矿渣水泥水化动力学研究

应用恒温导热量热仪对矿渣水泥和波特兰水泥的水化动力学进行了研究。实验结果表明,水泥水化在不同反应阶段具有不同的反应机理,所适用的动力学公式及动力学参数亦不同。加速期由自动催化反应控制,衰减期由扩散过程控制,减速期由化学反应和扩散过程双重控制。矿渣水泥对温度的敏感性高于波特兰水泥,原因在于矿渣玻璃相具有较高的表观反应活化能。提高温度(热激发)对矿渣水泥的水化更为有利。采用了两种活性不同的矿渣,它们的活性的差别可由水化动力学参数K、E与N反映出来。     

矿渣-水泥胶凝体系的水化动力学模型

矿渣是由高炉炼铁熔融的矿渣骤冷时形成的细粒状玻璃态物质,它是一种活性掺和料.将矿渣粉作为掺合料掺入水泥基材料中,其活性可以得到充分的发挥,使得水化反应充分,进而改善水泥基材料的力学性能.本文分析了矿渣和水泥的水化动力学影响因素,建立了矿渣-水泥胶凝体系的水化动力学方程,主要从水胶比、温度以及比表面积这三个因素来分析矿渣掺量对矿渣-水泥胶凝体系水化过程的影响.结果表明,增大水胶比、升高温度及增大水泥颗粒的比表面积均能够不同程度的加速矿渣-水泥胶凝体系的水化进程.     

矿渣-水泥复合胶凝体系低温水化动力学研究

研究了低温下矿渣-水泥复合胶凝体系的水化反应特性和水化反应动力学.研究表明:低温下,复合胶凝体系的水化放热速率随着矿渣掺量的增加和环境温度的降低而下降;非蒸发水含量随着矿渣掺量的增加呈现降低的趋势;对已有水泥水化动力学方程进行计算,得到了低温条件下复合胶凝体系的动力学参数以及不同阶段反应速率和水化度间的关系,通过计算获得的动力学参数,可以对低温条件下复合胶凝体系不同反应阶段水化反应程度进行预测;在水化早期,复合胶凝体系中矿渣水化程度较低,消耗少量Ca(OH)2,使生成C-S-H凝胶的Ca/Si降低较少.在水化后期,复合胶凝体系中矿渣水化消耗较多的Ca(OH)2,使生成C-S-H凝胶的Ca/Si降低较多.矿渣掺量为50％时,硬化浆体C-S-H凝胶的Ca/Si远小于纯水泥体系.     

水泥基材料的水化动力学模型

介绍了水泥基材料的水化动力学模型.根据实验测定的水化放热数据,采用模型给出的积分和微分方程,对水泥基材料的水化反应中的3个基本过程即结晶成核与晶体生长(NG)、相边界反应(I)和扩散(D)进行了表征,得到反应速率常数K、反应级数n和表观活化能Ea等动力学参数以及各反应阶段的反应速率与反应度的关系.计算得到的各阶段的反应速率曲线能较好地分段模拟由量热实验得到的胶凝材料实际水化速率dα/dt曲线.观察3个阶段的相互关系,可对水泥基材料复杂的水化机理进行解释.水泥基材料的水化反应存在两种不同的历程:NG-I-D或NG-D.在水化初期NG是控制因素,随着水化程度提高,逐渐转由I或D控制反应.     

氯氧镁水泥水化历程的影响因素及水化动力学

为了深入研究氯氧镁水泥的水化机理,进而对其性能进行预测和改进,采用美国TAM Air热导式等温量热仪研究了氯氧镁水泥的水化动力学。测定了不同条件下氯氧镁水泥体系的水化放热过程,根据水化放热曲线,研究了该体系水化各阶段的动力学过程,探讨了实验因素对该体系水化过程的影响,并通过实验数据拟合得到了氯氧镁水泥水化过程的动力学方程。结果表明:氯氧镁水泥水化过程的不同阶段受不同作用机理控制,加速期是受成核控制的自动催化反应时期,衰减期受扩散作用控制,而减速期受自动催化反应和扩散作用双重控制。同时,原料MgO的活性、反应温度及矿物外加剂的种类和数量都不同程度地影响了该体系的水化过程。     

