## 3 Pavement Design Process Based on Scientific Principles
### Required Fundamental Engineering Properties  
#### 3.5.1 Stresses, Strains and Durability  
The engineering requirements depend on the design estimated traffic loading over the design period and the required bearing capacity of the pavement structure. In terms of Mechanistic-Empirical design approaches these engineering properties are defined in terms of the stresses and strains within each pavement layer in the pavement structure. In line with these modern analysis and design methods, tests are recommended to be performed to indicate the compressive and tensile strengths of the stabilised material. The criteria for the various structural layers are defined in terms of generally available test equipment indicative of the compressive and tensile strengths that can routinely and cost-effectively be performed in design laboratories as well as for quality control laboratories during construction. The Unconfined Compressive Strength (UCS) and the Indirect Tensile Strength (ITS) are recommended for use to evaluate the NME stabilised materials, in line with industry recommendations in place for Bituminous Stabilised Materials (BSM) (Bitumen Emulsion and Foam stabilised materials) [43]. Figure 22: Materials with a high percentage of fines as demarcated, indicating materials which may present challenges in terms of construction practices in the field. In order to prevent confusion between the testing and evaluation of various stabilising agents used in the roads industry, technical terms and tests procedures are standardised as much as possible. However, in contrast to BSM designs, NME stabilised materials contain no cement additive, and samples for testing are consequently not placed in plastic bags, which is needed to assist with the hydration of the cement [13]. The testing of numerous naturally available materials throughout southern Africa have also shown results exceeding by some considerable margins, results usually obtained based on BSM designs. This aspect is to be expected due to the introduction of the organofunctional nano-silane modifier that acts, inter alia, as an aggregate adhesive. In addition, the particle surfaces within the material that is being stabilised are chemically altered to become hydrophobic, rendering the individual material particles to be lipophilic (oil/fat loving), not allowing water molecules to have access to the material minerals within the materials and hence, improving long-term durability. Hence, an additional material classification is added in terms of retained compressive and tensile strengths to assess the hydrophobic resistance that is achieved with the NME stabilisation. This is done by comparing the test results after a rapid curing process (UCS\({}_{\text{dry}}\); ITS\({}_{\text{dry}}\)) and after being soaked in water for 4 h (UCS\({}_{\text{wet}}\); ITS\({}_{\text{wet}}\)) [13]. A high dry result associated with a low percentage of retained strength indicates that the water is able to affect the material strength properties. It follows that the volume of the nano-silane modifier as part of the NME stabilising agent, needs to be increased for the specific material to achieve the specified level of hydrophobic action required. Not only is the Retained UCS (RCS) and ITS (RTS) specified, but the results are also compared to the minimum specifications to assess the level to which the specifications are being met and exceeded in order to more accurately assess the potential bearing capacity of the NME stabilised material. NME stabilisation allows for naturally available materials not conforming to the current traditional specifications to be effectively stabilised and utilised within a pavement structure in the upper pavement layers below the surfacing. The meeting of specifications with regard to the RCS and RTS protect the material particles from chemical weathering within the pavement structure. The former is a new concept introduced as an indication of resistance of the stabilised material to the effect of type pressures in association with water on an exposed layer.