Influence of Structural and Humidity Changes at the Inner Part of Hardened Cement Paste on Autogenous Shrinkage

ABOUT THE INTERNATIONAL CONCRETE ABSTRACTS PORTAL

  • The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.

International Concrete Abstracts Portal

  


Title: Influence of Structural and Humidity Changes at the Inner Part of Hardened Cement Paste on Autogenous Shrinkage

Author(s): Hiroshi Uchikawa, Shunsuke Hanehara and Hiroshi Hirao

Publication: Special Publication

Volume: 170

Issue:

Appears on pages(s): 949-964

Keywords: Blast furnace slag; blended cements; humidity; microstructure; porosity; self dessication; shrinkage.

Date: 7/1/1997

Abstract:
The relationships between the autogenous shrinkage, and the hydration reaction of cement and the structural change of hardened cement paste have been investigated by hermetically curing the cement pastes of normal portland cement, type B - blast furnace slag cement and 10% silica-fume blended cement prepared at W/C of 0.5 and 0.25 and continuously measuring the humidity changes and the shrinkage strains of hardened cement pastes to obtain the basic data for elucidating the mechanism of autogenous shrinkage. Although there was a time lag between the autogenous shrinkage and the humidity change of hardened cement paste, no autogenous shrinkage took place in the cement paste prepared at W/C of 0.5 showing no humidity reduction. The autogenous shrinkage observed in the cement paste prepared at W/C of 0.25, therefore, is considered to be caused by the self dessication at a relative humidity (RH) from 100 to 80%. The autogenous shrinkage occured mainly during a period from 8 hours to 4 days and slightly increased after that. It is considered that the autogenous shrinkage takes place because the free water contained in pores particularly in fine gel pores formed by producing a large quantity of C-S-H is consumed by the hydration reaction and the humidity in the hardened cement paste is reduced. The autogenous shrinkage of type B - blast furnace slag cement paste was approximately 1,800~ which was about 1.8 times that of normal portland cement paste. Since type B - blast furnace slag cement paste produces more C-S-H than normal portland cement paste, thereby causing remarkable autogenous shrinkage. The autogenous shrinkage of 10% silica-fume blended cement paste is about 1,000u almost same as that of normal portland cement paste, since the pozzolanic reaction is suppressed in its paste prepared at W/C of 0.25 up to 4 days.