Organo-silane antistripping agents for asphalt conglomerates

Abstract

The invention discloses the use of epoxy-silane compounds as anti-stripping agents for asphalt compositions with improved UV resistance, water-proofing ability and adhesion between the aggregates and the asphalt matrix.

Description

[0001] ORGANO-SILANE ANTISTRIPPING AGENTS FOR ASPHALT CONGLOMERATES

[0002] Field of invention

[0003] The object of the present invention is the use of epoxy-silane compounds as antistripping agents for asphalt compositions with improved UV resistance, water-proofing ability and adhesion between the aggregates and the asphalt matrix.

[0004] Background of the invention

[0005] Asphalt is one of the most used binders in industrial paving of motorways and airport lanes thanks to its large availability, low cost and versatility coupled with its outstanding performance in terms of durability and mechanical properties. Nevertheless, the aggregates used in the asphalt conglomerates more and more are selected among basalt, porphyry, and granite materials, all of them characterized by a poor affinity with bituminous binders. This is the main reason for the early deterioration of the conglomerates due to the detachment of the bitumen phase from the aggregates, as a consequence of aging, mechanical stress and whether conditions.

[0006] In order to prevent such phenomena, starting from decades ago surfactants based on different chemical families comprising fatty amides and amines, organosilanes, phosphoric esters and quaternary ammonium salts were introduced as adhesion promoters and wetting agents.

[0007] Some of them were recognized to be suitable with some aggregates but poorly effective with other ones. Moreover, some of those compounds, particularly those containing nitrogen in their moiety, revealed thermally unstable, with the consequence they lose large part of their properties in a short period of time.

[0008] Organo-silanes were largely employed in the past, as described in US 2,985,678, US 5,130,354, US 4,170,484 and US 4,038,096.

[0009] More recently, cationic salts of organosilane compounds were introduced to prevent the thermal degradation during the storage of hot asphalt conglomerate and to improve the wettability, as described in US 8,771,413.

[0010] One drawback of the previous anti-stripping agents is their poor resistance to UV oxidation, which causes premature loss of the rheological characteristics of bitumen.

[0011] Description of the invention

[0012] The present invention discloses a method for enhancing the adhesion of bitumen or polymer modified bitumen to gravel, with improved hydrophobic effect and UV resistance which comprises the addition to the bitumen of epoxy-alkoxy silanes as both anti-stripping and water-proofing agents. Furthermore, we have surprisingly found that they also prevent the UV oxidation of asphalt compositions, even when used at very low dosage.

[0013] The epoxy-silanes used in the method according to the invention have the following formula: w herein:

[0014] R is a 3-gycidyl-oxypropyl group;

[0015] R’, R” and R’”, which are the same or different, represent a C1-C6 alkoxy group, preferably methoxy, ethoxy, propoxy groups and n is an integer from 1 to 4.

[0016] One or more epoxy silanes of formula (1) may be used in the method of the invention

[0017] Epoxy-alkoxy-silanes both in monomeric and oligomeric form are preferred. 3-glycidyl- oxypropyl-trimethoxy-silane and its oligomers are more preferably used.

[0018] According to the invention, the epoxysilanes of formula (1) are added to antistripping agents in bitumen / asphalt compositions for road, airports, dams, micro-surfaces and similar engineering or building applications.

[0019] According to the use and method of the invention, the dosage for the effective application of the epoxy-silane anti-stripping agent is much lower compared to other classes of anti-stripping agents for asphalt. Different from the other anti-stripping agents which are typically used in the range from 0.4 to 1.5 % by weight of bitumen, the dosage of the antistripping agent of the invention is in the range from 0.01 to 0.5 by weight of bitumen, preferably from 0.05 to 0.15 % by weight of bitumen.

[0020] The invention is described in more detail in the following examples.

[0021] Example 1

[0022] In this example the advantages of the antistripping agent of the invention in improving the water resistance of asphalt compositions are demonstrated by the Indirect Tensile Strength Ratio (ITSR) test. This test, which is described in the European Norm EN 12697-12:2003, consists in measuring the loss of indirect tensile strength of a set of specimens of an asphalt mix conditioned in water at 40 °C for 72 hours in comparison to a set of the same asphalt mix kept dry at room temperature. The ratio of the indirect tensile strength of the water conditioned samples compared to that of equivalent dry samples conditioned at room temperature is a measure of the water sensitivity of bitumen compositions, expressed in percent (ITSR %).

