Early Shrinkage Behavior and Mechanism of Cement Mortar for Rapid Repair of Airport Pavement

In order to grasp the early shrinkage behavior of cement mortar used for rapid repair of airport pavement, this study tested the early shrinkage deformation of modified portland cement mortar and phosphate cement mortar, with ordinary portland cement mortar serving as a control group. The time-dependent model of the thermal expansion coefficient of rapid-repair cement mortar was fitted, and the temperature shrinkage deformation of rapid-repair cement mortar was calculated in conjunction with internal temperature changes of the mortar. The shrinkage behavior mechanism was explained based on the heat-release characteristics of cement hydration, the composition of cement hydration products, and the loss rate of cement mortar quality. The main conclusions are as follows: The final stable values of shrinkage deformation of different rapid-repair cement mortars varied significantly, with phosphate cement mortar having the fastest rate of shrinkage deformation and the smallest shrinkage at 28 days. The 28-day shrinkage rate of modified portland cement mortar increased by 60.6% compared with ordinary portland cement mortar; the exponential thermal expansion coefficient model provided a better fit for rapid-repair cement mortar. Temperature shrinkage was the main form of early total shrinkage deformation in rapid-repair cement mortar, overshadowing the volume changes caused by other factors. Shrinkage deformation of modified portland cement mortar can be divided into three stages. The first stage is dominated by temperature shrinkage, the second stage is primarily due to expansion deformation caused by the massive formation of ettringite (AFt), and the third stage involves shrinkage deformation due to the partial transformation of AFt into monosulfate (AFm). Finally, shrinkage deformation of phosphate cement mortar can be divided into two stages, with temperature shrinkage being the main form of deformation in both stages.