Concrete curb, gutter, and sidewalk: the site flatwork field guide

Site concrete flatwork, and where it fits the job

Site concrete flatwork is the cast-in-place concrete around a building and a parking lot that nobody parks a truck on but everybody depends on: the curb, the gutter, the sidewalk, the driveway approach, and the pads and aprons that tie the structure to the lot. It does two jobs at once. It moves water where you want it, and it moves people from the car to the door without a step or a heave in the way. The pavement carries the traffic. The flatwork drains it and walks it.

Three things decide whether site flatwork is right: drainage, accessibility, and durability. The curb and gutter has to drain, so it lives or dies on the flow line and the grade. The sidewalk and the curb ramp have to be accessible, so they live on slope, and the slope is governed by federal law, not by taste. And all of it has to last through freeze and salt and the snowplow, so it lives on the mix, the joints, and the cure. Miss the drainage and the lot ponds. Miss the slope and the lot fails an ADA check. Miss the cure and the surface scales off in two winters.

The geometry is not yours to invent. Curb height, gutter pan width, the curb shape, the sidewalk width, and the approach detail come from the local agency standard detail, the DOT or city or county drawing the project is held to, and that detail governs. This guide walks the chain from the string line to the day the owner takes it. For the rigid slab that carries traffic, the joint sawcut window, and the curing compound in detail, the concrete pavement jointing and curing guide is the companion to this one.

What slope does curb and gutter need to drain?

Curb and gutter drains along the flow line, the low invert where the gutter pan meets the face of the curb, and that flow line needs a positive longitudinal grade the whole way to an inlet. A common minimum is in the range of 0.4 to 0.5 percent, and some agencies want more, around 0.7 percent, because a flatter gutter silts up and ponds. The flow line is not the top of the curb and it is not the lip of the pavement. It is the bottom of the channel, and that is the line you set grade to and the line water actually follows.

The killer here is the birdbath: a sag in the flow line where water stops instead of running. It comes from a low form, a stake that walked, or a hand-formed transition that lost grade through a curb return. Water sits there, freezes, stains, and grows algae, and on the day of the inspection somebody pours a bottle of water in the gutter and watches where it goes. If it does not run to the inlet, you own the fix, and fixing a sag in finished curb means saw it out and re-pour. Shoot the flow line with a level or a laser before you place, not after.

The gutter pan itself slopes across toward the curb so water collects at the flow line, commonly on the order of a few percent of cross slope across the pan, and the pan width is a spec dimension that ranges by detail, often around 12 to 24 in. Set the flow-line grade first, then the pan and the curb height follow it. The rule that holds on every site is positive drainage to the inlet with no flat spot and no reverse, and the agency standard detail sets the actual numbers, so confirm the minimum grade and the pan dimension against the drawing before you set the string.

The subgrade and base under the flatwork

Flatwork fails from the bottom as often as the top, and the bottom is the subgrade and the base under the slab. The subgrade is the prepared, compacted native soil. The base is the granular layer on top of it, and on most curb, gutter, and sidewalk work it is a few inches of compacted aggregate that gives the slab a uniform, free-draining bearing surface. The slab does not need a thick structural section the way a truck-loaded pavement does. It needs uniform support and it needs water out from under it.

Uniform is the word. A soft spot under a sidewalk panel lets that panel settle while its neighbor stays put, and now you have a faulted joint and a trip hazard the owner trips somebody on. A soft spot under a curb lets the curb crack and rotate. Proof-roll or probe the subgrade and chase the soft spots before the base goes down, because a soft spot you find with a probe costs a wheelbarrow of stone and a soft spot you find after the pour costs a saw and a re-pour. The same uniform-support principle runs under the rigid pavement in the concrete pavement jointing and curing guide, and it starts here.

Compact the base, trim it to grade, and dampen it before you place so it does not pull water out of the bottom of the fresh concrete. A slab placed on a dry, dusty base loses water out the bottom and that face never cures right. In freeze country, get the base draining, because water trapped under a sidewalk freezes, heaves the panel, and cracks it from below. The concrete is only as good as what it lands on.

How do you form curb and gutter, and what is slip-form?

Curb and gutter goes down one of two ways: hand-formed, or slip-form. Hand-formed work, also called cast-in-place on stationary forms, sets steel or wood forms to grade on stakes, places concrete between them, strikes it off, and finishes it by hand with a curb tool that shapes the face and the pan. It is the method for short runs, tight radii, curb returns, handicap ramps, transitions, and anywhere the geometry changes, because a person can follow a curve and a varying section that a machine cannot. The labor is high and the production is slow, but the control is total.

