Commonwealth of Pennsylvania PA Test Method No. 517 Department of Transportation 10 Pages 1. SCOPE LABORATORY TESTING SECTION Method of Test for DETERMINATION OF ACCELERATED POLISH OF COARSE AGGREGATE USING THE BRITISH WHEEL 1.1 This test method describes a laboratory procedure by which an estimate may be made of the extent to which different coarse aggregates may polish under traffic. 2. DEFINITIONS 2.1 The "Polished Stone Value", (PSV) is defined as the state of polish reached by each sample when subjected to accelerated polish for ten hours in the presence of water and abrasive by means of a special machine. 2.1.1 Samples of coarse aggregate are subjected to an accelerated polishing action in a special machine. 2.1.2 The state of polish reached by each sample is measured by a British Pendulum Tester (ASTM E 303 and is expressed as the Polished Stone Value (PSV). 3. APPARATUS 3.1 Accelerated Polishing Machine 1 - A polishing device as shown in Figure l. An accelerated polishing machine shall be mounted on a firm, level, and non-resilient base of stone or concrete and shall include: 3.1.1 A cylindrical wheel (referred to as the specimen wheel) having a flat surface periphery and such size and shape as to permit 14 specimens, as described later, to be clamped onto the periphery to form a continuous surface of aggregate particles, 44.45 mm (1¾") wide and 406.40 mm (16") in diameter. 3.1.2 A means of rotating the specimen wheel about its own axis at a speed of 315 to 325 revolutions per minute. 3.1.3 A means of bringing the surface of a smooth solid rubber tire of 203.20 mm (8") diameter and 40.00 mm (1 9/16") width to bear on the aggregate specimens mounted on the surface of the specimen wheel with a total load of 391.44 ± 4.45 N (88 ± 1 pound). The tire rubber hardness shall be 69 ± 3 IRHD measured according to ASTM D 1415. The tire shall be 1 Originally manufactured by Wessex, Engineering and Metal Craft Co., Ltd. Merchants Barton, Rome, Somerset England.
Page 2 free to rotate about its own axis, which shall be parallel to the axis of the specimen wheel. The plane of rotation of the tire shall coincide with that of the specimen wheel. 3.1.4 A means to feed the 125 µm (120) silicon carbide grit at the rate given in Section 6.5 of this PTM, in such a way that the silicon carbide grit is fed continuously with a uniform distribution directly onto the specimen wheel surface near the point of contact with the rubber-tired wheel. Alternately, the grit may be fed continuously onto the rubber-tired wheel at its highest point. 3.1.5 A means to feed the water at the rate shown in Section 6.5 in such a way that the water is spread continuously and uniformly over the surface of the specimen wheel near the point of contact with the rubber-tired wheel. 3.2 Metal Molds- A number of accurately machined metal molds for preparing specimens (these are usually supplied with the machine). The specimens formed from these molds are 88.90 mm long by 44.45 mm wide by 16.00 mm thick (3.50" long by 1.75" wide by 0.63" thick). 3.2.1 Metal cradles- A number of sheets of metal approximately 114.30 mm long by 76.20 mm wide by 1.60 mm thick (4.5" long by 3" wide by 1/16" thick) shaped to fit the curvature of the mold. These cradles will be used to give the epoxy a curved surface. 3.3 British Pendulum Tester- A friction measuring device. The British Pendulum Tester used shall conform to ASTM Designation E 303 with the following modifications: 3.3.1 The slider contact path shall be 76.20 ± 1.59 mm (3 ± 1/16"). 3.3.2 The slider width shall be 31.75 mm (1¼"). 3.3.3 The rubber that is bonded to the slider shall meet the following dimensional requirements, 6.35 x 25.40 x 31.75 mm (1/4 x 1 x 1¼"). 3.3.4 The zero adjustment shall be checked before and after testing the specimens and as often as the operator deems necessary. 4. MATERIALS AND SUPPLIES 4.1 Water- A supply of tap water for use where water is required for any purpose in this PTM. 4.2 Fine Sand- A supply of fine sand for filling the spaces between the aggregate pieces prior to placing of the bonding material. Silica-rich sand of minus 150 µm (No. 100) mesh size works well.
