| Concrete is widely used in construction,water conservancy,ports,highways,bridges and other fields.The quality of concrete structures is closely related to the safety of people’s lives and properties.Therefore,quality assessment of concrete has become an important topic in the field of civil engineering.Concrete strength is the most important parameter for evaluating the quality of concrete,and stress waves play a very important role in concrete strength testing.Traditional ultrasonic testing uses compression waves(P waves),but the corresponding relationship between P-waves speed and concrete strength is affected by the porosity and moisture content of the concrete,so it is impossible to establish a unified standard when using P waves for strength testing.The corresponding relationship between the wave speed of the shear-horizontal waves(SH waves)and the concrete strength is not affected by the porosity and moisture content of the concrete,which makes it possible to establish a unified testing standard.In this paper,a research on non-destructive testing of concrete strength based on shear-horizontal waves is carried out.The specific research contents are as follows:(1)The current research status of non-destructive testing of concrete strength in our country and abroad is introduced,and the current problems of ultrasonic testing of concrete strength are found,there are many influencing factors and it is difficult to establish a unified testing model.(2)The propagation characteristics of stress waves in concrete and the relationship between the speed of waves and concrete elastic modulus are studied.An experiment was designed to study the relationship between the speed of P waves and SH waves passing through the concrete,and the relationship between the concrete elastic modulus and the dynamic elastic modulus was studied through the elastic modulus experiment.(3)The influence of porosity and water content on the propagation of stress waves in concrete is studied.The porosity and water content of the specimen were changed by adding air-entraining agent and soaking the them in water respectively,and the changes of the velocity and energy of the two kinds of stress waves under different porosity and water content were obtained.(4)The strength detection regression models based on stress waves are established.The wave velocity test and rebound test of concrete have been carried out.The stress velocity of waves and rebound value of each group of concrete were measured,and then the compressive strength of the corresponding concrete was measured through the compressive strength test.A single factor regression model based on stress wave velocity and a two factors regression model based on stress wave velocity and rebound value were established respectively.(5)The fitting relationship was verified.Verification experiments were designed to compare the measured strength of concrete with the strength conversion value obtained by using the regression model,and the accuracy of the regression model based on SH waves was proved. |
