多壁碳纳米管增强水泥基复合材料的纳米力学性能

Nanomechanical properties of multi-wall carbon nanotubes/cementitious composites

采用纳米压痕技术探讨了多壁碳纳米管(MWCNTs)对有骨料水泥基复合材料纳米尺度上力学性能的影响,分别对压痕模量(M)小于50 GPa和压痕硬度(H)小于4.0 GPa的数据进行了统计,对其频率分布进行了Gaussian函数(PDF)的解卷积分峰处理,并对低密度水化硅酸钙凝胶(LD C-S-H)和高密度水化硅酸钙(HD C-S-H)凝胶进行了定量的体积分数计算。结果表明,除LD C-S-H、 HD C-S-H、 Ca(OH)2(CH)外,还出现了一个假相。MWCNTs降低了水化产物中LD C-S-H的体积分数,提高了HD C-S-H的体积分数,提高了C-S-H凝胶的压痕模量,但利用压痕模量和压痕硬度统计结果计算出的各相体积分数存在一定的差异。MWCNTs作为一种纳米晶核,对HD C-S-H凝胶形成起到了一定的诱导作用,从纳观尺度阐释了MWCNTs对水泥基材料的改性机制。

The effect of multi-wall carbon nanotubes(MWCNTs) on the nanomechanical properties of cementitious materials with sand was investigated by nanoindentation technique. The original mechanical values of the indentation modulus(M) and indentation hardness(H) under 50 GPa and 4.0 GPa were statistically analyzed. The experimental frequency plot and fitted Gaussian probability density functions(PDF) were got by deconvolution technique. The quantitative computation of the volume fraction of the low density C-S-H gel(LD C-S-H) and the high density C-S-H gel(HD C-S-H) was performed. In addition to LD C-S-H, HD C-S-H and calcium hydroxide(CH), a spurious phase is found in the hydration products. With the addition of MWCNTs, the volume fraction of LD C-S-H decreases and the volume fraction of HD C-S-H increases, the modulus of C-S-H is improved. But the volume fractions of each phase calculated from the testing results of modulus and indentation hardness are different. MWCNTs induce the formation of HD C-S-H as nanocrystals, which reveals the mechanism of how MWCNTs enhance the properties of cementitious materials.