Increase the fracture energy of foamed concrete: Two possible solutions

The aim of the present paper is to investigate the influence of the curing conditions and the addition of an eco-friendly filler, biochar, on the flexural strength and fracture energy of a "green" special concrete characterized by lightness, high thermal and acoustic insulation properties and excellent fire resistance: foamed concrete. The study aims to highlight the properties of this promising material that, depending on its density, can be used for both structural and non-structural purposes. In fact, if the material is designed with a density not exceeding 800 kg/m3, it can be employed in interior partitions or in high energy-efficiency building envelopes; on the other hand, if the material is designed with a density greater than 1400 kg/m3, it can be used for structural purposes. All this makes it legitimate to state that it is a material that can be engineered according to specific needs. In this contribution the possibility to improve the fracture energy through biochar addition in this special concrete is also analyzed and presented. In particular, two different dry density were investigated: 800 kg/m3, and 1600 kg/m3. The first one for non-structural applications, the second for structural purposes. With regard to the biochar, used for 1600 kg/m3density, two different percentages, 2% and 4%, were investigated. Two different curing conditions were analyzed, namely in air at 20°C, wrapped in cellophane at the same room temperature and cured in water at 20 °C. Three-point bending tests in CMOD (crack mouth opening displacement) mode and compressive tests on the two-halves of the broken specimens have shown interesting results. Curing conditions significantly affect the fracture energy and the addition of biochar at 2% concentration seems to be beneficial in improving the fracture behavior of foamed concrete.