Raman imaging of cementitious carbonation: A spatio-temporal investigation

Srivastava, Sonali

Permalink

https://hdl.handle.net/2142/115952 Copy

Description

Title

Raman imaging of cementitious carbonation: A spatio-temporal investigation

Author(s)

Srivastava, Sonali

Issue Date

2022-07-19

Director of Research (if dissertation) or Advisor (if thesis)

Garg, Nishant

Department of Study

Civil & Environmental Eng

Discipline

Civil Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• Cement
• Carbonation
• Raman spectroscopy

Abstract

To reduce the carbon dioxide emission to 43% by 2030 set by United Nations IPCC’sixth assessment, several steps are taken by cement-based industries. Among them, carbon dioxide sequestration and utilization using cement and concrete-based materials are getting attention. Carbon-rich hydrated cement products have huge potential in absorbing anthropogenic carbon dioxide from the atmosphere and leading us to a carbon-neutral environment. With this state of-art advancement, studying and quantifying carbon absorption is vital. Several methods such as pH indicators, thermogravimetry analysis (TGA), and X-ray diffraction (XRD) have been used to study carbonation in cement. However, these existing methods are either very primi tive (pH test) or require intensive sample preparation. Methods like TGA and XRD are bulk methods that require the crushing of samples. Also, none of the above-mentioned methods provide advection and depth growth during carbonation. Moreover, because of the complexity of cement’s hydrates and carbonates, estimating the carbonated products are still little under stood. With all the limitations, there is room for developing a complementary non-destructive tool that can investigate carbonation over space and time. This work uses confocal Raman spectroscopy to understand the spatially and temporally carbonated products formed during carbonation (advection and depth study). High-resolution mapping of calcium carbonate and calcium hydroxide is used to study a dynamic phenomenon. It is observed that the calcite precipitation is not only around portlandite but also around the initial limestone. This suggests that limestone filler in cement acts as a nucleation site for precipitation of calcite from portlandite carbonation. Moreover, the thin carbonated layer formed around portlandite crystals can slow down further carbonation. Also, calcium hydroxide is not only the hydration product reacting with CO2. From Raman spectra of calcium hydroxide, it is clear that the decrease in calcium hydroxide is not as drastic as the increase in calcium carbonate; these results are evidence that other hydration products like calcium silicate hydrate (C-S-H) and ettringite are also potentially contributing significantly towards carbonation. After nearly two weeks of carbonation exposure, the final saturation in terms of area covered by calcite growth is around 40%. Furthermore, for the depth study, a cost-effective method is opted using a hand-held Raman probe. Carbonation depth can be measured by observing the occurrence of the C-O characteristic vibration peak at 1086 cm−1 when the signal-to-noise ratio is ≥ 3. The carbonation front measured from the phenolphthalein indicator is lower than the depth measured using Raman spectroscopy. Also, a high water-cement ratio leads to higher carbonate contents and increases carbonation depth. The initial curing and pre-treatment of cement are crucial for the carbonation process.

Graduation Semester

2022-08

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Sonali Srivastava

Owning Collections