Microstructural Changes Induced by CO2 Exposure in Alkali-Activated Slag/Metakaolin Pastes
Microstructural Changes Induced by CO2 Exposure in Alkali-Activated Slag/Metakaolin Pastes
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DOI：
10.3389/fmats.2016.00043
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发表时间：
2016-09-16
影响因子：
3.2
通讯作者：
Bernal, Susan A.
中科院分区：
文献类型：
--
作者：
Bernal, Susan A.
研究了碱矿渣/偏高岭土（MK）水泥中加速碳酸化引起的结构变化。在CO2浓度为1.0 +/-0.2%、温度为20 +/- 2 ℃、相对湿度为65 +/-5%的环境室中将试样碳酸化540 h。加速的碳酸化导致这些水泥的主要结合相脱钙，其是铝取代的硅酸钙水合物（C-（N-）A-S-H）型凝胶，并且随后形成碳酸钙。在含有高达10 wt.%的水泥中鉴定出富钠碳酸盐天然碱（Na 2CO 3中心点NaHCO 3中心点2 H（2）O）和钙铝石（Na 2Ca（CO 3）（2）中心点5 H（2）O MK作为碳酸化产物。这些碳酸盐的形成主要与孔隙溶液中存在的游离碱与CO2之间的化学反应有关。碳酸盐胶结物的结构主要由铝硅酸盐水合物（N-A-S-H）型凝胶组成，与MK含量无关。所鉴定的N-A-S-H型凝胶可能来源于MK的活化反应，形成低钙凝胶产物，其在CO2暴露时似乎不发生结构变化，以及C-（N-）A-S-H型凝胶的脱钙作用。碳酸化浆体呈现出高度多孔的微观结构，随着水泥中MK含量的增加而更加显著，这可能对这些材料在使用中的耐久性产生负面影响。
The structural changes induced by accelerated carbonation in alkali-activated slag/metakaolin (MK) cements were determined. The specimens were carbonated for 540 h in an environmental chamber with a CO2 concentration of 1.0 +/- 0.2%, a temperature of 20 +/- 2 degrees C, and relative humidity of 65 +/- 5%. Accelerated carbonation led to decalcification of the main binding phase of these cements, which is an aluminum substituted calcium silicate hydrate (C-(N-)A-S-H) type gel, and the consequent formation of calcium carbonate. The sodium-rich carbonates trona (Na2CO3 center dot NaHCO3 center dot 2H(2)O) and gaylussite (Na2Ca(CO3)(2)center dot 5H(2)O) were identified in cements containing up to 10 wt.% MK as carbonation products. The formation of these carbonates is mainly associated with the chemical reaction between the CO2 and the free alkalis present in the pore solution. The structure of the carbonated cements is dominated by an aluminosilicate hydrate (N-A-S-H) type gel, independent of the MK content. The N-A-S-H type gels identified are likely to be derived both from the activation reaction of the MK, forming a low-calcium gel product that does not seem to undergo structural changes upon CO2 exposure, and the decalcification of C-(N-) A-S-H type gel. The carbonated pastes present a highly porous microstructure, more notable as the content of MK content in the cement increases, which might have a negative impact on the durability of these materials in service.