What is an expansion joint?
In building construction, an expansion joint is a mid-structure separation designed to relieve stress on building materials caused by building movement induced by:
- thermal expansion and contraction caused by temperature changes,
- sway caused by wind,
- seismic events, etc.
Because the joint bisects the entire structure, it marks a gap through all building assemblies--walls, floors, roofs, decks, planters, plazas, etc. This gap must be filled to restore the waterproofing, fire proofing, sound proofing, air barrier, roof membrane, trafficable surface and other functions of the building elements it bisects.
Expansion joint systems are used to bridge the gap and restore building assembly functions while accommodating expected movements.
The term "movement joint" has been widely adopted in preference to "expansion joint" as it more appropriately encompasses the fact that building movement results in both compression and expansion of the material installed.
For example, when a structure heats up, the building materials from which it is built expand. This causes the "expansion joint" to close down, thereby compressing the expansion joint system installed in the gap.
Conversely, when the temperature drops, the materials cool causing the joint gap to open. This requires the expansion joint material to expand to follow the joint movement.
- Compression Set
- Continuity of Seal
- Expansion Joint
- Nosing Material
- Non-Invasive Anchoring
- Split Slab
- Sound Transmission Class (STC)
- Thermal Shock
Adhesion in Tension--In principle, the weakest way to use an adhesive, yet the principle on which many expansion joint and sealant technologies rely for their performance. Adhesives are best used in shear. The more durable joint sealing technologies rely either on adhesives in shear as in "membrane/nosing" type products, or use inherent compression to diminish or eliminate adhesion in tension on the bond line as well as within the sealant or adhesive material itself.
Blockout--A blockout is a condition present at a joint gap edge to accept different types of expansion joint profiles. Also referred to by regional terminology such as knockout, cutout, and others.
COMPRESSION SET--Compression set is the permanent loss of the ability to self-expand that results after a material is subject to normal compression cycles. Compression set is made worse by simultaneous exposure of certain materials to heat.
Impregnated, open-cell, foam is used as the backing for precompressed sealants because it features very low compression set.
Closed-cell foams suffer on average 25% permanent compression set under movement and temperature cycles typical in construction applications.
Continuity of Seal--The assurance of watertightness in an expansion joint throughout its length and through all changes in plane, direction, and intersection within a single joint sealing technology or between one or more technology types.
Nosing Material--
A resin material (usually polyurethane based) with aggregate additives that is mixed and poured in the field on each side of a structural expansion joint gap. The material when cured is less rigid than the adjacent concrete substrate and as a result is more forgiving of traffic impact and suddenly applied vehicle loads. A high performance nosing material should be conservatively loaded with aggregates so as to preserve flexibility and avoid brittleness.
Used as a bedding material beneath cover plate systems, a conservatively-aggregate-loaded nosing material can be used as a leveling course to take any play out of the plates while additionally serving to absorb the loud bangs typical of plates mounted directly to hard, uneven, concrete surfaces.
Non-Invasive Anchoring--Refers to the attachment of an expansion joint system to the joint faces or substrates to be sealed without the use of any fasteners that are required to be screwed into or embedded in the substrate.
Non-invasive anchoring on EMSEAL's joint systems is eliminated in favor of the use of the mechanical backpressure of precompressed, foam combined with a pressure-sensitive adhesive impregnation and in some case a field application of a high-bond epoxy adhesive. The result is that the substrates are not violated be they window mullions, bricks, masonry, historic materials, or even jumbotrons or other sensitive equipment.
Screws and expansion anchors are commonly used to fasten rails, plates, and other systems offered for expansion joint sealing and bridging. By nature, screws are either self-tapping or require holes to be drilled and then the screws tapped into the holes. On brittle substrates like concrete, masonry or brick, drilling often results in spalling of the substrates and improper grip. Usually installed at an angle to the face of the joint substrate the act of screwing is often imprecise resulting in further substrate damage, shearing of the fasteners and loose attachment of the joint system. At inside corner applications common in additions or building plane changes, it is impossible to position a drill or driver to install anchors in the substrate opposite the inside corner. This often-overlooked condition results in the joint system being installed into an unreliable adhesive or not anchored at all.
