Stability of concrete containing blast-furnace slag following exposure to cyclic elevated temperature

Concrete is widely used in constructions such as industrial floors or airducts in steel- and casting industry where it is often exposed to long-term or cyclic elevated temperatures. For these applications, thermal stability of concrete is of vital importance. The strength reduction dueto elevated temperatures depends on the temperature level and concrete composition. In this study, the effects of blast-furnace slag cement (CEM III/A) and basaltic aggregates were investigated at temperatures 250◦C to 700 ◦C in comparison to conventional Portland cement (CEM I) containing quarzitic aggregates. The concretes were cyclically exposed to high temperatures. Special attention was paid to mass loss, residual compressive and residual flexural strength depending on type of cement and aggregate as well as the number of thermal cycles. Mass loss and strength loss increased with increasing maximum temperature level, as expected. It was generally observed that concretes containing CEM III/A displayed significantly higher residual mechanical properties for almost all temperature levels. Concretes containing a combination of CEM III/Awith basaltic aggregates showed significantly higher stability at elevated temperatures compared to other concrete mixtures. It is further shown that apart from the maximum temperature the number of thermal cycles is important for the residual mechanical properties

On the Molecular and Submolecular Structure of the Semiquinone Cations of Alloxazines and Isoalloxazines as Revealed by Electron-Paramagnetic-Resonance Spectroscopy

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66144/1/j.1432-1033.1981.tb05295.x.pd

Comment on "The mechanism for activation of GTP hydrolysis on the ribosome".

Voorhees et al. (Reports, 5 November 2010, p. 835) determined the structure of elongation factor Tu (EF-Tu) and aminoacyl-transfer RNA bound to the ribosome with a guanosine triphosphate (GTP) analog. However, their identification of histidine-84 of EF-Tu as deprotonating the catalytic water molecule is problematic in relation to their atomic structure; the terminal phosphate of GTP is more likely to be the proper proton acceptor

A recent intermezzo at the Ribosome Club

Two sets of ribosome structures have recently led to two different interpretations of what limits the accuracy of codon translation by transfer RNAs. In this review, inspired by this intermezzo at the Ribosome Club, we briefly discuss accuracy amplification by energy driven proofreading and its implementation in genetic code translation. We further discuss general ways by which the monitoring bases of 16S rRNA may enhance the ultimate accuracy (d-values) and how the codon translation accuracy is reduced by the actions of Mg2+ ions and the presence of error inducing aminoglycoside antibiotics. We demonstrate that complete freezing-in of cognate-like tautomeric states of ribosome-bound nucleotide bases in transfer RNA or messenger RNA is not compatible with recent experiments on initial codon selection by transfer RNA in ternary complex with elongation factor Tu and GTP. From these considerations, we suggest that the sets of 30S subunit structures from the Ramakrishnan group and 70S structures from the Yusupov/Yusupova group may, after all, reflect two sides of the same coin and how the structurally based intermezzo at the Ribosome Club may be resolved simply by taking the dynamic aspects of ribosome function into account. This article is part of the themed issue 'Perspectives on the ribosome'