CONSTRUCTION SPECIFICATION

NE-32. CONCRETE FOR MINOR STRUCTURES

1\. [SCOPE]{.underline}

The work shall consist of forming, placing, finishing, and curing
Portland cement concrete including steel reinforcement.

2\. MATERIALS

Cement shall be Type I or Type II Portland cement.

Aggregate shall meet Department of Roads \"47-B\" or \"AX\" gradation
for commercial concrete or the coarse gravel aggregate gradation (see
Section 3 for job mixed concrete).

Water shall be clean and free of harmful chemicals. Reinforcing steel
shall be deformed billet-steel bars, Grade 40 or 60.

3\. CONCRETE MIX

A. Commercial (3000 psi)

> Nebraska Department of Roads \"47B\" concrete (crushed limestone and
> sand) or \"AX\" concrete (coarse gravel aggregate) with 4-7% air
> entrainment.

B. Job Mixed (6 bags cement/cu yd)

> Use coarse gravel aggregate, maximum size of 1 inch with the following
> gradation:

  -------------------------------- --------------------------------------
  Sieve Size                       Percent Passing

  1\"                              100%

  #4                               60-90%

  #30                              15-25%

  #100                             0-5%
  -------------------------------- --------------------------------------

> Mix 500 lbs. aggregate and 6 gal. of water per bag of cement.

C. A ratio of 5 parts fine and coarse aggregate to 1 part cement can
also be used as a guide.

4\. REINFORCING STEEL

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

Reinforcing shall be accurately placed and secured in position in a
manner that will prevent its displacement during placement of concrete.
No welding of steel will be permitted. Reinforced 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, plastic chairs or hard
(igneous) field stone.

Splices of reinforcing bars shall be lapped 30 diameters but not less
than 12 inches. Bars shall not be spliced by welding. Welded wire fabric
shall be lapped at least one mesh width.

5\. FORMS FOR CONCRETE

All forms shall be true to line and grade, mortar tight, and rigid so
that they don\'t move or bulge during placement of concrete. All forms
shall be removed from the concrete prior to backfill.

6\. PLACING CONCRETE

Concrete shall be placed in final position within one and one-half hours
after mixing with cement and shall be consolidated by tamping or by
mechanical vibration.

All concrete placed on earth shall be placed on clean damp surfaces,
free of frost, ice, or running water. Concrete shall not be dropped more
than 5 feet vertically unless suitable equipment is used to prevent
segregation. Unformed surfaces (excluding slip form concrete) exposed in
the completed work shall have a wood float finish. Exposed concrete
edges shall be chamfered or finished with molding tools.

Concrete shall be placed at air temperatures between 40oF and 80oF,
unless special measures are taken to protect the concrete. Review
special concrete placement procedure with the NRCS Inspector prior to
placement of concrete. Concrete shall be protected from freezing for 7
days after placement.

7\. CURING CONCRETE

All concrete shall be cured by keeping the exposed surfaces wet for 7
days or by applying a spray type curing compound. Curing compound shall
be sprayed immediately after the free water has disappeared.

8\. DEFECTIVE CONCRETE

Honeycombed areas and other voids in concrete will be promptly repaired
immediately upon discovery.

9\. BACKFILL

Do not backfill against finished concrete until it is 3 days old.