Practices for Unbound Aggregate Pavement Layers (2013) / Chapter Skim
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9 chapter two aGGREGaTE TYPES aND MaTERIaL SELECTION INTRODUCTION Continuous removal of available natural resources and increased material hauling and transportation costs have put an emphasis on finding "acceptable" materials to be used in pavement construction. The performance of any constructed pavement system largely depends on the quality of materials used in different layers.
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10 to see with a naked eye, and the rock has a coarsegrained texture, but extrusive igneous rocks, which cool rapidly from magma at or near the earth's surface, are too fine-grained to distinguish individual minerals. Igneous rocks often have high amounts of silica.
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11 approximately 83 million metric tons of construction sand and gravel were used for road base and subgrade coverings (Bolen 2012)
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12 example, the average reported loss by abrasion for granite was 4.3%, whereas the corresponding values for limestone and dolomite were 5.7% and 5.5%, respectively. Particle Size Distribution and Fines Content One of the primary variables in any laboratory testing of aggregate materials is the grain size distribution.
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13 derived with an aggregate sample, assuming sufficient compaction is provided. Angularity, a measure of crushed faces and sharpness of edges in an aggregate, is important because it determines the level of internal shear resistance that can be developed in the particulate medium.
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14 increased use of the AIMS2 device as an automated device capable of providing objective and reproducible shape characterization of aggregates. Degree of Compaction Before the aggregate samples are tested for strength, modulus, and deformation behavior, the first task is to compact them at the corresponding gradation to determine their moisture–density relationships.
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15 aggregates with higher fines contents did develop pore pressures that resulted in a reduction in resilient modulus values. Thom and Brown (1987)
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16 TESTS TO CHECK AGGREGATE QUALITY FOR PAVEMENT APPLICATIONS Background An extensive review of published literature indicates the previously discussed properties are critical in governing the performance of UAB and subbase layers in pavement systems. Accordingly, agency specifications for aggregate usage in pavement base/subbase applications often include requirements related to gradation (particle size distribution)
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17 testing, selection, and control testing of aggregates are listed here: • AASHTO T 2: Standard Method of Test for Sampling of Aggregates • AASHTO T 11: Standard Method of Test for Materials Finer than 75-µm (No.
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18 quality assurance tests on virgin aggregate materials. Results from the survey are presented in Figure 9.
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19 ing six agencies require partially crushed particles for base course applications (often by requiring at least one fractured face or by specifying a minimum proportion of fractured particles in the aggregate blend)
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20 (Mishra et al. 2010a, 2010b; Mishra and Tutumluer 2011; Mishra 2012)
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21 the excessive movement of the coarse particles with respect to each other. On the other hand, the presence of excessive fines in an aggregate matrix compromises particle interlock through lubricating action at the contact points.
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22 1 4 2 4 1 1 1 1 1 0 2 4 6 N um be r o f A ge nc ie s Maximum Allowable Fines Content (%) FIGURE 16 Base/subbase open-graded drainage layers: maximum allowable fines content in aggregates used (17 respondents)
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23 SUSTaINaBLE PRODUCTION aND UTILIZaTION OF aGGREGaTES Aggregate crushed stone quarry processes such as blasting, crushing, and screening of coarse aggregates produce by-product materials, at approximately 8% of the mined aggregate, commonly known as quarry waste or quarry dust. Quarry wastes typically are less than 0.25 in.
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24 and that field monitoring indicated low permanent deformation during service. A recent Iowa DOT study also focused on road construction using admixture stabilized limestone fines and found that stabilized fines could perform satisfactorily as a structural layer in road construction through visual observations (Rupnow et al.
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FIGURE 19 Nonstandard material groups and their likely problems (Cook and Gourley 2002)
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26 Source: Cook and Gourley (2002)
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27 in pavement layers. The mechanistic nature of the responses of unbound aggregate materials can be characterized by resilient modulus (stiffness)
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28 Best Value Granular Material Concept Continual depletion of available natural aggregate resources has led an increasing number of transportation agencies to haul aggregate material for use in pavement construction from long distances. Such long distance hauling significantly increases the material cost for aggregates.
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29 RECYCLING AGGREGATES AND RECYCLED GRANULAR MATERIALS Fluctuating oil prices in recent years have magnified the importance of building sustainable pavement systems with stronger and less moisture-susceptible unbound granular layers as the primary load-bearing structural components. High construction demands and accompanying geologic restrictions imposed by urbanization and environmental concerns have resulted in a scarcity of good-quality aggregate sources in many locations.
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30 In addition to the general evaluation framework listed in AASHTO PP 56-06, agencies may sometimes adopt the toxicity characteristic leaching procedure (TCLP) to chemically evaluate the potential harmful effects of leaching through an UAB/subbase layer constructed using recycled materials.
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31 review, laboratory testing, accelerated performance testing and pavement distresses monitoring, FWD testing, and theoretical analysis of pavements, Kuo et al. developed the following specifications for use of RCA in Florida (see Table 2)
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32 POTENTIaL ENVIRONMENTaL IMPaCTS FROM USING RECYCLED MaTERIaLS The potential environmental impact from using recycled materials in UAB and subbase layers remains a concern for transportation agencies. Although the environmental concerns regarding the use of RAP and RCA in unbound aggregate layers are not as pronounced as are those associated with the use of some other recycled materials, such as fly ash and silica, several transportation agencies require these materials to meet environmental quality requirements (Saeed 2008)
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33 sion concerns if used in new PCC with steel. The alkalinity decreased rapidly when diluted with low pH water and exposure of the dissolved calcium hydroxide with CO2.
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34 local experience has found these methods to be satisfactory. In lieu of the sulfate soundness tests, agencies may opt to waive the soundness requirements or adopt one of the following alternative test methods: • AASHTO T 103: Soundness of Aggregates by Freezing and Thawing; • New York State DOT Test Method NY 703-08: Resistance of Coarse Aggregate to Freezing and Thawing; or • Ontario Ministry of Transportation (MOT)
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35 SUMMaRY This chapter presents an overview of different types of aggregate materials available as natural resources in the United States. Geologic phenomena responsible for the formation of different rock types are discussed, and the distribution of different rock types in the conterminous United States is presented.
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36 Grading Design," Proceedings of the Institution of Civil Engineers, Transport, Vol.
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37 able: http://www.dot.il.gov/bridges/pdf/subgrade stability manual.exe. Janoo, V.C., Quantification of Shape, Angularity, and Surface Texture of Base Course Materials, U.S.
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38 Muethel, R.W., Calcium Carbonate Precipitate from Crushed Concrete, Michigan Department of Transportation, Lansing, 1989.
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39 Thompson, M.R.
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