Effects of Decalcification on the Microstructure and Surface Area of Cement and Tricalcium Silicate Pastes

Published

January 15, 2004

Author(s)

J Thomas, J J. Chen, Hamlin M. Jennings, Andrew J. Allen

Abstract

Thin coupons of white portiand cement (WPC) and tricalcium silicate paste were decalcified by leaching in concentratedammonium nitrate solutions, resulting in calcium-to-silicon molar ratios (Ca/Si) ranging from 3.0 (control) down to 0.3. Themicrostructure and surface area were measured using both small angle neutron scattering (SANS) and nitrogen gas sorptionDecalcification caused the SANS data regime corresponding to the volume fractal C-S-H gel phase to exhibit a decrease infractal exponent. The data indicate that the basic 5-nm diameter C-S-H globules rearrange from a volume-fractal structureinto a sheet-like structure of increasing thickness as the Ca/Si decreases. The intensity in the entire volume fractal regimeincreased significantly on leaching, and the total surface area per unit specimen volume measured by SANS doubled onleaching from Ca/Si = 3.0 to near Ca/Si = 1.0. The nitrogen BET surface area of the WPC pastes, expressed in the sameunits, increased on decalcification as well, although not as sharply. These results indicate that the overall rearrangement ofC-S-H gel on leaching leads to an increase int he C-S-H gel surface area accessed by these two techniques.

Citation

Chemistry of Materials

Volume

34

Pub Type

Journals

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Keywords

celcium silicate hydrate gel, cement and concrete, microstructure characterization, nanostructure of tricalcium silicate, neutron scattering, small-angle scattering

Citation

Thomas, J. , Chen, J. , Jennings, H. and Allen, A. (2004), Effects of Decalcification on the Microstructure and Surface Area of Cement and Tricalcium Silicate Pastes, Chemistry of Materials, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=850714 (Accessed October 17, 2025)