## 4 Challenges and Solutions
### Environmental and Cost Considerations
#### 4.4.1 Cement  
Large-scale cement manufacturing, driven by the extensive utilization of cement-based materials, presents significant environmental challenges, affecting the suitability of these materials [13; 196]. It is crucial to address the environmental impact of bulk cement production, which contributes approximately 8% of global CO\({}_{2}\) emissions, thus playing a substantial role in air pollution, climate change, and global warming [197]. Exploring alternative binder agents as substitutes for traditional cement is essential in mitigating this issue [198]. Geopolymer-based and alkali-activated binders offer a dual advantage by reducing global CO\({}_{2}\) emissions and diminishing the costs associated with multifunctional cementitious composites [199; 200]. Comparative evaluations have shown that alkali-activated slag composites exhibit lower electrical resistance under dry conditions compared to cement-based composites, although their electrical resistance performance becomes comparable under saturated conditions [192].  
Introducing sustainable binders like EVIzero, as proposed by [PERSON] et al. [201], presents an opportunity to replace cement and produce cost-effective, intrinsic carbon fiber-based self-sensing pavements. The study reported significant performance in the dispersed and fabricated samples achieved through practical and economically viable mechanical mixing, which is especially suitable for large-scale projects. Another innovative approach, as suggested by [PERSON] et al. [202], involves incorporating a 15% super hydrophobic carbonaceous powder derived from biochar (a forest byproduct) into cementitious composites to reduce cement usage. The findings indicated a 45% reduction in carbon footprint by substituting 15% modified biochar for cement. Additionally, the inclusion of biochar in cementitious composites increased electrical conductivity by up to 22%, enhancing the linearity of FCR against stress. Meanwhile, geopolymer binders based on metkaolin, devoid of conductive fillers, exhibit remarkable sensing capabilities with a gauge factor ranging from 18.3 to 38.3 [203].  
Table 2 provides an overview of previous studies in which researchers employed alkali-activated binders instead of cement in the fabrication of self-sensing cementitious composites. Due to their alkaline nature, geopolymers can offer sensing capabilities without the need for conductive fillers, but the conduction mechanism relies on ionic movement. Therefore, the sensing capability of geopolymer binders without conductive fillers diminishes under dry conditions, highlighting the necessity of incorporating conductive fillers.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Reference** & **Material Type** & **Activator** & **Precursor** & **Conductive Filler** \\ \hline
[204] & Paste & Na\({}_{2}\)SiO\({}_{3}\) + NaOH & Fly ash class C & Carbon fiber (0.5 wt.\%) \\
[205] & Paste & K\({}_{2}\)SiO\({}_{3}\) + KOH & GGBFS & SWCNTs (0.2 wt.\%) \\
[206] & Mortar & Na\({}_{2}\)SiO\({}_{3}\) & GGBFS & Graphite powder (30 wt.\%) \\
[207] & Mortar & Na\({}_{2}\)SiO\({}_{3}\) + NaOH & Fly ash class C + GGBFS & Carbon fiber (0.5\% volume) \\
[208] & Mortar & Na\({}_{2}\)SiO\({}_{3}\) + NaOH & Fly ash Class F & MWCNTs (1 wt.\%) \\
[209] & Paste & Na\({}_{2}\)SiO\({}_{3}\) + NaOH & Fly ash Class F & Graphene oxide (0.35 wt.\%) \\ \hline \hline \end{tabular}
\end{table}
Table 2: Self-sensing alkali activated composites.