Title:Study on the Influence of Carbonation on the Microstructure of
Cement-based Materials Based on BSE Technique
Volume: 17
Issue: 4
Author(s): Qizhen Shen*Gaoxiang Lou
Affiliation:
- College of Civil Engineering, Ludong University, Yantai, Shandong, 264025, China
Keywords:
Backscattered electron imaging, carbonation, microstructure, interfacial transition zone, matrix, cement-based materials.
Abstract:
Background: The influence of carbonation on the interfacial transition zone (ITZ) microstructure
of cement-based materials was significant. However, the width of ITZ is about tens
of microns, and studying its micro-characteristics (such as porosity, hydration products, content of
unhydrated cement, etc.) by macro test was difficult.
Methods: Backscattered electron (BSE) imaging technology and gray scale analysis method were
used to analyze the cement-based materials with water-binder (W/B) ratios of 0.53 and 0.35, respectively.
Results: BSE and gray scale analysis showed that in the ITZ, the porosity of 0.53P (Portland cement
paste), 0.35P (Portland cement paste), 0.53F (fly ash), and 0.35F (fly ash) decreased by
24.1%, 28.9%, 49.5%, and 64.2% respectively, whereas the content of hydration products increases
after carbonation, and the matrix also shows the same rule. At the same time, the smaller
W/B ratio, the greater the porosity reduction, and the filling effect of carbonation on the specimens
with supplementary cementitious material (SCM) was more significant than that of pure
cement specimens.
Conclusion: The porosity of the ITZ decreased after carbonation, however it remained higher
than that of the matrix. Consequently, the ITZ remained a vulnerable zone with a greater diffusion
rate of CO2 compared to the matrix even after carbonation.