US2471227A

US2471227A - Method of producing and testing specimens of paving mixtures

Info

Publication number: US2471227A
Application number: US667573A
Authority: US
Inventors: Bruce G Marshall
Original assignee: Individual
Current assignee: Individual
Priority date: 1944-02-09
Filing date: 1946-05-06
Publication date: 1949-05-24
Anticipated expiration: 1966-05-24

Description

May 24, 1949. B. G. MARSHALL 2,471,227

METHOD 0F PRODUCING AND TESTING SPECIMENS 0F PAVING MIXTURES Original Filed Feb. 9, 1944 4 2 Sheets-Sheet 1 I is .5/

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1' f 25 27 Z; 29 I l J0 ll 47 ll 3 I 5'43 Inventor WW 3m May 24, 1949. B. G. MARSHALL 2,471,227

METHOD OF PRODUCING AND TESTING SPECIMENS 0F PAVING MIXTURES ori inal Filed Feb. 9, 1944 2 Sheets-Sheet 2 Inventor Zrace mm'MZ Patented May 24, 1949 UNITED STATES PATENT OFFICE METHOD OF PRODUCING AND TESTING SPECIMENS OF PAVING MIXTURES 3 Claims. 1

The present application is a division of my U. S. application for Letters Patent, Serial Number 521,692, filed February 9, 1944, upon Compression testing and like apparatus, which application was issued on August 24, 1948, as Patent No. 2,447,586.

The present invention relates to a method of producing test specimens of bituminous paving mixtures and stabilized soil mixtures, and testing the quality and durability of said specimens, so that mixtures of controlled or predetermined quality and durability may be produced.

Bituminous paving mixtures are produced by mixing bituminous material with aggregates. Stabilized soil mixtures are produced by the use of any additional agent which will add to stability of the soil. The quality and durability of bituminous paving mixtures and stabilized soil mixtures depend on the quality, quantity, type and properties of the ingredients or materials used, and proper preparation and compaction of the mixture. By means of the present invention, exact qualities and quantities may be determined by trial, by varying the proportions and the quality and type of materials, and from the materials available, controlled mixtures can be produced so as to insure the desired predetermined qualities and durability in the finished pavements.

The simplicity of the present method makes possible its use where frequent transporting of equipment is necessary. Simplicity of performing the test makes possible its advantageous use by unskilled operators. The technique of forming and then testing a specimen practically eliminates the entrance of human errors by different operators. These advantages render the invention valuable for both design criteria and for control of quality of bituminous paving mixtures on the job during construction.

The exact nature of the present invention and specific objects thereof will become apparent from the following description when considered in connection with the accompanying drawings, in which:

Figure 1 is a front elevational view showing part of an apparatus, for carrying out the present method, as it appears in use while testing a specimen.

Figure 2 is a central vertical sectional View of part of the apparatus as it appears when in use for producing a test specimen.

Figure 3 is a horizontal section taken on line 3--3 of Figure 1.

Figure 4 is a top plan View of the test mould,

forming part of the apparatus shown in Figure 1.

Figure 5 is a side elevational View of the mold shown in Figure 4, together with a deformation indicating device.

Referring in detail to the drawings, the essential parts of an apparatus used in carrying out the present method are as follows:

1. A cylindrical compaction mold D and a compression head or plunger F for use in compacting paving mixtures to produce specimens for testmg.

2. A testing machine A by means of which load is applied to the mixture for compression in compaction mold D, and for use in measuring the stability and flow of specimens tested in test mold B. The essential parts of the testing machine A are a frame having a base '5', spaced uprights 5, top cross piece I, and a second cross piece 8 at the upper portion of the frame but below the top cross piece 1. The machine further includes a screw jack G positioned between the uprights 8 and upon the base 5, a proving ring R which is resilient and of calibrated or predetermined spring strength, and a deflection or fiexure indicating dial I.

3. A test mold B in which specimens are placed for testing as to stability and flow value.

4. A deformation indicating device C which is used to measure the degrees to which specimens deform at the times when failure or fracture of the specimens occurs.

After production of a test mixture, a quantity of the mixture is placed in compaction mold D- as shown at 9 in Figure 2, the quantity being sufficient to fill the lower portion 28 of said mold and to produce a disk-like compacted specimen. Compaction is accomplished by first tamping the mixture and then applying static load thereon in the mold D. Compression head F is centered over the specimen in the compaction mold D, and the desired load is applied by us of the testing machine A, the compaction mold D being placed on jack head 8 of screw jack G, and jack crank Hi being turned to force the rod 25 of compression head F up against the contact pin 5 of the testing machine. The specimen is then removed from the compaction mold D for future testing.

In preparing the specimen for stability and flow testing, said specimen is brought to an appropriate temperature, and the standard temperature at which hot mixed bituminous paving mixtures and stabilized soil mixtures are tested is 140 F. The specimen is brought to this temperature by immersion of th specimen for a period of one hour in water having a temperature of 140 F.

