Rubber composite and process for obtaining same

Abstract

This disclosure provides a rubber composite for use in a variety of applications, and methods for its preparation.

Claims

1. A process for obtaining a rubber composite in particulate form, the process comprising the steps of: (a) mixing heavy-fraction oil distillate with particulate rubber at a first elevated temperature under conditions of high sheer rate to obtain oil-swollen rubber particles; (b) adding at least one first powdered additive to the oil-swollen rubber particles to obtain a mixture; (c) reducing the temperature of the first mixture by at least 20 C.; (d) heating the first mixture to a second elevated temperature under conditions of high sheer rate; (e) reducing the temperature of the mixture to about 20 C. at a cooling rate of at least 2 C./min; and (f) adding at least one second powdered additive to said mixture under conditions of high sheer rate to said rubber composite, such that the rubber composite comprises between about 10 and about 20% wt of said heavy-fraction oil distillate, the heavy-fraction oil distillate and said at least one first additive being substantially contained within an internal structure of the rubber, and the rubber's external surface being substantially oil-dry and said at least one second additive is present at the external surface of the rubber composite.

2. The process of claim 1, wherein the at least one first additive is present in the rubber composite at a content of between about 10 and about 30 wt %.

3. The process of claim 1, wherein the at least one second additive is present in the rubber composite at a content of between about 5 and about 10 wt %.

4. The process of claim 1, wherein said first elevated temperature is between about 100 and 170 C.

5. The process of claim 1, wherein said second elevated temperature is between about 130 and 180 C.

6. The process of claim 1, wherein the mixture is maintained at said second elevated temperature of a period of time of between about 1 and 60 minutes.

7. The process of claim 1, wherein said high sheer rate is obtained by mixing at at least 1200 rpm.

8. The process of claim 1, wherein said first and second additives are mineral-based powders, each being independently selected from the group consisting of limestone, hydrated lime, cement, silica, and mica.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order to understand the disclosure and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

(2) FIG. 1 shows the viscosity change over time of paving compositions comprising various contents of rubber composites of the invention (marked as RSCR) compared to rubber asphalt.

(3) FIG. 2 shows a comparison of JnR at 3.2 kPa between RSCR and reactive-activated rubber (RAR) as function of additives' content.

(4) FIG. 3 shows a comparison of positive PG Grade level obtained for RSCR and RAR formulations.

(5) FIG. 4 shows Ring and Ball variation function of RSCR and RAR percentages.

(6) FIG. 5 shows variation of resilience the paving composition as a function of RSCR and RAR percentages.

(7) FIG. 6 shows rutting performance of mixes with RSCR and other known formulations.

DETAILED DESCRIPTION OF EMBODIMENTS

(8) In the present invention, the rubber composite may be used in asphalt mixtures, thereby providing the following technological and operational advantages, as compared to standard existing asphalt mixtures: better mechanical stability under low and high usage temperatures; improved rutting resistance and fatigue resistance; improved wearing resistance; improved resistance to water damage; self-healing propertiesasphalt mixtures comprising the modified-rubber composite show mechanical recovery, as well as recovery of geometrical form and dimensions after unloading; Improving elasticity of the paving formulation; Reducing the amount of oil needed to obtain improved mechanical properties of the rubber composite; Simplifying and reducing costs of the manufacture process.

(9) FIG. 1 demonstrates the change in viscosity of various paving compositions, comprising various amounts of rubber composite (marked as RSCR) over time, compared to standard asphalt rubber formulations. The tests were carried out according to AASHTO TP48 standard test method. As clearly be seen, no significant change in viscosity was observed over time for the compositions containing RSCR over a wide verity of RSCR contents, while significant increase in viscosity was observed for the standard asphalt-rubber formulations. This attests to the improved stability of the RSCR-based compositions, indicating that the rubber composite does not absorb light fractions of the bitumen binder from the paving composition. In comparison it can be seen that crumb rubber alone (either cryogenic from car tires ASPHALT RUBBER 18% CRYOGENIC or ambient grind from truck tires ASPHALT RUBBER 18%) is not stable as the viscosities increase over time (as the rubber swells and absorbs the lighter fractions over time).

(10) To demonstrate the differences between RSCR and RAR, a series of comparative tests were conducted, using the same base bitumen and same percentages of RSCR and RAR in paving compositions. The PG grade and JnR values (as measured by Multi Stress Creep Recovery (MSCR) AASHTO TP 70, standard RTFO test as per AASHTOT 240 and ASTM D 2872Effect of Heat and Air on a Moving Film of Asphalt (Rolling Thin-Film Oven Test) and standard DSR test as per AASHTO T 315: Determining the Rheological Properties of Asphalt Binder Using a Dynamic Shear Rheometer) were determined as a function of additives' percentage as it can be observed, as shown in FIGS. 2 and 3.

(11) It can be observed that with only 6.5% of RSCR the 1 kPa for JnR@3.2 kPa (to simulate very heavy traffic) was reached, while the same values were obtained only when adding at least 12% of RAR. To reach the level 0.5 kPa (for Extremely Heavy Traffic) only 17.2% of RSCR was needed instead of 20% RAR.

(12) Similarly to reach the positive grade 76 C., only 10.5% of RSCR was needed instead of 13.3% of RAR. While to reach the 82 C. only 18.7% of RSCR were needed instead of 22% of RAR. These temperatures were used since they are typical PG grade test temperatures.

(13) Therefore, it is clear that significantly less RSCR compared to RAR needs to be added to the pacing composition to reach the same results, attesting to the higher reactivity of RSCR compared to RAR.

(14) Using traditional tests, the advantage of the rubber composite (RSCR) of the invention is further demonstrated.

(15) Seen in FIG. 4 are the comparative results of a softening point test, carried out according to ASTM D 36. To reach 65 C. of Softening Point, only 21% of RSCR is needed instead of 27% of RAR.

(16) Resilience was evaluated according to ASTM D 5329-96. As further seen in FIG. 5, to reach a 40% Resilience only 19% of RSCR is needed instead of 27% of RAR. As such, RSCR consistently showed higher activity than RAR, requiring in average about 24% less product to achieve the same level of performance.

(17) The effect of RSCR in the mixes is also significantly different, especially when it is added in low amounts to the paving composition, for example about 4 wt %, turning the RSCR/bitumen combination far more elastic then mixtures known in the art. Wheel tracking tests executed as per Standard NLT 173/00 (Spanish Norm) show comparatively the effect of those very elastic binders. FIG. 6 shows the most reduced value obtained in a mixture with 3.8% RSCR by weight of the mixture (bitumen content was 6.2%). It is clearly the lowest value as compared with tradition Asphalt Rubber gap graded mixtures (with and without RAR) or even compared with traditional SMA mixtures with highly modified bitumen and fibres.