Study On Mechanical Property And Cracking Resistance Evaluation Of Ultra-high Volume Fly-ash Concrete

With the constant development of concrete technology,fly ash as a mineral admixture in concrete engineering applied more widely.But the content of fly ash in concrete is generally low,increasing the content of fly ash in concrete can improve its performance.Cracking in concrete is destructive not only to appearance and performance,but also to durability of structures.So for high volume fly ash concrete,accurately study of crack resistance is one of the key issue.In this paper,taking the fly ash content of 35% concrete that have been put into practical engineering as reference concrete,using slurry volume method to configure fly ash content of 80% concrete that called ultra-high fly ash concrete,and according to the early mechanical properties and the index of crack resistance to study their crack resistance.The main contents are as follows:1.Ordinary content fly ash concrete and ultra-high content fly ash concrete were experimented with the temperature stress testing machine(TSTM).The straint conditions was 100%.The pattern was temperature matched and adiabatic.By Bentur’s method of measuring their creep and using Kanstad’s elastic modulus development model to calculate the stress relaxation capacity.Analyzing the development of the restraint stress of two kinds of concrete,and put forward the evaluation method of early crack resistance.Conclusion: The creep in early age of ultra-high volume fly ash concrete was superior to ordinary volume fly ash concrete in TMC pattern,but slightly worse than ordinary volume fly ash concrete in adiabatic pattern.The stress relaxation ability in early age of ultra-high volume fly ash concrete is better than ordinary volume fly ash concrete.From the crack evaluation method,the crack resistance of ultra-high volume fly ash concrete is better than ordinary volume fly ash concrete.2.The basic mechanical properties such as compressive strength,tensile strength,ultimate tensile elongation and elasticity modulus of ordinary content fly ash concrete and ultra-high content fly ash concrete were measured.Then,according to the concept of equivalent age and fitting formula,taking compressive strength,tensile strength,ultimate tensile elongation and elasticity modulus to convert into basic mechanical properties after considering the temperature factor.Next,calculating the ratio of adiabatic temperature and tensile strength,the ratio of elasticity modulus and tensile strength and the ratio of compressive strength tensile strength.Lastly,two kinds of concrete crack resistance were evaluated with ultimate tensile elongation and three kinds of ratio.Conclusion: The ratio of adiabatic temperature and tensile strength and the ratio of elasticity modulus and tensile strength of ultra-high volume fly ash concrete is better than ordinary volume fly ash concrete.But ordinary volume fly ash concrete is better in ultimate tensile elongation and the ratio of compressive strength tensile strength.