**Sung-Hoon Kang 1, Sung-Gul Hong 1,\* and Juhyuk Moon 2,3,\***


Received: 5 August 2020; Accepted: 31 August 2020; Published: 3 September 2020

**Abstract:** Silica fume (SF) is a key ingredient in the production of ultra-high performance fiber-reinforced concrete (UHPFRC). The use of undensified SF may have an advantage in the dispersion efficiency inside cement-based materials, but it also carries a practical burden such as high material costs and fine dust generation in the workplace. This study reports that a high strength of 200 MPa can be achieved by using densified SF in UHPFRC with Portland limestone cement. Additionally, it was experimentally confirmed that there was no difference between densified and undensified SFs in terms of workability, compressive and flexural tensile strengths, and hydration reaction of the concrete, regardless of heat treatment, because of a unique mix proportion as well as mixing method for dispersing agglomerated SF particles. It was experimentally validated that the densified SF can be used for both precast and field casting UHPFRCs with economic and practical benefits and without negative effects on the material performance of the UHPFRC.

**Keywords:** ultra-high performance fiber-reinforced concrete; densified silica fume; agglomeration; pozzolanic reaction; densification