[0023] A polymer modified bitumen mixture with maximum aggregate size of 22 mm was prepared with 0.13 % of monomeric 3-glycidyl-oxypropyl-trimethoxy-silane by weight of bitumen. A Performance Grade polymer modified bitumen PG 76 according to ASTM D6373- 21 was used. Six equivalent cylindrical specimens were prepared with diameter of 100 mm. Three of these specimens were stored in dry conditions at the laboratory temperature of 20 °C. The other three specimens were immersed in water and vacuum was applied to a residual pressure of 6.7 kPa for 30 minutes to allow water to penetrate all the porosity of the specimens. After that, the specimens were transferred into a water bath at 40 °C and left for 72 hours. This time elapsed, the samples were externally dried and indirect tensile strength was measured with a compression testing machine mod. Uniframe 50KN by Controls. The average values were calculated for the 2 sets of specimens (wet and dry) and the ITSR % was calculated according to the following formula:

[0024] ITSw ITSR = 100 X — — - ITSd wherein:

[0025] ITSR is the indirect tensile strength ratio, in percent (%);

[0026] ITSw is the average indirect tensile strength of the wet group, expressed in kilopascal (kPa); ITSd is the average indirect tensile strength of the dry group, expressed in kilopascal (kPa).

[0027] The results are summarized in Table 1.

[0028] Table 1. Indirect Tensile Strength Ratio of polymer modified bitumen mixture with 0.13 % by weight of the antistripping agent of the invention.

[0029] Similar specimens were prepared without the antistripping agent of the invention as reference and tested under the same procedure. Results are shown in Table 2.

[0030] Table 2. Indirect Tensile Strength Ratio of the same polymer modified bitumen mixture without the antistripping agent of the invention (reference).

[0031] The results of the tests of Table 1 and Table 2 confirm that the antistripping agent of the invention is highly effective in improving the resistance to water of asphalt conglomerates.

[0032] Example 2

[0033] 200 grams of the residual silica aggregates from the specimens 4 of Table 1 and Table 2, both dry-conditioned, the first without antistripping agent, used as a reference, and the second with 0.13 % by weight on bitumen of the anti-stripping agent of the invention, were separately boiled in 600 grams of distilled water for 10 minutes, according to EN 12697-11 and the resulting aggregates were visually compared after drying, as shown in Figure 1. The pile on the left of Figure 1 is representative of the specimen 4 without the antistripping agent of the invention (Sample 1) and the pile on the right is representative of the specimen 4 with 0.13 % by weight of the antistripping agent of the invention (Sample 2). By visual comparison of the two piles, it is quite evident that a higher fraction of bitumen remained attached to the aggregates to Sample 2 (100% of coverage) compared to Sample 1 (35% of coverage), confirming the beneficial effect of the antistripping agent of the invention in promoting the adhesion between the bitumen and the aggregates.

[0034] Example 3

[0035] In this example the effect of the antistripping agent of the invention in improving the UV resistance of bitumen is demonstrated.

[0036] 62.5 ml of Performance Grade polymer modified bitumen PG 76 according to ASTM D6373-21 containing 0.1 % on bitumen of oligomeric 3-glycidyl-oxypropyl-trimethoxy-silane were homogeneously distributed over a 25 x 25 cm glass plate to form a layer 1 mm thick and then irradiated by a Hg lamp for 7 hours, simulating a 5-year solar exposure. Equivalent volume of PG 76 modified bitumen according to ASTM D6373-21 without the antistripping agent of the invention was treated in the same way and used as a reference for comparison. Both samples were characterized by rheological measurements in oscillatory regime by using a Dynamic Shear Rheometer mod. Anton Paar Physica MCR 101. Measurements were performed in the temperature range of interest from 4 °C to 86 °C. Results were plotted as Complex Shear Modulus vs Reduced Frequency curves, as shown in Figure 2. Triangle-based plot refers to the sample with 0.1 % by weight on bitumen of the antistripping agent of the invention and squarebased plot refers to the reference sample without the antistripping agent of the invention. The results of Figure 2 indicate that the Complex Elastic Modulus of the sample of bitumen containing 0.1 % by weight of the antistripping agent of the invention is higher than the corresponding reference sample over the whole range of temperature, confirming that the antistripping agent of the invention prevents the UV degradation of bitumen and contributes to keep the original performances for long time.

Claims

CLAIMS1. A method for enhancing the adhesion of bitumen or polymer modified bitumen to gravel, with improved hydrophobic effect and UV resistance which comprises the addition to the bitumen of compositions comprising epoxy-alkoxy silane compounds of formula (1)wherein:R is a 3-gycidyl-oxypropyl group;R’, R” and R’”, which are the same or different, represent a C1-C6 alkoxy group, n is an integer from 1 to 4.

2. A method according to claim 1 wherein R’, R” and R’”, which are the same or different, represent methoxy, ethoxy, propoxy groups.

3. A method according to claim 1 or 2 wherein the silane is a mono, di or tri alkoxy-silane.

4. A method according to any one of claims 1-3, wherein the epoxy-silane compound is 3- glycidyl-oxypropyl-trimethoxy-silane monomer or its oligomeric form.

5. A method according to any one of claims 1-4 wherein the composition is added to bitumen in asphalt mixtures for road, airports, dams, micro-surfaces and similar engineering applications.

6. A method according to claim 5 wherein the dosage of the composition by the weight of bitumen is in the range from 0.01 to 0.5 per cent.

7. A method according to claim 6 wherein the dosage of the composition by the weight of bitumen is in the range from 0.05 to 0.15 per cent.

Images