A sulfate analysis may be required to determine if sulfate has entered the concrete from the environment, if sulfate compounds (e.g., calcium sulfate hemihydrate-plaster) have been added to the concrete as an admixture, to determine cement content, or to determine reasons for unusual
setting times.
setting times.
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Sulfate Procedure
Digest 5 grams of concrete, pulverized to pass a No. 30 screen, in 20 ml of 1:4 hydrochloric acid solution. Filter through a coarse-textured paper inside or over a fine-textured paper into a 400 ml beaker. Determine sulfate by the procedures of ASTM C114 or as follows: place a small piece of filter paper in the beaker and hold down with a glass rod. Bring the solution to boiling and add drop-wise, through a pipet, 20 ml of barium chloride solution (10 g per 100 ml water). Boil until the white precipitate settles, then digest below boiling in the glass-covered beaker.
Filter through a retentive filter paper, wash the paper 10 times with hot distilled water, place in a tared porcelain crucible, ignite over a flame without inflaming, then in a muffle furnace at 820°C. Weigh. Calculate SO3 as 0.343 × weight of precipitate.
Sulfide Procedures
Sulfide may be determined by evolution of hydrogen sulfide using the procedure of ASTM C114. Alternatively, total sulfur may be determined by evolution/titration (e.g., LECO furnace) and sulfate sulfur by Sulfate Procedure. The difference between these values, both calculated as SO3, multiplied by 0.4, is sulfide sulfur.
Digest 5 grams of concrete, pulverized to pass a No. 30 screen, in 20 ml of 1:4 hydrochloric acid solution. Filter through a coarse-textured paper inside or over a fine-textured paper into a 400 ml beaker. Determine sulfate by the procedures of ASTM C114 or as follows: place a small piece of filter paper in the beaker and hold down with a glass rod. Bring the solution to boiling and add drop-wise, through a pipet, 20 ml of barium chloride solution (10 g per 100 ml water). Boil until the white precipitate settles, then digest below boiling in the glass-covered beaker.
Filter through a retentive filter paper, wash the paper 10 times with hot distilled water, place in a tared porcelain crucible, ignite over a flame without inflaming, then in a muffle furnace at 820°C. Weigh. Calculate SO3 as 0.343 × weight of precipitate.
Sulfide Procedures
Sulfide may be determined by evolution of hydrogen sulfide using the procedure of ASTM C114. Alternatively, total sulfur may be determined by evolution/titration (e.g., LECO furnace) and sulfate sulfur by Sulfate Procedure. The difference between these values, both calculated as SO3, multiplied by 0.4, is sulfide sulfur.
It is a testing instrument. In muffle furnace, the test sample is kept away from any other element that can affect the result of the test such as fuel of combustion, ash from burning, the smoke of burning.
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