Effects of Mineral Admixtures and Recycled Aggregate on Mechanical Properties and Volume Stability of CLP–RA Concrete

To investigate the effects of compound mineral admixtures and recycled aggregates on the performance of concrete, a total of 16 concrete mixture ratios were designed, including ordinary concrete, recycled aggregate concrete, composite limestone powder (CLP) concrete, and composite limestone powder–recycled aggregate (CLP–RA) concrete. Subsequently, tests were conducted on the mechanical properties and volume stability of these concrete samples, followed by a comprehensive analysis that integrated relevant theories. The results indicate that the appropriate regulation of the mixing ratio of mineral admixtures and recycled aggregates can enable CLP–RA concrete to demonstrate a significant superposition effect regarding its mechanical properties and volume stability. In the initial stages, the high water absorption of the recycled aggregates reduces the effective water–binder ratio of concrete, which initially increases its strength. In later stages, the pozzolanic effect of the mineral admixtures enhances the development of the strength. In the initial stages, the porous structure of the recycled aggregates limits the water absorption of the cementitious materials in concrete, thereby reducing wet expansion deformation. However, with increasing age, the absorption of saturated water exacerbates the deformation caused by wet expansion. Mineral admixtures can significantly reduce the shrinkage of concrete due to their various effects, including filling, microaggregates, and volcanic ash. By contrast, recycled aggregates tend to promote concrete shrinkage because of their high porosity and water absorption characteristics. As the substitution rate of recycled aggregates increases, this negative effect becomes more pronounced. In addition, by introducing the replacement rate of recycled aggregate (r), along with a strength conversion relationship and a volume stability prediction model for CLP–RA concrete, we achieved a correlation of >90%. The results of this study provide theoretical support for the widespread adoption and application of this concrete.