Fracture behavior of hardened cement paste incorporating mineral additions

Various powder materials have been added on the hydration of cement to improve its mechanical and chemical properties. Industrial waste or by-product powder is consumed in large quantities as aggregates or hydraulic reactants. In the present study, hardened cement pastes (HCP) were prepared with ordinary Portland cement containing fine powder consisting of isotropic graphite or glass waste to investigate their microstructure and mechanical properties. Fracture behavior was investigated by compact tension, by which the fracture energy and fracture toughness of a specimen were obtained. The amount of calcium hydroxide and Ca Si molar ratio of CSH were constant in spite of being mixed with graphite. Graphite powder did not take part in the hydration of cement. An improvement in fracture toughness and a remarkable plastic behavior were observed because of the dispersion of graphite particles. On the other hand, glass waste powder reacting with alkaline solution in the pores resulted in decreasing the Ca Si molar ratio of CSH. Similar behavior was observed in a mixture of cement and fine blast furnace slag. Bending and compressive strength increased, but fracture toughness decreased. The lower elastic fracture energy in HCP containing reactive fine powder facilitated crack propagation and enlarged the fracture surface.