ORIGINAL ARTICLE Deterioration of mortar bars immersed in magnesium containing sulfate solutions Wolfgang Kunther • Barbara Lothenbach • Karen L. Scrivener Received: 13 July 2012 / Accepted: 14 February 2013 / Published online: 21 February 2013 Ó RILEM 2013 Abstract Mortars prepared with a CEM I and a CEM III/B binder were investigated in different magnesium sulfate solutions. The main deterioration mechanism for the CEM I was expansion, while surface erosion was dominant for CEM III/B. The presence of sodium, potassium and calcium in a magnesium sulfate solution led to less expansion and less surface deterioration for both, CEM I and CEM III/B, than which was observed in solutions containing only sodium or magnesium sulfate. The presence of a mixture of different cations seems to lower both the surface deterioration and the expansion and might explain why sulfate attack damages are not as frequent in the field as in laboratory tests. Sulfate binding before cracking/expansion is similar in the presence of all different solutions investigated, indicating that the speed of sulfate ingress and the amount of bound sulphate depends during the first months mainly on the binder. Keywords Sulfate attack Á Magnesium sulfate Á Portland cement Á Slag blended cement Á Brucite Á Magnesium-silicate-hydrate 1 Introduction Magnesium is a common cation in natural waters and thus often in contact with concrete structures. The attack is labeled as sulfate attack when the magnesium is combined with sulfate ions, such solutions have been extensively investigated in laboratory studies. The combined occurrence of sulfate and magnesium ions is known to be a severe form of sulfate attack as both the sulfate and magnesium ions interact with cement hydrates [1]. Gollop and Taylor [2, 3] reported that the deterioration is more severe at the edges and corners than at the plane surfaces. The solubility of magnesium sulfate in water is high. However, magnesium hydroxide (brucite) pre- cipitates in high pH environments due to a very limited solubility of this mineral. The hydroxide ions are supplied by destabilization of cement hydrates like portlandite and C-S-H. The result of this process is decalcification of the binder with precipitation of gypsum as the released calcium reacts with the sulfate ions in solution. Testing with magnesium sulfate is reported as being more deleterious for blended cements, like slag blended CEM III/B cement with high levels of cement substitution [4, 5]. Slag blended cements have been reported to show surface deterioration rather than expansion compared to CEM I binders [6]. The formation of M-S-H and brucite have been reported for different cements exposed to magnesium sulfate solutions [5, 7, 8]. M-S-H phases are the last stage of W. Kunther (&) Á B. Lothenbach Laboratory for Concrete & Construction Chemistry, EMPA, U ¨ berlandstrasse 129, 8600 Du ¨bendorf, Switzerland e-mail: wkunther@googlemail.com K. L. Scrivener Laboratory of Construction Materials, EPFL, 1015 Lausanne, Switzerland Materials and Structures (2013) 46:2003–2011 DOI 10.1617/s11527-013-0032-6