Research On Influence Of Creep Of Fly Ash Concrete At Early Age On Cracking Sensitivity

With the vigorous development of the social economy,the urgent demand of the natural environment protection and the rapid production and application of various additives,the fly ash concrete have been widely used.At present,the fly ash has been used as an independent component to add the concrete,and the proportion of the more and more large.However,the standards or regulations of many countries,including our country,have a limited amount of fly ash content.Our school and Gezhouba group company through the experimental study of the high content of fly ash concrete,found that the amount of fly ash reached 80%,the configuration of the concrete can still meet the basic requirements of the dam.High performance concrete can be made by adding fly ash in concrete,can effectively improve the durability of concrete and reduce the cracking sensitivity of concrete.In this paper,based on the practical engineering application of the 35% volume of fly ash concrete as the reference concrete,preparation the 80% volume of ultra high volume of fly ash concrete,the mechanical properties and cracking sensitivity of concrete at early age were studied based on the temperature stress testing machine(TSTM).Two kinds of fly ash concrete under the full constraint conditions were tested by adiabatic mode and temperature matching(TMC)model,and the restraint stress of two kinds of early-age concrete was measured by TSTM.According to the Kolver’s creep test method,the creep of the two kinds of concrete was separated out,and the evaluation indexes such as the creep coefficient and the specific creep are obtained.It was found that the thermal condition had great influence on restraint stress and creep properties of the same kind of early-age concrete,the higher the temperature was,the greater the restraint stress and creep was.The growth rate of creep in the early-age concrete under the same curing mode is larger,by comparison of creep coefficient and specific creep,the creep properties of the two kinds of concrete was no different.The relaxation coefficient of two kinds of early-age concrete was calculated based on the Kanstad’s elastic modulus model,and the stress relaxation degree of two kinds of early-age concrete creep was analyzed,the stress relaxation was compared.The study results show that early-age ultra-high volume fly ash concrete stress relaxation ability was better than that of ordinary fly ash concrete.Creep can relax 15%~60% restraint stresses in early-age reference concrete,and creep can relax 25%~90%can relax 15%~60% restraint stresses in early-age ultra-high volume fly-ash concrete under full restrain condition and temperature matching mode.Based on the test results of the basic mechanical properties,the development of the tensile strength of the two kinds of concrete was fitted,calculate the early-age concrete cracking sensitivity coefficient.Based on the proposed comprehensive crack resistance index of new analytic hierarchy process,and compared the advantages and disadvantages of two kinds of crack resistance of concrete.The results showed that the cracking sensitivity of the early-age ultra-high volume fly ash concrete was lower than that of the reference concrete,which was beneficial to the practical engineering.