Influences Of Fly Ash On Early-Age Mechanical Properties And Tensile Creep Of High Performance Concrete

Fly ash is one of frequently-used mineral admixtures in the construction industry.It has been used to replace a part of cement for making more durable and sustainable concrete.Fly ash makes it possible to reduce costs and to improve performances of concrete.Therefore,it often been used in productions of high performance concrete(HPC).Based on earlier studies on HPC early-age properties and performances by the author’s research team,by updating the experimental methods and increasing testing parameters,a more comprehensive study on the influences of fly ash on early-age properties of HPC mixtures,especially on mechanical properties and deformation characteristics is performed.Based on the experimental data,it is validated that the applicability of the modified ZC model on early-age tensile creep of HPC mixtures containing fly ash.The work in this thesis is expected to provide technical guidances for early-age cracking issue in the engineering applications of HPC.Within the scope of this thesis,main conclusions can be drawn as follows:(1)Since an addition of fly ash,early-age strength of HPC mixtures reduce.The higher the dosage of fly ash is,the lower the strength is.In comparison,the later-age strength of HPC mixtures containing fly ash is faster than mixtures without fly ash.It is can be predicted that fly ash HPC achieves the same or even higher strength than pure cement HPC.(2)An addition of fly ash can inhibit autogenous shrinkage of HPC mixtures and with an increase of the dosage of fly ash,the inhibition effect becomes more obvious.The inhibition effect of autogenous shrinkage is particularly significant before the age of 1 day.This can provide a great help to control early-age cracking of HPC.(3)An addition of fly ash results in increases of early-age tensile creep of HPC mixture.And with the increase of dosage of fly ash,this effect is more robust.For the HPC mixture without fly ash,the influences of initial stress level(or stress-strength ratio)on tensile creep can be observed when the load is imposed before 1 d(i.e.,0.5 d and 0.7 d).However,after 1 d,the effects of stress level no longer appear.(4)The predicted values of early-age tensile creep match well with the test data at the initial stage of the load duration.With an increase of the duration under loading,the both diverge from each other,but on the whole,the deviations hold in the range of(-10%~+10%)errors.