Page 3 4.3 Mold Release Agent- A supply of mold release agent used to prevent a bond between the mold and the bonding material. Number 10-30 SAE oil has been found to suitable for this purpose. 4.4 Silicon Carbide Grit- A supply of silicon carbide grit 125 µm (No. 120) grit size to be used as a polishing agent. 4.5 Bonding Agent- A supply of polyester resin and catalyst or other suitable bonding material, such as some epoxy resin, having a pot life of 20 to 30 minutes and curing time of 3 to 6 hours. 4.6 Coarse Aggregate- Approximately a 0.014 m 3 (one-half cubic foot) supply of coarse aggregate to be tested. The aggregate shall be from a normal plant run, but laboratory crushed material may be tested, if so identified. 4.7 Test Specimens and Test Control 4.7.1 Aggregate specimens shall be tested in sets of two or three for each aggregate to be evaluated. For control purposes, two positions of the specimen wheel shall be filled with two specimens made from a standard aggregate. The aggregate shall be of a uniform texture that will give consistent results for many years. 4.7.2 Adjustments to the polish value for a given run of the wheel shall be made by comparing the polish value of the standard sample to the polish value of the run. The following formula shall be used: Where: BPNS x BPN Adjusted PSV = BPNes ea PSV BPN s = polished stone value = British Pendulum Tester Number for the aggregate sample value) BPN ea = Average British Pendulum Tester Number of the standard (established polish BPN es = British Pendulum Tester Number of the standard for a given test.
Page 4 5. PREPARATION OF TEST SPECIMENS 5.1 The aggregate to be tested shall pass the 9.5 mm (3/8") sieve and shall be retained on the 6.3 mm (1/4") sieve. 5.2 The aggregate to be tested shall be thoroughly washed and dried at 60 ± 3 o C (140 ± 5 o F) to essentially constant mass. 5.3 The mold shall be coated with a mold release agent. 5.4 A thin layer (about 1.6 mm (1/16") thick) of fine sand described in Section 4.2 shall be placed in the bottom of the mold. This sand layer shall be moistened to produce a very viscous mud. 5.5 Each specimen shall contain a single layer of dry aggregate placed by hand as densely as possible with a flat surface down to cover the bottom surface of the mold. Each piece of aggregate should be pushed into the layer of wet sand so that its flat side is against the surface of the mold (NOTE 1). NOTE 1- Pieces selected should be representative of the material to be evaluated. Flat, elongated, or other non-equant shaped pieces shall be avoided because they can cause difficulty in placement and bonding. Misleading polish values can result from an inadequate surface area for polishing. 5.6 Prepare the bonding agent described in Section 4.5 according to the manufacturer's instructions. The consistency of the bonding material shall be such as to allow it to flow freely between the aggregate particles. 5.7 Fill the prepared mold just to overflowing with the bonding material. Place a metal cradle described in Section 3.2.1 on the plastic epoxy and work it back and forth to distribute the epoxy and force out the excess. Place some kind of mass (about 2 kg) (5 lbs. in weight) on the cradle to keep it in place until the epoxy hardens (NOTE 2). NOTE 2- If a thick epoxy-based mixture is used, (as described on supplementary notes at end of this test method), it is not necessary to use sand (Section 5.4) or a metal cradle (Section 5.7). 5.8 When the bonding material has cured properly (2 to 4 hours) remove the specimen from the mold. 5.9 Brush the sand from the face of the specimen. If necessary, use a pointed instrument to pick out any epoxy that has gotten on the surface of the aggregate pieces.
