MXPA98004733A - Additive for asphalt emulsion based on h - Google Patents

Abstract

The present invention relates to a gel-like emulsion prepared by adding an additive containing natural rubber and crumbled rubber from used vehicle tires to a pavement emulsion at room temperature, for chip coating, grout sealing, microsurfacing , ground stabilization or paving

Description

ADDITIVE FOR EMULSION OF ASPHALT BASED ON RUBBER The present invention relates to asphalt road paving materials, and to a method for adding an emulsion including rubber to the asphalt paving material. The addition of rubber to asphalt paving was first proposed in the middle of the last century. However, it was not until the present century that the idea of adding tire rubber from vehicles to the asphalt was developed, and crushed rubber from vehicle tires was added. The crushed rubber is an elastic and flexible asphalt emulsion, and is used as a crack sealer with satisfactory results. The problem of waste tires in the environment is well known. In the United States alone, 282 million tires are discarded each year. Although it is used in different ways, there is a supply stack of 1 to 2 billion waste tires. Many are burned as fuel in cement production, and some are used as landfills, but the number of waste tires continues to increase. The waste rubber, the crushed rubber and the recovered rubber, are all terms that are used to describe rubber % $ recycled from other uses, mainly car tires. This rubber is a mixture, and it is not a pure polymer. Most of the tires manufactured in the United States are mainly composed of styrene-butadiene rubber (SBR), or polyisoprene and carbon black. However, with the availability of synthetic polymers of known composition and performance, and their moderate cost, there seems to be no particular economic benefit in the use of waste rubber. It can be made from recycled tires, but the processing cost is substantial, so that the final cost to the consumer is comparable with the synthetic ones in most cases. Waste rubber has been used in road applications since the 1950s in Australia in sealed applications, as well as in crack sealing and joint filling. In other countries, used tires are actually imported as fuel and for other purposes; In Europe, the used tires are an export to the countries of the third world and South America. There seems to be no particular impetus for paving. However, rubber tires, especially as crushed rubber, have a valuable polymeric component, which could be expected to improve properties, such as cohesion, elasticity, tensile strength and resistance to deformation of the compounds to which they are subjected. add For example, it has been discovered that, when added to asphalt, the crushed rubber from scrap vehicle tires improves the durability of the road. The crushed rubber recovered from the tires has been used successfully for many years in road applications such as interlayers, membrane seals and hot mix. The increase in viscosity, in the elasticity, and in the cohesion of the binders and resulting mixtures have been shown to increase rolling resistance, fatigue life, resistance to cracking, and stone retention. The decrease in thermal susceptibility makes modified asphalt with crushed rubber a positive choice for these applications. Most of the asphalt is the product of the distillation of crude oil. The bulk properties of asphalt are from hard and brittle solids to liquids almost as thin as water. Asphalt cement is the basis of these products, and can be liquefied for construction purposes by heating, adding solvents, or with an emulsifier. The addition of diesel fuel to the base asphalt results in a product called "diluted". The use of emulsions instead of diluted ones results in substantial fuel savings. In the general method to emulsify the asphalt, concurrent streams of molten asphalt cement and water containing an emulsifying agent are directed, by means of a positive displacement pump, to a colloid mill, and are divided into small droplets by an intense shear stress. The emulsifier disperses the asphalt cement in water for pumping, for prolonged storage, and for mixing. The emulsion must "break" quickly when it comes into contact with the aggregate in a mixer, or is sprayed onto a roadbed. To perform its function of foundation and water test, the asphalt must be separated from the water phase. In the "breaking up" of the water, the asphalt droplets coalesce, and produce a continuous asphalt film on the aggregate or pavement. When cured, the residual asphalt retains all the adhesive properties, durability, and water resistance of the asphalt cement, from which it was produced. Although the application of crushed rubber in emulsions has been somewhat limited, this limitation does not result from the difficulty of emulsifying the rubber. Instead, the limitation is a reflection of the other components of the crushed rubber, and of the reticulated nature of the product, which have meant that even the best wet process mixes are distinctly two-phase. Polymer emulsions have been used in chip sealing and paste / microsurface coating. The polymers are usually pre-mixed with the asphalt, co-milled as latex, or added after mixing as latex. These methods are not available for use with crushed rubber. The previously mixed rubber, if completely digested, could be emulsified, but rubber systems crushed in asphalt are generally two-phase, and additives, such as carbon black, are not easily emulsifiable. The methods by which the material can be incorporated into the emulsion, therefore, are largely confined to the addition before