Influence of Recycled Cement Paste Powder on Early-Age Plastic Shrinkage and Cracking of Cement-Based Materials

Cement-based materials, especially those with low water-cement ratios, often experience premature cracking due to plastic shrinkage in the early curing stages. In this study, the development mechanism of early-age plastic shrinkage of cement paste, and the crack shrinkage control effect of recycled cement paste powder on cement paste, was quantitatively investigated using non-contacting two-dimensional digital image technology. The influence of different replacement rates (5%, 10%, 20% and 30%) of recycled cement paste powder on the major principal strain and crack patterns of cement paste was investigated. Furthermore, the mechanism of recycled cement paste powder on the early-age plastic shrinkage of cement-based materials was explored. The results show that the addition of recycled cement paste powder could suppress the early-age plastic shrinkage of cement paste. An appropriate replacement ratio (10%) of recycled cement paste powder shows a 33.3% time delay in crack appearance and a 28.0% reduction in the major principal strain. However, the higher replacement ratio of 30% shows an adverse effect on the major principal strain, with an increase of 35.1%. The core mechanism of the appropriate recycled cement paste powder on plastic shrinkage reduction lies in its porous nature, which allows for water absorption and release and regulates the moisture state inside the pores. This quantitative research of the major principal strain development of the early-age plastic shrinkage of cement paste can facilitate a better understanding of plastic shrinkage reduction in recycled cement paste powder on cement paste.