Classifications

• • E—FIXED CONSTRUCTIONS
  • E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
  • E01C—CONSTRUCTION OF, OR SURFACES FOR, ROADS, SPORTS GROUNDS, OR THE LIKE; MACHINES OR AUXILIARY TOOLS FOR CONSTRUCTION OR REPAIR
  • E01C19/00—Machines, tools or auxiliary devices for preparing or distributing paving materials, for working the placed materials, or for forming, consolidating, or finishing the paving
  • E01C19/02—Machines, tools or auxiliary devices for preparing or distributing paving materials, for working the placed materials, or for forming, consolidating, or finishing the paving for preparing the materials
  • E01C19/10—Apparatus or plants for premixing or precoating aggregate or fillers with non-hydraulic binders, e.g. with bitumen, with resins, i.e. producing mixtures or coating aggregates otherwise than by penetrating or surface dressing; Apparatus for premixing non-hydraulic mixtures prior to placing or for reconditioning salvaged non-hydraulic compositions
  • E01C19/1059—Controlling the operations; Devices solely for supplying or proportioning the ingredients
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/34—Silicon-containing compounds
  • C08K3/36—Silica
• • E—FIXED CONSTRUCTIONS
  • E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
  • E01C—CONSTRUCTION OF, OR SURFACES FOR, ROADS, SPORTS GROUNDS, OR THE LIKE; MACHINES OR AUXILIARY TOOLS FOR CONSTRUCTION OR REPAIR
  • E01C19/00—Machines, tools or auxiliary devices for preparing or distributing paving materials, for working the placed materials, or for forming, consolidating, or finishing the paving
  • E01C19/02—Machines, tools or auxiliary devices for preparing or distributing paving materials, for working the placed materials, or for forming, consolidating, or finishing the paving for preparing the materials
  • E01C19/10—Apparatus or plants for premixing or precoating aggregate or fillers with non-hydraulic binders, e.g. with bitumen, with resins, i.e. producing mixtures or coating aggregates otherwise than by penetrating or surface dressing; Apparatus for premixing non-hydraulic mixtures prior to placing or for reconditioning salvaged non-hydraulic compositions
  • E01C19/1013—Plant characterised by the mode of operation or the construction of the mixing apparatus; Mixing apparatus
• • E—FIXED CONSTRUCTIONS
  • E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
  • E01C—CONSTRUCTION OF, OR SURFACES FOR, ROADS, SPORTS GROUNDS, OR THE LIKE; MACHINES OR AUXILIARY TOOLS FOR CONSTRUCTION OR REPAIR
  • E01C7/00—Coherent pavings made in situ
  • E01C7/08—Coherent pavings made in situ made of road-metal and binders
  • E01C7/18—Coherent pavings made in situ made of road-metal and binders of road-metal and bituminous binders
• • E—FIXED CONSTRUCTIONS
  • E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
  • E01C—CONSTRUCTION OF, OR SURFACES FOR, ROADS, SPORTS GROUNDS, OR THE LIKE; MACHINES OR AUXILIARY TOOLS FOR CONSTRUCTION OR REPAIR
  • E01C7/00—Coherent pavings made in situ
  • E01C7/08—Coherent pavings made in situ made of road-metal and binders
  • E01C7/18—Coherent pavings made in situ made of road-metal and binders of road-metal and bituminous binders
  • E01C7/182—Aggregate or filler materials, except those according to E01C7/26

Definitions

• the present invention makes such a trade-off unnecessary. It has been found that by adding diatomite to high-asphalt-containing asphalt and, preferably, sufficient to theoretically adsorb all the asphalt, a mix having optimum cohesive strength and extended pavement life can be achieved. This is due to the fact that the adsorption of the asphalt maintains the film thickness of the asphalt mastic at its optimum minimum thickness and, at the same time, forms a thicker mortar layer that shields the mastic bond interface between aggregate particles from the atmosphere and from water, thereby reducing the amount of age (oxidation) hardening and the water susceptibility of the pavement. Further, diatomite increases resistance to asphalt flow to such an extent that bleeding, rutting and shoving of the pavement are effectively minimized.
• diatomite-containing mix By limiting the quantity of diatomite in the mix to an amount not substantially greater than the amount capable of adsorbing all of the asphalt in these high-asphalt-content mixes, water susceptibility can be avoided.