Slip-form curb is the production method. A slip-form machine, often a curb-and-gutter machine running off a stringline or a stringless guidance system, takes concrete into a hopper, drives it through a mold shaped to the exact curb section, and extrudes a continuous, finished curb and gutter behind it in one pass with no forms to set or strip. It runs straight or large-radius work fast, lays a consistent section, wastes less concrete, and cuts the labor a hand crew needs. The trade-off is that a slip-form machine wants a stiff, low-slump mix that holds its shape coming out of the mold, and it does not do tight radii or constantly changing sections well.

Most real jobs use both. The machine runs the long tangents and the sweeping curves, and a hand crew forms the returns, the ramps, the transitions, and the tie-ins the machine cannot reach. Whichever way the curb goes down, the section has to match the agency standard detail and the flow line has to hold grade. A slip-form run that drifts off the stringline lays a beautiful curb to the wrong line, so the stringline and the grade control are the job, not the machine.

Curb and gutter shapes: barrier, mountable, roll, and integral

The curb shape is a design call with consequences for drainage, parking, and fire access, and the names shift by jurisdiction, so always tie the shape back to the detail number on the plans. Barrier curb, also called vertical or Type A in many places, has a vertical or near-vertical face, commonly around 6 in high, and it keeps vehicles on the pavement and channels water hard against the flow line. It is the default along streets and lot edges where you want a real edge.

Mountable curb has a sloped face, often around a 3:1 or 4:1 batter and a lower height near 4 to 6 in, so a vehicle, usually a fire apparatus, can drive over it without damage. Roll curb takes that further with a rounded profile a car can cross at low speed, which is why it shows up at residential driveways and crossovers where vehicles need to mount the curb anywhere along it. Roll curb drains and parks differently than barrier curb, so it is a deliberate choice, not a substitute.

Curb and gutter can be cast as one integral section, the combination curb-and-gutter most lots and streets use, or the curb can be cast monolithic with the pavement, or the curb can be a separate piece placed against existing pavement. Integral curb-and-gutter is the common economical form: one pour gives you the curb, the pan, and the flow line together. The curb height, the gutter pan width, the face batter, and the reveal are all spec dimensions on the standard detail, so confirm the shape and the numbers against the drawing before you set forms or fill the machine.

One field note that costs money when missed: the curb height is the reveal above the finished pavement, not above the gutter pan or the base. If the pavement comes in thicker or thinner than planned, the reveal changes, and a curb that reveals 4 in where the detail wants 6 in is a curb that does not hold water or stop a tire. Tie the curb height to the finished pavement grade, not to the base you are standing on.

The concrete mix for exterior flatwork

Exterior flatwork in freeze country lives or dies on the mix, and the two numbers that matter most are strength and air. A common specified strength for exterior curb, gutter, and sidewalk exposed to freezing is 4000 psi at 28 days, and the reason is durability against freeze-thaw and deicing salt, not load. The slab is not carrying much. It is fighting water and ice for thirty years.

Air entrainment is the one that protects the surface. Entrained air puts millions of microscopic bubbles in the paste, and when water in the concrete freezes those bubbles give the ice room to expand without blowing the surface apart. For exterior flatwork in a severe freeze-thaw exposure, a common target is on the order of 5 to 7.5 percent air, often near 6 percent for 3/4 in aggregate, and you verify it on the truck with an air meter before you place, not after. No air in an exterior slab and the surface scales off in the first hard winter with salt on it. That failure is permanent and it shows up after you are gone.

Slump is workability, and on flatwork you want it stiff enough to hold an edge and a finish, commonly in the 3 to 5 in range for hand work and stiffer still for slip-form curb that has to stand up coming out of the mold. The thing rookies do is add water at the truck to make the pour easier, which raises the slump, drops the strength, and brings extra bleed water that wrecks the finish. Order the right mix and place it as batched. The exact strength, air, slump, and aggregate are spec items, so the mix design and the project specification control the numbers, not the gut feel at the chute.

Placing and finishing: screed, float, and the broom

On flat work the sequence is place, consolidate, screed to grade, float, edge and joint, then texture. Place the concrete close to final grade so you are not dragging it across the slab. Consolidate it enough to close it around any steel and against the forms without overworking it. Strike it off with a screed riding the forms or the grade so the surface matches the flow line and the cross slope you set. Then float it with a bull float to knock the ridges down and bring up a tight, closed surface.

