Study On Predictive Feedback-based Techniques For Quality Control In Structural Concrete Construction

At present time the mainly means of the concrete quality control is that when the fresh concrete was cast, the concrete specimens were left and cured for 28 days in 20±1℃water or atmosphere, and then test standard compressive strength or flexible strength as the basis of evaluating the strength grade of concrete. But this quality control method has two limitations:(1)Hysteresis. The specimens are cured for some days in laboratory; but in site, the concrete in the real structure has been already hardened. By then if we find the properties of concrete specimens are not fit to the designed requirements, it will endanger the structure safety and increase the expense of mending later.(2)Diversity. In traditional quality control approaches, the methods of cast, the size of concrete structure, and the condition of curing between the specimens and concrete in site are different. So, the compress strength of specimens in the laboratory does not represent the actual strength of concrete in structure.This dissertation relied on the Wuhan-Yichang expressway reconstruction project in Hubei province. In this dissertation, a new technology named Predictive Feedback-based techniques for Quality Control (PFQC), about quality control of concrete construction, had been set up, after comprehensively reviewed and analyzed through the overseas and domestic investigations of fresh concrete. Water weight and cement weight per cubic meter, water to cement ratio, slump and strength can be fast predicted by this technology. And the states of concrete's later strength development also can be monitored and predicted through the application of PFQC.The results showed that: for the normal concrete, the error of water weight per cubic meter predicted by the PFQC is between of±10%, the error of cement weight per cubic meter is 2%, the error of water to cement ratio is 4%.The density of fresh concrete correlated with the water weight per cubic meter perfectly. PFQC used the theory of concrete rheology and maturity to predict the concrete's strength of 28 days in site.PFQC was applied in Wuhan-Yichang expressway reconstruction. This technology controlled the quality of concrete in advance, and whether the designed mix proportion was carried out or not in site could be known, some suggestions were given. The traditional quality control method was also applied to control the quality of concrete in this project. The quality of Han-Yi expressway reconstruction had been controlled by the two methods, and had well benefited in the economy and society.PFQC correlated with the traditional quality control methods perfectly, and it is fast, convenient and exact. The application of this method is the basis of the quality advance prediction in concrete projects.