What is waterstop?
A waterstop is a material inserted in concrete that has the sole aim of preventing water from passing through the joint.
To put it another way, it’s not an elastomeric sealant applied to a joint’s exposed surface. Waterstops cannot prevent water vapor or capillary moisture potential from migrating through a concrete slab to safeguard the flooring system (such as hardwood or tile) from adhesion failure or deterioration beyond the junction. Waterstops are also unable to prevent water infiltration through fissures in the concrete caused by building settlement or live load deflection; for these difficulties, specifiers and contractors can use waterproofing membrane systems, vapor retarders, and other construction items.
It is critical that the waterstop is made from high-quality raw materials and is free of flaws. Many different material kinds and profiles are available for different uses and situations, therefore the specifier must choose waterstops that are appropriate for all of the joint conditions, ideally with manufacturer consultation.
Water penetration into below-grade concrete buildings is most likely to occur at joints created between adjacent concrete casts and where mechanical parts penetrate the concrete. Waterstops are typically specified and built at every joint in the concrete below grade to prevent this from happening.
To protect below-grade elements of a concrete structure, a waterstop put in concrete joints is an integral component of an overall waterproofing design. The use of these items in construction joints (also known as “cold joints”), whether with or without a positive-side waterproofing membrane, is a smart design practice for building foundations. To put it another way, the waterstop can be a belt-and-suspenders strategy to keeping the occupants and owner dry.
Water, which is present under intermittent or constant hydrostatic pressure, is very likely to infiltrate through the concrete joints in below-grade constructions. As a result, waterstops are employed on a range of concrete structures as part of the overall waterproofing protection, including:
Subway, automobile, and pedestrian tunnels; parking structures; water and sewage treatment facilities; and canals, locks, and dams are all examples of underground constructions.
When most construction professionals think of a ‘waterstop,’ they usually think of a 102 to 305 mm (4 to 12 in.) wide dumbbell or ribbed profile extrusion of thermoplastic or rubber material put in a concrete joint. Polyvinyl chloride (PVC) has been the most extensively used waterstop since the 1950s. Because of their ease of welding and natural resistance to groundwater and typical wastewater treatment chemicals, these items have been used. To prevent water infiltration through joints in concrete structures, a variety of myriad metal, plastic, asphaltic, and hydrophilic materials with various compositions and profiles are now used.
Three Types of Concrete Joints
Construction (cold) joint—intentional connections between adjacent concrete pour created to make construction easier;
The expansion (or isolation) joint protects nearby concrete pours (such as walls, slabs, footings, and columns) from compressive stresses caused by thermal expansion, seismic occurrences, or live load deflection.
Intentional grooves to produce a weaker plane to control the placement of cracks occurring from shrinkage of concrete while curing are known as contraction (or control) joints.
It is necessary to understand the various product kinds and material compositions in order to select a waterstop that is appropriate for the project’s joint-sealing requirements. The majority of variants are designed specifically for use in cast-in-place concrete construction joints, however, certain varieties can also be utilized with expansion joints. The projected lateral, transverse, and shear joint movements, as well as the expected hydrostatic pressure, must be accommodated by selected waterstops.
The waterstop must be resistant to the fluids or chemicals contained within the structure if it is used for primary or secondary containment. They are available in a variety of types, shapes (profiles), and sizes, as well as various material compositions, including:
PVC, HDPE, and thermoplastic vulcanizate (TPV) extrusions are examples of thermoplastic extrusions.
Extrusions of thermoset rubber, hydrophilic bentonite and rubber strips, myriad metal, asphaltic and butyl rubber non-swelling strips, metallic extrusions, and injection hose systems are among the products available.
Extrusions of Thermoplastics and Rubber
Most thermoplastic and rubber waterstops available in a variety of extruded shapes, widths, and thicknesses to suit variable hydrostatic pressure and movement. For many years, the most popular waterstops were those with a dumbbell form at each end that provided a ‘cork-in-the-bottle’ seal when the joint opened. However, according to the American Concrete Institute (ACI) 504R, Guide to Joint Sealants for Concrete Structures, this seal is inadequate for small joint motions, and the waterstop is placed under significant tension at larger joint movements. Waterstop manufacturers created profiles with many raised ribs to improve anchoring and sealing performance in order to address these difficulties.