Page 5 6. ACCELERATED POLISH TEST PROCEDURE 6.1 Determine the original friction number of the prepared test specimens and control specimens by following the procedure outlined in Sections 8.1 and 8.2 of AASHTO T-278, as modified by Section 3.3.4. Average the readings from the final four swings and record this average as the original friction number. 6.1.1 An arrow shall be marked on the bottom of each specimen with a diamond pencil to indicate the direction of placement in the testing machine. This is done so that the sample can be run in the machine and tested on the British Pendulum Tester in the same direction each time. 6.2 Fourteen specimens shall be clamped around the periphery of the specimen wheel, using an O-ring near the edge of the specimens, to form a continuous strip of particles on which the pneumatic-tired wheel shall ride freely without bumping or slipping. The O-ring provides a tight fit for the specimens when the retaining rim of the specimen wheel is clamped into place. If the specimens move during the test they may break in half (NOTE 3). NOTE 3- Sometimes there is a small gap between the last two specimens when all fourteen are in place. This gap can be closed by placing a properly cut section of an epoxy specimen into this gap. 6.2.1 Samples must be positioned on the specimen wheel so that the arrows on them coincide with the direction of travel of the rubber-tired wheel. 6.3 Maintain the temperature of the specimens, water, and apparatus at 24 ± 3 o C (75 ± 5 o F) during the entire time of the test. 6.4 Feed No. 120 silicon carbide grit at a rate of 25 ± 5 grams (0.88 ± 0.18 ounces) per minute for ten hours. Feed water at the same rate as the silicon carbide grit. 6.5 Bring the specimen wheel to a speed of 320 + 5 rev./min., and bring the pneumatic-tired wheel to bear on the surface of the specimen with a total load of 391.44 ± 4.45 Newtons (88 ± 1 Pound). 6.6 Remove the specimens from the specimen wheel and wash thoroughly to remove grit after the test is completed. 6.7 After cleaning, test the specimens to determine the Polished Stone Value (PSV), using the British Pendulum Tester, and the same procedure used in Section 6.1 to determine the original friction number. 6.8 Determine adjustments to the PSV by comparison of the PSV obtained for control specimens to the established value for the control specimen.
Page 6 6.9 If the rate of polish is desired, repeat the procedure in Sections 6.2-6.7 at regular intervals of machine time such as 2, 4, 6, 8, and 10 hours. 7. REPORT 6.9.1 If the rate of polish is determined by repeating the readings at intervals of time throughout the test then proceed as follows: Graph the results on graph paper or in a spreadsheet program with the time intervals plotted along the x-axis of the graph, and the beginning, intermediate, and final polished stone values along the y-axis of the graph. (See Figure 2.) 7.1 The report shall contain the following information as is appropriate to the needs of the users. 7.1.1 Identification of the coarse aggregate tested, including the gradation of the aggregate 7.1.2 Before-test friction values for the control specimens 7.1.3 After-test friction values for the control specimens 7.1.4 Before-test friction values for specimens containing aggregates to be evaluated 7.1.5 After-test friction values for specimens containing aggregates to be evaluated 7.1.6 Interim test time friction values for specimens containing aggregates to be evaluated and for control specimens when the rate of polishing is to be determined 7.1.7 Adjusted polish value for the aggregates evaluated 7.1.8 Temperature of the specimens during the determination of the British Pendulum Tester number 7.1.9 Dates of the testing period
Page 7 Figure 1: Accelerated Polishing Machine with a Specimen Wheel Cover Removed
Page 8 APPENDIX FORMULA FOR MAKING POLYESTER BINDER USED IN PREPARING COARSE AGGREGATE SPECIMENS FOR THE ACCELERATED POLISH TEST A. Composition of the Resin Component 100 parts by mass - polyester resin 30 parts by mass - wollastonite P-4 extender pigment 4 to 5 parts by mass - collodial silica 0.5 parts by mass - 6% cobalt naphthanate solution (cobalt drier) B. Compounding of the Resin Component Add the wollastonite to the polyester resin and mix the two together. Add silica that is extremely light (very low sp.gr.) and floats on top of the resin. Therefore, thorough mixing is needed to disperse the silica throughout the resin. After the silica is dispersed, the 6% cobalt solution is stirred in. This resin solution may be stored up to six months and used as required. When ready for use, simply add the correct amount of catalyst (hardener) and disperse it throughout the resin (All the mixing at the Pennsylvania Department of Transportation Testing Lab is done by hand using a rubber spatula in a plastic container). C. Molding the Specimen After mixing all the previously mentioned ingredients together, the finished product has the consistency of thick putty. It holds its shape and does not run. After mixing in the hardener, fill the specimen molds with the resin mixture using a metal spatula. Make sure the resin is pushed down around the rocks that have previously been placed in the bottom of the mold. When the mold is filled, strike off the resin to the shape of the specimen mold. Because of its thick consistency, the resin mixture will hold this shape.
March 2012 Page 9 Run XXX - Limestone Standard 70 60 50 PSV 40 30 Standard #1 Standard #2 20 10 0 0 1 2 3 4 5 6 7 8 9 10 Time in Hours Figure 2. Graph of British Wheel results taken at set time intervals throughout the test
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