Hydrated Calcium Silicate (C–S–H) Improves the Performance of Stone Powder as Cement Admixtures

The low pozzolanic activity of recycled stone powder limits its application in cement-based materials. Calcium silicate hydrate (CSH) is one of the hydration products of cement and also has the function of promoting hydration and improving strength. Therefore, the behavior of CSH in enhancing the activity of stone powder has been studied, including the workability and mechanical properties, and the mechanism of activity enhancement has been explained at the microscopic level. The results showed that when the amount of stone powder was 30%, the setting time was shortened by 26.14% to 34.34%, the slump increased by 7.89%, and the compressive strength at 3 and 28 days decreased by 40.94% and 37.99%, respectively. On this basis, when CSH was added at a dosage of 1%, compared with the specimen with a dosage of 30% stone powder, the setting time was shortened by 18.29% ∼ 21.53%, the slump was increased by 2.44%, and the compressive strength at 3 and 28 d was increased by 15.95% and 16.25%, respectively. The pozzolanic activity of stone powder has increased from 62.00% to 71.82%, reaching the pozzolanic activity level of fly ash. The mechanism of CSH enhancing pozzolanic activity was explained at the micro level, which broadened the application channels for the high-dosage application of stone powder.