29Si固体核磁共振技术在水泥基材料定量分析中的应用

29 Si固体核磁共振技术是目前研究水泥基材料定量分析的有效工具之一,在水泥化学领域应用广泛.从现代分析测试技术入手,突出了29 Si固体核磁共振技术在水泥化学中的优势,并结合29 Si固体核磁共振定量分析技术和数据,从硅酸盐水泥熟料矿物组分、硅酸盐水泥水化过程量化表征及硅灰掺入的其他水泥基材料的定量分析等方面综述了29 Si固体核磁共振技术在水泥基材料定量分析中的应用,总结了29 Si固体核磁共振技术在水泥基材料领域定量分析存在的问题并展望了核磁共振技术在水泥基材料领域的发展趋势.     

固体核磁共振技术在C-S-H中的研究进展

C-S-H是水泥水化的主要胶凝材料,其结构直接影响混凝土工程性,由于其结晶度较低,中短程有序,采用固体核磁(NMR)可作为分析其结构的方法之一。本文从C-S-H的模型,NMR中特征参数,平均分子链长(MCL)和聚合度三个角度,对水化龄期、掺合料、钙硅比三个方面进行了综述,并展望了固体核磁技术在C-S-H中的发展趋势。     

低Ca/Si比的C-S-H凝胶产物在抑制AAR中的作用

碱是混凝土发生碱-集料(AAR)反应的重要因素之一。许多资料报道低Ca/Si比的C-S-H凝胶对碱有强烈的吸附作用。从C-S-H凝胶的组成出发,指出低Ca/Si比的C-S-H凝胶在抑制AAR中的作用,解释了低Ca/Si的C-S-H凝胶对碱的吸附能力强的原因及其影响因素。为在实际工程应用中掺加混合材来抑制AAR反应,提高混凝土耐久性有重大指导意义。     

C-S-H凝胶产物的Ca/Si比对碱-骨料反应的影响

采用混凝土加速实验,对添加不同混合材试样的膨胀率和试样中生成的C-S-H凝胶产物进行了研究,测定了不同混合材对试样膨胀率的影响以及所生成的C-S-H凝胶的化学组成,进一步验证C-S-H凝胶的Ca/S i比对碱骨料反应(AAR)的影响。     

硬化水泥浆体中C-S-H凝胶体内纳米孔的稳定性分析

运用毛细管张力、表面自由能及弹性力学理论,建立了硬化水泥浆体中C-S-H凝胶体内纳米孔的失稳坍塌模型;根据Gibbs自由能理论从二维饱和孔隙水状态下分析了孔洞的稳定性.结果表明,当孔径在纳米量级范围内变化时,孔洞越大形状越圆越稳定,进入微米量级后,发生坍塌的可能性很小;当孔径一定时,水化产物的弹性模量越大则孔洞越稳定.     

提钛尾渣对硅酸盐水泥水化性能的影响

提钛尾渣是高钛型高炉渣提取合金后的残渣,与铝酸盐水泥的化学、矿物组成相近,具有较好的水化活性.分析不同掺量的提钛尾渣对硅酸盐水泥复合胶凝体系的凝结时间、水化放热、力学性能和水化产物的影响.结果发现,掺量20％提钛尾渣会导致复合胶凝体系早凝,水化初期的水化放热速率加快,累积放热量降低,1 d的水化产物中氢氧化钙减少,单硫型水化硫铝酸钙和三水铝石增多.不同掺量的提钛尾渣均会促进水泥早凝,降低力学性能.随着提钛尾渣掺量的增加,水泥的早凝不明显,力学性能有所增长,水化产物中出现CAH10和C3 AH6的特征峰.     

硅酸盐水泥在使用及养护过程中的化学反应

论述了硅酸盐水泥在使用及养护过程中的化学反应,对硅酸盐水泥在使用及养护过程加以理论指导,以提高建筑工程强度和其它物理力学性能指标。     

硅(铝)酸盐类矿物晶体的27Al、29Si固体高分辨率核磁共振图谱解析方法

从核磁共振的基本原理入手,结合硅(铝)酸盐类矿物材料晶体结构特点,总结了利用27Al、29Si-NMR测试技术对该类材料的晶体结构进行分析时,应考虑的因素和注意事情,并以变高岭石例进行解析,为核磁共振方法在硅(铝)酸盐类矿物晶体结构分析中的合理运用和分析提供了参考.     