milling. Crushed solid milled rubber can be added to pasta mixes as a dry ingredient. In this case, the rubber becomes a part of the aggregate phase, and acts primarily as a filler. The abrasion resistance of the rubber gives even a thin coating, a life of reasonable use, especially if it is modified with another polymer, such as rubber latex of styrene-butadiene. However, to change the elasticity and other desirable properties, the crushed rubber needs to be completely digested, in such a way that it covers the particles. This is the basis of the process in the present invention. The invention has applications in chip seals, pastes, micro surface coating, roofing, pipe covering, soil stabilization, and in any other application where emulsions are used. With the system of the present invention, thick conventional pastes are made, and conventional chip seals are improved. The present invention provides a rubber-containing emulsion, which is easily added to substantially any subsequent mixture of conventional asphalt emulsion. The invention promotes greater cohesion in the emulsified mixtures. The increase in cohesion improves the properties, such as the resistance to deformation (in the filling of potholes), resistance to surface abrasion, and resistance to cracks, and allows to use films with more binder without flooding. In seals, the retention of stones should be improved, as well as the resistance to cracks. Two relevant patents are the patents of the United States Nos. 4,018,730, Method for Emulsifying Asphal t-Rubber Paving Material and a Stable Thixotropic Emulsion of Said Material, and 4,137,204, Cationic Method for Emulsifying Asphal T-Rubber Paving Material and a Stable Thixotropic Emulsion of Said Material. Patent No. 4,018,730 discloses a method that requires heat to emulsify a recovered asphalt and rubber pavement repair material in a stable thixotropic emulsion that flows as a liquid over a slight agitation, and reaches viscosity when allowed to settle . Patent No. 4,137,204 substantially discloses the same emulsion as a base, and an asphalt-rubber soap containing a water-soluble cationic emulsifier. The present invention is different from these patents, in forming an emulsion of asphalt paving material, mixed at room temperature, and containing a relatively high percentage of recovered rubber, which is added to, and mixed with, substantially any mixture of known asphalt paving material that contains less than a previously determined percentage of rubber required to increase the rubber content of the same at room temperature. In one embodiment, the emulsion of the present invention contains equal parts by weight of rubber and solvent, which form a total base for calculating the amounts of water, non-ionic emulsifier, binders, anti-separation agent and color. The additive optionally includes latex or other natural and / or synthetic rubbers. All the ingredients are mixed at room temperature before adding and mixing the crushed rubber with the emulsion. The main object of this invention is to provide an emulsion containing a relatively high percentage of rubber, which is added to substantially any emulsion of asphalt at room temperature or up to 150 ° F (66 ° C), in order to increase the content rubber to a previously determined percentage, thus providing the physical properties that improve flow and distribution, improve the rheological values, improve the characteristics of the emulsion, and provide cross-linking to make possible the applications in paving, wall covering, ceilings, soil retention and land conservation. This emulsion of crushed rubber modifier of asphalt, consists of a semi-swollen dispersion of crushed rubber (40 to 50 percent) in a light aliphatic petroleum solvent. It is supplied as a high viscosity material that runs freely, which is easily poured and pumped. The present invention is used by adding after mixing to any of several asphalt emulsions with a simple mixture. The tests of several of these formulations developed the following data: The particular additive was prepared as described below. These results are expected, since the emulsion is a separate phase, and indicate that the emulsion must be completely mixed before use. It is believed that the increase in viscosity can be attributed to the initial swelling of the asphalt particles by the solvent. There was no obvious breakage caused by the addition of the emulsion in concentrations greater than 20 percent. The residual properties of the binders are similar to those expected for emulsions containing about 2.5 to 10 percent residual crushed rubber. This provided a torsional recovery up to 10 percent, and an increase in viscosity, and indicates the method of recovery and digestion of the rubber in the asphalt, due to the application of heat. The results with an additive prepared as described below, were as follows: The increase in penetration can be attributed to solvent retention. The emulsions used in each of the last two tests were prepared by mixing the additive of the present invention with the mentioned emulsions following the ISSA guidelines., with mechanical agitation. A single rock, granite rock scent was selected, and the emulsion was adjusted to give a rubber level of 5 weight percent on the asphalt. The content of the emulsion was equated as optimal for the design of asphalt with approximately 8 percent bitumen or 13.5 percent emulsion over Type II rock. The additive was added to the residual 5 percent, and the other polymers were 2.5 percent for latex, and 3 percent for styrene-butadiene-styrene. The additive was 3 percent latex with the rubber added. The