CA1300818C - Method of producing an asphalt mixture having high skid resistance - Google Patents
Method of producing an asphalt mixture having high skid resistanceInfo
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- CA1300818C CA1300818C CA000551571A CA551571A CA1300818C CA 1300818 C CA1300818 C CA 1300818C CA 000551571 A CA000551571 A CA 000551571A CA 551571 A CA551571 A CA 551571A CA 1300818 C CA1300818 C CA 1300818C
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- asphalt
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Abstract
Abstract of the Disclosure Heated aggregate containing nickel slag by amount more than 25% by weight relative to the whole aggregate and filler having a room temperature are introduced into a mixer, the thus introduced materials of aggregate and filler are dry mixed in the mixer, asphalt by an amount of 3.5 to 9.5% by weight relative to the whole mixture is added to the latter and the thus prepared mixture is wet mixed in the mixer whereby a product having higher skid resistance than the conventional asphalt mixture is obtainable. To practice the method of the invention the asphalt used therefor is heated to such an extent that it has viscosity in the range of 150 to 300 centistokes.
Further, powder of ethylene ethylacrylate copolymer by an amount of 0.1 to 0.8% by weight relative to the whole mixture is added to the mixture prepared in that way and the mixture is then mixed further, resulting in a product having much less deformation rate than the conventional mixture containing rubber, olefin-based copolymer or the like being obtained.
Further, powder of ethylene ethylacrylate copolymer by an amount of 0.1 to 0.8% by weight relative to the whole mixture is added to the mixture prepared in that way and the mixture is then mixed further, resulting in a product having much less deformation rate than the conventional mixture containing rubber, olefin-based copolymer or the like being obtained.
Description
SPECIFICATION
1. TITLE OF THE INVENTION
~ethod of producing an asphalt mixture having high skid resistance 2. BACXGROUND OF THE INVENTION
The present invention relates to a method of producing an asphalt mixture and more particularly to a method of producing an asphalt mixture having high skid resistance.
DESCRIPTION OF THE PRIOR ART
Nickel slag employable for antiskid bitumen-based pavement material (asphalt mixture) is usually obtained by crashing or grinding slag with the aid of a ball mill, which is produced when ferronickel is refined from nickel oxide ore by means of Krupp-Renn process and therefore it j is an artificial product. Accordingly, it is known that its properties such as hardness, ductility or the like fluctuate very little and it reveals remarkable characte-ristics in terms of high skid resistance, durability of the asphalt mixture for a long period of time, wear resistance and stability. However, a problem is that sufficient data concerning a ratio of nickel slag additive is not available at present.
Further, it is anticipated that pavement material having more excellent characteristics in respect of skid resistance, .
. .
~ , l~OC~
durability, wear resistance and stability is obtainable when olefin-based copolymer or its mixture is added to an asphalt mixture with the aforementioned nickel slag added thereto. However, another problem is that proper condi-tions concerning amount of olefin-based copolymer to be added are not disclosed at present.
On the other hand, drawbacks inherent to conventional asphalt road pavement materials have become noticeable in recent years. Typical drawbacks are "tire digging", wearing, cracking, flowing, local sinking or the like road damage or injury each of which is caused by enlarged vehicles and remarkably increased amount of traffic.
Accordingly, it has been requested that a running life of pavement is improved by sufficiently studying combination ratio, combination process, work executing process or the like on the assumption that road pavement material is conventionally composed of aggregate, filler and asphalt.
In view of the current ci~cumstances as mentioned above it has been strongly requested that a method of producing asphalt mixture with proper amount of nickel slag added thereto and a method of producing a reformed asphalt mixture with proper amount of olefin-based polymer added thereto are established and proper conditions for practicing the aforesaid methods are offered.
SUMMARY OF THE INVENTION
The present invention has been made with the foregoing :L3~?818 background in mind and its object resides in providing a method of producing an asphalt mixture having high skid resistance which is entirely free from the problem inherent to conventional pavement materials as mentioned above.
To accomplish the above object there is provided according to one aspect of the present invention a method of producing an asphalt mixture having high skid resistance comprising the steps of introducing into a mixer heated aggregate containing nickel slag by amount more than 25%
by weight relative to the whole aggregat~ and filler having room temperature, dry mixing the thus introduced materials of aggregate and filler, adding to the mixture heated asphalt by amount of 3.5 to 9.5% by weight relative to the whole ~ixture, the asphalt being heated to such an extent that it has viscosity in the range of 150 to 300 centistokes, and then wet mixing the thus prepared mixture.
Further, according to other aspect of the present invention a method of producing an asphalt mixture having : high skid resistance comprising introducing into a~mixer heated aggregate containing nickel slag by an amount more than 25~ by weight relative to the whole aggregate and filler ~: having room temperature, dry mixing the thus introduced materials of aggregate and filler, adding to said mixture heated asphalt by amount of 3.5 to 9.S~ by weight relative to the:whole mixture, the asphalt being heated to such an extent that it has viscosity in the range of 150 to 300 : - 3 _ ;:
~3~
centistokes, wet mixing the thus prepared mixture, adding to the mixture a powder of thermoplastic resin comprising olefin-based copolymer, particularly ethylene ethylacrylate by amount of 0.1 to 0.8~ by weight relative to the whole mixture, the thermoplastic resin having affinity to asphalt and belng molten to flow at a temperature lower than the heating and mixing temperature of the asphalt mixture, and then continuing to mix the mixture.
