§ 15.01.1080. Strength requirements.

A.

Required average strength. Unless otherwise specified, F'c (twenty-eight-day strength) shall be four thousand psi for flatwork or for reinforced concrete, and two thousand five hundred psi for thrust blocks anchors or mass concrete. Concrete minimum strength per ACI 301.

B.

Rejection of concrete on the basis of strength. Rejection of concrete on the basis of strength shall be considered if: a) the average of any three consecutive strength test falls below F'c or b) any individual strength falls below five hundred psi less than F'c.

In the event of such occurrence the engineer shall investigate the concrete in question as to strength and durability requirements and if the adequacy of the concrete remains in doubt such concrete may be required to be replaced at no expense to the city. Investigation of low strength concrete test results in reinforced concrete structures shall conform to ACI 318-77 Section 4.8.4. Should load tests be required to determine strength, the load tests shall be carried out at the expense of the contractor/developer.

C.

Strength test procedures. Samples for strength tests shall be taken in accordance with ASTM C31, "Method of Making Curing Concrete Test Specimens in the Field," ASTM C39, "Method of Test for Compressive Strength of Cylindrical Concrete Specimens," and ASTM C142, "Method of Obtaining and Testing Drilled Cores and Sawed Beams of Concrete."

The average strength of the concrete shall be verified based on the "strength test" in which the average strength of three standard cylinders is determined. The cylinder strength shall be determined at twenty-eight days. One strength test shall be made for the first fifteen yards of concrete poured and for each additional fifty yards of concrete placed.

When the average of the strength test shall show strength below that require, the concrete may be subject to rejection. The contractor may elect to have made an alternate strength test on three core samples obtained in accordance with AASHTO designation T-24. The city engineer or public works director will determine the location, in the particular pour in question, where the cores will be taken. They shall be tested as soon as practicable under his supervision. All costs for securing the testing will be paid by the contractor/developer or ready-mix supplier.

(Ord. No. 2007-07-31, §§ 12.3—12.3.3, 7-10-2007)