As a materials engineer in charge of designing concrete mix and facing the following problems, which admixture would you use in each case during mixing or at the jobsite? a. There is a large quantity of freshly mixed concrete and the work at the job-site had to stop because of rain. b. More time is expected to be needed for finishing concrete. c. The structure is subject to freezing. d. Concrete is to be around tightly spaced reinforcing steel. e. Concrete mix will be hauled a long distance. f. High early strength concrete is required, but not necessarily high ultimate strength.