## 5 International Standards and Current Regulations
### Challenges in Standard Adaptation  
The integration of AW-based materials into RC elements poses unique challenges, particularly when it comes to adapting existing standards to accommodate these unconventional materials. These challenges can be categorized into material-specific limitations, modeling uncertainties, and assessment methods, including force-based and displacement-based evaluations.  
Material-Specific Limitations. The heterogeneity and variability in the properties of AW materials present significant obstacles in achieving consistent performance predictions:  
* Material Homogeneity: AW aggregates and fibers exhibit varying physical and chemical properties, influencing both mechanical and durability characteristics [6, 11]. This variability complicates standard calibration efforts.
* Durability Concerns: Long-term performance under environmental exposure, such as carbonation and freeze-thaw cycles, is insufficiently addressed in existing standards [34]. For instance, the absence of provisions for bio-based material degradation in codes such as BS8110 and ACI 318 limits their application [25, 72].  
Modeling Uncertainties. Incorporating AW-based materials into structural design introduces modeling complexities, as conventional methods may not fully capture their mechanical behavior * Force-Based Evaluations: Standards like ACI 318 [72] rely on force-based design principles, which assume isotropic and homogenous material properties. However, AW materials often deviate from these assumptions, leading to discrepancies in predicted versus observed behaviors [69]. For example, PO shell concrete beams exhibited deviations of up to 25% in shear force predictions under force-based methods [69].
* Displacement-Based Methods: Advanced assessment techniques, such as displacement-based design, can better account for the ductility and cracking patterns observed in AW-modified concretes [26; 80]. Coconut aggregate beams, for instance, demonstrated high ductility under displacement-controlled loading conditions, challenging the current reliance on force-based metrics [26]. Assessment and Calibration Gaps. Despite the progress in experimental studies, the lack of harmonization between experimental findings and code provisions limits the broader application of AW materials:
* Seismic Performance Considerations: The absence of guidelines for displacement-based seismic design using AW-based concretes is a critical gap. Experimental results, such as those from banana fiber-reinforced beams, suggest significant energy dissipation potential, yet these characteristics are not reflected in existing seismic design codes [91].
* Calibration for Bio-Based Materials: Standards like ASTM C330 [37] focus on lightweight aggregates but do not account for bio-based material properties such as moisture absorption and fiber-matrix bonding. Studies on palm kernel shell concretes have revealed the importance of these factors in predicting shear capacity [77]. Broader Implications. Bridging these gaps requires coordinated efforts to adapt and expand existing standards:
* The development of material-specific calibration factors for force- and displacement-based methods.
* Incorporating environmental degradation factors and bio-material interactions into durability provisions [22; 83].
* Harmonizing experimental findings, such as those summarized in Annex 1, with the predictive models employed in international standards [73; 80].  
The inclusion of AW materials in RC elements represents a pivotal opportunity for sustainable construction. However, addressing the challenges in adapting standards will require a collaborative approach, combining experimental evidence, advanced modeling techniques, and regulatory updates.