Abstract:
Powdery bitumen concentrates are prepared containing 10 to 85 weight %, preferably 40 to 80 weight %, of synthetic silica. The concentrate is used in asphalt mixtures for building roads to give high stiffening value thereto.

Description:
BACKGROUND OF THE INVENTION 
     According to DIN 55946 (German Industrial Standard 55946) bitumens are a dark colored, semisolid to brittle, meltable, high molecular weight hydrocarbon mixtures which are obtained in the careful refining of petroleums and the portion of the natural asphalts as well as mineral wax and montan wax soluble in carbon disulfide (see Rompp Lexikon der Chemie, 7th Edition, page 377). 
     These kinds of materials which in the Anglo-Saxon region (above all the U.S.A.) are designated as asphalt are employed admixed with limestone powder, granite powder, basalt powder, greenstone powder and gabbro powder in the building of streets. 
     In this connection of especial significance is the use of natural asphalt. 
     Natural asphalt can be employed in admixture with bituminous binders according to DIN 1995 for the production of mortar rich coating layers (e.g., cast asphalt, asphalt concrete, sand asphalt and asphalt mastic). A natural asphalt of this type is, e.g., Trinidad-Epure (Trinidad-refined) which has the following composition: 
     
         ______________________________________Soluble bitumen     53 to 55 weight %Mineral portion     36 to 37 weight %Residual constituents                9 to 10 weight %______________________________________ 
    
     (compare Handbuch fur Strassenwesen Planung-Bau-Verkehr-Betrieb 1979, Otto Elsner Verlagsgesellschaft, Darmstadt). 
     Trinidad-Epure as well as the other known natural asphalts have the disadvantage that in spite of the very high filler content they are solid and must be melted before use. 
     SUMMARY OF THE INVENTION 
     According to the invention there is prepared a powder (or pulverulent) bitumen concentrate containing 10 to 85 weight %, preferably 40 to 80 weight %, of synthetic silica. 
     As synthetic silicas there can be used precipitated silica as well as pyrogenically produced silica. 
     The precipitated silica can have a BET-surface area of 120 to 500 m 2  /g. In a given case it can be ground by a steam jet, spray dried or spray dried and ground. 
     The pyrogenically produced silica can have a BET-surface area of 100 to 400 m 2  /g. 
     The bitumen concentrate of the invention can be produced by simply mixing the liquid bitumen with the synthetic silica or spraying the liquid bitumen on the synthetic silica. 
     The bitumen concentrate of the invention has the advantage that in spite of the high proportion of bitumen it is powdery, temperature stable and flowable. 
     Furthermore according to another aspect of the invention, the use of the powdery bitumen concentrate in asphalt mixture for building roads, results in a surprisingly high stiffening effect. 
    
    
     The powdery bitumen concentrate of the invention is described in more detail in the following examples. 
     The process can comprise, consist essentially of or consist of the steps set forth with the stated materials. 
     Unless otherwise indicated all parts and percentages are by weight. 
     DETAILED DESCRIPTION OF THE INVENTION 
     For the production of powdery bitumen concentrate there was carried out the following operation: 
     1. Heat the particular silica and the bitumen to 140° C. in the drying oven. 2. There is present in the mixing vessel the weighed out amount of silica. Add the bitumen in portions with stirring (by hand or with a wing stirrer according to the amount), powerful subsequent mixing until visible homogenization. 3. Bringing out the still hot composition into a sheet, spreading until cooling to room temperature. 4. The cold, friable to granulate type composition is disintegrated and ground in the Braun mixer. 5. The powder is placed on a 0.75 mm sieve, sieved, homogenized in the glass container in a Turbula mixer. 
     The bulk density of the powders in each case was determined (g/cm 3 ). In order to find an indication of the storage stability there were carried out pressure testings over 36 hours in pressure cylinders (diameter 49 mm, impressions 3.2 kp=1.7 N/cm 2  and 11.2 kp=5.95 N/cm 2 ) at normal temperature. The recording was according to the school annotation system. The results are compiled in Table 1. 
     In order to check the temperature stability of the individual bitumen powders, in each case the samples were tempered at increasing temperature in the drying oven (increasing in each case around 10° C. to 20° C.). The results are compiled in Table 2. 
     
