330


strain criteria, established by the Shell Oil Company, ensures that per-

manent deformation in the subgrade will not lead to excessive rutting at

the pavement surface (133). The results summarized in Table 8.6 suggest

that these pavements are not susceptible to functional deterioration,

provided the desirable levels of moisture and loading conditions are

maintained.

8.2.3 Summary

 The previous discussion has demonstrated that layer moduli from NDT

tests can be valuable in predicting the response of a pavement to the

combined effects of load and environment. Also, the use of the maximum

deflections from NDT equipment as an indicator of structural adequacy

may lead to erroneous interpretation. High deflections do not necessar-

ily mean high stresses or a structurally deficient pavement.

 The computations for US 441 and SR 80 suggest that the performance

and response characteristics of pavement materials are highly dependent

upon the effects of moisture, temperature, and the properties of the

asphalt binder. A pavement's resistance to load-induced cracking can be

improved by either increasing the stiffness of support layers or using a

lower viscosity asphalt to eliminate excessively high asphalt concrete

moduli at the minimum pavement temperatures. In those environmental

situations where rates of cooling and thermal stresses are very high, it

is important that both factors, improved stiffness of underlying support

layers, and softer asphalts, be incorporated in the pavement's struc-

ture. Provision of proper drainage--adequate camber, side drains, free-

draining materials, etc.--would help to ensure that the in-place

materials would maintain desirable levels of strength.