粉煤灰在蒸养条件下的氯离子固化性能

通过模拟粉煤灰在硅酸盐水泥中的水化环境,采用二次等温吸附法研究了标准养护和蒸汽养护条件下粉煤灰水泥体系中粉煤灰氯离子固化能力的变化,采用灰色关联分析法对实验结果进行了分析.研究结果表明:粉煤灰氯离子化学结合能力随恒温温度和恒温时间的增加而降低,而物理吸附能力基本不变;在标准养护条件下粉煤灰水化生成的铝酸盐是C4 AH1...     

活化煤矸石对水泥水化的影响

研究了活化煤矸石-氢氧化钙体系的水化热、水化产物成分以及活化煤矸石水泥体系的水化过程、水化产物的微结构,结果表明,在石膏的激发下,活化煤矸石能够发生二次水化,与Ca（OH）2反应形成钙矾石、水化硅酸钙、水化铝酸钙等有利于提高水泥石强度的水化产物;活化煤矸石水泥硬化浆体中Ca（OH）2的含量在水化3d时最多,而后随龄期逐渐减少;阐明了活化煤矸石能够降低水化产物中氢氧化钙的含量、抑制氢氧化钙晶体的生长和聚集,并改善水泥石结构．     

碱激发烧煤矸石胶凝材料的硬化机理研究

利用XRD,IR,SEM等方法,研究了NaOH、KOH和钠水玻璃激发烧煤矸石的反应进程和水化产物,对其力学性能、微观结构和硬化机理进行了探讨.结果表明:水化产物是类似于沸石类结构的无定形碱-硅铝凝胶,碱溶液、液固比、养护温度和养护时间等因素影响着水化产物及其强度的形成.采用模数为1.23钠水玻璃与烧煤矸石混合(液固比0.3),在90℃养护条件下反应生成无定型的碱-硅铝酸盐凝胶,而在65℃养护时,硬化浆体中还存在有一定量未反应的硅酸钠晶体.     

MTC浆固化体的微观结构研究

用微观结构分析方法研究了MTC浆固化体的显微结构及其对固化效果的影响。MTC浆在高温碱性环境中能够生成大量凝胶水化产物 ,使泥浆固化。为了提高固化效率 ,泥浆中应预先掺加潜在活性的材料 ,并在强碱性环境中使用MTC浆。温和条件下长时间的养护使固化浆体结构致密 ,固化效果好 ;短时高温使胶凝材料的固化反应剧烈 ,所得结构较疏松 ,固化效果差     

碳酸化钢渣和矿渣作硅酸盐水泥混合材水化性能研究

通过对钢渣碳酸化前后的硅酸盐相提取及水化放热性能和将碳酸化钢渣和矿渣作为混合材的硅酸盐水泥的胶砂强度和水化产物种类的测定,以及对它们微观形貌的观察,研究了碳酸化钢渣对胶凝体系水化性能的影响.结果表明,碳酸化使钢渣中硅酸盐相的含量由47.06％下降至14.38％;碳酸化促进了钢渣的早期水化,抑制其后期水化;在配比相同的条件下,碳酸化钢渣-矿渣-硅酸盐熟料体系试样的3、28d抗压强度较未碳酸化钢渣-矿渣-硅酸盐熟料体系试样的高;碳酸化生成的CaCO3促进了熟料的水化;碳酸化钢渣促进了胶凝体系中AFt的生成,且生成水合碳铝酸钙.     

低水灰比对硅酸盐水泥水化程度的影响

研究了低水灰比硅酸盐水泥的水化程度，并利用XRD和SEM分析了其水化产物的微观结构。结果表明在低水灰比条件下，水泥的水化程度较低，其硬化水泥浆体中存在较多的未水化水泥；同时由于自身的密实性增强和体系的低孔隙率，使水泥水化产物的结晶、生长情况也受到影响。     

