Abstract:
An automated apparatus for preparing material samples includes a rotatable drum support assembly, a drum rotatably contacting the drum support assembly, a fan, and a powered drive mechanism. The drum includes a hollow main section and first and second hollow end sections attached to the main section. The first hollow end section includes a first end wall tapering to a first outer aperture. The second hollow end section includes a second end wall tapering to a second outer aperture. The fan is mounted approximate to the first outer aperture for establishing forced air flow through the drum toward the second outer aperture. The drive mechanism rotatably communicates with the drum support assembly for rotating the drum. The apparatus is useful for preparing samples such as paving materials for test such as the determination of specific gravity and absorption.

Description:
TECHNICAL FIELD 
   The present invention generally relates to material sample preparation. More particularly, the present invention relates to the preparation of samples of paving materials, including bituminous materials and aggregates, for subsequent measurement of properties such as specific gravity. 
   BACKGROUND ART 
   Samples of solid materials, and particularly road and paving materials such as bituminous mixtures and aggregates, are commonly subjected to standardized tests to determine certain properties such as specific gravity. For example, ASTM International has published the following standards, the contents of which are incorporated herein: ASTM D 2041—95, entitled “Standard Test Method for Theoretical Maximum Specific Gravity and Density of Bituminous Paving Mixtures” (also known and referred to hereinafter as “the Rice test”); and ASTM C 128—97, entitled “Standard Test Method for Specific Gravity and Absorption of Fine Aggregate” (hereinafter “the fine aggregate test”). Results from such tests are used both for the purpose of design and quality control. 
   The Rice test is employed to determine the theoretical maximum specific gravity and density of uncompacted bituminous paving mixtures at 25° C. Prior to subjecting the sample paving material to the Rice test, the sample must be prepared so as to be uncompacted, meaning that the sample must be brought to a loose, cool state. The conventional preparation method requires that a technician manually separate the particles of the sample so that the particles of the fine aggregate portion are no larger than 6.3 mm (¼ inch) each. This preparation process is labor intensive and time consuming, as it involves heating a sample to 100+/−° C. in an oven, and stirring the heated sample in a flat pan for twenty minutes or more while the pan is positioned in front of a fan. 
   The fine aggregate test is employed to determine bulk specific gravity (for example, the percentage of voids in a mineral aggregate) and absorption (for example, the amount of asphalt binder absorbed by the aggregate) on the basis of the weight of a sample aggregate that has reached a saturated-surface-dry (SSD) condition after being immersed in water for twenty-four hours. Thus, preparation of an aggregate sample for the fine aggregate test requires drying the sample to the SSD state. The conventional dry back method for fine aggregate, as described in ASTM C128-97, is performed manually or with the use of a mechanical tumbler, and the sample is frequently tested for SSD condition using one of three methods described therein. Typically, this process takes at least two hours and, accordingly, like the preparation required for the Rice test, is labor intensive and time consuming. 
   It would therefore be advantageous to provide an automated apparatus adapted to perform a sample preparation process, whether in preparation for the Rice test, the fine aggregate test, other tests, or for mixing. Such an automated apparatus would significantly reduce the expenditure of time and labor conventionally involved in material sample preparation, thereby allowing the technician to perform other tasks while the sample is being prepared by the apparatus. In addition, particularly in the case of fine aggregates, a need is recognized for developing more accurate and reproducible test methods. See, e.g., Kandhal et al., “Measuring Bulk-Specific Gravity of Fine Aggregates,” Transportation Research Record 1721, Paper No. 00-1230, p. 81 (2000). The need for improved accuracy and reproducibility can be addressed by the use of an automated apparatus, since the automation would reduce the degree of subjectivity and manual effort involved in the sample preparation. 
   Kandhal et al. have proposed an automated technique for preparing a fine aggregate sample for the testing of bulk specific gravity. Their technique involves placing a wet sample of fine aggregate in a rotating drum and subjecting the sample to a steady flow of warm air. The temperature gradient of the incoming and outgoing air and the relative humidity of the outgoing air are monitored to establish the SSD condition. The drum was equipped with screens to confine the sample in the drum. However, it has been found that a drum such as that proposed by Kandhal et al. allows an unacceptable amount of sample to be lost through the inlet and outlet of the drum. This material loss is a consequence of the air flowing through the drum carrying away sample particles as the sample is being dried and/or cooled, as well as a result of the rotation of the drum and comcomitant agitation and movement of the sample. It would therefore also be advantageous to provide an automated apparatus adapted to perform a sample preparation process while preventing or at least reducing the amount of material loss unrelated to drying of the sample. 
