Strength Prediction Of Cement-based Materials Based On Microwave Open-ended Probe Methods

Cement-based materials are indispensable materials for civil engineering construction and come in a wide variety.Concrete is a traditional and commonly used cement-based material,but its characteristics such as heavy,brittle and poor seismic performance are difficult to withstand increasingly frequent natural disasters such as floods and earthquakes.Therefore,high specific strength materials typified by ultra lightweight cement composites(ULCC)and high seismic materials represented by engineering cementitious composites(ECC)have been extensively studied and used.Nowadays,the quality requirements of cement-based materials are getting higher and higher,and it is of great theoretical and practical value to carry out research on the strength of cement-based materials in early age prediction.Basd on microwave electromagnetic characteristics,this topic takes Chinese-standard concretes,lightweight cement composites,ultra lightweight cement composites and engineering cementitious composites as research objects,and early prediction of cement-based material strength for research purposes.The following parts are carried out:(1)Four kinds of cement-based materials are used to make up the materials and their chemical and physical parameters are introduced.According to the test content,the test block is poured and maintained.The traditional mechanical properties of three kinds of water-binder ratio Chinese-standard concretes,three kinds of water-binder ratio lightweight cement composites,three kinds of water-binder ratio ultra lightweight cement composites composites and three kinds of water-binder ratio engineering cementitious composites were studied on the 3th,7th,14 th and 28 th day after demoulding.The results show that the strength of the four materials increases with the increase of age and the decrease of water-binder ratio,and the strength of the same water-binder ratio material increases with the increase of fiber and cement content.(2)The open-ended coaxial probe method was used to measure and analyze the electromagnetic properties of the first three materials for one week.The experimental results show that the dielectric constant and loss factor of the three materials at early age decrease with the increase of age,and decrease with the decrease of water-binder ratio and cement dosage.Using the open-ended rectangular waveguide method,the electromagnetic properties of the engineering cementitious composites were measured and analyzed for one week.The experimental results show that the equivalent conductance decreases with the increase of age and decreases with the decrease of water-binder ratio.(3)The traditional mechanical test data of four kinds of materials are analyzed by using MATLAB,and a unified relationship model between compressive strength,flexural strength and age is established.At the same time,the above electromagnetic characteristics data were analyzed,and the relationship models of dielectric constant,loss factor,equivalent conductance and age were established.Taking the age as the intermediate variable,a unified dielectric constant prediction strength model,conductivity prediction strength model and equivalent conductivity prediction strength model were finally established.(4)The traditional Jonscher model is improved,which has a wider operating bandwidth and can locate the minimum loss factor of cement-based materials.The appearance of the minimum loss factor has been analyzed by using molecular theory,and the corresponding frequency of the minimum value is further verified by using Cole-Cole model.The real variation of loss factor of cement-based materials has been revealed by using the improved model proposed in this paper.