Study On Preparation Method Of Early Strength Ultra-high Performance Concrete

In recent years,with the increasing traffic volume,many highway bridges have suffered various degrees of damage.The defects and cracks on the bridge surface and bridge joints will not directly affect the bridge structure,but if not treated in time,with time The transition will inevitably lead to a decrease in durability and safety of the bridge.At present,how to effectively and permanently repair and strengthen bridges is an urgent problem we need to solve.Compared with ordinary concrete,UHPC has extremely high mechanical properties and high toughness and durability.Therefore,the use of UHPC for bridge deck surface defect repair and bridge joint reinforcement can effectively solve the problem of insufficient durability of conventional maintenance materials.Based on the study of the internal microstructure of UHPC,this paper proposes an ultra-high performance concrete composition design and preparation technique suitable for bridge repair with high early strength and relatively small early shrinkage.The main research is on the early strength components of lithium carbonate and nano-CaCO₃.The effects of blending and compounding on the early mechanical properties and early autogenous shrinkage of UHPC were as follows:?1?Lithium carbonate has no obvious influence on the fluidity of UHPC.Nano-CaCO₃ has a great influence on the fluidity of UHPC.With the increase of nano-CaCO₃ content,the fluidity of UHPC decreases continuously.When the dosage reaches 6%,the slurry The body is relatively viscous and has poor fluidity.The recommended dosage is 2%⁴%.The UHPC has good fluidity and the test piece is easy to form.?2?When the lithium carbonate and nano-CaCO₃ were separately mixed,the early strength of UHPC was significantly improved.When the amount of lithium carbonate was between 0.075%and 0.1%,the growth trend tends to be gentle,and th e highest compressive strength can be improved.About 44%,the 1d flexural strength increased by about 28%,but with the increase of lithium carbonate content,it will adversely affect the 28d strength of UHPC;the reasonable content of nano-CaCO₃ is about 3%,and the compressive strength of 1d is up to 45%.The flexural strength increases by 28%,and the strength of the matrix 28d is still enhanced.When the two materials are compounded,the 1d strength of UHPC is greatly improved due to the synergistic effect,and the 28d resistance is avoided due to the action of nano-CaCO₃.The compressive strength loss,the 1d compressive strength can reach 72.1MPa,the increase is 68%,the 1d flexural strength can reach 13.9MPa,the increase is 38%,the recommended dosage is 0.075%⁰.1%,nano-CaCO₃3%⁴%.?3?Both single-doped nano-CaCO₃ and lithium carbonate increase the early self-shrinkage of UHPC.Nano-CaCO₃ can increase the early self-shrinkage of UHPC by more than 50%in 2%⁴%dosage;lithium carbonate can increase the early self-shrinkage of UHPC by 16%⁶7%;the combination of lithium carbonate and nano-CaCO₃ will greatly increase UHPC.Self-shrinking value.?4?Under the combined action of lithium carbonate and nano-CaCO₃,due to the small radius of Li⁺ion,its strong polarization accelerates the destruction of the hydration protective film on the surface of cement particles,greatly shortens the induction period of cement hydration,and accelerates.The hydration rate of cement greatly improves the early mechanical properties of UHPC.On the other hand,due to the micro-aggregate effect of nano-CaCO₃,the structure of UHPC is more compact,which reduces its internal defects and improves the early mechanical properties of UHPC.?5?Through comprehensive consideration,select the composition of the rapid repair material of bridge deck defects,such as:water-to-binder ratio is 0.18,sand-to-binder ratio is 1.1,silica fume is 20%,fly ash and mineral powder are both5%,polycarboxylate superplasticizer is 1%?external blending method?,lithium carbonate and nano CaCO₃ are 0.075%,3%?both in proportion to cement content?;The composition ratio of the repairing and strengthening materials:the water-to-binder ratio is 0.18,the sand-to-binder ratio is 1.1,the silica ash content is20%,the fly ash and the ore powder are both 5%,and the polycarboxylic acid superplasticizer is blended.The amount is 1%?external blending method?,and the amount of lithium carbonate is 0.075%.