1、Standard Method of Test for Accelerated Polishing of Aggregates Using the British Wheel AASHTO Designation: T 279-14 ASTM Designation: D 3319-11 American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-5a T 279-1 AASHTO Sta
2、ndard Method of Test for Accelerated Polishing of Aggregates Using the British Wheel AASHTO Designation: T 279-14 ASTM Designation: D 3319-11 1. SCOPE 1.1. This method covers a laboratory procedure by which an estimate may be made of the extent to which different coarse aggregates may polish. 1.2. T
3、he values stated in SI units are regarded as the standard. 1.3. This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns associated with its use. It is the responsibility of the users of this standard to consult an
4、d establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: M 261, Rib-Tread Standard Tire for Special-Purpose Pavement Frictional-Property Tests T 2, Sampling of Aggregates T 278, Surface
5、Frictional Properties Using the British Pendulum Tester 2.2. ASTM Standards: C 778, Standard Specification for Standard Sand D 1415, Standard Test Method for Rubber PropertyInternational Hardness 2.3. Other Document: Giles, C. G., Barbara E. Sabey, and K. W. F. Carden. Development and Performance of
6、 Portable Skid-Resistance Tester. Road Research Technical Paper No. 66. Road Research Laboratory, Department of Scientific and Industrial Research, Crowthorne, England, 1964. 3. SIGNIFICANCE AND USE 3.1. This test method simulates the polishing action of vehicular traffic on coarse aggregates used i
7、n bituminous pavements. 3.2. A polish value is determined that may be used to rate or classify coarse aggregates for their ability to resist polishing under traffic. 2014 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of appl
8、icable law.TS-5a T 279-2 AASHTO 4. TERMINOLOGY 4.1. Definitions: 4.1.1. initial friction value (PV-i)the initial British Pendulum Tester readings on the test specimens before they are polished in the accelerated polishing machine. 4.1.2. polish value (PV-n)a measure of the state of polish reached by
9、 a test specimen subjected to the specified hours (n) of accelerated polishing using the materials, equipment, and procedures described in this method. The measurement is made using the British Pendulum Tester as described in Section 5.3 and T 278. 4.1.3. residual polish value (RPV-n)the residual po
10、lish value is obtained when a constant PV-n is achieved four consecutive times with repeated swings of the pendulum. 5. APPARATUS 5.1. Accelerated Polishing Machine1An accelerated polishing machine, also known as the British Wheel, and based upon a 1958 design by the Road Research Laboratory of Grea
11、t Britain. This machine shall be mounted on a firm, rigid, and level base. The equipment shall include the following: 5.1.1. Cylindrical WheelHereafter referred to as the road wheel, and having a flat surface periphery and of such size and shape as to permit 14 specimens described below to be clampe
12、d onto the periphery to form a continuous surface of aggregate particles, 44.5 mm (13/4in.) wide and 406.4 mm (16 in.) in diameter. 5.1.2. A means of rotating the road wheel about its own axis at a speed of 320 5 rpm. 5.1.3. A means of bringing the surface of a rubber-tired wheel 203.2 mm (8 in.) in
13、 diameter and 50.8 mm (2 in.) wide to bear on the aggregate specimens mounted on the surface of the road wheel with a total load of 391.44 4.45 N (88 1 lbf). The tire shall be treated, if necessary, to obtain a true running surface. The tire shall be free to rotate about on its own axis, which shall
14、 be parallel to the axis of the road wheel. The plane of rotation of the tire shall coincide with that of the road wheel. Before a new tire is used on a test, it should be conditioned by a preliminary run of 6 h with a 150-grit silicon carbide using dummy specimens (extra or used) on the road wheel.
