Research On Ohmic Curing Of Properties Of Seawater Cement-Based Materials In Negative Temperature Enviorment

It is a big problem that the concrete structure cannot form strength in severe cold area.The traditional winter concrete construction method is not suitable for the maintenance work in severe cold area due to the disadvantages of large energy consumption and slow strength formation.At the same time,the coastal severe cold area is rich in seawater resources.If the seawater is used to prepare concrete,it will greatly reduce the construction cost.Therefore,once the content of chloride ion in the components is limited within the scope of national standards,the use of seawater to prepare concrete will become a feasible scheme for future facility construction.Ohmic heating curing as a curing method exhibits the advantage of fast formation for early strength under severe cold environment.Under this circumstance,if the content of harmful chloride ion can be reduced during the process of ohmic heating curing,it can be used as a new way of construction and maintenance in severe cold coastal areas.In this paper,carbon fiber was used as conductive phase to construct conductive network in seawater cement-based materials.The ohmic heating effect of carbon fiber is used to generate ohmic heating inside seawater cement-based materials to ensure the curing temperature under low temperature environment and accelerate the early strength formation.At the same time,the effects of ohmic heating curing on the mechanical properties,free chloride ion content and micro characteristics of seawater cement-based materials were studied.The strengthening mechanisms of mechanical properties and chloride ion binding of seawater cement-based materials were also studied.The main research contents and achievements are as follows.Firstly,the preparation process of carbon fiber seawater cement-based materials was studied.Through a series of experiments,the resistance and electrothermal stability of fresh seawater cement-based materials were analyzed,and the appropriate preparation process was determined to ensure that the matrix has a good conductive path;The gradient ohmic heating curing strategy was utilized to reduce the thermal expansion effect of fresh seawater cement-based materials in the acceleration stage.The effect of alternating electric field on binding chloride ion in seawater cement-based materials during ohmic heat curing was studied,and the bonding mode of chloride ion in seawater cement-based materials under alternating electric field was reasonably speculated.Secondly,the mechanical properties of seawater and fresh water cement-based materials under different curing conditions were studied.It was found that the formation of early strength of seawater cement-based materials could be accelerated with ohmic heating curing under low temperature.The pore structure,hydration products and chloride ion amount of the above experimental groups were studied and analyzed by scanning electron microscope(SEM).The test results showed that the hydration products of seawater cement-based materials were more complex than those of fresh water cementbased materials,and the harmful pores affecting mechanical properties were less.The above advantages are further enhanced in ohmic heating cured sea water cement-based materials.In addition,ohmic heating curing has a significant effect on the improvement on binding chloride ions of seawater cement-based materials.Finally,in order to improve the mechanical properties and lower chloride ions of seawater cement-based materials,it is suitable for more severe working conditions.In this paper,metakaolin is taken as an example to study the mechanical properties of metakaolin seawater cement-based materials cured by ohmic heating in negative temperature environment.The optimal content of mechanical properties is 15%,and the optimal content of chloride ion is 10%.The pore structure and hydration products of ohmic heating cured seawater cement-based materials under negative temperature were studied.The results of mercury intrusion method(MIP)and thermogravimetric analysis(TG)showed that the addition of metakaolin could further promote the formation of more hydration products in the sample and improved the mechanical properties of the samples;The content of harmless pore was increased and free chloride ion was reduced.