ABSTRACT
Natural groundwater and soil can contain substances which are aggressive to concrete and cement-based structures. Especially aggressive carbon dioxide occurs frequently. Chemical attack by aggressive carbon dioxide occurs in several phases in commercial cements used in foundation engineering. After a period of carbonation a leading front where calcium hydroxide is dissolved, depending on the availability in the binder matrix, is generated. As the attack progresses, the calcium carbonate formed is dissolved, leaving a layer rich in amorphous silicon dioxide, which has lower mechanical strength. This can result in problems in the long-term load-bearing behavior of more sensitive components with smaller dimensions and under tensile stress, in particular ground anchors and micro piles, which are manufactured using cement suspensions in the subsoil. This study evaluates the mechanisms induced by aggressive carbon dioxide in CEM III/A and CEM III/B compared with CEM I paste. Cement paste specimen with water-cement ratios of 0.4 and 0.5 stored in about 90 mg/l (exposure class XA2) aggressive CO2 for 3, 6 and 12 months are investigated. The methods include X-Ray fluorescence analysis as well as polarized light microscopy on thin sections. The depth of impact is measured and evaluated in terms of durability of geotechnical elements.
