Thermally induced changes in microstructure and their effects on the mechanical parameters of AAC

1 Structure of the test equipment for determining temperature-­dependent parameters of building materials
1 Structure of the test equipment for determining temperature-­dependent parameters of building materials
2 Scanning electron photomicrographs of the microstructure of P2‑0.35 AAC before thermal treatment
2 Scanning electron photomicrographs of the microstructure of P2‑0.35 AAC before thermal treatment
3 Comparison of the DTG curves of AAC after thermal treatment for 120 minutes
3 Comparison of the DTG curves of AAC after thermal treatment for 120 minutes
4 X-ray diffractograms of the thermally treated P2-0,35 AACs
4 X-ray diffractograms of the thermally treated P2-0,35 AACs
5 Section of microstructure after thermal treatment at a) 350 °C and b) 850 °C (SEM)
5 Section of microstructure after thermal treatment at a) 350 °C and b) 850 °C (SEM)
6 Measured thermal contraction (eth) without preload (VL) and total contraction (ew) of P2-0.35 AAC in the temperature interval 20-900 °C
6 Measured thermal contraction (eth) without preload (VL) and total contraction (ew) of P2-0.35 AAC in the temperature interval 20-900 °C
7 Measured thermal contraction (eth) without preload (VL) and total contraction (ew) of P2-0.4 AAC in the temperature interval 20-900° C.
7 Measured thermal contraction (eth) without preload (VL) and total contraction (ew) of P2-0.4 AAC in the temperature interval 20-900° C.
8 Measured thermal contraction (eth) without preload (VL) and total contraction (ew) of P4-0.5 AAC in the temperature interval 20-900 °C
8 Measured thermal contraction (eth) without preload (VL) and total contraction (ew) of P4-0.5 AAC in the temperature interval 20-900 °C
9 Mean compressive strengths of the P2-0.35, P2-0.4 and P4-0.5 AACs as function of temperature after 2-hour heating of the test piece to the respective temperature stages (preload 2 kN)
9 Mean compressive strengths of the P2-0.35, P2-0.4 and P4-0.5 AACs as function of temperature after 2-hour heating of the test piece to the respective temperature stages (preload 2 kN)

Summary: Investigations into the thermally induced changes in the microstructure of autoclaved aerated concrete (AAC) were compared with the systematic determination of the parameters of high temperature stressing of the three currently most widely used types of aerated concrete (P2-0.35; P2-0.4 and P4-0.5) to gain an insight into how masonry made of aerated concrete would behave in the case of fire. The determination of temperature-dependent building material parameters in AAC has made a contribution to the creation of a systematic material database for the application of engineering methods of structural fire protection in accordance with Eurocode 6, Part 1–2.

1 Introduction and present state of knowledge

Autoclaved aerated concrete (AAC) is an inorganic, mineral, walling material that unites a very favourable combination of the parameters of bulk density, compressive strength and thermal conductivity. Quartz sand, lime and/or cement as the binder, gypsum and/or anhydrite (depending on the mix formulation) and water are required for its production. The building material acquires its characteristic porous structure through the addition of aluminium powder, which reacts in the aqueous alkaline environment with the evolution of hydrogen and foams the...

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ZKG 04/2011

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ZKG 04/2011

Ressort:  Materials Science
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