                       TABLE 1______________________________________      Bulk   Pressure Testing        Density  1.7Sample Designation        g/cm.sup.3                 N/cm.sup.2                         5.95 N/cm.sup.2                                 Notes______________________________________50% B 80 (bitumen)                    dry50% SIPERNAT 22        0.349    3       3-4     powder60% B 80 (bitumen)                    dry40% SIPERNAT 22        0.373    4       4-5     powder66.7% B 80 (bitumen)                  dry33.3% SIPERNAT 22        0.437    4       5       powder70% B 80 (bitumen)                    dry30% SIPERNAT 22        0.440    4       5       powder80% B 80 (bitumen)                    dry20% SIPERMAN 22        0.459    5       6       powder60% B 80 (bitumen)                    dry40% FK 320   0.450    4       5       powder66.7% B 80 (bitumen)                  dry33.3% FK 320 DS        0.578    5       6       powder______________________________________ 
    
     The determination of the bulk density was according to DIN 53 194. 
     Evaluation Table for Pressure Testing 
     3=satisfactory--loosely shaped, with slight finger pressure substantially powdery disintegration 
     4=adequate--loosely adhered together, still most finely disintegrated with finger pressure 
     5=imperfect--semisolidly adhered together, no longer most finely disintegrated with finger pressure 
     6=insufficient--solidly adhered together. 
     A detailed description of this procedure for evaluation is found in Seifen-Ole-Fette-Wachse 8900 Augsburg, Year 94/1968, Part 12, pages 849-858. 
     A special printing of this literature appears as No. 31 in the series of pigment publications of the firm Degussa. 
     
                                           TABLE 2__________________________________________________________________________            1 hour                  1 hour  1 hour                               14 hours                                    1 hour                                         1 hour                                              1 hourSample Designation      Start 80° C.                  90° C.                          100° C.                               120° C.                                    140° C.                                         160° C.                                              1880° C.__________________________________________________________________________50% B 80   gray-brown            gray-brown                  gray-brown                          gray-                               light                                    light                                         light                                              light                          brown                               beige                                    beige                                         beige                                              brown50% SIPERNAT 22      loose loose loose   loose                               loose                                    loose                                         loose                                              loose60% B 80   gray  gray  gray    gray beige                                    beige                                         medium                                              brown                                         brown40% SIPERNAT 22      loose loose loose   loose                               loose                                    loose                                         loose                                              loose66.7% B 80 gray  gray  light brown                          medium                               dark dark dark black                          brown                               brown                                    brown                                         brown33.3% SIPERNAT 22      loose loose loose   loose                               loose                                    lightly                                         adhered                                              adhered                                    adhered                                         together                                              together                                    together70% B 80   gray  gray  light brown                          medium                               dark dark dark black                          brown                               brown                                    brown                                         brown30% SIPERNAT 22      loose loose loose   loose                               loose                                    lightly                                         adhered                                              adhered                                    adhered                                         together                                              adhered                                    together80% B 80   gray  brown dark brown                          dark black                                    black                                         black                                              black                          brown20% SIPERNAT 22      loose loose lightly adhered                          adhered                               adhered                                    adhered                                         adhered                                              adhered                  together                          together                               together                                    together                                         together                                              together60% B 80   gray  gray  light brown                          brown                               light                                    brown                                         brown                                              dark                               brown          brown40% FK 320 loose loose loose   loose                               lightly                                    lightly                                         adhered                                              adhered                               adhered                                    adhered                                         together                                              together                               together                                    together66.7% B 80 gray-brown            gray-brown                  medium brown                          brown                               brown                                    dark dark black                                    brown                                         brown33.3% FK 320 DS      loose loose loose   loose                               lightly                                    adhered                                         adhered                                              adhered                               adhered                                    together                                         together                                              together                               together__________________________________________________________________________ 
    
