**UNITED STATES DEPARTMENT OF AGRICULTURE**

**NATURAL RESOURCES CONSERVATION SERVICE**

#### **CONSTRUCTION SPECIFICATION**

##### CS-41: "REINFORCED CONCRETE"

41.1 [SCOPE]{.underline}

> The work shall consist of furnishing, forming, placing, finishing, and
> curing Portland cement concrete. The structures shall be constructed
> at the location and to the line and grades as shown in the plan.

41.2 [MATERIALS]{.underline}

> The materials required for reinforced concrete are detailed in
> material specification MS-201, Concrete Aggregates; MS-202, Portland
> Cement; MS-203, Concrete; and MS-213, Steel Reinforcement.

41.3 [HANDLING AND STORAGE]{.underline}

> Materials shall be stored and handled in a manner that will minimize
> degradation, segregation, contamination or intermixing of materials.

41.4 [MIXERS AND MIXING]{.underline}

> Mixers shall be capable of thoroughly mixing the concrete ingredients
> into a uniform mass within the specified mixing time and discharge
> without segregation. Each mixer or agitator shall bear a
> manufacturer's rating plate indicating the rated capacity and
> recommended speeds of rotation, and shall be operated in accordance
> with the manufacturer's recommendations.
>
> Concrete shall be uniform and thoroughly mixed when placed.
>
> Water in excess of the amount specified in the mix design shall not be
> permitted. This includes any water added at the site.

41.5 [TRUCK-MIXED CONCRETE]{.underline}

> When concrete is mixed in a truck mixer loaded to its maximum
> capacity, the number of revolutions of the drum or blades at mixing
> speed shall not be less than 70 nor more than 100 RPM.
>
> The resultant concrete mix must produce a dense and durable concrete
> during curing. The ready-mix concrete shall be mixed and delivered in
> accordance to ASTM C-94, "Standard Specification for Ready-Mix
> Concrete".

41.6 [SITE PREPARATION]{.underline}

> Prior to placement of concrete, the forms, reinforcing steel, and
> subgrade shall be free of chips, sawdust, debris, water, ice, snow,
> extraneous oil, mortar, rust or other harmful substances and/or
> coatings. Rock surfaces shall be cleaned by wire brushing, wet
> sand-blasting, air water jets or other means satisfactory to the
> technical representative. Earth surfaces shall be firm and damp before
> placing concrete. Placement of concrete on mud, dried earth,
> uncompacted fill or frozen subgrade will not be permitted.

41.7 [SUBGRADE PREPARATION]{.underline}

> The foundation area shall be cleared of all vegetation, organic
> material and rocks with a dimension greater than 2 inches. If fill
> material is required, it shall be placed in horizontal layers with a
> maximum lift of 4 inches before compaction. The moisture content of
> the earth fill material shall be controlled so that a firm dense
> foundation can be achieved. Earth fill sections with a height of 2
> feet or greater will be constructed using the compaction requirements
> of NRCS Construction Specification CS-14, Earth Fill Class A or CS-15,
> Earth Fill Class S.

41.8 [FORMS]{.underline}

> Forms shall be wood, plywood, steel or other approved materials and
> shall be mortar tight. The forms and associated falsework shall be
> substantial and unyielding conforming to dimensions of the finished
> grade. Form surfaces shall be smooth and free from holes, dents, sags,
> or other irregularities. Forms shall be coated with a nonstaining form
> release agent before being set into place.
>
> All permanently exposed concrete edges shall be chamfered 3/4" unless
> otherwise indicated on the drawings.
>
> Items to be embedded in concrete shall be positioned accurately and
> anchored firmly.
>
> Metal ties or anchorages within the forms shall be equipped with
> cones, she-bolts or other devices that permit their removal without
> injury to the concrete. Ties designed to break off below the surface
> of the concrete shall have removable cones.
>
> Steel tying and form construction adjacent to fresh concrete shall not
> be started until the concrete has cured at least 12 hours.

