Experimental Study And Theoretical Analysis On Cracking Performance Of Double-combined With Mineral Admixture Concrete

With the development of material and structure science of concrete, high performance concrete are extensively used in more and more projects, but consequently early age cracking of concrete structure are more and more serious. The early age cracking of concrete can lead to the concrete deterioration of engineering structures and affect the durability of the structure. Especially, express highway and tunnel appear many this phenomena, which had affected economical quickly development. Preparing the concrete that can resist cracking and research systemically of the early age cracking problem of concrete in theory and experiment will make good sense in reducing the arise of the early age crack of concrete structure, which will also improve the durability of engineering, guarantee the long-term quality and safety of concrete structures.This paper take cracking performance of double-combined mineral admixtures as main subject investigated, study the basic mechanic properties and shrinkage of double-combined mineral admixtures concrete in development, discuss different admixture quantity, polyacrylonitrile fiber and cement strength grade influence on cracking performance of concrete by ring test and slab test, and predict cracking age of concrete. At last, double-combined mineral admixtures concrete are studied in microstructure by X-Ray diffraction (XRD) and Scanning Electron Microscope (SEM), and analyze mechanism of good performance in resisting cracking.In the light of experimental results and theoretical analysis, this paper indicated: Proper admixture quantity can increase concrete cracking capability. Polyacrylonitrile fiber can improve concrete cracking capability. As cement strength grade increased, concrete cracking capability declined. The analysis of the early age crackinginfluencing factor, took the basic mechanical properties, shrinkage, creep and restrained level of double combined mineral admixtures concrete into consideration, and restrained shrinkage leading to tensile stress was established. Base on maximum tension stress theory, trying to relate concrete tensile stress to cracking age, the cracking age of concrete were well predicted. Double-combined mineral admixtures can improve interfacial transition zone and Ca(OH)2 crystal pattern, increase C-S-H gel quantity and make lots of type I C-S-H gel which had higher strength and more stable.