Research On Deformation Development And Cracking Sensitivity Of Ultra-high Volume Fly Ash Dam Concrete At Early Age

Gezhouba group test co.,LTD and Zhejiang University of Techonlogy has prepared and systematically studied high-volume fly ash conventional dam concrete.The study found that the concrete mixed with as high as 80%fly ash can also meet the basic specifications required by the dam design.But the ultra-high volume fly ash dam concrete still need more new powerful supportive test data to be approved and widely used,especially in the aspect that the research of the deformation development.This is because the deformation induced by the change of temperature field and humidity field as well as chemical reaction,during the the setting and hardening,may lead to cracking of concrete and reduce the dam’s service life.“standard concrete” and “ultra-high volume fly ash conventional dam concrete(UHVFACDC)” were prepared,refer to the concrete mix design provided by the Gezhouba group test co.,LTD.This dissertation has emphatically studied the evolution rules of thermal deformation,autogenous shrinkage deformation and creep deformation about UHVFACDC at early age,based on the temperature-stress testing machine(TSTM),refer to the standard concrete.Besides,this dissertation also studied the cracking sensitivity difference at early age between two kinds of fly ash concrete,combining uniaxial direct tension test and TSTM.Two kinds of fly ash dam concretes cured by two modes,i.e.adiabatic curing and temperature matched curing(TMC),were studied through the TSTM.No matter what kind of curing mode,shrinkage deformation and thermal deformation would occur at the same time under the variable temperature curing.Based on the maturity theory of concrete,this dissertation figured out the heat expansion coefficient and thensuccessfully to separate thermal deformation and autogenous shrinkage deformation,by a deformation development contrast under two kinds of curing modes.The mathematic model were established to describe the development law of heat expansion coefficient and autogenous shrinkage deformation,using the method of the equivalent age.The study found that both thermal deformation and autogenous shrinkage deformation were small for UHVFACDC,that is benefit to improve the crack-resistant of concrete.Refering to the method proposed by Bentur,creep deformation was isolated by contrasting deformation development between restraint specimens and unrestraint specimens through the TSTM.Then the creep degree and creep-shrinkage ratio of the concrete were calculated,the results showed that there was almost no difference in terms of the characteristics of creep between standard concrete and UHVFACDC.Uniaxial direct tensile experiments were carried out to fit the tensile strength development curve of concrete at early age.Then stress-strength ratio development curve were gained in the cooling stage,on the basis of the development course of restraint stress measured by TSTM.It was found that the UHVFACDC showed lower cracking sensitivity,whether adiabatic curing or temperature matched curing,compared with standard concrete.