mixing time was changed by the addition of rubber and retarder levels, comparing with the asphalt emulsion, from 0.25 to about 1 percent. When the wet track was tested using conventional industrial testing methods, the emulsion including the additive of the present invention demonstrated better resistance to stone loss. Consistent with the increase in viscosity shown in the data described above, emulsions containing an additive including latex, showed even better results. The results are stipulated in Figure 1; in Figure 1, and in each of Figures 1 to 6, the emulsions modified by the addition of the additive of the present invention are identified with the figure legend "RG-1". Similar results were obtained when emulsions were tested with and without the additive of the present invention, to determine their resistance to deformation, again in accordance with a conventional industrial test method, referred to as the loaded wheel test. As was the case in resistance to stone loss, when the additive included latex, the results improved further. The results of these tests are shown in Figure 2. In the same way, the setting time was not compromised by the addition of crushed rubber to the asphalt in the additive of the present invention. In addition, when polymer was added to the additive to be added to the emulsion, the setting time was improved. These results are shown in Figure 3. An additional test was conducted to compare the effect of using other polymers on stone retention (the same test that was used to obtain the data presented in Figure 1). Figures 4 and 5 show the results, and it is evident that the crushed rubber adhesion by the method of the present invention had a significant effect on stone retention, which was superior even to the modified emulsion with latex. The combination of latex with the additive of the present invention provided an even better performance. The viscosity increase of the high flotation emulsions was increased when they were modified with the additive of the present invention, and the effect was concentration dependent. The viscosity of the cationic emulsions was not significantly affected, and decayed with time, as shown in Figure 6; the decrease was greater as the addition quota increased. Emulsions already modified with latex showed similar results, indicating once again the advantage of mixing the additive of the present invention in the emulsion after mixing, for example, on site, according to the present method. The emulsion modified with crushed rubber asphalt used in these tests, for which these data are reported, consisted of equal parts by weight of a solvent and crushed rubber. The total parts by weight of these two ingredients comprised 100 percent of a base to calculate the amounts of the remainder of the formula, which included an emulsifier, an anti-separation agent, binders, and color. The solvent is an aliphatic solvent, more particularly an alkane, olefin or a mixture thereof, and in one embodiment Shell Sol 340HT is used, a complex combination of predominantly hydrocarbons of 9 and 12 carbon atoms, available from Shell Oil Co. This solvent tends to dissolve the natural rubber recovered from tires of discarded vehicles, and it swells and softens the crushed rubber of the recovered vulcanized tire. However, other solvents have been used with essentially similar results, including Exxon 3641 and 2024, Exxon 1520 naphtha, Exxon Varsol 1 or 18, and any other naphthas. The proportion of solvent used varies depending on the size of the crushed rubber particles, and the particular emulsion with which the additive is to be used. It is believed that the solvent participates in the crosslinking reaction, or to partially dissolve the rubber particles (and / or latex or synthetic rubbers that may also be added) in the emulsion, and it is believed that this result is an important aspect of the superior performance of asphalt emulsions that are modified in accordance with the present invention. In general, proportions of between about 30 and about 70 percent are used; however, better results are usually achieved with ratios of between about 40 and about 60 percent. The rubber is a natural rubber and crushed rubber particles vulcanized, in a 20-50 mesh, obtained from the tires of discarded vehicles. Although the size of the particles is preferably 20-50 mesh, a range of particle sizes from about 20 to about 100 can be used with advantage relative to the additive of the present invention. The proportion of rubber particles added is from about 30 to about 70 percent, depending on the size of the particles and the particular emulsion with which the additive is to be used. In general, proportions of between 40 and 60 percent are used; however, better results are usually achieved with proportions of approximately 50 percent. It is preferred that the amount of water used is generally 30 to 40 percent of the basis weight. It will be recognized by experts in this field who have the benefit of this disclosure, that the amount of water can be varied according to the particle size of the crushed rubber and the proportion of solvent used. Depending on these factors, satisfactory results are achieved when water is used on a scale of about 25 to about 45 percent of the basis weight. Many emulsifiers are known in the art for use in connection with asphalt mixtures. The additive of the present invention utilizes many of these emulsifying agents, regardless of whether they are anionic, cationic or non-ionic, and can be of any degree, including RS, MS, SS and QS. For example, anionic emulsifiers, such as petroleum sulphonates or sulfates, soaps