Additives for Hot Mix Asphalt

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.

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.

According to this invention, there is provided a material consisting of the reaction product of an asphalt, a polymerizable vinyl monomer and an acrylamide.

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 acrylamide.

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.sub.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.sub.1 to C.sub.3 alkoxy group, a C.sub.1 to C.sub.3 alkyl group, a hydroxy group, a nitro group and the like; R.sub.2 is preferably hydrogen or lower alkyl group, for example, a C.sub.1 to C.sub.5 alkyl; and R.sub.3 is hydrogen, a lower alkyl or a group selected from the group consisting of ##STR2## and CH.sub.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.sub.4 is a divalent aromatic group containing 6 to 12 carbon atoms, and preferably a phenylene group; and R.sub.5 and R.sub.6 have the same meaning as described above with respect to R.sub.2 and R.sub.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.

Of the foregoing, styrene is preferred.

The acrylamides employed in the present invention are unpolymerized and have a double bond. Desirably, they may be secondary amides or tertiary amides. Preferably, the acrylamide will be a compound of the formula

wherein R.sub.1, R.sub.2 and R.sub.3 are independently selected from hydrogen or an alkyl containing 1 to 3 carbon atoms; R.sub.4 and R.sub.5 are independently selected from hydrogen, an alkyl containing 1 to 3 carbon atoms, or preferably a radical of the formula

wherein R.sub.7 and R.sub.8 are independently selected from hydrogen or an alkyl having 1 to 3 carbon atoms, and R.sub.6 is an alkylene group containing 1 to 5 carbon atoms. The preferred acrylamide is dimethylaminopropylmethacrylamide, that is, a compound of the formula

The double bond in the acrylamides provides for the ability to chemically incorporate the acrylamide into the composition. Additionally, the amino groups present in the acrylamides provide for highly desirable polarity which serves to greatly enhance the adhesive bonding of the present compositions to various substrates, including, for example, aggregates commonly employed in road repair and maintenance, as well as cementitious and other substrates. Representative acrylamides include

N,N-dimethylaminoproplymethacrylamide,

N,N-dimethylaminoisopropylmethacrylamide,

N,N-dimethylaminoethylmethacrylamide,

N-methylaminopropylmethacrylamide,

N-methylaminoisopropylmethacrylamide,

N-methylaminoethylmethacrylamide, aminopropylmethacrylamide, aminoisopropylmethacrylamide, aminoethylmethacrylamide,

N,N-diethylaminopropylmethacrylamide,

N,N-diethylaminoisopropylmethacrylamide,

N,N-diethlaminoethylmethacrylamide,

N-ethylaminopropylmethacrylamide,

N-ethylaminoisopropylmethacrylamide,

N-ethylaminoethylmethacrylamide,

N-ethyl,N-methylaminopropylmethacrylamide,

N-ethyl,N-methylaminoisopropylmethacrylamide,

N-ethyl,N-methylaminoethylmethacrylamide,

N,N-dimethylaminopropylacrylamide,

N,N-dimethylaminoisopropylacrylamide,

N,N-dimethylaminoethylacrylamide,

N-methylaminopropylacrylamide,

N-methylaminoisopropylacrylamide,

N-methylaminoethylacrylamide, aminopropylacrylamide, aminoisopropylacrylamide, aminoethylacrylamide,

N,N-diethylaminopropylacrylamide,

N,N-diethylaminoisopropylacrylamide,

N,N-diethylaminoethylacrylamide,

N-ethylaminopropylacrylamide,

N-ethylaminoisopropylacrylamide,

N-ethylaminoethylacrylamide,

N-ethyl,N-methylaminopropylacrylamide,

N-ethyl,N-methylaminoisopropylacrylamide,

N-ethyl,N-methylaminoethylacrylamide.

Any suitable combination of asphalt, monomer and acrylamide can be employed. The monomer and acrylamide 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 10 percent of the acrylamide and from about 3 to about 10 percent of the monomer.

In the preferred embodiment, the chemically-modified asphalt will be comprised, in weight percent, of about 83 percent asphalt, 6 percent acrylamide and 13 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 asphalts.

The chemically-modified asphalt employed as the additive to conventional asphalt is an integrated material believed to be a chemical reaction product. This additive chemically-modified asphalt is prepared by heating, with agitation, a mixture consisting of asphalt, a vinyl aromatic monomer and an acrylamide at a temperature of at least about 110.degree. C. for at least about 8 hours. Suitably, the integrated addition material is prepared by heating at about 110.degree. C. to about 170.degree. C. for about 8 to about 24 hours.

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.