Abstract:
The adherence between an asphalt and aggregate is increased by incorporating into the asphalt a vinyl monomer and an alkenyl azabenzene.

Description:
TECHNICAL FIELD 
     This invention pertains to chemically-modified asphalts. 
     In one of its more specific aspects, this invention pertains to chemically-modified asphalts as additives for hot mix asphalts. 
     BACKGROUND OF THE INVENTION 
     The use of hot mix asphalts is well known. Frequently, such asphalts comprise an asphaltic mixture in combination with suitable aggregate, the combination being employed for the laying of asphalt surfaces. Such surfaces are frequently laid at elevated temperatures and the combination is cooled to form a durable surface, the combination being known as an asphalt mix. 
     In such mixes, the asphalt is generally the most expensive material and continuing efforts are made to decrease the quantity of asphalt required in such mixes without decreasing the stability properties of the mix. It is also desirable for the purposes of minimizing energy costs to lower the temperature at which the asphalt mix is laid. 
     This invention is directed to those objectives. 
     STATEMENT OF THE INVENTION 
     According to this invention, there is provided a material consisting of the reaction product of an asphalt, a polymerizable vinyl monomer and an alkenyl azabenzene. 
     Also, according to this invention, there is provided a method of increasing the adherence between an asphalt and an aggregate which comprises incorporating into the asphalt a vinyl monomer and an alkenyl azabenzene. 
    
    
     DESCRIPTION OF THE INVENTION 
     This invention is employable with any suitable asphalt useful in producing asphalt mixes, that is, mixes comprising asphalt and aggregate. Such asphalts include natural asphalts, petroleum asphalts anad petroleum tars. The natural asphalts include, for example, asphaltite, such as Gilsonite, grahamite, glancepitch, lake asphalt, and rock asphalts. The petroleum asphalts include asphalts derived from petroleum regardless of how processed or derived. Preferably, the asphalt which will be employed are asphalts, for example, suitable for the preparation of AC-5, AC-10 and AC-20 grade asphalts. Such asphalts typically have penetrations ranging between about 20 to about 200. 
     As the polymerizable vinyl monomer, any suitable monomer can be employed which monomer has the general formula ##STR1## wherein R 1  is an aromatic group containing 6 to 12 carbon atoms including a phenyl group, a substituted phenyl group wherein the substituent is any one of an amino group, a cyano group, a halogen group, a C 1  to C 3  alkoxy group, a C 1  to C 3  alkyl group, a hydroxy group, a nitro group and the like; R 2  is preferably hydrogen or lower alkyl group, for example, a C 1  to C 5  alkyl; and R 3  is hydrogen, a lower alkyl or a group selected from the group consisting of --CH 2  OH, --CHO; ##STR2## and CH 2  --CN; wherein X is a halogen and preferably chlorine or bromine. 
     Also, a polyfunctional vinyl aromatic monomer containing 6 to 12 carbon atoms in the aromatic ring and two or more polymerizable vinyl groups chemically bonded to the aromatic ring can optionally be employed. Preferred polyfunctional monomers are those having the general formula ##STR3## wherein R 4  is a divalent aromatic group containing 6 to 12 carbon atoms, and preferably a phenylene group; and R 5  and R 6  have the same meaning as described above with respect to R 2  and R 3 , respectively for the monofunctional vinyl aromatic monomer. Illustrative of a suitable polyfunctional vinyl aromatic monomer is divinyl benzene. When use is made of a polyfunctional vinyl aromatic monomer in combination with a monofunctional vinyl aromatic monomer such as styrene, generally the monofunctional vinyl aromatic is present in a weight ratio of about 1:1 to 40:1 based on the weight of the polyfunctional vinyl aromatic monomer. 
     Representative of suitable alkenyl azabenzenes are the alkenyl pyridine compounds of the formula ##STR4## wherein R 1 , R 2 , R 3 , R 4  and R 5  are independently selected from the group consisting of hydrogen, a C 1  -C 3  alkyl, a C 1  -C 3  alkoxy, halogen, cyano, nitro, amino with at least one of said R 1 , R 2 , R 3 , R 4  or R 5  groups being an alkenyl group containing 2-5 carbon atoms. Representative of such alkenyl groups are 1 propenyl, 1 butenyl and 1 pentenyl. Preferably the alkenyl group is ethenyl. Preferred compounds are 2 vinyl pyridine and 4 vinyl pyridine. 
     Any suitable combination of asphalt, monomer and alkenyl azabenzene can be employed. The monomer and alkenyl azabenzene will preferably be incorporated into an asphalt to form a chemically-modified asphalt. This chemically-modified asphalt will then be incorporated into the principal portion of the asphalt and an amount within the range of from about 1 to about 10 weight percent of the total weight of the asphalts, preferably about three percent. 
     Generally, the chemically-modified asphalt will be comprised, in weight percent, of 85 to about 94.5 percent asphalt, of about 0.5 to about 5 percent of the alkenyl azabenzene and from about 5 to about 15 percent of the monomer. 
     In the preferred embodiment, the chemically-modified asphalt will be consist, in weight percent, of about 87 percent asphalt, 3 percent alkenyl azabenzene and 10 percent of the monomer. 
     This chemically-modified asphalt will be blended with the principal asphalt in an amount within the range of from about 1 to about 5 weight percent, preferably in an amount of about 3 weight percent of the total weight of the asphalt. 
     The chemically-modified asphalt employed as the additive to conventional asphalt is an integrated material believed to be a chemical reaction product. This additive, a chemically-modified asphalt, is prepared by heating, with agitation, a mixture consisting of asphalt, a vinyl aromatic monomer and an alkenyl azabenzene at a temperature of at least about 110° C. for at least 8 hours. Suitably, the integrated additive material is prepared by heating at about 110° C. to about 170° C. for about 8 to about 24 hours. 
     EXAMPLE 
     This example demonstrates the effectiveness of the invention. 
     AC-20 asphalt, unmodified, was mixed with limestone in a 50/50 asphalt to limestone mixture in parts by weight, and the bonding energy, in terms of microcalories per gram minute, was found to be 0.05. 
     AC-20 asphalt was then reacted in a mixture consisting essentially of 87 weight percent asphalt, 3.0 weight percent vinyl pyridine and 10 weight percent styrene and the mixture was mixed with limestone in a 50/50 ratio of asphalt to limestone mixture. The bonding energy, in terms of microcalories per gram minute was found to be 0.65. 
     These data demonstrate the improvement in bonding energy of asphalt to aggregate by the inclusion in the composite of an amine of an unsaturated acylic hydrocarbon. 
     It will be evident from the foregoing that various modifications can be made to the method of this invention. Such, however, are within the scope of the invention.