核磁共振技术在HDPE耐候性研究中的应用

本文介绍了核磁共振的基本原理及特点，用＾１３Ｃ ＮＭＲ谱分析法对ＨＤＰＥ老化机理，晶态变化进行了分析。     

差热分析在水泥水化研究中的应用

简述了差热分析与热重分析的测定原理，介绍了差热与热重分析在研究水泥水化速度及进程上的应用，和水化产物转变温度及其热效应的确定方法。结论是热分析方法可以确定水泥的水化产物种类、水化产物在加热过程中转变的温度范围、热效应以及水泥水化的进程和速度等。     

Composition, morphology and nanostructure of C-S-H in white Portland cement pastes hydrated at 55 °C

The C-S-H present in water- and alkali-activated hardened pastes of white Portland cement hydrated at 55 °C has been characterized. The mean length of the aluminosilicate anions in the C-S-H was similar in both systems and increased with age. Inner product C-S-H generally had a fine scale, homogeneous morphology. Outer product C-S-H was generally fibrillar with water, and foil- or lath-like with alkali. There were some regions of C-S-H with coarse morphology. It was not possible to determine the chemical composition of C-S-H using the SEM; TEM-EDX was necessary. The C-S-H formed in the alkali-activated paste had a lower mean Ca/(Al + Si) ratio than that formed with water, which was offset by a larger quantity of calcium hydroxide. The potassium in the KOH-activated paste was present either within the C-S-H structure charge balancing the substitution of Al³⁺ for Si⁴⁺, or adsorbed on the C-S-H charge balancing sulfate ions.     

Indirect determination of the Ca/Si ratio of the C-S-H gel in Portland cements

An alternative method for the indirect determination of the Ca/Si ratio of the C-S-H gel in Portland cements is proposed. It is based on graphical correlations of experimental determinations of the degree of hydration of alite and the amount of calcium hydroxide formed with theoretical data based on the hydration reactions of the alite and belite present in the cement. The initial composition of the cements is of prime importance in these calculations; the phase composition obtained by use of the Bogue, Taylor's modified Bogue, and quantitative X-ray diffraction methods gave rise to some differences in the results obtained. Ca/Si ratios determined using the Bogue composition were consistently lower than those from Taylor's method and the quantitative X-ray diffraction analysis methods for both the Portland cements studied. The Ca/Si ratios estimated based on the mineralogical phase compositions determined from these latter methods agreed well with those from energy dispersive X-ray spectroscopy measurements.     

Zr K-Edge XAS and 29Si MAS NMR Studies on Hexagonal Mesoporous Zirconium Silicate

Hexagonal mesoporous silicate (HMS) molecular sieve containing zirconium species (Zr-HMS) has been synthesized using a neutral template of hexadecylamine with ethanol and water. A disordered channel structure with a uniform diameter of 44.1 Å was confirmed by powder X-ray diffraction after calcination. From N₂ adsorption/desorption measurement, it is found that Zr-HMS has a very high surface area of about 910 m²/g (BET) and a mesopore with a size of 21 Å (BJH). According to the X-ray absorption spectroscopy at the Zr K-edge, it is confirmed that Zr atoms are coordinated by six oxygen neighbors with a distance of 2.13 Å, which is shorter than the (Zr—O) bond distance found in ZrO₂ or ZrOCl₂·8H₂O. The ²⁹Si MAS-NMR spectrum for Zr-HMS shows two additional peaks around –94.6 and –107.2 ppm due to the Q³Zr and Q⁴Zr components, respectively, besides three peaks at –91.1, –101.5, and –111.3 ppm due to the silicate network. The relation between the pore and crystal structures and the local environment around Zr is discussed in detail.     

