Several modifications of the ‘hexagonal’ tetracalcium and dicalcium aluminate hydrates have been obtained, some of which have not been described previously. Only a newly established 4CaO,Al2O3, 19H2O hydrate, and an α‐form and a hitherto undescribed β‐form of a 2CaO,Al2O3,8H2O hydrate have been found to occur in the aqueous system at 25°. Other modifications are produced on drying under various conditions. The 4CaO,Al2O3,19H2O hydrate, characterized in the X‐ray patterns by a longest basal spacing of 10·6Å, is dehydrated relatively easily to give a mixture of α‐and β‐forms of a 13H2O hydrate, characterized by longest basal spacings of 8·2Å and 7·9Å, respectively. There is little difference in stability between the two forms and it appears to be a matter of chance as to the relative amount of each which may be formed. Two other tetracalcium aluminate hydrates have been obtained with water contents of 11H2O and 7H2O, both of which give longest basal spacings of 7·4Å. The α‐ and β‐forms of 2CaO,Al2O3,8H2 are characterized by longest basal spacings of 10·7Å and 10·4Å respectively. The α‐form appears to be more stable than the β‐form. Three other states of hydration of the dicalcium compound exist, having water contents of 7·5H2O, 5H2O and 4H2O, and giving longest basal spacings of 10·6Å, 8·7Å, and 7·4Å, respectively. With various preparations of the compound 3CaO,Al2O3,CaSO4,aq., basal spacings of 10·3Å, 9·6Å, 8·9Å, 8·2Å, and 8·0Å have been observed, but these modifications await further study.

Color etchants have a huge potential in industrial applications and numerous investigations have been made to obtain a better understanding of the etching process. However, reproducibility and a solid knowledge of the ongoing processes are still missing. The work presented is a systematic study of the reproducibility of the Beraha color etching with potassium metabisulfite. By in situ observation of the etching process, the different states of the Beraha etching could be followed. It was shown that, at the beginning of the etching of dual-phase steels, the contrasting of the second phase by dissolving the less noble part of the second phase is the predominant contrast. Uncommonly, grain boundaries are hardly attacked. The color development of matrix grains is orientation sensitive and it was shown by comparison with electron backscatter diffraction (EBSD) measurements, that similar orientated grains have similar colors.

Summary This paper gives in the first place an account of investigations which were made to determine the extent to which calcium chloride may be present in the free state in concrete at various temperatures, since this will have a bearing on the extent of corrosion of embedded steel. It has been concluded that while there is a tendency for a large proportion of the added calcium chloride to react with the hydrating cement at normal temperatures, the residual small amount of free chloride always retained in solution will give an appreciable chloride concentration in solution and will cause a certain amount of corrosion of embedded steel. The amount of free chloride in solution is influenced by the composition of the cement, and will increase with an increase in the amount of calcium chloride added and with increasing temperature. These conclusions offer a reasonable interpretation of some of the findings of the second part of the paper which covers a direct study of corrosion of high-tensile steel embedded in different concretes containing calcium chloride. The present results indicate that with good concrete practice in mix design, depth of cover, and specification of materials, the additional corrosion induced by the use of flake calcium chloride up to about 2 % by weight of the cement in dense normally cured ordinary Portland cement concrete will have no structural significance. However, corrosion is greater under other conditions, and it appears that the degree of corrosion obtained in the presence of calcium chloride will depend on a number of factors, such as the quality of the concrete and adequacy of the casting procedures, the composition of the cement, the amount of calcium chloride added, the conditions of curing and storage of the concrete, and the diameter and initial surface condition of the steel wires.

Synopsis The performance in concrete of nine commercial superplasticizing admixtures has been examined by using a particular test procedure to evaluate their performance and to provide comparative data on their effects. All the superplasticizers were observed to have an appreciable fluidifying action in fresh concrete so that, under appropriate conditions, they either considerably improved its workability at normal water content or permitted a water reduction of at least 10% to be made while maintaining normal workability. For very-high-workability concrete deficient in fine material, or with exceptionally high additions of superplasticizer, excessive bleeding and segregation of the fresh concrete occurred, resulting in its rejection. Some superplasticizers also tended to increase the air content of concrete and/or to have a retarding influence upon its setting and hardening characteristics; these effects produced a reduction in compressive strength in some circumstances. For water-reduced superplasticized concretes with air contents below 3%, the compressive strength values obtained at ages from 7 days to 2 years exceeded those to be expected from water reduction alone. Concretes containing super-plasticizers and with appropriate entrained air contents showed a high resistance to freezing-and-thawing actions under wet conditions.

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