Effect Of Fly Ash Content And Particle Size Distribution On Pore Structure Of Cryogenic Concrete

The pore structure of concrete relates to the strength and durability of concrete materials,and the good pore structure can remarkably improve the mechanical properties and durability of concrete.Fly ash as a good performance of mineral admixtures,has a good physical filling effect,morphological effects and chemical pozzolanic effect.Therefore,it is very important to study the influence of fly ash content and particle size distribution on the pore structure and macroscopic properties of concrete.In this paper,the effects of fly ash content and particle size on the compressive strength of concrete are studied.Combined with the hydration heat release characteristics of fly ash-cement system with different particle size distributions,the influence of particle size distribution of fly ash on concrete compressive strength Strength and hydration mechanism.Secondly,the effects of fly ash content and particle size distribution on the pore structure and micro structure of concrete were studied.Thirdly,in order to clarify the relationship between the size distribution of fly ash and the macroscopic mechanical properties of concrete,The relationship between the particle size distribution of fly ash and the conpressive strength of concrete and the gray of pore structure parameters are studied by using the gray relational theory which is often used to analyze small sanple,poor information and uncertainty.Correlation.The effects of fly ash content and particle size distribution on the conpressive strength and hydration characteristics of concrete were studied.The results show that the early compressive strength of concrete decreases with the incorporation of fly ash,and the compressive strength of concrete with fly ash gradually approaches the strength of the control group with age.The finer the particle size of fly ash,the more obvious its contribution to the compressive strength of concrete.The exothermic characteristics of hydration of cementitious materials show that the addition of fly ash can reduce the total heat release of fly ash-cement composite cementitious materials,and the change of particle size will also affect the hydration of fly ash-cement compound cementitious material Heat rate.With the decrease of the particle size of fly ash,the peak value of hydration heat release rate of compo site cementitious material is advanced,and the fine fly ash can promote the hydration of cement,and then increase the exotherm of cement.The effects of different fly ash content and particle size distribution on the pore structure parameters and microstructure characteristics of concrete were studied.The results show that the incorporation of fly ash can significantly improve the pore size distribution of concrete,reduce the porosity of concrete and refine the average pore diameter.When the content of fly ash is 15%,the content of harmless and less harmful holes in concrete is relatively high,and the contents of harmful and harmful holes are relatively low.In the condition of variable temperature curing,the porosity and average pore diameter of the concrete corresponding to 15%fly ash content are relatively low.In the condition of normal temperature curing,the porosity and average pore diameter of the concrete corresponding to 20%fly ash content are relatively low.When the particle size of fly ash is F2(grinding time 1h),the pore size distribution of the concrete is improved,the porosity and the average pore diameter are obviously reduced,and the pore structure parameters of concrete are the best.The results of microscopic analysis show that the proper coMPaction of fly ash can improve the density of the internal structure of concrete.When the content of fly ash is 15%,the density of the concrete is relatively high.With the extension of curing age,the degree of hydration of fly ash particles in concrete is more and more,and the secondary hydration products are more and more,which can improve the pore structure of concrete and improve its macroscopic properties.The relationship between the particle size distribution and the compressive strength of concrete and the pore structure parameters such as average pore size and porosity were studied by using gray relational theory.The results show that the vol?me fraction of particles larger than 20?m in fly ash is negatively correlated with compressive strength,average pore size and porosity of the concrete,and the vol?me fraction of particles less than or equal to 20?m is positively correlated with them.The compressive strength of concrete and the average pore diameter and porosity are positively related to the particle size distribution of the particle size distribution in the range of 10?20?m particle vol?me,fraction with the maxim?m correlation value.