Performance evaluation of blended cement concretes under MgSO4 attack

Abstract

The increased use of blended cements in marine concrete structures necessitates the evaluation of their performance in the presence of magnesium sulfate (MgSO4). In the present study, the behaviour of concrete containing three cements such as ordinary Portland cement (OPC), Portland pozzolana cement (PPC) and Portland slag cement (PSC) is studied by exposing the concrete specimens in 10% magnesium sulfate solution under laboratory condition and in the tidal zone of seawater. The studies reveal that under both conditions the order of resistance to sulfate attack of three cements is OPC > PPC > PSC. Because of the presence of a greater amount of calcium-aluminate-rich glasses, the concretes containing PSC are more susceptible to sulfate attack. Both in OPC and blended cements, the magnesium sulfate attack is greater in low water to cement (w/c) ratio concretes than in high w/c ratio concretes. Unlike sodium sulfate (Na2SO4) attack, magnesium sulfate attack is more active in blended cements and reduces the time to failure (T-f) of concrete by 1.2 times in 20 and 30 MPa concretes and by 4 times in 40 MPa concrete. Compared to PSC, the T-f of PPC is longer and the behaviour is similar to OPC. Differential thermal analysis shows that the major expansive product is gypsum and the method of attack is mostly by softening rather than by swelling and expansion. The combined action of chemical attack by sulfates and mechanical attack by waves is the major influencing parameter when concrete specimens are exposed to the seawater.