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abrasion | Wear | Construction Aggregate

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But will the Micro-Deval test supplement or supplant the L. A. Abrasion test for some aggregate applications? It has in Ontario for measuring the quality of aggregates for transportation construction. It has replaced the L. A. Abrasion test (more formally named Test for Resistance to Degradation of Aggregate by Abrasion and Impact in the Los Angeles Machine) for coarse aggregate and the magnesium sulfate soundness test for fine aggregate.For many decades throughout the world, the L. A. Abrasion
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  But will the Micro-Deval test supplementor supplant the L. A. Abrasion test for some aggregate applications? It has inOntario for measuring the quality of aggregates for transportationconstruction. It has replaced the L. A.Abrasion test (more formally named Testfor Resistance to Degradation of Aggregate by Abrasion and Impact in theLos Angeles Machine) for coarseaggregate and the magnesium sulfatesoundness test for fine aggregate.For many decades throughout the world, theL. A. Abrasion test (ASTM andAASHTO) has been the standard for evaluating coarse aggregate degradationand toughness in dry conditions.It also isa standard in the EU. Rogers wrote,“Despite the name, the Los Angeles testdoes not measure abrasion but rather impact resistance.” Many believe that thisdry test is a measure principally of  breakdown due to impact anddegradation during handling, batchingand lay-down operations.ASTM C 131, C 535AASHTO T-96The L. A. Abrasion Machine is used as aquality control tool for aggregates,including crushed rock, gravel and slag.The testing method determines thedegradation when subjected to abrasion,attrition, impact and grinding. Thesample is placed in the drum along with ahardened steel abrasive charge. After rotating the drum a specific number of times, samples are removed andexamined for wear.Durham Geo offers two models; a basicmodel and an enclosed model. Bothmachines are constructed from structuralsteel with a welded 1/2 in (1.27 cm) thick drum wall. The drum is fitted with aremovable shelf in accordance withASTM preferred design recommendations. Rotation is provided by an electric motor with speed reductionand enclosed chain drive to allow thedrum to turn at 30-33 rpm. The enclosedmodel is a new design that meets OSHAsound and mechanical safetyrequirements. An interlock preventsoperation unless the double hinged lid isclosed. Both models, (C-658 and C-660)come with a 25 kg abrasive charge and aheavy duty catch pan. Overview The Los Angeles (L.A.) abrasion test(Figure 1) is a common test method usedto indicate aggregate toughness andabrasion characteristics. Aggregateabrasion characteristics are important because the constituent aggregate inHMA must resist crushing, degradationand disintegration in order to produce ahigh quality HMA.The standard L.A. abrasion test subjects acoarse aggregate sample (retained on the No. 12 (1.70 mm) sieve) to abrasion,impact, and grinding in a rotating steeldrum containing a specified number of steel spheres.After being subjected to the rotatingdrum, the weight of aggregate that isretained on a No. 12 (1.70 mm) sieve issubtracted from the srcinal weight toobtain a percentage of the total aggregateweight that has broken down and passedthrough the No. 12 (1.70 mm) sieve.Therefore, an L.A. abrasion loss value of 40 indicates that 40% of the srcinalsample passed through the No. 12 (1.70mm) sieve.The standard Los Angeles abrasion testis: Background Aggregates undergo substantial wear andtear throughout their life. In general, theyshould be hard and tough enough to resistcrushing, degradation and disintegrationfrom any associated activities includingmanufacturing (Figure 2), stockpiling(Figure 3), production (Figure 4), placing(Figure 5) and compaction (Figure 6)(Roberts et al., 1996). Furthermore, theymust be able to adequately transmit loadsfrom the pavement surface to theunderlying layers and eventually thesubgrade. These properties are especiallycritical for open or gap graded HMA,which do not benefit from the cushioningeffect of the fine aggregate and wherecoarse particles are subjected to highcontact stresses (Wu et al., 1998).Aggregates not adequately resistant toabrasion and polishing may cause premature structural failure and/or a lossof skid resistance. Furthermore, poor resistance to abrasion can produceexcessive dust during HMA productionresulting in possible environmental problems as well as mixture control problems.Because of the preceding issues, a test to predict aggregate toughness and abrasionresistance is valuable. The L.A. abrasiontest is the predominant test in the U.S.; itis used by 47 States (Wu et al., 1998). Test Concept The L.A. abrasion test measures thedegradation of a coarse aggregate samplethat is placed in a rotating drum withsteel spheres (Figure 7). As the drumrotates the aggregate degrades byabrasion and impact with other aggregate particles and the steel spheres (called the charge ). Once the test is complete, thecalculated mass of aggregate that has broken apart to smaller sizes is expressedas a percentage of the total mass of aggregate. Therefore, lower L.A.abrasion loss values indicate aggregatethat is tougher and more resistant toabrasion. Summary A sample of aggregate retained on the No. 12 (1.70 mm) sieve is placed inside a rotating steeldrum containing a specifiednumber of steel spheres or  charge . As the drum rotates, ashelf inside the drum picks upthe aggregate and steel spheres.The shelf carries them arounduntil they drop on the oppositeside of the drum, subjecting theaggregate to impact andcrushing. Then, the aggregate issubjected to abrasion andgrinding as the drum continuesto rotate until the shelf picks upthe contents, and the process isrepeated. The drum is rotated for a specified number of revolutions. Afterward, theaggregate is removed from thedrum and sieved on a No. 12(1.70 mm) sieve. The aggregateretained on the sieve is weighedand the difference between thisweight and the srcinal weight isexpressed as a percentage andreported as the L.A. abrasionloss value. Figure 11 showsmajor equipment used in theL.A. abrasion test. Parameters MeasuredNote 1 There is no standard L.A.abrasion specification for Superpave mixdesign; specifications are typicallyestablished by state or local agencies.Typically U.S. state specifications limitthe abrasion of coarse aggregate for HMA use to a maximum ranging from 25  to 55 percent, with most states using aspecification of 40 or 45 percent (Figure14). Requirements for Stone MatrixAsphalt (SMA) tend to be lower;AASHTO specifies a maximum L.A.abrasion loss of 30 percent for SMA.
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