The cardinal rule, and the most common rookie failure on flatwork, is no finishing while bleed water is on the surface. Concrete bleeds water to the top after placement, and if you float or trowel that water back in, you seal a weak, high-water layer right at the surface, and that layer is exactly what dusts, scales, and crazes under traffic and salt. Wait for the sheen to leave. On a hot, windy day the bleed water can flash off before it ever shows, so judge the surface, not the clock.

The texture on a sidewalk is a broom finish, and it is a safety item, not a look. After floating, drag a stiff-bristled broom across the surface to leave grooves commonly about 1/16 to 1/8 in deep, run perpendicular to the direction of travel, so the tooth gives a pedestrian grip when the walk is wet or iced. Perpendicular to travel matters: grooves running with the walk channel water but do little for a foot sliding forward. On a curb ramp the broom tooth is what keeps a wheel and a shoe from slipping on the slope. A troweled, slick walk is a slip claim waiting to happen, which is why exterior walks get broomed and interior floors do not.

How far apart are sidewalk joints?

Sidewalk joints come in two families, and getting them right is what keeps the walk from cracking at random. Contraction joints, the tooled or sawed grooves across the walk, control shrinkage cracking by giving the crack a planned line to follow, and on a sidewalk they are commonly spaced at roughly the width of the walk: a 4 to 5 ft walk gets contraction joints near every 4 to 5 ft. The broader rule of thumb caps contraction joint spacing at about 24 to 36 times the slab thickness, so a 4 in walk would top out near 8 to 12 ft, but on sidewalks the practice runs tighter, close to the walk width, because narrow panels look right and crack clean.

Expansion and isolation joints are the other family, and they do a different job. An isolation joint is a full-depth separation with a compressible filler that lets the flatwork move independently of anything fixed it should not be tied to, and that is where it goes: against the building foundation, against the curb where the sidewalk meets it, around light poles, hydrants, manholes, utility vaults, and at the start of every approach. Put an isolation joint where the walk meets the building, always. Bond a sidewalk hard to a building foundation and the two move differently, and the walk cracks at the wall or pries on it.

Full-width expansion joints also show up at intervals on long runs of curb and sidewalk, with spacing that varies widely by agency, often somewhere in the range of every 40 to 60 ft and at all radius points and structures on curb, but the interval is a spec call, so confirm the detail. The contraction joint depth and the sawcut timing follow the same physics covered in the concrete pavement jointing and curing guide: deep enough and early enough to pull the crack down to the groove before the slab cracks on its own. Lay the joint pattern out before the pour, isolate every fixed object, and the walk cracks where you put the joints instead of wherever it wants.

What does ADA require at a curb ramp?

Where the accessible route steps up a curb, a curb ramp carries it, and the slopes are governed by federal accessibility standards, not by what fits. The running slope of the ramp run is 1:12 maximum, about 8.3 percent, and the cross slope is held to 1:48, about 2 percent, the same flat limit that applies to the sidewalk and the accessible route. The flared sides where someone might walk across them are commonly held to 1:10, and the ramp needs a level landing at the top so a wheelchair is not parked on the slope. These are maximums, so build the ramp run closer to 7.5 percent and the cross slope closer to 1.5 percent, because a ramp shot right at the limit has no margin and the inspector's level will find the tenth of a percent the finish work crept over.

Detectable warnings are the truncated-dome panels, the textured field a cane and a foot can read that warns of the edge between the walk and the vehicular way. Truncated domes are the only detectable warning surface the federal Access Board recognizes, and the federal accessibility guidelines for public rights-of-way (PROWAG) require them at curb ramps, with a defined dome size, height near 0.2 in, and spacing. Set the dome rows so a wheelchair can track between them, perpendicular to the grade break. Whether a given curb ramp must carry domes, and the color and placement, depend on the standard the project is held to and the AHJ, so confirm it before you order the panels.

Sidewalks and the accessible route carry their own limits: the route holds a running slope no steeper than 1:20, about 5 percent, before it has to be built as a ramp, and a cross slope no steeper than 1:48, about 2 percent. The accessible parking stalls, the access aisles, the stall count, and the signage that tie into this flatwork are their own subject, covered in the parking lot ADA accessibility layout guide. The numbers are enforceable law and state codes can be stricter, so the adopted standard and the local amendments control, and these are the items a plaintiff checks from the parking lot with a level.

