§ 27-605 Mixes.
AC § 27-605
Concrete may be proportioned, batched, and mixed by any of the following methods: (a) Method I. Mixes with minimum cement content.
(1)MINIMUM CEMENT CONTENT. The cement content used in the work shall not be less than the content given in table 10-3 for the corresponding strength of concrete. TABLE 10-3Minimum Cement Content Specified Compressive Strength in 28 Days (f'c) - psiMinimum Pounds of Cement Per Cubic Yard of Concrete (all aggregates)3,000 540 3,500 610 4,000 660 5,000 800 Over 5,000 Permitted only by reference standard RS 10-36,000 and over Permitted only by reference standard RS 10-3, "Special Requirements for High Strength Concrete." Note: Minimum pounds of cement may be reduced up to 8 percent by the addition of an accepted admixture.
(2)WATER-CEMENT OR STRENGTH-CEMENT RATIO. Normal weight concrete proportioned on the basis of preliminary tests shall be produced by using a water-cement ratio corresponding to a point on a strength-cement or water-cement ratio curve. Proportioning of lightweight and heavyweight concrete, and concrete using an aggregate other than natural sand, gravel or stone shall be by using a strength-cement content curve. The point on the respective curves shall represent a strength of concrete at the slump and age called for on the plans at least twenty-five percent higher than the specified strength, f'c. The cement content shall not be less than the content shown in table 10-3.
(3)PRELIMINARY TESTS. Preliminary tests of concrete shall be made in advance of any concreting operation by a licensed concrete testing laboratory acceptable to the architect or engineer of record. Preliminary tests shall consist of compression strength tests of molded concrete cylinders made in accordance with reference standards RS 10-17 and RS 10-21. A curve representing the relation between the average strength of the concrete at twenty-eight days, or at any other specified age filed with the department, and the strength-cement ratio or the water-cement ratio shall be established for the range of strength values at the slump required for the work. The tests shall include at least four mixes with different strength-cement ratios or four mixes with different water-cement ratios and at least four cylinder specimens for each mix. The cylinder strength tests shall be supplemented by tests to confirm that the cement and aggregates conform to the provisions of reference standard RS 10-3.
(4)PREVIOUSLY ACCEPTED MIXES. In lieu of the requirements of paragraph three of this subdivision, the architect or engineer designated for controlled inspection may permit the use of mix proportions of aggregates having the same specific gravity, size and gradation; cements of the same type and batch weight; admixtures of the same type and quantity; and other ingredients the same as or equal to those that have been previously submitted with applicable preliminary tests which complied with paragraphs one and two of this subdivision, and which have been accepted by the commissioner within the past year. If any of the mix proportions or ingredients are changed, a separate submission for acceptance shall be required.
(5)QUALITY CONTROL AND INSPECTION OF MATERIALS AND OF BATCHING. Where concrete materials are used for structural elements defined in section 27-585 of article one of this subchapter, quality control and inspection shall be provided at the batch plant by a licensed concrete testing laboratory under the supervision of the architect or engineer designated for controlled inspection, in accordance with the requirements of table 10-1 and in sufficient scope to: a. Determine and record the actual batched weights of the ingredients and the volume of water charged into the mixer; b. Verify that such weights conform to the weights and proportions required by the preliminary test mix, adjusted for moisture content, fineness modulus and gradation of aggregates; c. Verify conformance of the quality and condition of the materials to reference standard RS 10-3. d. Verify that the aggregates have the same specific gravity, size and gradation; the cement is the same type and batch weight, the admixtures are the same type and quantity; and that any other ingredients are the same as or equal to those used for the preparation of the preliminary test mixes; e. For all concrete, whether or not designated for controlled inspection, attestation of the results of quality control and inspection at the batch plant shall appear on a ticket accompanying each load of concrete. The attestation for subparagraphs a, b, c and d of this paragraph shall be executed by the licensed concrete testing laboratory. f. The licensed concrete testing laboratory shall also attest that the slump entrained air content and unit weight of the fresh concrete, as discharged from the mixer at the job site, were tested in accordance with reference standards RS 10-49, RS 10-51, RS 10-52, RS 10-61, RS 10-62, RS 10-63 and RS 10-64, and that all were in compliance with the accepted mix design.
(b)Method II. Proportioning on the basis of field experience.
(c)Method III. Average Concrete.
