Limestone and silica fume to improve concurrent flowability–segregation limits of concrete

The demanding performance criteria of high-performance concrete (HPC) such as high flowability and low segregation make superplasticiser (SP) indispensable in concrete production. SP is commonly added to concrete to increase flowability without undermining its strength. However, over-dosage of SP will cause segregation. This not only decreases the strength but also implies that there is a maximum limit of flowability that can be reached before segregation occurs. Increasing this maximum limit, or in general the overall flowability–segregation performance, is essential for HPC. In this study, limestone (LS) and silica fume (SF) were used as partial replacements of cement and the overall flowability–segregation performance of concrete was studied. The results showed that, with the addition of LS or SF, more SP was needed to achieve similar flowability but the maximum limit of flowability before reaching unacceptable segregation (>20% sieve segregation ratio) was improved, implying that replacement of cement by LS or SF with additional SP actually enhances the overall flowability–segregation performance of concrete. Accordingly, the design limits of flowability and segregation can be improved when LS or SF is added to the concrete, which is a very useful result for the design of self-compacting concrete.