• An additional benefit of this diatomite-containing mix is its retention of skid-resistance.
• One of the factors contributing to loss of skid-resistance in a pavement is its compaction under traffic loading which reduces the void content and, hence, reduces the water permeability of the pavement surface. With a less permeable surface, water drainage is decreased which increases the dangers of hydroplaning and skidding.
• Many diatomite-containing mixes resist over-compaction and maintain a sufficient quantity of voids under traffic loading to insure permeability.
• voids provide a place for the water trapped between tire and pavement to go, thereby reducing the likelihood of hydroplaning and skidding.
• the diatomite provides the mortar portion of any pavement mix with abrasion-resistance which greatly reduces the rate at which the asphalt and sand is eroded from the pavement and, in turn, prevents exposure of the larger aggregate, thereby protecting it from polishing. Exposure and polishing of certain types of aggregate make even a well-drained pavement slippery.
• the present invention also solves the previous problems related to diatomite mix consistency.
• Conventional practice in pavement batch mixing plants involves dry mixing the hot aggregate and any mineral filler prior to the addition of liquid asphalt. This was believed to be necessary to achieve proper dispersion of the filler in the mix and to avoid clumping. Further, it was believed an extended mixing time after the asphalt was added was necessary to insure complete coating of the mineral filler in order to avoid water susceptibilit .
• premixing the diatomite with the aggregate resulted in crushing of the diatoms making the resultant mix 'soupy' .
• the process of the present invention involves premixing the components of the aggregate (usually sand and stone) , adding the asphalt, mixing for a conventional period of time which thoroughly coat the aggregate with asphalt and then adding the diatomite to the mix.
• the diatomite is able to achieve satisfactory dispersion in the mix even though added so late in the mixing process.
• the diatoms do not suffer the crushing effects noticed in the conventional procedure; the asphalt apparently acts as a cushioning agent or lubricant for the diatoms protecting them from the abrasive action of the aggregate.
• FIG. 1 is an enlarged view at 250X magnification of one grade of diatomite that may be used in the present invention
• FIG. 2A is a schematic depiction of two particles of prior high-asphalt-content mixes
• FIG. 2B is a schematic depiction of two particles of the present diatomite-containing asphalt
• FIG. 3 is a graphic representation of the improvement in durability that can be expected from the diatomite-modified, high- asphalt content mix
• FIG. 4 is a graph illustrating the effects of water on various mixes that do and do not contain diatomite
• FIG. 5 A-D are photographs of core samples of actual pavements following 11 months of high traffic usage.
• FIG. 1 is a 250X magnification of one type of diatomite which has been found suitable for use in the pavement mix of the present invention.
• This grade of diatomite is sold under the trademark "CELITE 292" and is available from MANVTT,T,F, PRODUCTS CORPORATION.
• CELITE 292 One of the primary functions of a filler material in a high-asphalt-content paving mix is to thicken the mastic and inhibit flow of the asphalt. ⁇ ie capability of the filler to inhibit flow will be a primary factor in determining how much additional asphalt can be added without the asphalt seeping or bleeding out of the pavement during placement or under subsequent heavy traffic.
• the internal structure of the diatoms increases this filler's ability to hold the asphalt once it has absorbed the asphalt.
• the combination of high surface area and internal structure produce a "filtration barrier" for the viscous asphalt. This barrier would require a pressure several times greater than that experienced under heavy truck traffic to overcome its resistance to flow.
• the present invention contemplates a procedure which, although contrary to proven techniques of mixing pavement materials, has been shown to be effective.
• This process involves mixing and heating the aggregate components (generally sand and stone) in a pugmill or the like, adding and mixing the asphalt with the aggregate and, lastly, adding the diatomite to the mixture with a rather short mixing period being necessary to achieve dispersion of the diatomite.
• this is contrary to established techniques which dictate that mineral fillers be added to the aggregate early in the mixing process to achieve proper dispersion. This was particularly true with asbestos, the only filler prior to this invention which has been shown effective at stabilizing high-asphalt-containing pavements.
• each of the mixing steps of the present invention can be completed in one minute or less and, preferably, in h minute or less.