碱激发矿渣水泥水化C-A-S-H凝胶微观结构的研究

通过核磁共振、扫描电镜和纳米压痕技术研究了普通波特兰水泥和碱激发矿渣水泥水化28 d形成的C-S-H和C-A-S-H凝胶的微观结构.结果表明,波特兰水泥水化形成的C-S-H凝胶的结构主要由5链14 nm的托贝莫来石(60％)和2链硅钙石(40％)组成;碱激发矿渣水泥的主要水化产物是C-A-S-H凝胶,随激发剂的性质不同而具有不同的组成和结构:当激发剂为NaOH溶液(Na2 O含量为矿渣质量的4％)时,形成的C-A-S-H凝胶是介于5链14 nm和14链11 nm的托贝莫来石之间的中间结构;当激发剂为水玻璃溶液(Na2 O含量为矿渣质量的4％)时,C-A-S-H凝胶的结构主要由11链14 nm和14链11 nm的托贝莫来石组成,与NaOH作激发剂一样,以水玻璃作激发剂的碱激发矿渣水泥水化的C-A-S-H凝胶不具有超高密度状态.     

活化煤矸石在水泥基材料中的早期水化动力学研究

采用活化煤矸石(CCG)部分取代波特兰水泥的方式,对比研究了CCG对CCG-水泥复合胶凝材料的凝结时间、力学性能和水化热反应等的影响.利用水化热法研究了CCG-水泥复合胶凝体系的水化特性;并基于Krstulovic-Dabic模型,分析了CCG-水泥复合胶凝体系的水化反应机理.试验结果表明,活化煤矸石取代硅酸盐水泥熟料的最佳掺量为30％,此掺量下,能保证良好的力学性能与工作性能;CCG对CCG-水泥复合胶凝材料的早期水化无明显影响,后期活化煤矸石中的铝相、硅相会与氢氧化钙反应发生火山灰效应;活化煤矸石能增大水泥水化结晶成核与晶体生长(NG)、相边界反应(Ⅰ)过程的反应程度并降低扩散(D)阶段的反应程度;同时能降低NG、I过程的反应速率,并在不高于30％的掺量下,对D过程的反应速率有一定的增强作用.     

装饰水泥用活性矿物混合材

生产白色矿渣波特兰水泥是增加装饰水泥产量和降低成本的途径之一。由于缺乏具有足够白度和水硬活性的矿渣,因而目前尚未安排生产。生产白色矿渣波特兰水泥时掺入高炉矿渣和磷渣是有益的,因为含有少量着色元素(它们结合成强着色化合物-铁和锰的硫化物和磷化物,亦即矿淹矿物呈大量类质同晶变体)和未参与反应的碳,按现有处理方法尚不能利用它们。为了用磷渣作生产白色矿渣波特兰水泥时的活性矿物混合材对磷渣的漂白和活化进行了研究,并研究了粒状的和高温液态矿渣的漂白方法。     

水化热抑制剂对复合胶凝材料体系早期水化动力学的影响

本文研究了水化热抑制剂(TRI)对水泥-粉煤灰-矿渣复合胶凝材料早期水化过程。通过改变矿物掺合料在胶凝材料中的质量占比以及TRI的掺量,研究了胶凝材料的水化特性,并基于Krstulovic-Dabic水化动力学模型计算了反应速率常数、几何晶体生长指数等动力学参数。结果表明,矿物掺合料和TRI复合使用会延缓胶凝材料水化并降低最大放热速率;复合胶凝材料的水化过程均有结晶成核与晶体生长、相边界反应以及扩散3个阶段,Krstulovic-Dabic水化动力学模型能较好地模拟各复合胶凝材料的水化过程;矿物掺合料和TRI会影响复合胶凝材料水化产物的结晶成核以及晶体生长,并降低复合胶凝材料各阶段的水化速率。     