Immediately after bringing the specimen to the appropriate temperature, the stability and flow value of the specimen are determined at the same time by testing in machine A. Load application is accomplished by means of screw jacl; G mounted in the testing machine frame, and the load is measured by means of the resilient proving ring R and deflection or fiexure measuring dial I. Load applied to the proving ring B through the specimen causes deflection or fiexure of the proving ring R, and the degree to which proving ring R is deflected or flexed is measured by means of the de ection measuring dial 1. Th number of pounds required to cause any given deflection of the ring R is determined prior to its use as a load measuring device, and a calibration chart is used to convert flexural readings to pounds. The specimen is centered on edge in the lower are 22 of test mold B, and the upper are 23 of mold B is fitted so as to be guided to testing position of the specimen by guide rods 24 and 24' fixed in ears 23a, and 26b provided on opposite sides of the lower are 22, said rods slidably extending through ears Edie and 2411 provided on opposite sides of the upper arc member 23, and through sleeves 24c and 247 fixed to and depending from the

ears

24c and 24d. The assembly is then placed on the head 8 of screw jack G and centered under the contact pin as shown in Figure 1. The deformation indicating device C is then placed in testing position over guide rod 24 of test mold B, and jack crank is turned to force the top of the test mold B against pin 5. Sufficient downward hand pressure on the outer sleeve 33 of the device C is exerted to maintain the same against the upper arc member 23 of the test mold during testing. The graduated plunger or indicator 32 of device C is slidably fitted in the sleeve member 33 thereof, and is of substantially the same diameter as guide rod 24 so that the latter may move upwardly into said sleeve 33. Jack crank it is then turned at a uniform set rate per second until the reading on load meter dial I reaches its maximum and begins to l'ecede towards the zero. The pressur on outer sleeve 33 of the device C is instantly released the moment the pointer of load measuring dial I begins to recede from the maximum reading. The maximum load reading obtained in this Way during testing is recorded, and such reading is converted into pounds from the calibration chart furnished with the proving ring assembly. The reading in pounds is recorded as the stability value of the mixture. The number of graduations of the core 32 of device C which protrude above the top of the sleeve 33 gives a reading which is recorded as the flow value of the mixture.

Flow of bituminous pavements under wheel load of parked vehicles will occur if the paving mixture is excessively plastic in nature. The plastic nature of the mixture is indicated by the flow value obtained during testing for stability, and the flow value is an index to the degree that a specimen will deform up to the point that failure occurs. This value is obtained, as has been shown, by lightly pressing the outer sleeve of the deformation indicating device C against the upper arc member of the stability mold and over the guide rod 24. Pressure against the sleeve 33 of the device C is released instantly when the stability load reaches its maximum value. For calibration to zero, th device C is placed in position for testing when a freshly formed specimen is, contained in the test mold. In this position, the device C is adjusted to read zero when its inside indicator or plunger 32 is against the guide rod 24 and the outer sleeve 33 is against the upper arc of the test mold. Graduations are marked on the indicator or plunger 32, and the number of divisions protruding above the top of the outer sleeve 33 after testing for stability, is recorded as th flowvalue of the mixture.

The present method of measuring stability of bituminous paving mixtures is defined as a semiconfined compression shear test. The total mass of the specimen is subjected to the applied stresses, and the shear planes produced by failure result in separation of the specimen into four segments. Visualizing the failed specimen resting on its rounded or annular edge, the two end segments of the specimen are practically identical. The tendency is toward reproduction of identical shear planes in all specimens. This tendency is brought about by the distribution of forces applied by the test mold, and course aggregates contained in a specimen tend to shift the normal planes of shear and to thereby produce stability results higher than those containing, fine aggregates. Within limits, the higher the proportion of course to fine aggregates, the greater the diversion of the shear planes from their normal paths, thereby yielding higher stability values. The stability value obtained is a measure of the resistance to slippage of the entire masses of the specimen. Value of a bituminous pavement under load is a result of the masses slipping, and if shear occurs, the pavement is not sufficiently staple to resist the load. If excessive flow occurs without shear, the pavement is excessively plastic in nature, and for this reason rutting and shoving can be prevented by controlling the stability of the paving mixture. The stability of a. paving mixture should not. be below that required tov prevent shear under stresses to which the pavement is to be subjected.

As shown clearly in Figur 2, the compaction mold D consists of a circular base plate 3| having a reduced upper portion 31' fitting into the cylindrical body 23 of the mold, and a removable ring 27 having a rabbeted lower end fitting over the reduced upper end 28" of the body 28. The ring 2? is latched to the body 28' by means of notched latch members 29 provided on opposite sides of ring 21 and engageable with pins 30 provided on opposite sides of body 28. As shown in Figure 2, the internal diameter of removable ring 27 is slightly greater than the internal diameter of cylindrical body 28.

The compaction head F simply consists of a circular plunger having a central rod or stem 26. Also, contact pin 5 is slidable in a bushing 40 provided in the central opening of cross piece 8, and has a head M at its. upper end engageable with cross piece 8 to prevent the pin from falling through the bushing 49 and to contact the bottom of proving ring R. The graduations on the indicator or plunger 32 of the deformation indicating device C are indicated at 42 in Figures 1 and 5. As shown clearly in Figures 1, 4 and 5, the test mold B includes a base plate 25. to which is securely fastened the lower arc member 22, and which is adapted to fiatly rest against the head 8 of jack G. A slight segmento-spherical depression orrecess 35' is provided centrally in the upper surface of the upper arc member 23 of the mold B to provide a seat for reception of the lower end of contact pin 5 when the test mold is in position for testing a specimen.

