Hydration of slag-blended cements

In this paper, the hydration of slag in blended cements is investigated through the measurement of hydration reaction indicators such as portlandite content, non-evaporable and free water, and hydration heat. Three substitution rates of cement by slag were used (30%, 50% and 70%). The tests were performed at two constant temperatures (20 °C and 40 °C) in order to assess the activation energy of the different components. A multiphasic hydratation model is proposed to take account of the difference of kinetics of each main phase (clinker and slag) and the hydration kinetic law proposed considers interactions between the two phases. It includes the activation of the dissolution of slag by alkalis released by the clinker phases in the pore solution, the portlandite consumption by slag and the effect of temperature and moisture content on the reaction kinetics. The model is able to simulate the evolution of hydration products and adjust the hydration product stoechimetry to the rates of slag and the current temperature automatically and instantaneously. Its reliability is shown through its ability to fit the whole experimental plan results with a single parameter set. Among these parameters are the hydration heat of slag and its water consumption. The model and its parameters should be useful to simulate other types of slag-blended cement.     

Sulfate resistance of Portland-limestone cements in combination with supplementary cementitious materials

In this study, the sulfate resistance of five different high-C₃A Portland and Portland-limestone cements and their combinations with 30–50 % slag were examined at both 5 and 23 °C according to CSA A3004-C8 (similar to ASTM C1012). Also, XRD was used to identify the phases formed after sulfate attack. It was found that in 23 °C exposure, while 100 % cement mixes deteriorated due to conventional ettringite-based sulfate attack, partially replacing the cements with 30 or 50 % slag was effective in making the mixes highly sulfate-resistant. At 5 °C, all of the 100 % cement mortar bars expanded more than the test limits and eventually completely disintegrated due to the formation of thaumasite. Partially replacing cement with 30 % slag was only effective in controlling the deterioration for Portland cements but not Portland-limestone cements. However, all the Portland-limestone cements with 50 % slag were resistant to the thaumasite form of sulfate attack after 2 years.     

水玻璃常压制备多孔材料

以水玻璃为硅源,在酸性条件下,通过溶胶凝胶的方法,经去离子水洗去钠离子,然后溶剂交换,用三甲基氯硅烷进行表面修饰,在常压下干燥,制备成20～50nm孔径的介孔材料。     

PMMA-based composite materials with reactive ceramic fillers Part III: Radiopacifying particle-reinforced bone cements

New acrylic bone cements were prepared from alumina particles previously treated by 3-(trimethoxysilyl)propylmethacrylate (-MPS), able to act both as radiopacifying and reinforcing agents. The present study deals with the handling characteristics and the compressive behavior of such cements. The influence of the particles morphology, their surface-modification by -MPS bonding agent, their concentration in the cement, the powder-to-liquid ratio and the benzoyl peroxide concentration are reported. The role of grafted -MPS molecules as coupling agent was confirmed. For several formulations, compressive strength and modulus reached 150 MPa and 3400 MPa respectively. Limitations in the use of such formulations are also comprehensively discussed. ©2000 Kluwer Academic Publishers     

Carbon-loaded porous materials produced from fine-particle silica

Carbon-loaded porous materials have been produced by modifying inorganic matrices with pyrolytic carbon prepared via polystyrene carbonization at 750°C in an argon atmosphere. The matrices have been produced from silica particles about 80 nm in size, and polystyrene has been introduced either via impregnation or using polystyrene solutions as dispersion media in the fabrication of the composites. The structure and state of the carbon formed in pores of the composites have been studied by x-ray photoelectron spectroscopy and transmission electron microscopy. The results demonstrate that the pyrolytic carbon has the form of nanotubes or segmented nanospheres.     

