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2 2011

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AAC with low thermal conductivity

100%

Straube B. , Walther H.

2011

tom nr spec.

78-80

The structure of this optimized autoclaved aerated concrete (AAC) consisting essentially of calcium silicate hydrate phases, especially of 11 A tobermorite does not contain inorganic filler like calcite. The absence of quartz and crystalline fillers ensures lower thermal conductivity values even though the crystal structure of the silicate hydrate phases (CSH). According to the tests, the calcium silicate hydrate pore structure wilh the residual quartz grain contents below 10% by mass is producible by ensuring that the SiO2 component in the hydrothermal process reacts fully or nearly fully (< 10% by mass of residual quartz grains) with the CaO component to give CSH phases, especially crystalline CSH phases, preferably to give 11 A tobermorite which crystallizes out particularly efficiently. In terms of production, this is achieved by a common autoclaving process and by the use of very fine quartz flour as the SiO2 component. The production is not possible using cryptocrystalline or amorphous silica, for example with fumed silica or precipitated silica or with microsilica (amorphous SiO2 which forms in the preparation of silicon metals from ferrosilicon).

Pore size distribution effects on the thermal conductivity of light weight autoclaved aerated concrete

61%

Kreft O. , Hausmann J. , Hubalkova J. , Aneziris C. G. , Straube B. , Schoch T.

2011

tom nr spec.

49-52

Aim of the present study was to correlate thermal conductivities of highly porous autoclaved aerated concrete (apparent density < 100 kg/m3) with appendant micro- and nano-structural properties. AAC specimens with approximate apparent densities, but different pore size distributions were fabricated through utilizing specially selected, surface active additives when preparing the slurry of raw materials, aluminum and water. The main focus of this study is on the quantitative analysis of size and morphology of both pores and solid skeleton by 3D X-ray tomography (CT) and scanning electron microscopy (SEM). Moreover, specific surface areas and pore size distributions were determined by the methods of gas adsorption and mercury porosimetry. Apparent thermal conductivities depend on the number of pores, pore size distributions and thicknesses of the separating walls of the solid skeleton. The present study provides further inside in the mechanisms of heat transfer in light weight autoclaved aerated concrete.