     The silica FK 320 used is a precipitated silica with the following physical chemical properties: 
     
         ______________________________________Apperance       loose, white powderX-ray structure amorphousSurface area    170 m.sup.2 /g (according to BET)Average size of theprimary particles           18 nanometerSpecific gravity           2.05 g/mlDegree of purity           SiO.sub.2.sup.(6) 98%           Na.sub.2 O.sup.(6) 1%           Al.sub.2 O.sub.3.sup.(6) 0.2%           SO.sub.3.sup.(6) 0.8Loss on drying.sup.(1)           6%Loss on ignition.sup.(2)(3)           5%pH.sup.(4)      6.3%Solubility      practically insoluble in waterCharacteristics precipitated silicaTamped density.sup.(5)           200 g/lSieve residue accordingto Mocker (DIN 53 580)           0.2%______________________________________ .sup.(1) DIN 53 198, Method A .sup.(2) Based on the material dried for 2 hours at 105° C. DIN 55 921 .sup.(3) DIN 52 911 .sup.(4) DIN 53 200 .sup.(5) DIN 53 194 .sup.(6) Based on the material ignited for 2 hours at 1000° C. 
    
     A silica 320 DS is a precipitated and steam jet ground silica having the following physical chemical properties: 
     
         ______________________________________Appearance      loose, white powderX-ray structure amorphousSurface area    170 m.sup.2 /g (according to BET)Average size of theprimary particles           18 nanometerSpecific gravity           2.05 g/mlDegree of purity           SiO.sub.2.sup.(6) 98%           Na.sub.2 O.sup.(6) 1%           Al.sub.2 O.sub.3.sup.(6) 0.2%           SO.sub.2.sup.(6) 0.8Loss on drying.sup.(1)           6%Loss on ignition.sup.(2)(3)           5%pH.sup.(4)      6.3%Solubility      practically insoluble in waterCharacteristics precipitated silica having a           high fineness of grindingTamped density.sup.(5)           70 g/lSieve residue accordingto Mocker (DIN 53 580)           0%______________________________________ .sup.(1) DIN 53 198, Method A .sup.(2) Based on the material dried for 2 hours at 105° C. .sup.(3) DIN 52 911 .sup.(4) DIN 53 200 .sup.(5) DIN 53 194 .sup.(6) Based on the material calcined at 1000° C. for 2 hours 
    
     The silica Sipernat 22 is a precipitated and spray dried silica having the following physical-chemical properties: 
     
         ______________________________________Surface area according to BET                 m.sup.2 /g                           190Average size of the primary particles                 nanometer 18Average size of the secondary particles                 micrometer                           80Tamped density (DIN 53 194)                 g/l       220Loss on drying (DIN 55 921)(2 hours at 105° C.)                 %         6Loss on ignition.sup.(1) (DIN 55 921)(2 hours at 1000° C.)                 %         5pH (DIN 53 200)                 6.3SiO.sub.2 (DIN 55 921)                 %         98Al.sub.2 O.sub.3      %         0.2Fe.sub.2 O.sub.3      %         0.03Na.sub.2 O            %         1So.sub.3              %         0.8Sieve residue according to Mocker(DIN 53 580)          %         0.5Oil number (according to DIN 53 199)                 g/100 g______________________________________ .sup.(1) Based on the material dried for 2 hours at 105° C. .sup.(2) In water: acetone or methanol 1:1 .sup.(3) Based on the material ignited for 2 hours at 1000° C. .sup.(4) Contains about 2% chemically bound carbon 
    
