Process for manufacturing asphalt containing rubber from scrap tires

Abstract

A method for producing asphalt, comprising: a heating treatment step, in which rubber particles derived from a granulation process of scrap tires are subjected to a temperature between 80 and 300°C for a desired time to obtain rubber particles having a density between 1.0 and 1.5 g / cm 3 3; and a mixing step in which the rubber particles from the heating treatment step are mixed with stone aggregates and asphalt to obtain asphalt.

Description

[0001] This invention relates to a method for using rubber derived from scrap tires in the preparation of asphalt.

[0002] In this article and below, the term asphalt refers to asphalt conglomerate used to construct road surfaces.

[0003] Typically, road asphalt consists of about 94% stone aggregate and about 6% bitumen.

[0004] The use of rubber from scrap tires (PFU) or end-of-life tires has been known for some time (hereinafter referred to as ELT, an acronym for end-of-life tire). In addition to its environmental advantages due to the use of waste materials, the use of ELT rubber also offers advantages in reducing rolling noise generated by dynamic tire-road contact.

[0005] The solutions implemented to date have inspired two methods for using rubber powder from ELT. One method (commonly referred to as the "dry process") inspires the direct addition of powder to the aggregate and bitumen during the mixing step of the bitumen conglomerate, where the amount of powder is in the range of 1-2% by weight relative to the mixture. The other method (commonly referred to as the "wet process") inspires the mixing of bitumen and powder and its reaction at a temperature that causes rubber particles to expand, thereby obtaining the substance referred to in the English term Crumb Rubber Modified Binder (CRMB); the amount of powder to be introduced into CRMB varies between approximately 15% and 22% by weight relative to the bitumen.

[0006] Given that, according to these existing technologies in the field, the powder used in both the "dry" and "wet" processes accounts for only about 2% by weight of the asphalt, it is evident that, according to the solutions implemented to date, the amount of ELT rubber that can be used in the asphalt is very low. Such limitations, in addition to demonstrating a significant hindrance to the recycling of ELT rubber in asphalt, also preclude the possibility of investigating the potential performance advantages of asphalt obtained with a greater presence of ELT rubber.

[0007] Therefore, there is a need to be able to use ELT rubber in asphalt in greater quantities than that permitted by the aforementioned techniques in the prior art.

[0008] The inventors of this invention have developed a solution that allows ELT rubber to be processed in a manner that enables the use of ELT rubber as an inert material and as a partial substitute for stone aggregate, thereby overcoming the need to dissolve it in bitumen to produce CRMB and thus satisfying the aforementioned requirements.

[0009] The object of the present invention is a process for the production of asphalt, comprising: a heating treatment step, in which rubber granules deriving from a granulation process of end-of-life tyres are subjected to a temperature between 80 and 300°C, preferably between 100 and 200°C, for the time required to obtain rubber granules having a density between 1.0 and 1.5 g / cm 3 , preferably between 1.2 and 1.3 g / cm 3 ; and a mixing step, in which the rubber granules from the heating treatment step are mixed with stone aggregates and bitumen to obtain asphalt.

[0010] Preferably, said mixing step comprises a first mixing operation, in which stone aggregates and bitumen are mixed together at a temperature between 150 and 200°C; and a second mixing operation, in which the rubber granules are added to the mixture from the first mixing operation.

[0011] Such mixing sequence ensures a better granular distribution in the resulting asphalt.

[0012] Preferably, the rubber granules from the heating treatment step constitute between 1 and 30% by volume of the amount of inert material contained in the asphalt.

[0013] Herein and hereinafter, the term inert material means a combination made up of stone aggregates and ELT rubber granules.

[0014] Preferably, the rubber granules deriving from the granulation process have a substantially polyhedral conformation, in which the ratio between the largest dimension and the smallest dimension is less than 2.

[0015] In fact, it was found that granules having a three-dimension similar to each other give better results.

[0016] Preferably, the rubber granules deriving from the granulation process have a size passing through a sieve having a mesh size between 10 mm and 1.5 mm, more preferably having a mesh size between 2.0 mm and 6.0 mm.

[0017] Preferably, the process comprises a pre-heating step, before said heating treatment step, in which the rubber granules deriving from the ELT granulation process are subjected to a temperature between 120 and 200°C for a time between 15 and 30 h.

