## 3 Pavement Design Process Based on Scientific Principles
### Required Fundamental Engineering Properties
#### 3.5.1 Stresses, Strains and Durability
The specified RCS will delay the formation of deep potholes. This aspect has been observed in practice on pavement sections with damaged surfacings, with no increase in the depth of potholes over a rainy season for a period of 2 to 4 months (Figures 23 and 24). Accelerated Pavement Testing (APT) results on a pavement structure with a damaged surfacing with free-flowing water over the exposed NME-treated base layer during testing have shown similar results [26]. A built-in resistance to pothole escalation (all too familiar on roads containing granular base layers protected by thin bituminous surfacings) is of high importance. Such behaviour trends will allow more time for maintenance teams to repair road surfacings before hazardous conditions develop, especially during rainy seasons and a lack of institutional capacity in terms of preventative periodic maintenance. These observations are to be confirmed and calibrated under laboratory conditions with comparisons between the RCS of various materials and traditional laboratory tests indicative of mechanical durability under wet-dry conditions. The project specifications applicable to four categories of NME-stabilised naturally available materials (NME1 to NME4) are given in Figure 25. These recommendations take into consideration original APT tests performed on bitumen-emulsion-treated base layers [44], laboratory work performed on NME materials varying from relatively good to poor materials (including fine grained sands) [4; 25], the experience obtained in practice through the use of NME-stabilised materials [24], the results of APT performed on two pavement structures [26; 27] and the South African specifications for Bituminous Stabilised Materials (BSM) [43]. Adjustments are incorporated in the recommendations to allow for results obtained under ideal laboratory conditions and results to be obtained during construction in the field for quality control (shown in red in Figure 25). As an additional safety factor, the RCS and RTS are also assessed in terms of the minimum requirements for the material category specified, further ensuring that the implementation of an NME road pavement structure is associated with a low-risk scenario, allowing for any practical challenges to be timely resolved. Figure 23: Stripping of asphalt (35 mm) (December 2019) due to placement of the asphalt in wet conditions (rain)—anionic NME stabilised base has been exposed for 2 months during the rainy season (Original material quality: CBR 15 to 25 @ 93% mod AASHTO) (Mpumalanga Province, South Africa). Figure 24: Stripping of surfacing (double seal with an elastomer modified binder) due to a contaminated binder (December 2018), resulting in little damage to an exposed NME stabilised base-layer after 2 months of traffic in the rainy season (in situ material originally of quality CBR > 10 @ 93% mod AASHTO) (Gauteng Province, South Africa). It should be noted that the limitations with regard to the minimum material properties that can effectively be used and treated as NME4 layers in pavement structures are yet to be established. Materials with a CBR as low as 7 at 93 per cent mod AASHTO [22; 23] have been proven both in laboratories as well as in practice to be able to meet the minimum criteria for a NME4 layer with ease. Laboratory work is continuing with even poorer quality materials to establish the limits achievable with materials containing high percentages of clay, as demonstrated in Figure 25.  
Figure 25: Minimum recommended standard specifications for New-age (Nano) Modified (NME) stabilised materials, addressing four different classifications in terms of engineering requirements.