Effect Of Ultrafine Mineral Admixtures On The Durability And Microstructure Of High-Performance Airport Pavement Concrete

Cement concrete pavement is the main form of the airport pavement.Under the double effect of natural environment and aircraft load,the pavement performance will be damaged.Therefore,durability of pavement concrete is very important.As one of the indispensable components of concrete,the supplementary materials has different effects on the performance of concrete.In this paper,the influence of ultrafine mineral admixtures on the macroscopic properties and microstructure evolution of airport pavement concrete was systematically studied,and the improved mechanism was illustrated,which was of great significance for the better application of airport pavement concrete and ultrafine mineral admixtures.First,the effects of the ultrafine mineral admixtures on the mechanical properties of airport pavement concrete,including strength and durability,were investigated.The results showed that（1）the incorporation of ultrafine mineral admixtures improved strength of concrete,in which the strength began to be better than the blank group at 7 d.With the development of the curing age,the strength was improved more obviously.When the specimens were maintained to90 d,the increase was up to 21.5%.（2）The incorporation of ultrafine mineral admixtures significantly improved the durability of airport pavement concrete.Among them,the number of freeze-thaw cycles was increased about 1.6 times.The chloride ion permeability coefficient of the concrete with ultrafine mineral admixture was about 3.4×10^-14 m²/s,and the resistance to chloride ion permeation increased nearly four times.The resistance to water permeation was also significantly improved.Secondly,the heat of hydration,TG-DTG,QXRD,MIP and SEM were carried out to characterize the hydration characteristics of cement and the microstructure of concrete,to illustrate the improvement mechanism of ultrafine mineral admixture.The results revealed that（1）the ultrafine mineral admixtures significantly decreased the exothermic heat of hydration of the cement and enhanced the exothermic rate of hydration of the cement.（2）The high pozzolanic effect of ultrafine mineral admixtures enhanced the proportion of hydrated calcium silicate and accelerated the hydration process of C₂S and C₃S.（3）The ultrafine mineral admixtures refining the microstructure of concrete,increasing the volume of less harmful pores and harmless pores in the total pore volume.（4）After the admixture of ultrafine mineral admixture,the morphology of calcium alumina was more petal-like,thus making the microstructure of concrete denser.Finally,the mechanism of ultrafine mineral admixture in C₃S hydration system was investigated.The results showed that（1）the appearance of the silica-phase reaction peak of C₃S was about 51 min earlier after the incorporation of ultrafine mineral admixture,and the 3 d hydration exotherm of the comparison sample was about 12.2%lower than that of the blank group.（2）The ultrafine mineral admixture increased the hydration of C₃S in the late hydration period,while consuming more CH to generate C-S-H.（3）After the admixture was incorporated,the morphology of C-S-H tend to be two-dimensional foil-like,and the bonding ability was higher.The admixture of ultrafine mineral admixture increased the proportion of Q³ and Q⁴ in the molecular structure,and improved the degree of polymerization of C-S-H.