8.7 Technical Detailing: Pavements, Curbs & Joint Assemblies
Key Takeaways
- Every detail must be keyed to a plan location and carry its own scale, title, and number, because an unreferenced detail is not enforceable against the contractor.
- Concrete contraction joints are cut to approximately one quarter of slab thickness, with spacing in feet roughly two to three times the slab thickness in inches.
- Welded wire reinforcement controls crack width after cracking occurs; it does not prevent cracking and must be positioned in the upper third of the slab to work.
- Interlocking concrete pavers transfer load through joint sand interlock and require a compacted aggregate base plus a bedding course of uniform thickness; a thick bedding layer used to correct base grade produces rutting.
- Flush headers and curbs serve different functions: a curb provides vertical containment and drainage control, while a flush header only restrains the pavement edge.
Last updated: September 2026
Core Focus: Construction details represent the microscopic structural reality of the landscape architecture profession. A poorly drafted detail results in cracking pavements, collapsed retaining walls, tripping hazards, and catastrophic water intrusion. The LARE Section 3 blueprint heavily weights technical detailing, focusing on rigid versus flexible pavement assemblies, joint mechanics, unit paver edge restraints, retaining wall hydrostatic drainage, frost depth footings, and ADA/IBC-compliant exterior stairs and ramps.
1. Technical Detail Drafting Conventions & Standards
Construction details (L-700 series) are drawn in section or elevation at large, highly legible architectural scales (typically $1/2" = 1'-0"$, $3/4" = 1'-0"$, $1" = 1'-0"$, or $1-1/2" = 1'-0"$). Standard detailing conventions require:
- Cut Line Weight Hierarchy: Solid, extra-heavy cut lines (0.70 mm to 1.00 mm) delineate objects sliced through in the section plane (such as the concrete slab or wall stem); light lines delineate elements visible in the background elevation.
- Leader Lines: Straight, angled leader lines terminating in an arrow pointing directly to the material. Leader lines must feature a horizontal shoulder (landing) pointing toward the text callout, and leaders should never cross one another.
- Break Lines: Used to truncate repetitive vertical or horizontal elements (such as showing the bottom of an 8-foot-deep footing or the continuation of an expansive subbase) without wasting sheet space.
2. Rigid Concrete Pavement Detailing: Slabs, Reinforcement & Joint Assemblies
Rigid pavement consists of cast-in-place Portland cement concrete (compressive strength typically 3,500 to 4,500 psi). Structurally, a rigid slab acts as a beam, distributing concentrated vehicular or pedestrian wheel loads across a broad area of the underlying subbase.
+-----------------------------------------------------------------------------+
| RIGID CONCRETE JOINTING ASSEMBLIES |
| |
| EXPANSION / ISOLATION JOINT CONTRACTION / CONTROL JOINT |
| |
| Elastomeric Sealant Sawcut Joint (Depth = T/4) |
| +---+ | | |
| | | V V |
| ====+ +======================== ============= ================ |
| SLAB| | SLAB SLAB | SLAB |
| | | | |
| |===| <-- Smooth Dowel (Lubricated) | Crack Propagates
| ----+ +------------------------ ----------------.--------------- |
| 1/2" Preformed Fiber Filler Compacted Dense Aggregate Base |
| ================================= ================================ |
| Compacted Subgrade (95% Mod. Proctor) Compacted Subgrade (95% Mod.) |
+-----------------------------------------------------------------------------+
The Three Essential Concrete Joint Types
- Contraction (Control) Joints:
- Purpose: Concrete shrinks as it cures (losing roughly 0.6 inches per 100 feet). Contraction joints create an intentional, weakened vertical plane that forces the inevitable tensile shrinkage cracks to occur in a straight, neat line at the bottom of the joint rather than wandering randomly across the slab.
- Depth Rule: The sawcut or tooled groove must be cut to a depth of exactly one-fourth the slab thickness ($T/4$) (e.g., a 1-inch-deep cut for a 4-inch slab; 1.5 inches for a 6-inch slab).
- Spacing Rule of Thumb: Joint spacing in feet should not exceed 2 to 2.5 times the slab thickness in inches (up to a practical maximum of 15 feet). For a 4-inch sidewalk, joints must be spaced at $8\text{ to }10\text{ feet}$ max. For a 6-inch slab, joints are spaced at $12\text{ to }15\text{ feet}$ max.
- Slab Aspect Ratio: Square panels ($1:1$) are ideal; rectangular panels should never exceed an aspect ratio of $1:1.25\text{ to }1:1.5$ to prevent diagonal cracking.
- Expansion (Isolation) Joints:
- Purpose: Accommodate thermal expansion during hot summer months and completely isolate the concrete slab from immovable, rigid structures (building foundations, catch basins, retaining walls, manholes, light pole footings).
- Assembly: Full-depth 1/2-inch preformed bituminous-impregnated fiber or closed-cell polyethylene foam filler extending from the bottom of the slab to within 1/2 inch of the surface, capped with backer rod and polyurethane elastomeric sealant.
- Spacing: In continuous pedestrian walks, full-depth expansion joints are placed every 20 to 30 feet.
- Construction Joints:
- Purpose: Formed stopping boundaries at the end of a day's concrete pour, or between adjacent pour lanes. Built with a formed tongue-and-groove keyway or doweled reinforcement.
Reinforcement: Dowels vs. Tie Bars vs. Mesh
- Smooth Steel Dowels: Round, smooth steel dowels (lubricated on one side with grease or plastic sleeves) are installed across transverse expansion and contraction joints in vehicular slabs. They permit horizontal sliding expansion and contraction while transferring heavy vertical shear wheel loads across the joint, preventing slab faulting (differential vertical displacement).
