Additive composition and method of using same

An additive composition and a method for using same are disclosed. The additive is useful in preparation of foamed bitumens such as asphalt used in manufacture of bituminous pavements. The additive is comprised of a metal stearate and a carrier oil, and is added to asphalt used to manufacture asphalt foam compositions to improve the foaming characteristics of the asphalt.

BACKGROUND OF THE INVENTION 
In an effort to improve the basic asphalt paving process, attempts have 
been made to utilize foamed asphalt processes in place of conventional 
asphalt pavement mixing methods. 
One foamed asphalt process is described in U.S. Pat. No. 2,917,395 to L. H. 
Csanyi. This process involves use of steam to produce foamed asphalt, 
which is then mixed with a substrate. 
Another approach was proposed in U.S. Pat. No. 3,423,222 to McConnaughay. 
The method disclosed in that patent involves heating aggregate in a drum 
and coating the hot aggregate with a turbulent dispersion or cloud of 
asphalt. 
More recently, a process of making foamed asphalt suitable for mixing with 
unheated aggregate has been developed. This process involves combining 
cold water with hot liquid asphalt to produce a foamed asphalt, and is 
described in detail in Australian Pat. No. 433,003. 
The use of cold water and heated asphalt to produce a foamed product has 
showed considerable promise as an alternative to the conventional hot mix 
paving process. However, it is essential that the asphalt used have good 
foaming characteristics in order for the foamed asphalt process to be 
successful. 
Unfortunately, it is not uncommon in the manufacture, storage and handling 
of asphalt to use a silicone defoamer to prevent froth formation. This 
silicone additive is very effective as a froth preventer, but it remains 
in the asphalt, and when a silicone-containing asphalt is subsequently 
used in a foamed asphalt process, the resulting foam is not easily formed 
and is of poor quality. Some asphalts simply do not have good foaming 
characteristics, whether or not a defoamer has been added, and the 
additive of this invention may be used to improve the foaming 
characteristics of these asphalts. 
Prior attempts to improve the foaming characteristics of asphalt which is 
used to produce a foamed asphalt paving composition have included addition 
of foaming agents to the water or asphalt prior to generating the foam. 
One fairly satisfactory material is powdered sodium stearate, which has 
been added in amounts of a few tenths of a percent based on weight of 
asphalt to be foamed. This powdered sodium stearate effectively overcomes 
silicone defoamer if present and allows formation of a good foamed 
asphalt. However, the use of powdered material is very difficult in an 
actual paving operation, presenting handling problems and causing 
difficulty in obtaining uniform dispersion of the additive. Attempts to 
dissolve metal stearate in a satisfactory oil carrier have not been very 
successful, as the resulting solutions thicken such that they are not 
readily pumpable by an additive metering pump or the like. 
Solutions of metal stearates in light hydrocarbon solvents are used in the 
paint industry, but these solutions are unsatisfactory for use around 
heated asphalt due to adverse effects of light hydrocarbons on the asphalt 
properties and because of hydrocarbon emission and safety considerations. 
SUMMARY OF THE INVENTION 
According to the present invention, an additive composition for improving 
the foaming characteristics of asphalt is provided. According to another 
aspect of the invention, a method for using such an additive is provided. 
The additive according to the invention comprises a metal stearate 
dispersed in a carrier oil having specific properties. The stearate is 
present in an amount of at least 20 percent by weight, with the balance 
being carrier oil. Minor amounts of other materials can be present, but 
are not required. 
The method of using the additive comprises adding it to an asphalt material 
to be foamed prior to generation of the foam.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The active ingredient in the additive of this invention is the metal 
stearate. It is theoretically possible to obtain the advantages of the 
invention using a powdered material, but as a practical matter it has been 
determined that a more satisfactory method of adding this material is as a 
liquid. A satisfactory liquid additive should be readily dispersable in 
hot asphalt, and should contain no appreciable amount of volatile 
fractions which might create safety or health hazards or product 
specification problems. It is also essential that the additive be stable 
during extended storage over a fairly wide range of ambient temperature, 
that the additive have no appreciable effect on the properties of the 
asphalt, and that the additive have good flow characteristics over a 
fairly wide temperature range. 
It has been found that the above properties can be obtained by dispersing 
powdered metal stearate in a hydrocarbon carrier oil having a pour point 
of not more than 0.degree. C., an initial boiling point of at least 
200.degree. C., and a flash point (Cleveland Open Cup) of at least 
150.degree. C. 
