Chapter 4, Problem 38E

Compare the mean compressive strength at each rodding level from Exercise 4.37 with a scaled t distribution. What conclusions would you draw from this plot?

4.37. An article in the ACI Materials Journal (Vol. 84, 1987, pp. 213–216) describes several experiments investigating the rodding of concrete to remove entrapped air. A 3-in.-diameter cylinder was used, and the number of times this rod was used is the design variable. The resulting compressive strength of the concrete specimen is the response. The data are shown in Table 4E.5.

TABLE 4E.5

Compressive Strength Data for Exercise 4.37

1. (a) Is there any difference in compressive strength due to the rodding level? Answer this question by using the analysis of variance with α = 0.05.
2. (b) Construct box plots of compressive strength by rodding level. Provide a practical interpretation of these plots.
3. (c) Construct a normal probability plot of the residuals from this experiment. Does the assumption of a normal distribution for compressive strength seem reasonable?