Concrete shall consist of a mixture of Portland cement, fine and coarse aggregate and water in such proportions that will secure a dense, plastic, workable concrete of the strength specified at 28 days. The quantity of water specified per sack of Portland cement shall include the moisture on the surface of the aggregate, but shall not include the amount of water absorbed by the aggregates in 30 minutes. Concrete which has partially set shall not be retempered or remixed by adding additional ingredients. Concrete shall not be mixed during freezing weather, and shall not be placed when the temperature is 40°F. or less. No frozen ingredients or conglomerates shall be used in concrete. Test for slump of concrete shall be made in accordance with the Method of Test for Consistency of Portland Cement Concrete (Serial Designation C-143-52) of the A.S.T.M. All tests for ingredients and concrete shall be made in accordance with the current applicable methods of tests of the A.S.T.M. (Ord. 8590)