8-07Precast Traffic Curb

8-07 Precast Traffic Curb8-07 Precast Traffic Curb

8-07.1 Description

This Work consists of furnishing and installing precast sloped mountable curb, or dual faced sloped mountable curb of the design and type and location shown in the Plans in accordance with these Specifications and the Standard Plans or as staked by the Engineer.

8-07.2 Materials

Materials shall meet the requirements of the following sections: Portland Cement 9-01.2(1) Blended Hydraulic Cement 9-01.2(1)B Aggregate 9-03.1 , 9-03.2 Reinforcing Steel 9-07 Mortar 9-20.4 Water Repellent Compound 9-23.3 Sodium Metasilicate 9-23.4 Paint 9-34.2

8-07.3 Construction Requirements

8-07.3(1) Aggregates and Proportioning

The cement concrete mix design for precast concrete curb shall meet the requirements of Section 6-02.3 for concrete class 4000 with a 4,000 psi compressive strength at 28 days and an air content between 4.5% and 7.5%. Aggregates used in the manufacture of precast concrete traffic curb shall conform to the requirements of Section 9-03 and shall have a coarse aggregate nominal maximum size of ¾ inch. The precast concrete mix shall contain sufficient fine fractions to achieve the type of surface finish specified herein.

8-07.3(2) Mixing

The mixers shall be kept in good repair and be equipped with an automatic timing device and a positive device for regulating the quantity of water added to each batch. Such a device must be authorized by the Engineer before use. After all materials, including water, have been placed in the mixer, the materials shall be mixed for a period of not less than 1¾ minutes, or as much longer as may be necessary to produce a thorough and uniform mixture of the concrete. No water shall be added to any batch after the completion of the initial mixing period. Each batch of concrete shall be completely emptied from the mixer before placing more materials in it. A batch which has not been placed within 30 minutes from the time water was first added shall not be used. The amount of water in the concrete shall be kept at a minimum consistent with the manufacture of dense curb, free from air bubbles and surface defects in excess of the tolerance limits specified.

8-07.3(3) Forms

Forms shall be of concrete or steel. The use of forms or molds made of plaster of paris, wood, or other absorptive material will not be permitted. Bulkheads shall be tight fitting so that there is no leakage of mortar between the bulkhead and form. The materials and methods used for lubricating the forms shall be such that they will not result in discoloration of the curb at any time. A minimum quantity of lubricant shall be used and all excess lubricant shall be removed. M 41-10 Page 8-55 Precast Traffic Curb 8-078-07.3(4) Placing Concrete The concrete shall be consolidated by external vibration, or by other means if allowed by the Engineer, to produce a dense concrete throughout, having a minimum of air bubbles and honeycombing. Reinforcing steel shall be placed and maintained in its proper position as shown in detail drawings. Curb shall not be manufactured in an atmospheric temperature of less than 50ºF.

8-07.3(5) Removal of Forms

The curb shall be removed from the molds or forms in accordance with the instructions or by some other method acceptable to the Engineer. The loosening of the curb from the molds shall be carefully performed to avoid excessive shock and straining of the curb. When, in the opinion of the Engineer, undue shock is required to remove the curb from the molds, the stripping operation shall be deferred until such time as the curb may be removed without breakage.

8-07.3(6) Curing Concrete

Immediately after the concrete has been placed and consolidated in the mold, each unit shall be placed in a curing room fitted with water sprays and maintained at a relative humidity of not less than 90 percent and a temperature of not less than 60ºF, nor more than 100ºF. Each unit shall remain in the curing room for a period of not less than 10 days, except that if Type III cement is used, the period in the curing room may be reduced to 5 days.

8-07.3(7) Finish

The curb shall have a smooth, glassy finish on all exposed surfaces. Excess honeycombing in the back of the curb may be cause for rejection of the curb. Honeycombing areas in the back of the curb which, in the opinion of the Engineer, are not detrimental to the curb need not be patched. The workmanship of the bottom finish shall be such that no mechanical interlocking of the mortar bed and the curb bottom or anchor groove will occur.

8-07.3(8) Surface Treatment

As soon as the units have been taken out of the curing room and thoroughly surface dried to a depth of at least ¼ inch, two coats of a water repellent compound, meeting the requirements of Section 9-23.3 , shall be brush applied. When the first coat has dried, the second coat of water repellent compound shall be applied.

8-07.3(9) Dimensions and Shape

The curb shall conform to the dimensions and shape shown in the Plans within a tolerance of ¼ inch in length and ⅛ inch in alignment.