Other objects, features and advantages of the present invention will become readily apparent from reading the following description which has been prepared in conjunc-tion with a drawing.
BRIEF DESCRIPTION OF THE DRAWING
Fig.1 illustrate results of Marshal Stability Tests conducted in respect of degree of stability (kg), density (g/cm3), flow value ~lcm/100), air void ratio (%) and degree of saturation of the asphalt mixture produced by the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Now, the present invention will be described hereunder in detall with reference to preferred embodiments thereof.
To meet requirements relative to watertightness,durabil-:
ity and wear resistivity, asphalt pavement, particularly,rolled asphalt pavement is conventionally made in such a manner that asphalt mortar comprising sand, rock powder :
:
-- 13~ 8 and asphalt is first prepared as matrix, a mixture including thus prepared asphalt mortar with a predetermined amount of crashed rocks having a relatively uniform grain size contained therein is paved on a road and asphalt coated crashed rocks (that is called chip material) are uniformly distributed and then compacted over the whole surace of the road.
A typical example of preparation of standard matrix for the rolled asphalt mixture is specified in accordance with British Standard BS-549..1973 such that a ratio of sand to rock powder is 6 : 1. However, the rolled asphalt mixture of the British Standard tends to have reduced stability on account of the kind of sand used therefor and is easy to flow. To obviate the above~mentioned problems, measures are so taken that weight ratio of sand to rock powder is changed to 3 to 1 and Trinidad lake asphalt is added to the mixture as a binder to obtain reformed asphalt mixture. The thus obtained mixture having increased watertightness and stability is employable for pavement work. However, the current situation is such that the reformed asphalt has still problems such as complicated preparing process, increased cost and an unsatisfactory skid resistivity, durability and wear resistivity.
The present invention has been made with the foregoing problems in mind and its object resides in obtaining good results with respect to the asphalt mixture employable 1~0~1~
for rolled asphalt pavement by substituting sand-shaped nickel slag as shown in Tables 1 and 2 for conventional sand. This is based on the fact that any good result can be very easily applied to popular asphalt mixture, if it is found that it is obtainable after various tests are conducted with rolled asphalt containing fine granular aggregate of which grain shape has the most strong effect on properties of the asphalt mixture.
Table 1 Chemical properties of nickel slag (1) chemical composition :percentage by weight Si2 53.35 FeO 7.41 A123 2.37 MgO 30.47 CaO 4.89 Table 2 Physical properties of nickel slag ~2) item value in percentage 5.1 mm 100 %
2.5 100 1.2 93 under-mesh size 0.6 66 0.3 38 0.15 16 specific gravity ~ 3.08 water absorption rate 0.65 Mohs hardness 5.5 to 7.0 weight per unit volume l.83 t/m3 ~30~
Embodiment 1 To accomplish the above object, the method of the present invention was practiced by way of the steps of mixing aggregate with nickel slag having the above-noted proper-ties by an amount more than 25% by weight relative to the whole aggregate comprising crashed rocks, dry mixing the thus prepared mixture together with filler having room temperature in a mixer, adding hot asphalt of which vis-cosity is adjusted in the range of 150 to 300 centistokes by heating to the mixture bv an amount of 5.0 to 7.0% by weight relative to the whole mixture and then wet mixing the mixture. After the method was practiced in that way, the excellëntly-good results were:obtained.-~-~For^~staRce, the results obtained from a number of tests conducted in respect of stability of the asphalt mixture were very satisfactory in terms of degree of stability, density, flow value, air void ratio and saturation as shown in Fig.1.
Nickel slag applied for practicing the method of the invention is an aggregate of which quality fluctuates very little and which contains Enstatite (MgO, SiOz), Horstelite (2MgO, SiO2) glassy material and mineral material as main components. Further, it is hard enough to exhibit a value close to 7 in Mohs hardness an~ has many sharp ridges. It is produced in a semi-molten state while it is agitated. When the asphalt mixture is mechanically compacted w:th tbe use o~ road roller or the ~30~81~3 like, nickel slag grains are sufficiently combined with one another while gap between the adjacent grains is filled with filler bitumen which is a mixture of rock powder and asphalt. Thus, by employing nickel slag, increased watertightness and high stability of various properties of the mixture are produced.
Since this nickel slug is a crystal assembly which has many sharp ridges as aforementioned and of which hardness is different from grain to grain, it exhibits high skid resistivity. Thus, it does not become flat when it is subjected to shock and grinding action caused by movement of motorcar, but it wears stepwise. Since it has a number of ruggednesses at all time and moreover a part thereof projected above the paved surface continues to have sharp ridges, no reduction occurs with respect to a value of resistance against skidding.
For the purpose of reference, results of comparative examination works conducted to examine how skid resistivity varies with conventional rolled asphalt with sand used therefor as well as rolled asphalt with nickel slag used in accordance with the present invention as time elapses are shown in Table 3. It should be noted that a number of tests were conducted with the use of a portable skid resistance tester.
