## 4 Discussion and Conclusions  
Using natural fibers as an alternative for concrete reinforcement is of interest not only due to increasing ductility and versatility of the material but also from an environmental perspective. On the other hand, the binder needs to be compatible with the fibers and be environmentally friendly to make a favorable composition. SCMs including SF, FA, slag, and LC\({}^{3}\) can enhance mechanical and durability properties, reduce the environmental impacts, and adjust the alkaline environment and pore structure of the matrix. The latter can be of interest when dealing with the durability of nature-based materials into concrete. While resources for SCM materials which are industrial by/products are limited and may be challenging to approach in the near future, LC\({}^{3}\) can be an available choice in most parts of the world. Furthermore, the clay can be calcined by using renewable energy which can lead to zero \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Fiber** & \begin{tabular}{c} **Elastic Modulus** \\ **(GPa)** \\ \end{tabular} & \begin{tabular}{c} **Tensile Strength** \\ **(MPa)** \\ \end{tabular} & \
\begin{tabular}{c} **Elongation at** \\ **Break (\%)** \\ \end{tabular} &
\begin{tabular}{c} **Density** \\ **(g/cm\({}^{3}\))** \\ \end{tabular} & **Reference (s)** \\ \hline Kenaf & 40 & 731.64 & 1.8 & 1.2 & [120, 129] \\ Jute & 26.5 & 393–773 & 1.5–1.8 & 1.3 & [133] \\ Sisal & 9–22 & 400–700 & 2.0–2.5 & 1.43–1.5 & [134, 135] \\ Flax & 27.6–65.5 & 345–1500 & 1.86–3.2 & 1.5 & [107, 136] \\ Hemp & 70 & 690 & 1.6–4.0 & 1.47 & [136, 137, 138] \\ Pineapple & 34.5–82.5 & 170–1627 & 1–3 & 1.44–1.56 & [139, 140, 141] \\ Cotton & 5.5–12.6 & 400 & 7.0–8.0 & 1.5–1.6 & [140] \\ Oil Palm & 0.48–9 & 24.9–550 & 4–18 & 0.7–1.55 & [142, 143] \\ E–glass & 70–71 & 2000–3500 & 0.5–3.4 & 2.5–2.55 & [120, 137, 144] \\ Carbon & 224–240 & 2650–4000 & 1.4–1.8 & 1.4–1.75 & [145, 146] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Mechanical properties of natural fiber. emissions for the calcination process. The weight proportion of calcined clay to limestone as 2:1 and the cement replacement ratio of 50% are reported to be optimal for normal uses in different studies. The kaolinite content of the clay, which is reported to play an important role in cementitious functionality of calcined clay, varies significantly in different types of clay. However, studies have shown that calcined clay with low or medium kaolinite content can also be used in LC\({}^{3}\) achieving acceptable mechanical properties for common applications. This means the LC\({}^{3}\) is not sensitive to kaolinite concentration and different types of clay available with minimum transport can be suitable for concrete production leading to reduction in cost and environmental impacts. Furthermore, improvement in durability properties in terms of chloride resistance, ASR, and sulfate attack are reported for LC\({}^{3}\) concrete with medium kaolinite content in the clay. On the other hand, the performance of kenaf fibers as short-length natural fiber concrete mixture is investigated in different studies mainly using OPC. Mechanical properties of concrete such as toughness, tensile strength, and impact resistance can be improved using this type of fiber. Moreover, durability properties such as carbonation, sulfate, and chloride resistance were reported to be enhanced compared to OPC concrete. Natural fiber volume content under 1% and fiber length of about 50 mm are reported to be a proper performance in the concrete mix. Combination of LC\({}^{3}\) with natural fibers such as kenaf fiber can be a promising composition to get green concrete with low GHG emission and energy consumption due to the replacement of cement by LC\({}^{3}\) as well as significant properties of kenaf plant in absorbing the CO\({}_{2}\) from the air and introducing proper fibers for concrete mix. Current studies on this composition are limited and need to be taken into account for further investigation.