Strength Prediction Of Early-Age Cement-Based Materials Based On Microwave Properties

Nowadays,cement-based materials?CBMs?,which are made up of water and Portland cement,are one of the most vital building materials in the world.In particular,concrete is the most consumed and widely used building material in modern civil engineering.However,since concrete is brittle material,it is difficult to meet the demand for ductility of materials in the practical engineering.Therefore,the high ductility fiber reinforced cement-based materials represented by Engineered Cementitious Composite?ECC?have been highly valued by researchers.At present,the traditional method used for evaluate the quality of concrete in China is comparing the compressive strength of the cubic specimens of concrete with the standard value of compressive strength(f_cu,k).However,it is time consuming with a long maintenance period and it is hard to reflect the true state of the CBMs on the structure by using this evaluation method.Based on this,it is particularly important to predict the strength of cement-based materials on structure in the early age.At present,the methods for evaluating concrete strength widely used in the engineering field have the disadvantages of increasing the porosity of concrete and so on.The development of nondestructive testing?NDT?provides a new approach to predict the strength of CBMs in the early-ages.The strength of CBMs can be obtained without destroying the test specimens via means of sound,electricity,heat and light.In this paper,two kinds of CBMs,namely,Chinese standard concrete and engineered cementitious composite?ECC?were investigated.The objective of this research is to predict the strength of CBMs with different water-to-cement/water-to-binder ratio in the early-ages by using NDT techniques.The main work is described in the following statements:?1?Four types of Chinese standard concrete specimens conforming to the national standard were obtained based on the design of the mixture.Next,the compressive strength of Chinese standard concrete was obtained at the age of 3d,7d,14d and 28d.Meanwhile,the complex permittivity of Chinese standard concrete was measured within one week after demolding.In addition,the rebound number test was carried out after 28d curing.?2?The variation of the complex permittivity of Chinese standard concrete in the frequency range of 0.03¹0.03 GHz was analyzed and fitted by modified Jonscher model.Then the regression models between complex permittivity and the age of concrete were obtained.After that,the correlation model between compressive strength of concrete and the real and imaginary parts of the complex permittivity was respectively established by using MATLAB.?3?There types of ECC specimens conforming to the national standard were obtained based on the design of the mixture.Next,the compressive strength and the flexural strength of ECC were obtained at the age of 3d,7d,14d and 28d.Meanwhile,the effective conductance of ECC was measured within one week after demolding.?4?Based on the regression analysis of the test results,mathematical models between compressive strength of ECC and age was firstly established.The regression models of flexural strength and effective conductance of ECC with age were obtained in the same way.Secondly,the correlation models between effective conductance and compressive strength and flexural strength are deduced via data mapping.Finally,the relations between compressive strength and flexural strength of ECC were obtained based on the predicted data,and verified with the measured data.