3L30081~
Table 3 Table showing how a value of skid resistance measured by means of a portable tester varies as time elapses number of days 100 200 360 460 560 material used nickel slag 73 71 70 72 75 conventional sand 51 52 46 45 40 As is apparent from the table, in the case where conventional sand is used, an expected value of 60 is not reached from the first and it rather decreases as time elapses. On the other hand, in the case where nickel slag is used, a high value of skid resistance can be maintained for a long period of time.
Next, as a modified embodiment of the present invention it has been found that not only reinforcement effect but also unexpected effects such as improvement of resistance against brittleness at lower temperature, improvement of heat resistance or the like which can not be expected with asphalt with rubber contained therein are obtainable merely ::by adding a very small amount of ethylene ethylacrylate copolymer. It should be noted that this modified embodim-~t~is practiced without any change of heating condition and mixing condition by utilizing the~aforementioned asphalt mixture producing installation as it is. The modified em~bodiment can be satlsfactor1ly achieved by simple : ~ _ g _ .~
13~081~3 operation of adding ethylene ethylacrylate copolymer by amount of 0.1 to 0.8% by weight relative to the total weight without any need for changing mixing time. Since an additional step required for the modified embodiment can be automatically and continuously carried out, there is not seen any factor of increasing production cost from the view point of installation and production step.
Accordingly, the method in accordance with the modified embodiment can be practiced very economically.
It is well known that asphalt itself can be reformed by uniform mixing of rubber or plastics. On the other hand, the present invention consists in that an asphalt mixture is reformed with the use of ethylene ethylacrylate copolymer which has excellent affinity to asphalt and is fusible at mixing temperature of aggregate, filler and asphalt wherein ethylene ethylacrylate copolymer is introduced in a molten state into a so-called interface between the adjacent granular materials of aggregate and filler of which surface is covered with asphalt and it is then adhered thereto as they are cooled. Namely, it has been found that an amount of ethylene ethylacrylate copolymer to be added is only in the range of 0.1 to 0.8%
by weight relative to the asphalt mixture but a sufficient reforming effect is obtainable by addition of such a small amount.
As mentioned above, ethylene ethylacrylate copolymer .
-` 13~)0~:~8 has excellent affinity to asphalt and it is molten at a temperature lower than mixing temperature of road pavement material so that it can flow. It should be emphasized that it becomes brittle at a lower temperature, it is relatively easy to be crashed or pulverized at room temperature and moreover it has a sufficient structural strength at a higher temperature in the summer season.
Condensation polymerization type polymers such as nylon, PET, PBT or the like have inferior affinity to asphalt and many of them are molten at a temperature higher than mixing temperature of pavement material. Accordingly, they are not preferable for practicing the method of the invention. Further, polymer such as polystylene, poly-vinyl ~hloride, PMMA or the like are also not preferable from the view point of brittleness at lower temperature.
Embodiments 2 and 3 Aggregate comprising the following composition were prepared.
nickel slag (aggregate) 27.5 parts rock powder (filler) 5.0 parts No.6 crashed rock (aggregate) 39.0 parts No.7 crashed rock ~aggregate) 28.5 parts The aggregate heated to the temperature of 160C was introduced into a mixer and filler having room temperature was then added so that they were dr~ kneaded together for a period of time longer than S seconds. Thereafter, .
, , :13~ i8 asphalt of which viscosity amounted to 230 centistokes by heating to the temperature of 140C was supplied into the mixer by 5.5% by weight relative to the whole mixture and wet mixing was effected. Thereafter, powder of ethylene ethylacrylate copolymer having room temperature was added by amount of 0.4 to 0.6~ by weight relative to the whole mixture.
Incidentally, it is observed from the results of ex-periments conducted in consideration of grain distribution, grain size and ratio of grains having under-mesh size of each of the aggregates that required effects are not obtainable unless the amount of addition of asphalt is determined more than 3~5% by weight and less than 9.5% by weight relative to the whole mixture. Further, it is observed from the results of experiments that when an amount of ethylene ethylacrylate copolymer to be added is determined less than 3~ relative to an amount of asphalt, no desirable effect is recognized in respect of a rate of deformation and only when it is determined in excess of 3%, an effect of reduced rate of deformation is recogni~ed.
Moreover, it is observ~d that when ethylene ethylacrylate copoIymer is mixed with asphalt by amount more than 8%
relative to the amount of asphalt, curing speed is accele-rated and a phenomenon of brittleness takes place when pavement work is forcibly caused to proceed, resulting in flexibility inherent to asphalt being lost. Thus, it 4~818 is confirmed that an amount of ethylene ethylacrylate copolymer to be added should be preferably determined less than 8~. Accordingly, it is preferable that when an amount of asphalt to be supplied is determined more than 3.5% by weight but less than 9.5% by weight relative to the whole mixture, an amount of ethylene ethylacrylate copolymer to be added is determined in the range of 0.1 to 0.8% by weight relative to the whole mixture.
