Title: Shrinkage-Reducing Admixtures

Author(s): Charles Nmai, Rokuro Tomita, F. Hondo, and Julie Buffenbarger

Publication: Concrete International

Volume: 20

Issue: 4

Appears on pages(s): 31-37

Keywords: admixtures; concretes; cracking (fracturing); drying shrinkage; durability; shrinkage; warpage

DOI:

Date: 4/1/1998

Abstract:
The loss of moisture from concrete as it dries results in a phenomenon known as drying shrinkage. With adequate restraint, drying shrinkage can cause cracking if induced tensile stresses exceed the tensile strength of the concrete. Cracks provide easy access for oxygen, moisture, chlorides, and other aggressive chemicals into the matrix, and can therefore impact the long-term durability of concrete. Differential drying shrinkage between the top surface and the bottom of a slab can result in curling of the slab. To minimize the potential detrimental effects of drying shrinkage on concrete, innovative admixtures that reduce drying shrinkage have been developed. These products, called shrinking-reducing admixtures (SRAs), were first introduced in Japan in the early 1980s and are now available in the United States. Data for the world’s first SRA, referred herein as SRA-M, is presented. Data show that SRA-M is effective in reducing the magnitude of drying shrinkage and subsequent cracking in concrete. An overview of the mechanism and factors that affect drying shrinkage is also presented.