## 4 Self-Sensing Geosynthetics
### Carbon-Black-Based Self-Sensing Geosynthetics
Indeed, the CB agglomerates and particles break the weak chemical connections and bonding between PP monomers, thereby promoting porosity and amorphous areas in the polymer and reducing the polymer strength [117]. The findings of [PERSON] et al. also showed that adding a modest CB content to both the PP and LDPE composites markedly reduced the strain at failure. Recent research on the development of self-sensing geosynthetics has primarily focused on woven and knitted ones. CB-filled PVC is a polymer composite often used to coat woven and knitted geosynthetics. Polyvinyl chloride (PVC) is a low-crystallinity thermoplastic insulating polymer, which means that incorporating even low CB concentrations into the PVC matrix could weaken the composite mechanical performance including the elastic modulus, ductility, and strength. Hence, the CB content should be minimised in PVC composites. However, to fabricate a conductive PVC composite, a high CB concentration (i.e., 5 wt.%) is typically required. These opposing requirements should be met simultaneously through a well-controlled manufacturing process that includes proper mixing, moulding, and curing stages. In PVC-coated PET yarn self-sensing geosynthetics, the inner woven PET yams are the load-bearing components; thus, any high-CB-concentration-induced changes in the coating tensile strength will not unfavourably affect the mechanical properties of the self-sensing geosynthetic product. However, the composite must be coated to maintain its structural integrity and shield the PET from negative environmental influences and installation damage (i.e., electrical interference from wet soils and corrosive and other bio-active materials such as acids, aqueous salt solutions, and alkalis). The mechanical properties and piezoresistivity of CB-filled PVC composites were first investigated by [PERSON] et al. [118] for the potential application of the composites to the \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Polymer Type**} & **Type of CB** & \begin{tabular}{c} **Percolation** \\ **Structure** \\ \end{tabular} & \
\begin{tabular}{c} **Maximum** \\ **Threshold** \\ **(wt.\%)** \\ \end{tabular} &
\begin{tabular}{c} **Gauge Factor** \\ **Strain (\%)** \\ \end{tabular} \\ \hline \multirow{3}{*}{LDPE} & Low & 10 & 10 & 3–15 \\  & Moderate & 5 & 10 & 10 \\  & High & 5 & 10 & 9 \\ \multirow{2}{*}{PP} & Low & 7 & 4 & 25 \\  & Moderate & 7 & 10 & 17 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Average gauge factors obtained for different polymer composites composed of various CB structures. production of self-sensing geosynthetics. To prepare PVC/PET self-sensing geosynthetics, the authors mixed regulated concentrations of powdered low- and moderate-structured CBs with plasticised PVC. The in-isolation strain sensitivity was adequate for both CB-filled composites, indicating that they could be used in field applications. Nevertheless, low-structured carbon black PVC composites such as LDPE and PP [113] exhibited increased piezoresistivity responses because the conducting networks were more prone to discontinuities and rupturing under tensile loads. These investigations focused on the strain conductivity of self-sensing geosynthetic materials subjected to monotonic loading. Geosynthetics are also widely employed to stabilise various earthwork structures subjected to time-dependent loads (i.e., traffic). Time-dependent loading can irreversibly change the strain and electrical conductivity in CB-formed conductive networks in self-sensing geosynthetics. To investigate the effect of cyclic loading on the piezoresistivity of CB/PVC composites, [PERSON] et al. [119] employed the identical CBs used by [PERSON] et al. [118] and examined how the strain magnitude, loading rate, stress relaxation, and pre-straining influenced the cyclic loading performance of the CB/PVC composites.