mined as prescribed below. The determinations will be made after the materials furnished by the Contractor have been accepted.

a. Trial mixes.—The Engineer will determine the proportions on the basis of trial mixes conducted with the materials to be used in the work. The proportions will be such as to produce concrete of the cement content shown in table 601-1 within a tolerance of plus or minus 2 percent for the particular class of concrete being made; provided, that if the materials furnished by the Contractor are of such a nature or are so graded that these proportions cannot be used without exceeding the maximum water content specified in table 501-1, the proportions will then be adjusted so as to require the least amount of cement that will produce concrete of the specified plasticity and workability without exceeding the maximum water content.

As an aid to the Engineer, approximate weights for a suggested trial mix for each class are given in table 601–1. These weights also will be of value to bidders or contractors in determining approximately the quantities of aggregates that will be required.

The weights of aggregate per bag of cement in table 601-1 are based on the use of aggregates which have a bulk specific gravity of 2.65 when in a saturated surfacedry condition, the use of a uniformly graded natural sand having a fineness modulus of 2.75, and the use of a uniformly graded coarse aggregate of the size indicated. For aggregates having other specific gravities, the weights will be corrected by multiplying the weights shown in the table by the specific gravity and dividing by 2.65. When angular, manufactured sand or a sand having a fineness modulus greater than 2.75 is used, the amount of fine aggregate will be increased and the amount of coarse aggregate decreased. When using sand having a fineness modulus less than 2.75, the amount of fine aggregate will be decreased and the amount of coarse aggregate increased. For each change in fineness modulus of 0.10 as compared to 2.75, the percentage of sand will be changed by 1 percent in relation to the total weight of combined fine and coarse aggregates. The fineness modulus of fine aggregate will be determined by adding the cumulative percentages, by weight, of material retained on each of U.S. Standard sieves Nos. 4, 8, 16, 30, 50, and 100, and dividing by 100.

The correction for fineness modulus will be made prior to making a correction in the weights of table 601-1 for variations from 2.65 in specific gravity.

The Contractor may, subject to prior approval in writing

by the Engineer, use alternative sizes of coarse aggregate as shown in table 601-1.

If the use of an alternative size of coarse aggregate produces concrete which exceeds the permissible water content, thereby requiring additional cement above that specified, no compensation will be made to the Contractor for the additional cement.

Designated sizes of coarse aggregate need by separated into component sizes only as specified in the special provisions. However, two sizes are preferred when the maximum size exceeds 1 inch. If one or more of the component sizes used fails to meet the specified grading for its respective size, but a combination of the sizes can be used that meets the specified grading for the combined size, they may be used with the written permission of the Engineer.

b. Proportions and batch weights.—The Engineer will designate the weight in pounds of fine and coarse aggregate (in a saturated surface-dry condition) per 94-pound bag of cement for the specified class of concrete and these proportions will not be changed except as provided in subsection 601.02(2)(b), immediately following. In addition, the Engineer will also designate the batch weights of aggregates after he has made moisture determinations and corrected the saturated surface-dry weights for free moisture.

In batching aggregates for structures containing less than 20 cubic yards of concrete, the Contractor may substitute approved volumetric measuring devices in lieu of weighing devices. In such event, weighing will not be required but the volumes of coarse aggregate and of fine aggregate measured into each batch shall be those designated by the Engineer.

(2) Adjustments in proportions:

(a) Adjustment for variation in workability.—If it is found impossible to obtain concrete of the desired placeability and workability with the proportions originally designated by the Engineer, he will make such changes in aggregate weights as are necessary, provided that in no case shall the cement content originally designated be changed except as provided in subsections 3 and 4, which follow.

(b) Adjustment for variation in yield.—If the cement content of the concrete, determined by means of the yield test, AASHO T 121, varies more than plus or minus 2 percent from the designated value in table 601-1, the proportions will be adjusted by the Engineer to maintain a cement content within these limits. The water content shall in no case exceed the specified amount.

(c) Adjustment for excess water content.-If, when using the designated cement content, it is impossible to produce

concrete having the required consistency without exceeding the maximum allowable water content specified in table 601–1, the cement content shall be increased as directed by the Engineer so that the maximum water content will not be exceeded.

(d) Adjustment for new materials. No change in the source or character of the materials shall be made without due notice to the Engineer and no new materials shall be used until the Engineer has accepted such materials and has designated new proportions based on tests on trial mixes as provided herein.

Materials

601.03 Materials. Materials shall meet the requirements specified in the following subsections:

601.04 Cement Requirements. When not otherwise specified, the Contractor may use any type of portland cement except type IV or type V. Whenever a non-air-entraining type is used, an air-entraining agent shall be used. When an air-entraining type is used, the Contractor shall maintain a supply of non-air-entraining cement as well as air-entraining admixtures, for use where adjustment of air content may be required.

