2001-04-25 Concrete Curb Specs
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CONCRETE CURB SPECIFICATIONS
Description... ... ... ... ... ... ... ... ... '" ... ... ... ... ... ... ... ... '" page 1
Concrete...... ... ... ... ... ...... ...... ...... ... ...... ............ ... page 1
Base Preparation... ... ... ... ... '" ... ... ... ... ... ... ... ... ... ..... page 1
Machine Placement... ... ... ... ... ... ... ... ... ... ... ... ... ... ... page 1
Formed Method... ... ... ... ... ... ... ... '" ... ... ... ... ... '" ..... page 2
Finishing... ... ... ... ... '" ... ... ... '" ... ... ... ... ... ... '" '" ... ... page 2
Jointing... ... ... ... ... '" ... ... '" ... '" ... ... ... ... ... ... ... ... ... .. page 2
Protection... ... ... ... ...... ... ......... ... ...... ...... ... ...... .... page 3
Curing... ... ... ... ... ... ... '" ... ... ... ... ... ... ... ... ... ... ... ... ... page 3
Backfilling... ... '" ......... ............... ...... ............ ... ... ..page 3
Testing............ ... ... ............... ... ...... ... ... ......... ... ... page 4
Revised 4/25/01
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CONCRETE SPECIFICATIONS
DESCRIPTION
Curb or combined curbs and gutters, sidewalks and driveway aprons, shall consist of air-entrained portland
cement concrete constructed on a prepared sub grade in accordance with these specifications. This work shall be
in reasonable cost conformity with the lines and grades, thicknesses, and typical cross sections shown on the
Plans or established by the Engineer. All work shall be performed in accordance with MnDOT Specifications
for Highway Construction, 2000 Edition, except as modified herein by the following specifications and the
Special Provisions.
All curb not conforming to the design as specified on the Plans is to be removed and replaced at no cost to the
Owner. Type B curb is to be placed at all curb returns with a minimum 10' transition to other curb types.
CONCRETE
The air-entrained portland cement concrete shall meet the requirements of MnDOT Specification 2461. The
component parts shall be batched by weight, in proportions, to produce a concrete developing a minimum
compressive strength of 3900 psi in 28 days. Concrete mix shall be mixture 3A32 for hand placement and 3A22
for machine placement, per MnDOT Specification 2461.
A design mix shall be submitted to the Engineer for approval prior to installation. Any addition of excess water,
as determined by the Engineer, to the concrete during placement, will result in removal and replacement of
affected material.
BASE PREPARATION
The base shall be a minimum thickness of 6 inches of Class 5 gravel under all curb and gutter and all driveway
aprons. A minimum base thickness of 4 inches of pit run sand shall be placed beneath all sidewalks. The base
shall be compacted and shall extend a minimum of one foot outside the curb and drives and 0.5 feet outside
sidewalk forms. The base shall be reasonably dense, firm, trimmed to a uniform smooth surface and in a moist
condition when the concrete is placed.
MACHINE PLACEMENT
The slipforml extrusion machine approved shall be so designed as to place, spread, consolidate, screed, and finish
the concrete in one complete pass in such a manner that a minimum of hand finishing will be necessary to
provide a dense and homogeneous concrete section. The machine shall shape, vibrate, and! or extrude the
concrete for the full width and depth of the concrete section being placed. It shall be operated with as nearly a
continuous forward movement as possible. All operations of mixing, delivery, and spreading concrete shall be
so coordinated as to provide uniform progress, with stopping and starting of the machine held to a minimum.
FORMED METHOD
The forms shall be of wood, metal, or other suitable material that is straight and f~e from warp, having
sufficient strength to resist the pressure of the concrete without displacement, and sufficient tightness to prevent
the leakage of mortar. Flexible or rigid forms of proper curvature may be used for curves having a radius of 100
feet or less. Division plates shall be metal.
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Other Joints
Construction joints may be either butt- or expansion-type joints. Curbs or combined curbs and gutters
constructed adjacent to existing concrete shall have the same type of joints as in the existing concrete,
with similar spacing; however, contraction joint spacing shall not exceed 15 feet. Curbing placed in
conjunction with concrete paving shall be jointed according to the type of joint indicated on the Plan
and Profile.
Reinforcin~ Steel
The Contractor shall install two (2) No.4 steel reinforcing bars, twenty feet in length, across each service trench
or any other trench which crosses the curbing. Two (2) No.4 steel reinforcing bars four feet in length shall be
installed at all transitions from machine placed versus hand placed curbing. Reinforcing cages to be installed
behind the catch basin castings shall conform to detail 4.017 A.
Protection
The Contractor shall always have material available to protect the surface of the plastic concrete against rain.
These materials shall consist of waterproof paper or plastic sheeting. For slipform construction, materials such
as wood planks or forms to protect the edges shall also be required
When concrete is being placed in cold weather, and the temperature may be expected to drop below 350 F,
suitable protection shall be provided to keep the concrete from freezing until it is at least 10 days old. Concrete
injured by frost action shall be removed and replaced at the Contractor's expense.
Curing
Concrete shall be cured for at least three days after placement to protect it against loss of moisture, rapid
temperature change, and mechanical injury. Moist burlap, waterproof paper, white polyethylene sheeting,
white liquid membrane compound, or a combination thereof, may be used as the curing material. Membrane
curing shall not be permitted in frost-affected areas when the concrete will be exposed to de-icing chemicals
within 30 days after completion of the curing period.
Backfillin~
After the concrete has set sufficiently, the spaces in front and back of curbs shall be refilled with suitable
material to the required elevations. the fill material shall be thoroughly tamped in layers. It shall be the
Contractor's responsibility to protect the curbing during all phases of the backfilling operation. Any curbing
damaged during this process shall be removed and replaced at the Contractor's expense.
Testing
Not less than three test cylinders of standard size and manufacture shall be made for each 50 cubic yards of
concrete placed, or for each day's operations unless otherwise directed by the EngL.'1eer. One cylinder from each
set shall be tested at seven days and one cylinder at 28 days, in accordance with ASTM C;31. The third cylinder
shall be retained as a spare in case problems OCcur with either of the other two.l
Air entrainment and slump tests shall be taken on each load prior to placement.
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