[0018] Preferably, the process comprises a surface treatment step, after said heating treatment step, in which the rubber granules from the heating treatment are subjected to a surface abrasion operation.

[0019] By means of the abrasion operation, a powder is obtained which allows a greater compactness of the asphalt to be achieved. Moreover, the present inventors believe it to be extremely important that this powder should derive from the outer layer of the pre-treated rubber granules.

[0020] Preferably, the process comprises a final heating treatment step after the surface treatment step and before the mixing step; during the final heating treatment step, the rubber particles deriving from the surface treatment process are subjected to a temperature between 80 and 300°C, preferably between 100 and 200°C, for the time required to obtain rubber particles having a density between 1.0 and 1.5 g / cm 3 , preferably between 1.2 and 1.3 g / cm 3 .

[0021] Another object of the present application relates to rubber particles and / or powders deriving from a granulation process of end-of-life tyres having a size by sieve with a mesh size up to 10 mm and subjected to a temperature between 80 and 300°C for the time required to obtain rubber particles and / or powders having a density between 1.0 and 1.5 g / cm 3 , preferably between 1.2 and 1.3 g / cm 3 .

[0022] Preferably, a pre-heating step is carried out on the particles and / or powders before the heating treatment step, in which the rubber particles and / or powders deriving from the ELT granulation process are subjected to a temperature between 120 and 200°C for a time between 15 and 30 h.

[0023] Preferably, a surface treatment step is carried out on the particles and / or powders after the heating treatment step, in which a surface abrasion operation is carried out on the rubber particles and / or powders coming from the heating treatment.

[0024] Preferably, a final heating treatment step is carried out on the particles and / or powders after the surface treatment step; during the final heating treatment step, the rubber particles and / or powders deriving from the surface treatment process are subjected to a temperature between 80 and 300°C, preferably between 100 and 200°C, for the time required to obtain rubber particles and / or powders having a density between 1.0 and 1.5 g / cm 3 , preferably between 1.2 and 1.3 g / cm 3 .

[0025] The maximum diameter of the rubber powders is 1.5 mm.

[0026] The following are non-limiting embodiments shown by way of illustration only.

[0027] Two asphalt conglomerate mixtures according to the present application were produced.

[0028] The two conglomerates differ from each other depending on the type of treatment undergone by the rubber particles originating from the ELT. In particular, the first bituminous conglomerate mixture is obtained using rubber particles subjected to a heating treatment only, while the second bituminous conglomerate mixture is obtained using rubber particles subjected to both a thermal treatment and a mechanical surface treatment.

[0029] In the following examples, the basalt material has a maximum diameter of 8 mm; the fine gravel material has a maximum diameter of 6 mm; the basalt sand material has a maximum diameter of 4 mm; the filler material and the reinforcing fibres must meet the requirements shown in the following tables.

[0030] Requirements for the filler

[0031]

[0032] Requirements for the reinforcing fibres

[0033] Length (pm) 200÷6000 Diameter (pm) 8÷20 Tensile strength (GPa) 1.5÷3.0 Maximum elongation (%) 1.0÷3.0 Melting point (°C) >300

[0034] - First bituminous conglomerate mixture -

[0035] The particles having a size between 2.5-4.0 mm are taken from the rubber originating from the ELT granulation process.

[0036] The particles are subjected to a heating treatment step in a static laboratory oven, at atmospheric pressure, according to the following sequence:

[0037] - at 175°C for a period of 24 h;

[0038] - at 250°C for a period of 10 h, with periodic mixing of the material every hour.

[0039] The density of the particles originating from the heating treatment described above is > 1.25 g / cm 3 .

[0040] During the treatment at 250°C, periodic checks are made on both the density and the water absorption.

[0041] The rubber particles produced as described above are used for the preparation of the bituminous conglomerate mixture.

[0042] Table I shows the composition of the inert materials of the first bituminous conglomerate mixture, both in vol% and in wt%.

[0043] Table I

[0044] Basalt Basalt sand Limestone filler Pre-treated ELT particles Vol. % 51.0 21.0 8.0 20.0 Wt. % 57.3 23.6 8.7 10.4

[0045] As will be described hereinafter, the bituminous conglomerate mixture also comprises bitumen in an amount equal to 8 wt% with respect to 100 wt% of inert materials.

