Preparation And Properties Of Solid Waste-based Low Viscosity And Low Shrinkage UHPC

This thesis aims at the contradiction between the urgent demand for ultra-high performance concrete(UHPC)materials in modern concrete structures and the high cost,high viscosity and large shrinkage of UHPC which limit its wide application.To find and prepare a solid waste-based ultrafine mineral admixtures to replace part of the cement or silica in UHPC,which can be used for the preparation of low-cost solid waste-based UHPC.Based on solid waste-based UHPC,the rheological properties of UHPC slurry are controlled through physical-chemical synergistic effects.A new three-element cooperative shrinkage inhibition system is established,including chemical self-excitation compensating plastic shrinkage,water release factor inhibiting self-shrinkage,and compound expansibility compensating dry shrinkage.The hydration reaction mechanism of UHPC with low viscosity and low shrinkage is also revealed.It provides theoretical basis and technical support for the design and application of low viscosity and low shrinkage UHPC.The high-activity ultrafine mineral admixture with specific surface area of 714m~2/kg,fluidity ratio of 99.1%,7 day activity index of 86.8%,28 day activity index of96.3%is prepared by mechanical ball milling with 1:1 mixture of water-quenched manganese slag and fly ash.The effects of ultrafine mineral admixtures,silica fume,cement-sand ratio and water-cement ratio on the workability,mechanical properties and heat of hydration of UHPC are studied by orthogonal test.The results show that the most suitable ratio is when the content of ultrafine mineral admixture is 10%,the content of silica fume is 10%,the ratio of cement to sand is 1.1,and the ratio of water to cement is 0.17.At this time,the fluidity of UHPC slurry is 261 mm,and the compressive strength at 7 d and 28 d age is 128 MPa and 154.6 MPa,respectively.The average hydration heat release of cementing materials in 3 days is 139.8 J/g.In conclusion,the prepared ultrafine mineral admixtures can replace 50%of silica fume for the preparation of UHPC,which is beneficial to the reduction of the cost of UHPC.On the basis of solid waste based UHPC,the rheological properties of solid waste based UHPC are studied by introducing fly ash cenosphere and modified polycarboxylic acid water-reducing agent(JN-PCE).The results show that the viscosity of UHPC slurry can be reduced by fly ash cenosphere,but the yield stress of UHPC slurry can be increased by excessive fly ash cenosphere.JN-PCE can significantly improve the rheological properties of UHPC slurry,and good rheological properties can also be obtained under the synergism of physical and chemical effects.Both of them can meet the grade requirements of slump expansion degree of self-compacting concrete SF2.The expansion of UHPC slurry is 730 mm and the viscosity is 202.4 Pa·s under the physical-chemical synergistic effect.Compared with the blank group,the mechanical properties of UHPC at 28 days are better under the physical-chemical synergy,and the compressive strength of UHPC at 28 days was 10.8%higher than that of the blank group.Based on the low viscosity UHPC,plastic expander is used to compensate plastic shrinkage,internal curing agent is used to compensate self-shrinkage,and composite expander is used to compensate dry shrinkage.The results show that the optimal low shrinkage performance of UHPC is achieved when the content of plastic expansion agent is 0.04%,the content of internal curing agent is 0.05%,and the content of composite expansion agent is 10%.The total shrinkage of UHPC in 28 days is 161με.The mechanism of hydration process of UHPC with low viscosity and low shrinkage is analyzed.It is found that the pore size of UHPC with low viscosity and low shrinkage under the coupling effect of ternary admixture increased,the harmful pores increased,and the micromorphology density is poor,which had adverse effects on the mechanical properties,but the mechanical properties could still reach more than 130 MPa.It can meet the actual requirements of engineering for the mechanical properties of UHPC and solve the problem of large shrinkage and cracking risk of UHPC.