• the asphalt apparently coats the aggregate cushioning and lubricating the diatomite against the abrasive effects of the aggregate. Further, the exposure time resulting from mixing has been reduced, further protecting the diatoms.
• the aggregate which is typically 75-90% of the mix by weight and, which was in this case, 35% coarse stone (median size of h n diameter) , 30% medium stone (k" diameter or less) and 35% sand (below no. 10 mesh) , was pre ixed for 15 seconds in a pugmill before the asphalt (55-100 penetration grade) was added and 15 seconds more before the diatomite was added. Because the diatomite had to be dumped from the bags by hand, the time needed for its addition to the pugmill varied from 5 to 20 seconds, depending on the amount of diatomite that was added.
• the mixture was blended for 10 seconds (total mix time to obtain an average of 4055 lbs. of asphalt mix, varied from 45 to 60 seconds) .
• the diatomite will be packaged in plastic bags made of, for example, 'T ⁇ VEK' plastic available from Dupont, which will melt without a trace at 290°F, below the temperature of the asphalt mix. This will permit preroeasured quantities of diatomite to be added, bag and all, in a shorter, simplified procedure.
• the asphalt mastic (asphalt, 200 mesh fines and, in this case, filler) in conjunction with the fine aggregate, perform the function of a mortar holding the coarse aggregate together.
• the tensile strength of a mastic is inversely proportional to its film thickness.
• the effects of increasing asphalt content in prior mixes can be seen in FIG. 2A.
• Two stones 10, depicted as spherical (the worst case for surface contact) are coated with asphalt mastic film 12.
• Increased asphalt content means increased film thickness and, hence, a reduction in the tensile strength of the mastic (a reduction in the cohesive strength of the mix) .
• the limestone filler merely increased the density of the mastic doing little to prevent loss of ' cohesive strength. Further, limestone is not entirely effective at preventing asphalt flow, which generally leads to bleeding of the asphalt from the pavement.
• FIG. 2B Contrast the mix of the present invention as depicted in FIG. 2B.
• the diatomite adsorbs the extra asphalt, thereby keeping the thickness of asphalt mastic film 12 at its optimum minimum thickness for the greatest cohesive strength.
• Hie "reservoir" 14 of asphalt which is held fcy the diatomite, surrounds and protects the adhering interface from oxidation giving the pavement longer life due to a reduced rate of age hardening.
• FIG. 3 is a graphic representation of the anticipated benefits in pavement life expectancy, ⁇ he graph indicates at least a doubling of pavement life for typical standard dense-graded pavements.
• FIG. 3 graphically depicts the benefits of adding diatomite to standard asphalt concrete pavements, it should be noted that similar benefits are anticipated with other dense-graded pavements such as sand asphalts (those lacking coarse stones) and stone-filled sheet asphalts. .
• the following chart depicts some examples of the maximum asphalt contents for each of these three pavement types with and without diatomite added.
• the paver may wish to add sufficient diatomite to adsorb only the asphalt which exceeds normal " concentrations. ⁇ iis will maintain the mastic film thickness at the level it would have had, had not additional asphalt been added.
• the preferred embodiment has sufficient diatomite present to theoretically adsorb all the asphalt present in the mix. Due to the recommended mixing procedure in which the aggregate is precoated with asphalt and to physical constraints of the diatoms, the diatomite will not adsorb all of the asphalt that it is theoretically capable of adsorbing. Tests have shown providing sufficient diatomite to theoretically adsorb all the asphalt, produces optimum results.
• ⁇ iis optimum amount of diatomite to be added to the pavement mix can be calculated for any particular grade of diatomite using the wet density of the diatomite (computed by using Lompoc S ⁇ 234) , in the following mariner.
• 'CELITE 292' has a wet density of 16.1 pcf and an apparent density of a 'solid' diatom structure of 1.8 gt ⁇ /cc or 112.3 pcf.
• V ⁇ occupied by 16.1 lbs. of 'solid' diatom structure we calculate the volume V ⁇ occupied by 16.1 lbs. of 'solid' diatom structure.
