Effects of selective decalcification on the chemical structure and dimensional stability of cement and tricalcium silicate paste

Title: Effects of selective decalcification on the chemical structure and dimensional stability of cement and tricalcium silicate paste
Author(s): Jeffrey J. Thomas, Jeffrey J. Chen, Hamlin M. Jennings, Andrew J. Allen, Dan A. Neumann
Paper category : conference
Book title: International RILEM Symposium on Concrete Science and Engineering: A Tribute to Arnon Bentur
Editor(s): J. Weiss, K. Kovler, J. Marchand, and S. Mindess
Print-ISBN: None
e-ISBN: 2912143926
Publisher: RILEM Publications SARL
Publication year: 2004
Nb references: 27
Language: English

Abstract: Experiments measuring the significant changes to the chemical structure, nanostructure, and dimensional stability of C-S-H gel on decalcification are discussed. Thin specimens of cement or C3S paste were rapidly and selectively decalcified in concentrated NH4NO3 solutions to Ca/Si ratios as low as 0.30. Several techniques were used to analyze the chemical structure and microstructure, including small angle neutron scattering (SANS), inelastic neutron scattering (INS), and 29Si MAS NMR. The volume fractal microstructure of C-S-H gel, which is formed from roughly equiaxed 5 nm building blocks, is transformed by decalcification into sheetlike structures of increasing thickness. In addition, the high density form of C-S-H is transformed into a morphology with a high surface area, causing the overall specific surface area to double. INS measurements show that ~23% of the Ca in C-S-H gel with Ca/Si = 1.7 exists as Ca-OH groups. On decalcification, Ca-OH groups are preferentially removed and are eliminated by Ca/Si = 1. Further decalcification removes of Ca from Ca-O-Si bonds, allowing adjacent silicate groups to polymerize and causing a significant rearrangement of the phase. This polymerization causes significant shrinkage strains to occur during the latter stages of the decalcification process.

Online publication: 2004-03-25
Classification: Degradation
Publication type : full_text
Public price (Euros): 0.00
doi: 10.1617/2912143926.067