Rehydration activity of hydrated cement paste exposed to high temperature

Subjected to the wet surrounding, hydrated cement paste (HCP) exposed to high temperature may exhibit rehydration behavior. This paper presents the influence of the dehydration temperature and the initial water/cement ratio on the rehydration activity of dehydrated cement paste (DCP). Original HCPs were prepared with two water/cement ratios of 0.3 and 0.5, respectively, and cured under the fog‐spraying standard condition for 30thinspacedays. The DCP powders used were obtained by grinding dry HCP less than 75µm and then subjecting to different temperatures, up to 900^°C. The rehydration properties of DCP were evaluated by the required water for standard consistency, the setting time, the rehydrated compressive strength and the microstructure evolution. X‐ray diffraction (XRD) was employed to identify the crystalline phases before and after rehydration. Experimental results showed that the coupled rehydration effect from the dehydrated hydration products and the initially unhydrated cement determined the rehydration behavior of DCP. The rehydration of DCP strongly depended on the dehydration temperature and the water/cement ratio of the original HCP. Copyright © 2010 John Wiley & Sons, Ltd.     

环氧树脂流变学的研究进展

综述了近20年来环氧树脂流变学的研究进展。利用流变学来指导环氧树脂的最新应用,包括环氧树脂电子浆料例如底部填充胶（underfill）,环氧树脂基复合材料,环氧树脂涂料,环氧树脂黏合剂,环氧树脂与其他树脂/橡胶的复合体系等。环氧树脂体系中的填料规格、加入量以及环氧树脂的固化过程与黏度等流变指数息息相关。随着芯片等领域技术的快速发展,流变学在环氧树脂中的应用还会得到进一步加强。     

Development of Carbon Nanotube Modified Cement Paste with Microencapsulated Phase-Change Material for Structural–Functional Integrated Application

Microencapsulated phase-change materials (MPCM) can be used to develop a structural–functional integrated cement paste having high heat storage efficiency and suitable mechanical strength. However, the incorporation of MPCM has been found to degrade the mechanical properties of cement based composites. Therefore, in this research, the effect of carbon nanotubes (CNTs) on the properties of MPCM cement paste was evaluated. Test results showed that the incorporation of CNTs in MPCM cement paste accelerated the cement hydration reaction. SEM micrograph showed that CNTs were tightly attached to the cement hydration products. At the age of 28 days, the percentage increase in flexural and compressive strength with different dosage of CNTs was found to be up to 41% and 5% respectively. The optimum dosage of CNTs incorporated in MPCM cement paste was found to be 0.5 wt %. From the thermal performance test, it was found that the cement paste panels incorporated with different percentages of MPCM reduced the temperature measured at the center of the room by up to 4.6 °C. Inverse relationship was found between maximum temperature measured at the center of the room and the dosage of MPCM.     

Fabrication of apatite-type lanthanum silicate films and anode supported solid oxide fuel cells using nano-sized printable paste

Apatite-type lanthanum silicate based films have attracted significant interests to use as an electrolyte of solid oxide fuel cells (SOFCs) working at intermediate temperature. We have prepared Mg doped lanthanum silicate (MDLS) films on NiO–MDLS cermet substrates by spin coating and sintering of nano-sized printable paste made by beads milling. Changes in crystal structure and microstructure of the paste films with the sintering temperature have been investigated to show that porous network structure with a grain growth evolves up to 1300 °C, whereas densification occurred above 1400 °C. Anode supported SOFCs using the pasted MDLS films were successfully fabricated: an open circuit voltage of 0.91 V and a maximum power density of 150 mW cm⁻² measured at 800 °C were obtained with the electrolyte film sintered at 1500 °C.     

高温-水冷循环作用下的水泥石劣化分析

通过失重率与表层损伤评价高温-水冷循环作用对水泥石的劣化方式,利用X射线衍射(XRD)、热分析技术(TG/DTA)对不同循环条件下的水泥石进行物相组成分析.结果表明:高温-水冷循环作用实质是高温损伤、水化以及碳化的耦合作用,水泥石中氢氧化钙(CH)碳化严重,水化硅酸钙(C-S-H)大多脱水分解;不同温度下的循环破坏中,各个作用所占的比重不同;随着循环次数增加,水泥石的破坏历程相近;长时间后,水泥石的脆硬性大大增加,表层出现网状裂纹,破坏样中留有大量碳酸钙(CaCO3).     

Effect of the type of superplasticizer on the properties of cementitious systems incorporating slag

Superplasticizers have become an integral ingredient in the formulation of concretes. After 40?years, their use and dosage remain uncertain due to variations in their compositions and those of cement. In addition, the substitution of cement by supplementary cementitious materials having different chemical compositions exacerbates the problem without counting the multiplicity of superplasticizers to choose from. The present work consists of a study of the rheological and mechanical properties of cementitious systems containing slag and various types of superplasticizers. The tests were carried out on pastes, mortars and concretes incorporating slag in partial cement replacement and four superplasticizers types, polynaphthalene sulphonate (PNS) and three polycarboxylates (PC). The results of this study demonstrate that the viscosity and the yield stress increase with the rate of incorporation of the slag. The air increases with the polycarboxylates but this effect is less perceptible in the presence of the slag. Polycarboxylates improve workability more than PNS. The use of polycarboxylates reduces the viscosity and the yield stress. The compressive strength of concretes containing slag is low at early age but high at long run. They exhibit good resistances to scaling. The permeability to chloride ions is considerably reduced in the presence of the slag independently of the type of superplasticizer, suggesting good durability of these concretes in potentially aggressive external environments.     

大容量矿热炉用电极糊的研制

大容量矿热炉用电极糊，采用电煅无烟煤为主要原料，加入一部分石墨碎，选用合适的配方，其理化指标高，使用效果好．     

缓凝剂对水泥与减水剂相容性的影响及其作为助磨剂组分的试验研究

以水泥净浆流动度为评价指标,试验研究了多种常用缓凝剂对水泥与减水剂相容性的影响,结果表明,多数缓凝剂都能不同程度改善水泥与减水剂的相容性,其中白糖和＂六偏磷酸钠＋葡萄糖酸钠（1∶1）＂的效果最好。选取几种相容性效果较好的缓凝剂作为助磨剂组分之一配制的复合助磨剂,试验表明,3种复合助磨剂均能改善水泥与减水剂的相容性且助磨效果优异,其中0.05%型复合助磨剂还显著提高水泥各龄期抗压强度。     

新型着色材料——速溶色浆粉的测试与应用

介绍了通过初级颜料的润湿、研磨与分散、稳定处理技术,使助剂和树脂均匀地包裹在颜料表面,并通过特殊工艺制得水性和油性色浆粉,并赋予了很好的速溶性和分散性。     

Product design: Formulation of a screen-printable sintering-type conductive paste

Due to the complexity of the screen-printing operation and the rheological behaviors of the screen-printable paste, such a paste is usually formulated by trial-and-error. In this report, a systematic procedure, based on heuristics and mechanistic models, for the design of a screen-printable paste is developed. The procedure is demonstrated by a case study of the formulation of a conductive paste of copper particles.