Application Research On The Rebound Method Of Pumping Concrete In Panjin Area

It has been 60 years since the rebound testing concrete technology appeared,the Hammer was introduced to China in 1950s,and rebound method was applied practically when the project scene began to test concrete strength.Because the operation of rebound method is simple,low costing,and will not damage to the concrete structure,it has been applied to accept and test the current age of concrete component main body in our country.Strength-measuring curve of concrete is evaluated through rebound method in the Chinese national standard.The curve was draw based on dates from 9843 specimens according to least square method,the strength-measuring curve is attained by regression.Owing to vast territory of China,performance of raw materials,construction technology,curing conditions in different regions are greater than the differences.It lead to the experiment value is not rather tally with the theory value which calculated by strength-measuring curve in the Chinese national standard.In order to reduced errors and increase accuracy of strength-measuring curve,this paper fitted strength-measuring curve of Pan Jin region with different compression strength,rebound value and carbonization value.These values of building components and specimens of concrete with different strength grades from C25 to C45 were tested after same curing conditions in Pan Jin.Strength-measuring curve and equation of concrete was obtained though regression analysis and Microsoft Excel.The concrete strengths predicted by the optimum regression equation were compared with the actual engineering value.According to the selection of mathematical modeling the following curve was established:①.The linear fit curves between the compressive strength of concrete member’s which under th e same curing condition and the rebound value;②.The binary fitting curve between the compre ssive strength of concrete member’s which under the same curing condition and the rebound val ue,carbonization depth of concrete member;③.The linear fit curves between rebound value-com pressive strength;④.The rebound value,carbonization depth-compressive strength’s binary fittin g curve.After curve fitting analysis.comparison and engineering validation,the linear fit curves of rebound value-compressive strength the exponential function(F1-2=0.0160R2.1463) correlation coefficients is 0.514,the correlativity is good,relative standard deviation is 10.9%.For the rebound value,the average relative error is 14.3%,carbonization depth-compressive stren gth’s binary fitting curve:linear function is F2-5=0.0730R1.783810-0.0247d,average relative error is11.3%,the relative standard deviation is 15.3%.According to the concrete specimen can get the fitting curve F1-6=-211.039+70.7087lnR-5.57511nd,the average relative error is 9.0%and the relative sta ndard deviation is 12.7%,which all of the error below the national standard requirements.The curve has been verified through the strength of practical project case in Pan Jin region.The results show that the fitted curve was the similiar to the actual measurement values approximately.It’s error within the permissible range.The accuracy of pumping concrete which was estimated though the curve was higher than the national standard recommended in the region.This curve could improve the accuracy of estimating structural strength of concrete by rebound method in this region.