Alkali-activated fly ash-based geopolymers with zeolite or bentonite as additives

Geopolymers were synthesized by using fly ash as the main starting material, zeolite or bentonite as supplementary materials, and NaOH and CaO together as activator. An orthogonal array testing protocol was used to analyze the influence of the mix proportion on the properties of the geopolymers. The results indicate that the concentration of NaOH solution and the CaO content play an important role on the strength of the materials. Especially, with zeolite as additive, the fly ash-based geopolymer shows the highest strength and the best sulfate resistance. Infrared spectroscopy, X-ray, and SEM–EDX demonstrate that supplementary zeolite may involve the process of geopolymerization to form a stable zeolitic structure and improve the properties of the geopolymer. Bentonite simply acts as a filler to make the geopolymer more compact, but shows no improvement on the compositions and the microstructures of the geopolymer.     

Effect of supplementary cementitious materials on shrinkage and crack development in concrete

The autogenous and drying shrinkage of Portland cement concrete, and binary and ternary binder concretes, were measured and compared. The binary and ternary binder concretes were formed by replacing part of the cement with fly ash, very fine fly ash and/or silica fume. Restrained shrinkage test was also performed to evaluate the effect of binder type on early age cracking. After the cracking of the restrained ring samples, crack widths were measured and compared with the results of an R-curve based model, which takes post-peak elastic and creep strains into account.The incorporation of fly ash and very fine fly ash decreased the autogenous shrinkage strain but increased the drying shrinkage strain. Since the total shrinkage strains of both the ternary and the binary concrete mixtures were similar, the strength development became an important factor in the cracking. The lower strength of the concrete with ternary binders led to earlier cracking compared to the binary binder concrete. Portland cement concrete cracked the earliest and had the greatest crack width. Measured crack widths were in accordance with the crack widths calculated with the R-curve model.     

环氧树脂/二氧化硅杂化材料的制备与性能表征

溶胶-凝胶法制备环氧树脂/SiO2杂化材料,利用FTIR、SEM和综合热分析仪对杂化材料的结构、显微形态及热性能进行了表征.结果表明,杂化材料中SiO2与环氧树脂两相间存在氢键作用;SiO2质量分数＜7%时SiO2与环氧树脂之间无明显相界面,可获得有机聚合物链段与无机网络互穿的有机/无机杂化材料;SiO2质量分数为11%时材料具有最佳耐热性能.     

A silica sol-gel design strategy for nanostructured metallic materials

Batteries, fuel cells and solar cells, among many other high-current-density devices, could benefit from the precise meso- to macroscopic structure control afforded by the silica sol-gel process. The porous materials made by silica sol-gel chemistry are typically insulators, however, which has restricted their application. Here we present a simple, yet highly versatile silica sol-gel process built around a multifunctional sol-gel precursor that is derived from the following: amino acids, hydroxy acids or peptides; a silicon alkoxide; and a metal acetate. This approach allows a wide range of biological functionalities and metals--including noble metals--to be combined into a library of sol-gel materials with a high degree of control over composition and structure. We demonstrate that the sol-gel process based on these precursors is compatible with block-copolymer self-assembly, colloidal crystal templating and the St?ber process. As a result of the exceptionally high metal content, these materials can be thermally processed to make porous nanocomposites with metallic percolation networks that have an electrical conductivity of over 1,000 S cm(-1). This improves the electrical conductivity of porous silica sol-gel nanocomposites by three orders of magnitude over existing approaches, opening applications to high-current-density devices.     

Review: Improving cement-based materials by using silica fume

The effects of silica fume as an admixture in cement-based materials are reviewed in terms of the mechanical properties, vibration damping capacity, freeze-thaw durability, abrasion resistance, shrinkage, air void content, density, permeability, steel rebar corrosion resistance, alkali-silica reactivity reduction, chemical attack resistance, bond strength to steel rebar, creep rate, coefficient of thermal expansion, specific heat, thermal conductivity, fiber dispersion, defect dynamics, dielectric constant and workability. The effects of silane treatment of the silica fume and of the use of silane as an additional admixture are also addressed.     

碱激活水泥研究进展

碱激活水泥是一种不同于普通硅酸盐水泥的胶凝材料,简要评述了碱激活水泥的性能特点和其强度发展的影响因素,并介绍了碱激活水泥的研究进展,分析了碱激活水泥存在的问题,提出了相应的解决方案。