Next, in order to conduct wheel tracking test~of which result is indicative to flow resistance as well as ravelling test of which result is indicative of property of resistance against lower temperature, a number of samples were prepared with the use of roller compactor from a mixture which was obtained by way of the steps of supplying asphalt by amount of 5.5~ by weight relative to a mixture of aggregate and filler and then adding ethylene ethylacrylate copolymer by amount of 0.4 to Q.6% by weight.
The results obtained on completion of the above-noted tests are as shown in Table 4. The ravelling tests were conducted without any use of test chain but with the use of tire chain under an appreciably severe testing condition that reciprocable movements were carried out 66 times per minute. The results of each of the wheel tracking tests reveal that a rate of deformation is less than 2 x lO 2 of which fact means that it is substantially less than 3 x 10~ which is assumed to be a necessary condition for .
~3(~0~18 crowded traffic. With respect to an amount of wearing measured by the ravelling test, the results were very good.
Comparative Example 1 There are data in the case where no copolymer is added but it can be said that both a rate of deformation and an amount of wearing are not satisfactory.
Comparative Example 2 This comparative example is such that latex containing solid component by amount of 50% is added to aggregate by the same amount as in the foregoing embodiments in terms of amount of polymer. It is found that both rate of deformation and amount of wearing are improved in comparison with Comparative Example 1 but required properties fail to be attained satisfactorily.
Comparative Example 3 This comparative example is concerned with a premixing process in which ethylene vinyl acetate copolymer and asphalt are previously mixed with one another uniformly.
An improvement effect can be seen in respect of an amount of wearing but a rate o deformation at an elevated temper-ature is increased.
Comparative Example 4 This comparative example is such that a master batch comprising ethylene ethylacrylate copolymer and asphalt is previously prepared, it is diluted with asphalt and the ~: ' .. . .
~3~
thus diluted master batch is mixed with aggregate and filler. It is found that properties at lower temperature are good but value of deformation rate is somewhat unsatis-factory.
Comparative Example 5 This comparative example is such that high pressure polymerized polyethylene is used in place of ethylene ethylacrylate copolymer in Embodiment 2. In this example it is found that properties as road pavement material are improved but the results obtained from tests conducted for a long period of time reveal that considerable deteri-oration took place.
Table 4 polymer amount of rate of amount of used addition deformation wearing ~ x10 2mm/min) ~cm3) Embodiment 2 ethylene ethyl- 0.4 1.8 1.1 acrylate melt index 2 ethvlacrylate 15 Embodiment 3 ethylene ethyl- 0.6 0.8 0.95 acrylate ~same as Embodiment 2 Comparatlve Example l : no polymer used 0 25.4 2.69 remark: conventional pavement material ~continued) 13~
Comparative Example 2 rubber (SBR) 0.4 8.0 1.8 remark: latex added Comparative Example 3 ethylene vinyl 0.412.5 1.5 acetate copolymer melt index 30 vinyl acetate 20%
remark: premix process employed Comparative Example 4 ethylene ethyl- 0.43.4 1.5 acrylate melt index 20 ethylacrylate 18%
remark: master batch process employed Comparative Example 5 high pressure 0.42.6 2.0 polymerized polyethylene melt index 2 remark: results of tests for long time reveals deterioration.
Advantageous Effect of the Invention According to the method of the invention ethylene ethyl-acrylate copolymer is scattered on the interface between the adjacent granular materials comprising aggregate, filler and asphalt and it is molten and then collapsed under the effect of temperature and pressure in a mixer. Sometimes it is existent thereon in an expanded state. After the ' `` ~3~
asphalt mixture is used as road pavement material, ethylen~
ethylacrylate copolymer functions as a binder for fixedly securing granular materials to one another and strengthen-ing them. Since the ethylene ethylacrylate copolymers are omnipresent on necessary parts of the interface, a remarkable effect can be obtained by less number of steps and less amount of polymer than in the case of asphalt reformed by uniform mixing. This is attributable to the fact that the asphalt mixture of the invention can reduce air void ratio much more than the conventional asphalt pavement material or reformed asphalt road pavement material under the synergistic functions of air void filling effect and adhering effect.
Further, a characterizing feature of the present inven-tion consists in that ethylene ethylacrylate copolymer having high molecular weight can be used. Polyethylene and its copolymer are superior in respect of hardness, lower temperature properties and higher temperature proper-ties when they have high molecular weight. The premix process is difficult to be used when melt index is less than 10 in the case od the master batch process but the present invention makes it possible to employ the premix process when melt index is in the range of 0.1 to 10.
Rather, the last-mentioned case is often preferable from the vlew point of perfor~ances.
1. TITLE OF THE INVENTION
~ethod of producing an asphalt mixture having high skid resistance 2. BACXGROUND OF THE INVENTION
The present invention relates to a method of producing an asphalt mixture and more particularly to a method of producing an asphalt mixture having high skid resistance.
DESCRIPTION OF THE PRIOR ART
Nickel slag employable for antiskid bitumen-based pavement material (asphalt mixture) is usually obtained by crashing or grinding slag with the aid of a ball mill, which is produced when ferronickel is refined from nickel oxide ore by means of Krupp-Renn process and therefore it j is an artificial product. Accordingly, it is known that its properties such as hardness, ductility or the like fluctuate very little and it reveals remarkable characte-ristics in terms of high skid resistance, durability of the asphalt mixture for a long period of time, wear resistance and stability. However, a problem is that sufficient data concerning a ratio of nickel slag additive is not available at present.