水泥-粉煤灰-砷渣三元体系水化动力学研究

通过水化热和水化动力学模拟,研究了含砷废渣对水泥-粉煤灰复合体系早期水化进程的影响机制。结果表明,与基准试样相比,含砷废渣的掺入显著延长了复合体系的诱导期,降低了复合体系加速期水化速率,并延长了加速期时长,这种延迟效应随着含砷废渣掺量增加也愈加明显。三元体系总放热量随砷渣掺量增加而降低。加速期由结晶成核与晶体生长控制,减速期由相边界反应和扩散过程共同控制,稳定期由扩散速率控制反应进程。含砷废渣的掺入增大反应阻力,且反应阻力随含砷废渣掺量的增加而增大。     

Hardened portland cement pastes of low porosity VI. Mechanism of the hydration process

The hydration of low-porosity portland cement pastes may be divided into three stages. The first stage starts with a fast hydration until 10 to 15% of the cement is hydrated (pre-dormant period), which is followed by a very slow hydration, caused by the formation of a coating on the cement grains (dormant period). After 15 to 20% of the cement is hydrated, the coating is ruptured, and a fast reaction starts, which lasts until about 30% of the cement is hydrated. This is the second stage of the reaction. In the third stage, the hydration slows down, due to retardation by the accumulating hydration products. The mechanism of the third stage is treated quantitatively. The diffusion through the very narrow pores between the hydration products is activated diffusion, and the apparent energy of activation of the diffusion is calculated.     

高掺量混合材复合水泥的水化性能

通过水化微量热、化学结合水测定和X射线衍射、热重-差热分析、扫描电镜等测试方法研究了3种高掺量矿渣、粉煤灰、石灰石复合水泥的水化性能,并与硅酸盐水泥的水化进行了对比。结果表明：高掺混合材复合水泥的水化放热特征与硅酸盐水泥有明显不同,早期水化反应速度低于硅酸盐水泥,但后期由于矿渣、粉煤灰的二次水化反应使其水化速度增长较快。主要的水化产物亦为水化硅酸钙凝胶、钙钒石和Ca(OH)2晶体,但Ca(OH)2含量明显低于硅酸盐水泥浆体中的Ca(OH)2含量。     

含硫铝酸钙硅酸盐水泥中粉煤灰活化机理

用差示扫描-热重分析扫描电镜和化学分析法研究了含硫铝酸钙粉煤灰硅酸盐水泥和含硫铝酸钙矿渣硅酸盐水泥水化过程中水化产物的种类、形状、数量和孔溶液离子浓度等方面的变化规律.借助固体高分辨核磁共振波谱技术对水泥中硅氧四面体不同聚合状态的分布,Al的不同配位状态进行分析.结果表明:含硫铝酸钙硅酸盐水泥对粉煤灰激发作用大于对矿渣的激发作用,含硫铝酸钙粉煤灰水泥水化放热量多,促进粉煤灰玻璃体中AlO2-的溶出,在较高温度粉煤灰玻璃体网络结构激活,解聚速率加快.     

Kinetics of Slag Hydration in the Presence of Calcium Hydroxide

The reaction between ground granulated blast furnace slag (GGBFS) having an empirical formula of C_7.88S_7.39M₃A and calcium hydroxide (CH) was investigated. The kinetics of the reaction were explored. Thermogravimetric analysis was used to monitor the consumption of CH from which rate constants were determined. Based on Knudsen's kinetic model, activation energies of 14.5, 17.9, and 22.6 kJ/mol were determined for three different mass ratios of slag and CH reacted over a temperature range of 15° to 50°C and hydrated for a period of time from 0 to 32 days. A comparison of the kinetics of the slag/CH reaction was made with slag/portland cement hydration. The basic features of both appear similar.     

Early stage hydration of slag-cement

The early hydration characteristics of slag cements (blends of separately ground granulated blast furnace slags with portland cement) have been examined. Isothermal calorimetry, chemical shrinkage and compressive strength measurements were made. The kinetics of hydration have been treated; apparent activation energies determined for a slag cement were ～49 KJ/mole compared with ～44 KJ/mole for the portland cement used in the blends.     

