Mechanism of Sea Water Attack on Cement Mortar


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Title: Mechanism of Sea Water Attack on Cement Mortar

Author(s): M. L. Conjeaud

Publication: Special Publication

Volume: 65


Appears on pages(s): 39-62

Keywords: chemical analysis; corrosion mechanisms; C3A; C3S; electron microscopy; hydration; magnesium hydroxides; marine atmospheres; mortars (material); portland cements; sea water; water-cement ratio; x-ray diffraction .

Date: 8/1/1980

Five kinds of commercial Portland cements and one C3S sample were used for the study. The test prisms were made of mortar with a cement-sand ratio of 1 : 3 and a water-cement ratio chosen in order to give an ASTM flow of 110 +_ 5 %. After 28 days water curing, the test prisms were immersed in seawater, then, at fixed periods, up to 3 years, they were investigated by means of strength tests, chemical analysis, X-ray diffraction and scanning electron microanalysis. Results obtained show that SO3 and especially Cl diffuse rapidly in the cement mortars, but their penetration is soon slowed down by the formation of an almost impermeable Mg(OH)2 and/or aragonite layer on the mortar. It is postulated that this formation of a protective layer which occur with all the cements investigated is the main reason why immersed cement mortars are little attacked by seawater, even when the cement is C3A-rich whereas attack is greater at tide level where the Mg(OH)2 and/or aragonite layer is subject to cracking.