Abstract:
An apparatus for the drying of aggregate and aggregate-binder mixtures includes a housing containing a fan within a housing that pulls air through various materials held in a drying sieve, or multiple drying sieves, and then exhausts the air to the ambient environment. The apparatus is particularly useful in determining the saturated surface dry state of materials which is an important factor in various testing procedures. The apparatus may include activation means, such as switches and controls, and may incorporate weight sensors to aid in determining the drying state of the material. Various input, output, memory, and display functions are provided to allow calculations and display of observed and calculated indicia.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates generally to paving materials, and in particular, to an apparatus for determining liquid absorption by aggregate or binder-aggregate mixtures. The method and apparatus aids in determining the saturated surface dry state of such mixtures as an aid in designing effective compositions.  
         BACKGROUND OF THE INVENTION  
         [0002]    Most paved surfaces, including roadways, consist of a plurality of materials and layers. Typically, these mixtures include a binder such as cement or asphalt-cement, and a plurality of different aggregates composed of rocks, stones, or other materials. These paving mixtures are described as “compacted mixtures.” 
           [0003]    The composition of these compacted mixtures is an important factor in the service life of the construction project. In order to predict a certain minimum service life, most paving projects require conformance to predetermined minimum build specifications or standards. Among these standards are requirements relating to the capacity of the aggregate or binder-aggregate material to absorb fluid. To properly design a paving mix, by way of example and not limitation, asphalt paving mixes, the proper amount of binder must be added to a given amount of aggregate in order to maintain a mixture which will result in a strong and durable paved surface. If there is too much binder, that is for example, too much asphalt-cement in an asphalt-aggregate paving mix, the paved surface will be soft and excessive wear and rutting will result. If there is not enough binder in the composition, the paved surface will be brittle and will crumble or break apart, particularly under loading stresses associated with vehicular traffic.  
           [0004]    A particularly difficult problem in designing appropriate mixtures lies in the fact that aggregates, such as rock and stone, are not hydraulically neutral agents. That is, they have the ability to both absorb fluid, such as binder and water, into their interior matrix and to adsorb fluid onto their surfaces. When binder, such as asphalt-cement, is absorbed internally into a porous aggregate, that absorbed binder does not contribute to the effective volume of the asphalt mix. In order to account for this absorbed binder, additional binder must be added to the mix. The need to add such compensatory binder can lead to incorrect formulation of the mix. The measurement of the binder absorbed by the aggregate which does not contribute to the volume of the asphalt mix is the percent absorption (PA), by weight, of water absorbed into the aggregate relative to the weigh of the aggregate itself.  
           [0005]    In general, the procedure for testing aggregate for PA involves saturating the internal matrix of the aggregate, and then drying the aggregate to determine the amount of fluid that has been internally absorbed. As a first step, a sample of dry aggregate is prepared to a condition where the internal voids are saturated by water, but the external surface of the aggregate is dry. This condition is known as the saturated surface dry (SSD) state. The sample is then dried completely in an oven, and weighed again in the dry state. The difference between the SSD and dry weights, divided by the dry weight, converted to a percentage, is the PA.  
           [0006]    Additionally, asphalt-aggregate mixes are commonly tested for specific gravity and density using what is usually denominated the “Rice test.” Such a test also requires surface drying of the sample before testing.  
           [0007]    Besides the necessity of thoroughly saturating the tested material to establish a baseline for fluid absorption, an obvious difficulty in this process is drying the surface of the material after saturation to the point where the surface of the material is dry, but where fluid is not extracted from the internal matrix.  
           [0008]    One method of preparing a sample of material to the SSD condition is what is known as the “towel dry” method. In this method, totally saturated material, generally aggregate, is lightly hand dried with paper towels to just the point where the aggregate surface is dry. This technique is best used for larger aggregate such as that for concrete. Obviously, it suffers from the necessity for hand labor and the crude estimation of surface drying that must be made.  
           [0009]    Another method is a “slump test,” used for both concrete and asphalt aggregates, where a cone of saturated aggregate is allowed to slump following removal of a cone shaped form. Saturated aggregate will tend to retain a cone shape, while surface dried aggregate will tend to slump. This method suffers from observational error induced by the subjective judgment of slump made by technicians, and for differences in various aggregates&#39; tendency to slump based on factors other than surface moisture, such as angularity or fineness of the aggregate.  
