Specifications - Laserfiche WebLink

Home Browse Search

' 3.02 MIXING A. Concrete shall be ready -mixed or transit - mixed, as produced by equipment acceptable to the Engineer. No hand - mixing will be permitted. Adding water in controlled amounts during the mixing cycle shall be done only with the express approval of, and under the direction of, the Engineer. B. Ready -mix or transit -mixed concrete shall be transported to the site in watertight agitator or mixer trucks loaded not in excess of rated capacities for the respective conditions as stated on the name plate. Discharge at the site shall be within 1 -1/2 hours and within one hour when ambient temperature is above 85 degree F after cement was first introduced into the mix. Central mixed concrete shall be plant -mixed a minimum of 1 -1/2 minutes per batch and then shall be truck -mixed or agitated a minimum of 8 minutes. Agitation shall begin immediately after the pre -mixed concrete is placed in the truck and shall continue without interruption until discharge. Transit -mixed concrete shall be mixed at mixing speed for at least 10 minutes immediately after charging the truck, followed by agitation without interruption until discharged. C. All central plant and rolling stock equipment and methods shall conform to the latest Truck Mixer and Agitator Standards of the Truck Mixer Manufacturers' Bureau of the National Ready -Mixed Concrete Association, as well as ACI Standard 304 and ASTM Specification C94. 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 batching ' 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. 06/06 03300 -7 03-4138.0