Influence of Raw Material Composition on the Performance of Lightweight Ultra-High Performance Concrete

The workability and mechanical properties of lightweight ultra-high performance concrete （LUHPC） are greatly affected by its raw material composition. Clarifying the influence law is of great significance for the engineering application of LUHPC. The effects of fly ash content， silica fume content， steel fiber content， and expansion agent content on the workability and mechanical properties of LUHPC were analyzed by orthogonal test method. The optimal mix proportion was obtained based on the intuitive analysis method and the analytic hierarchy process， and the optimal dosage of the expansion agent was further determined in combination with the shrinkage index. The results showed that： 1） With the increase of fly ash content or expansion agent content， both the mechanical properties and slump of LUHPC decreased first and then increased； with the increase of silica fume content， both the mechanical properties and slump first increased and then decreased； with the increase of steel fiber content， the mechanical properties continuously increased while the slump continuously decreased. 2） The steel fiber content had the greatest influence on slump， cubic compressive strength， and axial compressive strength， and the silica fume content had the greatest influence on the splitting tensile strength. 3） The optimal mix proportion， considering both the workability and mechanical properties， was as follows： fly ash content of 28%， silica fume content of 24%， steel fiber content of 2.0%， and expansion agent content of 6%. 4） In the range of 0% -8%， the cube compressive strength， axial compressive strength and slump of LUHPC decreased in varying degrees with the increase of the content of expansive agent， while the splitting tensile strength increased. The optimal content of expansive agent for comprehensive mechanical， shrinkage and working performance indexes was 6%.