## 4 Geotechnical Characteristics of the PKS-Improved Fine Laterites
### Particle Size Distribution and Afterberg Limits
 \\ \hline \multirow{4}{*}{**Mixtures**} & Min & 75.650 & 93.650 & 68.510 & 38.830 & 29.010 & 1.010 & 1.505 & 26.010 & 14.890 & 17.000 \\  & Max & 78.980 & 95.920 & 72.840 & 44.610 & 30.000 & 1.010 & 1.596 & 27.900 & 17.700 & 20.210 \\  & Mean & 78.203 & 95.060 & 71.700 & 41.700 & 30.000 & 1.010 & 1.575 & 27.500 & 16.000 & 18.000 \\  & SD & 13.603 & 7.100 & 2.600 & 1.800 & 3.700 & 0.000 & 0.117 & 0.996 & 1.500 & 1.600 \\ \hline \multirow{4}{*}{**Mixtures**} & Min & 61.110 & 67.150 & 63.900 & 43.010 & 19.320 & 1.000 & 1.501 & 23.500 & 15.980 & 18.780 \\  & Max & 64.720 & 69.250 & 65.710 & 46.002 & 21.210 & 1.200 & 1.573 & 26.400 & 18.500 & 20.500 \\  & Mean & 62.590 & 68.893 The results of the modified Proctor test produced the curves as given in Figure 11. The addition of PKS to the studied soils is characterized by a decrease in maximum dry density (MDD) and optimum moisture content (OMC) values (Figure 11a; Tables 4 and 5). The MDD decreased slightly from 1.685 to 1.3 t/m\({}^{3}\) (from BL31 + 00%PKS to BL31 + 45%PKS) and from 1.59 to 1.29 t/m\({}^{3}\) (from BL32 + 00%PKS to BL32 + 45%PKS). Likewise, the OMC also decreased slightly, from 24.4 to 24.0% and 27.5 to 24.8%, respectively (Figure 11c; Tables 4 and 5). The decrease in MDD indicates that the compaction energy is less than what is obtained in the natural state [88]. This may be due to the addition of a lighter material to a much denser one. Furthermore, the decrease in MDD values could be related to the decrease in fine particle content of the new material and, more importantly, to the volume occupied by PKS particles, which are much lighter than the clay-rich laterites [45; 89; 90; 91]. Meanwhile, the decrease in OMC values could be due to the absorption of water by the PKS particles, which, according to [44], leads to a gain in the strength of the lateritic soils. It may further be due to the fact that compaction reduces voids in the mixture and makes it less permeable [45]. However, [90; 92] mentioned that over certain values of water absorption (10.23%), the pores of PKS behave as a water transmitter and convey water between the particles of fine laterites. Overall, the decrease in both MDD and OMC values is indicative of an improvement in treated materials. It was also noticed that there is a continuous increase in SCBR and UCBR values with an increase in PKS content. This pattern is in contrast to the decrease in maximum dry density values. According to [45], this concludes that the bearing capacity does not only depend on dry density after compaction, but also on the amount of the solids fractions they contain. Additionally, the UCBR values are higher than those of SCBR (Figure 12). The UCBR values range from 16 to 72% (from BL31 + 00%PKS to BL31 + 45%PKS) and from 18 to 65% (from BL32 + 00%PKS to BL32 + 45%PKS) (Figure 13). This behavior confirms the fact that the new materials have good trafficability. SCBR values rise from 14 to 66% (from BL31 + 00%PKS to BL31 + 45%PKS) and from 16 to 54% (from BL32 + 00%PKS to  
Figure 11: Modified Proctor curves of the PKS—improved fine laterites. (**a**) BL31 sample; (**b**) BL32 sample. (**c**) Variation of MDD and OMC. BL32 + 45%PKS) (Figure 13). The increase in these parameters associated with the decrease in OMC is in accordance with the study of [92; 93]. As mentioned by [91; 94], the CBR value increments are related to the increase in shear strength and density. Accordingly, in this study, the characteristics of UCBR, SCBR, and MDD of PKS-improved fine laterites disagrees with the previous findings. Indeed, a minimum value of CBR accepted in subbase and base layers for high pavement traffic (T3) is equal to or greater than 30 with S5 bearing class and 300 MPa of elastic moduli [72]. In accordance with this specification, and despite their low \(\gamma^{\rm d}\) max, the mixtures from BL31 + 25%PKS to BL31 + 45%PKS and from BL32 + 25%PKS to B32 + 45%PKS are suitable for sub-base and base layers for high pavement traffic (T3).