The Importance of Joint Sand Compaction in Interlocking Concrete Pavements

By Phillip Graves, Techniseal

Un-stabilized joints offer no resistance to ants. Running a plate compactor over both of these styles yields a surprising amount of void space. Without compaction, that void space remains hidden below the surface but will surely become apparent later when the pavement is exposed to traffic and weather.

As pavers continue to evolve toward closer approximations of natural stone, joint widths have grown noticeably wider. As a result, the apparent ease of joint sand installation raises the temptation to skip the step of joint sand compaction. Doing so however is an open invitation for future problems.

Rapid erosion, loss of vertical interlock and even failure of stabilized joints all become distinct possibilities. As these natural looking shapes (in addition to permeable pavers) appear to represent the foreseeable future of the paver market, it?EUR??,,????'???s critical to understand and embrace the importance of joint sand compaction.

It?EUR??,,????'???s All in the Interlock

While the joints of many new paver styles do appear much wider to the casual observer, it?EUR??,,????'???s important to realize what?EUR??,,????'???s going on just below the surface. Interlock still consists of the same three components: horizontal, vertical and rotational. Of those three, rotational interlock depends on the thickness of the pavers and the facts that they?EUR??,,????'???re tightly abutted and constrained by an appropriate edge restraint. Today?EUR??,,????'???s apparently wider joints seem to be at odds with the requirement of a tight laying pattern.

However, a few different circumstances may exist below the surface that can fool the installer into skipping joint sand compaction. Some pavers are actually rectangular at the bottom while the top half is rounded. This results in an old world cobble stone look while still providing for sufficient rotational interlock, but because the pavers fit so tightly at the bottom, sand particles don?EUR??,,????'???t easily reach the bedding layer. Still other pavers have replaced the traditional small spacer bars with much larger ?EUR??,,????'??lugs?EUR??,,????'?? that remain below the paver surface and virtually disappear upon initial sand sweeping. A third emerging style of paver are those with false joints that create the appearance of random and natural bond lines in shapes that can still be installed efficiently. A dense joint is still important in these instances where vertical interlock isn?EUR??,,????'???t impacted, even if joint stabilization is employed.

Vibratory plate compaction after joint sand sweeping ensures full joints.

Avoiding Void Space

Too much void space jeopardizes vertical interlock, and void space typically results from insufficient compaction. Void space also allows the infiltration of more water, both in the joints and to the bedding layer. On a pavement designed as impermeable, this tends to be a highly erosive event.

Though joint stabilization is a virtual requirement for wide jointed pavers, it is no substitute for compaction. A joint with more void space has inherent weakness that can?EUR??,,????'???t be overcome by a liquid stabilizer. Eventual failure is all but guaranteed. Likewise, the installation of polymeric sand cannot be viewed as an excuse to avoid compaction. Techniseal lab tests have revealed that proper compaction can result in joints accepting 10 to 12 percent more sand on standard paver shapes and likely more on some of the newer styles. While this may seem to be a marginal difference, the uncompacted sand absorbs up to 62% more water during the wetting process. With existing polymeric sand technology, this increased absorption leads to the migration of polymers to the surface where they form a thin film. More importantly, this migration means less polymer remaining in the rest of the joint, leaving it porous and spongy. Finally, more water absorption means increased cure time, leaving it vulnerable longer to unforeseen weather events.