New cementitious composite building material with enhanced toughness

• Carbon nano/micro-particles were obtained from polyethylene beads and coconuts choir by CVD.
• When added to cement paste, up to 0.08 wt%, both materials increase compressive strength and toughness.
• These small particles disturb the propagation of microcracks that have to contour them for going on.
• Crack and crack pinning are the mechanisms which can explain the increase of toughness in the samples.

In the present work, carbon nano/micro-particles obtained by chemical vapor depostion (CVD) process and controlled pyrolysis from polyethylene beads (CNBs) and coconuts choir (CCNs) are presented. These materials were characterized by Raman spectroscopy, thermogravimetry and field emission-scanning electron microscopy (FE-SEM). FE-SEM observations evidenced that CNBs particles proved to be spherical and interconnected, while the CCNs were irregular in shape, as the result of the grinding step. When added to cement paste, up to 0.08 wt%, both materials were effective in increasing the cement matrix compressive strength and toughness. From FE-SEM observations it is evident that the presence of these small particles disturb the propagation of microcracks that have to deviate from their trajectory and have to follow the carbon nano/micro-particles contour. This mechanism increases strongly the fracture surface during the test performed by imposing the monotonic increment of crack opening. The crack and crack pinning are the mechanisms which can explain the increase of toughness in the composite samples.