Driveways, approaches, and heavy-load flatwork

The driveway approach, or apron, is the piece of flatwork that takes a real wheel load, so it is built heavier than the sidewalk it crosses. Where a sidewalk is commonly 4 in thick, an approach is commonly 6 in or more, because the apron carries vehicles turning in off the street and a 4 in slab cracks under that. Many jurisdictions set the apron thickness in their standard detail, often a minimum around 6 in, and that detail governs. Carry the thickness through the whole approach, not just the middle, and thicken the edge where the load concentrates.

A thickened edge is the cheap insurance on a loaded slab. Deepening the perimeter of an apron or a loaded pad, commonly to 6 in or more for a strip in from the edge, gives the slab a beam at the edge where the wheel hits and keeps the corner from breaking off. On heavier site pads, a transformer pad, a generator pad, a dumpster pad, or a loading apron, the thickness, the steel, and the edge detail come off the structural drawings, because the load is the reason the slab is concrete in the first place.

Where the approach meets the curb and the street, isolate it. The approach moves with traffic and temperature differently than the curb and the walk, so an isolation joint at the curb line and at the sidewalk keeps the approach from prying on them. The same goes for the dumpster pad against the curb and the loading apron against the building. Heavy-load flatwork is a designed structure, so build it to the structural detail and do not value-engineer the thickness or the steel on the fly at the truck.

Reinforcement: where steel earns its place

Most curb, gutter, and sidewalk is plain concrete with no structural steel in it, and that is by design. Plain flatwork controls cracking with joints, not bars, and adding mesh to a sidewalk that is jointed right buys little except a place for the finisher to step it down into the bleed water. The steel earns its place at specific spots, not across the whole slab.

At construction joints and across joints that have to transfer load, the bars matter. Smooth dowels carry a wheel load across a transverse joint while letting the joint open and close, and deformed tie bars hold a longitudinal joint or a curb tight to the slab beside it without sliding. The two look similar and do opposite jobs, and swapping them is a classic costly error: a smooth sliding dowel where you needed a tie lets the pieces drift apart, and a bonded tie bar across a joint that needs to open locks it and cracks the slab. The dowel-versus-tie-bar distinction, the sizes, and the placement are laid out in the concrete pavement jointing and curing guide, and they apply wherever a curb or approach joint has to carry or hold.

Welded wire mesh or light bars show up where the slab is loaded or restrained: thickened approaches, heavy pads, slabs over questionable subgrade, and where the detail calls for it. When mesh goes in, it has to sit in the upper third of the slab to do anything, held up on chairs, not dragged up off the ground with a hook after the concrete is placed, which is where it usually ends up doing nothing on the bottom. Put steel where the plans call for it, at the height the plans call for, and leave it out where the joints do the work.

How do you cure curb, gutter, and sidewalk?

You cure flatwork by keeping water in the surface long enough for the cement to gain strength, and on flatwork that is harder than on almost any other pour because the slab is nearly all surface: thin, flat, and fully open to sun and wind. Lose that water and the top of the slab stops gaining strength, then dusts, scales, and crazes under the first salt. The cure is not a finishing nicety on exterior flatwork. It is the difference between a surface that lasts and one that powders off.

Two methods do the work. A liquid membrane-forming curing compound sprayed over the surface right after the broom finish seals the water in, and on flatwork a white-pigmented compound is the common choice because it reflects heat and shows you where you have and have not sprayed. Wet curing, keeping the surface continuously damp under wet burlap, cotton mats, or a soaker for several days, is the other method and the more thorough one where the spec calls for it. Either way the cure goes on right behind the finish, while the surface is still damp, not after it has flashed off in the wind.

The worst curing failures on flatwork are not no-cure, they are late-cure and thin-cure: a crew that lets the broomed walk sit twenty minutes too long in the sun before spraying, or runs the spray rig too fast and lays a film you can see through. On a hot, dry, windy day the slab loses water fastest, and that is the day the cure matters most, so get it on fast. The curing compound type, the rate, and the wet-cure duration are spec items, and the concrete pavement jointing and curing guide covers the compound and the timing in detail.

Hot and cold weather, and the timing

Weather attacks the two things that make flatwork last: the cure and the finish window. In hot, dry, windy conditions the surface crusts while the inside is still soft, the bleed water flashes off before it shows, and the slab races toward set. The moves are practical: cool the mix and dampen the base, place in the cooler part of the day, keep evaporation retarder on hand for the surface, and get the broom and the cure on fast because the window is short. Plastic shrinkage cracks, the short random surface cracks that open before the slab is hard, are a hot, windy-day failure, and they come from water leaving the surface faster than the slab can bleed it back.

