Chapter 5.85 STRUCTURAL CONCRETE

Structural concrete shall include the furnishing of all labor, tools, equipment and material necessary for the installation of all concrete, reinforced concrete, reinforcing steel, grout, and mortar, as detailed on the plans or in the special provisions.

Concrete work shall also include the treatment of concrete surfaces; the provision of construction joints; the placing and setting of all anchor bolts, pipe railings, manhole steps and floor opening frames and covers, and all appurtenances to the mechanical and electrical equipment that must be attached to or set into the concrete; the setting of all anchor bolts for structural steel; and all miscellaneous items attaching to the concrete as detailed on the plans or in the special provisions under the equipment section of the work. [Ord. 2014-2 (Att. § 17-01).]

5.85.020 Standards.

All concrete materials and construction shall comply with the requirements of, and be in accordance with, the American Concrete Institute Standard 301, “Specifications for Structural Concrete for Buildings,” except as supplemented and modified as follows (all references to “Architect/Engineer” in the ACI Standard shall be interpreted as referring to the District). Design and construction shall conform to the latest Uniform Building Code. Arrangement and details of reinforcing steel, including bar supports and spacers, shall be in accordance with the latest ACI 315 detailing manual. [Ord. 2014-2 (Att. § 17-02).]

5.85.030 Strength.

All concrete shall be working stress type concrete for use in structures or structural elements which have been analyzed and proportioned by working stress (straight line) theory.

The concrete for all structures shall have a minimum compressive strength of 3,500 pounds per square inch 28 days after placement.

All structural concrete shall be Class A containing a minimum of 564 pounds (six sacks) of Portland cement per cubic yard. [Ord. 2014-2 (Att. § 17-03).]

5.85.040 Submittals.

The contractor shall submit to the District for favorable review the following, even though items proposed to be furnished conform to the exact description stated in the specifications or as shown on the plans:

(1) A notarized statement stating that the cement conforms to ASTM C-150.

(2) Concrete mix design and strength data.

(3) Shop drawings of reinforcing detail and layout. [Ord. 2014-2 (Att. § 17-04).]

5.85.050 Cement.

All cement for all structures shall be Type II, ASTM C-150. [Ord. 2014-2 (Att. § 17-05).]

5.85.060 Admixtures.

Admixtures may be used subject to District approval. [Ord. 2014-2 (Att. § 17-06).]

5.85.070 Aggregates.

All aggregates shall conform to “Specifications for Concrete Aggregates” (ASTM C-33). All aggregates shall have a minimum C.V. (cleanliness value) and S.E. (sand equivalent) of not less than 75. Three samples shall be tested in each case and shall be taken from the weight hopper. The average of the results of the individual tests will be the accepted value in each case. These values shall be maintained throughout the course of the work, and any indicated deviation therefrom will be cause for rejection of such material, pending additional tests. Tests shall conform to Test Method No. Calif. 227 for cleanliness value and Test Method No. Calif. 217 for sand equivalent (Materials Manual, Testing and Control Procedures – Materials and Research Department, State of California).

The nominal maximum size of aggregates shall be 12 inches; gradation shall be based on a 12-inch nominal maximum size aggregate. In thin section (six inches or less in thickness), a six-inch nominal maximum size aggregate may be used if expressly approved in writing by the District. [Ord. 2014-2 (Att. § 17-07).]

5.85.080 Selection of proportions.

The contractor shall have his mix designed and shall submit the proposed proportions to the District for review and approval. The cement content shall be not less than six sacks of cement (94 pounds per sack) per cubic yard of concrete, and the water-cement ratio shall not be greater than five and three-quarter gallons of water per sack of cement. Only clean, fresh water shall be used for making concrete. [Ord. 2014-2 (Att. § 17-08).]

5.85.090 Reinforcing steel.

Unless otherwise specified, reinforcing steel shall be deformed and plain billet-steel bars for concrete reinforcement conforming to ASTM A-615 Grade 60. Bars smaller than No. 4 bars shall be ASTM A-615 Grade 40. Reinforcing bars shall be placed in accordance with the size and spacing shown on the plans.

Mesh reinforcement shall conform to the requirements of ASTM A-185. The gauge of the wire and the dimensions of the mesh shall be as detailed on the plans or in the special provisions. [Ord. 2014-2 (Att. § 17-09).]

