The calcium silicate hydrates

This review examines the detailed chemical insights that have been generated through 150 years of work worldwide on magnesium-based inorganic cements, with a focus on both scientific and patent literature. Magnesium carbonate, phosphate, silicate-hydrate, and oxysalt (both chloride and sulfate) cements are all assessed. Many such cements are ideally suited to specialist applications in precast construction, road repair, and other fields including nuclear waste immobilization. The majority of MgO-based cements are more costly to produce than Portland cement because of the relatively high cost of reactive sources of MgO and do not have a sufficiently high internal pH to passivate mild steel reinforcing bars. This precludes MgO-based cements from providing a large-scale replacement for Portland cement in the production of steel-reinforced concretes for civil engineering applications, despite the potential for CO2 emissions reductions offered by some such systems. Nonetheless, in uses that do not require steel reinforcement, and in locations where the MgO can be sourced at a competitive price, a detailed understanding of these systems enables their specification, design, and selection as advanced engineering materials with a strongly defined chemical basis.

Magnesia-Based Cements: A Journey of 150 Years, and Cements for the Future?

mented, if not .particularly new. Chapter 15, on the boron hydrides, has been almost entirely rewritten by the translators, with curious results. Historically, Syrkin and Dyatkina were among the first authors to revive the bridged structure for diborane and related molecules, and their views on the electronic structure of the bridge are clearly not entirely acceptable to the translators, who give prominence to Pitzer's subsequent ideas, and ignore altogether the extension of the bridge theory to beryllium and aluminium borohydrides. The effect is confusing, and the altered chapter has lost in clarity what it may have gained in modernity. The more theoretical chapters are not quite so good. I t is, of course, wellnigh impossible to do justice to the wave mechanics of atoms and molecules in 140 pages without oversimplifying or passing over the mathematical and physical difficulties. One must admire the ambitious a t tempt of the authors to do this, and much of the fundamental theory--for instance, the exclusion principle and the variation method--is well explained. But surely some mention should have been made of the fixed-nucleus approximation, and the fact tha t the Aufbauprinzip is only an approximation, even for atoms ? Chapters 5 and 6 show up the resonance theory at its worst, though this does not seem to have been the intention of the authors. We now know that the 'unexcited structures' of large aromatic molecules make scarcely any contribution to the ground state; and counting resonance structures is a theoretically unjustifiable procedure. Also, t h e theory of ionic-covalent resonance, in its simple form, has not stood up to recent critical examination, and can no longer be taken very seriously. These last two criticisms, however, are mainly based on work which has been done since the book was written, and can hardly be laid at the door of the authors. Chapter 7 has been added in translation, and is a good chapter in its own right, t-hough, as one might have expected, it is not particularly well integrated into the rest of the book. The printing is good, and the translation intelligent, though it is regrettable t h a t Mulliken's name should have been misspelt every time it is mentioned--more than twenty times. Taken as a whole, the book is an important contribution to the literature, and is to be recommended to everyone interested in molecular structure. H. C. LONGUET-HIGGINS Department of Chemistry University of Manchester England

X‐Ray Identification and Crystal Structures of Clay Minerals

AbrstractThe present study is part of a wider investigation to develop an alternative cementing system for the encapsulation of problematic low and intermediate level radioactive waste. It has been suggested that alternative cementing systems, with lower internal pH than conventional Portland cement based composite cements, may reduce the corrosion of some reactive metals and may be beneficial for the long term durability of wasteforms. A potential alternative is an acid–base cementing system, based on mixing calcium aluminate cement (CAC) with acidic phosphate solutions. Although these systems have been studied previously, there has been no systematic investigation to identify phosphates for producing suitable matrixes for application in radioactive waste encapsulation. In the current study, monophosphate modified CAC formulations did not set or develop significant strength, whereas polyphosphate modified CAC formulations exhibited rapid setting and strength development. It is proposed that polyp...

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Phosphate modified calcium aluminate cement for radioactive waste encapsulation

The potential for using slags activated with near neutral salts as immobilisation matrices for nuclear wastes containing reactive metals

Legacy radioactive wastes arising from reprocessing of nuclear fuels in the UK are classified as intermediate level waste (ILW), which contain things such as aluminium and magnesium. Blast furnace slag (BFS) composite cements are used to encapsulate ILW. These cements have a high pH which is advantageous to limit the mobility of some of the radioactive species but can cause corrosion of metals. The present paper describes some fundamental aspects of corrosion of aluminium and magnesium in BFS composite cements.The corrosion of aluminium produced an interface between aluminium and cement which was porous with a series of zones containing bayerite (Al(OH)3) and stratlingite (2CaO.Al2O3.SiO2.8H2O). With magnesium, the main corrosion product was found to be brucite (Mg(OH)2) and the porous zone was less pronounced. The hydration of the bulk cement did not appear to be affected by the corrosion of these metals.

A. Setiadi

Papers

Corrosion of aluminium and magnesium in BFS composite cements