Shrinkage reducing admixture (SRA), shrinkage compensating admixture (SCA), and superabsorbent polymer (SAP) have been commonly used to reduce shrinkage of high-performance concrete (HPC); however, their comparative effectiveness is still not clear. In this article, the effects of SRA, SCA, and SAP on strength, autogenous/drying shrinkage, restrained ring shrinkage, and pore structure of HPC were studied. The dosages of SRA, SCA, and SAP were varied within 2.5–7.5 L/m3, 2.5–7.5 %, 0.4–1.4 g/kg, respectively. The results indicated that SRA and SCA decreased the shrinkage with their dosages increasing. However, the presence of SAP in HPC mitigated the autogenous shrinkage weakly and raised the free drying shrinkage. SRA, SCA, and SAP all reduced restrained ring shrinkage. SCA was the best admixture to increase compressive strength and reduce shrinkage in HPC. Additionally, the micromechanisms of SRA, SCA, and SAP on shrinkage reduction were addressed based on pore structures. The reduction of mesopore percentage was a primary reason to restrain the shrinkage behavior with the addition of SRA, SCA, and SAP. Moreover, linear fitting models of shrinkages in function of mesopores percentage were proposed. The shrinkage property of HPC could be explained by the mesopores percentage.

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2025
ASTM International
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