Waterstops with flat-web or bulbed centers are available in both ribbed and dumbbell styles. They come in 15.2-meter (50-foot) rolls with widths ranging from 102 to 305 mm (4 to 12 in.) and thicknesses ranging from 5 to 13 mm (3/16 to 12 in.). Waterstops with a flat web are advised for use in construction and contraction joints where there will be little or no movement. These waterstops can be utilized in expansion, contraction, or construction joints since the center bulb bends to allow both shear and transverse movements. The center bulbs are available in a variety of sizes to accommodate varying degrees of joint movement, with larger-diameter center bulbs suited for more joint movement.
The center bulb of some ribbed waterstops has a thin tear-web on one side that ruptures when the joint expands. The tear-web has been broken, allowing the center bulb to open up to the joint’s full width without stressing the embedded ribbed parts. During concrete placement, the tear-web keeps concrete out of the center bulb. When there will be a lot of movement, tear-web waterstops are recommended. They should be fitted with the tear-web side facing the positive pressure direction.
While rubber thermoset waterstops have good mechanical properties (high tensile strength and elongation), they are difficult to fabricate in the field because the rubber is vulcanized, which means it has already taken a ‘set’ (i.e. thermoset) and cannot be heat-welded together like thermoplastic materials.
The estimated head of water pressure at the joint determines the size of the waterstop (i.e. width). The stronger the hydrostatic pressure resisted by a waterstop, the larger the size of the waterstop (e.g. widths of 102, 152, 229 mm [4, 6, 9 in.]).
However, performance is influenced by more than just size and width; profile thickness and ribbing also play a role, with thicker goods enduring higher hydrostatic pressures. When real project design conditions are available for assessment, waterstop manufacturers can recommend size and type. In addition, the manufacturer can advise on the minimum depth of embedment the waterstop should have in the concrete to withstand the projected hydrostatic pressure.
Failures in the Installation of Waterstops
The issue with waterstops is that they are prone to damage or faulty installation during concrete placement. The following is a list of some of the many potential waterstop installation failures. center-bulb roll ends of dumbbells or ribbers overlapped but not welded or spliced together;
- erected too close to the steel reinforcing;
- splices on dumbbells are bonded together with sealant rather than welded.
- install a strip waterstop with a concave space (void) beneath it;
- no manufactured part—polyvinyl chloride (PVC) transition bonded together
- PVC welded only on the border of the profile, not all the way across;
- concrete that hasn’t been properly compacted near the waterstop;
- thermoplastic welds that have been overheated, burned, or charred;
- a dumbbell or a ribbed center-bulb product that isn’t centered in the joint;
- because the dumbbell was not correctly secured to the reinforcement, it shifted during the concrete pour;
- to pass the rebar through, a hole was made in the flange of the dumbbell.
- hydrophilic strip roll ends that overlap but do not butt;
- dumbbell’s flange is narrowed to fit around reinforcing steel;
- ribs or center bulb are misplaced at the splice;
- previous to the second pour, concrete extending on the flange that had not been removed from the waterstop; and
- only fasteners are used to install hydrophilic-strip waterstops.
Special Thermoplastic Materials and Its Profiles
Dumbbell and ribbed center-bulb waterstops are made of thermoplastics and rubbers, such as polyethylene and TPV, for superior chemical resistance to fluids—the latter for primary and secondary containment structures, as well as ozone contactor wastewater structures. Oils, solvents, and industrial chemicals are all resistant to TPV waterstops. TPV, unlike PVC, does not include a plasticizer that can leach out when exposed to chemicals or fuels.
According to one producer, TPV can resist lengthy exposure to both low and high temperatures (100 to 135 C [150 to 275 F]) without harm, however it becomes very soft about 150 C (300 F) and melts at roughly 200 C. (400 F).
