## 2 Design and Investigations Preceding Construction
### Incompatibility of Materials  
A problem generally applicable to pavement engineering is combining incompatible materials in the same design. The same principles apply to the use of NME stabilising agents. These incompatibilities are not normally addressed in design documents and represent a major problem associated with the general use of catalogue designs in combination with documents addressing available stabilising and binder modifications without emphasizing the basic principle of material compatibility. A first rule of thumb borrowed from basic chemistry is \"likes prefer likes\", i.e., similar binders prefer and work well with the same type of binder. Figure 14 shows the application of two binders on the same anionic NME stabilised sample. On the left, a similar NME modified binder was used in the placement of the chip seal. The chip seal could not be separated from the sample with a trowel resulting in breaking of the stone chips without separating the applied chip seal from the stabilised sample. The binder of the chip seal on the right contained a latex modified binder which showed little adhesion to the anionic NME stabilised sample. In fact, the chip seal on the sample on the right could easily be removed by hand. The differences in the application of a compatible versus a non-compatible prime to a stabilised base layer are shown in Figure 15. Figure 15a shows the application of a diluted anionic NME prime applied to the surfacing of an anionic NME stabilised sample. Figure 15b shows the consequences of applying a diluted cationic prime to an anionic NME stabilised base layer, resulting in little (or no) adhesion and catastrophic failures. Figure 14: Application of different binders to the same anionic NME stabilised samples showing the results using: (**a**) Compatible binders; (**b**) incompatible binders. Any selection of a modified binder also needs to be compatible with the future expected performance of a pavement structure. A pavement structure normally requires in the order of two seasons to reach an equilibrium moisture condition. It follows that any surfacing selected, must provide for the pavement structure to expel excess moisture in the form of vapour, independent of the type of modification (or not) used in the construction of the base layer. Unfortunately, many of the newly introduced modifications to bituminous binders \"inhibit\" the escape of moisture in the form of fumes. Industry documents often include warnings regarding the disadvantages of the use of specific modifications to bituminous materials. However, in practice these warnings are often not taken notice off, with designers only focussing on the possible advantages. It is yet to be seen that researchers confined to laboratories develops test methods that also includes measurements of the \"breathability\" of modified binders--a practical aspect generally overlooked or just ignored. The use of a modified binder on a newly constructed road could have severe repercussions, including the following:  
* Collection of moisture underneath the surfacing resulting in stripping or detachment of the surfacing from the base, especially in the use of a thin chip seal (Figure 16a,b), or
* Collection of moisture underneath the surfacing in the top of the base layer, resulting in the punching of chips into the base (in the case of a chip seal) with severe bleeding and resultant failure (Figure 16c,d). Addressing and Assuring the Depth of Stabilisation during the Rehabilitation of Roads Utilising In-Situ Materials  
Many premature failures have been investigated and could directly be associated with the depth of reworking and in-situ stabilisation not meeting the specified depths. Modern recyclers are easily programmed to change the depth of reworking which could result in considerable savings both in time and costs of the application of the stabilising agent. Without permanent supervisory staff monitoring every detail, these changes are sometimes difficult to detect.