ABSTRACT:

Many specifications for concrete coated offshore pipelines require that the normal weight or heavyweight concrete be manufactured with either ASTM C150 Type II (moderate sulphate resistance) or Type V (high sulphate resistance) Portland cement due to the presence of sulphate in seawater. An important property of cements that determine their resistance to sulphate attack is the tricalcium aluminate (C3A) content and therefore the amount of this mineral phase is limited to 8% and 5% in Type II and Type V cement, respectively. This paper presents a literature review of laboratory and long term field studies which indicate that sulphate attack is not the primary mechanism of deterioration caused by seawater. Furthermore, cement composition does not affect long term performance provided that the concrete has a low water/cement ratio and is impermeable. The available information therefore supports the use of either ASTM C150 Type I (with a maximum C3A content of 12%) or Type II Portland cement for the manufacture concrete pipeline coatings. A potential secondary benefit of using Portland cements with C3A levels greater than 5% will be their greater capacity to bind chlorides, reducing the apparent diffusion rate of chlorides in concrete. A reduction in the ingress of chlorides will extend the service life of offshore pipelines by delaying the onset of steel reinforcement corrosion

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