Effect of cementitious material composition on the mechanical properties of ultra-high strength concrete

In order to investigate the effect of cementitious material composition on the mechanical properties of ultra-high strength concrete, a series of UHSC were fabricated by changing the addition of silica fume (SF) and fly ash. The mechanical properties, including compressive strength, flexural strength, and splitting tensile strength, were evaluated using a hydraulic servo universal testing machine. Fracture parameters such as fracture toughness and characteristic length were measured using the three-point bend loading method after prefabricating a crack in the sample. The results showed that the strength of UHSC increased with SF content and the maxi- mum compressive strength and flexural strength can reach 130.24 MPa and 20.61 MPa, respectively. Adding fly ash may decrease the compressive strength of UHSC slightly. UHSC exhibited pronounced brittle fracture characteristics, with an increasing brittleness trend as its strength rises. Incorporating fly ash into the concrete can enhance its characteristic length and fracture energy while diminishing its fracture toughness. Our study may offer recommendations to reduce the brittleness of ultra-high-strength concrete.