- Deformed Rebar Tie Bars: Deformed rebar rods installed across longitudinal construction joints to tie adjacent lanes mechanically together and prevent horizontal lane separation.
- Welded Wire Reinforcement (WWR) / Fibers: WWR (e.g., $6\times 6-\text{W}1.4/\text{W}1.4$) or synthetic structural polypropylene fibers do not prevent cracks from initiating; their primary function is to hold micro-cracks tightly closed after they occur, preserving aggregate interlock.
3. Flexible Asphalt Pavements & Interlocking Unit Paver Systems
FLEXIBLE ASPHALT SECTION INTERLOCKING UNIT PAVER SECTION
================================== +---+ +---+ +---+ +---+ (Pavers)
Surface Wearing Course (1.5" - 2") | | | | | | | | 2-3/8" Ped.
---------------------------------- +---+ +---+ +---+ +---+ 3-1/8" Veh.
Bituminous Binder Course (2" - 3") ....................... (1" Sand Bed)
================================== ======================= (Geotextile)
Crushed Aggregate Base (6" - 12") Crushed Aggregate Base (4" - 8")
---------------------------------- -----------------------
Compacted Subgrade (95% Mod. Proc) Compacted Subgrade (95% Mod. Proctor)
Flexible Asphalt Pavement Mechanics
Unlike rigid concrete, asphalt (bituminous concrete) has minimal tensile flexural strength. It distributes wheel loads downward through grain-to-grain frictional contact across an expanding cone of aggregate base:
- Surface Course (Wearing Course): Dense-graded asphalt concrete (1.5 to 2.0 inches thick) with fine aggregates providing a smooth, skid-resistant, waterproof riding surface.
- Tack Coat: A thin application of emulsified asphalt applied between the existing binder course and new wearing course to ensure a monolithic structural bond.
- Intermediate / Binder Course: Coarser asphalt concrete (2.0 to 3.0 inches thick) providing structural load distribution.
- Prime Coat: An application of liquid cutback or emulsified asphalt sprayed directly over an untreated crushed aggregate base to penetrate, bond, and seal the base before asphalt paving.
- Crushed Aggregate Base Course: Dense-graded, crushed stone (6 to 12 inches thick) compacted to 98% Modified Proctor density.
Interlocking Concrete Unit Pavers (ASTM C936)
Unit paver systems are classified as flexible modular pavements. The three-dimensional interlock (vertical, rotational, and horizontal) relies on strict layer tolerances:
- Paver Thickness: Minimum $2-3/8\text{ inches } (60\text{ mm})$ for pedestrian plazas and sidewalks; minimum $3-1/8\text{ inches } (80\text{ mm})$ for vehicular drives, fire lanes, and parking lots.
- Bedding Sand Layer: Exactly 1.0 inch (25 mm) of clean, well-graded, angular concrete sand conforming to ASTM C33 (never masonry sand or limestone screenings/stone dust). Screeded uncompacted; pavers are placed on loose sand and then vibrated into place with a plate compactor, which forces sand 1/2 inch up into the bottom of the joints.
- Joint Sand: Dry ASTM C144 or polymeric sand swept into joints and compacted until full.
- Geotextile Separation Fabric: Non-woven needle-punched geotextile placed between the open subbase and aggregate base to prevent fine soil migration.
- Rigid Edge Restraint (Mandatory!): Interlocking pavers cannot function without an immovable perimeter restraint (cast-in-place concrete curb, buried concrete flush curb header, or anchored commercial aluminum/steel edging). Without an edge restraint, edge pavers migrate outward under foot and wheel loads, joints open, sand washes out, and the entire system unzips.
4. Curb, Gutter & Flush Header Detailing
Curbs provide three essential functions: structural edge containment for pavements, stormwater channelization, and vehicular delineation.
INTEGRAL CURB & GUTTER FLUSH CONCRETE CURB HEADER
+----+ (Bioretention / Infiltration)
| | 6" Reveal
+---+ | PAVEMENT FLUSH HEADER BIORETENTION
| GUTTER | +--------------+------------+ (Turf / Swale)
| 12" | 6" | Asphalt / | Concrete | |
+--------+---+ | Pavers | 6" x 12" | V
| Base Stone | +--------------+------------+---------
+------------+ | Crushed Stone Base |
- Integral Concrete Barrier Curb & Gutter: Combines a 6-inch vertical curb face with a 12- to 24-inch horizontal gutter pan. The gutter pan matches the street cross-slope (typically 2% to 4%) to channel high-velocity stormwater toward catch basin inlets.
- Granite Curb: Specified in historic districts, cold-weather northern climates, and heavy commercial corridors. Granite resists snowplow impacts, deicing salt scaling, and freeze-thaw spalling. Must be detailed with a poured concrete footing cradle (haunch) behind and below the stone.
- Flush Concrete Curb Header: Installed flush with adjacent asphalt, pavers, or pervious concrete. Acts as a permanent edge restraint while allowing surface runoff to sheet-flow unobstructed into roadside bioretention rain gardens or bioswales.
Test Your Knowledge
A landscape architect is detailing a 6-inch-thick cast-in-place concrete vehicular loading apron for a commercial facility. To reliably control tensile shrinkage cracking along designated alignments, what minimum sawcut depth and maximum joint spacing should be specified for the contraction (control) joints?
A
B
C
D