Precast Concrete Curb

The three ways a concrete curb gets made

Cast in place is the default in almost every state and municipal specification. Ohio DOT's Item 609 is typical: "Set the curb on a thoroughly compacted subgrade" with a "1 in 20 batter from the vertical", and on clay soils "place a minimum 3-inch (75 mm) thick firm bed of porous material as a foundation."

Machine extruded or slipformed is permitted in most specifications, but note how it is permitted: as a contractor's option, not as the specified method. Ohio DOT again: "The Contractor may use a self-propelled machine to place concrete curb or curb and gutter. Force the concrete through a mold of the proper cross-section to obtain the proper density." Memphis is more explicit still: extruding machines "may be used if approved by the Owner."

Precast is manufactured in a plant, cured there, trucked in and set. That one difference, that it arrives cured, is what drives everything else about it.

One consequence worth knowing before you compare prices: because extrusion is a method inside the cast-in-place pay item rather than a pay item of its own, no bid tabulation anywhere carries a separate unit price for extruded curb. So there is no honest published price comparison between extruded and formed curb, and anyone showing you one has made it up.

Which agencies actually allow precast curb

This is worth checking before you specify it, because the answer is not uniform.

So precast curb is a minority but genuine option in public work, and municipal practice is where all three methods most often sit side by side as parallel standard plans.

Sizes and weights, published and derived

Only one manufacturer in this research publishes a weight, so the rest have to be derived, and the derivation turns up something useful about unit weight. United's 20 inch section is a trapezoid of (6 + 7) / 2 x 20 = 130 square inches, which is 0.903 cubic feet per linear foot. At the usual 145 lb per cubic foot rule of thumb that is 131 lb per foot; at 150 it is 135, which matches their published figure exactly. Reinforced, low-slump, machine-consolidated precast runs denser than plain concrete, and if you are sizing lifting equipment, use 150.

On that basis the Scituate 18 inch section is about 118 lb per foot, so an 8 foot piece is roughly 940 lb. That is the number that decides whether a crew sets it by hand or brings a machine.

A useful reference point: NJDOT's standard 9 by 16 inch concrete vertical curb has a cross-section of exactly 1.000 square foot, so it is 145 lb of concrete per linear foot cast in place. A 20 inch precast section is about the same mass per foot as a standard DOT vertical curb.

Both precast manufacturers publish 5,000 psi at 28 days, with one adding "Entrained air: 6-7% controlled" and two #4 bars with fiber. Compare that with the 3,000 to 3,500 psi typical of cast-in-place curb in the same specifications. That strength difference is the clearest real advantage of plant production, and it is the one thing precast marketing understates rather than overstates.

Parking curbs and wheel stops

The parking curb, car stop or wheel stop is the other half of what people mean by precast curb. Published dimensions settle around a 5-1/4 by 7-1/2 inch section in 4, 6 and 8 foot lengths, at 105, 165 and 210 lb respectively from one manufacturer, with two #4 bars to ASTM A615 Grade 60, two #5 anchor pins, and "4,500 PSI minimum (ASTM C39, cylinder-tested)".

The weight ratio against the alternatives is the whole argument, on both sides. A 4 by 6 by 72 inch rubber or recycled plastic unit weighs about 38 lb. The same envelope in concrete is exactly one cubic foot, so 145 lb: 3.8 times heavier for the identical shape. Concrete stays where it is put without relying on its fasteners. Rubber can be carried and set by one person with a drill, which is why the rubber units in a published master specification have five anchor holes against concrete's two pins: the light unit depends entirely on its anchors.

Prices, derived from published figures: concrete 6 foot units at $38.85 to $85 each, which is $6.47 to $14.17 per linear foot; rubber $25 to $40, so $4.17 to $6.67; recycled plastic $20 to $30, so $3.33 to $5.00.

On which material lasts, the two fullest sources contradict each other and both are conflicted. A concrete wheel stop manufacturer rates rubber as degrading under UV and impact and needing re-anchoring every one to two years, and plastic as the shortest-lived. A trade publication says the opposite of rubber, that it resists UV, moisture and chemicals and "does not chip or crack even with repeated impacts", while concrete gets "chipped and cracked from repeated contact" and needs repainting. One sells concrete and the other does not sell either. No standards body, agency or university has compared them, so there is nothing to break the tie.

There is also no national product standard for a concrete wheel stop at all. No ASTM, AASHTO or ANSI specification covers it. The strengths and dimensions above are manufacturer practice, and where a size is mandated it is mandated by a local zoning code.

The ADA question, and the federal contradiction underneath it

Two things get asked here constantly and both have clean answers.

Is a wheel stop required by the ADA? No. Section 502.7 of the 2010 Standards sets a performance requirement: "Parking spaces and access aisles shall be designed so that cars and vans, when parked, cannot obstruct the required clear width of adjacent accessible routes." The accompanying Advisory 502.7 then says "Wheel stops are an effective way to prevent vehicle overhangs from reducing the clear width of accessible routes." An advisory is explanatory, not mandatory, so a wheel stop is a recommended solution to a mandatory requirement, not a requirement itself.