As a result, metallic waterstops (described later in this article) should be specified and installed for applications needing extreme heat tolerance. ‘Arctic-grade’ PVC waterstop is particularly developed for very cold conditions, retaining its flexibility and physical qualities down to 45 C (50 F).
Thermoplastic waterstops can also be extruded into split-leg, labyrinth, base-seal, and retrofit designs.
Although the split-leg profile avoids the need to separate the formwork for waterstop installation, proper splicing at intersections and plane transitions is challenging. For the first concrete pour, the split side of the split-leg can be laid flat against the formwork. The two parts of the split-leg are cemented together and then enclosed in the second pour after the first pour has set and the formwork has been removed.
When the shape of the forms or the location of the reinforcing steel prevents the split flange from opening, the split-leg profile should not be employed. In a plane transition or fitting configuration, the split cannot open properly and be put against formwork. For these reasons, such profiles are rarely employed for chemical containment.
Waterstops with a labyrinth design are typically utilized in vertical construction joints when little or no movement is expected. They, like the split-leg, can be inserted without causing a split. Because of the unique profile shape of the labyrinth, quality splicing at crossings and changes of direction is particularly challenging. For these reasons, labyrinth profiles are not commonly employed for chemical containment.
Waterstops with a base seal have a broad flat profile with only one side of ribs. They’re employed at slab-on-grade joints and for property, line shoring walls when the waterstop is put on the concrete’s outside surface rather than incorporated within it. This design is simple to make and provides proper functionality.
Special extrusion forms are also available to offer a fluid-tight seal between old and new construction. These retrofit waterstops don’t require the time-consuming and structurally damaging saw-cutting and grouting of existing concrete to embed half of the waterstop. Waterstops with retrofit profiles can also be used to isolate structural elements like pilasters, columns, and tank pads. For both construction and expansion joints, retrofit profiles are provided.
Hydrophilic Type Waterstops
Hydrophilic strip waterstops react with water and swell to form a positive watertight barrier in the concrete joint, unlike PVC dumbbell waterstops, which function by passively stopping water migration. Hydrophilic waterstops have been on the market for decades and have a solid track record. Water infiltration through concrete construction joints, including joints under high hydrostatic pressure and intermittent hydrostatic circumstances, is effectively protected by a hydrophilic waterstop.
Rolls or strips of hydrophilic waterstops are available. The profile is usually a tiny rectangle, with the two most common sizes being 20 × 25 mm (3/4 x 1 in.) and 20 x 10 mm (3/4 x 3/8 in.). Bentonite and rubber hydrophilic strip systems are mostly utilized in construction joints; most are not suitable for use in expansion joints. These systems are straightforward to install and do not require portions to be heat-welded together before the initial concrete pour. In order for the second concrete pour to construct the joint, the material is bonded directly to the cured surface of the first concrete pour.
Using an adhesive or primer, the strips are bonded to hardened concrete. This stickiness is necessary to ensure that the waterstop does not move during the concrete pour. To fix the waterstop, a covering strip of steel mesh placed over the strip can be nailed 300 mm (12 in.) on-center (o.c.).
Only mechanical fasteners (i.e. nails without steel mesh covering) should be used to install hydrophilic-strip waterstops along the product length. A small layer of concrete paste might extrude under the waterstop when it is installed merely using screws, causing it to lose most, if not all, of its effectiveness.
Even worse, concrete placement can rip the waterstop off the fasteners, causing this component of the joint to be moved into the concrete and out of the joint plane. As a result, these strip waterstops must always be specified and installed adhered in place or with the steel mesh cover system.
Hydrophilic waterstops can be used for more than just cast-in-place concrete construction joints. Hydrophilic waterstops are easy to place around pipe penetrations, I-beams, concrete pilings, and irregular-shaped surfaces because of their flexibility and conformability.
Waterstops that are hydrophilic are also utilized to seal new concrete against old concrete. They’re also lightweight and adaptable, and they don’t require any specific prefabricated Ts, Ls, or crosses. This style of waterstop is popular among contractors because of its ease of installation.
