This study examines the influence of the mass percentage and maturation stage of bottom ash on bio-composite mechanical strength. Two kinds of bottom ash were used: matured and non-matured. To elaborate the composites, several different percentages of bottom ash were mixed with an organic matrix. Casein, starch, alginate, polyethylene glycol, pre-vulcanized natural latex, and water are the components of matrix. The idea was to use as much bottom ash as possible, since it can be used as 80% or more as the main charge, which was in prismatic form for mechanical testing after drying. The results show that whatever the state of maturation of the bottom ash, the resistances present a maximum for a percentage of bottom ash equal to 85%. It could also be noticed that non-matured bottom ash composites have better mechanical strengths than composites with matured bottom ash. This is due to the decrease in porosity of the composites and to the improvement in their structural integrity. These new composites could solve some of the solid waste problems created by bottom ash production. As the matrix is made from organic resources, it saves energy and reduces the carbon footprint. This bio-composite contributes to the circular economy by giving waste a second life.