Eco-mechanical analysis of two lightweight fiber-reinforced cement-based composites

The mechanical and environmental performances of two different lightweight concretes are compared in the present paper. Since an optimal compromise between structural and environmental requirements needs to be reached in building materials, to tailor such cement-based composites the so-called eco-mechanical approach is adopted. The first mixture is a traditional lightweight concrete, containing industrial aggregates made with expanded clay (to reduce the weight) and polymeric fibers (to reach a ductile failure) in place of the traditional stone aggregates and steel rebars, respectively. The second mixture is a non-conventional lightweight cement-based composite, in which recycled rubber from end-of-life tires partially replaces the aggregates. Also in this concrete, polymeric fibers have been used as reinforcement. Concerning the mechanical properties, the results of an experimental campaign, performed on materials (i.e., uniaxial compression tests on cylinders) and on full-scale structures (i.e., plates in three point bending), are taken into consideration. In particular, the plates have been used to retrofit the sidewalks of a famous bridge in Italy. On the other hand, the carbon footprint and the embodied energy of the two types of concrete define the environmental impact. If the analysis is performed at the material level, considering only the compressive strength, the traditional lightweight concrete behaves better than the non-conventional composite. Conversely, the plates made with fiber-reinforced rubber concrete show better eco-mechanical performances than those made with the traditional lightweight composite reinforced with fibers. As a result, the above-mentioned differences suggest the necessity of a proper definition of the level (i.e., material or structural) where the eco-mechanical analysis needs to be performed.