Multi-modal imaging of cementitious carbonation front – insights on performance of low-clinker blends

Sudharsan Rathna Kumar, -

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https://hdl.handle.net/2142/125807 Copy

Description

Title

Multi-modal imaging of cementitious carbonation front – insights on performance of low-clinker blends

Author(s)

Sudharsan Rathna Kumar, -

Issue Date

2024-07-16

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)

carbonation, multi-modal imaging, low-clinker blends, Raman imaging

Abstract

Practical solutions to reduce the embodied energy of concrete, i.e., the energy consumed by all processes associated with concrete’s production, and CO2 emissions associated with cement production necessitate the use of supplementary cementitious materials (SCMs). Another method to reduce the overall CO2 footprint of concrete is via carbonation. Carbonation is a natural process, by which atmospheric CO2 reacts with calcium bearing phases in concrete, forming stable carbonates. The formation of carbonates mineralizes atmospheric CO2, which throughout the service life of a structure allows concrete offset historical CO2 emissions and prove to be a carbon sink. However, measuring and quantifying the carbonation front has been an entangling debate over the past decades. Measurement of carbonation is vital as we shift newer sources of alternate SCMs like calcined clays due to dearth in the quality and quantity of conventional SCMs like fly ash and slag. Moreover, increased replacement of cement with alternate materials lead to an increased carbonation rate, which induce a fear of carbonation-induced steel-corrosion. Thus, this thesis has two main objectives – (1) to compare existing methods with advanced imaging methods to understand the nature of the carbonation front, and (2) to elucidate the carbonation performance of low-clinker systems and investigate opportunities to enhance its carbonation resistance to facilitate applications as structural concrete. We approached the first problem by employing a multi-modal imaging approach where we took multiple imaging techniques and deployed them on the same surface that had undergone carbonation. We report that the carbonation front is non-planar and is diffused. Irrespective of what technique is used to measure the shape of the front, whether it is optical imaging post spraying of a pH indicator or advanced imaging techniques such as laser confocal microscopy and Raman imaging, all indicate a diffused front. Moreover, using laser profilometry and contact angle goniometry, we show pore refinement in the carbonated region. Despite many advantages of LC3-50 such as superior resistance to alkali-silica reaction, chloride ingress and sulfate attack, several challenges limit progressing towards low-clinker LC3 with 70-80% clinker replacement. Among them, a major hurdle is the higher carbonation rates of low-clinker LC3 due to relatively low carbonatable content or low CaO buffer capacity to bind CO2 in such low-clinker systems which raise concerns about carbonation-induced steel corrosion. Addressing the ‘carbonation debate’ is key to allowing large-scale utilization of these low-clinker systems in structural applications. We try to deconvolute the carbonation performance of low-clinker LC3 systems by exploring the dual role of adding portlandite as a performance enhancer. The dual roles of portlandite are to increase the degree of reaction in metakaolin and provide a buffer against carbonation. To provide experimental evidence supporting the use of low-clinker systems in all applications, various blended systems were subjected to a 3-year long-term natural carbonation exposure and short-term accelerated carbonation exposure regime. A ~55% reduction in the carbonation depth at every exposure time is observed for low-clinker LC3 when doped with portlandite. The reduction in the carbonation depth can be attributed to an improved buffer capacity relative to low-clinker LC3 systems without portlandite. Furthermore, stabilization of some AFm phases, such as strätlingite, is observed post-carbonation, indicating greater microstructural refinement of portlandite doped low-clinker LC3. Our study supports the large-scale utilization of these low-clinker concretes, providing a paradigm shift of carbonation-induced steel corrosion in such systems.

Graduation Semester

2024-08

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/125807

Copyright and License Information

Copyright 2024 - Sudharsan Rathna Kumar

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