     USE OF THE POWDERY BITUMEN CONCENTRATE IN ASPHALT 
     In connection therewith there are concerned the following materials and combinations of materials: 
     Sipernat 22 
     B 80 to Sipernat 22 (50/50), powder 
     Natural asphalt-Trinidad Epure, non-comminuted 
     The additives were added in the laboratory to the mixtures of an asphalt concrete 0/11 mm suited for use in the classified road construction. In this connection in consideration of the amounts of crushed rock and binders contained in the additives the remaining composition of the mixtures are the same. 
     As binder for a comparison mixture and the mixture with additives road construction bitumen B 80 there is provided for a second comparison mixture road construction bitumen B 65. 
     The following tests were undertaken: 
     1. Production of specimens according to Marshall from the various asphalt mixtures. 
     2. Determination of space density, hollow space content, as well as stability and flow value according to Marshall on the specimens according to 1. 
     3. Carrying out creep tests on every three specimens produced according to 1. 
     INVESTIGATIONS AND INVESTIGATION RESULTS 
     Composition and Production of the Specimens 
     There were used for the mineral mixture for the production of an asphaltic concrete 0/11 mm according to TV bit 3/72 full of chips of basalt rich chips, basalt rich broken sand, a natural sand and a commercial limestone powder. The mineral materials with the exception of the limestone powder were sieved in particle classes and the mineral mixtures again combined according to a provided recipe. 
     Portion above 2.0 mm: basalt rich chips 2/5, 5/8 and 8/11 
     Sand 0.09/2.0 mm: basalt rich broken sand and natural sand (in the ratio 3:1) 
     Filler 0/0.09 mm: limestone powder, basalt true filler+additive 
     Therewith for all mixtures there was reached the following particle size distribution of the mineral mixture: 
     
         ______________________________________Sieve Passage:______________________________________0.09 0.25    0.71   2.0   5.0  8.0   11.2  mm8.6  15.0    25.0   40.0  67.0 84.0  100.0 weight %______________________________________ 
    
     The binder content of all mixtures was 5.9 weight %. 
     Table 3 gives a summary of the composition of the mixtures. 
     Mixing Process and Specimen Production 
     Asphalt mixtures were mixed in batches of 6,300 grams or 4,000 grams in the laboratory mixture while maintaining a homegeneous discharge. 
     The powdery additives were brought into the hot mixture according to the proportion of bitumen but before the limestone powder. 
     The corresponding amount of Trinidad-Epure was melted and added in advance to the bitumen portion. 
     No peculiarities were observed in the asphalt mixtures. In all cases there resulted a homogeneously encased, normal appearing mixed goods. 
     There were produced from each mixture variant 5+3=8 specimens according to Marshall. 
     
                                           TABLE 3__________________________________________________________________________                      BinderAdditive                   From            Amount    additive                           Original                                Total            (parts by                 Type (parts by                           (parts by                                (parts byMixtureType of Additive            weight)                 (original)                      weight)                           weight)                                weight %)__________________________________________________________________________1      --        --   B 65 --   6.27 5.92      --        --   B 80 --   6.27 5.93    SIPERNAT 22 0.5  B 80 --   6.27 5.98    TRINIDAD-EPURE            2.0  B 80 1.1  5.17 5.99    SIPERNAT with B 80            2.0  B 80 1.0  5.27 5.9(Powder 50/50)__________________________________________________________________________Mineral From  From         True Additive       Granulation              Limestone                    Filler                          Sand  Chips (parts by       (parts by              (parts by                    (parts by                          (parts by                                (parts byMixture weight)       weight)              weight)                    weight)                          weight)                                weight)__________________________________________________________________________1     --    100    6.0   2.6   31.4  602     --    100    6.0   2.6   31.4  603     0.5   99.5   5.5   2.6   31.4  608     0.9   99.1   5.1   2.6   31.4  609     1.0   99.0   5.0   2.6   31.4  60__________________________________________________________________________ 
    
