Effect of SCM and nano-particles on static and dynamic mechanical properties of UHPC

In this paper, fiber-matrix interfacial bond and static and dynamic mechanical properties of non-fibrous UHPC matrix and UHPC containing 2% steel fibers made with different types of supplementary cementitious materials (SCMs) and nano-particles were investigated. A mixture containing 20% silica fume, by mass of binder, was used as a reference. Five other mixtures prepared with 20% silica fume as well as 20% fly ash, 20% slag, combination of 20% fly ash and 20% slag, 3.2% nano-CaCO3, or 1% nano-SiO2 were also investigated. The drop weight impact testing method was used to evaluate the impact flexural properties. The static flexural behavior was also investigated using specimens with the same size. Mercury intrusion porosimetry (MIP) was used to examine the microstructure of the matrix. Test results indicated that the incorporation of 20% silica fume in addition to either SCMs or nano-particles resulted in improvement in fiber-matrix bond and mechanical properties of UHPC. This can be attributed to the optimization of hydration products and densification of microstructure. The highest fiber-matrix bond and flexural strengths were found in the UHPC mixture containing 20% slag or 3.2% nano-CaCO3. Their 28d fiber-matrix bonds were increased by 30%-48% compared to the reference mixture, while 20%-30% greater for the 7d impact flexural strength. Therefore, slag and nano-CaCO3 are recommended for enhancing the flexural properties of UHPC.