Cold is the opposite problem. Below about 40 degrees F the hydration reaction slows and strength gain stalls, and if the fresh slab freezes before it reaches a set strength the paste is damaged for good. The number people miss is the base. Place on frozen ground and the bottom of the slab never cures right no matter what you do on top. Keep the base from freezing, protect the fresh flatwork with insulating blankets, and plan the protection before the truck shows up, not after. The ACI cold-weather and hot-weather provisions give the framework, and the project spec sets the limits.

Timing ties it together on every pour. The finishing window, the jointing window, and the cure all run on the clock from the moment the concrete starts to set, and that clock speeds up in the heat and slows down in the cold. The skill is reading the slab and staging the crew so the broom and the cure land in the window instead of chasing it.

What does the inspector check on flatwork?

The inspector checks the things that are visible and measurable from the lot, and on flatwork that is a short, hard list. Grade and drainage first: a level or a laser on the flow line and a water test in the gutter to confirm it runs to the inlet with no birdbath. Thickness next, often by coring or by checking the edge at the forms, because a sidewalk that came in at 3 in where the detail wants 4 in is a finding. Then the joints: spacing, depth, and an isolation joint at every fixed object and the building.

Slope is where the punch list fills up on the accessible work. The inspector puts the level on the curb ramp run, the cross slope, the landing, and the sidewalk both ways, and a reading over the limit is a finding that cannot be painted out: it is a grind or a re-pour. The detectable warnings get checked for presence, placement, and dome pattern where they are required. The finish gets checked for the broom texture and for scaling, dusting, or crazing that says the cure was missed.

Build the as-built check into your own punch before you call for inspection. Shoot the flow line and the ramp slopes and write the readings down. Water-test the gutter. Tape the widths and the joint spacing. Finding your own slope failure costs a grind. Finding it after the owner has opened costs a grind plus a complaint, and on the ADA items it can cost a lot more than that.

Campus and data center sitework

On a commercial campus or a data center, the site flatwork is a system, not a few isolated pours, and it carries more weight than people expect for concrete nobody parks on. The curb and gutter has to drain a large impervious site to the storm system without ponding, the accessible routes have to connect every entrance people use, and the heavy pads, the generator pads, the transformer pads, the fuel pads, and the equipment aprons, are designed slabs on the structural drawings, not standard details.

What changes at this scale is the coordination and the consequence. The flow lines tie into a designed storm network, so a birdbath in a gutter is not just unsightly, it backs up an inlet the hydraulics counted on. The accessible routes have to be dispersed to each building, which is the same logic the parking lot ADA accessibility layout guide applies to the accessible stalls. And the equipment pads see sustained point loads and sometimes fuel and heat, so the thickness, the steel, the isolation around conduit stub-ups and bollards, and the cure all matter more, because a void or a scaled surface under a loaded pad fails fast.

Treat the heavy pads as the designed structures they are and build the curb, gutter, and walks to the agency and project details. The site is large enough that a layout error repeats across the whole job before anyone catches it, so verify the grade, the slope, and the detail on the first pour, not the fortieth.

What the owner has to maintain

Site flatwork is the part of a project the owner deals with for decades, so a foreman who builds it right is building down the owner's maintenance bill. Two things drive that bill: water and movement. Seal the joints and keep the flow lines draining and the flatwork lasts. Let water sit in the joints and under the slab and it works the concrete apart freeze by freeze.

Joint sealing is the maintenance the owner inherits whether they know it or not. The contraction and isolation joints get sealed to keep water and grit out, and that sealant has a life and gets renewed. Skip it or let it fail and water runs down the joint, undermines the base, and the panels start to rock and fault. A faulted joint is a trip hazard, and a trip hazard on a public walk is a claim, which is the version of this problem that ends up with a lawyer instead of a caulk gun.

The trip hazard is the failure mode the owner cares about most, because it is the one that hurts somebody. A panel that heaved on a frozen base, a corner that broke off an under-thick approach, a joint that faulted because the base pumped out: each is a vertical lip a foot catches. Many jurisdictions set a vertical offset, often around 1/4 to 1/2 in, above which a walk is a hazard that has to be ground, shimmed, or replaced. Build the base uniform, drain the joints, and cure the surface, and the owner inherits a walk to sweep instead of a walk to grind and defend.