     Of the eight specimens three were used for determination of stability and flow value, and three for the creep test. 
     Space density and hollow space content were ascertained on all specimens. 
     The results are collected in Table 4. 
     There were carried out at 3 specimens of each mixture creep tests with static load. Thereby the bases of the specimens were evened up through a compensating layer. 
     In the test there was applied to the specimen at a testing temperature of 40° C. a uniform surface load. 
     The uniaxial compressive strength was 0.1 MN/m 2 . The formation of the uniaxial strength state was promoted by arrangement of a sliding layer. The resulting compressions Σ=Δh/h×1,000 in .permill. were plotted in the double logarithmic scale, so that the function of the tensions could be recognized from the time after 1 to 5 hours of an asymptotic end value. 
     From the transition t→∞ there can be derived a final tension and a strain modulus S mix  as material index of the logarithm. 
     The final tension and the strain modulus are compiled in Table 5. 
     
                                           TABLE 4__________________________________________________________________________Test Results on Specimens According to Marshall          Hollow Space          Content               In theSpace     Raw  In the               Mineral                     Degree of  FlowDensity     Density          Asphalt               Framework                     Packing                           Stability                                ValueMixtureg/cm.sup.3     g/cm.sup.3          Vol. %               Vol. %                     %     kN   mm__________________________________________________________________________1    2,569     2,635          2.50 17.3  85.5  7.6  6.02    2,570     2,635          2.47 17.3  85.7  6.9  5.33    2,561     2,635          2.81 17.6  84.0  7.5  5.98    2,561     2,635          2.81 17.6  84.0  7.0  6.09    2,556     2,635          3.00 17.7  83.1  7.7  5.9__________________________________________________________________________ 
    
     
                       TABLE 5______________________________________Results of Creep Tests                  Strain Modulus Mixture     .permill.Final Tension                   ##STR1##______________________________________1           5.8        17.22           6.2        16.23           5.6        17.98           6.1        16.59           5.6        17.8______________________________________ 
    
     EVALUATION OF THE TEST RESULTS 
     Appearance Evaluation of the Asphalt Mixtures 
     The mixtures with additives (3, 8, 9) do not differ in behavior and appearance with the mixes without additives (1, 2) 
     Peculiarities were not established compared to normally mixed goods. 
     Properties of Specimens 
     The specimens produced under the same compression conditions at 135° C. show differences in the space densities between the zero mixtures on the one hand and the mixtures with additives on the other. Therewith they give an indication of the relations in mixed goods structures. 
     In the laboratory tests the compression resistance of the mixed goods characterized by the hollow space proportion increased at 135° C. both with addition of SIPERNAT 22 and also Trinidad-Epure, i.e., both additives cause stiffening. 
     The greatest effect was produced by the addition of Sipernat/bitumen powder (Mixture 9), in which case it should be observed that the Sipernat portion in the total mixture is once again increased compared to Mixture 3. An interesting comparison is offered by Mixture 9 and Mixture 8 (Trinidad-Epure), since in both cases there are added mineral material/binder combinations with quantitatively about the same ratios. Based on the results it can be established that the stiffening produced by Trinidad-Epure is exceeded by the synthetically produced products. 
     Creep Tests 
     Creep tests at 40° C. give information in regard to the resistance to deformation of the mixed goods. They refer in this connection to the ratios in service with elevated outside temperatures. 
     The results of the laboratory tests clearly show increases of the decisive strain modulus (Deformation Modulus) of the mixtures with SIPERNAT 22. (Mixtures 3 and 9) compared to the comparison mixture with B 80 (Mixture 2), with simultaneous reduction of the corresponding final tensions. 
     The results of the creep tests at 40° C. show that an equal increase of the resistance to deformation of the mixture with Trinidad-Epure. 
     The entire disclosure of German priority application No. P 29 33 339.9-44 is hereby incorporated by reference. 
     As used in the claims the term road is intended to include streets, bike paths, sidewalks, and other surfaces for vehicle or pedestrian use.