利用红外和核磁技术分析矿渣硅酸盐复合胶凝材料的水化产物

采用傅里叶红外光谱(FTIR)和高分辨29Si固体核磁共振技术(NMR),研究了不同水化龄期的水泥-矿渣复合胶凝硬化浆体的微观结构。结果表明:纯硅酸盐水泥随着水化时间的增长,水化程度变大,聚合度增加,生成更多的长链水化硅酸钙(C-S-H)凝胶;矿渣硅酸盐水泥试样水化早期主要生成二聚体凝胶,随着龄期增长,逐渐转变为长链型凝胶,平均链长逐渐增加;随着矿渣掺量的增加,激发矿渣所需时间增长,早期Q~2(1Al)很少,但随着龄期延长,矿渣逐渐被激发,C-A-S-H凝胶变多。     

MTC浆固化体的微观结构研究

用微观结构分析方法研究了MTC浆固化体的显微结构及其对固化效果的影响。MTC浆在高温碱性环境中能够生成大量凝胶水化产物，使泥浆固化。为了提高固化效率，泥浆中应预先掺和潜在活性的材料，并在强碱性环境中使用MTC浆。温和条件下长时间的养护使固化浆体结构致密，固化效果好；短时高温使胶凝材料的固化反应剧烈，所得结构较疏松，固化效果差。     

高密实多元复合水泥浆体组成设计与抗侵蚀性能研究

Cl^-与SO₄^2-侵蚀是造成海洋环境下水泥混凝土劣化的主要原因，掺入辅助胶凝材料(SCMs)是改善水泥浆体抗侵蚀性能的有效方法。引入细粒度、高活性胶凝材料能加速复合水泥力学性能的发展并改善其抗蚀性，但会造成浆体流变性差、收缩应力大、开裂风险高等问题。基于Dinger-Andersen颗粒级配模型，在硅酸盐水泥基础上引入细矿渣、粗粉煤灰以及偏高岭土活性组分，设计并制备了SCMs含量高达60%的高密实度多元级配复合水泥。研究结果表明:多元级配复合水泥强度接近硅酸盐水泥，抗Cl-与SO₄^2-侵蚀性能显著提升，采用快速氯离子迁移系数法(RCM)测得氯离子扩散系数降低81%,30次干湿循环硫酸盐侵蚀后耐蚀系数仍有77%。高密实度多元级配复合水泥浆体初始堆积密实、持续水化，使得孔隙显著细化，同时水化产物对氯离子固化作用强，有效阻滞有害离子向内部迁移。此外，SCMs的高效水化大量消耗Ca(OH)₂，抑制了二次钙钒石等侵蚀产物的生成。通过颗粒级配调控与组成设计，可充分发挥...     

硫铝酸盐复合水泥体系水化特征研究

通过正交试验研究了硫铝酸盐复合水泥中不同掺量的普通硅酸盐水泥、石膏、硅灰及粉煤灰对其强度、自收缩以及水化热的影响。结果表明:普通硅酸盐水泥及石膏的掺入显著改变了硫铝酸盐复合水泥水化进程,硅灰及粉煤灰是影响后期强度的主要因素;自收缩试验结果表明普通硅酸盐水泥和石膏是影响硫铝酸盐复合水泥水化早期自收缩的主要因素;水化热测试结果表明粉煤灰和普通硅酸盐水泥在水化前6 h起到显著作用,粉煤灰降低了水化放热,而普通硅酸盐水泥增加水化放热;硅灰及石膏对6~24 h水化放热影响显著。结合XRD及SEM测试结果,表明普通硅酸盐水泥和石膏的存在加速了硫铝酸盐复合水泥水化早期钙矾石生成,随着石膏浓度的下降,发生转晶(AFm),随着后期硫铝酸盐水泥中β-C₂S的水化以及硅灰、粉煤灰的火山灰反应产生C-S-H凝胶,使得体系致密化。     

Micro-structural development of gap-graded blended cement pastes containing a high amount of supplementary cementitious materials

To clarify the strength improvement mechanism of gap-graded blended cements with a high amount of supplementary cementitious materials, phase composition of hardened gap-graded blended cement pastes was quantified, and compared with those of Portland cement paste and reference blended cement (prepared by co-grinding) paste. The results show that the gap-graded blended cement pastes containing only 25% cement clinker by mass have comparable amount of gel products and porosity with Portland cement paste at all tested ages. For gap-graded blended cement pastes, about 40% of the total gel products can be attributed to the hydration of fine blast furnace slag, and the main un-hydrated component is coarse fly ash, corresponding to un-hydrated cement clinker in Portland cement paste. Further, pore size refinement is much more pronounced in gap-graded blended cement pastes, attributing to high initial packing density of cement paste (grain size refinement) and significant hydration of BFS.     

