Effects of Accelerated Carbonation Testing and by-Product Allocation on the CO2-Sequestration-to-Emission Ratios of Fly Ash-Based Binder Systems

Carbonation of cementitious binders implies gradual capture of CO2 and significant compensation for the abundant cement-related CO2 emissions. Therefore, one should always look at the CO2-sequestration-to-emission ratio (CO2SP/EM). Here, this was done for High-Volume Fly Ash (HVFA) mortar (versus two commercial cement mortars). Regarding their CO2 sequestration potential, effects of accelerated testing (at 1–10% CO2) on as such estimated natural carbonation degrees and rates were studied. Production related CO2 emissions were evaluated using life cycle assessment with no/economic allocation for fly ash. Natural carbonation rates estimated from accelerated tests significantly underestimate actual natural carbonation rates (with 29–59% for HVFA mortar) while corresponding carbonation degrees are significantly overestimated (67–74% as opposed to the actual 58% for HVFA mortar). It is advised to stick with the more time-consuming natural tests. Even then, CO2SP/EM values can vary considerably depending on whether economic allocation coefficients (Ce) were considered. This approach imposes significant portions of the CO2 emissions of coal-fired electricity production onto fly ash originating from Germany, China, UK, US and Canada. Ce values of ≥0.50% lower the potential CO2SP/EM values up to a point that it seems no longer environmentally worthwhile to aim at high-volume replacement of Portland cement/clinker by fly ash.

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On the Theoretical CO2 Sequestration Potential of Pervious Concrete

Infrastructures ◽

10.3390/infrastructures4010012 ◽

2019 ◽

Vol 4 (1) ◽

pp. 12 ◽

Cited By ~ 2

Author(s):

Ethan Ellingboe ◽

Jay Arehart ◽

Wil Srubar

Keyword(s):

Co2 Emissions ◽

Co2 Sequestration ◽

Pervious Concrete ◽

Theoretical Formulation ◽

Concrete Mixtures ◽

Sequestration Potential ◽

Carbon Dioxide Co2 ◽

New Applications ◽

Natural Carbonation

Pervious concrete, which has recently found new applications in buildings, is both energy- and carbon-intensive to manufacture. However, similar to normal concrete, some of the initial CO2 emissions associated with pervious concrete can be sequestered through a process known as carbonation. In this work, the theoretical formulation and application of a mathematical model for estimating the carbon dioxide (CO2) sequestration potential of pervious concrete is presented. Using principles of cement and carbonation chemistry, the model related mixture proportions of pervious concretes to their theoretical in situ CO2 sequestration potential. The model was subsequently employed in a screening life cycle assessment (LCA) to quantify the percentage of recoverable CO2 emissions—namely, the ratio of in situ sequesterable CO2 to initial cradle-to-gate CO2 emissions—for common pervious concrete mixtures. Results suggest that natural carbonation can recover up to 12% of initial CO2 emissions and that CO2 sequestration potential is maximized for pervious concrete mixtures with (i) lower water-to-cement ratios, (ii) higher compressive strengths, (iii) lower porosities, and (iv) lower hydraulic conductivities. However, LCA results elucidate that mixtures with maximum CO2 sequestration potential (i.e., mixtures with high cement contents and CO2 recoverability) emit more CO2 from a net-emissions perspective, despite their enhanced in situ CO2 sequestration potential.

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Mix design of high-volume fly ash ultra high performance concrete

Journal of Science and Technology in Civil Engineering (STCE) - NUCE ◽

10.31814/stce.huce(nuce)2021-15(4)-17 ◽

2021 ◽

Vol 15 (4) ◽

pp. 197-208

Author(s):

Nguyen Van Tuan ◽

Pham Sy Dong ◽

Le Trung Thanh ◽

Nguyen Cong Thang ◽

Yang Keun Hyeok

Keyword(s):

Heat Treatment ◽

Compressive Strength ◽

Fly Ash ◽

Co2 Emissions ◽

High Performance ◽

High Performance Concrete ◽

High Volume ◽

Mix Design ◽

Ultra High Performance Concrete ◽

High Volume Fly Ash

The addition of supplementary cementitious materials (SCMs) to replace cement, especially with a high volume (> 50%), is an effective way to reduce the environmental impact due to the CO2 emissions generated in the production of ultra-high performance concrete (UHPC). Unfortunately, no official guidelines of UHPC using a high volume of SCMs have been published up to now. This paper proposes a new method of mix design for UHPC using high volume fly ash (HVFA), that is referred to the particle packing optimization of the Compressive Packing Model proposed by F. de Larrard. This proposed method also considers the heat treatment curing duration to maximize the compressive strength of HVFA UHPC. The experimental results using this proposed mix design method show that the optimum fly ash content of 50 wt.% of binder can be used to produce HVFA UHPC with a compressive strength of over 120 MPa and 150 MPa under standard curing and heat treatment, respectively. Moreover, the embodied CO2 emissions of UHPC reduces 56.4% with addition of 50% FA.

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Accelerated and natural carbonation of concrete with high volumes of fly ash: chemical, mineralogical and microstructural effects

Royal Society Open Science ◽

10.1098/rsos.181665 ◽

2019 ◽

Vol 6 (1) ◽

pp. 181665 ◽

Cited By ~ 2

Author(s):

Philip Van den Heede ◽

Mieke De Schepper ◽

Nele De Belie

Keyword(s):

Fly Ash ◽

High Volume ◽

Test Results ◽

X Ray Diffraction ◽

Carbonation Reaction ◽

High Volume Fly Ash ◽

Carbonation Resistance ◽

Microstructural Effects ◽

Natural Carbonation ◽

Mineralogical Phases

Today, a rather poor carbonation resistance is being reported for high-volume fly ash (HVFA) binder systems. This conclusion is usually drawn from accelerated carbonation experiments conducted at CO 2 levels that highly exceed the natural atmospheric CO 2 concentration of 0.03–0.04%. However, such accelerated test conditions may change the chemistry of the carbonation reaction (and the resulting amount of CH and C–S–H carbonation), the nature of the mineralogical phases formed (stable calcite versus metastable vaterite, aragonite) and the resulting porosity and pore size distribution of the microstructure after carbonation. In this paper, these phenomena were studied on HVFA and fly ash + silica fume (FA + SF) pastes after exposure to 0.03–0.04%, 1% and 10% CO 2 using thermogravimetric analysis, quantitative X-ray diffraction and mercury intrusion porosimetry. It was found that none of these techniques unambiguously revealed the reason for significantly underestimating carbonation rates at 1% CO 2 from colorimetric carbonation test results obtained after exposure to 10% CO 2 that were implemented in a conversion formula that solely accounts for the differences in CO 2 concentration. Possibly, excess water production due to carbonation at too high CO 2 levels with a pore blocking effect and a diminished solubility for CO 2 plays an important role in this.

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