Concrete slump measuring device
TECHNICAL FIELD 
     The invention generally relates to a method and apparatus for measuring concrete slump. Specifically, the invention relates to a method and apparatus for measuring the slump of a specific concrete mix while in the discharge chute of a concrete mixing truck. 
     BACKGROUND OF THE ART 
     A variety of tests are presently available to measure the quality of unset concrete which is indicative of the strength and quality the concrete will have after it has set. The quantity of water contained in a concrete mix bears directly on the quality and strength of the finished concrete. A standard measure of the quantity of water in a concrete mix can be determined by measuring the slump of the mix. Slump is a measure of the degree to which a volume of unset concrete will settle when allowed to stand. 
     Typically, enough concrete is gathered from the discharge chute of a concrete mixing truck to fill a testing cone. The testing cone is a hollow frustum of rigid material having an opening at the top and an opening at the bottom. The cone is usually twelve inches high. The open bottom typically has a ten inch diameter and the open top typically has a four inch diameter. Concrete is packed into the cone in three equal layers and is tamped twenty-five strokes per layer. The cone is then topped off with concrete so that the concrete is flush across the top opening. The cone is then twisted gently and raised carefully off the concrete which then sags or slumps. The empty cone is placed next to the concrete so that the difference between the height of the cone and the height of the concrete can be measured. This difference in inches is the slump of the concrete. 
     This test is both time-consuming and subject to inaccuracies due to human variation. If the cone is not loaded properly or tamped properly an incorrect measurement will result. It often takes five or six minutes to complete the test. If the slump is greater than the known allowable slump for the specific mix in question, then the concrete mix contains too much water and must either be rejected or adjusted. Often, concrete is being discharged while an examiner completes the slump test. If the concrete fails the slump test, the remainder of the load must be rejected. 
     DISCLOSURE OF THE INVENTION 
     It is an object of the invention to quickly and accurately determine the slump of a specific concrete mix while in the discharge chute of a conventional cement mixing truck before the mix is poured. 
     Basically, the invention achieves this objective by providing a concrete slump measuring device which can repeatedly set the discharge chute at a predetermined slope angle with repect to the horizon and which has been calibrated to measure the slump of a specific concrete mix while in the discharge chute at the predetermined angle. 
     In one embodiment, the slump measuring device, or slump indicator, has a substantially triangular body. The body has a base, a first side and a second side. The first and second sides form acute angles with the base. A mechanism for repeatedly, horizontally aligning the slump indicator is provided. When so aligned, the first and second sides form predetermined angles with respect to the horizon for setting the angle of the discharge chute. For example, the first side can form an eighty degree angle with the base, and the second side a seventy-five degree angle with the base. Thus, when the indicator is aligned with the horizon the first side will drop away from the horizontal at a ten degree angle and the second side will drop away at a fifteen degree angle. The indicator is then used as a leveling device to set the slope angle of the discharge chute to one of two predetermined slope angles. 
     Two discharge angles are provided so that the chute can be set at lesser or greater angles dpending on the heights of the discharge chute. A greater angle is preferred for use with average truck chutes and a lesser angle is preferred for use with trucks having lower chutes or with concrete pumps having a high hopper. Other predetermined angles for the sides can be used as desired. 
     Once the discharge chute has been adjusted to one of the slope angles corresponding to the horizontal angular diplacement of the first or second side, concrete is allowed to flow down the discharge chute. The concrete is discharged until a small amount of concrete has fallen off the end of the chute. The flow of concrete is then stopped. The base of the slump indicator is inserted into the static concrete mass and into contact with the lowest point in the chute at a place in the concrete near the end of the chute wherein the concrete has essentially uniform depth. The sides of the indicator are calibrated with markings which indicate the slump of the concrete mix. The level of the concrete on the slump indicator is then read off the appropriately calibrated side corresponding to the angle at which the discharge chute was set. Thus, a quick and accurate determination of slump can be made before the concrete is poured. 
     The calibrations on the first and second sides of the slump indicator body are determined empirically for any specific concrete mix. For example, a sample of a known concrete mix is subjected to the standard concrete slump test utilizing the testing cone and tamping procedure. After determining the slump of the concrete in this conventional manner, an uncalibrated slump indicator in accordance with the present invention, is inserted into the discharge chute of the cement mixer from which the sample was taken, with the chute set at a slope angle corresponding to the angle of the first body sides to be calibrated. The level of the concrete on the slump indicator is then noted and engraved or otherwise marked on the side of the body. This procedure is then repeated for the same concrete mixture having various slumps. The procedure is also repeated for the second side of the body using a chute slope angle corresponding to the angle of the second side. The slump indicator thus calibrated, can be used in the field to measure the slump of a known concrete mix in the discharge chute of the concrete truck. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is an isometric view of a slump indicator in accordance with the present invention. 
     FIG. 2 is a side elevational view of the slump indicator and a conventional discharge chute illustrating the use of the slump indicator to set the angle of the discharge chute. 
     FIG. 3 is a perspective view of the slump indicator in use with a mass of concrete mix in the discharge chute. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Referring now in detail to the drawing, the numerals herein referred to like numbered parts in the figures. 
     In FIG. 1, a slump indicator, in accordance with the present invention, is generally indicated by reference numeral 10. The indicator has a plate body 12, with a first side 14, a second side 18 and a base 20 forming a substantially triangular shape with a truncated apex. The body can be constructed from any material which will provide sufficient rigidity and durability including metal, plastic or any other suitable material. 