15、 5.1.3.1. Alternate Tire No. 1An industrial 8 by 2 pneumatic smooth-tread hand-truck tire (Note 1). The tire rubber hardness shall be 55 5 IRHD measured in accordance with ASTM D 1415. The tire shall be inflated to a pressure of 310.26 13.79 kPa (45 2 psi). Note 1This is the tire originally supplied
16、 with the Accelerated Polishing Machine1 and known by the tire manufacturers designation DunlopRLI 8 2. Dunlop discontinued manufacturing this tire in February 1979. It is retained as an alternate in this test method for those users who may still have a supply and in the event that Dunlop should res
17、ume manufacturing it in the future. 5.1.3.2. Alternate Tire No. 2An industrial 2.80 by 4 (8-in. OD by 4-in. ID), 4 NHS 4-ply, crosshatch- pattern tread hand-truck tire (Notes 2 and 3). The tire shall be inflated to a pressure of 241.32 13.79 kPa (35 2 psi). Note 2When it became known that the Dunlop
18、tire (Section 5.1.3.1) was no longer being manufactured, the necessity of finding a replacement tire for the test method was evident. A search and study by the Texas State Department of Highways and Public Transportation culminated in finding this tire, a GoodyearIndustrial All Weather Hand-Truck ti
19、re size 2.80 4 (Goodyear 2014 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-5a T 279-3 AASHTO Product Code 202-008-002), to give polish values equal to those obtained with the Dunloptire.2A suitable inne
20、r tube such as GoodyearG250-4 (Product Code 199-010-700) is necessary. It was also found necessary to modify the 4-in. wheel furnished with the Accelerated Polish Machine to facilitate mounting the Goodyeartire. Approximately 0.10 in. should be removed from the wheel diameter and a larger hole provi
21、ded for the valve stem. This did not affect mounting and use of the Dunloptire. Goodyearis no longer manufacturing this tire. Note 3A 1998 study conducted by the Texas Department of Transportation shows that the use of crosshatch tires results in differential wear of the test specimen surface that m
22、irrors the pattern of the tire. This differential wear pattern produces falsely higher polish values, particularly for softer aggregates. Other research has shown that increased tire wear has an effect of accentuating the polishing of the test specimens and resulting in lower polish values. Laborato
23、ry control specimens should be used to monitor the effect of the tire wear on accelerated polishing and test results. 5.1.3.3. Alternate Tire No. 3A 203.2-mm (8-in.) diameter solid rubber tire (Note 4). The tire rubber hardness shall be 69 3 IRHD measured in accordance with ASTM D 1415. It is necess
24、ary to move the cylindrical wheel approximately 3/16in. away from the polishing machine to allow the tire to center over the test specimens. The tire shall be replaced when the RPV-10 of the control specimens described in Section 7.2 have decreased by more than 4 points from the RPV-10 obtained from
25、 a new tire. Note 4This is the tire presently supplied by the manufacturer of the Accelerated Polishing Machine1. Research has shown that increased tire wear has an effect of accentuating the polishing of the test specimens and resulting in lower polish values. Laboratory control specimens should be
26、 used to monitor the effect of the tire wear on accelerated polishing and test results. 5.1.4. A means to feed the 150-grit silicon carbide abrasive at the rate given in Section 8.5. The grit shall be fed continuously and with a uniform distribution across the width of the specimens. The grit shall
27、be applied directly onto the road wheel surface ahead of the point of contact with the rubber-tired wheel. 5.1.5. A means to feed the water at the rate given in Section 8.5 in such a way that the water is spread continuously and uniformly over the surface of the road wheel ahead of the point of cont
28、act with the rubber-tired wheel. 5.2. Metal MoldsA number of accurately machined metal molds for preparing specimens. The specimen formed is 88.9 by 44.45 by 16.0 mm (3.5 by 1.75 by 0.63 in.) and shall be curved to fit on a surface having a 203.2-mm (8-in.) radius of curvature. 5.3. British Pendulum
29、 TesterA friction-measuring device. The British Pendulum Tester used shall conform to T 278. 5.3.1. The slider contact path shall be 76.2 1.6 mm (3 1/16in.). 5.3.2. The slider width shall be 31.8 mm (11/4in.). 5.3.3. The rubber that is bonded to the slider shall be 6.4 by 25.4 by 31.8 mm (1/4by 1 by
30、 11/4in.). 5.3.4. The rubber shall be British natural rubber meeting the requirements of the Road Research Laboratory (see Section 2.3) or synthetic rubber as specified in M 261. 5.3.5. The zero adjustment shall be checked before and after testing the specimens and as often as the operator deems nec
31、essary. 5.3.6. The calibration procedures of T 278 shall be used. However, after calibration, the small slider shall be inserted. 2014 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-5a T 279-4 AASHTO 5.4.
32、 Sanding BlockA rigid metal block with a planed surface of 190-mm (7.5-in.) radius of curvature that is consistent with the radius of curvature of the road wheel-bearing surface. 6. MATERIALS AND SUPPLIES 6.1. WaterA supply of tap water for use where water is required for any purpose in this method.
