Effects of porosity on leaching of Ca from hardened ordinary Portland cement paste

• Published in: Cement and concrete research Vol. 35; no. 9; pp. 1764 - 1775
• Main Authors: Haga, Kazuko, Sutou, Shunkichi, Hironaga, Michihiko, Tanaka, Satoru, Nagasaki, Shinya
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Ltd 01.09.2005; Elsevier Science
• Subjects: Applied sciences; Buildings. Public works; BULK DENSITY; CALCIUM SILICATES; Calcium-silicate-hydrate; Cement concrete constituents; Cements; Degradation; DIFFUSION; ELECTRON MICROPROBE ANALYSIS; Exact sciences and technology; GELS; HYDRATES; LEACHING; Long-term performance; Materials; MATERIALS SCIENCE; Pore size distribution; POROSITY; PORTLAND CEMENT; Properties and test methods; Properties of anhydrous and hydrated cement, test methods; WATER; Degradation; Calcium-silicate-hydrate; Long-term performance; Diffusion; Pore size distribution; Performance evaluation; Calcium; Pore structure; Experimental study; Portland cement; X ray diffraction; Dissolution; Leaching; Long term; Modeling; Pore size; CSH phase; Electron probe; Hardened cement paste; Failure analysis; Solid phase; Porosity
• ISSN: 0008-8846; 1873-3948
• DOI: 10.1016/j.cemconres.2004.06.034

Aiming at evaluating the effects of porosity in hardened cement paste on dissolution phenomena, we prepared hardened ordinary Portland cement (OPC), with variation in pore volume, and then leached them in deionized water. It was found that the bulk density and pore volume were affected by the dissolution of portlandite. The larger the pore volume of the sample, the more rapidly portlandite is dissolved. An electron probe microanalysis (EPMA) performed on the cross-section of the solid phase showed the ‘portlandite (CH) dissolution front’. As the leaching period became longer, the CH dissolution front shifted towards the inner part. In addition, the movement of the CH dissolution front was described by the diffusion model, with consideration of the dissolution of portlandite. It was concluded that the transport of leached constituents is diffusion controlled, and the major leached constituents of hardened OPC are portlandite and C-S-H gel. Large pore, which was generated associated with the leaching of portlandite, was considered significantly to affect the diffusion of leached constituents.