Influence of carbon dioxide on shrinkage behavior and compressive strength of AAC in accelerated tests

Background

The German application standard DIN 20000‐404:2018‐04 for the use of AAC according to DIN EN 771‐4:2015‐11 describes a method to determine the long‐term resistance due to carbonation. Thus, the total value of the drying shrinkage as specified in DIN EN 680:2006‐03 must not exceed 0.40 mm/m. This threshold was evaluated using empirical methods.

Objective

In order to verify the above threshold, additional studies were carried out in this paper on AAC blocks from different manufacturers.

Experimental

Deviating from the standard climate according to DIN EN 680:2006‐03, a parametric study was carried out under laboratory conditions. All AAC specimens were stored at a relative humidity of 80% and a carbon dioxide concentration of 0.5% by volume. In addition to the shrinkage behavior, the compressive strength behavior of the AAC specimens with increasing carbonation progress was investigated.

Results

The degree of carbonation of the individual AAC types progresses at different rates. AAC that carbonates faster shows a greater change in length (up to about 5.2 mm/m) and a significant loss in compressive strength (up to about 50%). In some cases, the compressive strength initially increases before decreasing again. AAC containing fly ash only shows an increase in compressive strength with progressive carbonation.

Conclusions

The determination of the total value of drying shrinkage according to DIN EN 680:2006‐03 appears to be the most suitable method so far to identify AAC blocks with an increased risk towards carbonation with a manageable effort. The accompanying compressive strength tests indicate that the specified limit value of 0.40 mm/m according to DIN 20000‐404:2018‐04 is also appropriate.