Further, it is anticipated that pavement material having more excellent characteristics in respect of skid resistance, .
. .
~ , l~OC~
durability, wear resistance and stability is obtainable when olefin-based copolymer or its mixture is added to an asphalt mixture with the aforementioned nickel slag added thereto. However, another problem is that proper condi-tions concerning amount of olefin-based copolymer to be added are not disclosed at present.
On the other hand, drawbacks inherent to conventional asphalt road pavement materials have become noticeable in recent years. Typical drawbacks are "tire digging", wearing, cracking, flowing, local sinking or the like road damage or injury each of which is caused by enlarged vehicles and remarkably increased amount of traffic.
Accordingly, it has been requested that a running life of pavement is improved by sufficiently studying combination ratio, combination process, work executing process or the like on the assumption that road pavement material is conventionally composed of aggregate, filler and asphalt.
In view of the current ci~cumstances as mentioned above it has been strongly requested that a method of producing asphalt mixture with proper amount of nickel slag added thereto and a method of producing a reformed asphalt mixture with proper amount of olefin-based polymer added thereto are established and proper conditions for practicing the aforesaid methods are offered.
SUMMARY OF THE INVENTION
The present invention has been made with the foregoing :L3~?818 background in mind and its object resides in providing a method of producing an asphalt mixture having high skid resistance which is entirely free from the problem inherent to conventional pavement materials as mentioned above.
To accomplish the above object there is provided according to one aspect of the present invention a method of producing an asphalt mixture having high skid resistance comprising the steps of introducing into a mixer heated aggregate containing nickel slag by amount more than 25%
by weight relative to the whole aggregat~ and filler having room temperature, dry mixing the thus introduced materials of aggregate and filler, adding to the mixture heated asphalt by amount of 3.5 to 9.5% by weight relative to the whole ~ixture, the asphalt being heated to such an extent that it has viscosity in the range of 150 to 300 centistokes, and then wet mixing the thus prepared mixture.
Further, according to other aspect of the present invention a method of producing an asphalt mixture having : high skid resistance comprising introducing into a~mixer heated aggregate containing nickel slag by an amount more than 25~ by weight relative to the whole aggregate and filler ~: having room temperature, dry mixing the thus introduced materials of aggregate and filler, adding to said mixture heated asphalt by amount of 3.5 to 9.S~ by weight relative to the:whole mixture, the asphalt being heated to such an extent that it has viscosity in the range of 150 to 300 : - 3 _ ;:
~3~
centistokes, wet mixing the thus prepared mixture, adding to the mixture a powder of thermoplastic resin comprising olefin-based copolymer, particularly ethylene ethylacrylate by amount of 0.1 to 0.8~ by weight relative to the whole mixture, the thermoplastic resin having affinity to asphalt and belng molten to flow at a temperature lower than the heating and mixing temperature of the asphalt mixture, and then continuing to mix the mixture.
Other objects, features and advantages of the present invention will become readily apparent from reading the following description which has been prepared in conjunc-tion with a drawing.
BRIEF DESCRIPTION OF THE DRAWING
Fig.1 illustrate results of Marshal Stability Tests conducted in respect of degree of stability (kg), density (g/cm3), flow value ~lcm/100), air void ratio (%) and degree of saturation of the asphalt mixture produced by the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Now, the present invention will be described hereunder in detall with reference to preferred embodiments thereof.
To meet requirements relative to watertightness,durabil-:
ity and wear resistivity, asphalt pavement, particularly,rolled asphalt pavement is conventionally made in such a manner that asphalt mortar comprising sand, rock powder :
:
-- 13~ 8 and asphalt is first prepared as matrix, a mixture including thus prepared asphalt mortar with a predetermined amount of crashed rocks having a relatively uniform grain size contained therein is paved on a road and asphalt coated crashed rocks (that is called chip material) are uniformly distributed and then compacted over the whole surace of the road.
A typical example of preparation of standard matrix for the rolled asphalt mixture is specified in accordance with British Standard BS-549..1973 such that a ratio of sand to rock powder is 6 : 1. However, the rolled asphalt mixture of the British Standard tends to have reduced stability on account of the kind of sand used therefor and is easy to flow. To obviate the above~mentioned problems, measures are so taken that weight ratio of sand to rock powder is changed to 3 to 1 and Trinidad lake asphalt is added to the mixture as a binder to obtain reformed asphalt mixture. The thus obtained mixture having increased watertightness and stability is employable for pavement work. However, the current situation is such that the reformed asphalt has still problems such as complicated preparing process, increased cost and an unsatisfactory skid resistivity, durability and wear resistivity.
The present invention has been made with the foregoing problems in mind and its object resides in obtaining good results with respect to the asphalt mixture employable 1~0~1~
for rolled asphalt pavement by substituting sand-shaped nickel slag as shown in Tables 1 and 2 for conventional sand. This is based on the fact that any good result can be very easily applied to popular asphalt mixture, if it is found that it is obtainable after various tests are conducted with rolled asphalt containing fine granular aggregate of which grain shape has the most strong effect on properties of the asphalt mixture.
