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Section 30 – Concrete Structures

twenty-four (24) hours after the concrete has been placed, and until the concrete has sufficient

strength to prevent damage to the surface.

In no case should supporting forms be removed from horizontal members before concrete is

eighty percent (80%) of design strength. When high-early strength concrete is used, removal

time may be reduced at the discretion of the Agency. When retarding agents are used, removal

time should be increased at the discretion of the Agency.

Reinforcement in concrete structures shall be as shown on the Plans and conform to

Section 31, “Reinforcement”, of these Specifications.

30-6 MIXING AND TRANSPORTING

Mixing and transporting of concrete shall be in accordance with Section 90 of the State

Specifications. All concrete shall be mixed in mechanically operated mixers except when

permitted by the Contract. Concrete being transported must maintain consistency and

workability; no additional mixing water shall be incorporated unless authorized by the Agency.

The use of admixtures in concrete for structures will be subject to the written approval of the

Agency, or as otherwise specified in the Special Provisions.

Unless otherwise shown or specified in the Contract, concrete in structures shall be Class 1

as specified in Section 90-1.01 of the State Specifications.

30-7 PLACING CONCRETE

No concrete shall be placed in forms until the forms have been approved by the Agency.

Concrete shall not be placed on frozen or ice-coated ground or subgrade, or on ice-coated

forms, reinforcing steel, structural steel, conduits, precast members, or construction joints.

Under rainy conditions, placing of concrete shall be stopped before the quantity of surface

water is sufficient to damage surface mortar or cause a flow or wash of the concrete surface,

unless the Contractor provides adequate protection against damage, as determined by the

All concrete shall be fresh and shall be placed before it has taken an initial set.

Retempering with additional water to make concrete more workable after it has partially

hardened will not be permitted. The temperature of the concrete at the time of placement shall

not fall below fifty-five degrees (55°) or exceed ninety degrees (90°) F, per ACI Manual of

Concrete Practice Table 3.1.

When the Contract shows or specifies a concrete placement sequence or schedule, such a

sequence or schedule shall not be varied without written approval of the Agency.

Fresh concrete shall be placed in horizontal layers no deeper than can be satisfactorily

consolidated with the vibrators. The concrete shall be placed at or near its final position; the

use of vibrators for extensive shifting of fresh concrete will not be permitted. Fresh concrete

shall not be permitted to fall from a height greater than six feet (6’). Tremies or "elephant

trunks" shall be used if the concrete is to be placed in a deep or hard to reach area.

After being deposited, the fresh concrete shall be consolidated by mechanical vibration until

voids are filled and free mortar appears on the surface.

The use of additional water in mixing the concrete to promote free flow will not be permitted.