Influence of multi-walled carbon nanotubes on the hydration products of ordinary Portland cement paste
Influence of multi-walled carbon nanotubes on the hydration products of ordinary Portland cement paste
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DOI：
10.1016/j.cemconres.2020.106197
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发表时间：
2020-11-01
影响因子：
11.4
通讯作者：
Akono, Ange-Therese
中科院分区：
文献类型：
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作者：
Chen, Jiaxin;Akono, Ange-Therese
我们阐明了多壁碳纳米管（MWCNTs）影响水泥浆体的微观结构，断裂行为和水化的机制。我们使用多步骤方法分散多壁碳纳米管，该方法包括使用超声能量进行高能预分散，然后使用未水合水泥颗粒进行低能分散。低能量分散步骤又涉及高剪切混合和机械搅拌。水泥+0.2wt%MWCNT、水泥+0.5wt%MWNCT和水泥+1wt%MWCNT的高分辨率环境扫描电子显微镜显示，MWCNT桥接空气空隙，从而细化孔径并强化C-S-H基质。添加0.2wt%的多壁碳纳米管使复合材料的断裂韧性提高了9.38%，添加0.5wt%的多壁碳纳米管使复合材料的断裂韧性提高了14.06%，韧带桥接是主要的增韧机制。此外，对于所有增强水平，MWCNT诱导低密度C-S-H转化为高密度C-S-H沿着毛细管孔隙率的急剧下降：添加0.1-0.5重量% MWCNT导致高密度C-S-H的体积分数增加200%。因此，我们的实验表明，MWCNT通过以下方式增强机械性能和传输性能：（i）促进高密度C-S-H形成，（ii）促进氢氧化钙形成，（iii）填充微观空隙，（iv）降低毛细管孔隙率，（v）增加小凝胶孔（尺寸为1.2- 2nm）的分数，和（vi）桥接微裂纹。
We elucidate the mechanisms by which multi-walled carbon nanotubes (MWCNTs) influence the microstructure, fracture behavior, and hydration of cement paste. We disperse MWCNTs using a multi-step approach that involves high-energy pre-dispersion using ultrasonic energy followed by low-energy dispersion using un-hydrated cement particles. In turn, the low-energy dispersion step involves high-shear mixing and mechanical stirring. High-resolution environmental scanning electron microscopy of cement+0.2 wt% MWCNT, cement+0.5 wt% MWNCT, and of cement+1 wt% MWCNT show that MWCNTs bridge air voids, thereby refining the pore size and strengthening the C-S-H matrix. The fracture toughness increased by 9.38% with the addition of 0.2 wt% multi-walled carbon nanotubes, and by 14.06% with the addition of 0.5 wt% multi-walled carbon nanotubes and ligament bridging was the dominant toughening mechanism. Moreover, for all reinforcement levels, MWCNTs induced a conversion of low-density C-S-H into high-density C-S-H along with a drastic drop in the capillary porosity: adding 0.1-0.5 wt% MWCNT resulted in a 200% increase in the volume fraction of high-density C-S-H. Thus, our experiments show that MWCNT enhances the mechanical properties and transport properties by: (i) promoting high-density C-S-H formation, (ii) promoting calcium hydroxide formation, (iii) filling microscopic air voids, (iv) reducing the capillary porosity, (v) increasing the fraction of small gel pores (1.2-2 nm in size), and (vi) by bridging microcracks.