Manufacturers normally need a minimum concrete coverage depth of 50 to 75 mm (2 to 3 in.) for hydrophilic waterstops, depending on the profile size and material type. To avoid concrete spalling owing to insufficient concrete coverage, these waterstops must be installed in strict conformity with the manufacturer’s minimum concrete coverage standards.
They must be inserted without overlapping adjacent strip ends and must be closely abutted to produce a continuous system.
These items should not be wetted too soon because they expand when exposed to water. This necessitates that the second concrete is placed immediately after the waterstop; otherwise, the waterstop may expand if exposed to rain. The ‘free water’ in a concrete mix is insufficient to swell a hydrophilic waterstop physically.
For the waterstop to truly swell once the concrete has cured, it needs a substantial external supply of water that migrates into the joint and comes into touch with it. The hydrophilic waterstop remains dormant if no external water source comes into contact with it.
The hydrophilic ingredient in not all hydrophilic waterstops is bentonite clay. When in contact with water, hydrophilic rubber waterstops expand and keep solid material integrity that will not disintegrate owing to uncontrolled expansion.
They may, however, have varying expansive qualities (in terms of rate and volume) when exposed to water since they are made with different types of hydrophilic agents. Also, some are made with non-swelling rubber in parts of the profile, which means the entire profile does not activate and swell.
This type of hydrophilic waterstop has the same drawbacks as bentonite-based waterstops, such as the inability to swell in fluids other than water and the absence of expansion joint functioning.
Hydrophilics’ In-situ Performance
Water infiltration through concrete construction joints, even those under high-pressure and intermittent hydrostatic circumstances, is effectively prevented using hydrophilic waterstops. When hydrated in a non-confined, free-swell setting, such as a bowl of water, hydrophilic waterstops demonstrate a significant degree of expansion due to their product design.
As the product approaches maximal expansion in a non-confined state, it may fracture. Despite the fact that fracturing appears to be a disadvantage of the material, it is an indicator of positive performance for in-situ concrete joint circumstances.
It means that the waterstop compound stretches and molds well to the inside surfaces of a concrete joint, no matter how uneven they are.
It also has the capacity to extrude into cracks and progress through angle transitions in the joint because of its plasticity and expansion capabilities. Beyond the poorly consolidated concrete interface with the waterstop strip, bentonite compounded strips have been observed expanding through narrow cracks to fill larger void areas.
Because of the expanding qualities, this dynamic sealing ability is achievable; such capabilities would be unattainable with a high-tensile-strength material like a hydrophilic rubber waterstop. Due to their more rigid material qualities, hydrophilic rubber waterstops have been reported to have restricted expansion into fractures, gaps, and joints that surround them in lab testing.
The hardness of the rubber may limit the waterstop’s expansion to a small convex amount over the crack’s opening, rather than extruding into the crack’s depth.
In properly cemented concrete, the maximum expansion a hydrophilic material exhibits in non-confined, free-swell conditions will not manifest. Hydrophilic waterstops only need to expand slightly in place to provide a positive seal against the concrete interface.
This limited swell gives the product a reserve swell potential, allowing it to seal poorly consolidated concrete or prevent concrete cracks from later occurring due to building settling or seismic activity.
Hydrophilic waterstops rarely go through wet-dry cycling once they’ve been moistened. The material maintains its hydrated equilibrium when contained in concrete and below grade and does not shrink under regular water-table variations or intermittent water circumstances.
Bentonite, interestingly, can be hydrated and dried an endless number of times without losing its natural swelling potential. It can be frozen and thawed multiple times without losing its excellent effectiveness. Finally, even if in-situ drying occurs (a very unlikely scenario), bentonite has been shown to rehydrate to its original performance level.
Non-expanding Mastic Strips Waterstops
Although mastic-strip waterstops, unlike bentonite or hydrophilic rubber materials, are not vulnerable to pre hydration expansion, their reliance on concrete adhesion may hinder the complete sealing of the junction if some parts are not correctly bonded or linked together.
