essential that reduced stiffness be obtained by using softer and less

temperature-susceptible asphalts in the asphalt paving mixture.

 The limerock base course moduli for the two SR 80 test sections

were considerably lower than the other pavements. Based on the results

of this investigation, a modulus value of 85,000 psi is considered

typical of well-placed limerock materials in the state of Florida.

Because the moduli of the extremely thick subbase (36 in.) and the

subgrade for SR 80 were relatively low, this pavement probably cracked

due to the lack of support from the upper pavement layers, primarily the

base course and the thin (1.5-in. thick) asphalt concrete layers. Field

observations indicated that either poor drainage conditions increased

the moisture content of the base course or the as-compacted quality of

the base material was poor and resulted in a substandard modulus for E2.

 The base course modulus for SR 80 was increased to 85,000 psi

 (standard base) for a stress analysis comparison to illustrate the

 effect of an improved base course on pavement response and stresses.

 The other layer moduli were kept constant and BISAR was used to compute

 the response of this hypothetical pavement. These results are summa-

 rized in Table 8.7. Comparison of these results with the SR 80 test

 sections indicates that the percent failure stress level drops to 18.6

 percent. Thus, with a proper base course modulus, this pavement could

 have yielded moderate stresses and good performance.

 Table 8.6 shows that the vertical compressive strain on top of the

 subgrade layer was of the order of 2.0 x 10-4 in./in. An axial compres-

 sive subgrade strain of 2.6 x 10-4 in./in. corresponds to a 108 repeti-

 tions of vehicular loading on flexible pavements (133). This limiting