Behavior of High Performance Concrete Exposed to Internal Sulfate Attack (Gypsum-Contaminated Aggregate)

Contamination of aggregates with sulfate salts (especially gypsum) is a major problem in Middle East concrete construction. Fine aggregate has more detrimental effect due to its large surface area (fineness). An experimental work had carried out to investigate the behavior of high performance concrete exposed to internal sulfate attack in comparison with traditional concrete. Four sulfate contents (0.5, 1.5, 2.0, and 2.5 %) in fine aggregate were studied. Metakaolin was used as a pozzolanic material, which has proved itself as a good active one. Teasing program included compression, splitting, and ultrasonic pulse velocity tests. 168 cubes and 216 cylinders were cast throughout this program. The test period was extended to 210 days. The harmful effect (reduction in strength) of sulfate was obvious in early ages in contrast to external attack (as early as 7 days). The reduction in strength was continuous and higher in later ages and for higher SO₃ contents with reference to the mix with 0.5% SO₃. Test results showed that high performance concrete had lost strength, in such an environment, but it was more resistant than normal concrete and it may gain strength with age due to the pozzolanic action of metakaolin. The ultrasonic velocity results were positively proportional to strength development but with a slower rate of variation.