In window or curtain wall mullions, screws violate the mullions and can compromise the waterproofing principles inherent in the mullion design. In any substrate metal fasteners introduce thermal bridges and thermal breaks that lower or compromise the insulation value of the wall. EMSEAL systems for wall expansion joints that feature non-invasive anchoring include:SEISMIC COLORSEAL, COLORSEAL, and SEISMIC COLORSEAL-DS
In horizontal plane deck applications, anchors into concrete to secure cover plates are rapidly deteriorated by impact shocks of traffic. They are also stressed by differential vertical deflection across expansion joints as the result of transient traffic loads. Finally, anchors into the edges of concrete decks can induce a fault-line of pressure that weakens the concrete's strength and can result in spalling of the joint edge. EMSEAL systems for deck expansion joints that feature non-invasive anchoring include: SJS SYSTEM, SJS-HD, DSM SYSTEM, and HORIZONTAL COLORSEAL.
In building construction, an expansion joint is a mid-structure separation designed to relieve stress on building materials caused by building movement induced by:
- thermal expansion and contraction caused by temperature changes,
- sway caused by wind,
- seismic events, etc.
Because the joint bisects the entire structure, it marks a gap through all building assemblies--walls, floors, roofs, decks, planters, plazas, etc. This gap must be filled to restore the waterproofing, fire proofing, sound proofing, air barrier, roof membrane, trafficable surface and other functions of the building elements it bisects.
Expansion joint systems are used to bridge the gap and restore building assembly functions while accommodating expected movements.
The term "movement joint" has been widely adopted in preference to "expansion joint" as it more appropriately encompasses the fact that building movement results in both compression and expansion of the material installed.
For example, when a structure heats up, the building materials from which it is built expand. This causes the "expansion joint" to close down, thereby compressing the expansion joint system installed in the gap.
Conversely, when the temperature drops, the materials cool causing the joint gap to open. This requires the expansion joint material to expand to follow the joint movement.
Expansion Joint and Joint Sealant Glossary Index:
- Blockout- Compression Set
- Continuity of Seal
- Expansion Joint
- Nosing Material
- Non-Invasive Anchoring
- Split Slab
- Sound Transmission Class (STC)
- Thermal Shock
Adhesion in Tension--In principle, the weakest way to use an adhesive, yet the principle on which many expansion joint and sealant technologies rely for their performance. Adhesives are best used in shear. The more durable joint sealing technologies rely either on adhesives in shear as in "membrane/nosing" type products, or use inherent compression to diminish or eliminate adhesion in tension on the bond line as well as within the sealant or adhesive material itself.
Blockout--A blockout is a condition present at a joint gap edge to accept different types of expansion joint profiles. Also referred to by regional terminology such as knockout, cutout, and others.
Impregnated, open-cell, foam is used as the backing for precompressed sealants because it features very low compression set.
Closed-cell foams suffer on average 25% permanent compression set under movement and temperature cycles typical in construction applications.
Continuity of Seal--The assurance of watertightness in an expansion joint throughout its length and through all changes in plane, direction, and intersection within a single joint sealing technology or between one or more technology types.
Nosing Material--
A resin material (usually polyurethane based) with aggregate additives that is mixed and poured in the field on each side of a structural expansion joint gap. The material when cured is less rigid than the adjacent concrete substrate and as a result is more forgiving of traffic impact and suddenly applied vehicle loads. A high performance nosing material should be conservatively loaded with aggregates so as to preserve flexibility and avoid brittleness.