5.85.100 Formwork.

Lumber and plywood shall conform to the dimensions of the concrete surfaces shown on the plans, shall be sufficiently tight to prevent leakage, and shall be sufficiently strong and braced to maintain their proper shape and alignment.

All sharp edges and corners shall be chamfered with one-inch triangular fillets, unless otherwise directed by the District. The triangular fillets or chamfer strips shall be milled or surfaced on all sides. Curved surfaces shall be formed of strips of matched lumber not over four inches wide or of other material, such as plywood or metal, which has been approved by the District.

Unless specifically approved by the District, earth cuts shall not be used as forms for vertical surfaces other than foundations below grade. Where permitted, the cut shall be neat, straight and must stand vertical. [Ord. 2014-2 (Att. § 17-10).]

5.85.110 Reinforcing.

Reinforcing bars shall be tied and supported so as to maintain their exact shape and alignment during concrete placement. Lap bars 50 diameters at splices unless noted otherwise. [Ord. 2014-2 (Att. § 17-11).]

5.85.120 Depth of footings.

The elevations of the bottoms of footings, as shown on the plans, shall be considered as approximate only, and the District may order, in writing, such changes in dimensions or elevations of footings as may be necessary to secure a satisfactory foundation. Coarse bedding material shall be placed as a subgrade below the footing to a minimum depth of 12 inches, under the entire footing of all concrete structures, except standard manholes. [Ord. 2014-2 (Att. § 17-12).]

5.85.130 Control of water.

Water shall be controlled as required in SD5MCC 5.65.050(4). Pumping of water from the interior of any foundation enclosure shall be done in such a manner as to preclude the possibility of any portion of the concrete materials being carried away. No pumping will be permitted during the placing of concrete, or for a period of at least 24 hours thereafter, unless it be done from a suitable sump separated from the concrete work.

The contractor shall take all necessary precautions to preclude the discharge of silt or cement fines from newly poured concrete into natural waterways or into sewers. [Ord. 2014-2 (Att. § 17-13).]

5.85.140 Concrete placement.

The contractor shall notify the District at least 72 hours before concrete is placed. No concrete shall be placed until all excavations, forms, reinforcing, and inserts have been constructed and inspected by the District.

All concrete shall be thoroughly vibrated during the pouring operation by a mechanical vibrator. The contractor shall have a spare vibrator on the job prior to any pour. [Ord. 2014-2 (Att. § 17-14).]

5.85.150 Finishes on concrete surfaces.

The following specifications set forth the requirements for the classes of surface finish, which shall be applied to the various parts of concrete structures.

(1) Wearing Surface. Unless otherwise specified on the plans, in the special provisions, or directed by the District, the wearing surfaces of concrete steps and concrete walkways, together with the top surfaces of all floors of structures and slabs, shall be given a monolithic finish. All surfaces to be finished shall be thoroughly worked and brought to a uniform steel trowel finish. In addition, where directed by the District, stair treads, landings, walkways or floors shall be given a brush or broom finish.

(2) Ordinary Surface Finish. Ordinary surface finish shall be applied to all concrete surfaces either as a final finish or preparatory to a higher class finish. On surfaces which are to be buried underground and are in contact with the ground or specified backfill, the removal of fins and form marks and the rubbing of mortared surfaces to a uniform surface will not be required. Unless otherwise specified, ordinary surface finish shall be considered as a final finish.

During the pouring of concrete, care shall be taken that the methods of compaction used will result in a surface of even texture, free from voids, water or air pockets, and that the coarse aggregate is forced away from the forms in order to leave a mortar surface.

Immediately after the forms have been removed, all form bolts shall be removed to a depth of at least one inch below the surface of the concrete. All holes and depressions caused by the removal or setting back of such form bolts shall be cleaned and filled with a Class II mortar of matching color. Care shall be exercised to obtain a perfect bond with the concrete. All fins caused by form joints and other projections shall be removed and all pockets cleaned and filled. Cement mortar for filling pockets shall be treated as specified for bolt holes. In the judgment of the District, if rock pockets are of such an extent or character as to affect the strength of the structure materially or to endanger the life of the steel reinforcement, he may declare the concrete defective and require the removal and replacement of that portion of the structure affected.

