脱钙对水泥浆体中C-S-H凝胶结构的影响

Effect of Decalcification on C-S-H Gel Microstructure in Cement Paste

采用X射线荧光分析、X射线衍射、Fourier红外光谱、^(29)Si固体核磁共振谱结合去卷积技术研究了脱钙对水泥(ASTMⅠ型)浆体中C-S-H凝胶结构的影响.结果表明:对于水化3,28d的水泥浆体,其脱钙过程均为2个阶段,即:当水泥浆体的钙硅比(摩尔比)由2.78左右降至2.00左右时,几乎全部游离的CH被脱去,C-S-H凝胶部分脱钙,浆体的脱钙主要在这个阶段完成,C-S-H平均链长分别由2.4,2.9增加至4.4,5.8,且I(Q^2)/I(Q^1)增加;当水泥浆体的钙硅比降至1.83左右时,C-S-H凝胶脱钙,并产生了更显著的聚合,C-S-H平均链长进一步分别增加至6.2,9.9,且I(Q^2)/I(Q^1)继续增加;Alite和Belite在整个脱钙过程中的变化并不明显.脱钙过程中C-S-H二聚体向更高聚合态转变,但是Al掺杂会影响C-S-H结构的稳定性.从分子尺度理解,脱钙如能使桥硅氧四面体结构稳定,对于C-S-H结构的优化是有利的.

Effect of decalcification on microstructure of C-S-H gel in ASTMⅠcement paste were studied by X-ray fluorescence spectrometer（XRF）,X-ray diffraction（XRD）,infrared spectroscopy with Fourier transform（FTIR） and ^（29）Si MAS NMR with deconvolution technique.It is shown from test results that the decalcification process can be divided into two stages.When the molar ratio of CaO to SiO2 in the pastes at 3,28 d is lowered from～2.78 to～2.00,almost all of CH is removed and C-S-H gel is partially decalcified, the average chain length（ACL） of C-S-H is increased from 2.4 to 4.4 for 3 d paste and from 2.9 to 5.8 for 28 d paste respectively,and I（Q^2）/I（Q^1） is also increased.While the molar ratio of CaO to SiO2 in the pastes comes to～1.83,decalcification of C-S-H gel occurs.C-S-H polymerizes and I（Q^2）/I（Q^1） increases largely in this stage,which results in further increase of ACL to 6.2 for 3 d paste and 9.9 for 28 d paste.The mechanism of increase of C-S-H polymerization could be transformation of dimeric C-S-H toward highly polymerized C-S-H.However,Al doping could affect the stability of C-S-H microstructure. In molecular level,the existence of the pure bridging silicon-oxy tetrahedrons in C-S-H is beneficial to the optimization of the microstructure.