Long-term investigation of autoclaved aerated concrete produced from fluidized fly ash

The study contributes to the knowledge of properties of autoclaved aerated concrete (AAC) formed with the utilization of modified raw materials — new generation of fly ash from coal power plants (fluidized fly ash). The fluidized fly ash is a mixture of bed and fluid fly ashes, in the ratio 2 : 1. The data of chemical and phase composition confirmed the high contents of CaSO4, CaO and clay minerals (illit, diaspor). The fluidized fly ash was used in doses of 0 — 30 — 100 %-ages. The AAC from commercial production (with fly ash from classical combustion) was used for purposes of comparison. Presented will be the results of long-range experiments aimed at the durability of that material, the results of three years tests are discussed.
The strength of samples decreases with the addition of fluidized fly ash, the lowest values exhibiting by samples with 100 %-ages of fluidized fly ash in the raw mixture. Both phase analysis and strength values show the higher tendency of samples with fluid fly ash towards thaumasite formation as the result of partial conversion of hydraulic C-S-H and tobermorite-like phases to nonbinding thaumasite. However, the expansion of test probes connected with the formation of thaumasite, and also gypsum and ettringite, in AAC does not exert the scope of deterioration seen in the concretes. The difference is due to the sufficient and accessible pore space in AAC, these data contribute also to the discussion of topics of thaumasite formation vs. thaumasite sulfate attack. The results represent a basis of the proposals of modified production of AAC.
Author: M. Drábik, S. Balkovic, M. Peteja

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