Item No. 434

Concrete Medians and Islands

434.1 Description

This item shall govern construction of Portland cement concrete traffic islands and medians in accordance with these specifications and in conformity to the lines, grades, sections and details indicated on the Drawings or as established by the Engineer or designated representative.

434.2  Submittals

The submittal requirements of this specification item include:

A.   Class A  p.c. concrete mix design,

B.   Type of Installation (i.e. Median or Island) and construction details (i.e. cushion layer, base, reinforcing steel, joints, curing membrane),

434.3   Materials

A.  Portland Cement (p.c.) Concrete

The p.c. concrete shall conform to Class A Concrete, Section 403.7 (Table 4) of Standard Specification Item No. 403, "Concrete for Structures".

B.  Reinforcing Steel

Reinforcing steel and welded wire fabric shall conform to Standard Specification Item No. 406, "Reinforcing Steel".

C.  Expansion Joint Materials

Preformed expansion joint materials shall conform to Standard Specification Item No. 408, Expansion Joint Materials".

D.  Membrane Curing Compound

Membrane curing compound shall conform to Standard Specification Item No. 409, "Membrane Curing".

E.  Admixtures

Admixtures shall conform to Standard Specification Item No. 405, "Concrete Admixtures".

F.  Aggregate Cushion

Cushion layer shall consist of crusher screening, gravel, sand, crushed stone or "Flexible Base" materials (Standard Specification Item No. 210) approved by the Engineer or designated representative.

 

 

434.4 Construction Methods

All forms and forming, placement of reinforcement, placement of concrete, form removal, finishing and curing shall conform to Standard Specification Item No. 410, "Concrete Structures".

A.  PCC Mix Design

The p.c. concrete shall conform to an approved design mix for a Class A p.c. concrete on file with the New Braunfels Utilities or proposed Class A mix designs with the necessary test data may be submitted for approval by the Engineer or designated representative.

High range water reducing admixtures conforming to, "Concrete Pavements" may be used when approved by the Engineer or designated representative.

B.  Subgrade and Base Preparation

The subgrade shall be excavated, prepared and shaped to the lines, grades and cross section indicated on the Drawings or as directed by the Engineer or designated representative, and shall be thoroughly compacted conforming to, "Subgrade Preparation".  A cushion layer, 2 inches minimum thickness, shall be spread, wetted thoroughly, tamped and leveled.  The cushion shall be moist at the time the p.c. concrete is placed.

C.  Forms

Forms shall be of metal, well-seasoned wood or other approved material.  The length of the forms shall be a minimum of 10 feet.  Flexible or curved forms shall be used for curves of 100-foot radius or less.  Wood forms for straight sections shall be not less than 2 inches in thickness.  Forms shall be a section, that is satisfactory to the Engineer or designated representative, and shall be clean, free from warp, and of a depth equal to the finished work.  All forms shall be securely staked to line and grade and maintained in a true position during the placement of the p.c. concrete and, if required, forms shall be thoroughly oiled with a light form oil prior to p.c. concrete placement.  If the adjacent existing asphalt pavement is damaged during construction, it shall be restored to its original condition.

D.   Reinforcement

Reinforcement shall conform to the details indicated on the Drawings or the directions of the Engineer or designated representative.  Care shall be exercised to keep reinforcement in its proper position during the placement of the p.c. concrete.

E.  Joints

Joints shall be of the type and spacing shown on the Drawings.  Expansion joint material, ¾ inch in thickness, shall be placed as indicated on the Drawings with a maximum spacing of 40 feet or as directed by the Engineer or designated representative.  Expansion joints shall be placed on the same alignment when adjacent to a Portland Cement concrete pavement.  Weakened plane joints shall be made ¾ inch deep and equally spaced, normally at 5 foot on centers or as directed by the Engineer or designated representative.  Expansion joints shall be required between the curb and median p.c. concrete.

F.  P.C. Concrete Placement and Finishing

The p.c. concrete shall be placed in the forms to the depth indicated on the Drawings, and properly consolidated and until mortar entirely covers the surface and forms a monolithic finish.  If a vibrator is used, care shall be taken not to leave it in one location long enough to induce segregation.  The top surface shall be floated and troweled to a uniform smooth surface, then finished with a camel hairbrush or wood float to a gritty texture.  The outer edges shall be rounded with approved tools to the radii indicated on the Drawings.

When the ambient air temperature is above 85^oF, an approved retarding agent will be required in all p.c. concrete.  The maximum temperature of all p.c. concrete placed shall not exceed 95^oF, unless High Range Water Reducer Admixtures are used.

G.  Curing

Immediately after finishing the p.c. concrete median or island, the pcc surface shall be protected by a membrane-compound curing agent conforming with Standard Specification Item No. 409, "Membrane Curing".  The curing procedures shall be acceptable to the Engineer or designated representative.

434.5   Measurement

Accepted work as prescribed by this item will be measured by the square foot of surface area of p.c. concrete medians and/or p.c. concrete island, complete in place.

434.6   Payment

No direct measurement or payment will be made for the work to be done or the equipment to be furnished under this item, but shall be considered subsidiary to the particular items required by the bid.

 

End