钙硅比对水化硅酸钙加速碳化的影响

废弃水泥石、钢渣等碳酸化固定CO2不仅可以缓解温室效应还可以实现废弃物的再利用,同时制备出性能优良的建材制品。为了研究废弃水泥石矿物组成的碳酸化机理,探讨了钙硅比对水化硅酸钙加速碳化的影响。结果表明:随着钙硅比增加,水化硅酸钙(C-S-H)碳化率逐渐降低,高钙硅比的C-S-H具有相对粗大的孔结构使得早期的碳化速率增加;碳化产物中文石、球霰石、方解石在不同钙硅比时所占比例不同,钙硅比≤0.67时文石占较大比例,钙硅比≥1.00时方解石为主要碳化产物,钙硅比=0.83时球霰石含量最大;加速碳化条件下形成的碳酸钙分解温度分成两部分,在400~620℃范围内文石和球霰石都分解,方解石在650~800℃范围内分解。     

水化硅酸钙的碳化作用

本文研究水化硅酸钙的碳化作用。研究了低温合成β-C_2S和C_3S在的完全水化物及部分水化物的碳化性能,发现β-C_2S水化物比C_3S 水化物的碳化速率为高,说明碱度较低的水化硅酸钙比碱度较高的水化硅酸钙容易碳化。实验证实了碳化能够促进硅酸钙的水化,从而较好地解释了β-C_2S试体经碳化后强度迅速增长的现象。从β-C_2S碳化试体的长期强度低于正常养护的试件这一事实,提出这主要是因水化硅酸钙经碳化后体积减小,从而使碳化试体密实度低于正常养护试体而引起的。文章探讨了水化硅酸钙碳化过程中C-S-H凝胶化学组成的变化,得出 C-S-H 凝胶经碳化后,其C/S比逐渐下降直至完全分解为碳酸钙和硅胶。文章还探讨了水化硅酸钙的碳化动力学。以红外光谱分析和X射线衍射分析相结合研究了碳化生成的碳酸钙和硅胶的形态和性质,并采用透射电子显微镜对水化硅酸钙及其碳化产物的形貌进行了观察。     

水化硅酸钙的结晶度与碳化速度

本研究通过实验证明水化硅酸钙的结晶度对碳化速度有很大影响。水化产物的结晶度愈差,比表面积愈大,在相同条件下,碳化速度愈高,制品的碳化收缩剧烈,则在制品内部易引起收缩微裂缝,严重降低制品强度。结晶度高的制品,碳化速度很慢,碳化收缩引起的内应力可由制品的塑性变形消除,不会产生微裂缝,因此碳化后强度不会降低或降低很少。所以结晶度差的制品应设法提高其结晶度,以使制品的耐久性得到保证。     

用IR方法研究硅酸钙水化产物的碳化

本文用红外光谱分析研究了水化硅酸钙碳化产物的性质,发现水化βC_2S 的早期碳化产物为方解石和文石,但在后期,文石又转变成方解石,水化 C_3S 的碳化产物不管是早期还是后期均生成方解石,而无其它晶型的碳酸钙生成。水化硅酸钙碳化时生成硅胶。硅酸钙的水化产物 Ca(OH)_2和 C—S—H 凝胶这两者的碳化性能总的来说区别不大,但在碳化初期,Ca(OH)_2的碳化稍优先于 C—S—H 凝胶。     

纳米水化硅酸钙的制备及对水泥水化影响的研究进展

随着纳米技术的不断发展,纳米材料逐步开始应用于传统混凝土材料中,以提高混凝土的各项服役性能。纳米水化硅酸钙(纳米C-S-H)是一种新型的早强纳米复合材料,可通过晶核效应加快水泥早期水化速率,显著提高水泥基材料的早期力学性能,从而提高施工效率,满足特殊施工要求。本文系统总结了纳米C-S-H的制备方法,及纳米C-S-H对水泥基材料早期和长期性能的影响规律,探讨了其对于水泥水化过程和水化产物的影响机制,其中重点介绍了采用聚合物分散纳米颗粒制备的C-S-H/PCE(聚羧酸型减水剂,简称PCE)纳米复合材料。     

