High-performance Concrete Shrinkage And Applied Research

Nowadays, cement concrete is a kind of manmade material used widely and have been applied in many different projects with the rapid development of the construction. Many scholars and experts predict that concrete will be a main construct material in the 21st century.High Performance Concrete (HPC) usually takes the high durability as a chief character. Developing HPC is one of the necessities of the development of building industry, is one of the demands of the environmental and ecological protection as well as sustainable development of economy , is one of the requirements of the increasing the life-span of the building.Usability of HPC has been a focus along with more and more applications and increasing failures of HPC. Shrinkage of HPC has become one of the hot issues in the building engineering especially. Free shrinkage of concrete has no bad influences. Restrained shrinkage of concrete is a main source of cracks in concrete. Concrete usually causes tensile stress when shrinkage of concrete is under restrained conditions. However, tensile strength or tensile strain of concrete at early age is very low. The cracking will occur when restrained shrinkage stress exceeds tensile strength or when restrained tensile strain exceeds permissible tensile strain of concrete at early age.This paper develops a new and simple test method for measuring shrinkage of HPC aimed at one of the hot issue in the field of concrete research—shrinkage of HPC, called the method of improved ring shrinkage test. The apparatus, procedure, principle and applicability for this new test method are discussed especially. The new test method can be used to study free and different degree restrained shrinkage of HPC, discuss the tendency of shrinkage cracking and HPC behavior due to restrained. It overcomes the shortcoming of conventional ring test which can not provide the datum of stress .It also has some characters of uniaxial test which can identify some parameters of HPC at early age and evaluate the cracking of HPC as well as mechanism of cracking.Concrete technology has been developing differently in different areas of china. In southeast, concrete technology has been used in high level. But in northwest, concrete technology is in low level. The shortcomings of concrete mixes with ordinary strength in Lanzhou are analyzed and some solutions are presented to the problem of how to realize changing concrete with ordinary strength to Green High Performance Concrete (GHPC) according to the development of concrete technology in Lanzhou and the effects of fly ash on concrete are summarized. Through experiments of the effects on concrete performance of different fly ash content in concrete and the experiments of the restrained shrinkage of Fly Ash concrete, concrete mixes are optimized and used inpractice. Experimental results show that GHPC can be obtained certainly by using materials of local and Fly Ash concrete is just GHPC, which has more perfect workability and performance than concrete with ordinary strength generally used in Lanzhou. As the addition of strength-increased at early age causes greater increase of shrinkage and enhances the possibility of shrinkage cracking, we should be cautious of using the addition of strength-increased in Fly Ash concrete.