Published by department of transportation

73-1.03D Extruded and Slip Form Methods

Feed concrete into the extrusion machine at a uniform rate. Restrain forward travel of the extrusion machine to produce a well-compacted mass of concrete requiring no further finishing other than a light brushing. The brush may be filled with water. Do not finish the concrete surface with a brush application of grout.

If you use a slip form machine, automatically control the alignment, grade, and cross slope by one of the following methods:

1. Sensing from preset string lines

2. String line control of the alignment and grade and automatic control of the cross slope
The slip form machine must have traveling forms rigid enough to produce the required cross section. The machine must produce a dense, homogeneous concrete, true to grade and cross section and require minimum handwork. Consolidate the concrete with internal vibrators or other authorized method.

Use a smaller, maximum size of aggregate with an extruded or slip form machine if it is required to produce concrete (1) free from surface pits larger than 3/16 inch in diameter and (2) with well-defined web marks of water on the surface.

You may construct expansion joints by sawing through the concrete cross section to its full depth. The width of the cut must provide a tight fit for the joint filler. Insert preformed joint filler into sawed joints and mortar it in place.

If a joint is cut before the concrete has hardened:

1. Protect the adjacent surfaces with close fitting, firmly supported shields

2. Complete the saw cut and insertion of the preformed joint filler before curing the concrete

1. Mortar preformed joint filler in place using heavy trowel pressure

2. Cover the exposed portions of the concrete in the vicinity of the saw cut with an additional application of curing compound
After the concrete has cured, check the joint filler for a tight fit. If any loose joints are found, mortar the joint in place and recheck after the mortar has cured. Repeat as necessary to achieve a tight fit.

73-1.03E Curing

Completely coat the exposed faces of the concrete with curing compound.

73-1.04 PAYMENT

73-2 CURBS

73-2.01 GENERAL

73-2.02 MATERIALS

73-2.03 CONSTRUCTION

73-2.03A General

Anchor steel dowels in drilled holes with mortar made from equal parts by volume of portland cement, sand, and water. You may use anchor bolts instead of anchored steel dowels if authorized.

If adhesive is used, remove all dust, loose material, or oil from the surface of the existing pavement by either wire brushing or blast cleaning.

Construct contraction and expansion joints at right angles to the line of the curb. Space contraction joints at 20-foot intervals. For curbs adjacent to existing concrete, align the curb joints with the existing concrete's pavement joints.

The top and face of the finished curb must be true and straight. The top surface of the curb must be uniform in width and free from humps, sags, or other irregularities. Clean any discolored concrete by abrasive blast cleaning or other authorized method.

Except for curbs on structures, you may place curbs with an extrusion machine or a slip form paver if:

1. Finished curb is true to line and grade

2. Concrete contains the maximum quantity of water that maintains the curb's shape without support

3. Required surface texture is attained
Check the flatness of the top and face of the curb and the surface of the gutter with a 10-foot straightedge. The surfaces must be flat to within 0.01 foot except at grade changes or curves.

73-2.03B Fixed Form Method

The back forms may be constructed with 1/2-inch-thick bender boards.

Cleat the back forms together as required to attain the full depth of the curb.

Use form clamps to prevent interference with finishing activities.

Before removing the forms, finish the surface true to grade with a straightedge float at least 10 feet in length. Operate the straightedge float longitudinally over the concrete surface.

Remove the forms from the face of the curb from 1 to 6 hours after placing the concrete. Do not remove the forms if the concrete is plastic enough to slump.

After removing the forms, immediately use a steel trowel to attain a smooth finish. The smooth finish must extend (1) to within 0.17 foot of the flow line or (2) to the flow line of a curb with an integral gutter. After smoothing the curb's face, apply a fine-brush finish parallel to the line of the curb.

73-2.03C Extruded or Slip Form Methods

The machine must be capable of vertical adjustment during forward travel to construct curbs of varying height as determined by the offset guide line.

You may operate the extrusion machine on rails or forms set at a uniform depth below the established grade of the top of curb.