8-07.3(10) Curb Lengths

Curb lengths shall be in accordance with the Standard Plans, except in special cases where different lengths are specified. Circular curbing shall be made only for such radii as called for in the detail plans. Page 8-56 M 41-10

8-07 Precast Traffic Curb8-07.3(11) Defective Curb

Not more than 2 percent of the top area in any one piece of curb shall be defective, and not more than 5 percent of the total length of the top corners of reflecting faces in any one piece of curb shall be broken or rounded. There shall be not more than 50 holes in any linear foot of curb. All curb having defects in excess of any of the above will be rejected immediately upon inspection after removal from the forms. However, failure to reject the curb at that time will not ensure its final acceptance. Ninety percent of the curb laid shall not have more than 10 percent of the maximum allowable number of defects specified above. An air hole shall be defined as any hole ⅛ inch or larger in diameter or depth. All defects within the limits permitted, apparent upon removal of forms, shall be repaired immediately. The sum of the length of the lines of discoloration caused by a cracked mold in any one piece of curb shall not exceed 50 percent of the length of the curb, and the maximum length of any single line of discoloration shall not exceed 18 inches. 75 percent of the curb laid shall be entirely free from lines of discoloration. The employment of heat to obliterate lines of discoloration will not be permitted. The process used to obliterate lines of discoloration shall be subject to the approval of the Engineer. The repairing of molds which are chipped or broken shall be done in a manner that the broken or chipped areas will not be apparent on the curb made in those molds. All curb in which surface checking develops during the first five days after manufacture will be rejected. Hidden air holes at or immediately below the exposed surface of the curb, in excess of the limits specified that are disclosed by testing the surface by means of a rubber hammer will be cause for rejection of the curb. All curb in which cracking is in evidence immediately after removal from the molds will be rejected. A crack is defined as any separation of the concrete of a continuous length greater than 3 inches. All curb which varies in dimensions, alignment, or surface contour in excess of the tolerance specified will be rejected. Failure to comply with the Plans, Specifications, or instructions of the authorized representative of the Contracting Agency in the manufacture and laying of any curb will be cause for rejection of such curb.

8-07.3(12) Repairing Curb

Curb having defects which are not sufficient cause for its rejection shall be neatly repaired immediately after removal from the molds in a manner subject to the approval of the Engineer. However, no patching or other repairs shall be made without the permission of the Engineer. Patches shall be undercut if, in the opinion of the Engineer, this operation is necessary to achieve a satisfactory patch. All holes larger than ¹/ 16-inch diameter in the exposed surface of acceptable curb or buttons shall be filled with cement mortar.

8-07.3(13) Identification Marking

The date of manufacture, the length, and identification number corresponding to the detail layout shall be marked in black paint on the back or end of each piece of curb. Rejected curb shall be marked on the back or end surfaces in a practical and semi- permanent manner to identify each cause of rejection. M 41-10 Page 8-57 Precast Traffic Curb 8-078-07.3(14) Shipping No unit of curb shall be shipped from the manufacturing plant prior to 21 days after manufacture, except, however, that if Type III cement has been used, the units may be shipped 14 days after manufacture.

8-07.3(15) Sampling and Inspection

The Contractor shall submit, for the acceptance of the Engineer, an advance sample of curb which shall be at least equivalent in color, surface texture, and bottom finish to the standard as set forth in these Specifications. No repairing of any kind shall be done on the advance sample. Upon approval, the advance sample shall be stored at the plant or site of manufacture in a location readily accessible to the Inspector where there is adequate daylight for examination. The advance sample shall be protected from damage and discoloration and shall be used as a standard of comparison for color, surface texture, and bottom finish for all curb manufactured. All curb furnished shall be equivalent in the foregoing respects. The inspection at the plant will be made just prior to shipment, at which time examination will be made of the alignment, contour, color, cracks, surface damage or discoloration, broken corners or edges, and any other defects which may have developed, and to check the laboratory test reports for strength. However, intermediate inspections may be made to determine surface checking and hidden air holes if it is impractical to examine for these defects at the final inspection.

8-07.3(16) Installing Curbs

The curb shall be firmly bedded for its entire length and breadth on a mortar bed conforming to Section 9-20.4(3) composed of one part Portland cement or blended hydraulic cement and two parts sand. The anchor grooves in the bottom of the curb shall be entirely filled with the mortar. Before the cement mortar bed is laid, all dirt shall be cleaned from the pavement surface by washing. All old pavements and any portion of new pavements constructed under this Contract, which are covered with oil or grease within the curb limits, shall be further cleaned as follows:

8-07 Precast Traffic Curb8-07.3(17) Painting of Curbs

Precast concrete curbing shall be painted with two full coats of paint conforming to Section 9-34.2 , as shown in the Plans or as designated by the Engineer. The paint can be applied by brush or spray. The second coat shall have glass traffic paint beads sprinkled in the wet paint at the rate of 12 pounds per 100 linear feet of curbing. The beads shall conform to the requirements of Section 9-34.4 .

8-07.4 Measurement

Precast sloped mountable curb will be measured by the linear foot along the front face of the curb. Precast dual faced sloped mountable curb will be measured by the linear foot of tapered block and nosing block installed. Only one face of dual faced curb will be measured.

8-07.5 Payment

Payment will be made for each of the following Bid items that are included in the Proposal: “Precast Sloped Mountable Curb”, per linear foot. “Precast Dual Faced Sloped Mountable Curb”, per linear foot.