41.9 [STEEL REINFORCEMENT]{.underline}

> The steel reinforcement shall be grade 40 deformed steel bars unless
> otherwise specified on the drawings. The steel shall be securely tied
> and positioned to prevent movement during the placement of concrete.
> The reinforcing steel in slabs on grade shall be supported on blocks
> or chairs. All blocks shall have a strength equal to or greater than
> the 28-day compressive strength of the concrete.
>
> The length of splices shall be 30 diameters of the steel bar unless
> otherwise specified on the drawings. Welded splices are not permitted.
>
> The bends shall be standard bends with the length and radius as
> specified by the Concrete Reinforcing Steel Institute, CRSI, and/or
> the Portland Cement Association, PCA.

41.10 [CONVEYING]{.underline}

> The maximum length of time between introduction of the cement to the
> aggregates and placement of the concrete in the forms shall not exceed
> 1-1/2 hours for concrete temperatures below 85^o^ F or 45 minutes for
> concrete temperatures above 85^o^F.
>
> Concrete shall not be dropped more than 5 feet vertically unless
> suitable equipment is used to prevent segregation.

41.11 [PLACING]{.underline}

> Concrete shall not be placed until the subgrade, forms, and steel
> reinforcement have been inspected and approved by the technical
> representative.
>
> The person responsible for construction shall have all equipment and
> materials required for proper consolidation and curing, available at
> the site ready for use before placement of concrete begins.

The technical representative shall be notified a minimum of 24 hours
prior to placement to inspect the reinforcing steel, forms, subgrade,
curing preparation, vibrating equipment and plans for placement.

> The depositing of concrete shall be regulated so that concrete may be
> consolidated with a minimum of lateral movement, segregation,
> laitance, or honey-combing. Hoppers and chutes shall be used as
> necessary to prevent segregation and the splashing to mortar on the
> forms and reinforcing steel above the placing level. Temporary stays
> and braces can be removed when no longer needed.

41.12 [LAYERS]{.underline}

> Slab concrete shall be placed to design thickness in one continuous
> layer. Formed concrete in walls and columns shall be placed in
> horizontal layers not to exceed 20 inches.
>
> Successive layers shall be placed at a fast enough rate to prevent the
> formation of "cold joints". If a successive layer cannot be placed in
> a timely manner, a standard type construction joint shall be used
> between layers.

41.13 [CONSOLIDATION]{.underline}

> Each concrete layer shall be completely consolidated by spading, hand
> tamping, or mechanical
>
> vibrators as necessary to ensure smooth, dense concrete along form
> surfaces, in corners and around embedded items without segregation or
> laitance. Vibration shall extend into the previously placed layers of
> fresh concrete and laterally to ensure effective bond between layers.
>
> The use of vibrators to transport concrete in the forms shall not be
> permitted.
>
> Vibration shall not be applied directly to the reinforcement steel,
> forms, or to concrete that has begun to set.

41.14 [CONSTRUCTION JOINTS]{.underline}

> Construction joints shall be made at locations with the dimensions
> shown on the drawings.
>
> Surfaces of construction joints shall be cleansed of all
> unsatisfactory concrete, laitance, coatings, stains, or debris by
> washing and scrubbing with a wire brush or wire broom and kept moist
> for at least one hour prior to placement of new concrete.
>
> In addition, the top surfaces of walls and columns shall be
> immediately and carefully protected from any condition that might
> adversely affect curing of concrete.
>
> Where lap joints are used on horizontal slabs, the width on each side
> of the joint shall not be less than 6 inches and the depth shall be
> equal to one-half the slab thickness.

41.15 [EXPANSION AND CONTRACTION JOINTS]{.underline}

> Expansion and contraction joints shall be made only at locations shown
> on the drawings. Exposed edges on these joints shall be carefully
> tooled, chamfered and free of mortar and concrete spillage.
>
> Preformed expansion joint filler shall be held firmly in the correct
> position as the concrete is placed and shall be left exposed for its
> full length with clean and true edges.

41.16 [REMOVAL OF FORMS]{.underline}

> Forms shall not be removed before the expiration of the following
> minimum time intervals after placement of the concrete, exclusive of
> days when the minimum temperature of air adjacent to the concrete is
> below 40 degrees Fahrenheit.

