Antioxidant treatment of asphalt binders

Abstract

A combination of antioxidants and method of incorporating the antioxidants into an asphalt binder to make a modified asphalt binder are described. The antioxidants comprise a thioester and an aldehyde. The aldehyde and thioester, in a ratio between about 1:100 and about 100:1, are added to an asphalt binder. An acidic catalyst is also added in a concentration between about 0.1 wt % and about 18 wt % of the asphalt binder. The antioxidants, asphalt binder, and catalyst are mixed at a temperature between about 85° C. and about 135° C. for a time between about 30 minutes and about 6 hours. The antioxidants are capable of improving the performance grade of the asphalt binder. The modified asphalt binder possesses superior resistance to oxidative age hardening compared to other modified asphalt binder compositions that incorporate various antioxidants.

1 . An antioxidant composition comprising:
 an aldehyde; and   a thioester,   wherein the thioester and the aldehyde are present in an effective amount capable of lowering oxidative aging of an asphalt or polymeric materials.   
     
     
         2 . The antioxidant composition of  claim 1 , wherein the thioester is selected from the group consisting of dilauryl thiodipropionate, distearylthiodipropionate, and dimethyl 3,3′-thiodipropionate, and other esters of thiodipropionic acid. 
     
     
         3 . The antioxidant composition of  claim 2 , wherein the aldehyde is selected from the group consisting of formaldehyde, acetaldehyde, propionaldehydes, butyraldehyde, acrolein, crotonaldehyde, tiglaldehyde, benzaldehyde, salicylaldehyde, cinnamaldehyde, furfural alcohol, paraformaldehyde, and furfural. 
     
     
         4 . The antioxidant composition of  claim 1 , wherein the ratio of the aldehyde to the thioester is between about 1:50 and about 50:1. 
     
     
         5 . The antioxidant composition of  claim 1 , wherein the aldehyde is furfural and the thioester is dilauryl thiodipropionate. 
     
     
         6 . A modified asphalt binder composition made by the process comprising mixing an asphalt binder, the antioxidant composition of  claim 4 , and an acidic catalyst to create a modified asphalt binder characterized by an aging index that is lower than that of an untreated asphalt binder. 
     
     
         7 . The modified asphalt binder composition of  claim 6 , wherein the aldehyde reacts with phenols in the asphalt binder to form phenolic resins, the phenolic resins comprising novolacs, resoles, or combinations thereof. 
     
     
         8 . The modified asphalt binder composition of  claim 6 , wherein the thioester is bounded to the asphalt binder to allow stabilization of the thioester. 
     
     
         9 . The modified asphalt binder composition of  claim 6 , wherein the thioester and the aldehyde are provided in enhanced effective amounts for the reduction of the oxidative aging of the asphalt binder. 
     
     
         10 . The modified asphalt binder composition of  claim 6 , wherein the modified asphalt binder possesses at least about 50% lower flexural stiffness relative to an unmodified asphalt binder at a low temperature, the low temperature ranging from about −4° C. to about −58° C. 
     
     
         11 . The antioxidant composition of  claim 6 , wherein the modified asphalt binder possesses at least about 18% higher stiffness relative to an unmodified asphalt binder at a high temperature, the high temperature ranging from about 46° C. to about 82° C. 
     
     
         12 . The modified asphalt binder composition of  claim 6 , further comprising an antistripping agent that promotes adhesion of the modified asphalt binder with a mineral aggregate. 
     
     
         13 . The modified asphalt binder composition of  claim 6 , wherein the aldehyde is furfural and the thioester is dilauryl thiodipropionate. 
     
     
         14 . An antioxidant modified asphalt binder prepared by the process comprising:
 (a) heating an asphalt binder in an oxidation rich environment to a first temperature sufficient to liquefy the asphalt binder;   (b) adding an antioxidant mixture to the asphalt binder in the presence of an acidic catalyst to form the antioxidant modified asphalt binder, wherein the antioxidant mixture comprises an aldehyde and a thioester, and further wherein the thioester is added in a ratio of the aldehyde to the thioester that ranges between about 1:100 and about 100:1; and   (c) mixing the modified asphalt binder at a second temperature between about 85° C. and about 135° C. blend until a predetermined stiffness of the binder has been attained.   
     
     
         15 . The antioxidant modified asphalt binder of  claim 14 , further prepared by the process of:
 (d) adding an antistripping agent to the modified asphalt binder, wherein the antistripping agent promotes adhesion of the modified asphalt binder with a mineral aggregate.   
     
     
         16 . The antioxidant modified asphalt binder of  claim 14 , wherein the first temperature is between about 80° C. and about 200° C. 
     
     
         17 . The antioxidant modified asphalt binder of  claim 14 , wherein the antioxidant mixture comprises up to about 30 wt % based on the total weight of the unmodified asphalt binder. 
     
