**NATURAL RESOURCES CONSERVATION SERVICE\
CONSTRUCTION SPECIFICATION**

**CONCRETE CONSTRUCTION**

1\. SCOPE

This specification covers concrete construction for reinforced
structures, plain concrete for waste storage pond liners, and other
slabs.

2\. PREPARATION OF FORMS AND SUBGRADE

Unless otherwise indicated on the construction drawings, concrete shall
be placed on a smoothly graded soil or sand subgrade compacted, as
necessary, to a uniform density throughout. Plain concrete, where
vehicle traffic is expected, shall be placed on a minimum 3 inches of
gravel. Over-excavation shall be corrected by a procedure approved by
the NRCS Engineer or the designated representative.

Concrete shall not be placed until the subgrade, forms and steel
reinforcement have been inspected and approved by the NRCS Engineer or
the designated representative. The Engineer shall be notified far enough
in advance to provide time for the inspection.

Prior to placement of concrete, the forms and subgrade shall be free of
chips, sawdust, debris, standing water, ice, snow, extraneous oil,
mortar or other harmful substances or coatings.

Surfaces against which concrete is to be placed shall be firm and damp.
Placement of concrete on plastic, mud, dried earth, or uncompacted fill
or frozen subgrade will not be permitted.

3\. FORMS

Forms shall be of wood, plywood, steel or other approved material and
shall be mortar tight. The forms and associated falsework shall be
substantial and unyielding and shall be constructed so that the finished
concrete will conform to the specified dimensions and contours.

Items to be embedded in the concrete shall be positioned accurately and
anchored firmly.

Tolerance on formed concrete is + 3/8 inch. Tolerance on concrete formed
in earth is -- 1 inch to +6 inches.

4\. CONCRETE MIX

Portland cement shall be Type I, IA, II or IIA (Type I with an added air
entrainment admixture is preferred). If Type IA or IIA cement is used,
additional air entrainment admixture shall be the same type that was
used in the cement. Cement that is partially hydrated (hardened), or
otherwise damaged, shall not be used. Air entrainment shall be 4 to 7
percent.

Aggregates shall consist of clean, hard, strong and durable particles
that are free of silt, clay or any other material that may affect
bonding of the cement paste.

Fine aggregate shall meet the requirements of INDOT fine aggregate
number 23. Maximum coarse aggregate size shall be 3/4 inch.

Water shall be clean and free of injurious amounts of oil, salt, acid,
alkali, organic matter or other deleterious substances.

Concrete shall have a minimum 28-day compressive strength of 4,000 psi.
In lieu of strength tests, a mix containing an acceptable aggregate, 6
bags of cement per cubic yard and no more than 5.5 gallons or 46 pounds
of water per bag of cement (including moisture in the aggregate) may be
accepted.

The slump of the concrete shall be 3 to 5 inches.

5\. MIXING AND PLACING CONCRETE

Concrete shall be uniform and thoroughly mixed when delivered to the job
sites.

Concrete shall be discharged into the forms, vibrated and spaded within
90 minutes after the cement has been introduced into the aggregates.
When air temperatures are above 85 degrees, this time must be reduced to
45 minutes.

The Inspector may allow a longer time if an approved set retarding
admixture is used.

Concrete shall be deposited as close as possible in its final position.
It shall not be allowed to drop more than 5 feet in forms and must not
be required to flow laterally more than 8 feet.

If concrete must be dropped more than 5 feet, hoppers and chutes,
\"elephant trunks\", etc., shall be used to prevent segregation.

If concrete must be moved laterally more than 8 feet, it shall be moved
by shoveling, chutes, conveyors, wheelbarrows or similar equipment.
Vibration must not be used to make concrete flow in the forms.

Immediately after placement, concrete shall be consolidated by spading
and vibrating, or spading and hand tamping. It shall be worked into
corners and angles of the forms and around all reinforcement and
embedded items in a manner which prevents segregation or the formation
of \"honeycomb\". Excessive vibration which results in segregation of
materials will not be allowed. The vibrator head shall be kept vertical
when inserted into the concrete and shall penetrate at least 6\" into
the previously placed layer.

Slab concrete shall be placed at design thickness in one layer, but
walls should be placed in essentially horizontal layers not more than 24
inches high. Successive layers shall be placed and consolidated fast
enough to ensure a good bond between layers and to prevent \"cold
joints\".

If the surface of a layer in place will develop its initial set before
more concrete is placed on it, a construction joint (of the type shown
in the plan) shall be made.

If freshly mixed concrete is to be placed against hardened concrete, the
hardened concrete must be clean, sound, fairly level and roughened with
some coarse aggregate particles exposed. Any dirt, form oil, wood chips
or other foreign material shall be removed.

Concrete surfaces shall be smooth and even. Careful screeding
(striking-off) and/or wood or magnesium float finishing are required.

The addition of dry cement or water to the surface of screeded concrete
to expedite finishing will not be allowed.

