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D. The re- tempering of concrete or mortar which has partially hardened, that is, mixing with or without additional cement, aggregate, or water, will not be permitted. ' E. Attention is called to the importance of dispatching trucks from the hatching plant so that they shall arrive at the site of the work just before the concrete is required, thus avoiding excessive mixing of concrete while waiting or delays in placing successive layers of ' concrete in the forms. 3.03 FIELD TESTS A. Sets of four field control cylinder specimens will be taken at random by the Engineer during the progress of the work, in conformity with ASTM Designation C31; the total ' number of specimens taken on the project may average one set per 150 cubic yards, and in general not less than one set of specimens will be taken on any one day when concrete is being placed. When average ultimate 28 -day strength of control cylinders in any set falls below the required ultimate strength or below proportional minimum 7 day strengths where ' proper relation between 7 and 28 day strengths have been established by tests, proportions, water content, or temperature conditions shall be changed to secure the required strength. B. The Contractor shall cooperate in the making of such tests to the extent of allowing free access to the work for the selection of samples, providing heated (when required) moist storage facilities for specimens, affording protection to the specimens against injury or loss through his operations, and furnishing material and labor required for the purpose of taking ' concrete cylinder samples, curing boxes and shipping boxes. All shipping of specimens will be paid for by the Owner. ' C. Slump tests will be made in the field by the testing laboratory. 3.04 INSPECTION AND CONTROL - ' A. The preparation of forms, placing of reinforcing steel, conduits, pipes, and sleeves, hatching, mixing, transportation, placing and curing of concrete shall be at all times under the inspection of the Engineer. B. The Contractor shall engage the services of an approved testing laboratory to establish the basic mixtures of concrete as required by the specifications. rC. The Owner will engage the services of a testing laboratory to test field control cylinder specimens and to conduct other tests as specified herein or as deemed required by the ' Engineer to insure the quality. D. Air entrainment shall be measured by the testing laboratory or his representative at time of concrete deposit in accordance with ASTM Designation C231. ' 3.05 CONCRETE APPEARANCE A. Concrete for every part of the work shall be homogeneous structure which, when hardened, will have the required strength, durability and appearance. B. Formwork, mixtures and concrete placement workmanship shall be such that concrete surfaces, when exposed, will require only minimal finishing with no excess honeycombing, voids or irregular color lines. 01105 03300 -7 03-4138.B