• the weight of diatomite needed to theoretically adsorb all of the asphalt in the mix is 28.9% of the weight of that asphalt. Since
• 'CELITE 292' is the least dense and most adsorptive grade of diatomite that is ⁇ irmercially available, the amount needed for other grades will generally be greater, perhaps as high as 33%. Note, if the specific gravity of the asphalt used were higher, the volume a given weight would occupy and, hence, the .percentage of diatomite needed to adsorb it, would be less, perhaps as low as 26%. While this method has been termed a means of calculating the optimum diatomite content for a particular mix, it could obviously be used to calculate the amount of diatomite necessary to adsorb only the excess asphalt. Note also, that the Optimum* diatomite content is also the threshold value for creating additional voids as discussed hereafter.
• the percent of voids is primarily a function of the amount of asphalt content which,, in turn, partially determines hew much compaction a pavement undergoes during placement. The quantity of voids will continue to decrease during the life of the pavement due to co paction from traffic-loading. Tests, in which compaction of pavements is mechanically accelerated, have shown that the diatomite-modified pavement of the present invention resists
• the diatomite With excess absorptive capacity, the diatomite will, absorb asphalt needed to coat the sand or, absorb any water it may come in contact with, reducing the cohesive strength of the mix. In the former case. -li ⁇ the affinity for water displayed by the sand will produce a similar loss of strength.
• FIG. 4 graphically depicts the effects of water on standard pavement (6.0% asphalt) and the three sample mixes previously mentioned.
• Mix I had 6.6% asphalt (10% above normal) and .6% diatomite.
• Mix II had 7.4% asphalt and 1.8% diatomite.
• the diatomite in mix II is 24.3% of the asphalt by weight, slightly below the calculated optimum of 28.9%.
• Mix III contained 7.3% asphalt and 2.4% diatomite by weight, or diatomite-content representing 32.9% of the asphalt (exceeding optimum by 4% of asphalt weight) .
• Flexural strength of each pavement was tested initially and then following 24 hours of vacuum saturation in water. Die addition of diatomite to mix I prevented the added asphalt from decreasing cohesive strength.
• Cohesive strength of mix I would probably have been higher, had not the aggregate used been highly porous. Ihe porous aggregate adsorbed significant amounts of asphalt, adversely affecting the cohesive strength of this mix.
• the 1.8% diatomite mix (mix II) showed 78% retention of strength and a flexural strength exceeding 100 pounds.
• the 2.4% diatomite mix (mix III) showed only a 40% strength retention as compared with 49% for the standard mix. However, it should be noted that the final strength is more significant than the strength retention of the mix and the 2.4% diatomite mix was still three times as strong as the standard mix following saturation. ⁇ iese data do tend to indicate that excessive diatomite (more than 10% above the optimum percentage of asphalt wei ⁇ t) , could negate entirely the cohesive strength benefits of adding diatomite.
• OMPI of the diatomite-modified mix would still exceed the original strength of the standard mix.
• mixes II and III are sli ⁇ tly less than mix I but, still significantly better than the standard mix.
• mix III is still in good shape after almost one year exposure to the heavy Houston rainfalls, indicates that the additional diatomite has not made this pavement water susceptible.
• OPC pavement is a thin overlay (generally % to 3/4") which is intentionally quite porous so that the voids provide channels or water to penetrate the wearing course.
• Beneath the OPC pavement is a water-impermeable, usually sloped or crowned layer. Water drains through the OFC layer to the sloped impermeable layer and drains laterally to the edge of the roadway.

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• Architecture (AREA)
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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Health & Medical Sciences (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Road Paving Structures (AREA)
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Citations (2)

• 1983
  • 1983-01-17 EP EP19830900762 patent/EP0099400A4/de not_active Withdrawn
  • 1983-01-17 WO PCT/US1983/000078 patent/WO1983002619A1/en not_active Application Discontinuation
  • 1983-01-26 ES ES519271A patent/ES519271A0/es active Granted
  • 1983-01-26 FI FI830260A patent/FI830260L/fi not_active Application Discontinuation
  • 1983-01-27 ZA ZA83548A patent/ZA83548B/xx unknown
  • 1983-01-27 IT IT47622/83A patent/IT1164601B/it active
  • 1983-01-27 PT PT76154A patent/PT76154A/pt unknown
  • 1983-09-12 NO NO833251A patent/NO833251L/no unknown
  • 1983-09-26 DK DK4394/83A patent/DK439483D0/da not_active Application Discontinuation

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