such as alkali metal salts of fatty acids, acid mixtures of animal or vegetable oils, and emulsifiers mentioned, for example, in U.S. Pat. Nos. 3,635,863; 4,018,730; 4,137,204; 4,282,037 and 4,548,735. Nonionic emulsifiers that can be used advantageously in relation to the additive of the present invention include polyoxyethylene or long chain polyoxypropylene groups in fatty acids, alcohols, amides or amines, again as described in the U.S. Pat. No. 4,282,037. Cationic emulsifiers, such as diamines, amidoamines, imidazolines and quaternary amines, and the mixture of imidazoline and quaternary diamine (Tyfocat-R and Indulin, respectively) described in U.S. Patent 4,137,204, are also suitable for use in connection with the additive of the present invention. Preferred emulsifiers are nonionic emulsifiers, such as an ethoxylated nonylphenol or ionic emulsifiers, such as lignin sulfonate, such as the emulsifier available under the registered trademark INDULIN. Hydrochloric acid or caustic soda can also be added to the cationic or anionic emulsifiers, respectively, in such a way that these emulsifiers can be used with greater advantage. Particularly preferred emulsifiers are those mentioned below. The proportion of emulsifier used varies depending on the particle size of the crushed rubber and the particular emulsion with which the additive is to be used. In general, proportions of between 0.5 and 5 percent are used; however, better results are usually achieved with ratios of between about 1 and about 2 percent. When the emulsifying agent used is a nonionic ethoxylated nonylphenol (Crisonal 100/70, Christianson Chemicals, San Antonio, Texas, United States), the emulsifier comprises from about 10 to 15 percent of the base weight of the additive (from 1.5 to 2.5). percent) . The additive of the present invention may optionally include a binder, comprising from about 3 to about 10 percent of the basis weight. In one embodiment, the binder is a clay mineral traded under the trademark Imvite IGB by Industrial Minerals Ventures, 2030 East Flamingo, Las Vegas, Nevada 89119, United States. Other clays, including mineral clays, such as bentonites, bentones, hectorites, montmorillonite, and the clays mentioned in U.S. Patent No. 5,539,029, are also used with advantage. When these clays are used as a binder in the additive of the present invention, the binder is used to replace the lignosulfonic acid emulsifier. The best results are achieved when the clay is used in a ratio of about 8 to about 15 percent of the basis weight. Other substances that can be included in the additive of the present invention are natural and synthetic rubbers. As described above, the inclusion of approximately 2.5 to 3 percent (of the base weight) of latex provided synergistic results. Other synthetic and / or thermoplastic rubbers, such as SBS and SBR in the additive, may also be included in proportions of from about 0 to about 50 percent. (of the base weight). Regardless of whether or not natural rubbers or other rubbers are added, satisfactory results are obtained in proportions of about 2 to about 20 percent. An anti-separation agent is also used in the additive of the present invention. Anti-separation agents, such as quaternary amines and polyamines, are used with advantage, and the anti-separation agent generally comprises from about 0.5 to about 1.5 percent of the additive. Particularly preferred for use as the second binder, an aliphatic amine (polyamine), such as the polyamine available under the registered trademark Nrd Bottoms (Nova Technologies, Houston, Texas, United States) in a proportion of about 3 percent a approximately 10 percent of the base weight. This anti-separation agent improves the adhesion of the asphalt to the roadbed, and retards the bleeding of the asphalt through a microscopic seal wear surface. Other anti-separation agents suitable for use in the additive of the present invention include the quaternary amine sold as Unichem 8162 (Casper, Yoming, United States). The additive of the present invention also comprises from 1 to 4 percent of the basis weight of atactic polypropylene powder (PPA), and from 1 to 4 percent of the basis weight of a selected color, such as carbon black. The amount of each of the main ingredients, solvent, and rubber, can be varied from 2 to 8 parts by weight, to reach the basis weight. The amount of the remaining ingredients of the formula can be from 3 to 4 parts by weight of water; 1.5 parts by weight of emulsifying agent; 1/2 parts by weight of Imvite IGB binder; and the remaining three ingredients as follows: agent against separation, atactic polypropylene powder, and color, each 1/10 to 1/5 parts by weight. A preferred example of the emulsion consists of 100 pounds (45 kilograms) of solvent, 100 pounds (45 kilograms) of rubber, 60 pounds (27 kilograms) of water, 4 pounds (1.8 kilograms) of nonionic emulsifier, 5 pounds (2.25) kilograms) of Imvite IGB, and 2 pounds (0.9 kilograms) of each of Nrd Bottoms, atactic polypropylene powder, and black color for a total of 273 pounds (124 kilograms). Comparison tests conducted with emulsions with and without the additive of the present invention indicate that the additive improves the performance characteristics of the emulsion residue. In one test, a standard emulsion sample CRS-2 was obtained at Koch Asphalt (Austin, Texas, United States), modified by the addition of 10 percent rubber additive by weight of the distillation residue (6.87 total emulsion) ), and mixed with a mechanical agitator to ensure complete distribution. The two emulsions were then tested to give the following results.