Table 1 Chemical properties of nickel slag (1) chemical composition :percentage by weight Si2 53.35 FeO 7.41 A123 2.37 MgO 30.47 CaO 4.89 Table 2 Physical properties of nickel slag ~2) item value in percentage 5.1 mm 100 %
2.5 100 1.2 93 under-mesh size 0.6 66 0.3 38 0.15 16 specific gravity ~ 3.08 water absorption rate 0.65 Mohs hardness 5.5 to 7.0 weight per unit volume l.83 t/m3 ~30~
Embodiment 1 To accomplish the above object, the method of the present invention was practiced by way of the steps of mixing aggregate with nickel slag having the above-noted proper-ties by an amount more than 25% by weight relative to the whole aggregate comprising crashed rocks, dry mixing the thus prepared mixture together with filler having room temperature in a mixer, adding hot asphalt of which vis-cosity is adjusted in the range of 150 to 300 centistokes by heating to the mixture bv an amount of 5.0 to 7.0% by weight relative to the whole mixture and then wet mixing the mixture. After the method was practiced in that way, the excellëntly-good results were:obtained.-~-~For^~staRce, the results obtained from a number of tests conducted in respect of stability of the asphalt mixture were very satisfactory in terms of degree of stability, density, flow value, air void ratio and saturation as shown in Fig.1.
Nickel slag applied for practicing the method of the invention is an aggregate of which quality fluctuates very little and which contains Enstatite (MgO, SiOz), Horstelite (2MgO, SiO2) glassy material and mineral material as main components. Further, it is hard enough to exhibit a value close to 7 in Mohs hardness an~ has many sharp ridges. It is produced in a semi-molten state while it is agitated. When the asphalt mixture is mechanically compacted w:th tbe use o~ road roller or the ~30~81~3 like, nickel slag grains are sufficiently combined with one another while gap between the adjacent grains is filled with filler bitumen which is a mixture of rock powder and asphalt. Thus, by employing nickel slag, increased watertightness and high stability of various properties of the mixture are produced.
Since this nickel slug is a crystal assembly which has many sharp ridges as aforementioned and of which hardness is different from grain to grain, it exhibits high skid resistivity. Thus, it does not become flat when it is subjected to shock and grinding action caused by movement of motorcar, but it wears stepwise. Since it has a number of ruggednesses at all time and moreover a part thereof projected above the paved surface continues to have sharp ridges, no reduction occurs with respect to a value of resistance against skidding.
For the purpose of reference, results of comparative examination works conducted to examine how skid resistivity varies with conventional rolled asphalt with sand used therefor as well as rolled asphalt with nickel slag used in accordance with the present invention as time elapses are shown in Table 3. It should be noted that a number of tests were conducted with the use of a portable skid resistance tester.
3L30081~
Table 3 Table showing how a value of skid resistance measured by means of a portable tester varies as time elapses number of days 100 200 360 460 560 material used nickel slag 73 71 70 72 75 conventional sand 51 52 46 45 40 As is apparent from the table, in the case where conventional sand is used, an expected value of 60 is not reached from the first and it rather decreases as time elapses. On the other hand, in the case where nickel slag is used, a high value of skid resistance can be maintained for a long period of time.
Next, as a modified embodiment of the present invention it has been found that not only reinforcement effect but also unexpected effects such as improvement of resistance against brittleness at lower temperature, improvement of heat resistance or the like which can not be expected with asphalt with rubber contained therein are obtainable merely ::by adding a very small amount of ethylene ethylacrylate copolymer. It should be noted that this modified embodim-~t~is practiced without any change of heating condition and mixing condition by utilizing the~aforementioned asphalt mixture producing installation as it is. The modified em~bodiment can be satlsfactor1ly achieved by simple : ~ _ g _ .~
13~081~3 operation of adding ethylene ethylacrylate copolymer by amount of 0.1 to 0.8% by weight relative to the total weight without any need for changing mixing time. Since an additional step required for the modified embodiment can be automatically and continuously carried out, there is not seen any factor of increasing production cost from the view point of installation and production step.
Accordingly, the method in accordance with the modified embodiment can be practiced very economically.
It is well known that asphalt itself can be reformed by uniform mixing of rubber or plastics. On the other hand, the present invention consists in that an asphalt mixture is reformed with the use of ethylene ethylacrylate copolymer which has excellent affinity to asphalt and is fusible at mixing temperature of aggregate, filler and asphalt wherein ethylene ethylacrylate copolymer is introduced in a molten state into a so-called interface between the adjacent granular materials of aggregate and filler of which surface is covered with asphalt and it is then adhered thereto as they are cooled. Namely, it has been found that an amount of ethylene ethylacrylate copolymer to be added is only in the range of 0.1 to 0.8%
by weight relative to the asphalt mixture but a sufficient reforming effect is obtainable by addition of such a small amount.
As mentioned above, ethylene ethylacrylate copolymer .
