Van den Heede Philip, De Schepper Mieke, De Belie Nele
Magnel Laboratory for Concrete research, Department of Structural Engineering, Ghent University, Tech Lane Ghent Science Park, Campus A, Technologiepark Zwijnaarde 60, 9052 Ghent, Belgium.
R Soc Open Sci. 2019 Jan 16;6(1):181665. doi: 10.1098/rsos.181665. eCollection 2019 Jan.
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 levels that highly exceed the natural atmospheric CO 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 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 from colorimetric carbonation test results obtained after exposure to 10% CO that were implemented in a conversion formula that solely accounts for the differences in CO concentration. Possibly, excess water production due to carbonation at too high CO levels with a pore blocking effect and a diminished solubility for CO plays an important role in this.
如今，有报道称高掺量粉煤灰（HVFA）胶凝材料体系的抗碳化性能相当差。这一结论通常是基于在二氧化碳浓度远高于自然大气中0.03 - 0.04%的二氧化碳浓度下进行的加速碳化实验得出的。然而，这种加速试验条件可能会改变碳化反应的化学性质（以及碳化产物氢氧化钙（CH）和水化硅酸钙（C - S - H）的量）、形成的矿物相的性质（稳定的方解石与亚稳态的球霰石、文石）以及碳化后微观结构的孔隙率和孔径分布。在本文中，通过热重分析、定量X射线衍射和压汞法对高掺量粉煤灰（HVFA）和粉煤灰 + 硅灰（FA + SF）浆体在暴露于0.03 - 0.04%、1%和10%二氧化碳后的这些现象进行了研究。研究发现，这些技术中没有一种能明确揭示在将暴露于10%二氧化碳后通过比色法碳化试验结果代入仅考虑二氧化碳浓度差异的换算公式中得出的1%二氧化碳碳化速率被显著低估的原因。可能是由于在过高的二氧化碳水平下碳化产生过多水分，产生孔隙堵塞效应，且二氧化碳溶解度降低，这在其中起到了重要作用。
