With the uniaxial relaxation modulus E(t) results from the collocation method, this is translated to G(t) by assuming a Poisson‟s ratio of v=0.5 for incompressibility. The GPL results are only valid for a very narrow time range, between 0.1 and 100 seconds as shown in Figure 12,corresponding to 20-23 °C and encompassing the average creep hold times of 70 seconds.