PROTECT YOUR PAVEMENT INVESTMENT WITH PROPER JOINT SEALING
ACPA guidance on sealant selection, joint preparation and drainage for longer-lasting concrete
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Every unsealed or poorly sealed joint gives water, deicing chemicals and incompressibles a direct path into your pavement. Incompressibles are sand and other small, hard particles. Surface water is the largest source of moisture entering a roadbed, and it softens the base and subgrade, erodes support and pumps out fines. The results are corner cracks, faulted joints and settlement.
Incompressibles cause a different kind of damage. They block slab expansion in hot weather, building pressure that leads to spalling, slab migration and blow-ups. The American Concrete Pavement Association's (ACPA) Technical Bulletin, Concrete Pavement Joint Sealing/Filling, explains how a properly installed seal helps prevent these distresses and dowel bar corrosion. That means fewer emergency repairs, fewer service disruptions and safer streets.
The stakes are highest in three settings. Transverse joints open and close with every temperature cycle, so they place more strain on the sealant than longitudinal joints do. In cold and wet-freeze climates, sealants need a lower modulus, meaning they must stay flexible in freezing temperatures. They also have to protect the concrete from harsh deicers such as sodium, calcium and magnesium chloride. On airfields, sealing is mandatory to prevent joint spalling and foreign object debris (FOD) hazards, and sealants must be certified jet fuel resistant.
Long-term performance depends on five sealant properties:
· Extensibility: The ability to stretch with joint movement
· Modulus: The resistance (stiffness) of a sealant material when being stretched or compressed elastically
· Adhesion: The ability to stay bonded to the joint faces over time
· Cohesion: Resistance to tearing under tension
· Compatibility: No harmful chemical reactions with adjacent materials
Each sealant type has its own use case. Silicone cures upon exposure to air and performs across wide temperature ranges. Hot-pour asphalt is heated to 350°F to 400°F and offers excellent extensibility and adhesion. Preformed neoprene compression seals rely on lateral pressure against the reservoir walls and must stay 20% to 50% compressed.
Preparation matters just as much as material choice. Crews should follow this sequence:
1. Saw the reservoir to the correct dimensions.
2. Flush the joint with water immediately after sawing.
3. Abrasive blast the joint faces to add texture.
4. Air blow at 90 psi or more right before sealing.
Install a closed-cell or bicellular backer rod sized 25% to 50% wider than the joint. Never use an open-cell polyurethane rod.
Cleaning is the most critical step, yet it accounts for less than 10% of installation cost. A simple and quick test to check any reservoir for cleanliness is the “wipe test” developed by Wiss, Janney, Elstner Associates and adopted by ACPA as a standard quality control (QC) test.
Sealing works best as part of a sound pavement system. It cannot make up for poor drainage, nondurable concrete or weak foundations. Without free-draining bases, "bathtub" sections hold water, which leads to faulting, pumping and early sealant failure. ACPA also recommends keeping original reservoirs as narrow as practical so they can be widened later. Plan for one or two resealing operations over the pavement's life. This approach supports predictable lifecycle budgets and infrastructure that lasts.
Download the full ACPA tech brief here: https://ow.ly/QrGS5100WMm