摘要
基于分子动力学方法,探究了4种阳离子(
除冰环境中的钢筋混凝土结构在服役期间会受到氯盐侵蚀的作
分子动力学作为一种基于力场的纳观尺度模拟方法,可以辅助解释试验结果,并对从分子水平上理解结构的动力学性质方面起到补充作
本文采用分子动力学模拟,分析了除冰剂中4种典型的阳离子(
为研究4种阳离子(
采用硅链间距1.1 nm的托贝莫来石作为原始结构,在Materials Studio软件中进行建模计算.为了使结构细节更加贴近于C‑S‑H,参照文献[

图1 模型建立
Fig.1 Model establishment
本文中NaCl溶液的浓度设定为2.0 mol/L,其余氯盐溶液中氯离子浓度与之相同,具体离子比例见
Solution | Cation | Chloride ion | Water |
---|---|---|---|
NaCl | 18 | 18 | 500 |
KCl | 18 | 18 | 500 |
MgCl2 | 9 | 18 | 500 |
CaCl2 | 9 | 18 | 500 |
为建立溶液扩散模型,保证C‑S‑H模型最易暴露的面与氯盐溶液接触,需要对已有的C‑S‑H分子模型进行如下处理:首先,将C‑S‑H晶胞沿[0,0,1]方向切割,使层间水分子和钙离子暴露在表面,同时在x、y方向上保持周期性;然后,构建C‑S‑H凝胶/溶液/C‑S‑H凝胶孔扩散模型,2个C‑S‑H凝胶层之间距离为3 nm,见

图2 C‑S‑H凝胶孔扩散模型
Fig.2 C‑S‑H gel pore diffusion model

图3 离子强度分布
Fig.3 Ionic intensity distribution
由

图4 表面钙离子强度分布
Fig.4 Ionic intensity distribution of Ca
(1) |
(2) |
综上,由于双电层效应,C‑S‑H对阳离子的吸附量影响着对氯离子的吸附能力.钾离子和钠离子主要被吸附在C‑S‑H表面;由于较高的电荷量,钙离子和镁离子不仅被吸附在C‑S‑H表面,还会在溶液中形成团簇,使C‑S‑H中更多的Ca脱附进入溶液中,为氯离子提供了更多的吸附点位.

图5 离子对的径向分布
Fig.5 Radial distribution of ionic pairs
(3) |
式中:r为某离子与中心离子的距离;N为(r,r+dr)范围内包含的粒子数;ρ为系统离子总数与体积的比值.
由
由
由
由
由
由
文献[
均方位移M(t)和扩散系数D是估计离子动态性质的参数,可分别由式(
(4) |
(5) |
式中:表示离子i在t时刻的位置;表示离子i的原始位置.

