Control Method Of Concrete Layered Construction Based On Water State In Former Layer

The correct control method of layered construction is the key concern to ensure the quality of interlayer bonding during dam concrete construction.The research of this issue is of great significance and value on the safety and stability of dam.However,the construction control method is still difficult to fully guarantee the quality of the combination between the layers,and the main reason is that it can not achieve a comprehensive and accurate understanding of the former concrete.Therefore,it is necessary to further explore the accurate construction control method under the premise of deep research on the performance change of the lower concrete.In this paper,the control method of concrete layered construction is studied from three aspects: theoretical and experimental basis,achieving means and engineering application.Thus,comprehensive and correct construction control is gradually realized,as well as the optimization of construction programs.The main contents and innovative points of the paper are as follows.(1)The low-field nuclear magnetic resonance(NMR)tests of newly poured concrete were carried out.The total contents of water,the distribution of water content and the relaxation time of water molecules in the concrete with different ratio and materials,different environmental effects and different curing time are obtained in the test.Based on the comprehensive analysis of the water change mechanism,the model of water variation with time and space in newly pouring concrete is obtained and calculated by numerical method.And the relationship between water and concrete properties is discussed.The water state can more fully reflect the newly pouring concrete performance.(2)The interlayer strength of layered concrete with different ratio and materials,environmental effects and interval time is tested.The experimental results were analyzed and discussed.Based on the development model of concrete strength and the degree of real hydration,a method using water to predict the strength between the concrete layers is obtained.The prediction model is validated by water test and interlayer strength test results.(3)A simple and portable in-situ water measuring instrument is obtained by using the dielectric constant characteristics of concrete and the standing-wave rate method.At the same time the instrument has been improved to adapt to the construction site.The instrument measurement has a good linear relationship with the water content in the concrete.(4)Based on the prediction method of the interlayer strength,the control method of concrete layered construction using water state is obtained,and the control method examples are discussed.The surface reconstructing method is proposed,which uses deep concrete to alleviate the drying of surface concrete,to improve the quality of the warm joint.The process and problems of the concrete layered construction in Wudongde dam are discussed and analyzed.Compared with the penetration resistance value,moisture index can better guide the construction.Based on the water control method,the optimal construction scheme of roller compacted concrete is obtained.