## 3 The Use of Agro-Wastes in Concrete Production
### Use of Coconut Shells and Fibers  
Among AWs, CSs and other fibers, when combined with FA in the cement matrix, have improved properties such as compressive strength, flexural and tensile strength, water absorption, porosity, and permeability of concrete. Compared to concrete where only CS is used, this combination has shown better results [30; 35]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Agro-Wastes** & **Samples** & **Field of Usage** & **Environmental Benefits** & **Related References** \\ \hline Plant Wastes & Wheat straw, rice husk, coconut shell & Lightweight concrete, composite materials & Low density, strength enhancement, permeability control & [2; 15; 22; 29; 30] \\ \hline Animal Wastes & Manure, bone, blood & Organic fertilizer, biomass energy & Waste conversion, sustainable energy & [3; 31] \\ \hline Food Processing & Fruit peels, fruit juice pulp & Manure, pyrolysis energy & Chemical fertilizer reduction, carbon footprint reduction & [5; 32] \\ \hline Wood and Fiber & Wood chips, corn cobs & Insulation material, filling material & Sustainable construction material production & [1; 10] \\ \hline Agricultural Injury & Cotton fiber, corn husk & Reinforcement material & Strength enhancer, lightweight construction material & [23; 26] \\ \hline Other Agro-Wastes & Palm oil Ash, wheat straw Ash & Lightweight concrete, RC elements & Increasing the flexibility and durability of structural elements & [13; 21; 22] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Potential environmental benefits according to agro-waste types and usage fields (own research). Figure 2: Sources, processing methods, and results of agro-waste utilization (own research). For instance, CS + 0.75% steel fiber concrete exhibited a compressive strength of 47.8 MPa, compared to 35.6 MPa for CS concrete without fibers, representing a significant improvement [26]. Additionally, the inclusion of FA enhanced the workability of fresh concrete and mitigated the strength loss observed in mixes with higher CS content. The combination of CS and FA improved tensile strength by 15%, reaching up to 4.8 MPa in certain mixes [26; 30; 35]. CS can be partially used as a coarse aggregate in lightweight concrete production and is suitable for non-load-bearing structures, strip foundations, and non-structural elements. Using waste CS materials in sustainable and efficient applications is thought to minimize environmental concerns. With a specific gravity of 1.33 tons/m\({}^{3}\) compared to traditional concrete's 2.67 tons/m\({}^{3}\), CS allows concrete to be classified as lightweight [36]. According to ASTM C330 [37], the 28-day compressive strength of lightweight concrete containing CS aggregate is reported to be 16 N/mm\({}^{2}\). Replacing 20% of coarse aggregate with CS can yield higher strength. Initially, CS concrete shows low resistance to water absorption; however, this resistance improves in later stages as the bond between the cement paste and aggregates strengthens [36]. Studies indicate that adding not only CS but also fibers and FA enhances the mechanical properties of concrete [26; 30; 35]. The use of coconut fibers as reinforcement in a cement matrix offers potential for producing lighter composites due to its low intrinsic density and structure that allows air bubble accumulation [38; 39]. CS concrete partially substituted with FA is environmentally friendly, given that CSs are renewable and FA is an industrial by-product [35; 40]. Compressive strength decreases as the CS content increases, with a 24% reduction observed when 15% CS is substituted in regular concrete [36]. Experiments to determine the thermal conductivity of fiber bundles found that increasing the density of fiber bundles from 30 to 120 kg/m\({}^{3}\) reduced thermal conductivity from 0.052 to 0.024 W/m\(\cdot\)K [38]. While heat treatment reduced tensile strength, tensile stress at break increased significantly after chemical and physical treatments by 18% and 51%, respectively, with increased ductility [39; 41].