The responses, or response variables, are the concrete properties of interest. In most cases, the cost of the mix is also a response, because minimizing cost is usually an objective in optimizing the mixture proportions.

The performance criteria are the limits on the allowable values of the responses. They are often dictated by job requirements.

For example, the specifications for a particular job may indicate that the concrete must have a slump between 2 and 4 inches, an air content between 4.5 and 7.5 percent, and 28-day strength greater than 10,000 psi. The responses in this case are slump, air content and strength, and the performance criteria are the values of the responses that are within the acceptable ranges.

For each response, COST requires the following information:

• A name for the response (e.g., slump, 28-day strength). The name should be as short as possible (16 characters maximum) and may include alphanumeric characters and underscores.

• The units in which the response is measured.

• A lower limit for the response, if applicable. This would be a specified minimum value (e.g., minimum 1-day strength of 3000 psi). If there is not lower limit for the response, a value of -100 is used.

• An upper limit for the response, if applicable. This would be a specified maximum value (e.g., maximum RCT test result = 1000 coulombs). If there is no upper limit, a default value of 99999 is used.

• A result weight factor between 0 and 1, to indicate the relative importance of the response in optimization, compared to the other responses. A factor of 1 indicates most important. The default value is 1 for all responses.

• The type of weight function to use in optimization (selected by pull-down menu). Choices are:
  • Minimum is best (linear decreasing)

  • Maximum is best (linear increasing)

  • Target is best (middle of range is best)

  • Within range (all values in range equally acceptable, no values outside range acceptable)