A new aluminium-hydrate species in hydrated Portland cements characterized by Al and Si MAS NMR spectroscopy

Recent ²⁷Al MAS NMR studies of hydrated Portland cements and calcium-silicate-hydrate (C-S-H) phases have shown a resonance from Al in octahedral coordination, which cannot be assigned to the well-known aluminate species in hydrated Portland cements. This resonance, which exhibits the isotropic chemical shift δ_iso = 5.0 ppm and the quadrupole product parameter P_Q = 1.2 MHz, has been characterized in detail by ²⁷Al MAS and ²⁷Al{¹H} CP/MAS NMR for different hydrated white Portland cements and C-S-H phases. These experiments demonstrate that the resonance originates from an amorphous or disordered aluminate hydrate which contains Al(OH)₆³⁻ or O_xAl(OH)_6-x^(3+x)− units. The formation of the new aluminate hydrate is related to the formation of C-S-H at ambient temperatures, however, it decomposes by thermal treatment at temperatures of 70-90 °C. From the experiments in this work it is proposed that the new aluminate hydrate is either an amorphous/disordered aluminate hydroxide or a calcium aluminate hydrate, produced as a separate phase or as a nanostructured surface precipitate on the C-S-H phase. Finally, the possibilities of Al³⁺ for Ca²⁺ substitution in the principal layers and interlayers of the C-S-H structure are discussed.     

Characterization of white Portland cement hydration and the C-S-H structure in the presence of sodium aluminate by Al and Si MAS NMR spectroscopy

The effects of hydrating a white Portland cement (wPc) in 0.30 and 0.50 M solutions of sodium aluminate (NaAlO₂) at 5 and 20 °C are investigated by ²⁷Al and ²⁹Si magic-angle spinning (MAS) NMR spectroscopy. It is demonstrated that NaAlO₂ accelerates the hydration of alite and belite and results in calcium-silicate-hydrate (C-S-H) phases with longer average chain lengths of SiO₄/AlO₄ tetrahedra. The C-S-H phases are investigated in detail and it is shown that the Al/Si ratio for the chains of tetrahedra is quite constant during the time studied for the hydration (6 h to 2 years) but increases for higher concentration of the NaAlO₂ solution. The average chain lengths of “pure” silicate and SiO₄/AlO₄ tetrahedra demonstrate that Al acts as a linker for the silicate chains, thereby producing aluminosilicate chains with longer average chain lengths. Finally, it is shown that NaAlO₂ reduces the quantity of ettringite and results in larger quantities of monosulfate and a calcium aluminate hydrate phase.     

重金属离子对水化硅酸钙结构和形貌的影响

采用碱硅酸盐和钙盐的溶液反应方法,合成初始钙硅比为0.8、1.8的掺杂不同重金属离子的水化硅酸钙(C-S-H).对制备的C-S-H进行了XRD、IR、SEM测试分析,结果表明,掺杂重金属离子的低钙硅比C-S-H凝胶的衍射主峰强度下降,谱峰宽度增加;高钙硅比凝胶中钙和硅氧四面体的化学键遭到破坏,使Ca2+溶出,形成Ca(OH)2晶体;掺杂Pb的高钙硅比C-S-H凝胶,Q2伸缩振动峰向低波数方向偏移,Q1伸缩振动峰的吸收强度增加,硅氧四面体聚合度逐渐降低,链长变短;重金属离子可显著改变低钙硅比C-S-H凝胶形貌,使高钙硅比凝胶呈不规则团块状堆积.     

Si and Al NMR study of alkali-activated slag

This paper presents the results of the investigation of the hydration of alkali-activated slag (AAS) by nuclear magnetic resonance spectroscopy (NMR). The cross-polarization (CP) technique was used in combination with magic-angle spinning (MAS). This research was part of a systematic study of alkaline activation of slag by several different techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with X-ray microanalysis of energy dispersive spectra (EDS), differential thermal analysis (DTA) and calorimetry. This NMR study provides information on the polymerization of silicates, the role of aluminates in cement hydration and the nanostructure of C-S-H gel.