Metal stearates in general are useful in this invention. The most preferred 
stearate is magnesium stearate, although calcium, aluminum and sodium 
stearates have also been found to be particularly desirable. The 
concentration of metal stearate in the composition should be as high as 
possible without being so high as to be non-liquid at ambient 
temperatures. At least 20 percent by weight is needed to avoid having to 
ship and handle an unduly large volume of material. Preferably, an amount 
just short of the amount which causes thickening of the composition at 
ambient temperature is used. When amounts of metal stearates above about 
35 percent by weight are dispersed in carrier oils, the fluidity of the 
composition at ambient temperatures decreases quite rapidly, and in order 
to avoid potential field problems and at the same time minimize the amount 
of additive to be handled, an optimum amount of metal stearate has been 
determined to be about 33 to 38 percent by weight. 
Numerous hydrocarbon materials were tried as carrier oils. Essential 
properties of a satisfactory carrier oil in accordance with the invention 
are a pour point of not more than 0.degree. C., an initial boiling point 
of at least 200.degree. C., and a flash point of at least 150.degree. C. 
The most preferred carrier oil is a low viscosity, fully refined base 
lubricating pale oil. Oils that are too heavy and viscous result in too 
viscous a blend due to their initial viscosity and also present a problem 
in that the required higher blending temperatures cause solution of the 
metal stearate with resulting thickening of the blend. Oils that have too 
low an initial boiling point cause undesirable hydrocarbon emissions when 
mixed with hot asphalt and do not provide a stable blend. Oils with a high 
pour point present handling problems, and oils with a low flash point 
present a safety hazard. A particularly preferred oil is a fully refined 
paraffinic base lubricating oil having the properties shown in the 
following table. 
TABLE I 
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Flash Point (COC) 210.degree. C. 
Pour Point -15.degree. C. 
Specific Gravity 0.8697 
API Gravity 31.2.degree. 
Viscosity, cSt 34 at 40.degree. C. 
5.5 at 100.degree.C. 
Viscosity Index 98 
Distillation, ASTM D1160 
288.degree. C. Initial 
corrected to 760 mm Boiling Point 
360.degree. C. 10% Point 
427.degree. C. 50% Point 
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Dispersions of metal stearates in a carrier oil as defined in Table I were 
prepared, and had the following properties at ambient temperature: 
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Metal Stearate 
Concentration % by wt. 
Property 
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Calcium Stearate 
30 Fully Liquid 
35 Slightly Thickened 
40 Non-Liquid* 
Magnesium 30 Fully Liquid 
35 Slightly Thickened 
40 Non-Liquid* 
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*Not readily pourable from an open container at ambient temperature. 
The process of preparing the additive comprises dispersing powdered metal 
stearate in carrier oil while maintaining the carrier oil at a temperature 
below that at which appreciable dissolution of the stearate occurs. The 
carrier oil should not be at a temperature above about 50.degree. C. 
because the metal stearates tend to dissolve in hot oil and the resulting 
solutions thicken on cooling to the point that they are not readily 
usable. Additives prepared at ambient temperature contain no appreciable 
amount of dissolved metal stearate. 
The method of using the additive of this invention involves blending an 
effective amount of the additive into asphalt, contacting heated asphalt 
containing the additive with water, and expanding the heated asphalt and 
water through a nozzle as a foamed asphalt. The amount of additive used 
depends on the particular metal stearate and the desired results in terms 
of expansion volume and foam half life. For aluminum or magnesium 
stearate, about 0.15 percent by weight metal stearate based on weight of 
asphalt is adequate. For sodium stearate, about 0.3 weight percent is 
adequate. 
The asphalt to be foamed, containing the additive of this invention, must 
be hot enough to be liquid, and have sufficient heat capacity to vaporize 
the added water. The added water is heated above its boiling point by the 
heated asphalt, and the resulting mix is then expanded through a nozzle as 
a foam having an increased volume, preferably from 6 to 15 times the 
volume of the original asphalt. An aggregate material is then added to the 
foamed asphalt to provide a mix suitable for use in having projects and 
the like. The additive according to this invention makes it possible to 
utilize foamed asphalt in preparation of road beds in an economical and 
effective manner. 
Prior to development of this additive, there was no completely satisfactory 
way of overcoming the effects of poor foaming asphalt when the asphalt was 
to be used to produce a foamed asphalt mix.