           [0010]    There are constraints on the methods that maybe used for drying the aggregate surface, in order to prevent more than a negligible amount of internal fluid being driven off before the SSD weight can be calculated. Foremost among these is the avoidance of external heat in the drying, as such heat tends to drive fluid from the internal matrix to the surface of the aggregate. Additionally, heat is avoided during drying of asphalt-aggregate mixtures to avoid thermal effects on the asphalt binder.  
           [0011]    Determination of the SSD state of an asphalt-aggregate mixture is also critical in measuring the percentage of air voids in a compacted mixture, an important parameter for estimating wear effects and service life of a paving product.  
           [0012]    First the bulk specific gravity (G mb ) of a compacted asphalt mixture is determined. The procedure requires that the compacted mix be weighed in air, submerged, and in the SSD state, and is determined by the following equation:  
             G   mb   =A /( B−C ) 
           [0013]    Where:  
           [0014]    G mb =Bulk specific gravity of the collected specimen  
           [0015]    A=Oven dry mass (g)  
           [0016]    B=SSD mass (g)  
           [0017]    C=Submerged mass (g)  
           [0018]    The bulk specific gravity (G mb ) can then be employed in a standard test method to assess fluid absorption in asphalt-aggregate mixtures in ASTM 2041, known as “Theoretical Maximum Specific Gravity and Density of Bituminous Paving Mixtures Dry Back Process.” For the Rice test, a sample of the mixture is broken up into a voidless mass of particles less than 4.75 mm (0.25 in.) in size. The sample is placed in a calibrated container. The weight and volume of the voidless mix are then used to calculate the maximum specific gravity as shown in the following equation:  
             G   mm   =A /( A−C ) 
           [0019]    Where:  
           [0020]    G mm =Theoretical maximum specific gravity  
           [0021]    A=Mass of oven dry sample in air, (g)  
           [0022]    C=Mass of water displaced by sample at 25° C. (77° F.), (g)  
           [0023]    The bulk specific gravity of the collected specimen (G mb ) and the theoretical maximum specific gravity (G mm ) can then be used to calculate the air void content of the compacted material, according to the following equation:  
             V   a =( 1−(   G   mb   −G   mm ))×100 
           [0024]    Where:  
           [0025]    V a =Air voids in the compacted mix, percent  
           [0026]    G mb =Bulk specific gravity of the compacted mix  
           [0027]    G mm =Theoretical maximum specific gravity of the mix  
           [0028]    The derivation of these measurements requires an efficient means of determining the saturated surface dry (SSD) state of an aggregate or mixture. Typically, an ad hoc drying method is used in laboratories, similar to the arrangement seen in FIG. 1, such as placing the saturated material in a drying sieve (S), and then blowing air from a household fan (F) through the aggregate. The sieve (S) must be propped up upon some auxiliary device (P), generally another sieve, to permit air to flow through the sieve (S) and exit between the sieve (S) and the work surface (WS). In this configuration an extension device (E), often yet another sieve, must be used to provide some space between the fan (F) and the contents of the sieve (S). To achieve a reasonable seal and volume of air blown through the material, the fan is often set atop the drying sieve, with a prop underneath the sieve to allow air circulation, a cumbersome solution that sometimes leads to spillage of the pan contents and the need to begin the test anew. The fan is removed periodically to stir the material to assist in drying, and at any point the fan may fall off of the sieve, in particular as the designs of many fans do not allow for a symmetrical weight distribution on the sieve, again as seen in FIG. 1. The weight of the material, subtracting the tare weight of the drying sieve, approximates the SSD weight when successive weighings of the material vary by no more than 0.05%.  
           [0029]    Because of the inefficiency of a fan perched atop the sieve, drying time is often excessive. For example, a typical 1500-2000 gram sample takes approximately two hours, or more, to dry to the level upon with testing for the approach of SSD weigh can begin. The need to periodically remove the fan, stir the sieve contents, and repeatedly weigh the sieve consumes an inordinate amount of technician time and increases the possibility of error.  
           [0030]    What the art has needed is a drying apparatus that is capable of air drying the surface of mixtures to be tested, without the application of external heat, that is simple, inexpensive, easy to use, and, most importantly, fast. The apparatus should be stable and resist inadvertent spilling of the material while drying. Lastly, the material must be easily and reliably removable from the drying apparatus so that successive weighings can be carried out. Optimally, in some embodiments the drying device may be equipped to automatically perform the weighing operations. The instant invention satisfies these needs.  