图6 离子均方位移曲线
Fig.6 Mean square displacement curves of ions
由

图7 各氧盐溶液中离子扩散系数
Fig.7 Ionic diffusion coefficient in different chloride solutions
(1)在C‑S‑H凝胶孔中,氯离子强度峰位分布与阳离子的分布特点相似.钾离子和钠离子倾向于吸附在C‑S‑H层表面;钙离子和镁离子不仅能吸附在C‑S‑H表面,由于其较大的电荷密度,还能在溶液中吸引附近离子形成更加复杂的团簇结构,并导致部分表面钙离子从C‑S‑H结构中解离进入到溶液中,从而为氯离子提供更多的潜在吸附位点,引起C‑S‑H结构腐蚀破坏.
(2)C‑S‑H凝胶孔中不同氯盐溶液中的氯离子具有不同的扩散行为,各溶液吸附氯离子能力大小依次为CaCl2>MgCl2>NaCl>KCl.基于分子动力学将其归结为以下3个原因:氯离子会以O‑阳离子‑C
(3)在凝胶层间距为3 nm的C‑S‑H模型中,阳离子扩散能力低于氯离子.这主要是由于C‑S‑H表面带负电,阳离子易被限制在其表面附近.宏观上4种溶液中氯离子的扩散能力大小依次为KCl>NaCl>CaCl2>MgCl2,即氯离子扩散能力与C‑S‑H对氯离子的吸附能力顺序不同.这主要是由于自由氯离子越少,其扩散能力越低,且氯化镁溶液中氯离子易与凝胶孔中的水分子相互吸引形成水合结构,进一步限制氯离子扩散,导致氯化镁溶液中氯离子扩散能力低于氯化钙溶液.
参考文献
张鹏,庄智杰,鲍玖文,等.人工模拟海洋潮汐区应变硬化水泥基复合材料抗氯盐侵蚀性能[J].建筑材料学报, 2021, 24(1):1‑6,21. [百度学术]
ZHANG Peng, ZHUANG Zhijie, BAO Jiuwen. et al. Chloride resistance of strain hardening cementitious composites under the artificially simulated marine tidal zone[J]. Journal of Building Materials, 2021,24(1):1‑6, 21. (in Chinese) [百度学术]
AVIJA B, PACHECO J, SCHLANGEN E. Lattice modeling of chloride diffusion in sound and cracked concrete[J]. Cement Concrete Composites, 2013, 42:30‑40. [百度学术]
JIANG L H, LI C Z, ZHU C L, et al. The effect of tensile fatigue on chloride ion diffusion in concrete[J]. Construction and Building Materials, 2017, 151:119‑126. [百度学术]
ZHANG Y S, SUN W, CHEN S D, et al. Two‑ and three‑dimensional chloride ingress into fly ash concrete[J]. Journal of Wuhan University of Technology(Materials Science), 2011, 26(5):978‑982. [百度学术]
ZHANG T W, GJORV O E. Diffusion behavior of chloride ions in concrete[J]. Cement and Concrete Research, 1996, 26(6):907‑917. [百度学术]
汪林萍, 杨全兵.NaCl‑MgCl2复合除冰盐对混凝土盐冻破坏的影响及其作用机理[J].建筑材料学报, 2023, 26(2):129‑136,149. [百度学术]
WANG Linping, YANG Quanbing. Effect and mechanism of NaCl‑MgCl2 compounded deicing salt on the salt‑frost scaling of concrete[J]. Journal of Building Materials, 2023, 26(2):129‑136,149. (in Chinese) [百度学术]
李闯,范颖芳,王耀宇,等.钢筋-煤系偏高岭土水泥砂浆抗氯盐-硫酸盐侵蚀性能[J].建筑材料学报, 2022, 25(5):447‑453. [百度学术]
LI Chuang, FAN Yingfang, WANG Yaoyu, et al. Corrosion resistance to chloride and sulfate salt attack of steel bar‑cement mortar containing coal metakaolin[J]. Journal of Building Materials, 2022, 25(5):447‑453. (in Chinese) [百度学术]
岳青滢,丁宁,王石付,等.阳离子类型对混凝土固化氯离子能力的影响机理[J].混凝土, 2014(1):12‑16, 20. [百度学术]
YUE Qingying, DING Ning, WANG Shifu, et al. Effect of cationic types on concrete resistance to chloride ingress[J]. Concrete, 2014(1):12‑16,20. (in Chinese) [百度学术]
刘建华,陈磊,吴绍明,等.阳离子类型对粉煤灰混凝土氯离子扩散性能的影响[J].硅酸盐通报, 2022, 41(6):1920‑1929. [百度学术]
LIU Jianhua, CHEN Lei, WU Shaoming, et al. Effect of cation type on chloride diffusion properties of fly ash concrete[J]. Bulletin of the Chinese Ceramic Society, 2022, 41(6):1920‑1929. (in Chinese) [百度学术]
LIU H Q, YANG X Q, JIANG L H. Effect of combined cations on chloride diffusion behavior in concrete[J]. Construction and Building Materials, 2022, 339:127669. [百度学术]
杨永敢,康子豪,詹炳根,等.初始损伤混凝土的抗硫酸盐侵蚀性能[J].建筑材料学报, 2022, 25(12):1255‑1261. [百度学术]
YANG Yonggan, KANG Zihao, ZHAN Binggen, et al. Sulfate resistance of concrete with initial damage[J]. Journal of Building Materials, 2022, 25(12):1255‑1261. (in Chinese) [百度学术]