Cement may be shipped from pre-tested and approved bins at the mill. The cement shall be well protected from rain and moisture, and any cement damaged by moisture or which fails to meet any of the specified requirements shall be rejected and removed from the work. Cement stored by the Contractor for a period longer than 60 days shall require the Engineer's approval before being used on the work. Cement of different brands, types, or from different mills shall be stored separately.

Construction Requirements

601.05 General. All construction, other than concrete, shall conform to the requirements prescribed in other sec

tions of these specifications for the several items of work entering into the completed structure.

601.06 Batching. Measuring and batching of materials shall be done at a batching plant.

(a) Portland cement.-Either sacked or bulk cement may be used. No fraction of a sack of cement shall be used in a batch of concrete unless the cement is weighed.

All bulk cement shall be weighed on an approved weighing device. The bulk cement weighing hopper shall be properly sealed and vented to preclude dusting during operation. The discharge chute shall not be suspended from the weighing hopper and shall be so arranged that cement will not lodge in it nor leak from it.

Accuracy of bathing shall be plus or minus 1 percent of the required weight.

(b) Water. Water may be measured either by volume or by weight. The accuracy of measuring the water shall be within a range of error of not over 1 percent. Unless the water is to be weighed, the water-measuring equipment shall include an auxiliary tank from which the measuring tank shall be filled. The measuring tank shall be equipped with an outside tap and valve to provide for checking the setting, unless other means are provided for readily and accurately determining the amount of water in the tank. The volume of the auxiliary tank shall be at least equal to that of the measuring tank.

(c) Aggregates.-Stockpiling of aggregates shall be in accordance with subsection 106.06. All aggregates produced or handled by hydraulic methods, and washed aggregates, shall be stockpiled or binned for draining at least 12 hours before being batched. Rail shipment requiring more than 12 hours will be accepted as adequate binning only if the car bodies permit free drainage. In case the aggregates contain high or non-uniform moisture content, storage or stockpile period in excess of 12 hours may be required by the Engineer.

Batching shall be so conducted as to result in a 2 percent tolerance for weights of the required materials.

(d) Bins and scales.-The batching plant shall include ins, weighing hoppers, and scales for the fine aggregate and for each size of coarse aggregate. If cement is used in bulk, a bin, hopper and, unless otherwise indicated, a scale for cement shall be included. Bins with adequate separate compartments for fine aggregate and for each size of coarse aggregate shall be provided in the batching plant.

Scales shall be accurate to 0.5 percent throughout the range of use. Poises shall be designed to be locked in any position to prevent unauthorized change of position. Scales

shall be inspected and sealed in accordance with subsection 106.05.

Batching plants may be equipped to proportion aggregates and bulk cement by automatic weighing devices of an approved type.

(e) Batching.-When batches are hauled to the mixer, bulk cement shall be transported either in waterproof compartments or between the fine and coarse aggregates. When cement is placed in contact with the moist aggregates, batches will be rejected unless mixed within 12 hours of such contact. Sacked cement may be transported on top of the aggregates.

Batches shall be delivered to the mixer separate and intact. Each batch shall be dumped cleanly into the mixer without loss, and, when more than one batch is carried on the truck, without spilling of material from one batch compartment into another.

601.07 Mixing and Delivery. Concrete may be mixed at the site of construction, at a central point or by a combination of central point and truck mixing. Truck mixing or a combination of central point and truck mixing shall be in accordance with the appropriate requirements of AASHO M 157.

For mixing at the site of construction or at a central point, concrete shall be mixed in a batch mixer of an approved type. No mixer having a rated capacity of less than a one-bag batch shall be used. The volume of concrete mixed per batch shall not exceed the mixer's nominal capacity as shown on the manufacturer's standard rating plate on the mixer except that an overload up to 10 percent above the mixer's nominal capacity may be permitted, provided concrete test data for strength, segregation, and uniform consistency are satisfactory and provided no spillage of concrete takes place. The batch shall be so charged into the drum that a portion of the water shall enter in advance of the cement and aggregates. The flow of water shall be uniform and all water shall be in the drum by the end of the first 15 seconds of the mixing period. Mixing time shall be measured from the time all materials, except water, are in the drum. Mixing time shall be not less than 60 seconds for mixers having a capacity of 2 cubic yards or less. For mixers having a capacity greater than 2 cubic yards, the mixing time shall be not less than 90 seconds. If timing starts the instant the skip reaches its maximum raised position, 4 seconds shall be added to the specified mixing time. Mixing time ends when the discharge chute opens.

The mixer shall be operated at the drum speed as shown on the manufacturer's name plate on the mixer. Any con