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steel. For butt welded splices, pull tests from representative

specimens shall develop at least 75 % of the minimum speci-

fied tensile strength of the steel.

7. Precast Concrete Manufacture

7.1

Mixture—

The aggregates shall be sized, graded,

proportioned, and mixed with such proportions of cementitious

materials and water as will produce a thoroughly-mixed

concrete of such quality that the products will conform to the

test and design requirements of this specification. All concrete

shall have a water-cementitious ratio not exceeding 0.53 by

mass. Cementitious materials shall be as specified in

4.1.2

and

shall be added to the mix in a proportion not less than 280

kg/m

, unless mix designs with a lower cementitious materials

content demonstrate that the quality and performance of the

product meet the requirements of this specification.

7.2

Curing—

Concrete products shall be subjected to any

one of the methods of curing prescribed in

7.2.1 – 7.2.4

or to

any other method or combination of methods approved by the

owner that will give satisfactory results.

7.2.1

Steam Curing—

Concrete products are placed in a

curing chamber, free of outside drafts, and cured in a moist

atmosphere maintained by the injection of steam for such time

and such temperatures as may be needed to enable the products

to meet the strength requirements. The curing chamber shall be

so constructed as to allow full circulation of the steam around

the entire product.

7.2.2

Water Curing—

Concrete products are water-cured by

covering with water-saturated material, or by a system of

perforated pipes, mechanical sprinklers, porous hose, or by any

other approved method that will keep the products moist during

the curing period.

7.2.3

Sealing Membrane—

A sealing membrane conforming

to the requirements of Specification

C309

is applied and shall

be left intact until the required concrete strength requirements

are met. The concrete at the time of application of the

membrane shall be within 6°C of the atmospheric temperature.

All concrete surfaces shall be kept moist prior to the applica-

tion of the membrane and shall be damp when the membrane

is applied.

7.2.4 The manufacturer is not prohibited from combining

methods prescribed in

7.2.1 – 7.2.3

provided the required

concrete compressive strength is attained.

8. Acceptance

8.1

Acceptance Procedures:

8.1.1 Unless otherwise designated by the owner at the time

of, or before, placing an order, acceptance procedures for

precast reinforced concrete manhole products shall be as

specified in the Part II section for a particular product, and shall

not be prohibited from consisting of one or more of the

following:

8.1.1.1 Acceptance of a product on the basis of tests of

materials, including concrete compressive strength and absorp-

tion.

8.1.1.2 Acceptance of a product on the basis of inspection of

the finished product, including amount and placement of

reinforcement to determine conformance with the design

prescribed under this specification, and freedom from defects.

8.2

Test Methods:

8.2.1

Concrete Compressive Strength Test:

8.2.1.1

Type of Specimen—

Compression tests for satisfying

the minimum specified concrete strength requirement shall be

made on either concrete cylinders or, at the option of the

manufacturer, on cores cut from the concrete manhole product.

8.2.1.2

Compression Testing of Cylinders—

Cylinders shall

be made in accordance with Test Methods

C497

, and shall be

tested in accordance with Test Method

C39/C39M

. For man-

hole products, an owner shall not be prohibited from requiring

concrete compressive tests on cylinder specimens numbering

in the amount of 5 % of the total order of a manhole product,

but not to exceed two cylinders for each day’s production. The

average compressive strength of all cylinders tested shall be

equal to or greater than the specified strength of the concrete.

Not more than 10 % of the cylinders tested shall fall below the

specified strength of the concrete. In no case shall any cylinder

tested fall below 80 % of the specified strength of the concrete.

8.2.1.3

Compression Testing of Cores—

Cores shall be cut

from the concrete manhole product and tested in accordance

with Test Methods

C497

, except that the requirements for

moisture conditioning shall not apply. One core shall be taken

from a manhole product selected at random from each day’s

production run of a single concrete strength. When the concrete

compressive strength of the core is equal to or greater than

80 % of the specified strength of the concrete, the concrete

strength of the production run is acceptable. If the core does

not meet the preceding concrete strength requirement, another

core from the same manhole product may be taken and tested.

8.2.1.4 If the concrete compressive strength of the recore is

equal to or greater than 80 % of the specified strength of the

concrete, the concrete strength of the production run is accept-

able. If the recore does not meet the preceding concrete

strength requirement, that manhole product shall be rejected.

Two manhole products from the remainder of the day’s

production run shall be selected at random and one core taken

from each manhole product and tested. When the average

concrete strength of the two cores is equal to or greater than

80 % of the specified strength of the concrete with no core

below 75 % of the specified strength of the concrete, the

concrete strength of the day’s production run shall be accept-

able.

8.2.1.5 If the concrete strength of the two cores does not

meet the preceding concrete strength requirement, then the

remainder of the day’s production run shall be either rejected,

or, at the option of the manufacturer, each manhole product of

the remainder of the day’s production run is not prohibited

from being cored and accepted individually.

8.2.1.6

Plugging Core Holes—

Core holes on accepted man-

hole sections shall be plugged and sealed by the manufacturer

in a manner such that the manhole products will meet all of the

requirements of this specification. Manhole sections so sealed

shall be considered as satisfactory for use.

8.2.2

Absorption Test:

8.2.2.1 The absorption of a specimen from a concrete

product, as determined in Test Methods

C497

, shall not exceed

C478M − 15

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