33、 6.2. Fine SandA supply of fine sand for sifting into the interstices of the aggregate prior to placing of the bonding material. Standard sand conforming to the requirements of ASTM C 778 has been found suitable for this purpose. 6.3. Mold-Release AgentThe use of a mold-release agent is optional. A
34、mold-release agent may be used to prevent bonding between the mold and the bonding material. Silicon release agent and paste wax, as used for automobiles and floors, have been found suitable. The user should use care to prevent this agent from being absorbed by the aggregate as it could affect the m
35、easured polish value. 6.4. Silicon Carbide GritA supply of silicon carbide grit (150-grit size) to be used as the polishing agent. Grit should be checked for gradation using 150-m (No. 100), 106-m (No. 140), 75-m (No. 200) sieves and separated and recombined if necessary to maintain a uniform gradat
36、ion passing the 150-m (No. 100) sieve and retained on the 75-m (No. 200) sieve. 6.5. Bonding AgentA supply of polyester resin and catalyst (or another suitable bonding material, such as an epoxy resin) having a pot life of 20 to 30 min and a curing time of 3 to 6 h. This bonding agent shall not be s
37、o fluid as to flow through the fine sand. 6.5.1. An optional bonding agent may be used to eliminate use of the fine sand. This bonding agent must be quite viscous so that it will not flow completely around the aggregate particles and become part of the surface of the test specimen. Examples of suita
38、ble materials are given in Appendix X1. 6.5.2. Follow the manufacturers precautions concerning storage and use of resin and catalyst. 6.6. Coarse AggregateApproximately a 0.014 m3(1/2ft3) supply of coarse aggregate to be tested shall be sampled in accordance with T 2. The aggregate shall be normal p
39、lant-run, but laboratory-crushed material may be tested, if so identified. 7. TEST AND CONTROL SPECIMENS 7.1. Five test specimens for each coarse aggregate shall be tested. 7.2. Standard laboratory control specimens shall be included in each run to develop consistency in specimen preparation and pol
40、ishing. Four control specimens shall be included with two sets containing five test specimens each for each run. Aggregates used for fabrication of control specimens should be of consistent property and RPV-10 test history. Note 5It has been found that the polishing surface of control specimen can b
41、e successfully replicated by filling the bottom of the metal mold with a uniform mixture of four parts 20-30 grade Ottawa sand and 1 part polyester resin. The backing of the Ottawa sand control specimens should be 100 percent polyester resin to facilitate preparation of the surface bearing against t
42、he road wheel. 7.3. The aggregate to be tested shall pass the 12.7-mm (1/2-in.) sieve and shall be retained on a 9.5-mm (3/8-in.) sieve. 2014 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-5a T 279-5 AASH
43、TO Note 6Aggregate gradation may be varied to meet the needs of the user if reported with the test results. However, aggregates larger than 12.7 mm (1/2in.) may not be accommodated by the mold, and aggregates smaller than 9.5 mm (3/8in.) may not be adequately bonded in the specimen-molding process t
44、o be retained for the duration of the test. For laboratories and agencies evaluating and monitoring multiple aggregate sources, an alternate aggregate size passing a 9.5-mm (3/8-in.) sieve and retained on a 6.4-mm (1/4-in.) sieve may be used to represent the critical size of the bituminous mixture.
45、The two aggregate sizes described should not be used alternately for quality monitoring of friction aggregates. 7.4. Thoroughly wash and dry the aggregate to be tested at 110 5C (230 9F) to constant mass. 7.5. Coat the mold with mold-release agent. 7.6. Each specimen shall contain a single layer of
46、dry aggregate placed by hand as densely as possible with a flat surface down to cover the bottom 89.9-by-44.45-mm (3.5-by-1.75-in.) surface of the mold. Note 7Particles selected should be representative of the material to be evaluated. Flat, elongated, or unusually shaped particles can cause difficu
47、lty in placement and bonding. Misleading polish values can result from inadequate surface area for polishing. 7.7. Fill the interstices between the aggregate with the fine sand, described in Section 6.2, from one fourth to one half of the aggregate depth. 7.7.1. An optional method eliminates the san
48、d by using a viscous polyester resin. This material is described in Section 6.5. 7.8. Prepare the bonding agent described in Section 6.5 and in accordance with the manufacturers instructions. The consistency of the bonding agent shall be such that it will flow freely between the aggregate particles
49、but not so thin as to impregnate the sand or to bond this sand to the specimen surface, later preventing its removal. An ideal consistency would be such that the bonding agent must be forced into the voids between the aggregate particles by gentle hand pressure with a spatula. 7.8.1. The optional bonding agent requires a heavier consistency such that it will not flow except with the aid of a spatula. 7.9. Fill the prepared mold to overflow with the bonding material. Note 8Care should be used to ensure
