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Carbonatable binders have received extensive attention in recent years because of their potential to absorb environmental carbon dioxide (CO2) to form stable, durable, and environmentally friendly carbonate materials. However, the expanded use of these eco-friendly materials is still staggered due to their fundamental limitations (i.e., chemical and physical reaction barriers). This paper addresses the depth-dependent limitation of the external CO2 curing process using impregnated hydrogels for carbonated cementitious materials (CCMs). The CCMs with enzymatic solution-impregnated hydrogels in the presence of external CO2 have better mechanical (up to 80% improvement compared to control CCMs) and durability performance, and the calcium carbonate precipitation can reach up to 15 times higher compared to control systems (approaches the maximum theoretical degree of carbonation of binder). The experimental results show that external CO2 influx acts as an accelerator of the catalytic activity of urease and promotes CaCO3 precipitation over depth. The kinetic model shows that the addition of impregnated hydrogels with enzymatic solution significantly improved the early age reaction kinetics by accelerating the nucleation and growth of carbonate crystals. The developed CO2 curing process provides a uniform carbonation profile through depth which is crucial in upscaling CCM systems. This work provides a new path for the development of high-performance carbon sink construction materials.
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Coprecipitation of Crystalline Calcium Silicates and Carbonates from the Hydrothermal Reaction of Pseudowollastonite
Calcium silicates are abundant, but sparingly soluble, feedstocks of interest for making low-carbon alternative cements. Under hydrothermal and alkaline conditions, they can form crystalline calcium silicate hydrate (CCSH) products, which are abundant in Roman concrete, or they can form carbonates when CO2 is present. To understand when co-precipitation of CCSH and carbonate phases is possible, we studied the hydrothermal carbonation of a model calcium silicate, pseudowollastonite (-CaSiO3), at 150ºC and high pH as a function of CO2 source (CO2(g) or Na2CO3) and different concentrations of sodium, alumina, and silica. Our experiments produced a range of CCSH phases including tobermorite – 13Å, rhodesite, and pectolite, as early as one day after the start of our experiments. About 10.7% hydrated product was observed after 7 days of curing in 2 M NaOH solution. We also observed the formation of CaCO3 as both aragonite and calcite when carbon was introduced to our experimental system. The carbon source impacted the ratio of CaCO3 to CCSH phases in the reaction products. Availability of Na2CO3 produced a balance between CaCO3 and CCSH phases whereas CO2(g) produced more CaCO3 at about 36.4% by mass at the highest. Higher concentrations of Na+ increased precipitation of both CaCO3 and/or CCSH phases. The presence of excess silica, in the form of dissolved borosilicate glass from our reaction vessels under alkaline reaction conditions, also enhanced the formation of CCSH phases formed in some experiments. Supplemental Al2O3, a common constituent in many silicate feedstocks, also enhanced CCSH formation, likely by forming aluminum substituted phases under the conditions tested here. These chemical insights can be enabling in designing formulation and curing guidelines for novel cementitious materials.
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- Award ID(s):
- 2234543
- PAR ID:
- 10491266
- Publisher / Repository:
- American Chemical Society
- Date Published:
- Journal Name:
- ACS Sustainable Chemistry & Engineering
- Volume:
- 12
- Issue:
- 5
- ISSN:
- 2168-0485
- Page Range / eLocation ID:
- 1844 to 1856
- 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/10.1021/acssuschemeng.3c05110