These results show that the additive produces a softer residue at 77 ° F (25 ° C) than the unmodified emulsion, indicating that the modified emulsion works as well or better than the unmodified emulsion with respect to hardness and rock retention at elevated road temperatures, and is more resistant to rock separation or brittle failure at low road temperatures.

Both emulsion residues were subjected to the thin film furnace test to test the aging potential of the asphalt. The modified emulsion residue was softer at 77 ° F (25 ° C) than the unmodified emulsion after aging, while the viscosity was slightly higher. These results indicate that the modified emulsion has a better film strength or hardness after aging at an elevated road temperature than the unmodified emulsion, while still being less brittle at lower temperatures. The ductility of the aged modified emulsion was lower than the unmodified emulsion, but the ductility strand to the break was much thicker, indicating a harder asphalt and higher film strength. Additional tests measured the effect of different percentages of additive and different emulsions on chip retention and viscosity over time. The first was tested by modifying the Vialet Procedure, curing the plates in the oven at 90 ° F (32-2 ° C) for one hour, and / or for 12 hours, before measuring chip retention. The results (expressed as retained percentage) were as follows: The viscosity test over time was conducted according to conventional industrial methods. The results were as follows: These results indicate that the viscosity of the high-flotation emulsions is increased significantly by the addition of the additive, and that the effect depends on the concentration. The viscosity of the cationic emulsions was not significantly affected by the addition of the additive, and they decayed significantly with time. Emulsions already modified with latex exhibited the same tendency. Although it has already been observed that the additive of the present invention is added to the emulsion after mixing, i.e., at the site, in a surprising manner, these results with the emulsions that have been modified with latex, indicate that it is achieved better performance of the asphalt if the additive is mixed with emulsion on site, that is, after mixing. In the method for preparing an asphalt emulsion to be used as a paving material, roofing, or other coating material, the additive of the present invention, as noted above, has the very significant advantage of mixing with the emulsion afterwards. of grinding. In other words, the additive is prepared in bulk, by the addition of the emulsifier, atactic polypropylene powder, and agent against solvent separation, mixing, and addition of the carbon black or other color. The crushed rubber is then added and mixed, followed by the addition of water. Then the additive is transported to the place where the asphalt is going to be applied, where the quantity of the desired additive is poured, pumped, or sucked into the distributor truck (preferably using the truck pump), and mixed with the commercially purchased asphalt emulsion, at ambient temperatures, using the truck's internal circulation pump. Then the resulting mixture is sprayed on the road or other surface. The additive is mixed with the emulsion in a wide range of proportions, depending on the use and the nature of the surface to which the asphalt is to be applied. The proportions (by weight) range from less than 5 percent to as high as 20 percent, based on the residue of the asphalt in the emulsion, but it is preferred that the additive comprises between about 5 and about 15 percent by weight. percent of the modified emulsion. Generally the best results are obtained when the crushed rubber comprises from about 5 to 10 percent of the asphalt by weight, and, depending on the asphalt emulsion, that preferred level of rubber content is obtained by mixing the additive of the present invention with the emulsion in proportions of about 8 to about 12 percent additive. Although described in conjunction with the preferred embodiments, it is intended that certain variations in those modalities that are equivalent fall within the scope of the following claims. The invention also relates to a method for adding crushed rubber to an asphalt emulsion, and applying the asphalt emulsion to a surface, which comprises the steps of: mixing an emulsifying agent, an atactic polypropylene powder, and a anti-separation agent in an aliphatic solvent and water, to form an additive comprised of 3 to 7 parts of each of the solvent and the crushed rubber, about 1.5 parts of emulsifying agent; and less than about one part each of atactic polypropylene powder and anti-separation agent; adding the additive to an asphalt emulsion at room temperature and in a proportion such that the additive comprises from about 2 to about 20 percent of the asphalt emulsion, and mixing; and spray the asphalt emulsion on a surface. Another aspect of the invention relates to an additive for use in modifying an asphalt emulsion at room temperature, which comprises: equal parts of an aliphatic solvent and crushed rubber, each comprising aliphatic solvent and rubber crushed from about 3 to about 7 parts by weight of the additive; from about 0.5 to about 5 parts by weight of an emulsifier; from about 2.5 to about 4.5 parts by weight of water; and from about 0.3 to 1.5 parts by weight of an anti-separation agent.