As shown, the screw jack G has a worm shaft 43 whose worm meshes with a worm gear 44.

which threadedly receives the adjusting screw 46 of the jack. Crank is removably secured on a projecting end of another shaft 41 which is journaled in the front of the casing 48 of the jack G, and the shaft 43 is adapted for removable reception of the crank it when removed from the shaft 41. The second operating shaft 41 is operatively connected with the shaft 43 through a reduction gearing 49. Thus, the screw jack has two gear ratios. The shaft 43 is operated to move the jack head 8 at the rate of one inch to every sixty revolutions of shaft 43, while shaft 41 is operated to move the jack 8 at the rate of onesixteenth of an inch to sixty revolutions of said shaft 41. Shaft 43 is used for applying loads not exceeding fifteen hundred pounds on the jack head, and is intended only for use in testing asphalt paving specimens. The maximum load which may be applied on the jack head by use of the shaft 4'! is eight thousand pounds, and this shaft is used for the compression loads and soil testing. While the screw jack is shown as provided with a hand lever, it is obvious that the same may be motor driven for raising or lowering the jack head.

It will be understood that the proving ring R and the deflection dial may be removed from the testing machine frame. For this purpose, the upper portion of ring R is clamped between a disc 50 and a clamping bar 5| which are drawn together by bolts 52, and disc 50 is detachably secured to the under side of cross piece I by means of bolts 53. The dial I has a rearwardly extending arm 54 which slidably receives the lower end of a vertical rod 55 fixed to and depending from one end of clamping bar 5| and having nuts 56 threaded on the lower end portion thereof above and below the arm 54. By adjusting nuts 56, the dial I may be vertically adjusted to cause its pointer actuating contact pin 51 to properly contact the ring R so that the reading will be zero when the ring R is normal or unfiexed. It will also be noted that the disc 50 has a threaded socket 58 in the top thereof centrally of the same, which socket is of the same size as the reduced upper end 59 of the screw 46 of jack G. The head 8 is removable from this reduced end 59 so that the latter may be threaded into the socket 58 of the disc 50 of the removable proving ring assembly when this assembly is removed and inverted. This association of the screw jack and the proving ring assembly may be used as a load measuring device.

It is to be understood that the apparatus can be used for testing, for stability and flow and proper compaction, a core from any bituminous paving mixture or stabilized soil mixture pavement, and the pavement can be tested from time to time to check the stability, flow, and degree of compaction.

From the foregoing description, it is believed that the present method, as well as its advantages, will be readily understood and appreciated by those skilled in the art.

What I claim is:

1. The herein described method, which consists in pressing a quantity of paving mixture into a compact disk-like circular body to provide a test specimen, heating the specimen to an appropriate testing temperature, subjecting the heated specimen to compression diametrically thereof between a pair of opposed substantially similar arcuate members each embracing and contacting the peripheral edge of the specimen for nearly one half the circumference thereof and until failure of the same occurs, measuring the pressure to which the specimen is subjected and noting the degree thereof when failure of the specimen occurs to determine the stability value of the mixture, and measuring the diametric deformation of the specimen resulting from the compression thereof and noting the degree of such deformation at the time failure of the specimen occurs to determine the flow value of the mixture.

2. The herein described method, which consists in pressing a quantity of a paving mixture into a compact disk-like circular body to provide a test specimen, heating the test specimen to a testing temperature of approximately F., subjecting the heated specimen to compression diametrically thereof between a pair of opposed substantially similar arcuate members each embracing and contacting the peripheral edge of the specimen for nearly one half the circumference thereof and until failure of the specimen occurs, measuring the pressure to which the specimen is subjected and noting the degree thereof at the time failure of the specimen occurs to determine the stability value of the mixture, and measuring the degree of diametric distortion of the specimen resulting from the compression thereof and noting the degree of such distortion at the time of failure of the specimen to determine the flow value of the mixture.

3. The herein described method, which consists in pressing a quantity of a paving mixture into a compact body of disk-like circular form to provide a test specimen, heating the test specimen to an appropriate testing temperature, subjecting the heated specimen to compression diametrically of the latter between a pair of opposed substantially similar arcuate members each embracin and contacting the peripheral edge of the specimen for nearly one half the circumference thereof and until failure of the specimen occurs, measuring the pressure applied to the specimen and noting the degree thereof at the time failure of the specimen occurs to determine the stability value of the mixture, and measuring the diametric deformation of the specimen and noting the degree of such deformation at the time failure of the specimen occurs to determine the flow value of the mixture.

BRUCE G. MARSHALL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,630,110 Cole May 24, 1927 1,988,597 K-arrer Jan. 22, 1935 2,036,443 Taylor Apr. 7, 1936 2,041,869 Smith et a1 May 26, 1936 2,259,491 R011er Oct. 21, 1941