# Concrete with Organic Waste Materials as Aggregate Replacement
## 4 Conclusions and Future Developments  
This study presented an initial attempt to assess the mechanical properties and the environmental sustainability of partially replacing sand in concrete with four different organic waste materials, specifically rice husk ash, wood ash, corncob granules, and wheat straw. The environmental impact of sand is much lower than cement in concrete. However, the replacement of fine aggregates with organic waste could represent a potential mitigation strategy to further reduce the climate change impact of concrete, thanks to the carbon stored in the waste. Both addressed aspects are important; in particular, concrete strength is fundamental in order to evaluate the suitability for a specific application, i.e., the functionality of the concrete, while the aspect of storing carbon is paramount in a global warming mitigation perspective, at equal functionality. Notwithstanding the credit for storing carbon, traditional concrete appears to be the most-sustainable solution when the mixes are compared per unit of mechanical strength (i.e., (kg CO\({}_{2}\)-eq/m\({}^{3}\))/MPa). However, the wood ash and rice husk ash samples showed similar GWP impacts, positioning them as promising alternatives for further study. Additional research is necessary to establish these materials as viable alternatives:  
1. A thorough investigation into the actual carbon storage at the end-of-life of concrete is essential. This requires exploring potential end-of-life scenarios to comprehensively assess the impact of these concrete mixes;
2. While this study focused on the climate change impact category, the impact of using organic waste in concrete should be investigated more in detail for other environmental impact categories as well. The potential reduction in water consumption would be extremely important to investigate given the large water footprint of sand. In our study, we assumed that waste carries zero burden with it. However, if the waste is used in concrete, it could become a valorized co-product. Therefore, more research is needed on how to allocate the water consumed by the crop (and the other environmental impacts) to the products;
3. Integrating a consequential life cycle assessment (LCA) is endorsed to evaluate the broader implications, encompassing economic, social, and environmental aspects, including the potential trade-offs in using organic waste for different purposes [44]. Moreover, it could be important to carry out a social LCA to understand the implications of illegal mining of sand;
4. Further laboratory investigations are recommended to optimize the mechanical properties of concrete using organic waste. In particular, it is recommended to understand the evolution of the mechanical properties and durability of concrete with different organic waste replacement rates and consider longer curing times. Indeed, in this study, 14-day mechanical strength tests were performed, whereas a 28-day mechanical strength is more generally accepted. Furthermore, an extended observation period is recommended to assess the potential deterioration of organic waste particles within the concrete matrix. The following Supporting Information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app14010108/s1](https://www.mdpi.com/article/10.3390/app14010108/s1)]([https://www.mdpi.com/article/10.3390/app14010108/s1](https://www.mdpi.com/article/10.3390/app14010108/s1)). Table S1: LCI of the traditional concrete. Table S2: LCI of marine sand and gravel extraction ([PERSON], 2008) [41]. Table S3: LCI of land sand and gravel extraction ([PERSON], 2008) [41]. Table S4: Characterization factors of the biosphere flows according to the impact assessment method EF 3.1 EN15804, considered to compute the water use impact. Table S5: LCA results of the traditional concrete's ingredients. Table S6: LCA results for climate change impact category for the concrete samples. Conceptualization, T.Q. and D.S. ; methodology, T.Q., D.S., N.B. and A.A.; software, N.B. ; validation, T.Q., A.A. and G.D.; data curation, T.Q., D.S.