水泥石脱水相结构特征及其再水化能力

将水泥石在不同温度进行低温煅烧,得到不同的脱水相物质,通过热重-差示扫描热分析、X射线衍射、红外光谱及29Si核磁共振等对水泥石在400,650℃及900℃的脱水相结构特征及其再水化性能、再水化产物的结构特征进行研究.结果表明:在400℃,由水化硅酸钙(C-S-H)凝胶脱水生成了无定形相,在650℃生成了不完全结晶的β-硅酸二钙(C2S),而900℃脱水相中存在结晶程度高的β-C2S.在再水化过程中,400℃和650℃脱水相水化生成了C-S-H凝胶,并且650℃脱水相的水化活性和水化产物聚合程度更高;900℃脱水相的水化活性极低,水化前后矿物结构特征几乎没有发生变化.     

Microwave Dielectric Study of Water Structure in the Hydration Process of Cement Paste

Microwave dielectric relaxation measurements, via the time-domain reflectometry method, were performed on portland cement paste for the first time, and the water structure during the hydration process was observed. The relaxation process due to the orientation of free water, which is independent of calcium silicate hydrate (C-S-H), was observed at ∼10 GHz. The relaxation strength, in proportion to the amount of free water, decreased rapidly as the curing time increased for the first three days. This change is in good agreement with that of a chemical reaction that was reported by measurements of the heat that is evolved during hydration. The free water is taken into C-S-H and is transformed to hydrated water by the hydration process. When hydration proceeds, the relaxation processes due to the orientation of the hydrated water in C-S-H occur at ∼100 MHz and 1 MHz.     

The effectuation of seawater on the microstructural features and the compressive strength of fly ash blended cement at early and later ages

The current work scrutinizes the effectuation of seawater on morphological properties, pore structure, and compressive strength during the hydration process of fly ash blended cement at 3, 7, 28, 56, and 90 days to better understand the influence of salinity conditions of seawater on the microstructural modification and strength development of the hydration products as well as the total porosity. The chemical reaction's mechanism of mightily soluble salts, for example, Mg₂SO₄ and NaCl, with hydrated fly ash and blended cement (calcium-bearing phases) was also confirmed. Fourier-transform infrared spectroscopy has been appointed to observe and characterize the energetics of variation in the formulation of portlandite (CH), calcium silicate hydrate, gypsum (Gy), ettringite (AFt), and calcium chloroaluminate (Friedel's salt [FS]) throughout the hydration process of fly ash blended cement with seawater in comparison with deionized water. X-ray diffraction analysis exposed that the peak intensities of FS, portlandite, and some particular phases of the hydrated fly ash blended cement in seawater are higher and sharper than the comparable peaks in deionized water. Mercury intrusion porosimetry-measurements have been appointed that the total porosity of artificial seawater (ASW) was decreased from 28.9% at 3 days to 19.4% at 56 days. In addition, the average, median, and critical pore diameter were decreased in ASW while compared to deionized water (DIW). The reaction products of this work were also characterized using scanning electron microscopy, EDS, compressive strength, and isothermal calorimeter.     

Novel Use of Kaolin Wastes in Blended Cements

This paper describes the influence of different thermally activated clay wastes (ACW) on the hydration phases in cement pastes containing two percentages of addition (10% and 20%). Results show that the main products obtained during hydration of cement pastes containing ACW were portlandite, calcium aluminate hydrates, calcium silicate hydrates, and hydrotalcite-type compounds. Portlandite formation decreases when addition percentage is 20%, contrary to tetracalcium aluminate hydrate, which increases in similar conditions. The ACW that showed the most portlandite consumption was ACW1 (700°C, 2 h) according to thermogravimetric data.     

