The early stages of catastrophic optical damage (COD) in 808 nm emitting diode lasers are mapped by simultaneously monitoring the optical emission with a 1 ns time resolution and deriving the device temperature from thermal images. COD occurs in highly localized damage regions on a 30 to 400 ns time scale which is determined by the accumulation of excess energy absorbed from the optical output. We identify regimes in which COD is avoided by the proper choice of operation parameters.
Most lightweight aggregates (LWA) are produced by thermal Treatment of natural raw materials such as clay and shale. In addition to the high energy costs thereby incurred, the availability of suitable raw materials is limited. Other LWA manufactured from industrial by-products and wastes do not always meet the quality criteria for use in high-Quality lightweight concrete. A real alternative is the use of novel lightweight aggregates (referred to as LWA, aggregates and granules) made from mineral construction and demolition waste. An appropriate manufacturing technology has recently been developed in the framework of a German research project /1, 2/. Masonry rubble of variable grain size containing different amounts of brick material (25 to 70 %) serves as raw material. The LWA are obtained in a multistage manufacturing process by a thermal or hydrothermal treatment, which causes the expansion and the hardening of the material. The novel LWA meet the acceptance criteria for conventional lightweight aggregates. They are suitable for the production of lightweight concrete /2-6/. However to create tailor-made LWA from masonry rubble, the novel expanded materials and the influence of manufacturing conditions have to be understood in more detail. This paper reports on ongoing investigations of the chemico-mineralogical composition and microstructure of the novel LWA and focuses on the results of Chemical analyses, XRD, ESEM, TG/DTA and fusibility tests.
The pore structure of lightweight granules made from masonry rubble was studied in order to better understand their engineering properties. Thermally and hydrothermally hardened granules were tested. Analysis by ESEM, mercury porosimetry and sorption methods yield important insight into their microstructure. The thermal granules are characterised by partly melted vitreous areas and large internal macropores that are connected via narrow throats. They show a marginal specific surface area along with a hydrophobic behaviour. In contrast, the hydrothermal granules have an accessible mesoporous system containing plate-like and ink-bottle pores. The shape of their water isotherms depending on the granules CaO content is sensitive to the morphology of calcium silicate hydrate phases (CSH). The hysteresis changes from a narrow loop that closes at low pressures, which can be attributed to coarser more crystalline CSH, to a large triangular-shaped loop along with a low pressure hysteresis, which is characteristic for fine fibre-like CSH with ink-bottle and plate-like pore morphologies. Granules with fibre-like CSH have the higher specific surfaces areas but those with more crystalline CSH show stronger physisorption of water molecules.