Fate of Calcium Chloride Dissolved in Concrete Mix Water

The extent to which chloride ion incorporated in portland cement concrete as calcium chloride accelerator at the usual treatment levels remains dissolved in the pore solution was investigated. This was examined by direct analysis of pore solutions expressed from cement pastes. The chloride ion concentration of the pore solution remains high during the first day of hydration and only gradually declines. It appears that appreciable concentrations of chloride ion likely remain in solution indefinitely .     

The Conversion of a Boron-Containing Pyrotechnic Mix to a “Ceramic-Like” Material by Electron Beam Interaction

The transformation of a boron-containing pyrotechnic mix to a “ceramic” vitreous-like material by the impingement of an electron beam on a boron-barium chromate pyrotechnic, in a scanning electron microscope, is reported. The thickness of the “ceramic”-like material is ×250 the penetration depth for the electron beam and indicates that a self-sustaining chemical reaction was induced by interaction of the energetic material with the electron beam at temperatures well below the mix's ignition temperature of over 1000?°C. This links with earlier observations on the low-temperature liquefaction of boron to boron suboxides in an electron microscope.     

Apparent Temperatures Measured at Melting Points of Some Metal Oxides in a Solar Furnace

Six metal oxides (A1₂O₃, TiO₂, Nb₂O₅, Ta₂O₅, La₂O₃, and Dy₂O₃) were melted in a solar furnace and the apparent temperatures at their melting points were measured by means of a conventional optical pyrometer. The apparent temperatures of three of them (A1₂O₃, TiO₂, and Nb₂O₅) were 2025°, 1840°, and 1496°C. respectively, in close agreement with the melting points as determined by other investigators using other methods. The apparent temperatures of the other three varied widely and bore no relation to their melting points. The method therefore does not have general utility for the measurement of unknown melting points.     

Transitions in Vapor-Deposited Alumina from 300° to 1200°C

The transition of amorphous alumina to α-alumina was studied by X-ray diffraction, electron diffraction, DTA, TGA, and microscopic observation. The amorphous alumina was prepared by condensing vapor from evaporating molten alumina in vacuo onto the glass envelope of the vacuum chamber. The amorphous alumina was transformed to a poorly crystalline material by heating for 16 hr between 570° and 670°C. Between 670° and 1200°C, the poorly crystalline alumina was converted to α-alumina via two parallel series of transition aluminas. The principal series was γ-alumina to δ-alumina to α-alumina. A minor amount of θ-alumina developed from the initial crystallization and persisted throughout the duration of the principal series as a parallel path. Some conversion of δ- to θ-alumina was detected above 900°C. DTA produced an unexplained exothermic peak at 320°C and a second exothermic peak at 860°C which corresponded to formation of metastable aluminas.     

Micromorphology of the Interfacial Zone Around Aggregates in Portland Cement Mortar

Scanning electron microscopy showed that micromorphological features of the interfacial zone, which occur next to glass slide "model aggregates" occur also in mortars made with standard Ottawa silica sand. These features included formation of a duplex film on the sand-grain surfaces, development of large well-formed Ca(OH)₂ crystals at intervals near the interface with their c axes roughly parallel to it, development of stacked-platelet secondary Ca(OH)₂ in open spaces immediately adjacent the duplex film, and hydration leading to the presence of hollow-shell hydration grains (Hadley grains) in the interfacial region.     

GROWTH DYNAMICS OF INDIGENOUS MICROBIAL POPULATIONS ON VEGETABLES AFTER DECONTAMINATION AND DURING REFRIGERATED STORAGE

To ensure microbiological stability and safety in minimally processed (MP) salad vegetables, it is essential to consider the microbiology of this produce during cultivation and harvesting, and the potential changes to this microbiology through preparation, distribution and storage. This study takes two salad vegetables (lettuce and white cabbage) and, having enumerated a range of different physiological groups of microorganisms present on unwashed produce, determines the impact on each microbial group of applying a decontamination step in the preparation protocol. The disinfectant used was sodium dichloroisocyanurate. Decontamination reduced the total microbial load significantly on both vegetables. The levels of different microbial groups enumerated differed significantly between vegetables. All the microbial populations were reduced, but the biocidal effect of chlorine treatment varied with vegetable type. Reduction of the levels of lactic acid bacteria and aerobic psychrotrophs on cabbage was only achieved with inclusion of the decontamination step, and this effect, in general, did not last more than 3 days. Decontamination significantly reduced the levels of coliforms, and although the levels increased during refrigerated storage, they did not exceed initial levels found on unwashed produce. In addition, the levels found on treated cabbage remained lower than produce washed with water only.     

Specific Surface of Hardened Portland Cement Paste as Determined by Small-Angle X-Ray Scattering

Small-angle X-ray scattering was used to determine the specific surfaces of hardened portland cement pastes subjected to various treatments. Reasonably mature pastes yielded values of the order of 700 m²/g of ignited paste when examined in the original saturated condition. Drying to an intermediate relative humidity, P-drying, and D-drying reduce the surface areas to values of the order of 200 to 300 m²/g, but vacuum resaturation results in recovery of all the lost surface. Oven drying produces an additional loss in surface area, and in this case recovery on resaturation is not quite complete. The effect of w/c ratio appears to be minor, and pastes of hydrated C₃S yield essentially the same surface areas as corresponding portland cement pastes.     

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Swelling Properties of Synthetic Alkali Silica Gels

A suite of 10 synthetic sodium silica and sodium calcium silica gels was prepared to explore the basic mechanism of expansion of concrete by alkali-silica reaction. Methods were developed for measuring the free swelling capacity and the maximum swelling pressure generated by these gels when they are allowed access to free water. Free swelling ranged from as little as 0.5 to as much as 80%, maximum swelling pressures recorded varied from as little as 0.1 to almost 11 MPa, the latter well in excess of the tensile strength of most concretes. The relations observed between alkali:silica ratio of the gel and its free swelling and swelling-pressure characteristics were suggestive but not straightforward. The presence of calcium in the synthetic gels did not noticeably reduce their activity with respect to either test.