ARYA C, BUENFELD N R, NEWMAN J B. Factors influencing chloride‑binding in concrete[J]. Cement and Concrete Research, 1990, 20(2):291‑300. [百度学术]
DAS J K, PRADHAN B. Effect of cation type of chloride salts on corrosion behavior of steel in concrete powder electrolyte solution in the presence of corrosion inhibitors[J]. Construction and Building Materials, 2019, 208:175‑191. [百度学术]
杨清瑞,金祖权,王攀,等.温度影响epoxy/C‑S‑H界面黏结性能的分子动力学模拟[J].建筑材料学报, 2022, 25(10):1086‑1091. [百度学术]
YANG Qingrui, JIN Zuquan, WANG Pan, et al. Molecular dynamics simulation of temperature‑influenced epoxy/C‑S‑H interfacial bonding properties[J]. Journal of Building Materials, 2022, 25(10):1086‑1091. (in Chinese) [百度学术]
HOU D S, LI D K, YU J, et al. Insights on capillary adsorption of aqueous sodium chloride solution in the nanometer calcium silicate channel:A molecular dynamics study[J]. Journal of Physical Chemistry, 2017, 121(25):13786‑13797. [百度学术]
ZHOU Y, HOU D S, JIANG J Y, et al. Experimental and molecular dynamics studies on the transport and adsorption of chloride ions in the nano‑pores of calcium silicate phase:The influence of calcium to silicate ratios[J]. Microporous and Mesoporous Materials, 2018, 255:23‑35. [百度学术]
PELLENQ R J M, KUSHIMA A, SHAHSAVARI R, et al. A realistic molecular model of cement hydrates[J]. Proceedings of the National Academy of Sciences of the United States of America, 2009, 106(38):16102‑16107. [百度学术]
HOU D S, ZHANG J R, LI Z J, et al. Uniaxial tension study of calcium silicate hydrate (C‑S‑H):Structure, dynamics and mechanical properties[J]. Materials and Structures, 2015, 48(11):3811‑3824. [百度学术]
THOMAS M D A, HOOTON R D, SCOTT A, et al. The effect of supplementary cementitious materials on chloride binding in hardened cement paste[J]. Cement and Concrete Research, 2012, 42(1):1‑7. [百度学术]
CYGAN R T, LIANG J J, KALINICHEV A G. Molecular models of hydroxide, oxyhydroxide, and clay phases and the development of a general force field[J]. Journal of Physical Chemistry B, 2004, 108(4):1255‑1266. [百度学术]
LIU J, WANG Y D, SABERI F K, et al. Impact of deicers on low‑temperature performance of Missouri pavements[C]//International Conference on Transportation and Development 2022. Seattle:American Society of Civil Engineers(ASCE), 2022, 5:258‑268. [百度学术]
POURSAEE A, LAURENT A, HANSSON C M. Corrosion of steel bars in OPC mortar exposed to NaCl, MgCl2 and CaCl2:Macro‑ and micro‑cell corrosion perspective[J]. Cement and Concrete Research, 2010, 40(3):426‑430. [百度学术]
DAS J K, PRADHAN B. Impact of cation type of chloride salts on diffusion behavior and binding capacity of chloride ions in concrete containing sodium nitrite and disodium hydrogen phosphate[J]. Journal of Materials in Civil Engineering, 2022, 34(4):04022013. [百度学术]
ZHU Q, JIANG L H, CHEN Y, et al. Effect of chloride salt type on chloride binding behavior of concrete[J]. Construction and Building Materials, 2012, 37:512‑517. [百度学术]
SONG Z J, JIANG L H, LIU J Z, et al. Influence of cation type on diffusion behavior of chloride ions in concrete[J]. Construction and Building Materials, 2015, 99:150‑158. [百度学术]
MA H Y, LI Z J. Realistic pore structure of Portland cement paste:Experimental study and numerical simulation[J]. Computers and Concrete, 2013, 11(4):317‑336. [百度学术]