| The bond between steel strand and concrete is very important to the bearing capacity of the main structure of the bridge.In order to prevent corrosion and other diseases in the process of use,the organic coating based on epoxy resin and its derivatives is mainly used to protect it.However,the use of organic coating changes the ribbed structure of the steel strand surface,which may reduce the bond performance of the steel strand.With the increase of service time,durability problems such as aging and peeling will also occur.In addition,organic coating volatile toxic and harmful gases will also cause pollution to the environment.Therefore,it is necessary to explore a kind of bonding coating with good bonding effect,high performance,and environmentally friendly for bridge construction.Magnesium Phosphate Cement(MPC)has the characteristics of fast hardening and early strength,good bonding performance with steel and concrete,good compaction,environmental protection and no pollution,etc.At the same time,the material can effectively prevent the corrosion of steel bars by harmful ions such as chloride ion,and can be used as a potential new bonding coating.For this reason,three main experimental studies were carried out in this paper on the hydration characteristics of MPC,the bond strength between MPC and Portland cement-based materials and the application of bond coatings.The main research contents are summarized as follows:(1)The effects of borax on MPC strength and setting time were studied,and compound retarder was prepared based on the principle of pH optimization of reaction system to improve the performance of borax,and the improvement effect of compound retarder on the initial setting time of MPC was studied.Based on the compressive strength test,the effects of the cement-sand ratio,the specific surface area of magnesium oxide and the water-binder ratio on the early strength of the MPC were tested to find the corresponding mix ratio for the maximum compressive strength obtained by MPC.(2)The influence of specific surface area of magnesium oxide on the flexural bonding strength of MPC mortar and Portland cement-based materials was studied.Combined with the material selection research in content 1,four groups of three point bending bonding tests were designed for the combination of two kinds of specific surface area magnesium oxide with Portland cement mortar and concrete.By comparing the flexural bonding strength of different combinations,the bonding characteristics between MPC mortar and silicate cement-based materials under different magnesium oxide materials were analyzed,and the selected materials with the best bonding strength of magnesium oxide surface area were obtained.(3)Determine the bonding behavior of steel strand when MPC mortar of different thickness is used as bonding coating.In combination with the better specific surface area obtained in research content 2,MPC mortar of different thicknesses was designed as the central drawing specimens of steel wire bonding coating,and epoxy resin coating and unbonded coating were set as the contrast specimens.The bond failure modes,drawing loads and bond stress-slip curves of all drawing specimens were recorded by central drawing tests.Based on the above data,the effects of MPC coating thickness on failure mode,ultimate bond strength and drawing stiffness were analyzed.The MPC coating thickness corresponding to the maximum bond strength under this test configuration was obtained. |
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