| Ultra-high performance concrete(UHPC)is an ultra-high strength cement-based material with high strength,high toughness and low porosity formed based on the preparation principle of reactive powder concrete(RPC)[1].Although in the past 30 years,in-depth studies have been carried out on ultra-high performance concrete(UHPC)and its components,the preparation process of UHPC of 150 Mpa is relatively mature under the condition of vibration and high temperature curing,but it is very difficult to prepare UHPC without special treatment,such as thermal curing,pressurization or vibration [2].There is a lack of research on UHPC with micro-expansion.Based on the engineering requirements of jingxiong high-speed prefabricated bridge,this paper studies the micro-expansion UHPC materials used for the piers and socket joints of prefabricated Bridges.Since the construction and maintenance conditions in the field are self-compacting and free from steam curing,this paper,different from the preparation conditions of most RPC and UHPC,studies the preparation of self-compaction and free from steam curing and free from steam curing and free from steam curing and free from steam curing and free from steam curing and free from steam curing and free from steam curing and free from steam curing and free from steam curing and free from steam curing and free from steam curing and free from steam curing and free from steam curing and free from steam curing and free from steam curing and free from steam curing and free from steam curing.In this paper,based on Dinger-Funk equation,the density of wet particles was verified by the method of bulk density test,and the influence of water-cement ratio and rubber-sand ratio on UHPC strength was studied.On the basis of the optimal mixing ratio,the UHPC with micro-expansion was prepared by studying the effects of expansion agent and shrinkage agent on the mechanical properties of UHPC and the limiting expansion rate.The research results show that:(1)the fluidity of mortar(290mm)and net slurry(195mm)of cementitious material can be regarded as providing the threshold value for the release of bubbles of the mixture,which can obtain a higher accumulation density,but the fluidity should not be greater than310 mm and 210 mm.Through the experimental test method of the packing compactness of wet particles,the cementitious material ratio calculated by the d-f equation is verified,andthe conclusion is drawn that the optimal mixing ratio of cement and fly ash microbeads is consistent with the calculation of Dinger-Funk equation,cement: fly ash microbeads=1:0.36.(2)under standard curing conditions,the activity effect of silica fume is limited,and it is unfavorable to fluidity,and the fluidity loss is large,so it needs to be mixed with fly ash microbeads.Considering the strength and fluidity performance comprehensively,the optimal content of UHPC and RPC is significantly different from that of most UHPC and RPC by 15%-30%.The optimal content of self-compacted UHPC is 8%.It is suggested that the cementing material ratio is cement: fly ash beads: silica fume =1:0.36:0.1.(3)because the Dinger-Funk equation is based on contains coarse aggregate and vibration molding of ordinary concrete,but for the self-compacting UHPC of the coarse aggregate,the calculation of mortar is lower,in the case of ensure fluidity,further reduce the water cement ratio,for the self-compacting UHPC,under low water-binder ratio,needs to be thicker size film layer,to obtain greater liquidity.When the rubber sand ratio is 1~1.2,UHPC with good fluidity can be obtained.Steel fiber can increase the toughness of UHPC.When the steel fiber content is more than 3%,it will adversely affect the fluidity of UHPC and affect the efficiency of steel fiber.The optimal mix ratio of UHPC is: cement: fly ash beads: silica fume =1:0.36:0.1.The rubber sand ratio is 1~1.2.When the steel fiber content is 2%,the 28-day compressive strength of 150 Mpa UHPC can be obtained.(4)the UHPC with 10% calcareous expansion agent content(using the limited expansion test method)can be cultured for 28 days with a slightly expanded UHPC and slightly improved compressive strength.Although shrinkage reducers can effectively reduce the contraction of UHPC,they will not produce expansion and reduce the strength of UHPC to some extent.By mixing 6% expansion agent +0.5% shrinkage agent,the UHPC with micro expansion can also be obtained,which has no effect on the strength.The increase of the limiting expansion rate will effectively limit the debonding of the contact surface between UHPC and concrete and improve the bonding performance of the interface with concrete.The debonding rate is inversely proportional to the limiting expansion rate. |
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