## 2 Design and Investigations Preceding Construction
### Clean Equipment
#### 4.2.1 Reworking of NME Stabilised Pavement Layers  
Most construction contracts experience some challenges. In all probability, some NME stabilised sections may not meet the specified engineering criteria. There are numerous reasons for this problem, including equipment failure or a problem that results in a surfacing condition clearly not meeting requirements. Typical examples of construction equipment-related problems are shown in Figures 6 and 7. Figure 5: Severe movement of the NME stabilised layer, which is indicative of layer thicknesses that do not comply with specifications. The NME stabilising agent was added to a very thin layer (50 mm) instead of the specified 150 mm. Figure 6: Construction equipment-related surfacing problem, showing surface irregularities at regular intervals across the width of the stabilised section. Stabilisation was done using recycling equipment (these problems are associated with the condition of the equipment used and not related to the stabilising agent). is testimony to the resilient, forgiving nature of the stabilisation of naturally available gravel material (in this case G7 [27] quality material) stabilised with a material-compatible anionic NME stabilising agent. It should be emphasised that dry remixing of the layer is not the recommended method (as discussed in Section 4.1) to rework a layer not meeting the required specifications. \begin{table}
\begin{tabular}{l c c c} \hline \hline  & **UCS\({}_{\text{wet}}\) (MPa)** & **ITS\({}_{\text{wet}}\) (kPa)** &
\begin{tabular}{c} **Material Classification** \\ **(Construction—Figure 1)** \\ \end{tabular} \\ \hline
**Construction specification** & \(0.70\) & \(140\) & NME3 \\ \hline
**Initial stabilisation** & \(2.95\) & \(232\) & NME1 \\ \hline
**Dry reworking after 24 h** & \(2.40\) & \(199\) & NME2 \\ \hline
**Loss in strength measurement** & \(19\%\) & \(14\%\) & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Test results of initial stabilisation and dry reworking of the anionic NME stabilised layer after 24 h.  
Figure 7: Numerous seemingly random “holes” appearing on the surface, the day after stabilisation and compaction. The dry reworking of layers not meeting specifications, or the reworking of NME stabilised pavement layers in future rehabilitation works must be understood in the context of the science behind the anionic NME stabilising agent and the interaction thereof with the granular particles in a pavement layer [19; 20; 21; 22; 23]. It is essential to understand that the organofunctional silane modification of the stabilising agent (anionic NME) enables the ability to:  
* Cover each particle of the granular material within a pavement layer to become water repellent (hydrophobic) (provided a scientifically based design procedure is followed [8; 23]), and
* Form strong chemical bonds between the granular particles and the stabilising agent (i.e., bitumen emulsion or equivalent polymer). Should a layer need to be reworked for whatever reason, the weakest link will be broken, which is probably either the bitumen stabilising agent (especially when it is relatively freshly stabilised) or, in the case of severely weathered materials, the granular particles break. In the example shown in Figure 6 and Table 1, the primary minerals measured (determined using XRD scans [19]) contained a high percentage of silicon in the form of quarzitic material (40-50%) that is relatively hard [23]. These material particles probably did not break during reworking of the layer with the recycler. The strong chemical bonds between the primary minerals and the nano-silane [22] were also not broken. Hence, the bitumen stabilising agent (still relatively fresh and viscous) sheared during reworking, and then, bound together again during recompacting to generate adequate in-situ strength properties, as confirmed by the UCS and ITS test results.