碳纳米管改性水泥基复合材料早龄期水化反应的傅里叶红外光谱

通过FTIR方法对硅酸盐水泥及其碳纳米管改性试样早龄期的水化进程进行了表征。研究结果显示:FTIR是一种操作简便且能够快速取得分析结论的研究方法,能够反映水泥水化后主要产物的基本变化情况。随着水化反应的进行,FTIR中的Si—O振动吸收峰峰值由低波数向高波数迁移,这一过程反映了C—S—H凝胶体中硅氧四面体的聚合过程,也同时反应了该阶段水泥浆体的水化反应速度。在8~12h龄期时,掺CNTs试样与空白试样在800~1 025cm-1处特征峰的迁移速度完全相同。因此,可以认为CNTs材料在掺入到硅酸盐水泥时并未对早龄期的水化反应产生影响。水化温度的试验也证明了上述观点。     

Control of hydration rate of polymer modified cements by the addition of organically modified montmorillonites

The addition of polyvinyl alcohol (PVA) in concrete causes a delay in the hydration rate of Portland cement paste. Three different montmorillonites (MMTs) (Cloisite Na, 30B, and Nanofil) were previously mixed with PVA in order to control this delay. A comparison between the hydration rate of Portland cement paste and Portland cement paste modified with PVA and the different MMTs was made by means of semi-adiabatic calorimetry, thermal gravimetric analysis and contact angle measurements. Different rates of hydration were obtained with each MMT. The paste with PVA and Nanofil behaves almost the same as the unmodified cement paste. Mechanical properties were also studied. An increase in the flexural strength and a decrease in the compression strength were found, which is expected for a Portland cement paste modified with PVA. The addition of MMT to the cement paste with PVA hardly affects the mechanical properties.     

Strain and thermal expansion coefficients of various cement pastes during hydration at early ages

Cement pastes undergo elevated temperature histories due to hydration heat liberation at early ages. Thermal expansion coefficients of cement paste and concrete change with age, showing a decrease after mixing, a subsequent minimum and then a gradual increase. These changes contribute to thermal strain. In this study, effects of water–cement ratio and cement type on volume changes in early-age cement pastes were experimentally examined using a newly developed apparatus capable of simultaneously determining both thermal expansion coefficient and total strain of cement pastes. The dependence of the thermal expansion coefficient on hydration was affected by water–cement ratio, cement type, elevated temperature history and particularly by the free water content of the cement pastes, while the relationship between thermal expansion coefficient and free water content varied with water–cement ratio. A notable increase in thermal expansion coefficient at early ages was observed when water–cement ratio was low and alite content in cement was high. At a water–cement ratio of 0.30, low-heat Portland cement paste resulted in a small total strain while moderate-heat and ordinary Portland cement pastes showed larger strains. Because no particular difference was observed in the thermal strains, shrinkage in the low-heat Portland cement paste was attributed to autogenous strain. At a water–cement ratio of 0.40, self-desiccation had a significant influence upon autogenous shrinkage and dependence of thermal expansion coefficient on hydration, and the effect of the mineral composition of cements was notable. However, for cement pastes with a water cement ratio of 0.55, no significant effects of self-desiccation were observed, probably because considerable excess water was present.     

Investigating entrained air voids and Portland cement hydration with low-temperature scanning electron microscopy

This paper describes the application of low temperature scanning electron microscopy to the materials science of Portland cement. The details of low-temperature scanning electron microscopy are described, along with a number of specimen preparation techniques. There are three main research topics presented in this paper: (1) ice morphology in entrained air voids, (2) development of air voids during early hydration and (3) progression of hydration in Portland cement. The first research focus examines ice in air voids at freezing temperatures, and various cement paste ages. The second research focus tracks the development of the air voids during the first hour of hydration. In the third research focus, the progression of hydration with and without accelerating and retarding admixtures is described. Each of these research programs demonstrates how low-temperature scanning electron microscopy can be an effective tool in Portland cement research.     

