Improvement of shrinkage resistance and mechanical property of cement-fly ash-slag ternary blends by shrinkage-reducing polycarboxylate superplasticizer

Abstract

Fly ash and slag are two commonly used supplementary cementitious materials (SCMs) in modern concrete, which can significantly enhance the long-term durability of concrete. However, their application is somewhat limited due to the negative impact on early strength development and shrinkage cracking. This study proposed using a recently developed shrinkage-reducing polycarboxylate admixture (SR-PCA) to alleviate the above problems. The effect of SR-PCA on compressive strength, drying shrinkage, autogenous shrinkage, mass loss, pore structure and hydration process were also investigated. The results showed that SR-PCA enhanced the 28d compressive strength due to the refinement of pore structure and improved hydration degree. With the addition of SR-PCA, the drying shrinkage and autogenous shrinkage were significantly reduced, particularly in the mixture blended with 50% fly ash, while showing a slight impact in the sample with 50% slag. SR-PCA decreased the drying shrinkage by lowering the hydrous compressibility factor (CF) value and mesopore volumetric percentage. The incorporation of SR-PCA retarded cement hydration at an early age, thereby reducing the early-age autogenous shrinkage, while the long-term autogenous shrinkage was mitigated due to the enhancement effect on the hydration degree at 28 days. Therefore, SR-PCA is a practical approach for enhancing shrinkage resistance and compressive strength in cement-fly ash-slag blends, thereby contributing to the broader application of these industrial by-products.