Sulfate Resistance of Concrete Containing Mineral Admixtures

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Title: Sulfate Resistance of Concrete Containing Mineral Admixtures

Author(s): T. H. Wee, Arvind K. Suryavanshi, S. F. Wong, and A. K. M. Anisur Rahman

Publication: Materials Journal

Volume: 97

Issue: 5

Appears on pages(s): 536-549

Keywords: flexural strength; ordinary portland cement; sulfate resistance

Date: 9/1/2000

Abstract:
The present study evaluates the progressive deterioration of concrete mixtures containing various proportions of ground-granulated blast-furnace slag (GGBFS) and silica fume (SF) due to sulfate attack under tropical climatic conditions. The water-binder ratio (w/ b) (0.40 and 0.50), moist curing period (3, 7, and 28 days), and fineness of GGBFS (4500, 6000, and 8000 cm 2 g -1 ) were the other experimental variables. Concrete prisms were immersed in a 5% sodium sulfate solution for 32 weeks and periodically monitored for the change in flexural strength and linear expansion. The experimental results were compared with those of ordinary portland cement (OPC) and sulfate-resisting portland cement (SRPC) concrete specimens. The results demonstrate that the resistance of GGBFS concrete is a complex function of w/ b and proportion of GGBFS in the mixture. For example, the 65% GGBFS mixture of 0.50 w/ b, which was moist cured for 7 and 28 days, showed initial signs of deterioration. The same mixture with a lower w/ b (0.40) and even with a shorter moist curing period (3 days), however, indicated superior resistance to sulfate attack. This trend was also true for 100% OPC concrete mixtures with w/ bs of 0.40 and 0.50. The concrete mixtures incorporated with greater proportion of GGBFS (for example, 75 and 85%), however, showed greater resistance to sulfate attack, irrespective of w/ b (0.40 and 0.50) and moist curin period (3, 7, and 28 days). A similar trend was also true for con-crete mixtures with SF (5 and 10%) and also 100% SRPC concrete. Further, for a given proportion of GGBFS (65%), there was no consistent trend between the extent of deterioration and the fineness of GGBFS. For all the mixtures investigated, the moist curing period (3 and 7 days) had little influence on their resistance to sulfate attack. The observed sulfate-induced deterioration was due to the formation of poorly crystalline ettringite.