6\. REINFORCING STEEL

Reinforcing steel shall be deformed bars manufactured specifically for
concrete reinforcement and shall be Grade 60 or higher (more details can
be found in ASTM-A-615, A-616 or A-617).

Reinforcing steel shall be free from loose rust, concrete, oil, grease,
paint or other deleterious coatings.

Reinforcement shall be accurately placed and secured in position in a
manner that will prevent its displacement during the placement of
concrete. This shall be accomplished by tying reinforcing steel or
special tie bars to the form \"snap ties\" or by other methods of tying.
No welding of either stress steel or temperature and shrinkage steel
will be permitted. Reinforcing steel shall not be heated to facilitate
bending.

In slabs, steel shall be supported by precast concrete bricks (not clay
bricks), corrosion resistant metal chairs or plastic chairs.

The following tolerances will be allowed in the placement of reinforcing
bars.

a\. Where 1.5 inches clear distance is shown between reinforcing bars
and forms, allowable clear distance is 1.125 to 1.5 inches.

b\. Where 2 inches clear distance is shown between reinforcing bars and
forms, allowable clear distance is 1.625 to 2 inches.

c\. Where 3 inches clear distance is shown between reinforcing bars and
earth or forms, allowable clear distance is 2.5 to 3 inches.
Overexcavation backfilled with concrete shall not count toward clear
distance.

d\. Maximum variation from indicated reinforcing bar spacing: 1/12th of
indicated spacing, but no reduction in amount of bars specified.

Unless otherwise indicated on the drawings, splices of reinforcing bars
shall provide a lap of not less than 30 diameters of the smaller bar but
not less than 12 inches. Bars will not be spliced by welding. Welded
wire fabric shall be lapped at least one mesh width.

The ends of all stress or temperature and shrinkage bars shall be
covered with at least 2 inches of concrete.

7\. CURING

Concrete shall be prevented from drying for at least 7 days after it is
placed. Exposed surfaces shall be kept continuously moist during this
period by covering with moistened canvas, burlap, straw, sand or other
approved material, unless they are sprayed with a curing compound or
covered with a 4 mil or thicker polyethylene. Forms left in place during
the curing period shall be kept wet.

Concrete, except at construction joints, may be coated with a curing
compound in lieu of continued application of moisture. The compound
shall be sprayed on moist concrete surfaces as soon as free water has
disappeared, but shall not be applied to any surface until patching,
repairs and finishing of that surface are completed.

Curing compound shall be applied in a uniform layer over all surfaces
requiring protection at a rate of not less than 1 gallon per 150 square
feet of surface or to manufacturer\'s recommendation, whichever is
greater.

8\. FORM REMOVAL AND CONCRETE REPAIR

Forms for structure walls shall not be removed until 24 hours or more
after concrete placement. When forms are removed in less than 7 days,
the concrete shall be sprayed with a curing compound or be kept wet
continuously by methods allowed in Section 7 of this specification.

Forms shall be removed in such a way as to prevent damage to the
concrete. Forms shall be removed before walls are backfilled.

Where minor areas of the concrete surface are \"honeycombed\", damaged
or otherwise defective, it shall be removed, the area wetted and then
filled with a dry-pack mortar.

Dry-pack mortar shall consist of one part Portland cement and three
parts sand, with just enough water to produce a workable consistency.

9\. CONCRETING IN COLD WEATHER

Concrete shall not be mixed nor placed when the daily atmospheric low
temperature is less than 40 degrees unless facilities are provided to
prevent the concrete from freezing.

Facilities for cold weather concreting shall consist of:

a\. Use of warm concrete with temperatures from 55 degrees F to 65
degrees F.

b\. Adequate protection from the weather, including the use of
artificial heat, to prevent the temperature of the concrete from falling
below 50 degrees F for a period of 3 days, and the relative humidity of
the air near the concrete from falling below 40 percent.

c\. Accelerators such as calcium chloride may not be used to speed the
hardening of concrete.

d\. The contractor shall furnish to NRCS for approval, a written plan
that shows how the contractor will meet the requirements of this
specification. The plan must also show how the requirements of ACI
Specification 306 will be met.

10\. CONCRETING IN HOT WEATHER

Hot weather precautions should be taken when air temperatures are at or
above 85 gegrees F.

Concrete temperature shall be less than 90 degrees F during mixing,
conveying and placing.

11\. BACKFILLING NEW CONCRETE WALLS

Heavy equipment may not be operated within 3 feet of the new concrete
wall.

Compaction within 3 feet of the wall will be by means of hand tamping or
small hand-held tamping or vibrating equipment.

Backfilling and compaction of fill adjacent to new concrete walls shall
not begin in less than 10 days after placement of the concrete or until
the concrete strength at the site has been tested to be at least 3,000
psi. Backfill material shall be the type indicated on the drawings and
shall be free of large stones or debris.

12\. [ADDITIONAL ITEMS WHICH APPLY TO THIS JOB]{.underline}