Research On Preperation And Volume Stability Of High Mobility UHPC

Recently, ultra-high performance concrete has gained a significant number of research popularity. Its complex processing introduces difficulties to its o n-site application; furthermore,large shrinkage and other factors seriously affect its practical performance. This thesis optimized the basic mix proportion,prepared large liquidity, good mechanical properties ultra-high performance concrete materials by admixing superplasticizer and defoamer, and studied the influence of expanders and reducing agent for ultra-high performance concrete volume stability. The main obtained results are shown below.As the sand-cement ratio increasing,the mortar fluidity was been reducing, the compressive strength first increased and then decreased; When silica fume quantity was used at 25% in weight of cement in use, the compressive strength of UHPC was higher; Fly ash could partly improve fluidity of the mortar, but did not obviously alter strength; Quartz powder largely reduced UHPC mortar fluidity, but it increased compressive strength. Finally got basic mix proportion of the ultra-high performance concrete under room temperature curing :Cement: silica fume: quartz sand(coarse): quartz sand(fine): water = 1: 0.25: 0.6125: 0.4785: 0.2125.The introduced defoaming agent effectively reduced the air content of freshly mixing UHPC mortar by 50% and improved compressive strength by 20%. When under sufficient vibration, the air content of high water-cement ratio defoamer-contained UHPC would reduce by 60%,and the compressive strength could increase by 50%. For high water-cement ratio defoamer-contained UHPC, eliminated air bubbles was more effective than the lower water-cement ratio for improving strength.The introduction of shrinkage-reducing agent effectively inhibited shrinkage, but largely impacted on compressive strength. It reduced the autogenous shrinkage by 39.9% and drying shrinkage by 47.3%. Meanwhile, expansion agent was adopted for maintaining volume stability. It neither effectively restrain the shrinkage of UHPC nor impact on compressive strength, but reduced the autogenous shrinkage by 16% and drying shrinkage by 29.5%.The introduction of anti-foaming agent largely reduced the porosity of UHPC, but increased the amount of small pores. Based on the mechanical properties of the UHPC with defoaming agent, it had an overall positive role on optimizing pore structure and pore size distribution.