§ 6-127. Curing concrete.

(a)

Generally. Curing concrete is defined as providing a means to keep newly placed concrete moist and at the proper temperature so that hydration of the cement can continue. All concrete, other than concrete below ground surface not in forms, and except as elsewhere specified, shall be cured for a period of at least five (5) days after placing. Concrete made with high-early-strength cement or containing two (2) percent calcium chloride shall be cured at least seventy-two (72) hours. Whenever there is a cessation of placing of concrete, the concrete already placed shall be kept continuously moist with damp mats or burlap placed over the concrete or framework until concreting is resumed. Concrete shall not be directly sprayed with water prior to obtaining initial set.

(b)

Materials. Materials used for curing concrete shall conform to the following requirements as they are applicable:

(1)

Cotton mats: American Association of State Highway Officials (AASHO) Standard Specifications for Cotton Mats for Curing Concrete Pavements, designation M73;

(2)

Burlap: AASHO Standard Specifications for Burlap Cloth made from Jute or Kenaf, designation M182; Class 2, 3 or 4;

(3)

Waterproof paper: ASTM Tentative Specifications for Waterproof Paper for Curing Concrete, designation C171;

(4)

Liquid membrane: ASTM Standard Specifications for Liquid Membrane-Forming Compounds for Curing Concrete, designation C309.

(5)

Polyethylene sheeting: AASHO Standard Specifications for White Polyethylene Sheeting (Film) for Curing Concrete, designation M171.

(c)

Formed concrete.

(1)

Concrete adjacent to wood forms shall be cured by either keeping the forms continuously wet beginning not later than eighteen (18) hours after placing has been completed, or by loosening the forms when directed by the inspector and applying water to the top surfaces and allowing it to run down between the forms and the concrete.

(2)

When metal forms are used for vertical surfaces, the forms shall either be kept in contact with the concrete for the entire curing time or completely removed and one (1) of the other specified curing methods used.

(d)

Slabs. Slabs shall be cured either by wet covering, waterproof covering or liquid membrane seal.

(e)

Coverings application. One (1) of the following methods of covering shall be used as soon as possible after the final finishing operations and when the concrete has set sufficiently so that it will not be damaged in the process:

(1)

Wet coverings shall consist of either burlap, cotton mats, damp earth or sand, or poured water. Coverings shall be kept continuously moist for the duration of the curing period. Water shall be applied in a manner which will not damage the concrete. Curing water shall be free of impurities which may damage or discolor the concrete surface.

(2)

Waterproof coverings shall consist of either waterproof or polyethylene sheeting (film). The covering shall completely cover the concrete with sufficient material remaining at the sides for proper anchorage. Adjoining sheets shall be lapped six (6) inches or sealed. All tears and holes in the covering shall be promptly mended with adhesive tape or other approved means. The covering shall be continuously anchored around the edges and at laps, and shall be weighted on the surface as necessary to prevent billowing by the wind. The covering may be reused provided all holes and tears are properly repaired.

(3)

Membrane curing compounds used on concrete exposed to the sun may be white pigmented. Compounds for all other work shall be pigmented unless the buildings official directs that a clear type be used. When specified, clear compounds shall contain a fugitive dye. Spray application is recommended and shall be performed in such a manner that a uniform, continuous and water-impermeable film is provided. If an even covering cannot be applied in one (1) coat, the compound shall be applied in two (2) coats with the direction of application of the second coat being at right angles to the first. The amount of curing compound applied shall be not less than that recommended by the manufacturer. Pigmented compounds shall be stirred before use. Membrane curing compounds shall not be used where concrete is to be painted, unless otherwise specified by the architect-engineer. The membrane shall be protected from damage during the curing period and the contractor shall immediately repair all damage.

The edges of slabs shall be cured either by backfilling with moist earth or by one (1) of the other methods described herein.

The contractors attention is directed to the special requirements concerning curing specified for hot and cold weather concreting.

A combination of the various curing methods may be used with the approval of the building official; provided, the exposure time of the concrete to drying is less than one (1) hour. For example, concrete work may be initially cured for one (1) day using a wet covering and then followed by four (4) days of cure using a waterproof membrane covering.

(Code 1974, § 5-16)