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2 2011

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Water transport in air-pores

Tada S.

Cement Wapno Beton

2011

nr spec.

60-65

Water transport experiments were performed on AAC with known pore structure and well-controlled moisture content. Specimens with the critical moisture content for freeze/thaw resistance were observed with the cryo-SEM. Evidences were confirmed that the ice segregated on the surface of air-pores as a result of redistribution of unfrozen water coming from the matrix part between air-pores. The standpipe absorptivity test for specimens with an air-pore volume of approx. 45 vol.% while having different mean air-pores diameters showed an abrupt jump of permeability when the mean air-pores diameter was smaller than 0.15 mm or the air-pores connectivity was 20%. In the free water uptake test using a dried AAC specimen, the capillary suction precedes other water transports and saturates the capillaries of 35 vol. % instantly followed by a slow absorption process, i.e. escaping of entrapped air bubbles that controls the subsequent absorption rate.

Methods for moisture storage and transport property determination of autoclaved aerated concrete

Scheffler G. A., Plagge R.

Cement Wapno Beton

2011

nr spec.

70-77

The hygric performance of autoclaved aerated concrete is a key determinant for many other material properties as e.g. thermal conduction, carbonation or shrinkage behavior. Laboratory determination of hygric material properties, i.e. moisture storage and moisture transport, is hence a prerequisite and a standard in production and process supervision. In that context, prediction and simulation of the hygric material performance based on numerical calculation models has become a widely used research and design tool. However, for assessment of the material behavior under variable climatic conditions, the hygric material properties have to be determined in a first step. In a second step, these properties have to be transformed into the non-linear coefficients required by these numerical calculation models. This paper is the first out of two focusing on the first step. It introduces different methods for moisture property determination. The methods cover the full range of possible moisture stages. Moisture storage and moisture transport is distinguished. For moisture transport, vapor and liquid phase transport is considered by different direct and indirect methods. The methods are applied for an aerated autoclaved concrete. The obtained data is shown and discussed. In a second step, described in a second paper, this data is used to derive the non-linear material functions required for sophisticated numerical simulation of the hygric material performance.