Claims (21)

1. CLAIMS 1. A method for adding crushed rubber to an asphalt emulsion, and applying the asphalt emulsion to a surface, which comprises the steps of: mixing an emulsifier, atactic polypropylene powder, and an agent against separation in a solvent aliphatic add crushed rubber to the mixture of emulsifier, atactic polypropylene powder, and anti-separation agent, and mix; adding water to the emulsifier, the atactic polypropylene powder, and the mixed separation agent, to form an additive; mix the additive with an asphalt emulsion at room temperature; and spraying the mixture of asphalt additive and emulsion onto a surface.
2. 2. The method according to claim 1, characterized in that the aliphatic solvent is a naphtha.
3. 3. The method according to claim 2, characterized in that the aliphatic solvent comprises from about 30 to about 70 percent of the mixture of solvent, crushed rubber, emulsifier, atactic polypropylene powder, and antifeedant agent. separation.
4. 4. The method according to claim 1, characterized in that the crushed rubber comprises natural crushed rubber and vulcanized recovered.
5. 5. The method according to claim 4, characterized in that the crushed rubber comprises from about 30 to about 70 percent of the mixture of solvent, crushed rubber, emulsifier, atactic polypropylene powder, and agent against separation.
6. 6. The method according to claim 1, characterized in that the emulsifier is a nonionic ethoxylated nonylphenol.
7. 7. The method according to claim 4, characterized in that the emulsifier further comprises a lignosulfonic acid.
8. 8. The method according to claim 1, characterized in that the anti-separation agent is an aliphatic amine.
9. 9. The method according to claim 1, characterized in that the particle size of the crushed rubber is 20 to 50 mesh.
10. 10. A method to add crushed rubber to an asphalt emulsion, and apply the emulsion of asphalt to a surface, which comprises the steps of: mixing an emulsifying agent, an atactic polypropylene powder, and an anti-separation agent in an aliphatic solvent and water, to form an additive comprised of 3 to 7 parts of each of the solvent and the crushed rubber, approximately 1.5 parts of emulsifying agent; and less than about one part each of atactic polypropylene powder and anti-separation agent; adding the additive to an asphalt emulsion at room temperature and in a proportion such that the additive comprises from about 2 to about 20 percent of the asphalt emulsion, and mixing; and spray the asphalt emulsion on a surface.
11. 11. The method according to claim 10, characterized in that the aliphatic solvent is naphtha.
12. 12. The method according to claim 10, characterized in that the crushed rubber comprises natural and vulcanized crushed rubber recovered.
13. 13. The method according to claim 10, characterized in that the emulsifier is a nonionic ethoxylated nonylphenol.
14. 14. The method according to claim 13, characterized in that the emulsifier further comprises a lignosulfonic acid.
15. 15. The method according to claim 10, characterized in that the anti-separation agent is an aliphatic amine.
16. 16. The method according to claim 10, characterized in that the particle size of the crushed rubber is 20 to 50 mesh.
17. 17. The method according to claim claimed in any of claims 10., 11, 12 or 16, characterized in that the additive comprises from about 8 to about 15 percent of the asphalt emulsion.
18. 18. An additive for use in modifying an asphalt emulsion at room temperature, which comprises: equal parts of an aliphatic solvent and crushed rubber, each comprising aliphatic solvent and crushed rubber from about 3 to about 7 parts in weight of the additive; from about 0.5 to about 5 parts by weight of an emulsifier; from about 2.5 to about 4.5 parts by weight of water; and from about 0.3 to 1.5 parts by weight of an anti-separation agent.
19. 19. The additive according to claim 18, further comprising from about 2 to about 20 percent rubber.
20. 20. The additive according to claim 18, characterized in that it additionally comprises from about 1 to about 4 percent atactic polypropylene.
21. 21. The additive according to claim 18, characterized in that the emulsifier is a cationic, anionic or non-ionic emulsifier.