National Research Development Corporation

Holtronic Technologies Plc

Donald W Tomkins

Laurence Holden

Matthew C Ball

A holographic technique for the detection of position of known items so as to be able to reject those samples which do not lie within certain defined spatial parameters. A plate which contains a single exposure of the three dimensional holographic image of an object is illuminated by parallel reference beams from a laser to allow the reconstruction of a real focused image of the object. A displacement translator supports the object and permits displacement thereof in three directions all at right angles to one another. The coincidence of the object and its holographic image are detected either optically by means of a stereoscopic microscope, or electrically by means of a stereoscopic microscope and a photo-diode.

Method of and apparatus for the positional detection of objects

A modified hydraulic cement product comprises a hydraulic calcium silicate-based cement having a Blain surface area of at least 3,000 cm.sup.2 /g, and/or an iron content of less than 2.5% by weight expressed in terms of the ferric oxide content of the dry cement, in which the cement has been treated with an additive comprising an aldehyde or an amide or substance convertible to an aldehyde or amide under the alkaline conditions prevailing in the cement before or during the setting reaction. Treated cement may be hydrated subsequent to or in parallel with the additive treatment to give hydrated products which characteristically exhibit modified cement morphologies, in particular fibrous cement morphologies, and generally also modified physical strength properties, e.g. tensile strengths of at least about 10 MN/m.sup.2 and compressive strengths of at least about 60 MN/m.sup.2, as compared with untreated hydrated cement products. The cements may be used with other materials including aggregates and also reinforcing elements and in preferred embodiments may be used in the production of pre-cast units for use in the construction industry. Additionally some treated products prior to hydration exhibit desirable properties: cement slurries with certain aldehydes, e.g. acetaldehyde, providing extrudable cement compositions, and treatment of cements with salicylaldehyde, particularly in the absence of water, providing a quick-set cement composition which may be hydrated subsequently.

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Loughborough, United Kingdom

Donald W Tomkins