   DISCLOSURE OF THE INVENTION 
   The present invention provides an automated apparatus and related method for the preparation of samples such as bituminous materials and fine aggregates, wherein the apparatus comprises a rotatable drum structured so as to prevent or at least reduce the amount of material loss from the drum. 
   According to one embodiment, an automated apparatus for preparing material samples comprises a rotatable drum support assembly, a drum rotatably contacting the drum support assembly, a fan, and a powered drive mechanism. The drum comprises a hollow main section having first and second open ends, and first and second hollow end sections attached to the main section. The first hollow end section comprises a first inner aperture communicating with the first open end, and a first outer aperture, and a first end wall tapering from the first inner aperture to the first outer aperture. The second hollow end section comprises a second inner aperture communicating with the second open end, a second outer aperture, and a second end wall tapering from the second inner aperture to the second outer aperture. The fan is mounted proximate to the first outer aperture, and establishes forced air flow through the drum towards the second outer aperture. The drive mechanism rotatably communicates with the drum support assembly for rotating the drum. 
   According to another embodiment, an automated apparatus for preparing material samples comprises first and second axles spaced in generally parallel relation, a drum rotatably supported by the first and second axles, a fan, and a motor. The drum comprises a hollow main section having first and second open ends, a hollow first frustoconical section, and a hollow second frustoconical section. The first frustoconical section is attached to the first open end and comprises a first outer aperture. The second frustoconical section is attached to the second open end and comprises a second outer aperture. The fan is mounted proximate to the first outer aperture. Upon activation, the fan establishes a forced air flow through the drum toward the second outer aperture. The motor communicates with the first axle to drive the rotation of the drum. 
   According to a method for preparing a material sample, the sample is placed in a drum comprising a hollow main section, a hollow first tapered section, and a hollow second tapered section. The main section has first and second open ends. The first tapered section is attached to the first open end and tapers to a first outer aperture. The second tapered section is attached to the second open end and tapers to a second outer aperture. The drum is rotatably supported on a support assembly. After the sample has been placed in the drum, the drum is rotated. A flow of air is conducted through the drum, whereby heat transfer occurs between the air and the sample. A property of the sample is monitored. When the property reaches a desired value, the motor is de-activated to cease rotation of the drum. The sample can then be removed from the drum and subjected to a desired test such as the determination of the specific gravity of the sample, the absorption of the sample, or any other suitable test. 
   In another method for preparing a material sample, a heated sample is placed in a drum structured according to embodiments disclosed herein and rotatably supported on a support assembly. A motor connected to the support assembly is activated to rotate the drum. The sample is cooled by activating a fan to establish forced air flow through the drum. A temperature of the sample is monitored. When the sample temperature reaches a desired sample temperature, the motor is de-activated to cease rotation of the drum. According to one aspect of this method, the sample temperature is monitored by monitoring a temperature of the drum. 
   In yet another method for preparing a material sample, a wet sample is placed in a drum structured according to embodiments disclosed herein and rotatably supported on a support assembly. A motor connected to the support assembly is activated to rotate the drum. The sample is dried by activating a fan to establish forced air flow through the drum. The sample is monitored to determine whether the sample has reached a saturated-surface-dry state. When it is determined that the sample has reached the saturated-surface-dry state, the motor is de-activated to cease rotation of the drum. According to one aspect of this method, the saturated-surface-dry state of the sample is determined by monitoring a mass of the sample, and the saturated-surface-dry state is defined when the rate of change in the sample mass has fallen below a prescribed level. 
   It is therefore an object of the present invention to provide an automated apparatus for preparing material samples that automates the sample preparation process. 
   It is another object of the present invention to provide a material sample preparation apparatus that includes a rotating drum in which a sample is tumbled and is capable of preventing substantial loss of material during rotation of the drum. 
