Figure 13-32.-Cleveland open-cup flash point tester.In addition to grade determination, the penetrationtest is useful for other purposes, such as detectingoverheating or prolonged heating of asphalts in storagetanks. Also, when the asphalt is extracted from apavement, the penetration test is useful in determininghow the asphalt has changed with age and weathering.TESTS ON AGGREGATEThe desired characteristics of aggregates used forbituminous paving include angular shape, roughsurface, hardness, and gradation. These qualities andgrain distribution largely affect the quality of theresulting pavement. The larger, coarse aggregateparticles are the main structural members of thepavement; however, if there were nothing but largeparticles, there would be many unfilled voids betweenadjacent particles. The fewer voids the mixture has, themore dense the pavement and, therefore, the moreFigure 13-33.-Asphalt penetrometer.durable it is. Ideal density is obtained by filling the voidsbetween the largest particles with smaller particles, andsoon, right down through the whole range of sizes fromcoarsest to finest.Common practice divides the aggregates used forbituminous paving into coarse aggregate (retained onthe No. 10 sieve), fine aggregate (retained on the No.200 sieve), and mineral filler. Usually 65 percent ormore of the mineral filler will pass the No. 200 sieve.The distribution of the sizes determines how many voidswill remain and aids in determining how much bitumenwill be needed.The EA must be able to perform a number of testson aggregates to determine their acceptability y forbituminous construction. One test is the grain sizedistribution test that is done by sieve analysis, using thesame procedure as described for soil in the EA3TRAMAN. Tests for mineral dust and specific gravityare also needed. Instructions for conducting both thesetests are contained in the following paragraphs.13-45
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