Research On Restraint Stress,Relaxation And Cracking Sensitivity Of Ultra-high Volume Fly Ash Concrete

With the constant development of concrete technology,fly ash as a mineral admixture in concrete dam applied more widely.High volume fly ash concrete is a new type of high performance concrete,the early age cracking is one of the key issues in the study.In this paper,a study is made on the restraint stress caused by the thermal deformation and shrinkage deformation of the fly ash concrete at early ages.Experimental use the TSTM,studies that have been put into practical engineering ash content of 35% concrete and in the research stage of 80% ultra ash concrete in the full Constraints of the development law' early restraint stress and stress relaxation,based on the stress and relaxation,Combine cracking sensitivity and partial data parameters obtained from TSTM evaluate the early on fly ash concrete cracking sensitivity.The main work includes the following:First point:Study of fly ash concrete in 100% of full restraint conditions,the development process and the change law of the temperature deformation and the self shrinkage deformation are restricted to produce the restraint stress.By comparing the same kind of fly ash concrete of restraint stress development law under different temperatures,verify that the anti cracking performance of concrete is underestimated by the comparison of the adiabatic mode.At the same time,it is found that the high temperature rise will lead to the excessive stress of concrete,accelerate concrete cracking.Second point:By Banter 's method of measuring the amount of creep,analysis of the creep of 35% fly ash content concrete and 80% fly ash mixed with the mode of our temperature matching,the main factor affecting the early creep is the constraint stress,Interaction between them.Third point:by using Kanstad's elastic modulus development model and the concept of equivalent age,analyzes the influence of the stress relaxation effect caused by the viscoelastic behavior on the tensile stress of concrete.It defines the stress relaxation coefficient to the measured stress and elastic computing stress' ratio,the tensile stress relaxation degree of the concrete with 35% and 80% mixed with fly ash was calculated.In the end,the relationship between stress relaxation and cracking sensitivity is analyzed.The relaxation effect can be very effective to improve and enhance the anti cracking performance of concrete.Fourth points : by TSTM' parameters and calculations obtained by cracking sensitivity,analyze the Cracking sensitivity of two kinds of fly ash concrete.We put the parameter data into divided into comprehensive index,core index and detailed index 3 items,from these three aspects,we studied the anti cracking performance of two kinds of concrete,and based on the standard concrete to evaluate the high volume of fly ash concrete,the analysis of the core index is combined with the stress,creep and relaxation in this paper.in the end,found excellent performance of cracking performance in ultra-high content fly ash concrete.