## 2 Design and Investigations Preceding Construction
### Post-Construction Problems Blamed on the \"Nano\"-Stabilised Base Layer  
In this case, severe rut depth in excess of 50 mm (Figure 12a) crocodile cracking, potholes, and general failed conditions (Figure 12b) were detected at the end of the construction break over the summer holidays, on a section of road constructed just before the summer break. The pavement consisted of 35 mm asphalt surfacing with a 150 mm base layer stabilised with an anionic NME stabilised granular (G7 [27] quality) material. It was immediately argued that the extent of the damage must be related to the \"nano\" stabilised base layer.  
A forensic investigation was required to determine the actual cause and mechanism of distress; the evidence could be clearly seen on site by an experienced engineer and a simple  
Figure 12: Pavement section with 35 mm asphalt surfacing and a 150 mm anionic NME stabilised base layer. Condition of completed section of road one month after the summer break: (**a**) Rut depth in wheel tracks exceeding 50 mm; (**b**) severe distress with crocodile cracking, potholes, and general failures.  
investigation of construction records. An on-site investigation showed that the \"crocodile\" cracking started as parabolic cracking, indicative of shear during compaction. Similarly, the potholes contained primed sections still attached to the exposed base, indicating that the asphalt surfacing sheared from the primed base with a few potholes exceeding the depth of the surfacing, as shown in Figure 13.  
From the forensic investigation, it was established that, in a haste to finish the section of road before the summer break, the surfacing was placed in rain (specifically prohibited under the project specifications) and compacted under wet and relatively cold conditions. The placement of the surfacing in the rain (without supervision) created a slip plane and lit  
Figure 13: (**a**) Parabolic cracking indicative of shear; (**b**) exposed base layer with prime still sticking to the base layer; (**c**) action resulting in rut depth measurements in excess of 50 mm; (**d**,**e**) surfacing taken from road shows a thickness within the wheel tracks of less than 10 mm thickening towards the edge of the road where the thickness exceeded 60 mm.  
the adhesion to the base layer. The average compaction measured after construction showed an average compaction density of only 91.5 per cent as compared with the specification of a minimum of 93 per cent. On the hot summer days during the construction break, the asphalt compacted under the action of traffic and moved sideways towards the edge of the road, as shown in Figure 13. The thickness of asphalt examples taken from site indicated a thickness of less than 10 mm in the wheel tracks, resulting into a thickness of more than 60 mm towards the edge of the road. The result was a rut depth of more than 50 mm within the wheel tracks.  
The distress, shown and discussed in this example, could easily have been prevented if sound construction practices had been followed. However, the example demonstrates the \"first line of attack\" that can be used with the introduction of new technologies. It also demonstrates the importance of experienced designers, with necessary practical experience, to be available to construction supervision personnel to give expert advice and the required support to resolve construction problems.