Research On Acoustic Characteristics In The Hardening Process Of Concrete

Concrete is a multi-phase composite material formed by mixing cement or admixture with sand and stone and water(which may contain admixture)in a certain ratio.Condensation hardening is a key factor in the formation of concrete mechanical properties.The quality control of the condensation hardening process has a great impact on the quality and safety of buildings.Among many factors affecting the performance of concrete,the water-cement ratio is an important indicator,which not only affects concrete slump but also affects the setting time.Acoustic wave detection technology is a high-precision,widely used non-destructive testing technology.Considering the change of acoustic characteristics in the condensation hardening process,the acoustic wave nondestructive testing technology is applied to the concrete hardening process to establish the relationship between concrete slump,penetration resistance and acoustic wave characteristics.The main research contents and results are as follows:(1)A detection device for concrete solidification and hardening process,including mold,excitation and receiving transducers was designed.The device was used to study the changes of acoustic characteristics during concrete setting and hardening under different water-cement ratio conditions.The results show that with the increase of time,the longitudinal wave velocity increases gradually.At the same time,as the water-cement ratio increases,the longitudinal wave velocity decreases.The curve of the main frequency of concrete with time shows a three-stage change trend.The main frequency change is small at the beginning of the period,and then increases slowly with the age.After the initial setting,the main frequency increases rapidly and remains basically unchanged after the final condensation.(2)The relationship between slump and longitudinal wave velocity is established by experiments,which can be used to evaluate the change of mass during the process of concrete condensation and hardening.At the same time,the initial and final setting time of concrete was measured by the penetration resistance method.The variation of penetration resistance in different time periods was analyzed,and the relationship between penetration resistance and longitudinal wave velocity was established.The results show that the quadratic function can better reflect the relationship between slump and longitudinal wave velocity and slump loss rate.The relationship between penetration resistance and longitudinal wave velocity can be fitted by power function model.(3)The gradation of coarse aggregate and the influence of water-cement ratio on acoustic characteristics were studied by finite element method.The acoustic characteristics of ultrasonic waves propagating in concrete were simulated by establishing a two-dimensional concrete physical simplified model in the random distribution of coarse aggregates.The results show that the aggregate has an effect on the concrete wave velocity.The more the aggregate quantity in a certain range,the more obvious the wave velocity enhancement,the wave velocity decreases with the increase of the water-cement ratio,and the first wave amplitude increases with time.The law of variation of the dominant frequency is not as obvious as the change of the wave velocity.In this paper,the acoustic characteristics of concrete condensation hardening process are studied,which provides theoretical and practical guidance for evaluating the quality of concrete consolidation and hardening process by using acoustic wave characteristics,and promotes the detection of concrete condensation hardening process towards artificial intelligence.