     A bubble level 22, or other horizon finding mechanism, is provided on the body 12 to establish a horizontal reference for the sides 14, 18. The first side 14 and second side 18 form a first predetermined angle 26 and a second predetermined angle 28, respectively, with the horizon, when the indicator 10 is held in a vertical plane and horizontally aligned, as shown in FIG. 2, by the use of the bubble level. It has been found that first and second predetemined angles of ten degrees and fifteen degrees, respectively, provide chute discharge slope angles which are typically used with conventional cement mixing trucks for different applications. For example, the fifteen degree discharge slope angle is used for typical pouring situations. The ten degree angle can be used to discharge concrete mix into an elevated concrete pump hopper. 
     The bubble level 22 is positioned along the longitudinal center line of the body so that the first and second sides form the predetermined angles 26, 28 when the body is aligned with the horizon. The body may form any shape desired so long as a portion thereof indicates a discharge chute slope setting angle when the body is oriented with respect to the horizon using a horizon finding mechanism. 
     The slump indicator 10, constructed in this manner, provides a device which can be used to uniformly set the slope angle of the discharge chute 31 of a concrete truck according to the predetermined first or second angles. Thus, if the slump indicator is leveled using the bubble level 22 and the discharge chute is aligned with the first side 14, the discharge chute will form a 10 degree angle with the horizon to provide a relatively slow flow of concrete from the discharge chute. If the slump indicator is leveled and the discharge chute is aligned with the second side 18 of the body 12, as shown in FIG. 2, the discharge chute will be declined 15 degrees from the horizon. 
     Calibrations 32 and 34 are provided on the first side 14 and second side 18, respectively, of the body 12. The calibrations correspond to slump measurements for a concrete mix of the type with which the slump indicator 10 is to be used. These calibrations are empirically determined and correspond to a range of typically encountered slumps for a particular known concrete mix. 
     To calibrate the sides 14 and 18 of the slump indicator 10, a known mixture of concrete is prepared. A conventional slump test is then run on this mixture and the slump is determined in inches. This mixture is then discharged through the discharge chute 31 of a cement mixing truck. The discharge chute is first set at a horizontal slope angle corresponding to one of the predetermined angles 26 or 28 on the slump indicator for the side 14 or 18 which is to be calibrated. When concrete mixture begins to fall off a lower end 40 of the discharge chute 31, the flow is stopped. 
     As seen in FIG. 3, the base 20 of the slump indicator is inserted into the mass 35 of concrete mixture in the discharge chute 31 at a measuring location where the depth of the concrete mass is relatively uniform toward the end 40 of the chute. The body 12 is pushed downward into the concrete mass 35 until the full length of the base 20 engages the lowest part of the bottom of the chute to provide a repeatable positioning of the indicator. The body is inserted so as to be generally parallel with the flow of concrete in the chute, rather than crosswise to the flow. 
     The level of the concrete mass 35 is then engraved or otherwise marked on the side of the slump indicator being calibrated. This level corresponds to the slump measurement in inches determined by the conventional test. This procedure is then repeated for the same mixture but with different slumps. In this manner, the side of the indicator being calibrated may be calibrated for a range of slumps for a given type of concrete mixture. The procedure is then repeated for the other side of the indicator. 
     When using the slump indicator 10 in the field, the slump measurment is made in much the same manner as described for calibrating the indicator. The slope angle of the discharge chute 31 is first set at a discharge angle according to either the first side 14 or second side 18 of the indicator. In FIG. 2, the discharge chute has been set to an angle of fifteen degrees by aligning the chute with the second side 18 of the indicator 10 after aligning the body 12 horizontally using the bubble level 22. The mixture 35 is discharged until the mixture begins to fall off the end of the chute. As shown in FIG. 3, the base 20 of the indicator 15 is inserted into the lowermost portion of the curved chute at the measuring location near the end of the chute where the concrete depth is relatively uniform and parallel with the flow. The slump measurement for the mixture is indicated by the level of the concrete mass corresponding to the nearest calibration mark on the second side 18. Subsequent measurements can be quickly made of the mixture to confirm the slump measurement by momentarily stopping the discharge flow and inserting the indicator at the measuring location. Thus, measurements of slump can be made quickly and frequently during the pouring procedure, and the slump of the mixture adjusted if necessary. In this manner, the pouring of a mixture with improper slump can be avoided with a minimum of inconvenience. 
     In addition to the first predetermined angle 26 of 10 degrees and the second predetermined angle 28 of 15 degrees, other chute slope angles may be used, provided the corresponding first side 14 and second side 18 are correctly calibrated for those slope angles. Varying these angles will provide for different flow rates during discharge. For extremely viscous mixtures a large horizontal chute angle may be desired to provide accurate readings. For less viscous mixtures a smaller chute angle may be employed while maintaining the accuracy of the measurement. 
     Other embodiments and variations of the invention are also contemplated. These embodiments and variations employ the same charecteristics and essential features of the invention as described. For example, the shape of the body 12 need not be triangular. Any shape which allows the body to be used to repeatedly reference the discharge chute to the horizon to set slope angle is suitable. Thus, the scope of the invention is not to be limited by the above description but is to be determined by the scope of the claims which follow.