Sulfate Resistance of Concrete Containing High Volume of Mineral Admixtures

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Title: Sulfate Resistance of Concrete Containing High Volume of Mineral Admixtures

Author(s): E.F. Irassar, O.R. Batic, A. Di Maio and J.M. Ponce

Publication: Special Publication

Volume: 234

Issue:

Appears on pages(s): 589-606

Keywords: fly ash; microstructure; natural pozzolan; nondestructive test; slag; sulfate resistance

Date: 3/22/2006

Abstract:
This study evaluates the progressive deterioration of concrete specimens made with ordinary portland cement containing high volume of fly ash (40%), natural pozzolan (40%) and ground-granulated blast-furnace slag (80%) exposed to sulfate soil. The sulfate performance of these specimens was compared with those made with ordinary portland cement (OPC) and sulfate-resisting portland cement (SRPC).Concrete mixtures were formulated with a w/cm of 0.52 and total cementitious content of 350 kg/m3. Concrete specimens were partially (150 x 300 mm cylinders and 900 x 150 x 150 mm beams) and totally buried in sulfate permeable soil for fifteen years and the mechanical properties were monitored by nondestructive testing (dynamic modulus and ultrasonic pulse velocity) and by destructive testing (compressive strength). The microstructure of concrete was evaluated using XRD analysis and optical microscope observation. The results demonstrate that sulfate resistance of concretes containing a high volume of mineral admixtures is equivalent to concrete made with SRPC cement when they were buried in sulfate soil. Concrete specimens presented a good visual appearance, without cracking at the edges, and they retained the strength and the elastic modulus. Microstructural analysis revels that this behavior can be attributed to the removal of CH, decreasing the gypsum and ettringite formation and the enhancement of paste-aggregate interface of concrete. However, they presented an extent of deterioration aboveground, characterized by the progressive surface scaling due to salt crystallization cycles which is a physical nature damage. This observation confirms the poor performance of concrete containing high volume of mineral admixtures exposed to drying and soaking test.