May a wheel stop sit in the access aisle? No. The access aisle must be 60 inches wide minimum under 502.3.1, and under 502.4 "Changes in level are not permitted" in it. The Access Board's own guide adds that "Bollards, signs, columns, or other elements cannot be located in the access aisle". A wheel stop is a change in level.

And here is the contradiction nobody writes about. The ADA Standards' Advisory 502.7 recommends wheel stops. NIOSH, a US federal public health agency, says in print that they should not be used: "Concrete wheel stops in parking lots can be a tripping hazard and should not be used." Two federal documents, opposite advice, both current.

And NIOSH is not alone in that direction. An insurer's loss control bulletin states that wheel stops "are responsible for many trips and falls by pedestrians in parking lots", that they "may interfere with snow plowing in cold weather climates", and that "In many parking lots, paint striping is adequate to provide separation between vehicles". A professional position paper by a certified access specialist and two architects reports that ASTM F1637 on safe walking surfaces says parking lots "should be designed to avoid the use of wheel stops", and that the ITE Traffic Engineering Handbook recommends confining them to places pedestrians cannot walk. We have not read the ASTM or ITE text ourselves, because both are paywalled, so treat those two as reported by that paper rather than quoted from source.

The reconciliation is placement, and it is the practical answer. A wheel stop against a wall or a boundary where nobody walks does the overhang job the ADA advisory wants. A wheel stop across a pedestrian path is the trip hazard NIOSH is describing. The two documents are not really arguing about the product, they are arguing about where it goes.

How far back, and nobody federal will tell you

ADA 502.7 states the requirement and gives no overhang dimension at all. That number comes from local standards, and they disagree:

Three different answers to the same question, all defensible, none national. If you are designing to it, the governing number is your municipality's, and 2 to 3 feet is the band they sit in.

One more negative finding worth having: PROWAG, the public right-of-way accessibility guidelines, contains no wheel stop provision whatsoever. What it does impose is indirect: a 48 inch minimum continuous clear width "exclusive of the width of any curb", a quarter-inch limit on changes in level, and an obstruction-free center half of an on-street parking space.

Setting it

The published requirements are consistent across the agencies that have them, and they are more demanding than "drop it on the ground".

• A prepared bed. Hawaii DOT: "Place bed course material a minimum of 4 inches in depth. Compact with at least three passes of lightweight mechanical tamper, roller, or vibratory system."
• A mortar bed, full length and breadth. WSDOT: the curb "shall be firmly bedded for its entire length and breadth on a mortar bed" of one part cement to two parts sand, and "The anchor grooves in the bottom of the curb shall be entirely filled with the mortar."
• Mortared joints. Hawaii: "Set precast blocks approximately 1/2 inch apart and fill joints with mortar." WSDOT: all joints except designated expansion joints "shall be filled with mortar composed of one part Portland cement and two parts sand."
• A tight alignment tolerance. WSDOT allows a "maximum tolerance of 1/16 inch" between pieces, which tells you this is deliberate piece-by-piece work rather than a fast method.
• Expansion joints. Hawaii specifies half-inch preformed filler shaped to the curb cross-section.

Manufacturers add an interlocking dowel pin system, typically a 1 inch diameter pin into a 3 to 4 inch deep socket, plus 6 inch lengths of #5 rebar as connecting pins.

Parking curbs are anchored with two pins, usually 5/8 inch rebar at 16 to 24 inches long. One municipality specifies 24 inch anchors on unpaved lots specifically. Nobody publishes a required embedment by pavement type, so the asphalt-versus-concrete question that every installer asks has no sourced answer.

Precast against cast-in-place against extruded

A gap you should know about before trusting any comparison, including other people's: no DOT, no NCHRP or TRB study and no university has published a comparison of the three methods on cost, durability or performance. The one life-cycle study we found compares granite against precast concrete, assumes rather than measures the service lives, and was sponsored by a granite producer. NCHRP Report 537 compares curb geometries for vehicle safety, not production methods.

On that safety point, since it governs where any curb can go: AASHTO policy is that "if a curb is used in conjunction with a traffic barrier, the height of a vertical curb should be limited to 100 mm or it should be of the sloping type", and that opening condition matters, because the 4 inch limit applies in front of a barrier rather than to every curb (see the curb height standards for how often it gets dropped). Meanwhile WSDOT's design manual limits a 6 inch extruded curb to 50 mph and below while allowing 4 inch at any posted speed. Mountable curb covers the geometry side.

What it costs, and the hole in the data

Start with the gap, because it is unusual. No state DOT bid tabulation we could find carries a precast curb pay item with a quantity. Hawaii, which names precast as a curb type, pays for it "on a lump sum basis. Measurement for payment will not apply", which structurally prevents a per-foot price ever appearing in a Hawaii bid tab. So precast roadway curb has no bid-grade dollar per linear foot, while cast-in-place curb has thousands of them.

