A New High Performance Drying Shrinkage-Reducing Admixture


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Title: A New High Performance Drying Shrinkage-Reducing Admixture

Author(s): M. Masanaga, T. Yamamoto, T. Hirata, and T. Nawa

Publication: Special Publication

Volume: 239


Appears on pages(s): 297-308

Keywords: adsorbtion; drying shrinkage; shrinkage-reducing admixture; surface tension

Date: 10/1/2006

Cracking caused by autogeneous and/or drying shrinkage is one of the most important factors that affects to the early deterioration of concrete structures. In this study, the new high performance drying shrinkage-reducing admixture, NSR-1, is introduced. The NSR-1 shows higher drying shrinkage-reducing ability with very low dosage level compared with conventional drying shrinkage-reducing admixtures (DSRA) without effecting other concrete properties. Drying shrinkage-reducing mechanism of conventional DSRA is generally due to reducing the surface tension of water in capillary pores. On the other hand, NSR-1, having hydrophobic groups, adsorbs on cement particles and is able to give hydrophobicity on pore surfaces. As a result, NSR-1 reduces the interfacial tension between pore surfaces and water in these pores, and can reduce drying shrinkage effectively. Drying shrinkage behavior was measured by mortar with W/C of 44%. At 28 days, the shrinkage strain of NSR-1 was 390 × 10-6 at dosage of 0.3 % by mass of cement, and those of conventional DSRA were 380 × 10-6 to 405 × 10-6 at dosage of 2.0% by mass of cement. The NSR-1 showed the same drying shrinkage-reducing effect at a dosage of about one-seventh of the addition amount for the conventional DSRA.