         SUMMARY OF INVENTION  
         [0031]    In its most general configuration, the present invention advances the state of the art with a variety of new capabilities and overcomes many of the shortcomings of prior devices in new and novel ways. In its most general sense, the present invention overcomes the shortcomings and limitations of the prior art in any of a number of generally effective configurations. The instant invention demonstrates such capabilities and overcomes many of the shortcomings of prior methods in new and novel ways, thereby reducing drying time by as much as 50% over conventional methods. In one of the simplest configurations, the apparatus incorporates a means for drying the surface of material in at least one drying sieve. The apparatus includes a housing, at least one discharge opening, a fan assembly within the housing, and an activation device to control the operation of the fan assembly. The top surface of the housing has at least one sieve opening to cooperate with at least one sieve to permit fluid communication between the housing interior space and the surrounding atmosphere. The at least one discharge opening is formed in the housing fluidly connecting the interior space of the housing with the surrounding atmosphere. The fan assembly is oriented to draw air from the surrounding atmosphere through the mixture in the at least one sieve and the at least one sieve opening and to discharge air through the at least one discharge opening to the surrounding atmosphere. Lastly, the activation device controls the operation of the fan assembly.  
           [0032]    The housing may be of virtually any shape than defines an interior space and may include at least one drain hole formed in the housing bottom surface to permit fluid that may accumulate in the housing to drain from the housing. The bottom surface may be formed to pitch toward the at least one drain hole. The housing may be constructed of virtually any material, including coated materials. The housing may be elevated from an external surface by at least one support device, which may be as simple as fixed legs, or may include more advanced adjustability and rotational features.  
           [0033]    The at least one discharge opening of the fan assembly may be located on any of the surfaces of the enclosure and may be fitted with various accessories, such as a safety screen, sound attenuator, or exhaust ductwork.  
           [0034]    In one particular embodiment, the fan assembly consists of a housed fan having a fan housing, a fan wheel, and a motor. Alternative embodiments may incorporate a plurality of fans. The fan assembly may be mounted in the housing in a number of ways, such as rigidly attached to the housing, or mounted to the housing with a vibration isolation system.  
           [0035]    The apparatus includes the activation device for controlling the operation of the fan assembly. Such activation device may be as simple as a plug style connector to cooperate with a common electrical connector, or may involve more complex controls, such as electronic controls or variable speed drive controls. Further embodiments may include a weight measuring system having at least one weight sensor and at least one display device. The at least one weight sensor may be formed as a sieve receiver adapted to receive and releasably hold the sieve over the sieve opening, or may include multiple sensors to cooperate with the sieve, or may be part of the at least one support device. Having the weight sensor as part of the at least one support device would be particularly useful in the single sieve opening embodiment, as the fan assembly would not have to be turned off during the reading since the at least one weight sensor will be measuring the weight of the entire apparatus rather than just the sieve and its contents.  
           [0036]    A control module may be adapted to receive data from the weight measuring system and at least one input device. The at least one input device may be any number of external devices such as a keyboard, or may include an input device built into the control module. The control module may then perform calculations, and display data on one at least one display device. The control module may also include memory to retain the input and output data. The calculations performed may include bulk specific gravity of the compacted specimen, the theoretical maximum specific gravity, and the air void percentage in the compacted mix, according to the equations seen above. Further, the control device may incorporate the function of the activation device in controlling the operation of the fan assembly. Additionally, the control module may be adapted to transmit data to at least one printer, either external to the apparatus or integral to the control module.  
           [0037]    These variations, modifications, alternatives, and alterations of the various preferred embodiments, arrangements, and configurations may be used alone or in combination with one another as will become more readily apparent to those with skill in the art with reference to the following detailed description of the preferred embodiments and the accompanying figures and drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0038]    Without limiting the scope of the present invention as claimed below and referring now to the drawings and figures:  
         [0039]    [0039]FIG. 1 shows a prior art setup for drying the surface of aggregate, in side elevation view, not to scale;  
         [0040]    [0040]FIG. 2 shows an embodiment of the apparatus for drying the surface of aggregate in elevated perspective view, not to scale;  
         [0041]    [0041]FIG. 3 shows the apparatus of FIG. 1 in top plan view, not to scale;  
         [0042]    [0042]FIG. 4 shows the apparatus of FIG. 1 in cross-sectional view taken along section line  4 - 4  in FIG. 3, not to scale;  
         [0043]    [0043]FIG. 5 shows a variation of the apparatus of FIG. 1 in cross-sectional view taken along section line  4 - 4  in FIG. 3, not to scale;  
         [0044]    [0044]FIG. 6 shows a variation of the apparatus of FIG. 1 in cross-sectional view taken along section line  4 - 4  in FIG. 3, not to scale;  
         [0045]    [0045]FIG. 7 shows an embodiment of the apparatus for drying the surface of aggregate in elevated perspective view, not to scale;  
         [0046]    [0046]FIG. 8 shows an embodiment of the apparatus for drying the surface of aggregate in elevated perspective view, not to scale; and  
         [0047]    [0047]FIG. 9 shows a variation of the apparatus of FIG. 1 in top plan view, not to scale. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0048]    The apparatus for drying the surface of aggregate of the instant invention enables a significant advance in the state of the art. The preferred embodiments of the apparatus accomplish this by new and novel arrangements of elements and methods that are configured in unique and novel ways and which demonstrate previously unavailable but preferred and desirable capabilities.  