The morphology of C–S–H: Lessons from 1H nuclear magnetic resonance relaxometry

¹H nuclear magnetic resonance has been applied to cement pastes, and in particular calcium silicate hydrate (C–S–H), for the characterisation of porosity and pore water interactions for over three decades. However, there is now renewed interest in the method, given that it has been shown to be non-invasive, non-destructive and fully quantitative. It is possible to make measurements of pore size distribution, specific surface area, C–S–H density and water fraction and water dynamics over 6 orders of magnitude from nano- to milli-seconds. This information comes in easily applied experiments that are increasingly well understood, on widely available equipment. This contribution describes the basic experiments for a cement audience new to the field and reviews three decades of work. It concludes with a summary of the current state of understanding of cement pore morphology from the perspective of ¹H NMR.     

The magnesia-silica gel phase in slag cements: alkali (K, Cs) sorption potential of synthetic gels

Blends of Portland cement with blast furnace slag hydrate to yield two gel phases, one essentially a calcium silicate hydrate (C-S-H) composition, the other a magnesium silicate hydrate (M-S-H) composition: the two gel phases are essentially immiscible. Together, the gel phases comprise an important source of sorption potential for the alkalis present in ordinary cement and blending agents. M-S-H gels have been synthesised and their sorption potential measured for postassium (K) and cesium (Cs) at 25 °C by using fresh gels as well as gels previously aged at 85 °C for 6 months. The ability of slag-cement blends to lower pore fluid alkalinity generally, and in nuclear waste technology to incorporate Cs, is interpreted in terms of the sorption data.     

Hydration Kinetics and Phase Stability of Dicalcium Silicate Synthesized by the Pechini Process

Reactive dicalcium silicate (Ca₂SiO₄) has been synthesized by the Pechini process, and hydration kinetics studied. With increasing calcination temperature, the amorphous product first crystallizes to α'_L-phase and subsequently to the ß- and γ-phases. The specific surface area, ranging from 40 to 1 m²/g, strongly depends on the calcination temperature of 700°-1200°C for 1 h. Samples with a high surface area have a high water demand; a water/cement ratio >2.0 is required to produce formable pastes in some instances. Hydration kinetics are determined by XRD, ²⁹Si magic-angle spinning nuclear magnetic resonance (MAS NMR), and differential scanning calorimetry/thermogravimetry (DSG/TG). The hydration rate depends only on the surface area, not on the polymorph. Complete hydration occurs in as early as 7 d. Very little calcium hydroxide (Ca(OH)₂) is formed in the most reactive specimens (calcined at 700° and 800°C), which indicates the Ca/Si ratio in C-S-H gels is ∼2.0, but more Ca(OH)₂ forms from samples calcined at higher temperature. The silicate structure of the hydrated Ca₂SiO₄ pastes is investigated using ²⁹Si MAS NMR spectroscopy and trimethylsilylation analysis.     

高炉镍铁渣粉在水泥基复合胶凝材料中的水化特性研究

通过对不同高炉镍铁渣掺量的水泥-高炉镍铁渣粉复合胶凝材料水化放热速率、高炉镍铁渣粉的反应程度、硬化浆体化学结合水含量以及水化产物中C-S-H凝胶Ca/Si的测定,分别研究了水泥-高炉镍铁渣粉复合胶凝材料的早期、中长期水化进程、浆体微观形貌以及水化产物特点等水化特性.研究结果表明:高炉镍铁渣的掺入会降低水化放热速率,并推迟水化加速期放热峰的出现时间;在复合胶凝体系中,随着高炉镍铁渣粉掺量的增大,其反应程度和硬化浆体中化学结合水含量将降低.复合胶凝材料水化生成的C-S-H凝胶的Ca/Si低于水泥,且随着水化的进行呈降低趋势;高炉镍铁渣粉中的Al,在水化过程中会取代部分Si进入C-S-H凝胶中,形成C-A-S-H凝胶.     

Microstructure and texture of hydrated cement-based materials: A proton field cycling relaxometry approach

We show how the measurement of proton nuclear magnetic spin-lattice relaxation as a function of magnetic field strength (and hence nuclear Larmor frequency) can provide reliable information on the microstructure (specific surface area and pore size distribution) throughout the progressive hydration of cement-based materials. We present in details the experimental and theoretical characteristic features of the relaxation dispersion to support an interpretation in terms of coupled solid-liquid relaxation at pore interfaces, surface diffusion, and nuclear paramagnetic relaxation. The measurement does not require any drying temperature modification and is sufficiently fast to be applied continuously during the progressive hydration of the material. Coupling this method with the standard proton nuclear spin relaxation and high resolution NMR allows us to follow the development of micro-scale texture within the material.     