Mössbauer and X-ray investigations of some portland cements

The Mössbauer spectroscopic and x-ray diffraction investigations have been carried out on a variety of ordinary portland, portland pozzolanic, portland slag and sulphate resisting portland cements, using dry as well as hydrated samples. The discussion of the Mössbauer parameters shows that Fe atoms occupying distorted octahedral and tetrahedral sites in the dry cements are hydrated to form ferrite monosulphate without producing Fe(OH)₃ and its gel; hydration of the slag cement proceeds much faster than other cements; and that the composition of the iron-bearing phase in the sulphate resisting portland cement, studied in detail, is close to C₄AF.     

Early activation and properties of slag cement

Early age activation of granulated blast-furnace slag (BFS) and blends of slag and portland cement (OPC) has been studied. Activators include sodium-hydroxide, sodium sulfate, alum (potassium aluminum sulfate), superplasticizer, and calcium aluminate cement. Heat of hydration, x-ray phase characterization, compressive strength, viscometry, pore size distribution and related characterization studies have been made. Activated BFS-cement mortars having equivalent strengths at 1 day to OPC have been prepared, which also have 28- and 90-day strengths exceeding those of the OPC. Mechanisms of activation are discussed.     

Estimation of the degree of hydration of blended cement pastes by a scanning electron microscope point-counting procedure

A scanning electron microscope (SEM) point-counting technique was employed to study the hydration of plain portland and blended cement pastes containing fly ash or slag. For plain portland cement pastes, the results for the degree of cement hydration obtained by the SEM point-counting technique were consistent with the results from the traditional loss-on-ignition (LOI) of nonevaporable water-content measurements; agreement was within ±10%. The standard deviation in the determination of the degree of cement hydration via point counting ranged from ±1.5% to ±1.8% (one operator, one sample). For the blended cement pastes, it is the first time that the degree of hydration of cement in blended systems has been studied directly. The standard deviation for the degree of hydration of cement in the blended cement pastes ranged from ±1.4% to ±2.2%. Additionally, the degrees of reaction of the mineral admixtures (MAs) were also measured. The standard deviation for the degree of fly ash reaction was ±4.6% to ±5.0% and ±3.6% to ±4.3% for slag. All of the analyses suggest that the SEM point-counting technique can be a reliable and effective analysis tool for use in studies of the hydration of blended cement pastes.     

Analytical Model for the Alite (C3S) Dissolution Topography

The surface topography that develops during the dissolution of alite (or C₃S) has never been considered as an important aspect of the hydration of portland cement. Like many other minerals, alite dissolution results in the formation of etch pits. In this study, a simple model with a handful of parameters is proposed to explore the kinetic consequences of pitting on the dissolution of alite. The first consequence is an accelerating period during which the reactive surface, that is, the pit, expands. This new feature, to the authors’ opinion never reported previously for alite, is supported by experimental data. The mechanisms leading to the activation of the initial dissolution centers and to the growth of pits could be hindered by some inhibitory species such as aluminum ions or organic molecules. The model indicates that only a few assumptions about the formation of pits in the presence of these species are necessary to introduce an initial period of low dissolution prior to the accelerating phase. Such a low early reactivity is similar to the so‐called dormant period observed during portland cement hydration. The implications of this new model in cement hydration could go beyond this article and shed light on still unresolved fundamental questions on hydration behavior.     

Investigation of blended cement hydration by isothermal calorimetry and thermal analysis

Hydration of portland cement pastes containing three types of mineral additive; fly ash, ground-granulated slag, and silica fume was investigated using differential thermal analysis, thermogravimetric analysis (DTA/TGA) and isothermal calorimetry. It was shown that the chemically bound water obtained using DTA/TGA was proportional to heat of hydration and could be used as a measure of hydration. The weight loss due to Ca(OH)₂ decomposition of hydration products by DTA/TGA could be used to quantify the pozzolan reaction. A new method based on the composition of a hydrating cement was proposed and used to determine the degree of hydration of blended cements and the degree of pozzolan reaction. The results obtained suggested that the reactions of blended cements were slower than portland cement, and that silica fume reacted earlier than fly ash and slag.