   Some of the objects of the invention having been stated hereinabove, and which are addressed in whole or in part by the present invention, other objects will become evident as the description proceeds when taken in connection with the accompanying drawings as best described hereinbelow. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a sample preparation apparatus provided in accordance with the present invention; 
       FIG. 2  is an exploded view of a drum provided with the sample preparation apparatus; 
       FIG. 3  is a side elevation view of the sample preparation apparatus; 
       FIG. 4  is a front elevation view of the sample preparation apparatus; 
       FIG. 5  is a rear elevation view of the sample preparation apparatus; and 
       FIG. 6  is a perspective view of the sample preparation apparatus in which certain operative components are enclosed by cover members. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to  FIG. 1 , a sample preparation apparatus, generally designated SPA, is illustrated. Sample preparation apparatus SPA comprises a rotatable container such as a drum, generally designated D; a drum rotation assembly, generally designated DRA; an air moving device such as a fan F; and a framework such as a base plate B suitable for supporting drum D and preferably also drum rotation assembly DRA and fan F. As described in more detail hereinbelow, drum D is adapted for containing, agitating (i.e., stirring or tumbling), and drying a mass of a material sample and, in particular, a solid sample or aggregate sample that is heatable. Non-limiting examples of material samples suitable for processing in drum include bituminous and/or aggregate materials such as asphalt, bituminous concrete, sand, and other fine mineral aggregates. Typically, such material samples contain internal and/or external voids capable of trapping or otherwise holding a liquid such as water. Drum rotation assembly DRA is adapted for supporting and rotating drum D about an axis of rotation A in an automated manner. Fan F is adapted for establishing a flow of fluid such as air through the interior enclosed by drum D so that a material sample contained in drum D is cooled and/or dried as desired. 
   Referring to  FIG. 2 , drum D comprises a hollow main section  12  with first and second opposing open ends  14 A and  14 B, respectively, and first and second hollow end sections  17  and  19  serving as end caps for main section  12 . To facilitate agitation and/or mixing of a material sample loaded into drum D while drum D is rotating, agitation elements  22 A and  22 B such as fins or baffles are mounted within main section  12  to interact with the material sample. Preferably, agitation elements  22 A and  22 B are mounted to an inside wall surface  12 A of drum D and extend substantially radially inwardly toward axis of rotation A. Two agitation elements  22 A and  22 B mounted 180 degrees apart have been found sufficient in the practice of the invention as specifically illustrated in  FIG. 2 , though more may be used. Main section  12  is preferably cylindrical as illustrated, but could be rectilinear or otherwise polygonal. 
   The respective walls of first and second hollow end sections  17  and  19  of drum D taper from respective first and second inner apertures  17 A and  19 A to respective, smaller-diameter first and second outer apertures  17 B and  19 B. Preferably, first and second end sections  17  and  19  are frustoconical and main section  12  is cylindrical. In the case where main section  12  of drum D is not cylindrical, first and second end sections  17  and  19  could be predominantly pyramidal in shape, or could have any other shape characterized by a tapering profile. First inner aperture  17 A of first end section  17  fits onto first open end  14 A of main section  14 , and second inner aperture  19 A of second end section  19  fits onto second open end  14 B of main section  14 . 
   At least one of end sections  17  and  19  is removably attached to main section  12 , although both first and second end sections  17  and  19  could be removably attachable. In the illustrated embodiment, first end section  17  is removably attached to main section  12  by providing a suitable quickly releasable fastener system, such as one or more interlocking buckle-type fastener components  26 A and  26 B mounted on the respective peripheries of first end section  17  and main section  12  at or near their corresponding open end regions. The ability to detach first end section  17  from main section  12  facilitates access into the interior of drum D for cleaning drum D. Second end section  19  is either removably or permanently attached to main section  12  by means of one or more fasteners  28  such as rivets, screws, or the like. First and second outer apertures  17 B and  19 B can each be provided with a screen  31 , such as screen  31  shown in  FIG. 5 , but such screens are not needed for retaining a material sample within drum D as that function is accomplished by the tapered profile of first and second end sections  17  and  19 . 
   In one specific, exemplary embodiment of drum D, the respective outside diameters of main section  12 , first inner aperture of  17 A first end section  17 , and second inner aperture  19 A of second end section  19  are each approximately 12 inches. The axial length of drum D from first outer aperture  17 B to second outer aperture  19 B is approximately 24 inches. The respective diameters of first and second outer apertures  17 B and  19 B are each approximately 4.2 inches. These dimensions enable the overall footprint of sample preparation apparatus SPA to be minimized and thus enable sample preparation apparatus SPA to be placed on a lab bench. 
