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Roadway  and  Pavement  Design  

  Blending  and  mixing  materials  in  order  to  improve  certain  properties   Mechanical  (blending)    Additive  

  Stabilization  -­‐  Permanently  improve  engineering  properties,  including  significant  strength  gain  

  Modification  –  Process  that  results  in  some  property  being  improved,  but  not  a  significant  increase  in  strength  

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  Use  locally  available  materials    Conserve  high  quality  material    Recycle  existing  pavements/bases    Improve  durability    Reduce  pavement  thickness    Facilitate  construction  

  Lime    Portland  cement    Fly  ash    Bitumen  (asphalt  emulsions)    Combinations  of  the  above  

  Lime    High  PI  soils  (usually  >10)  

  Portland  Cement    PI  10-­‐30  

  Fly  ash  -­‐  fine  grained  silts    Bitumen  

  PI  <  10  (sands)  

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  Lime  (percent  by  weight)    High  PI  soils  (PI>10)    2%  for  modification    3-­‐6%  for  stabilization  

  Portland  cement  (percent  by  weight)    Granular  materials,  3-­‐7%    Silty  soil  &  lean  clays,  6-­‐15%    Do  not  use  w/  organic  materials  

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  Fly  ash    Commonly  used  w/  lime  on  silts  

  Pozzolanic    High  quantities  normally  required  

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  Bitumen  (PI<10)    Granular  material  ▪ Coarse-­‐grained,  2-­‐4%  ▪ Fine-­‐grained,  4-­‐6%  

 Waterproofing  ability  

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  Some  type  of  design  is  normally  used    Consider  

 Workability    Strength    Durability    Volume  sensitivity  

  In-­‐place  (most  common)    Central  plant  (bitumen  only)  

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  Preparation  by  pulverization    Apply  stabilizer    Water  application  (if  needed)    Mixing    Compaction  

  Initial,  final  w/  shaping    Cure  

  Remove  materials  to  plant    Prepare  site  (if  needed)    Mix  material  in  the  plant    Place      Compact    Cure  

  In-­‐place  density  usually  employed  for  QC/QA  purposes  

  Density/moisture  relationship  of  stabilized  materials  changes  with  curing  time  and  stabilizer  content  

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γd  (pcf)  

Moisture  Content  (%)  

No  Lime  

6%  Lime  2%  Lime  

γd  (pcf)  

Moisture  Content  (%)  

No  Lime  

24  Hours,  6%  Lime  

1  Hour,  6%  Lime  

  Soil  Stabilization  Index  System    Developed  by  Jon  Epps  for  the  Corps  of  Engineers  

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  Perform  sieve  analysis    Perform  Atterberg  limits    See  chart