-` 13~)0~:~8 has excellent affinity to asphalt and it is molten at a temperature lower than mixing temperature of road pavement material so that it can flow. It should be emphasized that it becomes brittle at a lower temperature, it is relatively easy to be crashed or pulverized at room temperature and moreover it has a sufficient structural strength at a higher temperature in the summer season.
Condensation polymerization type polymers such as nylon, PET, PBT or the like have inferior affinity to asphalt and many of them are molten at a temperature higher than mixing temperature of pavement material. Accordingly, they are not preferable for practicing the method of the invention. Further, polymer such as polystylene, poly-vinyl ~hloride, PMMA or the like are also not preferable from the view point of brittleness at lower temperature.
Embodiments 2 and 3 Aggregate comprising the following composition were prepared.
nickel slag (aggregate) 27.5 parts rock powder (filler) 5.0 parts No.6 crashed rock (aggregate) 39.0 parts No.7 crashed rock ~aggregate) 28.5 parts The aggregate heated to the temperature of 160C was introduced into a mixer and filler having room temperature was then added so that they were dr~ kneaded together for a period of time longer than S seconds. Thereafter, .
, , :13~ i8 asphalt of which viscosity amounted to 230 centistokes by heating to the temperature of 140C was supplied into the mixer by 5.5% by weight relative to the whole mixture and wet mixing was effected. Thereafter, powder of ethylene ethylacrylate copolymer having room temperature was added by amount of 0.4 to 0.6~ by weight relative to the whole mixture.
Incidentally, it is observed from the results of ex-periments conducted in consideration of grain distribution, grain size and ratio of grains having under-mesh size of each of the aggregates that required effects are not obtainable unless the amount of addition of asphalt is determined more than 3~5% by weight and less than 9.5% by weight relative to the whole mixture. Further, it is observed from the results of experiments that when an amount of ethylene ethylacrylate copolymer to be added is determined less than 3~ relative to an amount of asphalt, no desirable effect is recognized in respect of a rate of deformation and only when it is determined in excess of 3%, an effect of reduced rate of deformation is recogni~ed.
Moreover, it is observ~d that when ethylene ethylacrylate copoIymer is mixed with asphalt by amount more than 8%
relative to the amount of asphalt, curing speed is accele-rated and a phenomenon of brittleness takes place when pavement work is forcibly caused to proceed, resulting in flexibility inherent to asphalt being lost. Thus, it 4~818 is confirmed that an amount of ethylene ethylacrylate copolymer to be added should be preferably determined less than 8~. Accordingly, it is preferable that when an amount of asphalt to be supplied is determined more than 3.5% by weight but less than 9.5% by weight relative to the whole mixture, an amount of ethylene ethylacrylate copolymer to be added is determined in the range of 0.1 to 0.8% by weight relative to the whole mixture.
Next, in order to conduct wheel tracking test~of which result is indicative to flow resistance as well as ravelling test of which result is indicative of property of resistance against lower temperature, a number of samples were prepared with the use of roller compactor from a mixture which was obtained by way of the steps of supplying asphalt by amount of 5.5~ by weight relative to a mixture of aggregate and filler and then adding ethylene ethylacrylate copolymer by amount of 0.4 to Q.6% by weight.
The results obtained on completion of the above-noted tests are as shown in Table 4. The ravelling tests were conducted without any use of test chain but with the use of tire chain under an appreciably severe testing condition that reciprocable movements were carried out 66 times per minute. The results of each of the wheel tracking tests reveal that a rate of deformation is less than 2 x lO 2 of which fact means that it is substantially less than 3 x 10~ which is assumed to be a necessary condition for .
~3(~0~18 crowded traffic. With respect to an amount of wearing measured by the ravelling test, the results were very good.
Comparative Example 1 There are data in the case where no copolymer is added but it can be said that both a rate of deformation and an amount of wearing are not satisfactory.
Comparative Example 2 This comparative example is such that latex containing solid component by amount of 50% is added to aggregate by the same amount as in the foregoing embodiments in terms of amount of polymer. It is found that both rate of deformation and amount of wearing are improved in comparison with Comparative Example 1 but required properties fail to be attained satisfactorily.
Comparative Example 3 This comparative example is concerned with a premixing process in which ethylene vinyl acetate copolymer and asphalt are previously mixed with one another uniformly.
An improvement effect can be seen in respect of an amount of wearing but a rate o deformation at an elevated temper-ature is increased.
Comparative Example 4 This comparative example is such that a master batch comprising ethylene ethylacrylate copolymer and asphalt is previously prepared, it is diluted with asphalt and the ~: ' .. . .
~3~
thus diluted master batch is mixed with aggregate and filler. It is found that properties at lower temperature are good but value of deformation rate is somewhat unsatis-factory.
Comparative Example 5 This comparative example is such that high pressure polymerized polyethylene is used in place of ethylene ethylacrylate copolymer in Embodiment 2. In this example it is found that properties as road pavement material are improved but the results obtained from tests conducted for a long period of time reveal that considerable deteri-oration took place.
