18.9.1. Causes

• Poor joint surface preparation

Poor joint surface preparation refers to not adequately preparing the surfaces that will come into contact with the sealant. This preparation is critical because contaminants like dust, grease, or moisture can prevent the sealant from adhering properly. If the sealant doesn't bond well, it can lead to leaks and eventual failure. It's like trying to paint a wall that hasn't been cleaned; the paint won't stick well, and it will chip or peel later on.

Imagine you are trying to glue two pieces of paper together, but the surfaces are dirty and covered in crumbs. No matter how good the glue is, the bond will be weak because the surfaces weren't properly cleaned. This is similar to what happens when joint surfaces in concrete pavements aren't prepped correctly.

• Incompatible sealant material

Incompatible sealant material means that the sealant chosen to fill the joints doesn't match the materials or conditions of the pavement. Each type of sealant has specific properties suited for different environmental conditions or pavement materials. When an incompatible sealant is used, it may not adhere properly, may degrade quickly, or may not move with the pavement's expansion or contraction. This results in early sealant failure.

Think of it like using a cooking oil instead of a lubricant for a squeaky door hinge. While cooking oil may work temporarily, it might not withstand the environment and could lead to worse squeaking over time. Similarly, using the wrong sealant can cause problems that lead to joint failure.

• Incorrect sealant depth/geometry

Incorrect sealant depth or geometry refers to not applying the sealant at the right thickness or shape. If the sealant is too shallow or poorly formed, it may not provide adequate coverage, leading to openings where water or debris can enter. Proper depth ensures that the sealant can accommodate movements in the joint without being displaced, while the right geometry helps it bond effectively to the surfaces of the joint.

Imagine filling a bathtub with water using a thin layer of sealant; eventually, the water would spill over the top where the seal isn’t effective. Similarly, if the sealant isn’t the right depth in the joint, it may not prevent water from getting in.

• Thermal or mechanical overloading

Thermal or mechanical overloading refers to the joint being subjected to forces or temperature changes that exceed what it is designed to handle. For example, intense heat can cause the materials to expand drastically, while heavy loads from vehicles can compress them. If the joint seal isn't resistant enough to these stresses, it can crack or fail, leading to further damage of the pavement and failures of the sealant itself.

Think of a rubber band that you stretch too far; eventually, it snaps. If a joint sealant is pushed beyond its limits by temperature fluctuations or heavy traffic loads, it can also fail, just like that rubber band.

• Premature exposure to traffic

Premature exposure to traffic occurs when the sealant is subjected to vehicle loads before it has had the necessary time to cure and set properly. If traffic drives over a newly installed sealant, it can disrupt the curing process, leading to inadequate bonding. This can result in early degradation of the sealant and decreased performance, leading to the same issues it was meant to remedy.

It’s like trying to walk on freshly laid cement; if you step on it before it hardens, you’ll leave footprints and ruin its surface. Traffic on uncured sealant can create a similar effect, ruining its integrity.

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