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.     

钢渣水化产物的特性(英文)

用X射线衍射分析、水化热的测量、化学结合水量的测定、孔结构的测定、扫描电镜观察及强度测试研究了钢渣的水化产物的特性。结果表明:钢渣硬化浆体中主要含有水化硅酸钙(C–S–H)凝胶、Ca(OH)2、惰性组分[RO相、铁酸二钙(C2F)和Fe3O4]和未水化的胶凝相[硅酸三钙(C3S)和硅酸二钙(C2S)];总体而言,钢渣的水化过程与水泥的水化过程相似;钢渣早期的水化速率远低于水泥,但钢渣后期,尤其是90d之后的水化速率高于水泥的。钢渣水化产生的C–S–H凝胶不具有良好的胶凝性能,凝胶之间的相互黏结也不牢固,因此钢渣砂浆的强度很低。     

Hydraulic cement from the by-product of geothermal water desilication

Calcium silicate hydrate, produced from the desilication of siliceous geothermal water by the addition of calcium hydroxide, has been dried and then ground with calcium oxide to form a white hydraulic cement. During grinding, partial solid state reaction occurs between the CaO and the calcium silicate. On hydration, calcium hydroxide forms rapidly and then reacts with the calcium silicate hydrate to give a compressive strength of about half of that of ordinary Portland cement density.     

1H驰豫时间谱在水泥基材料研究中的应用

水泥水化、硬化体结构的形成及演化、水泥基材料内部不同水分之间的转化、吸水、干燥、水分在水泥基材料内部的扩散过程引起水分化学状态或所处环境物理状态的变化.这种变化可用1H核磁共振驰豫时间进行表征.已有的研究表明,1H驰豫时间谱可用于水泥水化过程、硬化体结构形成、孔结构、水分在水泥基材料内的传输过程等的表征,所得结果与其它方法所得结果有较好的一致性.且磁共振成像可直接观察水分在水泥基材料中的分布及传输,这是其它现代测试方法难以达到的.     

29Si Magic-Angle-Spinning Nuclear Magnetic Resonance Study of Hydrated Cement Paste and Mortar

This paper presents ²⁹Si magic-angle-spinning nuclear magnetic resonance measurements that trace the cement hydration process in cement paste and mortar specimens made from ordinary portland cement, type I. These specimens were moist-cured for 3, 7, 14, and 28/31 d at temperatures ranging from 21° to 80°C. Compressive strength for all tested specimens was also determined. The results show that the degree of hydration ( Q ¹+ Q ²) and the compressive strength increase with curing times and temperatures. However, at 80°C, the compressive strength decreases while the degree of hydration increases.     

Structure-texture correlation in ultra-high-performance concrete: A nuclear magnetic resonance study

The pore size distribution in three reactive powder concrete formulations has been studied by nuclear magnetic relaxation of protons. Confirming the discrete and fractal features of the distribution for this kind of concrete, each formulation is assessed a surface fractal dimension, which reveals the hierarchy of pores. The experimental results evidence a dependence between this dimension and both the filling ratio of cement grains and the reactivity of silica fume. ²⁹Si nuclear magnetic resonance (NMR) allows us to draw a relationship between the amount of calcium silicate hydrates (C-S-H) and this surface fractal dimension.     

