Factors affecting the strength of cement composite cold recycled mixture and its interface morphological characteristics

In this study, we used the SEM electron microscope to observe the morphological characteristics of each phase interface in the mixture, focusing on the effects of gradation, cement content, curing age, and mixing method on the unconfined compressive strength and splitting strength of the cold recycled mixture, to optimize the material composition design of cement composite recycled mixture. The results showed that dry shrinkage cracks and cement aggregates appeared on the surface of the three aggregates formed by conventional mixing, while the old cement that was not closely connected on the RBP surface of the mixture fell off using the vibration mixing method. The cement on the surface of all kinds of aggregates was evenly coated, with a reduced interface strength variability. The strength of the mixture increased with age was in line with the law of cement strength growth; The increase in cement content could increase the unconfined compressive strength and splitting strength of the mixture; The strength of the mixture increased and then decreased with the increase of RAP content. The unconfined compressive strength and splitting strength of the mixture were increased by 32.4% and 44.3%, and the coefficient of variation was reduced by 27.1% and 31.0%, respectively, by using vibration mixing compared with conventional mixing.