湿度对水化硅酸钙力学性能影响的分子动力学模拟

水化硅酸钙(C-S-H)是水泥水化产物中最重要的组成成分,是水泥基材料的主要胶凝相。C-S-H层间水对其纳米结构和力学性能会产生显著影响。利用分子动力学研究了不同湿度C-S-H在结构和力学性能方面的差异。通过原子径向分布函数和浓度分布、弹性常数以及应力应变关系分析了湿度对C-S-H结构和弹性性质以及拉伸、压缩、剪切力学性能和变形性能的影响。结果表明:湿度增加会导致C-S-H中Si、Ca原子近程范围内的O原子集聚增多,还会导致C-S-H层间距离增大,分层更加明显,同时会降低C-S-H的弹性性质;湿度的增加会降低C-S-H拉伸、压缩、剪切力学性能和变形性能;湿度对抗拉与抗剪强度影响较大,对抗压强度影响较小,对拉伸时的变形性能影响最大,对压缩时的变形性能影响最小。     

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.     

水化硅酸钙组成对蒸压硅酸盐材料力学性能的影响

为探究水化产物对加气混凝土(AAC)力学性能的影响规律,采用BET/XRD半定量水化硅酸钙组成,构建基材力学性能随其水化硅酸钙胶体(C-S-H)含量和托勃莫来石含量变化的等值线图,确定基材力学性能与水化产物的关系,建立AAC抗压强度模型。结果表明:砂质AAC中胶体及晶体含量明显高于粉煤灰质AAC;基材抗压强度最优时,水化硅酸钙胶体含量和托勃莫来石晶体含量有着一定的函数关系。抗压强度模型验证表明抗压强度计算值与实测值误差小于2%,抗压强度模型比较可靠。     

水化硅酸钙凝胶的研究进展

水化硅酸钙(C-S-H)凝胶是影响水泥基胶凝材料宏观力学性能与长期耐久性的核心组分,阐明结构和性能间的关联关系有利于实现C-S-H凝胶的合成及推广应用。本文首先对C-S-H凝胶不同阶段的典型结构进行了综述,并引出结构与性能间的内在联系;随后,介绍水热合成法对不同结构C-S-H凝胶的精确调控,并详细阐述了合成要素对其组成、形貌以及结构的影响规律;最后,综述了合成C-S-H凝胶在相关应用领域的基础研究。本文聚焦于C-S-H凝胶构效关系的梳理总结以及C-S-H凝胶工程应用的前景探索,可为充分完善水泥水化机理、开发高性能绿色化建材提供理论参考。     

Calcium Silicate Carbonation Products

calcium silicates such as C₃S, βT-C₂S, and γgM-C₂S ^† were carbonated under saturated humidity at room temperature. Carbonation products were examined by DT-TGA, gasphase mass spectroscopy, and XRD. Two types of carbonate were produced: one type, which was rather poorly crystallized, was decarbonated at a very low temperature, below 600°C; the other type was a crystalline phase such as calcite, aragonite, and/or vaterite which was decarbonated above 600°C. The data were compared to existing data for calcium carbonates and basic calcium carbonates. The results suggest that an amorphous calcium silicate hydrocarbonate was one of the carbonation products which formed during the hydration/carbonation reaction.     

Heteroepitaxial Growth of Calcium Silicate Hydrate on Calcium Germanate Hydrate

The hydration of tricalcium silicate at 25°C was accelerated by seeding with 5 wt% tricalcium germanate. Based on heat evolution, seeding resulted in the elimination of the induction period. However, the shape of the hydration peak remained the same. Because tricalcium germanate hydrates first, the microstructure of the calcium silicate hydrate which subsequently forms is influenced by the calcium germanate hydrate morphology. Calcium silicate hydrate formed in the presence of calcium germanate hydrate exhibits the morphology typical of the latter. Acceleration of hydration and morphological variation indicate heteroepitaxial growth.     

Pore Structure of Calcium Silicate Hydrate in Hydrated Tricalcium Silicate

Adsorption of N₂ and water vapor was studied in completely hydrated tricalcium silicate and in fully hydrated tricalcium silicate from which Ca(OH)₂ had been extracted. Compared with results obtained using N₂, water vapor adsorption led to increased values for small-pore volume, peak shifts to smaller sizes, and decreased values for large-pore volume. Marked hysteresis was observed in the case of water vapor adsorption; the resorption branch apparently represents the true pore structure. Extraction of Ca(OH)₂ from the paste increased the calculated volume of small pores strikingly, suggesting that adsorption is hindered by Ca(OH)₂; this tendency is more obvious in water vapor adsorption. The adsorption measurements indicate the existence of two kinds of pores, i.e. a wider intergel-particle pore and a smaller pore existing within the gel particle. The latter pore was further classified into intercrystallite and intracrystallite pores.     

