Development of mix proportions for ultra-high-performance concrete in the context of Bangladesh

Abstract

Ultra-high-performance concrete (UHPC) is a cement-based composite thatreceivedconsiderableattentionfromtheresearchers due to its outstanding performance and has grown popularity in many countries over the last two decades, with applications ranging from building components, bridges, architectural features, repair and rehabilitation. Many researchers have conducted studies on UHPC, but information on materials and structural property of UHPC differs from country to country. However, investigations in the development of UHPC in Bangladesh context is still a lesser travelled path. Therefore, the objective of current study is to develop the mix proportion of UHPC using locallyavailable materials. A comprehensive experimental program has been conducted in three phases: mix with OPC; mix with OPC and 33% replacement of OPC by silica fume; mix with OPC, silica fume and 2% to 10% short copper plated steel fibre, maintaining constant sand/cement ratio of 1.44 and using the traditional moist curing method without added heat or pressure to be representative of prospective applications requiring in-situ casting. The water/binder ratio ranges from 0.22 to 0.38 and high range water reducer is adopted for workability. The addition of silica fume and steel fibres to the UHPC matrix was found to significantly enhance the mechanical and durability properties of the UHPC material in compression, flexure and RCPT. The addition of randomly distributed copper plated short steel fibres to the UHPC mix with OPC and SF significantly improved the compressive strength by 15.41%, 17.34% and 28.57% for Wf of4% to 8% and water/binder ratio of 0.30 at 90 days, where maximum compressive strength attained of 80.1 MPa for UHPC-14. The addition of 2% to 10% steel fibrein UHPC mix with OPC and SF significantly increased the flexural strengththat surpassed to the flexural strength of UHPC mix with OPC and SF by 7.87%, 154.13%, 235.73%, 214.8% and 270.67 % respectively for water/binder ratio of 0.30 at 28 days, where maximum flexural strength attained of 25.19 MPa for UHPC-13 disregarding UHPC-15 for poor workability. For the same criteria of flexural strength, toughness surpassed by 115.38%, 872.64%, 876.07%, 863.25% and 1426.50% respectively. The addition of steel fibre also improved the post peak parameters. The chloride ion permeability of the UHPC mix significantly declined due to addition of silica fume and increased gradually due to addition of 2% to 10% steel fibre. The chloride ion permeability of UHPC-13 consisting of 6% steel fibre was very low and provided better resistance to the penetration of chloride ions which led to its better durability. It is recommended that the mix proportion of UHPC-13 shows better mechanical and durability properties.