Mechanical behaviors of nano-zirconia reinforced reactive powder concrete under compression and flexure

The properties of nano-zirconia (NZ) reinforced reactive powder concrete (RPC) with water curing and heat curing were compared. The underlying mechanisms of curing method to RPC were also studied through X-ray powder diffraction (XRD) analysis, thermogravimetry (TG) analysis and scanning electron microscope (SEM) observation. The mechanical behaviors of NZ reinforced RPC with heat curing were investigated. Experimental results showed that the flexural, compressive and splitting tensile strengths of RPC with 3% NZ cured in hot water at 90 °C for two days presents a 35.0%, 15.0% and 17.0% increase compared with that of RPC with 3% NZ cured in water for 28 days. Both of the calcium hydroxide (CH) mass and CH crystal orientation of RPC with heat curing are lower than that of RPC with the water curing. As a result, the compactness of the matrix was improved significantly. The elastic modulus of RPC with 3% NZ under uniaxial compression features a 12.7% decrease over that of RPC without NZ. The initial-peak deflection, initial-peak strength and fracture energy of RPC with NZ under four-point bending were increased by 78.2%, 5.6% and 85.7% compared to that of RPC without NZ, respectively. Whether incorporated with NZ or not, the ratio of the stress at precrack tip of notched beam to the bending strength of non-notched beam ​under three-point bending fracture is less than 1. The fracture peak load of RPC with NZ under four-point shear fracture increases by 25.4% compared to RPC without NZ when the crack-depth ratio is 0.25, and it decreases by 11.1% when the crack-depth ratio is 0.5. It can be therefore concluded that the introduction of NZ can reduce the stiffness of RPC and improve the compressive/bending toughness of RPC.