Experimental Study On Strength And Fracture Behavior Of Dam Concrete

Accurate assessment of the cracking and overall stability of concrete structures is the core subject for super-high dam concrete engineering.The accurate analysis of this core subject is highly dependent on the assessment of true mechanical properties of fully graded concrete.To obtain the true mechanical properties of fully graded concrete,we tested the strength performance of full grade and wet screen second grade concrete,the fracture performance of full grade and wet screen second grade concrete,and the strength and fracture performance of full grade and wet screen second grade concrete under different temperature and humidity conditions.The main process and results of the paper are as follows:Four batches of full-grade and wet-screen second-grade concrete specimens were cast and formed at the construction site in spring,summer,autumn and winter.We performed tests for compressive strength,splitting strength,axial compressive strength and static compressive strength of concrete at different ages.We analyzed the changes of the strength properties for the full grade and wet second grade concrete and the conversion relationship between them.The results show that the compressive strength and splitting strength of the fully graded concrete in different seasons all reached the designed strength;the strength performance of the 365 d fully graded concrete is significantly higher compared with the designed age;the conversion relationship of the compressive strength and splitting strength between fully graded and wet screen concrete follows a normal distribution,and the conversion value with 95% confidence between the full gradation and wet screen concrete for compression and splitting strength are 0.68 and 0.62,respectively.Four batches of fully graded and wet screen second grade concrete wedge specimens were cast and formed at the construction site in spring,summer,autumn and winter for splitting tests.We analyzed the changes of the performance of the full grade concrete and the wet screen concrete and also the conversion relationship between them.The results show that the fracture parameters of the full-graded and wet-screened second-graded concrete in different seasons vary with age,which is mainly due to the difference in their equivalent age;the conversion value between the full-graded concrete with a test height of 750 mm cracks and the wet sieve second-grade concrete with 300 mm height ranges between 1.12 and 2.04,and the conversion value of unstable fracture toughness is between 1.09 and 1.64.Twenty groups of first-grade concrete wedge split-pull specimens were poured in 5 working conditions and 4 ages,and fracture tests of first-grade concrete under different temperature and humidity curing conditions were carried out.The effects of curing temperature and humidity on the fracture parameters of concrete was analyzed,and the relationship between the fracture parameters and the equivalent age period was established.The results show that the higher the curing temperature,the faster the fracture performance of the graded concrete increases.When the curing temperature is 40 ℃,the fracture toughness value of 14 d is basically the same as 28 d,which can be considered as the final fracture toughness of the material;for those with less than 3d,the effect of curing humidity on the fracture parameters of concrete was not obvious,but the cracking value increased with the increase of humidity after 3 days;based on NS equivalent age and FP equivalent age,the relationship of the fracture parameters and the equivalent age can be explained with a logarithmic function,and the correlation coefficients of the regression curves are all above 0.92,but the FP equivalent age is better,.