Surface moduli

Figure 4.8. Evolution of the surface modulus

Figure 2 shows the SVM images for the PS film collected at various temperatures from 200 to 400 K [23]. The surface modulus of the silicon substrate should be invariant with respect to temperature in the employed range, meaning that the contrast enhancement between the PS and Si surfaces with temperature reflects that the modulus of the PS surface starts to decrease. In the case of a lower temperature, the image contrast was trivial, as shown in the top row of Fig. 2. On the other hand, as the temperature went beyond 330 or 340 K, the contrast between the PS and Si surfaces became remarkable with increasing temperature. This makes it clear that the PS surface reached a glass-rubber transition state at around these temperatures. Here, it should be recalled that the T of the PS by differential scanning calorimetry (DSC) was 378 K. Therefore, it can be claimed that surface glass transition temperature (7 ) in the PS film is definitely lower than the corresponding T. ...

The dynamic plate test is carried out in situ and determines the stiffness of the subgrade or unbound subbase/base course in terms of a stiffness modulus by using dynamic plate loading. The particular modulus is usually called surface modulus ( ). 

The foundation, constructed over the subgrade, consists of the sub-base layer and the capping layer, if used. The foundation is distinguished into four different classes of materials, known as foundation classes. The four foundation classes are defined by their surface modulus, known as foundation surface modulus. The materials for the foundation of the pavement may be unbound or hydraulically bound material. The latter are distinguished into fast-setting and low-setting material. 

The design CBR, for performance design, must be converted to subgrade surface modulus, E. The subgrade surface modulus is an estimated value of stiffness modulus based on subgrade CBR and is estimated by the following equation, derived from work on certain soils (Powell et al. 1984) ... 

The subgrade surface modulus used in the design must be the lower value of the long-term and short-term CBR obtained. 

Class 4 Cement-bound granular material CBGM A or B as perTable 10.10 achieving the required minimum foundation surface modulus >400... 

Table 13.5 gives details of the foundation classes and the expected foundation surface modulus, while Figure 13.14 explains the foundation and surface modulus concepts. 

According to IAN 73/06 (Highways Agency 2009a), foundation surface modulus is defined as a measure of stiffness modulus on the basis of the application of a known load at the top of the foundation it is a composite value with contributions from all underlying layers. 

Subgrade surface modulus is defined as an estimated value of stiffness modulus based on subgrade CBR and used for foundation design. 

The foundation classes are limited to classes 1, 2 and 3. Foundation class 4 is excluded since it is considered essential to measure the properties of such a foundation during construction to give adequate assurance that the appropriate long-term foundation surface modulus is likely to be achieved. 

The in situ test for foundation acceptance is the determination of foundation surface modulus immediately prior to the construction of the overlaying pavement layers. Table 13.6 gives the unadjusted mean foundation surface modulus and the minimum foundation surface modulus values, for each foundation class and for different categories of materials, to be achieved or exceeded. 

There are a large number of possible designs for the various combinations of subgrade surface modulus and foundation material, in order to achieve the desired foundation class. 

In figure 2, the results obtained in force modulation on various polymers are presented. As expected, the elastic response increases with the bulk modulus. Using Hertz models, the elastic modulus has been derived. For rigid polymers, the agreement between the surface modulus and the bulk modulus is quantitatively good. For softer polymers, a large discrepancy is observed, probably due to the fact that the adhesion force and the viscoelasticity are neglected. This could also be explained by... 

---