Holes or depressions in surfaces which are to receive Class 1 surface finish shall be cleaned and filled with mortar at least seven days prior to starting Class 1 surface finish. Exposed mortar shall be wetted with water at intervals during the day for two consecutive days after placing. After the mortar has thoroughly hardened, the surface shall be rubbed with carborundum as required to match the texture and color of the adjacent concrete.

(3) Class 1 Surface Finish. The application of Class 1 surface finish shall result in obtaining smooth, even surfaces of uniform texture and appearance, free of unsightly bulges, depressions and other imperfections. The degree of care in building forms and character of materials used in form work will be a contributing factor in the amount of additional finishing required to produce smooth even surfaces of uniform texture and appearance, free of unsightly bulges, depressions and other imperfections, and the District shall be the sole judge in this respect.

Unless otherwise indicated on the plans or in the special provisions, all exposed interior and exterior concrete surfaces of all treatment plant and pumping station structures shall be given a Class 1 surface finish as a final finish.

After completion of the ordinary surface finish, areas which do not exhibit the required smooth, even surface of uniform texture and appearance shall be sanded with power sanders or other approved abrasive means until smooth, even surfaces of uniform texture and appearance can be obtained. [Ord. 2014-2 (Att. § 17-15).]

5.85.160 Curing.

All concrete shall be properly cured in accordance with the requirements of the American Concrete Institute Standard 301.

Forms shall not be stripped until seven days have elapsed after the concrete was poured. [Ord. 2014-2 (Att. § 17-16).]

5.85.170 Concrete deposited under water.

In excavations for the footings of proposed structures, if conditions render it impossible or inadvisable in the opinion of the District to dewater the excavation before placing concrete, the contractor shall deposit under water, by means of a tremie or bottom dump bucket, a layer of concrete of sufficient thickness to thoroughly seal the cofferdam. Concrete deposited in water shall be Class A with 10 percent extra cement added. The exact thickness will depend upon the hydrostatic head, but in no case shall the seal be less than 18 inches. This seal shall, in general, be allowed to remain in place for not less than five days and preferably 10 days before dewatering so as to set sufficiently to withstand the hydrostatic pressure.

All portions of the structure for which concrete must be deposited under water shall be poured continuously until completed. When such portions are completed, all scum, laitance, and sediment shall be removed before fresh concrete is deposited. Concrete shall not be placed in running water. [Ord. 2014-2 (Att. § 17-17).]

5.85.180 Waterproofing.

When called for on the plans or in the special provisions, waterproofing of the type specified shall be installed in accordance with the requirements of Section 54 of the State Standard Specifications or as specified in the special provisions. [Ord. 2014-2 (Att. § 17-18).]

5.85.190 Drypack and special high-strength nonshrink mortar.

Where “drypack” is called for on the plans, a mixture containing one part cement to three parts clean sand shall be used. The moisture content shall be such that the mixture will ball when formed by hand, but will crumble when struck. The mixture shall be confined in the opening to be filled and driven home in small amounts, using a hammer and a stick or blunt metal tool in such a manner that a very dense mortar is obtained. Should the resulting joint leak, the material shall be chipped out and the opening refilled until a watertight joint is obtained.

As shown in the plans, the contractor shall provide concrete bases under all equipment. Cement grout shall be poured under all fabricated metal bases in such a way that all voids are filled with nonshrink mortar, giving support to all parts of the fabricated base. Mortar shall be placed by pouring with enough pressure (head) so that mortar will reach all portions of the fabricated base. A hole shall be drilled in fabricated base at each cell to let out air and a small amount of mortar to assure completely filling each cell.

Mortar used shall be nonshrinking, nonmetallic, level-fill grout, water and oil resistant, developing a compressive strength of at least 7,500 psi in seven days, nonmetallic and bond to metal. Mortar shall be used in accordance with the recommendations of the manufacturer. [Ord. 2014-2 (Att. § 17-19).]

5.85.200 Alterations to concrete structures.

All alterations, chipping, drilling or cutting of concrete shall be approved by the District. Where the contractor is required to cut openings through existing concrete or masonry walls, the hole shall be precut with a proper masonry saw on both sides of the wall. After removal of the concrete, all rough surfaces of the wall shall be ground smooth and patched with cement mortar.