[Element]{.underline} [Time]{.underline}

> Beams, arches - supporting forms and shoring 14 days
>
> Conduits, deck slabs - supporting (inside forms) and shoring 7 days
>
> Conduits, (outside forms), side of beams, small structures 24 hours
>
> Columns, walls, spillway riser - with side or vertical load 7 days
>
> Concrete supporting not more than 20 feet of wall in place above it 24
> hours
>
> Age of stripped concrete shall be at least 7 days before any load is
> applied other than the weight of forms, scaffolds and succeeding
> lifts.

41.17 [FINISHING FORMED SURFACES]{.underline}

> The following shall be done immediately after removal of forms.
>
> a\. Removal of all fins and other surface irregularities which affect
> appearance or function.
>
> b\. Removal all form bolts and ties to the depth of their cone.
>
> c\. All cavities, holes and honey-combing shall be thoroughly cleaned,
> wetted and
>
> filled with dry pack mortar.
>
> 1\. The area to be patched shall be kept damp for three hours
>
> immediately prior to patching.
>
> 2\. The patching mortar shall be one part cement to three parts
>
> sand passing the number 16 sieve.
>
> d\. The patching mortar shall be compacted to form a dense,
> well-bonded unit that is free from shrinkage cracks.
>
> e\. All patched areas shall be cured as specified in paragraph 41.19.

41.18 [FINISHING UNFORMED SURFACES]{.underline}

> All exposed surfaces of the concrete shall be accurately screened to
> grade and then wood float finished, except slip form lining which is
> finished by travel of the form.
>
> All exposed concrete edges and joints shall be chamfered or finished
> with molding tools.
>
> Excessive floating or toweling while the concrete is soft shall not be
> permitted. The addition of dry cement or water to the surface of the
> screened concrete shall not be permitted.

41.19 [CURING]{.underline}

> Concrete shall be prevented from drying for a period of at least 7
> days after placement.
>
> Exposed surfaces shall be kept continuously moist for the entire
> period or until curing compound is applied. Formed surfaces shall be
> kept wet until patching or repairs are made. Curing compound shall not
> be used on areas that are to be bonded to other concrete or mortar.
> Curing compound when used shall be sprayed on the moist concrete
> structure 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 meet the minimum requirements of ASTM C-309,
> Type 2, unless otherwise specified on the drawing.
>
> The curing compound shall be thoroughly mixed immediately before
> applying, and shall be applied at a uniform rate of not less than one
> gallon per 150 square feet of surface. It shall form a uniform,
> continuous, adherent film over the entire surface.
>
> Curing compound shall not be applied to surfaces requiring bond with
> concrete remaining to be placed, construction joints, reinforcing
> steel, and embedded items. These areas shall be wet cured.
>
> Concrete surfaces subjected to heavy rainfall, running water and/or
> other moisture damage within 3 hours after curing compound has been
> applied shall receive a second application.

41.20 [REMOVAL OR REPAIR]{.underline}

> Concrete that is honeycombed, damaged, or otherwise defective, shall
> be removed or repaired and approved by the technical representative.

41.21 [CONCRETING IN HOT WEATHER]{.underline}

> The temperature of the concrete shall be less than 90^o^F during
> mixing, conveying and placing. Concrete surfaces exposed to the air
> shall be kept continuously wet for the first 24 hours of the curing
> period, or until curing compound is applied. White pigmented coloring
> compound shall be used when the air temperature exceeds 90^o^F.

41.22 [CONCRETING IN COLD WEATHER]{.underline}

a\. Prior to placement of concrete, all ice, snow and frost shall be
completely removed from all surfaces to be in contact with the concrete.

> b\. The temperature of the concrete at the time of placement shall not
> to be less than 50^o^F, nor more than 90^o^F. Heated water of 140^o^F,
> or less may be used when cement is added to the mix.
>
> c\. The use of antifreeze or accelerator compounds is not allowed.
>
> d\. When the daily minimum ambient air temperature at the site is less
> than 40^o^F, the concrete shall be protected for a minimum of three
> days following placement with insulated blankets or housing and
> heating.

41.23 [DELIVERY TICKETS]{.underline}

> The delivery tickets for the mix delivered to the site shall identify
> all ingredients by weight except water and admixtures which may be
> measured by volume.

Delivery Tickets for each load of Ready-Mix concrete shall be furnished
to the technical representative.