   Referring back to  FIG. 1  as well as  FIGS. 3-5 , drum rotation assembly DRA is suitable for supporting and driving drum D for rotation about axis of rotation A that preferably is oriented along or substantially along the horizontal. In the illustrated embodiment, drum rotation assembly DRA comprises first and second axles  41  and  43 . As shown in  FIG. 1 , first axle  41  is rotatably mounted at its ends to a pair of first and second bearing blocks  45  and  47 , which are in turn supported by base plate B. As shown in  FIG. 3 , second axle  43  likewise is rotatably mounted at its ends to a pair of third and fourth bearing blocks  51  and  53  supported by base plate B. Suitable sleeve bearings  55 ,  57 ,  61  and  63  such as bronze sleeve bearings are interposed between each bearing block  45 ,  47 ,  51  and  53  and corresponding axle  41  and  43 . The respective pairs of bearing blocks  45 ,  47 ,  51 , and  53  are situated on base plate B such that first and second axles  41  and  43  are oriented parallel or substantially parallel to base plate B and offset from axis of rotation A. In this manner, drum D is fully supported on first and second axles  41  and  43  so as to rotate about axis of rotation A in a stable and uniform manner. To improve the stability of drum D rotation and frictional contact between drum D and first and second axles  41  and  43 , a pair of first and second rollers  66  and  68  are coaxially mounted to first axle  41  and a pair of third and fourth rollers  72  and  74  are coaxially mounted to second axle  43 . Preferably, as shown in  FIGS. 1  and  3 , roller pairs  66 ,  68  and  72 ,  74  are located such that mechanical communication between drum D and first and second axles  41  and  43  actually occurs between first end section  17  and rollers  66  and  72 , and between second end section  19  and rollers  68  and  74 . As an example, each roller  66 ,  68 ,  72  and  74  can take the form of a 4-inch nominal-diameter rubber wheel. 
   With continuing reference to FIGS.  1  and  3 - 5 , at least one of first and second axles  41  and  43  is driven by a source of rotational power so as to drive the rotation of drum D in an automated fashion. In the illustrated embodiment, second axle  43  is coupled to a power source in the form of a motor M. Motor M can be a conventional electric motor operative at 12 VDC, 24VDC, or 120 VAC. The rotating output shaft (not shown) of motor M can be directly coupled to second axle  43  or, as specifically illustrated, can be disposed offset from second axle  43  and coupled through a suitable transmission assembly such as a drive belt  77  wound around pulleys  79 A and  79 B. Motor M is mounted to a motor mounting bracket or block  81 , which in turn is supported by base plate B. 
   As indicated hereinabove, fan F is adapted for establishing a flow of fluid such as air through the interior enclosed by drum D. In the exemplary sample preparation methods described herein, the air moved by fan F is at a room or ambient temperature. However, as can be appreciated by persons skilled in the art, fan F could be incorporated into a closed fluid system in which cooled or heated air is circulated through drum D. Although in the illustrated example fan F is an axial-flow type unit in which the blades of fan F rotate about an axis coincident or substantially coincident with axis of rotation A, it can be appreciated that fan F could be a blower-type unit that includes a scroll-shaped or involute fan housing. Fan F can be configured to either blow or pull air through drum D. Referring to  FIGS. 1 and 3 , fan F preferably blows air through drum D, such that the direction of air flow is from second outer aperture  19 B of second end section  19 , through the interior of drum D, and out from first outer aperture  17 B of first end section  17 . Fan F can be a conventional unit operating at 12 VDC, 24VDC, or 120 VAC. Fan F is enclosed in a fan shroud  83  in a conventional manner. Fan F is elevated from base plate B so as to be aligned or substantially aligned with second outer aperture  19 B by mounting fan F or its shroud  83  to a fan mounting bracket  85 , which is in turn supported by base plate B. Base plate B can be constructed from any material suitable for supporting drum D, drum rotation assembly DRA, and fan F, with one example being aluminum. As shown in  FIG. 6 , cover members  87 A and  87 B can be provided to enclose motor M, fan F, and associated components and wiring. In addition, a heating coil HC or other suitable heating element could be mounted within lower member  87 B to heat the air supplied by fan F if desired. 
   In operation, sample preparation apparatus SPA can be used to as part of any sample preparation process that requires mixing, tumbling and/or drying, and which could benefit from the savings in time and labor associated with automating such mixing, tumbling and drying procedures. Accordingly, referring generally to  FIGS. 1-6 , the invention provides a general method of sample preparation involving the following steps. Sample preparation apparatus SPA is provided preferably in accordance with the embodiment described above and illustrated in  FIGS. 1-6 . First end section  17  is detached from main section  12  of drum D, a material sample is loaded into drum D, and first end section  17  is then re-attached to main section  12 . Motor M is then activated to initiate rotation of drum D, thereby agitating the mass of sample loaded therein. Fan F is activated to establish air flow through drum D. Depending on the initial temperature of the sample relative to that of the air flowing through drum D, the air flow causes heat energy to be transferred either to or from the sample. While drum D is rotating and air is flowing through drum D, a property of the sample such as temperature or mass can be monitored. The monitoring of temperature can be done directly by inserting a suitable temperature probe such as a thermocouple  90  ( FIG. 6 ) into or onto the sample, or by providing one or more readily available temperature strips  91  on the outer wall surface of drum D as shown in  FIGS. 1 ,  3  and  6 . While temperature strip  91  indicates the temperature of the wall of drum D, this can be correlated to the temperature of the sample. Alternatively, if the tumbling and/or drying process is allowed to continue for a sufficient period of time, the temperature indicated by temperature strip  91  can be assumed to correspond to the temperature of the sample. Once a target temperature has been reached, fan F and motor M are de-activated, first end section  17  detached from main section  12  of drum D, and the prepared sample then removed from drum D. 