Most non-expanding mastic waterstops are made in rolls or strips, similar to hydrophilic waterstops. The profile is usually a small rectangle form, with measurements of 20 × 25 mm (34 x 1 in.) for butyl-rubber compounds and 38 x 12 mm (1 12 x 12 in.) for asphaltic-based strips being the most frequent.
Waterstops made of mastic are often made of a sticky, asphaltic, or butyl rubber-based composition. They’re made to adhere to the prepped surface of a cured concrete cold joint. Following the manufacturer’s instructions, the strip is attached at a minimum embedment depth, and a second concrete pour is cast to encapsulate the remaining three sides.
Because of the heat from the hydrated concrete, the substance becomes even tackier, closing the joint by functioning as an internal, adherent sealant.
The importance of adhesion cannot be overstated. The waterstop can easily lose most, if not all, of its water barrier function if it is shifted during the concrete pour. Waterstops made of mastic are only intended for use in construction joints and should not be indicated for use in expansion joints.
The only barrier to migrating fluids is the low profile strip’s adhesive to the concrete, hence the performance of mastic waterstop hydrostatic resistance is quite restricted.
Mastic waterstops are the least effective of any commercially available waterstop and are hence the least expensive.
Waterstops for Injection Hoses
Waterstops for injection hoses are typically permeable or perforated hoses with a number of injection ports and valves added during new construction. These ports are exposed on the concrete’s inside surface for eventual access. A grout pump can be used to inject a resin (typically polyurethane) to seal the joint and fill any nearby voids in the concrete if a leak occurs after construction.
Some products are advertised as re-injectable,’ yet this is frequently not the case due to cured resin encircling the hose or contractors failing to follow the manufacturer’s instructions (i.e. chiefly not cleaning out the hoses properly after the initial resin injection).
Each injection hose system makes use of a permeable hose that is put in short lengths at building joints (typically less than 9 m [30 ft]). A woven mesh outer covering surrounds the hose core, allowing resin injected under pressure to travel out of the tube and into the joint while cement particles and aggregates are prevented from entering the hose and clogging it.
With mechanically fastened clamps, the hose is secured to the first concrete pour once it has set (typically 305 mm [12 in.] on center).
At the end of each section, adjacent perforated hoses are overlapped by 150 to 300 mm (6 to 12 in.) and a small non-perforated tube is added inline that leaves the concrete as the injection port. Following the construction of the structure, polyurethane resin is injected into the hose to seal the junction and repair any fractures or cavities.
They can also be utilized to seal the joints between new and old structures during construction. Secondary confinement, basements, and tunnels are all common uses.
Metallic Type Waterstops
Even at extremely high temperatures, metallic waterstops can restrict the passage of corrosive fluids. As a result, metallic waterstops are typically employed in harsh chemical and high-temperature settings where other materials would decay. There are many different metals, grades, and gauges to choose from.
Stainless steel has a wide range of corrosion resistance and is essentially unaffected by ozone, making it an appropriate material for ozone contactor structures in modern water treatment plants. Stainless steel waterstops come in a variety of standard shapes and sizes, as well as profiles for new and retrofit applications. All change-of-direction fabrications should be done ahead of time, leaving just straight butt-welding to be done on the job.
Metallic waterstops are the most difficult to install because split-forming using tungsten-inert-gas (TIG) or metal-inert-gas (MIG) welding is always required. Edge-to-edge welding should be done on any straight-run material (no overlapping).
The stiffness of metal waterstops can cause neighboring concrete to crack. As a result, solid metal waterstops with suitable concrete coverage should be erected.
Multiple Type Systems Installation
Because waterstop systems are very affordable, installing a secondary product might be a prudent and low-cost investment. This raises the question, “Why not utilize one waterstop as the primary barrier and another as a secondary barrier as an insurance policy if the concrete joint has the proper width clearance?”
The second system is there to provide fluid-tight integrity at the concrete junction if the primary system fails in any way due to a material or installation failure.