     
         18 . The antioxidant modified asphalt binder of  claim 14 , wherein the aldehyde is selected from the group consisting of formaldehyde, acetaldehyde, propionaldehydes, butyraldehyde, acrolein, crotonaldehyde, tiglaldehyde, benzaldehyde, salicylaldehyde, cinnamaldehyde, furfuryl alcohol, paraformaldehyde and furfural. 
     
     
         19 . The antioxidant modified asphalt binder of  claim 18 , wherein the thioester is selected from the group consisting of dilauryl thiodipropionate, distearylthiodipropionate, dimethyl 3,3′-thiodipropionate, and other esters of thiodipropionic acid. 
     
     
         20 . The antioxidant modified asphalt binder of  claim 19 , wherein the antioxidant mixture comprises from about 0.1 wt % to about 30 wt % furfural and from about 0.1 wt % to about 22.5 wt % dilauryl thiodipropionate based on the total weight of the unmodified asphalt binder. 
     
     
         21 . The antioxidant modified asphalt binder of  claim 20 , wherein the acidic catalyst is selected from the group consisting of sulfuric acid, toluene sulfonic acid, paratoluene sulfonic acid, ascorbic acid, phosphoric acid, and hydrochloric acid. 
     
     
         22 . The antioxidant modified asphalt binder of  claim 20 , wherein the antioxidant modified asphalt binder is characterized by an aging index that is lower than that of an untreated asphalt binder. 
     
     
         23 . The antioxidant modified asphalt binder of  claim 20 , wherein the dilauryl thiodipropionate and the furfural are provided in an enhanced effective amount for lowering of oxidative aging of the modified asphalt binder. 
     
     
         24 . The antioxidant modified asphalt binder of  claim 20 , wherein the modified asphalt binder possesses a reduction in flexural stiffness relative to that of an unmodified asphalt binder. 
     
     
         25 . The antioxidant modified asphalt binder of  claim 20 , wherein the modified asphalt binder possesses a higher complex shear modulus relative to that of an unmodified asphalt binder. 
     
     
         26 . The antioxidant modified asphalt binder of  claim 14 , wherein the asphalt binder is selected from the group consisting of a joint sealant, recycled asphalt pavement, emulsion, cut-back, and naturally occurring asphalt. 
     
     
         27 . The antioxidant modified asphalt binder of  claim 14 , wherein the antioxidant mixture is capable of improving the performance grade of the asphalt binder by extending the temperature range that the binder can be used within. 
     
     
         28 . The binder of  claim 14 , wherein the process further comprises:
 (d) coating the modified asphalt binder of  claim 14  onto a surface of the mineral aggregate.   
     
     
         29 . A method of making a modified asphalt binder, comprising the steps of:
 (a) heating an asphalt binder to liquefy the binder; and   (b) mixing an aldehyde and a thioester with the asphalt binder at a first temperature between about 100° C. to about 135° C. in the presence of an acidic catalyst, wherein the ratio of the aldehyde to the thioester is between about 1:100 and about 100:1, and wherein the mixing occurs until a predetermined stiffness of the modified asphalt binder has been attained.   
     
     
         30 . The method of  claim 29 , wherein the aldehyde is selected from the group consisting of formaldehyde, acetaldehyde, propionaldehydes, butyraldehyde, acrolein, crotonaldehyde, tiglaldehyde, benzaldehyde, salicylaldehyde, cinnamaldehyde, paraformaldehyde, furfuryl alcohol, and furfural, and wherein the thioester is selected from the group consisting of dilauryl thiodipropionate, distearylthiodipropionate, and other esters of thiodipropionic acid. 
     
     
         31 . The method of  claim 29 , wherein the ratio of the aldehyde to the thioester is in a ratio from about 1:50 to about 50:1. 
     
     
         32 . The method of  claim 29 , further comprising the steps of:
 (c) mixing the modified asphalt binder with an antistripping agent.   
     
     
         33 . The method of  claim 32 , further comprising the steps of:
 (d) mixing the modified asphalt binder with an unmodified bulk asphalt binder to form an end product asphalt, the end product asphalt comprising up to about 20 wt % of the modified asphalt binder based on the weight of the end product.   
     
     
         34 . The method of  claim 33 , further comprising the steps of:
 (e) coating the end product asphalt onto a surface of a mineral aggregate at a second temperature between about 125° C. and about 200° C.; and   (f) compacting the coated mineral aggregate to produce a laydown of asphalt concrete at a third temperature between about 120° C. and about 150° C.   
     
     
         35 . The method of  claim 29 , wherein the acidic catalyst is present in an amount between about 0.1 and about 0.8 parts by weight, the aldehyde is present in an amount between about 1 and about 2 parts by weight, and the thioester is present in an amount of about 1 part by weight. 
     
     
         36 . The method of  claim 31 , wherein the aldehyde is furfural and the thioester is dilauryl thiodipropionate.