Effect Of Ultrafine Powder On The Fluidity And Mechanical Properties Of Ultra-high Performance Concrete

Ultra-high performance concrete(UHPC)as a new type of building material has excellent performance,high mechanical properties and good durability.But UHPC with low water/cement ratio often gets poor work performance.In the light of the uncoordinated problems of UHPC low water/cement ratio and the work performance and the large amount of steel fiber,combined with the advantages and disadvantages of ordinary mineral admixtures and nano-mineral admixtures,the effects of superfine powder on performance and mechanical properties of UHPC were studied systematically.Superfine powder is made from mineral admixtures.The grinding process is not only the process of particle reduction,but also with the crystal structure and surface changes.The superfine will have new features and functioss,which will have a significant impact on the performance and mechanical properties of UHPC.To improve and enhance UHPC performance,this paper studied the plastic silicon powder,submicron silicon,superfine silicon aluminum powder,superfine slag powder on the mechanical behavior and work performance of UHPC,explores the many superfine powder gel system on the influence law of UHPC,implements a variety of superfine powder mixed with complementary advantages,was obtained under the condition of low water-binder ratio in 0.14 with good performance,excellent mechanical properties of the high content of steel fiber UHPFRC.The experiment revealed that:(1)when superfine powder replaces some silica fume in UHPC,it can improve the fluidity and compressive performance of UHPC,and in most cases,it is not good for bending strength.The effect of plastic silicon powder and superfine slag powder on UHPC performance is the best.And the performance of UHPC is improved by submicron silicon.Superfine silicon aluminum powder reduces the work performance of UHPC.The plastic silicon powder can increase the compressive strength and reduce the compressive strength and flexural strength when the mixing amount is too large.Submicron silicon can significantly improve the compressive strength of UHPC and reduce the flexural strength slightly.The compressive strength of UHPC can be improved when the content of superfine silicon aluminum is less than 30%.The superfine slag powder increases the compressive strength of UHPC first and then increases,and the flexural strength is slightly reduced.(2)When superfine powder replaces some cement and silica fume in UHPC,the compressive strength is significantly improved,and the strength increased first and then decreased with the content of mixing.When the superfine powder is mixed,each superfine powder is mutually beneficial and complementary,and the strength of the optimal proportion of all the composite groups is greater,and the fluidity is better than that of the benchmark group.Among them,the UHPC is the most liquid when the silicon micropowder and the submicron silicon material are doped.The maximum compressive strength of superfine silicon aluminum powder and superfine silicon powder is 151.6 MPa,which is slightly less than that of the reference group.When superfine powder is added composite,UHPC porosity decreased and pore size distribution was more uniform.(3)The utilization of steel fiber is affected by the mobility of the matrix,and the large flowing matrix can make the steel fiber better dispersed and improve the utilization rate,so that UHPFRC can reach a higher intensity.Compressive strength of UHPFRC of good matrix fluidity increases with the increase of steel fiber content,the highest can be increased by 34.7%,the compressive strength value of 191.8 MPa.The strength of UHPFRC with high strength but insufficient fluidity is not significant with the increase of steel fiber content.