   In the practice of any sample preparation method of the invention, the tapering profile of first and second end sections  17  and  19  of drum D is an advantageous feature. As drum D is rotated about axis of rotation A, the mass of sample loaded in drum D tends to spread out toward first and second outer apertures  17 B and  19 B. The spreading sample will encounter the inclined inside walls of the tapered regions of first and second end sections  17  and  19  and be rolled back to a centered position along main section  12 . In this manner, the sample is prevented from being discharged from drum D through first and second outer apertures  17 B and  19 B. 
   In one specific method of the invention, a bituminous paving material sample such as a mass of asphalt is processed by sample preparation apparatus SPA to produce a loose, cool sample in preparation for a laboratory test such as the above-described ASTM D2041 test (Rice test) or other test for specific gravity or density. The mass (for example, up to 6000 g) of asphalt or other appropriate material sample is heated to 100+/−5° C. in a suitable oven. In accordance with the general method described above, the heated sample is then loaded into drum D and rotation of drum D is initiated by activating motor M. In one embodiment, drum D rotates at 40+/−5 rpm. Air flow through drum D is then established by activating fan F. Preferably, drum D is rotated for approximately one minute prior to activating fan F. The operation of fan F is delayed in this manner because, in many cases, contact of the sample with the initially cold drum D will result in rapid conductive cooling during this initial phase of the procedure. Moreover, too much cooling during the initial phase could lead to undesirable clumping of the sample. The temperature of drum D is monitored as also described above. The target temperature is 25° C. or ambient room temperature, whichever is greater. When the target temperature is reached, preparation of the sample is complete and the sample can be removed for subsequent testing such as the Rice test, in which the specific gravity of the cooled, loose sample is determined. Sample preparation apparatus SPA provided in accordance with at least one embodiment of the invention is capable of cooling up to 6000 g of bituminous material without a material loss of more than 0.015%. 
   In another specific method of the invention, a wet sample aggregate material such as sand, gravel, stone or other mineral is processed by sample preparation apparatus SPA to bring the aggregate sample to its SSD state in preparation for further testing, such as the above-described aggregate tests for determining specific gravity and absorption. The aggregate sample is initially wetted such as by immersion in water for twenty-four hours. In accordance with the general method described above, the wet sample is then loaded into drum D and rotation of drum D is initiated by activating motor M. In one embodiment, drum D rotates at 40+/−5 rpm as previously described. Once drum D has rotated for about one minute, air flow through drum D is established by activating fan F. At appropriate intervals (for example, every fifteen minutes), drum D and the sample contained therein are weighed. The weighing can be accomplished by removing drum D from sample preparation apparatus SPA and placing drum D on a suitable scale. Alternatively, a weight scale WS could be integrated with base plate B or other supporting component of sample preparation apparatus SPA, as schematically shown in FIG.  6 . In either case, the weight of all non-sample components is subtracted from the weight readings in order to determine the weight of the sample. The steps of rotating drum D, operating fan F, and weighing the sample are repeated until the loss of sample mass per time interval is less than a specific level (0.05% for a 15 minute interval), at which point the sample is considered to be at the SSD state. As an alternative to weighing the sample, the humidity of the air exhausting from drum D (i.e., the output from first outer aperture  17 B of first end section  17 ) can be monitored by conventional means, in which case the SSD condition could be defined at the occurrence of an inflection point in a recorded humidity vs. time plot. 
   As compared to the conventional testing methods described hereinabove, the methods of the present invention can result in significant time savings. 
   It is therefore seen from the foregoing that an apparatus and method are provided for preparing material samples such as paving materials in an automated manner so as to render such samples suitable for commonly performed tests in which properties such as specific gravity, density, and/or absorption are determined. 
   It will be understood that various details of the invention may be changed without departing from the scope of the invention. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation, as the invention is defined by the claims as set forth hereinafter.