Practices for Unbound Aggregate Pavement Layers (2013) / Chapter Skim
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40 chapter three GRANULAR BASE AND SUBBASE CONSTRUCTION PRACTICES INTRODUCTION Aggregate storage, transportation, and construction practices are critical to ensuring adequate performance of constructed UAB and subbase layers under loading. Improper material handling and construction procedures often lead to aggregate segregation and/or degradation, ultimately resulting in a poorly compacted aggregate layer.
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41 "Material overrun," particles (regardless of size) moving down the side of the stockpile, is another major source of segregation in stockpiles.
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FIGURE 25 (a) Windrow configuration and (b)
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43 of aggregate particle sizes in the constructed layer. They also observed that low moisture in the aggregate mostly corresponded to increased segregation as a result of poor adhesion between finer and larger particles.
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44 indicating that adequate compaction levels could be achieved even for higher construction lift thicknesses. Constructing test pads in Texas, Bueno et al.
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45 the construction process while ensuring adequate compaction levels. For aggregate layers being constructed over "firm" prepared subgrades (often represented by subgrade CBR > 8%)
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46 aggregates as their primary constituent. Classic pavement design places higher modulus, more durable layers toward the surface.
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47 or 100 ksi (Maree et al.
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48 The compaction of unbound aggregate layers in the South African inverted pavement structures involves the following two phases: standard compaction phase and particle interlocking or slushing phase. The standard compaction phase is carried out using a combination of grid rollers, vibratory rollers, and pneumatic tire rollers.
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49 The pavement sections were subjected to a 28.9-kN cyclic load for the first 2 × 106 repetitions, followed by cyclic application of a 33.4-kN load until failure. Monitoring the performance of the test sections under loading, Barksdale and Todres observed that the two inverted pavement sections outperformed equivalent pavement structures in terms of lower resilient surface displacements, reduced transferred compressive stress onto the subgrade, and less tensile radial strain at the bottom of the asphalt concrete layer (Barksdale and Todres 1983; Avellandeda 2010)
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50 unbound aggregate layers in conjunction with a thin HMA surface layer, whereas the South African practice involves the construction of inverted pavement sections. Application of Stone Interlayer Pavements in Louisiana Stone interlayer pavement designs were introduced in Louisiana to reduce the problem of reflective cracking that is often observed in flexible pavements constructed using soilcement bases (Rasoulian et al.
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51 • The initial material cost for the stone interlay pavement was approximately 20% higher than that for the conventional pavement. However, considering the significantly higher number (300% higher)
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52 Summary of Past Experience on Inverted Pavements From extensive review of literature covering inverted pavement applications internationally as well as within the United States, it was observed that almost all applications of inverted pavements have resulted in favorable performance compared with conventional pavement structures. In addition to resulting in superior performance, inverted pavement sections often have led to significant cost savings over the life cycle of the pavement.
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53 Finally, this chapter discusses the concept of inverted pavements as an alternative application of UAB layers. The concept behind this application was described, as were the response mechanism and construction procedures.
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54 National Stone, Sand and Gravel Association (NSSGA) , Stone Base Construction Handbook, NSSGA, Alexandria, Va., 1989.
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