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Performance evaluation of recycled and stabilized bases in Texas Syed, Imran M ; Scullion, Tom

By: Syed, Imran MContributor(s): Scullion, TomPublication details: Transportation Research Record, 2001Description: nr 1757, s. 14-21Subject(s): USA | Roadbase stabilization | | Cement | Lime | Test | In situ | Deflectograph | Cone penetrometer | Radar | Modulus of elasticity | | Thickness | Layer | Cracking | Longitudinal | | Soil | Subgrade | 32 | 62 | 53Bibl.nr: VTI P8167:1757Location: Abstract: A structural evaluation was performed on 25 base recycling projects in the Bryan District of the Texas Department of Transportation. The recycled layers were stabilized with cement or lime. On higher volume roadways, an unstabilized flexible base was placed over the stabilized layer, followed by a two-course surface treatment. On other pavements, the two-course surface treatment was placed directly on the stabilized layer. Testing was performed using the Dynaflect, falling weight deflectometer, dynamic cone penetrometer, and ground-penetrating radar. A correlation was generated between backcalculated layer moduli and percentage of stabilizer. Tentative moduli values, for thickness designs, were proposed. In the first year, 23 of 25 sections were judged to be performing well, with little or no surface distress. However in the next year, after a severe summer, only 17 were judged to be performing well. The major distress found was severe localized longitudinal cracking, which originated in the subgrade. The shrink-and-swell potential of the subgrade soil appears to be the major factor controlling pavement performance. Sections constructed on soils with a plasticity index of more than 35 did not perform well. The severity of the surface cracking was also related to the following secondary factors: (a) the summer droughts of 1996 and 1998, (b) presence of trees near the edge of the pavement, (c) side slope conditions, and (d) strength of the stabilized layer. The base recycling technique applied by the Bryan District appears to work well if the subgrade soils have low to moderate plasticity indices. This technique is not recommended for sections constructed on high plasticity index subgrades.
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A structural evaluation was performed on 25 base recycling projects in the Bryan District of the Texas Department of Transportation. The recycled layers were stabilized with cement or lime. On higher volume roadways, an unstabilized flexible base was placed over the stabilized layer, followed by a two-course surface treatment. On other pavements, the two-course surface treatment was placed directly on the stabilized layer. Testing was performed using the Dynaflect, falling weight deflectometer, dynamic cone penetrometer, and ground-penetrating radar. A correlation was generated between backcalculated layer moduli and percentage of stabilizer. Tentative moduli values, for thickness designs, were proposed. In the first year, 23 of 25 sections were judged to be performing well, with little or no surface distress. However in the next year, after a severe summer, only 17 were judged to be performing well. The major distress found was severe localized longitudinal cracking, which originated in the subgrade. The shrink-and-swell potential of the subgrade soil appears to be the major factor controlling pavement performance. Sections constructed on soils with a plasticity index of more than 35 did not perform well. The severity of the surface cracking was also related to the following secondary factors: (a) the summer droughts of 1996 and 1998, (b) presence of trees near the edge of the pavement, (c) side slope conditions, and (d) strength of the stabilized layer. The base recycling technique applied by the Bryan District appears to work well if the subgrade soils have low to moderate plasticity indices. This technique is not recommended for sections constructed on high plasticity index subgrades.

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