Journal
JOURNAL OF CO2 UTILIZATION
Volume 38, Issue -, Pages 348-354Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.jcou.2020.02.012
Keywords
CO2 concentration; Cement paste; Calcite; XRD; Si-29 NMR
Funding
- Key Research Project of Hunan Provincial Science and Technology Program one-belt-one-road [2017WK2090]
- NSFC International (Regional) Cooperation and Exchange Program [51750110506]
- China Postdoctoral Science Foundation [2018M632219]
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Early-age carbonation can make a significant difference in the formation of hydration products in cement-based materials and alter the microstructural and mechanical performances. To understand in detail the impacts and their contribution to cement hydration, dry-mix cement pastes were exposed to instant carbonation with 0.04 %, 1%, 3%, 10 %, 20 % CO2 concentrations for 2 h prior to further water curing. By increasing the CO2 concentration, an increment in strength gain of samples at 2 h (right after early carbonation) as well as being prolonged by water curing at 1, 3, 7 days was noticed. This agrees with TGA and XRD results, demonstrating that the increases in CO2 concentration resulted in a higher carbonation reaction and hydration degree. Si-29 NMR results also indicate that the higher the CO2 concentration the lower the calcium to silica ratio (Ca/Si); thus, there is a higher degree of polymerization to promote early hydration. It can be concluded that early carbonation of 2 h in particular with a high CO2 concentration can be beneficial for further cement hydration due to the consumption of calcium hydroxide (CH) and nuclei site effect of calcite crystals, resulting in better microstructural properties and mechanical performance.
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