[0046] The process for the preparation of the bituminous conglomerate mixture will be described hereinafter.

[0047] The basalt, basalt sand and bitumen are heated separately from the other ingredients until a temperature of 165°C is reached. Once the temperature of 165°C is reached, the above ingredients are placed in a mixer which is then run at a speed of about 80 rpm. After about one minute of mixing, the reinforcing fibres are added. After about one minute of mixing, the fillers are added. After about one minute of mixing, the pre-treated ELT particles are added. After about one minute, the preparation is terminated.

[0048] Immediately after the mixture is used to determine the maximum density (according to UNI EN 12697-5).

[0049] To prepare the samples, the material mixed at a temperature of 165°C is subjected to a densification process by means of a rotary press (50 revolutions of the rotary press).

[0050] At the end of the densification, the samples are removed from the mould and allowed to cool to room temperature.

[0051] After 24 hours, the samples are cut according to the specifications to perform the subsequent mechanical tests (ITS, ITS R, CTI).

[0052] The parameters studied are:

[0053] The ITS parameter for evaluating the mechanical resistance (UNI EN 12697-23).

[0054] The ITS R parameter for evaluating the sensitivity to water (UNI EN 12697-12).

[0055] The CTI parameter for evaluating the deformation index (UNI EN 12697-23).

[0056] Table II shows the results obtained for the above parameters.

[0057] Table II

[0058] ITS (MPa) CTI (MPa) ITSR (%) 0.44 11.9 75

[0059] Table III shows the values of the volumetric characteristics as a function of the number of revolutions of the rotary press.

[0060] In particular, the volumetric characteristics studied are: percentage of voids (% Vv), percentage of volume of bitumen (% Vb), percentage of volume of aggregates (% Vag), percentage of voids in the dry mixture (% VMA), percentage of voids filled with bitumen (% VFA), real density of the sample (Gmb), maximum density (Gmm) and degree of densification (% Gmm).

[0061] Table III

[0062]

[0063] - Second asphalt conglomerate mixture -

[0064] The particles having a size comprised between 2.5 and 4.0 mm were taken from the rubber deriving from the ELT granulation process.

[0065] The particles were subjected to a first heating treatment step, in which the particles were subjected to a temperature of 150°C for a time of 48 h in a static oven at atmospheric pressure.

[0066] The particles coming from the first heating treatment step were subsequently subjected to a surface treatment step to increase the specific surface area of the particles themselves. During the surface treatment step, the particles were passed five times through two horizontal shaft rollers (P40 sandpaper) of a "Molino" machine.

[0067] The particles coming from the surface treatment step were subsequently subjected to a final heating treatment step, in which the particles were subjected to a temperature of 150°C for a time of 120 h in a static oven at atmospheric pressure, until reaching a density of the particles equal to 1.26 g / cm3. 3 .

[0068] During the final heating treatment step, both the density and the water absorption were periodically checked.

[0069] The rubber particles produced as described above were used for the preparation of the asphalt conglomerate mixture.

[0070] Table IV shows the composition of the inert materials of the second asphalt conglomerate mixture in both volume% and weight%.

[0071] Table IV

[0072] Basalt Fine gravel Basalt sand Limestone filler Pre-treated ELT particles Vol. % 52.0 19.2 5.6 3.2 20.0 Wt. % 58.3 21.5 6.3 3.5 10.4

[0073] As will be described hereinafter, the asphalt conglomerate mixture also comprises asphalt in an amount equal to 5.5% by weight with respect to 100% by weight of inert materials.

[0074] Hereinafter a process for the preparation of the asphalt conglomerate mixture will be described.

[0075] The basalt, fine gravel, basalt sand and asphalt were each heated separately from the other ingredients until reaching 165°C. Once the temperature of 165°C was reached, the above ingredients were placed in a mixing machine which was then run at a speed of about 80 rpm. After about one minute of mixing, the reinforcing fibers were added. After about one minute of mixing, the fillers were added. After about one minute of mixing, the pre-treated ELT particles were added. After about one minute, the preparation was terminated.

