4.2 Virgin and Modified-in-Place Materials

Below is a partial listing of typical design moduli by material type for virgin or modified-in-place materials to be used in FPS 21. For materials not listed, contact MNT – Pavement Asset Management for recommendations.
Table 5-6: Recommended Material Design Modulus Values
Material Type
2014 Specifications
Design Modulus
Poisson’s Ratio
Comment
Seal Coat
Item 316
200 - 250 ksi
0.35
Considered in the structural design only when placed on the surface. Not considered when used as an underseal.
Limestone Rock Asphalt Pavement
Item 330
200 - 350 ksi
0.35
Material typically placed as asphalt stabilized base or surface for low volume roads.
Hot-Mix Cold-Laid ACP
Item 334
300 - 400 ksi
0.35
  
Dense-Graded Hot-Mix Asphalt
Item 340, 341
Combined HMA thickness:
≤ 4 in. use 500 ksi
4.0 in. < T ≤ 8 in. use 650 ksi
≥ 8 in. use 850 ksi
0.35
 
Permeable Friction Course
Item 342
300 ksi
0.35
Thinness of the lift and high air voids do not allow significant contribution to the overall structural capacity.
Superpave Mixtures
Item 344
Combined HMA thickness:
≤ 4.0 in. use 650 ksi
4 in. < T ≤ 6 in. use 750 ksi
> 6.0 in. use 850 ksi
0.35
 
Stone-Matrix Asphalt
Item 346
Same as Item 344
0.35
 
Asphalt Treatment (base)
Item 292
250 - 400 ksi
0.35
Use Tex-126-E, “Molding, Testing, and Evaluating Bituminous Black Base Materials,” asphalt content.
Emulsified Asphalt Treatment (Base)
Statewide special specs
200 ksi
0.35
Contact MTD – Soils & Aggregates section for assistance in establishing optimum emulsion concentration and recommendations for adding cement or other filler material. Humid/wet regions require special considerations to ensure proper curing.
Foamed Asphalt Treatment (Base)
Statewide special specs
200 ksi
0.35
Contact MTD – Soils & Aggregates section for assistance in establishing optimum asphalt content and recommendations for adding cement or other filler material.
Flexible Base
Item 247
If historic data not available, modulus shall be no greater than 3-4 times the subgrade modulus or use FPS default, whichever is lower. Typical range 40-70 ksi.
0.35
In general, a finer graded base will have lower moduli than one that is a coarser gradation. As angularity and soundness of particles decrease, modulus will decrease to the lower end of the scale. Limiting the minus 200 clay fraction will improve resistance to moisture damage.
Lime Treated Base
Item 260, 263
60 - 75 ksi
0.30 - 0.35
Use Tex-121-E, “Soil-Lime Testing,” to establish optimum lime content. Long-term stiffness improvement will depend on concentration used and affinity of base material to undergo permanent chemical bonding.
Cement Treated Base
Item 275, 276
80 - 150 ksi
0.25 - 0.30
Use Tex-120-E, “Soil-Cement Testing,” to establish optimum cement content. For Item 276, a
minimum
 7-day unconfined compressive strength of 300 psi is established for Class L stabilized base. TTI research indicates that higher strengths can lead to detrimental shrinkage cracking. Micro cracking is encouraged for higher strengths. Also, very stiff, stabilized bases are not modeled effectively in FPS 21. Higher design moduli shall not be used.
Fly Ash or Lime-Fly Ash Treated Base
Item 265
60 - 75 ksi
0.30
Use Tex-127-E, “Lime Fly-Ash Compressive Strength Test Methods,” to establish optimum fly ash or lime fly ash content.
Lime or Cement Treated Subgrade
Item 260, 275
30 - 45 ksi
0.30
Use Tex-121-E or Tex-120-E, Parts 1, to establish optimum lime or cement content. Long-term stiffness improvement will depend on concentration used and affinity of subgrade material to undergo permanent chemical bonding. For cases when a subgrade will be treated (2-3% lime) to provide a working platform for construction equipment and a platform to improve compactive effort of the overlying layers,
this layer shall not be accounted for in the structural design.
Emulsified Asphalt Treatment (Subgrade)
Item 314, various special specs
15 - 25 ksi
0.35
Contact MNT – Pavement Asset Management for assistance in establishing optimum emulsion concentration.
Subgrade
(Existing)
Priority should be to use the project-specific backcalculated subgrade modulus. Defaults by county are available in the FPS design program. Typical range is 8-20 ksi.
0.35 - 0.45
Use of a backcalculated modulus is preferred. FPS 21 defaults to the average county subgrade modulus taken from a limited number of tests. For new highway construction on a new right-of-way, deflection testing on an adjacent highway, or intersecting highways can provide data for backcalculation. Alternatively, elastic modulus correlations to field or laboratory derived CBR or the program default may be used. Wetter or more highly plastic materials warrant higher Poisson ratios.