To be clear, there is no requirement for a secondary waterstop system when a ribbed center-bulb or hydrophilic waterstop is appropriately placed. These waterstop products, regardless of polymer or manufacturer, only leak because of faulty installation practices and a lack of quality assurance.
A ribbed center-bulb waterstop on the positive-pressure side of the joint and a hydrophilic or mastic strip-applied waterstop several inches away on the negative-pressure side of the joint is a common belt-and-suspenders technique. An injection tube system installed on the low-pressure side could be used as a supplementary waterstop.
Redundancy in established waterstop systems provides significant benefits at a low cost, particularly when amortized over the life of the concrete structure in which they are installed.
Hydrophilic waterstops can be specified for concrete construction joints, while PVC hydrophobic waterstops can be selected for pipe and mechanical penetrations.
Three waterstop systems were specified and implemented in the building joints of the thick concrete walls in critical infrastructure subway projects. A PVC ribbed center bulb on the positive pressure side, a bentonite hydrophilic strip in the center, and an injection hose waterstop closest to the inner face of the concrete wall were all part of the installation.
Contractors are responsible for the installation of waterstops, which is possibly the most significant job they play. For a project’s long-term success, these systems should be viewed as key building envelope barrier material. Proper design, installation, and concreting methods are required for any waterstop to be functional. To begin, choose a product size and profile that is appropriate for the predicted joint movement, hydrostatic head, and chemical resistance.
What is Waterstop? – Key Takeaway
Water penetration into below-grade concrete buildings is most likely to occur at joints. Waterstops are typically specified and built at every joint in the concrete below grade. Polyvinyl chloride (PVC) has been the most extensively used waterstop since the 1950s. It’s not an elastomeric sealant applied to a joint’s exposed surface. Waterstops cannot prevent water vapor or capillary moisture potential from migrating through a concrete slab.
The specifier must choose waterstops that are appropriate for all of the joint conditions. Waterstops with flat-web or bulbed centers are available in both ribbed and dumbbell styles. Some ribbed waterstops have a thin tear-web on one side that ruptures when the joint expands. These joints can be utilized in expansion, contraction, or construction joints. Waterstops are made of thermoplastics and rubbers, such as polyethylene and TPV.
TPV is particularly good for primary and secondary containment structures. Oils, solvents, and industrial chemicals are all resistant to TPV waterstops. Thermoplastic waterstops can also be extruded into split-leg, labyrinth, base-seal, and retrofit designs.
Arctic-grade PVC is particularly developed for very cold conditions, retaining its flexibility and physical qualities down to 45 degrees C (50 degrees F). Hydrophilic strip waterstops react with water and swell to form a positive watertight barrier in the concrete joint.
Water infiltration through concrete construction joints is effectively protected by a hydrophilic waterstop. Waterstops are easy to place around pipe penetrations, I-beams, concrete pilings, and irregular surfaces.
The ‘free water’ in a concrete mix is insufficient to swell a hydrophilic waterstop physically. For the waterstop to truly swell once the concrete has cured, it needs a substantial external supply of water that migrates into the joint and comes into touch with it. Some materials are made with non-swelling rubber in parts of the profile, which means the entire profile does not activate and swell.
Hydrophilic rubber waterstops have restricted expansion into fractures, gaps, and joints that surround them in lab testing. Bentonite can be hydrated and dried an endless number of times without losing its natural swelling potential.
It also has the capacity to extrude into cracks and progress through angle transitions. Waterstops made of mastic are often made of a sticky, asphaltic, or butyl rubber-based composition. Mastic waterstops are the least effective and hence the least expensive.
Waterstops for injection hoses are typically permeable or perforated hoses with a number of injection ports. Metallic waterstops are typically employed in harsh chemical and high-temperature settings.
Polyurethane resin is injected into the hose to seal the junction and repair any cavities.
There are many different metals, grades, and gauges to choose from. There is no requirement for a secondary waterstop system when a ribbed center-bulb or hydrophilic waterstop is placed.
An injection tube system installed on the low-pressure side could be used as a supplementary waterstop. Redundancy in established waterstop systems provides significant benefits at a low cost.