Study On Quantitative Analysis Of Concrete Under Compressive Loads And Initial Defects

Concrete has been the most widely used material in the world.Since its invention in the 19 th century,researchers have never stopped testing and studying its aging,damage and failure mechanisms.Based on the self-developed concrete panoramic microcrack quantitative analysis technology,the damage and failure mechanisms experiments of concrete under monotonic and cyclic compression loads is carried out,and the quantitative analysis of initial defects under inadequate curing is carried out based on the actual engineering.The relationship between the evolution laws of microcrack structure and the change of macroscopic performance in concrete was studied.In order to explore the damage mechanisms of concrete under mechanical loads,low-strength and high-strength concrete were selected to study the initiation and propagation of internal microcracks during compression loads.The damage and failure mechanisms tests of concrete under multi-load levels(10%-80%)under monotonic compression loads was carried out,and the evolution laws of microcracks inside the concrete was obtained,which was related to the macroscopic performance.The results show that the damage degree,microcrack density and the width of microcrack increase with the increase of load levels,and there is a good linear correlation between microcrack density and damage degree;microcrack density,average width and maximum width of high-strength concrete is larger than the low-strength concrete;the matrix microcracks caused by the compression failure process are mainly transition zone microcracks;with the increase of the load level,the diversity of the microcrack width gradually increases,and the distribution of the microcrack width gradually approaches to normal distribution;the direction of microcracks will show a preferential orientation that expands along the direction of the load as the load level increases.Based on the experimental experience of monotonic compression load,the damage and failure mechanism of concrete under cyclic compressive load(repeated 10 times during preloading)at low load level(10%-30%)was further tested,and the evolution law of microcracks inside the concrete was obtained.Then established a relation with macro performance.It is found that the evolution law of concrete microcracks under low load level cyclic compressive load is similar to that of concrete microcracks under monotonic compressive load of 70%～80% load level,indicating that that the cyclic loading at lower load level will still cause great damage to the interior of concrete.At the same time,based on the actual project,the quantitative analysis of the initial defects of concrete under inadequate curing was carried out.The main test contents include macroscopic performance test based on mechanical property test,temperature and humidity monitoring and quantitative analysis test of initial concrete defects.The evolution law of the initial defects of full-graded and two-graded aggregate concrete was obtained,and the relation with macro-performance was established.The study found that the strength of fully cured concrete is developing well,and the strength of concrete with insufficient curing is significantly reduced.The mechanical properties of concrete have a good correlation with the initial microcracks.To reduce the initial defects of concrete,ensured that the concrete has excellent microstructure and mechanical properties,full maintenance work should be done in site construction,and it is recommended that the age of curing should be at least 21 days.