[0076] The mixture prepared as described above was subjected to a treatment to characterize it in terms of density and mechanical parameters.

[0077] The mixture treatment process and the parameters and characterization process are the same as those described above for the first bituminous gravel mixture.

[0078] Table V shows the results obtained for the above-mentioned parameter values.

[0079] Table V

[0080] ITS (MPa) CTI (MPa) ITSR (%) 0.33 10.8 88

[0081] Table VI shows the values of the above-mentioned volumetric characteristics as a function of the number of rotations of the rotary press.

[0082] Table VI

[0083]

[0084] From the data shown in Tables II, III, V and VI, the person skilled in the art can appreciate that the bitumen deriving from the method, object of the present application, meets all the necessary conditions required for effective use.

[0085] The method, object of the present application, provides the significant advantage of allowing the use of large quantities of ELT rubber particles. This advantage derives from the modification of the ELT rubber particles, which thus become able to be treated in the same way as stone materials.

[0086] The method, object of the present application, also provides the advantage of avoiding the high-temperature dissolution operations of the particles deriving from ELT in bitumen, which has evident benefits in terms of safety for the operators.

[0087] The results of the water sensitivity tests carried out on the gravel mixtures obtained according to the present application show a significant advantage with regard to the possibility of introducing high percentages of particles deriving from ELT into bituminous gravel without the need to use high percentages of bitumen. If one considers that the prior art so far provides for a percentage of particles deriving from ELT of only 2% by weight for a bitumen content greater than or equal to 8%, it is evident that the re-use of particles deriving from ELT, with the consequent improvement in environmental sustainability of the road surface, is evident.

Claims

1. A method for producing asphalt, comprising: The heat treatment step involves subjecting rubber granules derived from the end-of-life tire granulation process to temperatures between 80 and 300°C for the required duration to obtain densities between 1.0 and 1.5 g / cm³. 3 The rubber particles between; The process includes a mixing step in which rubber particles from the heat treatment step are mixed with stone aggregate and asphalt to obtain tar. The mixing step includes: a first mixing operation, wherein the stone aggregate and the asphalt are mixed together at a temperature between 150 and 200°C; The second mixing operation involves adding the rubber particles to the mixture from the first mixing operation.

2. The method according to claim 1, characterized in that, During the heat treatment step, the rubber granules derived from the end-of-life tire granulation process are subjected to temperatures between 100 and 200°C for the required duration to obtain densities between 1.2 and 1.3 g / cm³. 3 The rubber particles between.

3. The method according to claim 1 or 2, characterized in that, The rubber particles from the heat treatment step constitute 1 to 30% by volume of the inert material contained in the asphalt.

4. The method according to claim 1 or 2, characterized in that, The rubber particles derived from the granulation process have a substantially polyhedral conformation, wherein the ratio of the largest size to the smallest size is less than 2.

5. The method according to claim 1 or 2, characterized in that, The rubber granules derived from the granulation process have a size that allows them to pass through a sieve with a screen having a size between 10 mm and 1.5 mm.

6. The method according to claim 1 or 2, characterized in that, The rubber granules derived from the granulation process have a size that passes through a sieve with a screen having a size between 2.0 mm and 6.0 mm.

7. The method according to claim 1 or 2, characterized in that, It includes a preheating step prior to the heat treatment step, wherein rubber particles derived from the end-of-life tire granulation process are subjected to a temperature between 120 and 200°C for a duration between 15 and 30 hours.

8. The method according to claim 1, characterized in that, It includes a surface treatment step following the heat treatment step, wherein the rubber particles from the heat treatment are subjected to a surface abrasion operation.

9. The method according to claim 8, characterized in that, It includes a final heat treatment step after the surface treatment step and before the mixing step; during the final heat treatment step, the rubber particles derived from the surface treatment process are subjected to a temperature between 80 and 300°C for the required time to obtain a density of 1.0 to 1.5 g / cm³. 3 The rubber particles between.

10. The method according to claim 9, characterized in that, During the final heat treatment step, the rubber particles derived from the surface treatment process are subjected to a temperature between 100 and 200°C for the required duration to obtain a density of 1.2 to 1.3 g / cm³. 3 The rubber particles between.

Images