Used as a bedding material beneath cover plate systems, a conservatively-aggregate-loaded nosing material can be used as a leveling course to take any play out of the plates while additionally serving to absorb the loud bangs typical of plates mounted directly to hard, uneven, concrete surfaces.
Non-Invasive Anchoring--Refers to the attachment of an expansion joint system to the joint faces or substrates to be sealed without the use of any fasteners that are required to be screwed into or embedded in the substrate.
Non-invasive anchoring on EMSEAL's joint systems is eliminated in favor of the use of the mechanical backpressure of precompressed, foam combined with a pressure-sensitive adhesive impregnation and in some case a field application of a high-bond epoxy adhesive. The result is that the substrates are not violated be they window mullions, bricks, masonry, historic materials, or even jumbotrons or other sensitive equipment.
Screws and expansion anchors are commonly used to fasten rails, plates, and other systems offered for expansion joint sealing and bridging. By nature, screws are either self-tapping or require holes to be drilled and then the screws tapped into the holes. On brittle substrates like concrete, masonry or brick, drilling often results in spalling of the substrates and improper grip. Usually installed at an angle to the face of the joint substrate the act of screwing is often imprecise resulting in further substrate damage, shearing of the fasteners and loose attachment of the joint system. At inside corner applications common in additions or building plane changes, it is impossible to position a drill or driver to install anchors in the substrate opposite the inside corner. This often-overlooked condition results in the joint system being installed into an unreliable adhesive or not anchored at all.
In window or curtain wall mullions, screws violate the mullions and can compromise the waterproofing principles inherent in the mullion design. In any substrate metal fasteners introduce thermal bridges and thermal breaks that lower or compromise the insulation value of the wall. EMSEAL systems for wall expansion joints that feature non-invasive anchoring include:SEISMIC COLORSEAL, COLORSEAL, and SEISMIC COLORSEAL-DS
In horizontal plane deck applications, anchors into concrete to secure cover plates are rapidly deteriorated by impact shocks of traffic. They are also stressed by differential vertical deflection across expansion joints as the result of transient traffic loads. Finally, anchors into the edges of concrete decks can induce a fault-line of pressure that weakens the concrete's strength and can result in spalling of the joint edge. EMSEAL systems for deck expansion joints that feature non-invasive anchoring include: SJS SYSTEM, SJS-HD, DSM SYSTEM, and HORIZONTAL COLORSEAL.
Split Slab -- In contrast to a solid-slab deck that is comprised of a single concrete element performing the roles of both the structural support and traffic surface, a split-slab, sometimes called a "sandwich slab" is deck comprised of a structural supporting slab over which a topping slab or wear course is installed to handle direct traffic contact and weathering.
Separating these two components is a waterproofing membrane applied directly to the structural slab and that is therefore covered by the wearing course. Because wearing slabs typically crack, wear, and can otherwise be compromised from the standpoint of preventing water passage, split-slab design separates the waterproofing function from the traffic-bearing function. In this way the waterproofing membrane is buried and therefore protected by the wear course. Water that passes through the wear course at cracks, cold joints, construction joints, perimeters, etc. is caught by the buried waterproofing membrane where it can be managed to drains. Drains used in split-slab design are of the bi-level variety allowing water to enter the drain at both the wear course and buried waterproofing levels.
Expansion joints in split-slabs are in fact designed gaps in the waterproofing. To properly address the waterproofing of expansion joints in split-slab design, it is essential to use an expansion joint system that integrates with the buried waterproofing membrane in a static connection while accommodating joint movement at the surface of the sandwich assembly as a purpose-designed movement gland. Buried "band-aid" style approaches to split-slab expansion joint treatment suffer from flex-fatigue, adhesion in tension and are typically not long-term solutions. In addition, buried systems fail to adequately reflect the structural expansion joint gap through the topping slab or wear course. This results in the need for retaining angles or some other way to define a joint-gap at the wear course that usually results in the need to attach these joint-defining components by penetrating the waterproofing membrane with anchors or fasteners.
