Mechanism of Deterioration of Cement Composites Due to Leaching of Calcium

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Title: Mechanism of Deterioration of Cement Composites Due to Leaching of Calcium

Author(s): K. Watanabe, K. Yokozeki, N. Otsuki, and M. Daimon

Publication: Special Publication

Volume: 192

Issue:

Appears on pages(s): 1155-1172

Keywords: calcium; cements; diffusion; leaching; radioactivity

Date: 4/1/2000

Abstract:
Leaching degration of cement composites is a phenomenon involving the removal of various solid constituents and may result in loss of strength. The leaching of calcium is not a major problem for most concrete structures, as the degradation rate is very slow. However, it is important for structures such as marine structures, dams, and radioactive-waste repositories that are in an environment that direct contact with water for a long term. In order to evaluate the leaching behavior, investigation of the fundamental degradation mechanism must be undertaken. Described in this paper is the degradation mechanism of cement composite derived from accelerated testing. Investigations were conducted using three different accelerated test methods, I.e. the immersion test method, the dissolution test method and the permeation cell test method. The main results of the study were as follows: 1) 30-50% of calcium in cement composites was leached out in several moths in the accelerated tests (the immersing test method and the permeation test method); 2) in all tests, calcium leaching from Ca(OH)2 and C-S-H was observed, and the change in the porosity and physical properties corresponding to the leaching degree was found; and 3) a possibility to predict the long-term degradation behavior of structures by using numerical analysis was demonstrated.