Table 4 polymer amount of rate of amount of used addition deformation wearing ~ x10 2mm/min) ~cm3) Embodiment 2 ethylene ethyl- 0.4 1.8 1.1 acrylate melt index 2 ethvlacrylate 15 Embodiment 3 ethylene ethyl- 0.6 0.8 0.95 acrylate ~same as Embodiment 2 Comparatlve Example l : no polymer used 0 25.4 2.69 remark: conventional pavement material ~continued) 13~
Comparative Example 2 rubber (SBR) 0.4 8.0 1.8 remark: latex added Comparative Example 3 ethylene vinyl 0.412.5 1.5 acetate copolymer melt index 30 vinyl acetate 20%
remark: premix process employed Comparative Example 4 ethylene ethyl- 0.43.4 1.5 acrylate melt index 20 ethylacrylate 18%
remark: master batch process employed Comparative Example 5 high pressure 0.42.6 2.0 polymerized polyethylene melt index 2 remark: results of tests for long time reveals deterioration.
Advantageous Effect of the Invention According to the method of the invention ethylene ethyl-acrylate copolymer is scattered on the interface between the adjacent granular materials comprising aggregate, filler and asphalt and it is molten and then collapsed under the effect of temperature and pressure in a mixer. Sometimes it is existent thereon in an expanded state. After the ' `` ~3~
asphalt mixture is used as road pavement material, ethylen~
ethylacrylate copolymer functions as a binder for fixedly securing granular materials to one another and strengthen-ing them. Since the ethylene ethylacrylate copolymers are omnipresent on necessary parts of the interface, a remarkable effect can be obtained by less number of steps and less amount of polymer than in the case of asphalt reformed by uniform mixing. This is attributable to the fact that the asphalt mixture of the invention can reduce air void ratio much more than the conventional asphalt pavement material or reformed asphalt road pavement material under the synergistic functions of air void filling effect and adhering effect.
Further, a characterizing feature of the present inven-tion consists in that ethylene ethylacrylate copolymer having high molecular weight can be used. Polyethylene and its copolymer are superior in respect of hardness, lower temperature properties and higher temperature proper-ties when they have high molecular weight. The premix process is difficult to be used when melt index is less than 10 in the case od the master batch process but the present invention makes it possible to employ the premix process when melt index is in the range of 0.1 to 10.
Rather, the last-mentioned case is often preferable from the vlew point of perfor~ances.
Claims (3)
1. A method of producing an asphalt mixture having high skid resistance comprising the steps of;
introducing into a mixer heated aggregate containing nickel slag by an amount more than 25% by weight relative to the whole aggregate and filler having room temperature, said nickel slag being produced when ferronickel is refined from nickel oxide ore by means of Krupp-Renn process, dry mixing the thus introduced materials of aggregate and filler, adding to the mixture heated asphalt by an amount of 3.5 to 9.5% by weight relative to the whole mixture, said asphalt being heated to such an extent that it has viscosity in the range of 150 to 300 centistokes, and then wet mixing the thus prepared mixture.
introducing into a mixer heated aggregate containing nickel slag by an amount more than 25% by weight relative to the whole aggregate and filler having room temperature, said nickel slag being produced when ferronickel is refined from nickel oxide ore by means of Krupp-Renn process, dry mixing the thus introduced materials of aggregate and filler, adding to the mixture heated asphalt by an amount of 3.5 to 9.5% by weight relative to the whole mixture, said asphalt being heated to such an extent that it has viscosity in the range of 150 to 300 centistokes, and then wet mixing the thus prepared mixture.
2. A method of producing an asphalt mixture having high skid resistance comprising the steps of;
introducing into a mixer heated aggregate containing nickel slag by an amount more than 25% by weight relative to the whole aggregate and filler having room temperature, said nickel slag being produced when ferronickel is refined from nickel oxide ore by means of Krupp-Renn process, dry mixing the thus introduced materials of aggregate and filler, adding to the mixture heated asphalt by an amount of
introducing into a mixer heated aggregate containing nickel slag by an amount more than 25% by weight relative to the whole aggregate and filler having room temperature, said nickel slag being produced when ferronickel is refined from nickel oxide ore by means of Krupp-Renn process, dry mixing the thus introduced materials of aggregate and filler, adding to the mixture heated asphalt by an amount of
3.5 to 9.5% by weight relative to the whole mixture, said asphalt being heated to such an extent that it has viscosity in the range of 150 to 300 centistokes, wet mixing the thus prepared mixture, adding to the mixture a powder of olefin-based copolymer by an amount of 0.1 to 0.8% by weight relative to the whole mixture, said copolymer having affinity to asphalt and being molten to flow at a temperature lower than the heat-ing and mixing temperature of the asphalt mixture, and then continuing to mix the mixture.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000551571A CA1300818C (en) | 1987-10-30 | 1987-10-30 | Method of producing an asphalt mixture having high skid resistance |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000551571A CA1300818C (en) | 1987-10-30 | 1987-10-30 | Method of producing an asphalt mixture having high skid resistance |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1300818C true CA1300818C (en) | 1992-05-19 |
Family
ID=4136826
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000551571A Expired - Fee Related CA1300818C (en) | 1987-10-30 | 1987-10-30 | Method of producing an asphalt mixture having high skid resistance |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1300818C (en) |
-
1987
- 1987-10-30 CA CA000551571A patent/CA1300818C/en not_active Expired - Fee Related
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