The up-front cost of a an integrated split-slab joint system is comparable to the perceived lower-cost multi-level approach when installed costs of two joint systems plus substrate materials are considered. Cost of repair or replacement of buried systems significantly outweighs the up front cost of a split slab joint system. This is because demolition of the topping, disruption to tenancy and traffic flow are considered.
Split-slab design is widely used in applications such as plaza decks (sometimes called podium decks); sports and assembly facility concourses and roadways, airport roadways, and anywhere occupied space is intended beneath the deck structure.
Separating these two components is a waterproofing membrane applied directly to the structural slab and that is therefore covered by the wearing course. Because wearing slabs typically crack, wear, and can otherwise be compromised from the standpoint of preventing water passage, split-slab design separates the waterproofing function from the traffic-bearing function. In this way the waterproofing membrane is buried and therefore protected by the wear course. Water that passes through the wear course at cracks, cold joints, construction joints, perimeters, etc. is caught by the buried waterproofing membrane where it can be managed to drains. Drains used in split-slab design are of the bi-level variety allowing water to enter the drain at both the wear course and buried waterproofing levels.
Expansion joints in split-slabs are in fact designed gaps in the waterproofing. To properly address the waterproofing of expansion joints in split-slab design, it is essential to use an expansion joint system that integrates with the buried waterproofing membrane in a static connection while accommodating joint movement at the surface of the sandwich assembly as a purpose-designed movement gland. Buried "band-aid" style approaches to split-slab expansion joint treatment suffer from flex-fatigue, adhesion in tension and are typically not long-term solutions. In addition, buried systems fail to adequately reflect the structural expansion joint gap through the topping slab or wear course. This results in the need for retaining angles or some other way to define a joint-gap at the wear course that usually results in the need to attach these joint-defining components by penetrating the waterproofing membrane with anchors or fasteners.
The up-front cost of a an integrated split-slab joint system is comparable to the perceived lower-cost multi-level approach when installed costs of two joint systems plus substrate materials are considered. Cost of repair or replacement of buried systems significantly outweighs the up front cost of a split slab joint system. This is because demolition of the topping, disruption to tenancy and traffic flow are considered.
Split-slab design is widely used in applications such as plaza decks (sometimes called podium decks); sports and assembly facility concourses and roadways, airport roadways, and anywhere occupied space is intended beneath the deck structure.
Sound Transmission Class (STC)--The Sound Transmission Class - STC- is a single-number rating of the airborne sound transmission loss (TL) performance of a construction measured at standard one-third octave band frequencies.
The higher the STC rating, the more efficient the construction will be in reducing sound transmission within the frequency range of the test.
Thermal Shock--The rapid opening or closing of an expansion joint gap as the result of abrupt temperature change. The abrupt change causes the rapid shortening or lengthening of the structure on either side of the expansion joint causing a rapid cycle of compression or extension in the joint material. Thermal shock can result from the passage of a fast moving rain storm that rapidly cools a sun-baked structure on a hot summers day. Can also result from abrupt seasonal temperature changes particularly in spring and fall. Materials used in sealing structural joints subject to thermal shock must be capable of handling the resulting rapid cycling while remaining bonded to the substrates and while preserving watertightness.
The higher the STC rating, the more efficient the construction will be in reducing sound transmission within the frequency range of the test.
Thermal Shock--The rapid opening or closing of an expansion joint gap as the result of abrupt temperature change. The abrupt change causes the rapid shortening or lengthening of the structure on either side of the expansion joint causing a rapid cycle of compression or extension in the joint material. Thermal shock can result from the passage of a fast moving rain storm that rapidly cools a sun-baked structure on a hot summers day. Can also result from abrupt seasonal temperature changes particularly in spring and fall. Materials used in sealing structural joints subject to thermal shock must be capable of handling the resulting rapid cycling while remaining bonded to the substrates and while preserving watertightness.
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