On a bridge repair, the engineer is requiring removal of all concrete containing more than 2 pounds of chloride ions per cubic yard. I've received chloride ion content reports from two materials testing labs. One reported the chloride ion content in percentage by weight of concrete, the other in parts per million. How do I convert these to pounds per cubic yard?
One part per million equals 0.0001 percent by weight, so both labs are giving you information in a similar format. But to convert either result to pounds of chloride ion per cubic yard of concrete you need to know the density of the concrete. In the laboratory, this requires weighing a sample of the concrete and determining its volume as described in Paragraph 8 of ASTM C 1084. If the chloride-content determination was based on powder samples from drilling, the lab wouldn't be able to provide density data. In this case, an assumed 3,800 pounds per cubic yard (about 142 pounds per cubic foot) for normal weight concrete can help you get an approximate conversion. As an example, let's say Lab A reports 0.0624 percent by weight of concrete and Lab B reports 580 parts per million (0.058 percent by weight). Divide Lab A's reported value by 100 and multiply by 3,800. Thus 0.000624 x 3,800 = 2.4 pounds per cubic yard. Using Lab B's 580 parts per million, 0.00058 x 3,800 = 2.2 pounds per cubic yard.