Fracture behavior of lightweight foamed concrete: The crucial role of curing conditions

The mechanical behavior of lightweight foamed concrete (LWFC) is markedly affected by microstructural properties, related to the distribution of air bubbles and development of hydration products. In this paper an experimental study on notched beams made of LWFC is carried out, wherein Crack Mouth Opening Displacement (CMOD) is also monitored to compute the fracture energy. To investigate the influence of the curing conditions, half of the specimens are cured in air and the other half in water. Experimental evidence on the load-CMOD curve reveals that foamed concrete absorbs a significant amount of energy before rupture, and curing conditions play a crucial role on the resulting mechanical properties and fracture energy. Both flexural strength and fracture energy are significantly higher in air curing conditions, while such pronounced difference is not so apparent in terms of compressive strength, although better results are still achieved for air-cured specimens. This is further investigated through images of crack paths across the tested beams obtained by Field Emission Scanning Electron Microscopy (FESEM): for all the samples cured in air the presence of diffuse micro-cracks was noted, while those in water show less microcracks but different hydration products.