Study On Evaluation Of Concrete Strength By Ultrasonic-rebound Combined Method

Ultrasonic-rebound combined method is a method of using ultrasonic meter and rebound hammer to test velocity of ultrasonic wave and rebound number.We use velocity of ultrasonic wave and rebound number to evaluate strength of concrete.Currently, among numerous nondestructive testing techniques,ultrasonic-rebound combined method is widely used in our country.There are many reinforced concrete and prestrssed concrete bridges in Heilongjiang province.However,a new request to the existing bridges is put forward along with increasing of traffic volume,special type vehicles appearing and reconstruction of roads. Whether the existing bridges can be used,we must evaluate their bearing capacity with testing technique.Strength of concrete is one of the major indexes for reference, especially for the existing bridges which have no sufficient technical data.Because of the large territory, variations in concrete quality, and improving of construction techniques,the unified curve of "Technical specification for detecting strength of concrete by ultrasonic-rebound combined method"(CECS 02:2005) is not suitable for the local condition, and cannot be used to evaluate the strength of concrete accurately.In this dissertation the local curve is established for detecting strength of concrete by ultrasonic-rebound combined method in order to evaluate concrete strength of the existing bridges eventually.All concrete test cubes of 150-mm side length are made up of cement,coarse aggregate, fine aggregate according to the optimum mixture ratio.All cubes are tested separately in specified age by ultrasonic meter,rebound hammer,and compression tester. Mathematical model of concrete strength,velocity of ultrasonic wave and rebound number is established by taking multivariate regression and error analysis.The local curve for detecting strength of concrete by ultrasonic-rebound combined method provides scientific approach and warrant for technical identification,consolidation and maintenance,and reasonable rehabilitation of existing bridges.Therefore,the local curve for detecting strength of concrete by ultrasonic-rebound combined method has extensive application foreground,and brings huge social benefit surely.