Mechanical Properties of Concretes Containing Biochar and Recycled Plastic Aggregate

The large quantity of concrete produced each year has a high impact on environment, especially in terms of carbon dioxide emissions and consumption of natural resources. For this reason, there is an emerging trend to address these environmental issues by developing innovative concretes that can be considered “eco-friendly”. One option to reduce the environmental impact of concrete industry concerns the incorporation of different kind of waste into concrete, thus promoting the recycling of by-products that are often difficult to dispose of. In this work, two waste materials resulting from very different processes are added into concrete: biochar and recycled plastics. Biochar is a by-product of biomass pyrolysis processes and is mainly composed by carbon. It can be used as carbon sequestrating additive in concrete, so to store - in a stable form - carbon in buildings for decades. Previous research on cementitious materials proved that biochar addition in a proper amount can preserve structural performance or even enhance mechanical properties. As concern recycled plastics, grains derived from industrial processes are used in this work. The addition of plastics into concrete, as partial volume substitutes for natural aggregates, can generally produce lightweight concretes, even if a reduction of mechanical properties is observed. By combining the different effects on concrete of biochar and recycled plastics, an innovative concrete mix design is developed: biochar in a percentage of 5% by weight of cement and plastic particles replacing about 13% of total aggregates are added into concrete mix. This new concrete is experimentally analysed from the chemical, physical and mechanical point of view. The results of compressive and tensile tests indicate that the proposed material can be promising to obtain innovative structural and performing concretes.