         [0049]    The detailed description set forth below in connection with the drawings is intended merely as a description of the presently preferred embodiments of the invention, and is not intended to represent the only form in which the present invention may be constructed or utilized. The description sets forth the designs, functions, means, and methods of implementing the invention in connection with the illustrated embodiments. It is to be understood, however, that the same or equivalent functions and features may be accomplished by different embodiments that are also intended to be encompassed within the spirit and scope of the invention. In its simplest form the apparatus for drying the surface of aggregate in at least one sieve S incorporates a housing  100 , at least one discharge opening  170 , a fan assembly  200 , and an activation device  400  to control the operation of the fan assembly  200 , as seen in FIG. 2. The housing  100  has an interior space defined by at least one top surface  110 , at least one bottom surface  120 , and at least one side surface. The at least one top surface  110  is formed to have at least one sieve opening  180  of a size and configuration to cooperate with the at least one sieve S and to permit fluid communication between the housing interior space and the surrounding atmosphere, illustrated best in FIG. 3. The at least one discharge opening  170  is formed in the housing  100  thereby fluidly connecting the interior space of the housing with the surrounding atmosphere. The fan assembly  200  is positioned within the housing  100  and oriented to draw air from the surrounding atmosphere through the aggregate, the at least one sieve S, and the at least one sieve opening  180 , seen in FIG. 4, and discharge air through the at least one discharge opening  170  to the surrounding atmosphere. Lastly, the activation device  400  controls the operation of the fan assembly  200 .  
         [0050]    Referring again to FIG. 2, in one particular embodiment, the housing  100  further includes a front surface  130 , a back surface  140 , a left side surface  160 , and a right side surface  150 , thereby defining the interior space. In this illustrative embodiment, the at least one sieve opening  180  is approximately twelve inches in diameter to cooperate with the sieve size commonly used in an aggregate testing laboratory, but it may be any shape or size. Further, the housing  100  may include any number of sieve openings  180 .  
         [0051]    A further variation of the apparatus includes at least one drain hole  190  formed in the housing bottom surface  120  to permit fluid communication between the housing interior space and the surrounding atmosphere, as illustrated in FIG. 5 and FIG. 6. Therefore, any moisture that may accumulate in the housing  100  may be permitted to drain from the housing  100 , reducing the health risks associated with stagnant water. Further, the bottom surface may be formed to pitch toward the at least one drain hole.  
         [0052]    The housing  100  may be constructed of virtually any material, including, but not limited to, sheet metal, plastic, wood, and various composites. The material of construction may further be coated with any number of commercially available coatings to perform such functions as inhibiting corrosion as well as inhibiting microbial growth, among many others.  
         [0053]    At least one support device  300  may be attached to the enclosure  100  to elevate the bottom surface  120  from an external surface, as seen in FIG. 5. The at least one support device  300  may be as simple as fixed legs, or may include more advanced adjustability and rotational features.  
         [0054]    The at least one discharge opening  170  may be located on any of the surfaces of the enclosure. Just one configuration, that of top surface discharge, is illustrated in the figures. The at least one discharge opening  180  may be outfitted with any number of accessories. As one with skill in the art will appreciate, the at least one discharge opening  180  may be outfitted with a safety screen to prevent objects from coming in contact with the fan assembly  200 . Further, the at least one discharge opening  170  may be formed with a duct connection point so that the discharge air may be ducted outside, or other discharge location. Additionally, the at least one discharge opening  170  may incorporate a sound attenuator to minimize the transmission of noise from the discharge opening. The at least one discharge opening  170  size may vary with the airflow of the fan assembly  200  and may be configured in any shape and size.  