Highly Reactive β-Dicalcium Silicate

Calcium silicate hydrate was prepared by hydrothermal reaction between calcium oxide and silica (C/S = 2.0) at a temperature of 205°–215°C and a pressure of 17–19 bar. This reaction with decomposition at 900°C produced highly reactive β-dicalcium silicate (specific surface area 4.55 m²/g) contaminated with small amounts of wollastonite as an impurity. Infrared spectral studies have shown that β-dicalcium silicate prepared at 900°C is less symmetric compared with the control prepared at 1450°C using boron trioxide as a stabilizer. The specific surface area of β-dicalcium silicate decreased with temperature. The hydration studies were done by determining the nonevaporable water, calcium hydroxide (CH) contents, and specific surface area of the hydrated samples. X-ray diffraction studies were also done. The results showed that prepared β-dicalcium silicate is highly reactive. Calcium chloride (1.0 wt%) and gypsum retard the hydration. Possible causes of high reactivity have been discussed.     

改性磷石膏对石膏矿渣水泥水化过程的影响研究

采用质量分数为5％～25％的改性磷石膏、15％的硅酸盐水泥熟料、60％～80％的矿渣混合磨细制成石膏矿渣水泥,研究了改性磷石膏掺量对石膏矿渣水泥浆体的抗压强度、水化热、孔溶液pH值及水化产物的影响情况.结果表明,掺入改性磷石膏使得石膏矿渣水泥的3 d、7 d抗压强度降低,其掺量为10％、15％时,水泥的28 d、90 d抗压强度超过普通硅酸盐水泥.在3 d至90 d龄期内,水泥孔溶液pH值随龄期增长而逐渐增大.在相同龄期时,随着改性磷石膏掺量的增大,水泥孔溶液pH值减小,水化放热峰出现时间延缓.微观分析表明,掺入改性磷石膏后,28 d龄期时的水泥水化产物主要为钙矾石和C-S-H凝胶,水化产物的生成量在改性磷石膏掺量为15％时最多.     

NMR Relaxation Study of Adsorbed Water in Cement and C3S Pastes

The deuteron and proton spin-lattice and spin-spin relaxation times T ₁ and T ₂ of adsorbed water in commercial portland cement and tricalcium silicate pastes were studied as functions of the hardening time at room temperature. The time dependence of the water self-diffusion coefficient of tricalcium silicate pastes was also followed. The proton and the deuteron T ₁ and T ₂ decrease markedly as hydration increases and the pastes harden due to the increase in the active surface and the number of adsorptive sites, thus providing convenient tools for studying the nature of the hydration process.     

Deconstructing water sorption isotherms in cement pastes by lattice density functional theory simulations

The moisture content in cement pastes influences their mechanical properties and durability. However, the complex, multiscale nature of cement pastes makes it challenging to isolate the contributions of each scale to their macroscopic water sorption isotherms. In particular, the contribution of the calcium–silicate–hydrate gel (the binding phase of cement pastes) remains only partially understood. Here, we introduce a density functional theory lattice model describing water sorption in calcium–silicate–hydrate, which properly reproduces experimental water sorption isotherms in cement pastes. Based on this model, we deconstruct the contribution of each pore scale (interlayer spacing, gel pores, and capillary pores) to the total sorption isotherm. We show that, when the relative humidity is below 80%, the calcium–silicate–hydrate gel accounts for more than 90% of the moisture content adsorbed in cement pastes. In turn, we find that the contribution of the interlayer space within the calcium–silicate–hydrate grains is governed by the competition between the rate of interlayer space opening and the increasing propensity for water to fill larger pores upon increasing relative humidity. Overall, our results highlight the key role played by the calcium–silicate–hydrate in governing the sorption isotherms of cement pastes.     

Investigations of Calcium Silicate Hydrate Structure Using Silicon-29 Nuclear Magnetic Resonance Spectroscopy

Silicon-29 nuclear magnetic resonance has been used to probe the effects of temperature and the addition of reactive silica on the silicate structure of amorphous calcium silicate hydrate (C-S-H), produced by the hydration of alite (Ca₃SiO₅). Both an increase in the temperature of formation and the addition of reactive silica increase the degree of silicate polymerization in the C-S-H. However, in all cases the data are consistent with the formation of linear chain silicates and the absence of any cross-linking. The initial formation of a hydrated orthosilicate is observed, and it is suggested that this species may form during the adsorption of water onto the surface of alite during storage.