Research On Early Prediction And Evaluation Methods Of Quality Of Concrete

That the performance of concrete at later ages can be predicted and the quality of concrete can be evaluated just within several hours or much shorter time after casting the concrete have been imperative issues for more and more people worked in concrete field. As we all know, water cement ratio and compressive strength of concrete are very important index to control the quality construction of concrete. How to measure water cement ratio and predict compressive strength of concrete at later ages, and then discover existing problems in time and response quickly to resolve the problems will be significant investigations in promoting durability and construction technology of concrete engineering.This paper mainly includes three parts: microwave heating was applied to measure water cement ratio; using microwave accelerated curing method to predict the compressive strength of concrete at later ages; the rules of ultrasonic velocity changed with the setting and hardening time were applied to monitoring the process of hydration of different mix proportion concrete and further to evaluate the quality of concrete.The results show that there existed three phase during the heating process of fresh concrete and mortar heated by microwave. They are evaporation at slow rate at initial one or two minutes, evaporation at high speed for several minutes and invariableness of weight. Ten minutes will be enough to complete the measurement of water/cement ratio of concrete. The water/cement ratio measured by screened slurry of concrete was a little more accurate than that of concrete.P20(45)+interval 160min+P20(40)+interval 160min was confirm to the optimal microwave accelerated curing system to predict the compressive strength of concrete at ages in this investigation. The experimental results proved that there existed a good relationship between 6h-compressive strength cured by microwave and 7d or 28d compressive strength cured in standard curing environment. The predicted equations are designed. The error range of prediction is within±9% ,±13%, respectively.The ultrasonic velocity of fresh concrete changed with the change of process of the setting and hardening of concrete. At initial phase the ultrasonic velocity of fresh concrete increased rapidly and then got stable gradually after 7 days. By monitoring the curve of ultrasonic velocity-time of fresh concrete in field and contrastively analyzing the curve of ultrasonic velocity-time of designed concrete in the lab, the quality of concrete in field can be predict at early ages.