Research On Frost Resistance And Related Transmission Performance Of Conductivecement Mortar Cured By Ohmic Heating In Negative Temperature

Ohmic heating curing as a new winter construction method in the cold region has broad prospects.It can overcome the shortcomings that traditional winter construction methods cannot be used in large areas.This method also does not require additional facilities such as heating sheds,which takes time and labor.And it uses clean energy such as electricity However,as a new maintenance method,its theoretical basis is still insufficient.At present,all research is limited to some short-term performance.In this paper,the method of ohmic heat curing is considered,and its application in cold regions is promising.The long-term service performance under freezing conditions is studied,and its microscopic analysis is carried out using scanning electron microscopy(SEM).At the same time,considering that some data that are critical to durability are very difficult to measure,even if it is measurable but time-consuming,starting from the most common durability problem,capillary water absorption and carbonization.The mechanism of water absorption and carbonization and the transmission mechanism were studied,considering the effects of freezing and ohmic heat curing on the transmission of moisture and gas.The main research contents and results are as follows:First,the effects of the preparation process and the carbon fiber content on the electrical and mechanical properties of cement mortar were studied.Finally,the improved co-doping method was used,and the 0.75vol% carbon fiber content was considered to be the optimal carbon fiber content;The curing process was optimized,using gradient power,and found that 30 W curing changed to 40 W curing after 12 h,which not only can quickly form strength,but also make the structure denser and reduce defects.Secondly,the effects of long-term mechanical properties,durability and microstructure of ohmic heat-cured specimens after reaching freezing critical strength,putting in negative temperature curing and then turning to positive temperature,were studied,setting standard curing as a control group.It shows that after the cement mortar reaches the design critical strength,even suffering from 28 d frost damage,its strength recovery rate is still above 95%,and its mechanical properties,durability and microstructure are better than standard curing samples at the same freezing time,which shows that the ohmic heat-cured sample has good frost resistance.Finally,the water migration mechanism of negative temperature ohmic heatcuring cement mortar was studied,a water absorption model was established,and the moisture distribution of ohmic heat-cured specimens was predicted;the existing carbonization model was improved,taking into account ohmic heat-curing and the effect of low temperature,and the carbonization depth of the ohmic heat-cured specimen under freezing was predicted,and the results were in accordance with the experimentally measured values.