         [0055]    The fan assembly  200  may incorporate air movement devices in virtually any form. In one particular embodiment, the fan assembly consists  200  of a housed fan having a fan housing  220 , a fan wheel  210  rotably and releasable housed in the fan housing, and a motor  230  rotably and releasably joined to the fan wheel  210 , as seen in FIG. 4. Such a double inlet centrifugal fan may be either direct drive, or belt drive as seen in FIG. 6. In the belt drive embodiment the motor  230  and the fan wheel  210  are rotably and releasably coupled by at least one belt  240 . Alternative embodiments may incorporate a plurality of fans within the housing  100 .  
         [0056]    The fan assembly  200  may be mounted in the housing  100  in a number of ways. For instance, the fan assembly  200  may be rigidly attached to the housing  100 . Alternatively, the fan assembly  200  may be mounted to the housing  100  with a vibration isolation system  250 , as seen in FIG. 6. Such vibration isolation system  250  may include an inertia base and a flexible connection at the interface of the fan housing and the at least one discharge opening. Further, the fan assembly  200  may be suspended within the housing  100  with suspension type vibration isolators.  
         [0057]    The apparatus includes the activation device  400  for controlling the operation of the fan assembly  200 . Such activation device  400  may be as simple as a plug style connector to cooperate with a common electrical connector, or may involve more complex controls. As illustrated in FIG. 2, the activation device  400  may be a switch. Alternatively, as will be seen later, the activation device  400  may consists of electronic controls specifying the start and stop of the fan assembly  200 . Similarly, the activation device  400  may incorporate more advanced controls such as variable speed drives to control fan activation, deactivation, and speed.  
         [0058]    Further embodiments may include a weight measuring system  600  having at least one weight sensor  610  and at least one display device  620 , as seen in FIG. 8. The at least one weight sensor  610  may be formed as a sieve receiver adapted to receive and releasably hold the sieve S over the sieve opening  180 , as illustrated on the leftmost opening of FIG. 8. Alternatively, the at least one weight sensor  610  may include multiple sensors to cooperate with the sieve S, as illustrated in the rightmost opening of FIG. 8. The at least one display device  620  receives data from the at least one weight sensor  610  and computes a weight associated with the data to be displayed on the at least one display device  620 . The weight measurement system  600  may include electronic memory to store and display many weight readings during the process of drying the surface of the aggregate, as well as timing features. The fan system  200  would have to be off while the weight measurement readings were taken so that the negative pressure acting on the interior space, and therefore the sieve S, does not to affect such readings. As one with skill in the art will recognize, a timing/sampling circuit may be incorporated into the weight measurement system  600  such that weight measurements may occur at predetermined intervals and such that the fan system  200  is disabled during such readings, when required.  
         [0059]    In a further embodiment, the at least one support device  300  may incorporate the at least one weight sensor  610 . This would be particularly useful in the single sieve opening  180  embodiment illustrated in FIG. 9. In such an embodiment the fan assembly  200  would not have to be turned off during the reading since the at least one weight sensor  610  will be measuring the weight of the entire apparatus rather than just the sieve S and its contents.  
         [0060]    Yet another embodiment may include a control module  500  adapted to receive data from the weight measuring system  600  and at least one input device  510 . The at least one input device  510  may be any number of external devices such as a keyboard, or may include an input device  510  built into the control module  500  such as that shown in FIG. 7. The control module  500  may then perform calculations, and display data on one at least one display device  520 . The control module  500  may also include memory to retain the input and output data. The calculations performed may include bulk specific gravity of the compacted specimen, the theoretical maximum specific gravity, and the air void percentage in the compacted mix, according to the equations seen above. Further, the control device  500  may incorporate the function of the activation device  400  in controlling the operation of the fan assembly  200 . Additionally, the control module  500  may be adapted to transmit data to at least one printer  530 , either external to the apparatus or integral to the control module.  
         [0061]    Numerous alterations, modifications, and variations of the preferred embodiments disclosed herein will be apparent to those skilled in the art and they are all anticipated and contemplated to be within the spirit and scope of the instant invention. For example, although specific embodiments have been described in detail, those with skill in the art will understand that the preceding embodiments and variations can be modified to incorporate various types of substitute and or additional or alternative materials, relative arrangement of elements, and dimensional configurations. Accordingly, even though only few variations of the present invention are described herein, it is to be understood that the practice of such additional modifications and variations and the equivalents thereof, are within the spirit and scope of the invention as defined in the following claims.  
         [0062]    The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or acts for performing the functions in combination with other claimed elements as specifically claimed.