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Unformatted text preview: protection and curing of the concrete and may be used to determine when the
forms may be stripped, shoring removed, or the structure placed in service. When, in the opinion of the
Engineer, the strengths of the job-cured specimens, the contractor may be required to improve the
procedures herein or when tests of field-cured cylinders indicate deficiencies in protection and curing,
the Engineer may require tests in accordance with ASTM Specification C42 or order load tests as
outlines in Section 5.31for that portion of the structure where the questionable concrete has been placed.
(f) Splitting Tensile Tests of Concrete.
To determine the splitting ratio, Fsp, for a particular
aggregate, tests of concrete shall be made as follows:
1. Twenty-four 15 cm. dia. by 30 cm. long (6 in. dia. by 12 in. long) cylinders shall be made in
accordance with ASTM Specification C192, 12 at a compressive strength level of approximately
210 kilograms per square centimeter (3,000 pounds per square inch) and 12 at approximately 280
kilograms per square centimeter (4,000 pounds per square inch) or 350 kilograms per square
centimeter (5,000 pounds per square inch). After seven days moist curing followed by 21 days
drying at 23°C (73°F) and 50 per cent relative humidity, eight of the test cylinders at each of the
two strength levels shall be tested for splitting strength and four for compressive strength.
2. The splitting tensile strength shall be determined in accordance with ASTM Specification
C496, and the compressive strength of all 16 splitting tensile tests and all 8 compressive tests.
The ratio, Fsp, of splitting tensile strength to the square root of compressive strength shall be
obtained by using the average of all 16 splitting tensile tests and all 8 compressive tests.
(g) Minimum strength. Concrete, other than fill, shall have a minimum ultimate compressive
strength at 28 days of 140 kilograms per square centimeter (2,000 lbs. per sq. in.).
Section 5.06: Formwork.
(b) Removal of Forms. No construction loads exceeding the structual design loads shall be
supported upon any unshored portion of the structure under construction. No construction load shall be
supported upon, nor any shoring removed from any part of the structure under the construction until that
portion of th structure has attained sufficient strength to support safely its weight and the loads placed thereon. This strength may be demonstrated by job-cured test speciments and by a structural analysis
considering the proposed loads in relation to these test strengths. Such analysis and test data shall be
furnished by the contractor to the Engineer.
Forms shall be removed in such manner as to insure the complete safety of the structure. Where the
structure as a whole is adequately supported on shores, the removable floor forms, beam and girder
sides, column and similar vertical forms may be removed after 24 hours provided the concrete is
sufficiently strong not to be injured thereby.''Form supports of pr...
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- Fall '12