Aspects of Portland cement hydration studied using atomic force microscopy

Aspects of the mechanisms of hydration and microstructural evolution in Portland cement are still not fully understood. Atomic force microscopy (AFM) is in many ways a powerful tool for investigating changes in surface structure that accompany the hydration of Portland cement, especially because surfaces can be imaged under aqueous solutions at normal temperature, pressure and high magnification. We have investigated changes in the surface characteristics of sections of Portland cement clinker immersed initially in saturated calcium hydroxide solution which was then replaced by water, and in sucrose solution. In the case of the former, the observations are consistent with the early formation of a protective membrane and the subsequent growth of calcium silicate hydrate (CSH) structures by an osmotic process. The dissolution of the clinker in sucrose solution has also been directly observed. It is concluded that the use of AFM will help to resolve many questions relating to cement hydration.Sadly deceased.Editors note: I am very saddened by the sudden loss of Derek Birchall and acknowledge his outstanding contribution to the subject and this journal over many years.     

缓凝剂对掺UNF-5高C3S水泥水化的调控

采用流动度、电阻率和水化热等实验方法,研究了缓凝剂对掺定量UNF-5高C3S水泥浆初始水化历程的调控,着重研究了3种缓凝剂与UNF-5的叠加效应在高C3S水泥浆初始水化历程中产生的主要现象,以及这些现象对改善UNF-5与高C3S水泥的相容性的影响.实验表明:在浆体流动性方面,葡萄糖酸钠和多聚磷酸钠与UNF-5叠加时存在一个最佳掺量,柠檬酸出现负效应.在一定的温度范围内,叠加前后水泥浆体的流动度均随温度的增加而增大.缓凝剂对早期C3A水化的作用效应显著影响含UNF-5水泥浆体的流动度与早期电阻率之间的关系.缓凝剂的参与延缓水泥浆体结构的形成,放热峰削弱且得以宽化,有效解决放热集中的问题.对水泥浆体结构形成的延缓能力,葡萄糖酸钠最强,多聚磷酸钠次之,而柠檬酸相对最弱.     

A method for predicting the alkali concentrations in pore solution of hydrated slag cement paste

The alkalinity of the pore liquid in hardened cement paste or concrete is important for the long-term evaluation of alkali-silica reaction (ASR) expansion and corrosion prevention of steel bar in steel reinforced structures among others. It influences the reactivity of supplementary cementitious materials as well. This paper focuses on the alkali binding in hydrated slag cement paste and a method for predicting the alkali concentrations in the pore solution is developed. The hydration of slag cement is simulated with a computer-based model CEMHYD3D. The amount of alkalis released by the cement hydration, quantities of hydration products, and volume of the pore solution are calculated from the model outputs. A large set of experimental results reported in different literatures are used to derive the alkali-binding capacities of the hydration products and practical models are proposed based on the computation results. It was found that the hydrotalcite-like phase is a major binder of alkalis in hydrated slag cement paste, and the C?CS?CH has weaker alkali-binding capacity than the C?CS?CH in hydrated Portland cement paste. The method for predicting the alkali concentrations in the pore solution of hydrated slag cement paste is used to investigate the effects of different factors on the alkalinity of pore solution in hydrated slag cement paste.     

Three-dimensional computer modeling of slag cement hydration

A newly developed version of a three-dimensional computer model for simulating the hydration and microstructure development of slag cement pastes is presented in this study. It is based on a 3-D computer model for Portland cement hydration (CEMHYD3D) which was originally developed at NIST, taken over in the authors’ group and further developed. Features like the digitized 3-D microstructure, the cellular automata (CA) algorithm for simulating the random walking, phase transformation for simulating the chemical reactions, are retained. But, the 3-D microstructure was reconstructed allowing for slag particles as binder in the system. Algorithms and rules are developed to account for the interaction between Portland cement hydration and slag reaction in the paste, of which the mechanisms were revealed in the studies by Chen and Brouwers [(2007) J Mater Sci 42(2):428; (2007) J Mater Sci 42(2):444] Methods for considering the various factors on the reactivity of slag in hydrating slag cement pastes are proposed, mainly for the oxide composition of slag and the alkalinity in the pore solution composition. A comparison between the model predictions and the experimental results in literature shows that the presented computer model can successfully predict the hydration process and the microstructure development of hydrating slag cement paste.