What can be priced is the parking curb, from published unit prices: $6.47 to $14.17 per linear foot of concrete unit bare, and roughly $13 to $18 with anchors and setting. For cast-in-place curb at public bid prices, with quantities, see concrete curb cost, which has nine jurisdictions and the small-job premium quantified.

Freight matters more here than on anything else on this site. These are 940 lb pieces. A price per unit at the plant gate is not a price delivered, and nobody publishes the delivery component.

What fails, and the service life nobody publishes

Joints are the inherent weakness, because precast has one every 3 to 8 feet where cast-in-place has one every 10 to 15. That is exactly why the specifications are so insistent about the bed: a 4 inch compacted bed course with three passes of a tamper, and a full-bearing mortar bed with the anchor grooves filled. Get the bed wrong and the joints tell you. No source quantifies joint opening or differential settlement rates, so the magnitude is unpublished.

Freeze-thaw and de-icer scaling are handled by prescription rather than by field data: air entrainment at 4 to 7 percent in the DOT specifications, 5 to 7 in the federal guide specification, 6 to 7 controlled in one precast plant's published figures. Precast has one genuine edge here that is testable at the plant rather than argued about afterwards, though note that the only pass-fail freeze-thaw criterion we found for a product of this kind belongs to an architectural cast stone standard, not to any curb standard.

Snowplough damage is the most asserted and least documented claim in the category. Every contractor page mentions it. We found no DOT study, no maintenance manual quantification and no published damage rate comparing precast with cast-in-place. The only institutional mention is an insurer noting that wheel stops interfere with ploughing.

And there is no service life figure for concrete curb of any production method, from any independent source. The numbers in circulation are an industry-sponsored study's assumed 10 and 20 year scenarios and manufacturers' unquantified "life of the pavement" claims. We are not going to give you a figure either.

For repair rather than replacement, see concrete curb repair.

Sources

• Hawaii DOT Section 638, Portland Cement Concrete Curb and Gutter - precast named as Type 3, the 4 inch compacted bed course with three tamper passes, the half-inch mortared joints, and the lump sum payment basis that is why no per-foot price exists.
• WSDOT Standard Plan GD-1 special provision, Precast Traffic Curb - the full-bearing mortar bed, the anchor grooves filled with mortar, the one part cement to two parts sand joint mortar, and the 1/16 inch alignment tolerance. The standard drawing carries the Type A and Type C dimensions.
• MaineDOT Standard Detail 609(08), Precast Concrete Transition Curb - precasting as an explicit contractor election, and the concrete class and reinforcing references.
• Ohio DOT Item 609, Curbing - the cast-in-place default, the 1 in 20 batter, the porous bed on clay, and the extrusion machine as a contractor option.
• United Concrete Products curbing brochure - the 20 inch section at 135 lb per linear foot, which is the only published weight we found, plus radii from 2 to 50 ft, transition pieces, 5,000 psi and the connecting pin detail.
• Scituate Concrete Products curbing brochure - 5,000 psi at 28 days, 6 to 7 percent controlled entrained air, two #4 bars with fiber, and the 1 inch dowel pin system.
• US Access Board, 2010 ADA Standards Chapter 5, Parking - section 502.3.1's 60 inch access aisle, 502.4's prohibition on changes in level, 502.7's requirement, and Advisory 502.7 naming wheel stops as "an effective way" to meet it. The Access Board's parking guide adds that elements cannot be located in the access aisle.
• NIOSH Publication 2011-123, Slip, Trip, and Fall Prevention for Healthcare Workers - page 17, "Concrete wheel stops in parking lots can be a tripping hazard and should not be used." A federal health agency saying in print the opposite of the ADA advisory.
• ISO Services loss control bulletin, Wheel Stops: A Hazard in Parking Lots - trips and falls, interference with snow ploughing, and the observation that striping is often sufficient. An insurer, so institutional rather than a standard, and it gives no statistics.
• Haughton, Agnello and Field, Let's Eliminate Parking Wheel Stops at Busy Storefronts - a professional position paper, and the route by which the ASTM F1637 and ITE Traffic Engineering Handbook positions are reported. Both of those are paywalled and we have not read either directly.
• PROWAG technical provisions - the 48 inch continuous clear width "exclusive of the width of any curb", the change-in-level limits, and the absence of any wheel stop provision.
• Wilmington NC off-street parking standards, Santa Barbara parking design standards and Milford OH section 1187.06 - the three different local answers to setback, overhang and wheel stop dimensions.
• Paveman Pro on concrete against rubber wheel stops and APC Wheel Stops' own comparison - the two fullest material comparisons, reaching opposite conclusions. One is trade press and the other manufactures concrete stops; both are cited here so you can see the disagreement rather than a resolution of it.
• UFGS 32 16 19, Concrete Curbs, Gutters and Sidewalks - the federal guide specification, read specifically for precast provisions, which it does not contain.