Autogenous Control of Autogenous Shrinkage


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Title: Autogenous Control of Autogenous Shrinkage

Author(s): A. Durán-Herrera, N. Petrov, O. Bonneau, K. Khayat, and P.-C. Aïtcin

Publication: Special Publication

Volume: 256


Appears on pages(s): 1-12

Keywords: autogenous shrinkage; quasi-adiabatic curing; swelling; total shrinkage

Date: 10/1/2008

The partial substitution of natural sand by lightweight sand has been used to reduce autogenous shrinkage in concretes with a low water/binder ratio, but when this substitution is combined with quasi-adiabatic curing conditions during the first 24 hours, it has been found that autogenous shrinkage can be mitigated and controlled. During an experiment done at Sherbrooke University on large concrete blocks measuring 0.6 × 0.6 × 0.6 m (2 × 2 × 2 ft) where 28% by volume of the natural sand in the concrete was replaced by the same volume of saturated lightweight sand, with absorption of about 20%, it was found that autogenous shrinkage was mitigated within the concrete blocks. Moreover, it has been found that the compressive strength and the elastic modulus of the substituted concrete were not affected by this substitution. For the first time in large concrete specimens, it can be reported that autogenous shrinkage can be mitigated and controlled without the help of any chemical product added to the concrete to induce an initial expansion to neutralize autogenous shrinkage. It seems that quasi-adiabatic conditions favor the development of large crystals that result in swelling of the apparent volume of the concrete block, and that the temperature increase also contributes to reduce chemical shrinkage. This could explain why Le Chatelier found more than 100 years ago that when a paste was cured under water, after a certain time, it swells enough to break the vase in which it had been placed.