What to document

The flatwork you cannot defend later is the one nobody wrote down. When a gutter ponds, a panel faults, or a ramp fails a slope check a year out, the record is what tells you whether the flow line was shot, the slab was the right thickness, the joints were placed, and the slope was held. Capture it as you build, element by element, while the crew is still on site with the level and the tape.

For each run or pour, record the element and the standard detail it was built to, the curb shape and height and gutter pan width, the slab thickness, the base type and compaction, the mix strength and air, the flow-line grade and the as-built drainage check, the joint type and spacing and the isolation joints placed, the running and cross slope on any ramp or accessible route, the finish and the cure, and the weather on the day. Note who checked the slope and the grade, because the ADA readings are the ones that get challenged.

Common mistakes

• Building a flow line that ponds, with a sag or a flat spot or a reverse instead of positive drainage to the inlet.
• Tying the curb height to the base instead of the finished pavement, so the reveal comes out wrong.
• Placing on a soft spot or a dry, dusty, or frozen base so the panel settles or the bottom never cures.
• Missing or random joints, so the slab cracks where it wants instead of at a planned line.
• Leaving out the isolation joint where the walk meets the building, so the walk cracks at the wall.
• Shooting an ADA curb ramp or sidewalk past the slope limit, which is a grind or a re-pour, not a re-stripe.
• Adding water at the truck to ease placement, dropping the strength and bringing bleed water that wrecks the finish.
• Finishing while bleed water is on the surface, sealing a weak high-water layer into the top.
• Troweling the walk slick instead of brooming it, leaving no slip resistance when it is wet or iced.
• Skipping or thinning the cure, so the surface dusts, scales, and crazes in the first salted winter.

Field checklist

Standards and references

The geometry of site flatwork is governed first by the local agency standard detail, the city, county, or DOT drawing the project is held to, and that detail sets the curb height, the gutter pan width, the curb shape, the sidewalk width, the approach thickness, and the joint layout. When the geometry is in question, the standard detail and the project specification settle it, not a rule of thumb in this guide. Do not invent a detail number on a submittal. Name the requirement and cite the detail you have confirmed.

ACI covers the concrete side. ACI 330 addresses concrete parking lots and site paving, and ACI 302 addresses concrete floor and slab finishing, both useful frameworks for the mix, the placing, and the finishing of flatwork. The exterior-exposure mix, the 4000 psi range and the air content for freeze-thaw, traces to ACI 318 durability provisions, and ACI cold-weather and hot-weather provisions cover placement in temperature extremes. Confirm the current edition, because they revise on a cycle.

The accessible work is governed by the ADA Standards and, for the public right-of-way, the federal accessibility guidelines for public rights-of-way (PROWAG), which set the curb ramp slopes, the cross-slope limit, and the detectable-warning requirements. State and local codes layer on top and are frequently stricter, and where they are, the stricter rule applies and it is enforceable, not advisory. Materials and test methods carry ASTM numbers, including the slump test, the compressive strength test, the air content test, and the curing compound specification. Cite the standard that controls the point, verify the section against the adopted edition, and let the project spec and the agency detail control the value.

Units, terms, and conversions

Site flatwork carries a vocabulary that shifts between the plan, the spec, and the field tape, so the same idea reads a few ways across a job.

Slope shows up as a ratio (1:48, 1:12), as a percentage (about 2 percent, about 8.3 percent), and as rise over run, and they are the same limit stated differently. The flow line is the low invert of the gutter where the pan meets the curb face, the line water follows. A contraction joint is also called a control joint. An isolation joint is the modern term for what older plans call an expansion joint, and it separates flatwork from a fixed object. Curb height is the reveal above the finished pavement, in inches on US plans and millimeters on metric ones. Strength reads in psi or MPa, slump in inches or millimeters, and air content as a percentage of the concrete volume.

Flow line

The low invert of the gutter where the pan meets the curb face; the line water follows, graded to drain

Gutter pan

The flat channel between the curb face and the pavement that carries water to the flow line

Barrier / mountable / roll curb

Curb shapes by face: vertical (barrier), sloped to drive over (mountable), or rounded (roll)

Slip-form curb

Curb and gutter extruded continuously through a machine mold, no stationary forms to set or strip

Isolation (expansion) joint

A full-depth joint separating flatwork from a fixed object such as a building, pole, or curb

Broom finish

Surface texture dragged perpendicular to travel, ~1/16 to 1/8 in deep, for slip resistance

Detectable warning

Truncated-dome panel at a curb ramp warning of the edge between walk and vehicular way

Thickened edge

A deepened slab perimeter, commonly 6 in or more, that beams the edge under wheel load

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