Change in reaction kinetics of a Portland cement caused by a superplasticizer — Calculation of heat flow curves from XRD data

The hydration process of a commercial Portland cement was followed by means of heat flow calorimetry. The measured heat flow was compared with calculated heat flow curves based on XRD data. Examined in particular was the influence of one selected superplasticizer on the hydration of the Portland cement. It was shown that the superplasticizer in question retards both the aluminate reaction and the silicate reaction. It is certainly conceivable that there are more than only one explanation for the interaction between the superplasticizer and the cement. A complexation of Ca^2 + ions from pore solution by the superplasticizer is as thinkable as the adsorption of the polymer on the nuclei or the anhydrous grain surfaces which in turn might lead to the prevention of the growth of the nuclei or the dissolution of the anhydrous grains.     

Self-report measures for the assessment of human–machine interfaces in automated driving

Cognition, Technology & Work - For a successful market introduction of Level 3 Automated Driving Systems (L3 ADS), a careful evaluation of human–machine interfaces (HMIs) is necessary....     

Solid state NMR and LVSEM studies on the hardening of latex modified tile mortar systems

Construction mortars contain a broad variety of both inorganic and organic additives beside the cement powder. Here we present a study of tile mortar systems based on portland cement, quartz, methyl cellulose and different latex additives. As known, the methyl cellulose stabilizes the freshly prepared cement paste, the latex additive enhances final hydrophobicity, flexibility and adhesion. Measurements were performed by solid state nuclear magnetic resonance (NMR) and low voltage scanning electron microscopy (LVSEM) to probe the influence of the latex additives on the hydration, hardening and the final tile mortar properties. While solid state NMR enables monitoring of the bulk composition, scanning electron microscopy affords visualization of particles and textures with respect to their shape and the distribution of the different phases.

Within the alkaline cement paste, the poly(vinyl acetate) (VAc)-based latex dispersions stabilized by poly(vinyl alcohol) (PVA) were found to be relatively stable against hydrolysis. The influence of the combined organic additives methyl cellulose, poly(vinyl alcohol) and latexes stabilized by poly(vinyl alcohol) on the final silicate structure of the cement hydration products is small. But even small amounts of additives result in an increased ratio of ettringite to monosulfate within the final hydrated tile mortar as monitored by ²⁷Al NMR. The latex was found to be adsorbed to the inorganic surfaces, acting as glue to the inorganic components. For similar latex water interfaces built up by poly(vinyl alcohol), a variation in the latex polymer composition results in modified organic textures. In addition to the networks of the inorganic cement and of the latex, there is a weak network build up by thin polymer fibers, most probably originating from poly(vinyl alcohol). Besides the weak network, polymer fibers form well-ordered textures covering inorganic crystals such as portlandite.     

纺纱设备发展新动向

回顾过去的几个月 ,任何目睹纺织品价格下跌、市场低靡的人 ,也许都不会再关心纺纱技术的革新或新的发展动向。然而 ,这种情形似乎正有所改善。人们的视线正被新工艺技术的发布所吸引。与此同时 ,“任何新技术必须经受经济可行性的检验”这一观点 ,正为更多的人所接受。要做到这一点 ,比较可行的途径是进一步改进现有的纺纱设备 ,如提高自动化程度或提高速度和产量等。要在成纱性质方面有显著的突破 ,则会困难得多 ,因为这要求对市场的反应进行准确的预测。1　纺纱准备在开松、除杂和梳理领域 ,《纺织世界》(Tex tileWorld)杂志一直关注现…     

纱线种类、织物结构及设备对平针织物常见疵点的影响

纬编织物的组织结构有多种，本文仅就几种平针结构织物在生产过程中经常出现的疵点现象进行讨论，所选择的织物分别是单面平针、条纹平针及凹凸纹平针织物，这些疵点将对后续加工及其服用产生很大的影响。     

Mode of growth in LP-MOVPE deposition of GalnAs/lnP quantum wells

GalnAs/lnP multiple quantum wells of 10 periods grown by low pressure metal organic vapor phase epitaxy were studied using a careful analysis of their photoluminescence (PL) spectra and of supporting x-ray data. The results demonstrate extremely precise control of the well width. The width of well and barrier can be reproducibly adjusted by a fraction of a monolayer. This allows one to distinguish between 3-dimensional (3-D) and 2-dimensional (2-D) growth, which determines the lateral extent of the atomically smooth interfacial areas. By varying the growth time per well a discontinuous energy shift of the PL peaks is obtained for wells with widths from 1 to 8 monolayers. We show that this discontinuous energy shift corresponds to a change in well width by one monolayer. It is also observed when growth at the upper interface is carried on without interruption and a thin quaternary film is deposited at the interface. From these results the presence of atomically flat surfaces during the growth is deduced; these give a strong indication of a 2-D mode of growth for an optimized set of parameters.     

圆形针织产品的生产和质量

在大量的短纤纱的纺织参数中，对短纤纱卷装的考虑、处理、运输、装载和储存以及与纱线相关的参数将会影响产量、质量和费用。本文就这些问题作以下讨论。     

Compatibility Investigations on Polymer‐Fiber‐Reinforced Cements Modified with Polymer Latexes

Summary: In construction, polymer fibers are commonly applied beside steel, glass and mineral fibers to improve material's flexibility to shear stress. As in other composite systems, there are compatibility problems present between the fibers and the cement due to the different chemical natures and the different thermal expansion coefficients of the cement and the polymers. Within this study the interactions between two Portland cements and polymer fibers were investigated by SEM and solid‐state NMR spectroscopy. To improve the wetting ability of the polymer fibers by the cement matrix, redispersible latex powders were successfully applied to improve the adhesion between the cement matrix and the fibers. Within this study, several solid‐state nuclear magnetic resonance (NMR) spectroscopy methods, detecting ¹H, ¹³C, ²⁷Al and ²⁹Si nuclei, and scanning electron microscopy (SEM) were applied. Thus, cement pastes, inorganic additives and organic admixtures could be monitored individually.

SEM images of the interface between poly(propylene) fibers and Portland cement, hardened and hydrated in the presence of a 2 wt.‐% poly[(vinyl acetate)‐co‐ethylene] latex.