Openings for installation of pipes up to 12 inches diameter shall be machine cored. For larger pipes, openings shall be made by drilling small holes around the periphery prior to chipping out the concrete. After the pipe has been installed, the opening shall be grouted and made completely watertight. [Ord. 2014-2 (Att. § 17-20).]

5.85.210 Grout for pipes and anchors.

Pipes, anchor bolts, manhole steps or other embedments installed in existing concrete shall be grouted using quick-setting, nonmetallic, hydraulic cement. The cement shall be “Waterplug,” or “Sika Plug W/C,” or equal. The installation shall be made in accordance with the recommendation of the manufacturer.

Where leaks occur in concrete walls, the concrete shall be chipped around the leak and sealed with cement grout above specified, in strict accordance with the manufacturer’s instructions. [Ord. 2014-2 (Att. § 17-21).]

5.85.220 Concrete surface repairs.

Repairs to spalled, cracked, pitted, or crazed concrete surfaces shall be made using Camp Latex Concrete Repair and Topping as manufactured by the Camp Company, Inc., Chicago, Illinois, or “Sikadur Lo-Mod Mortar” as manufactured by Sika Chemical Corp., Burlingame, California, or equal. As an alternate, the contractor may repair concrete surface defects with an approved nonshrink trowel grade epoxy filler, Tnemec 63-1500 filler and surfacer, Will-Cor No. 900 trowellable putty or equal. The repairs shall be made in strict conformance with the manufacturer’s recommendations. For smoothing or repairing large areas that require more than one-quarter-inch thickness, special instructions on the use of the material shall be obtained from the manufacturer. The finish painting shall be compatible with the patching material. [Ord. 2014-2 (Att. § 17-22).]

5.85.230 Bonding new concrete to old.

Where it is required to apply new concrete over old surfaces or to bond precast concrete sections or other types of material to concrete, the contractor shall first apply a brush-on epoxy resin concrete adhesive equivalent to Concresive No. 1 as manufactured by Adhesive Engineering, 1411 Industrial Road, San Carlos, California, or “Sikadur Hi-Mod” as manufactured by Sika Chemical Corp., Burlingame, California. The old surface shall be cleaned by sandblasting or chipping and the adhesive applied in strict accordance with the recommendations of the manufacturer. [Ord. 2014-2 (Att. § 17-23).]

5.85.240 Slump tests.

Slump tests shall be performed by the contractor in the presence of the Inspector at the beginning of each day’s pour and at such additional times as required by the District or its representative. Slump tests shall be made in accordance with current ASTM Designation C-143.

The amount of water used in the mixture shall be the amount required to produce concrete with a slump within the range shown as nominal slump in the following table:

Type of Work		Nominal Slump (Inches)	Maximum Slump (Inches)
Reinforced concrete structures
	Heavy sections	0 – 3	5
	Thin sections and columns	0 – 4	6
Nonreinforced facilities		0 – 3	4
Concrete pavement and walls		0 – 2	3
Concrete placed under water		6 – 8	9

When the slump of the concrete is found to exceed the nominal slump, the mixture shall be adjusted as directed by the District to reduce the slump to a value within the nominal range shown.

Where there are adverse or difficult conditions which affect the placing of concrete, the contractor may request permission of the District to increase the slump by increasing both the water and cement content. The cost of additional water and cement shall be at the contractor’s expense. [Ord. 2014-2 (Att. § 17-24).]

5.85.250 Cylinder testing.

For projects involving the placement of a total of 10 cubic yards or more of concrete, the contractor shall take a minimum of three cylinders for testing by the District.

Additionally, three test cylinders shall be made for each day’s pour where more than 20 cubic yards of concrete is poured, or for each 150 cubic yards of concrete placed.

The contractor shall furnish the cans for the test cylinders and pour the concrete into the cans. The test cans shall be marked with the date and stored on the job site in conditions similar to the structure which was poured. The District will pay for the testing. [Ord. 2014-2 (Att. § 17-25).]

5.85.260 Inspection.

The District shall inspect and approve formwork and reinforcing steel placement prior to concrete pours. The contractor shall provide at least 24 hours’ notice that inspections are required. [Ord. 2014-2 (Att. § 17-26).]