# Concrete with Organic Waste Materials as Aggregate Replacement
###### Abstract  
The disposal of high volumes of organic waste is a global issue. Using organic waste instead of sand as an aggregate material for concrete could reduce the strain on waste treatment processes and on the extraction of finite resources. At the same time, it could be a climate change mitigation strategy, by storing the biogenic carbon contained in the organic waste. This project investigated the viability of replacing 10% of fine aggregate in concrete with various organic waste materials, namely rice husk ash, wood ash, corncob granules, and wheat straw. The fresh concrete's properties were studied using the slump test, and the hardened concrete's mechanical properties were measured using the compressive strength and flexural strength tests. In this study, 14 days of curing were considered for the mechanical tests, although the 28-day mechanical strength is more generally accepted. The mechanical performances along with a life cycle assessment (LCA) comparison between the concrete with organic waste and traditional concrete were conducted. The results suggested that rice husk ash and wood ash are the most-suitable organic waste products for use as aggregate replacers considering the mechanical properties. The concrete samples incorporating wheat straw and corncob granules exhibited relatively low strength; unless advanced treatment methods are applied to enhance the concrete's performance, the utilization of these organic wastes in concrete may be limited. The environmental impact assessment of traditional concrete shows that the main contributor to almost every impact category is the production of Portland cement. Sand production contributes only marginally to the overall impact of the concrete. In terms of life-cycle greenhouse gas (GHG) emissions, traditional concrete exhibits the lowest GWP impact per cubic meter when mechanical properties are included in the functional unit used for the comparison. Nevertheless, concrete samples with wood ash and rice husk ash partially offset their lower compressive strength with higher carbon sequestration, showing a similar GWP impact to traditional concrete. This makes them promising alternatives, especially for cases where limited compressive strengths are needed. Further investigations to improve their mechanical properties and optimize their performance are warranted. concrete; organic waste; sand; LCA; mechanical properties 202  
sand consumption, the reduction of costs and environmental issues linked to the amount of organic waste disposal and management, and the possibility to store carbon in concrete through organic waste. Additionally, organic waste can serve as a suitable filler in concrete, with its size distribution closely resembling that of sand, making it a viable substitute. Sand consumption is estimated to be over 40 billion t each year, which is twice the amount of sediment carried by all the rivers in the world annually [6]. Due to population growth, urbanization, and economic development, the global demand for concrete aggregates is expected to increase to 60 billion t per year by 2030 [7], raising concerns about the potential depletion of raw materials. At the same time, the high demand for sand results in illegal mining operations, especially for riverbed sand in developing countries [8; 9]. Given the limited nature of sand as a resource and the significant environmental and social impacts of illegal mining, the quest for a sustainable substitute for sand in concrete is of paramount importance. Therefore, the primary focus of this investigation is to identify potential materials that can replace sand in concrete to reduce its environmental and social burden. Agricultural waste is investigated as a possible sand replacement, given its abundance and the necessity to treat it. Incorporating organic waste materials in concrete mixtures not only provides a practical solution to replace conventional aggregates, but also alleviates the environmental and financial challenges associated with waste disposal in a circular economy perspective [10].