Research On The Dam Concrete Water Content Measuring Instrument And Interlayer Performance

At present,two large arch dams a re under construction in China —Wudongde and Baihetan which are located in Yunnan and Sichuan.The valley is long and narrow,and the climate is hot.It is a typical dry-hot valley climate.During the construction,the surface moisture of concrete evaporates fast,whitening of the aggregate greatly shortens the allowable interva l between the layers.The harsh environmental conditions put forward higher requirements for construction control.Therefore,it is an urgent problem to study the performance change of concrete layers under dry hot wind conditions,determine the key indicators of the reaction concrete layers state and establish a set of control measures suitable for on-site construction.This paper based on the characteristics of the on-site environment of dry and hot wind,the research on the concrete moisture content meas uring instrument and the interlayer performance was carried out by using the test-based research method.The water evaporation,tensile strength permeability and microstructure of the concrete were mainly carried out under dry hea t and high wind conditions.The comparison of the water content measuring instrument,determine the use of TDR instrument for on-site water content measurement.The test results show that under dry and hot wind conditions,the water evaporation rate of concrete can reach 3-4 times under windless conditions.The long-term exposure to the conditions will rapidly develop the surface strength of the concrete and affect the bonding performance between the layers.Under high wind conditions,the tensile strength and impermeability of the layered concrete were significantly reduced.Scanning electron microscopy(SEM)and CT scanning were used to observe the microstructure of the layered concrete.There are many large and continuousl y distributed pores at the layers,and almost no coarse aggregate is embedded,which weakens the tensile strength and impermeability of the concrete.TDR was used in the normal concrete and roller compacted concrete in the field,and the effect was good.With the concrete water content as the key indicator,a set of water content early warning control system was established,which aims to monitor and control the on-site construction in real time.The system combines a computer and mobile(mobile phone,tablet,etc.)to establish a complete process from real-time acquisition,display to analysis and early warning.The layer control system obtains water content data by on-site water content measurement and enters the mobile end;the mobile end uploads the data to the computer end;the water content display function o f the computer end can view the measured water content change curve and its comparison with the designed water content.And meteorological conditions during the measurement period.On the other hand,the computer analyzes the deviation between the measured water content and the designed water content,and judges the deviation value.If the deviation exceeds the water content warning threshold,it sends an early warning message to the mobile terminal to remind the construction workers and the rear supervisors to pay attention.The layer is processed in time to achieve real-time control.