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Methods to sequester and store atmospheric CO2 are critical to combat climate change. Alkaline-rich bioashes are potential carbon fixing materials. This work investigates potential co-benefits from mineralizing carbon in biomass ashes and partially replacing high embodied greenhouse gas (GHG) Portland cement (PC) in cement-based materials with these ashes. Specifically, rice hull ash (RHA), wheat straw ash (WSA), and sugarcane bagasse ash (SBA) were treated to mineralize carbon, and their experimental carbon content was compared to modeled potential carbonation. To understand changes in the cement-based storage materials, mortars made with CO2-treated WSA and RHA were experimentally compared to PC-only mortars and mortars made with ashes without prior CO2 treatment. Life cycle assessment methodology was applied to understand potential reductions in GHG emissions. The modeled carbonation was ∼18 g-CO2/kg-RHA and ∼180 g-CO2/kg-WSA. Ashes oxidized at 500 °C had the largest measured carbon content (5.4 g-carbon/kg-RHA and 35.3 g-carbon/kg-WSA). This carbon appeared to be predominantly residual from the biomass. Isothermal calorimetry showed RHA-PC pastes had similar heat of hydration to PC-pastes, while WSA-PC pastes exhibited an early (at ∼1.5 min) endothermic dip. Mortars with 5 % and 15 % RHA replacement had 1–12 % higher compressive strength at 28 days than PC-only mortars, and milled WSA mortars with 5 % replacement had 3 % higher strength. A loss in strength was noted for the milled 15 % WSA, the CO2-treated 5 %, and the 15 % WSA mortars. Modeled reductions in GHG emissions from CO2-treated ashes were, however, marginal (<1 %) relative to the untreated ashes.
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On the Theoretical CO2 Sequestration Potential of Pervious Concrete
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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- Award ID(s):
- 1562557
- PAR ID:
- 10174022
- Date Published:
- Journal Name:
- Infrastructures
- Volume:
- 4
- Issue:
- 1
- ISSN:
- 2412-3811
- Page Range / eLocation ID:
- 12
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/infrastructures4010012
