tensile Strength implies therefore a higher strength of the bituminous conglomerate subjected to load and, therefore, the additive composition according to the present invention allows to formulate a bituminous conglomerate which allows to build a road paving characterized by a longer service life. The considerable increase of direct tensile strength obtained with the composition according to the present invention, if compared to a composition which is identical except for lacking a graphene quantity of only 0.01% by weight, has to be considered totally surprising.

Example 15 (Determination of the Stiffness Modulus)

(32) Six briquettes of conglomerate A, six briquettes of conglomerate B and six briquettes of conglomerate C were used to perform a test for determining the stiffness modulus, meant as capability of bituminous conglomerates to propagate in the superstructure the load exerted in the road surface from the track areas of the vehicle tyres.

(33) Each briquette was respectively placed on a designated housing of a servo-pneumatic system for dynamic tests, which was in turn contained in a climatic cell for temperature control; subsequently, a test for the determination of the stiffness modulus was performed according to the methodology UNI EN 12697-26.

(34) The test conditions used for the determination of the stiffness modulus were: Temperature: variable; Imposed horizontal strain: 5 m; Peak time: 124 ms (frequency 2 Hz); Poisson Coefficient: 0.35.

(35) The results of the individual tests are shown in Table 4, which follows.

(36) TABLE-US-00018 TABLE 4 Stiffness of the samples at different temperatures (MPa) Mixture T = 5 C. T = 20 C. T = 40 C. Conglomerate A 21124 7809 3003 Conglomerate B 20866 6685 2691 Conglomerate C 10169 5711 1096 Mixture (comparison) Percent change (%) A vs. B +1.2% +16.8% +11.6% A vs. C +107.7% +36.7% +174.0% B vs C. +105.2% +17.1% +145.5%

(37) As it is obvious, the additive composition according to the invention (Example 8), when used for the formulation of a bituminous conglomerate, determines in the latter a substantial increase of the stiffness modulus with respect to both the traditional conglomerate (conglomerate C) and the conglomerate comprising the additive composition according to Example 12, which is graphene-free (conglomerate B). In this sense, the conglomerate A shows to be particularly performing at moderately high temperatures (T=20 C.; T=40 C.). The increase in stiffness modulus found for conglomerate A with respect to conglomerate B is even higher of the already considerable increase of the tensile strength found in the previous example and therefore even more surprising.

Example 16 (Determination of the Fatigue Resistance)

(38) Six briquettes of conglomerate A, six briquettes of conglomerate B and six briquettes of conglomerate C were used to perform the fatigue resistance test. The failure due to fatigue of a paving happens because of the repetition over time of deforming states, induced by tensile stresses which are caused by both the vehicle traffic and the seasonal cycles and temperature change.

(39) Each briquette was respectively placed on a designated housing of a servo-pneumatic system for dynamic tests, which was in turn contained in a climatic cell for temperature control; subsequently, a test for the determination of the fatigue resistance was performed according to the methodology UNI EN 12697-24.

(40) The test conditions for the determination of the fatigue resistance were: Temperature: 20 C.; Imposed horizontal strain: 300 kPa; Peak time: 248 ms; Rest time: 252 ms; Frequency: 2 Hz; Poisson Coefficient: 0.35; Failure condition: 10% of the initial complex modulus.

(41) The results of the individual tests are shown in Table 5, which follows.

(42) TABLE-US-00019 TABLE 5 Mixture Number of cycles at failure Conglomerate A 1,056,933 Conglomerate B 473,167 Conglomerate C 157,639 Mixture (comparison) Percent change(%) A vs. B +123.4% A vs. C +570.5% B vs C. +200.2%

(43) From the data of Table 5 it can be understood that the conglomerate A, comprising the additive composition according to the invention (Example 8), has a number of fatigue cycles increased by 123% if compared to the bituminous conglomerate B, comprising the additive reference composition according to Example 12, which is graphene-free, and increased to 570% if compared to a traditional bituminous conglomerate (conglomerate C). This is a further, impressive evidence of the surprising improvement of the mechanical performances of the conglomerate, wherein said improvement is accomplished thanks to the presence of graphene, although added in an extremely low quantity (0.01% of the total weight of the additive composition added to the bituminous conglomerate).

Example 17 (Monitoring the Rutting Phenomenon)

(44) Three panels of conglomerate A, three panels of conglomerate B and three panels of conglomerate C were used to perform the test of monitoring the rutting, meant as a phenomenon of longitudinal deformation caused by a thickening under the loading axle with consequent lateral movement of the bituminous mixture during wheel passage. Each panel was respectively placed on a designated housing in a rutting machine (wheel tracking machine), which was in turn contained in a climatic cell for temperature control; subsequently, a test for the determination of the fatigue resistance was performed according to the methodology UNI EN 12697-22.

(45) The lab test which allows to simulate such phenomenon provides the following results: DEPTH: it physically indicates how deep is the rut (higher depth means lower resistance); PRD (Proportional Ruth Depth): it indicates the percentage of rut generated during the test at the predetermined cycle; by reducing said parameter, the deformation is decreased and therefore the service life of the paving is increased; WTS (Wheel Tracking Slope): it indicates the rate at which the bituminous conglomerate gets deformed; by reducing said value, the resistance to deformation is increased and the deformation over time is decreased, increasing the service life of the paving.

(46) The test condition imposed for the determination of the resistance to rutting was a temperature of 60 C.

(47) The results of the individual tests are shown in Table 6, which follows.

(48) TABLE-US-00020 TABLE 6 Rut depth at Rut depth at PRD air WTS air 5,000 cycles 10,000 cycles 10,000 (mm/1000 (mm) (mm) (%) cycles) Conglomerate A 0.43 0.48 0.8 0.009 Conglomerate B 0.88 0.98 1.6 0.022 Conglomerate C 1.39 1.55 2.5 0.025 Mixture (comparison) Percent change (%) A vs. B 51.1% 51.0% 50.0% 59.1% A vs. C 69.1% 69.0% 68.0% 64.0% B vs C. 36.7% 36.8% 36.0% 12.0%

(49) The tests performed allow to highlight the high performances of the conglomerate A, comprising the additive composition according to the present invention, with a considerable decrease of the rutting phenomenon (51%) if compared to the bituminous conglomerate B, with consequent further increase of the service life of the paving and of the road safety, if compared to the traditional paving (conglomerate C).

(50) In this case, too, it can be noted that the graphene contained in the additive composition according to the present invention, although said graphene is present in a definitely small quantity (0.01% by weight in the composition according to Example 8), determines a considerable and surprising increase of resistance to rutting.

(51) Ultimately, all the experimental evidences show that the additive composition according to the invention allows to produce bituminous conglomerates with increased performances in terms of mechanical properties, consequently determining an extension of the total life of the road paving made with them. This determines not only an economic saving (less maintenance of the road pavement), but also a considerable decrease of the environmental impact (possibility to make a thinner layer of conglomerate, if compared to a conglomerate without the additive composition according to the invention, given the same lifetime, with consequent reduced carbon dioxide emissions due to the production of the conglomerate itself), as well as an increase of the overall safety in using the road paving at issue.