Proposed Structure for Calcium Silicate Hydrate Gel

Calcium silicate hydrate gel is a very poorly crystalline material that is the main product of reaction of portland cement with water. Evidence is presented for a disordered layer structure, in which most of the layers are structurally imperfect ones of jennite (Ca₉Si₆O₃₂H₂₂), and others are similarly related to 1.4-nm tobermorite (Ca₅Si₆O₂₆H₁₈), both structures being modified by omission of many of their silicate tetrahedra. The evidence comprises conditions of formation, silicate anion type, Ca/Si ratio, H₂O/Ca ratios and densities for various drying conditions, thermogravimetric curve, X-ray powder and selected-area electron diffraction patterns, and results of analytical electron microfcopy.     

Developments in TEM Nanotomography of Calcium Silicate Hydrate

This investigation was designed to explore the possibility of using transmission electron microscope (TEM) tomography on cement‐based systems gain a greater understanding of their nanostructure and pore network. The preliminary results show a clearly a well‐defined pore network at the nanoscale, with pore size approximately 1.7–2.4 nm in diameter and spaced around 5–8 nm apart. A comparison of small angle X‐ray scattering data with 2‐D TEM images analyzed with the Fourier slice theorem documents an excellent structural correlation.     

聚乙烯醇对溶液沉淀法制备的水化硅酸钙纳米结构的影响

通过溶液沉淀法制备了初始钙硅比为1.0～1.7的掺杂PVA的水化硅酸钙(C-S-H-PVA)系列样品,研究了C-S-H-PVA的纳米结构特征.结果表明:PVA的加入增加了C-S-H的层间距,影响了C-S-H的层间结构;C-S-H-PVA样品的Fourier变换红外光谱中出现了CH2/CH伸缩振动峰,29Si核磁共振(NMR)谱中出现了1个Q1峰和2个Q2峰,而且PVA的加入使Q1、Q2峰向更负方向偏移,使Q2/Q1的比值以及硅酸盐链的平均链长(MCL)增长,说明PVA能增加C-s-H结构中的硅氧四面体聚合度.随着钙硅比的增加,C-S-H-PVA样品的29Si NMR谱中Q1、Q2峰的化学位移向正方向偏移,Q2/Q1的比值以及MCL减小,这一变化规律与未掺PVA的C-S-H样品的变化规律类似.     

Synthesis of Calcium Silicate Hydrate in Highly Alkaline System

Synthesis of calcium silicate hydrate (C‐S‐H) was conducted over the range of 50°C–90°C and C/S ratio of 0.86–2.14 in the highly alkaline Na₂O–CaO–SiO₂–H₂O system for silicon utilization in high alumina fly ash. Structural change in C‐S‐H formed in the highly alkaline system was investigated using XRD and ²⁹Si MAS NMR spectra. X‐ray photoelectron spectroscopy was used to confirm the amount of sodium ions in C‐S‐H. Conversion of Si may reach 99% under optimum conditions. A higher degree of polymerization of silicate was obtained at lower temperature and C/S ratio. Na⁺ was confirmed to exist as Na–OSi and Na–OH. The amount of Na⁺ is the least at C/S ratio of 1.43, which conform to the prediction of topological constraint theory. High Ca/Si ratio leads to the increasing in Na⁺ combined in the interlayer. Increasing in the Na⁺ concentration in the system also increases the amount of Na⁺ combined in the interlayer and reduces the polymerization. Ion exchange was proven to be an effective way to remove Na⁺ combined in the interlayer of C‐S‐H.     

Nanostructure of Calcium Silicate Hydrate Gels in Cement Paste

High-resolution electron microscopy study of calcium silicate hydrate (C-S-H) gels in ordinary portland cement (OPC) and a slag/OPC blend has been performed. Nanocrystalline regions on the scale of ∼5 nm or less in C-S-H are found in both cement pastes, and they are formed after a curing time as brief as 7 d. A change in the d -spacing of the nanocrystalline regions with time is observed for the first time, which is believed to correspond to the development of C-S-H with time. The nanoheterogeneous nature of C-S-H is demonstrated and correlated to the strong Ca:Si ratio fluctuations that are observed.