A waterstop is a material that is inserted into the concrete for the sole purpose of preventing water from passing through a joint.
In other words, it is not an elastic sealant applied to the exposed surface of the joint. Waterstops do not prevent water vapor or capillary water potential from migrating through a concrete slab to protect a floor system (such as hardwood or tile) from bond failure or deterioration beyond the joint. Waterstops also do not prevent water infiltration in concrete cracks 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 waterstops are made from quality raw materials and are free of defects. Many different material types and profiles are available for different uses and situations, so specifiers must choose a waterstop that is suitable for all joint conditions, preferably in consultation with the manufacturer.
Water penetration into underground concrete buildings is most likely to occur at joints between adjacent concrete castings and where mechanical components penetrate into the concrete. Waterstops are usually specified and constructed at each joint in below grade concrete to prevent this from occurring.
Waterstops placed in concrete joints are an integral part of the overall waterproofing design in order to protect the subsurface elements of the concrete structure. The use of these items in construction joints (also called "cold joints"), with or without a frontal waterproofing membrane, is a wise design practice for building foundations. In other words, waterstops can be a slinging strategy to keep occupants and owners dry.
Water that exists under intermittent or constant hydrostatic pressure is likely to infiltrate through concrete joints in underground structures. Waterstops are therefore used in a range of concrete structures as part of the overall waterproofing protection, including
Subway, car and pedestrian tunnels; parking structures; water and sewage treatment facilities; canals, locks and dams are all examples of underground structures.
When most construction professionals think of "water stops," they usually think of 102 to 305 mm (4 to 12 in.) wide dumbbells or ribbed extrusions of thermoplastic or rubber materials that are placed into concrete joints. Since the 1950s, polyvinyl chloride (PVC) has been the most widely used waterstop. These items have been used because they are easy to weld and are naturally resistant to groundwater and typical wastewater treatment chemicals. To prevent water penetration through the joints of concrete structures, a variety of metals, plastics, asphalt and hydrophilic materials with various compositions and profiles are now used.
The vibration isolation rubber water stop is adapted to local conditions and adapts randomly. Installation techniques of vibration isolation rubber water stop:
1. In the design of tunnel concrete construction joints, pre-embedded rubber waterstops are required.
2. As the main material for waterproofing of construction joints, the mid-buried rubber waterstop requires half reserved and half pre-buried, and must be set in the middle of the concrete. 2. As the main material for waterproofing of construction joints, the mid-buried rubber waterstop requires half reserved and half pre-buried, and must be set in the middle of the concrete section.
3. When the mid-buried waterstop is constructed on site, because it is long, it will not meet the design requirements with little attention, and it is easy to bend. 4. When pre-embedded, it will not meet the design requirements with little attention, and it is easy to bend.
4. When pre-embedded, generally, the pre-embedded installation is carried out after the concrete of the first part of the construction is in place, which requires multiple people to perform the installation at the same time, to barely install it in place, laborious and laborious.
The problem with water stops is that they are easily damaged or installed incorrectly during the concrete placement process. Below is a list of many potential waterstop installation failures. ● Dumbbells or ribs with overlapping but not welded or spliced together at the center ball and roll end.
● erected too close to the reinforcement.
● Joints on dumbbells glued together with sealant rather than welded together.
● Installation of strip stops with a concave space (void) beneath them.
● No manufactured parts - polyvinyl chloride (PVC) transition bonded together
● PVC is welded to the edge of the profile only, not all the way through.
● Concrete that is not properly compacted near the waterstop.
● Thermoplastic welds that are overheated, burning or scorched.
● dumbbells or ribbed center ball products that are not in the center of the joint.
● Movement during concrete placement because the dumbbell was not properly secured to the reinforcement.
● A hole was cut in the flange of the dumbbell to allow the rebar to pass through.
● overlapping but not docked ends of hydrophilic tape rolls.
● the flange of the dumbbell narrowed to fit the rebar.
● misalignment of ribs or center bulbs at the joint.
● Concrete extending over a flange that has not been removed from the hydrophilic strip prior to the second pour; and
● Only fasteners are used to install hydrophilic strip stops.
Hydrophilic strip stops react and swell with water, creating an active water barrier in concrete joints, unlike PVC dumbbell stops, which act to passively stop water migration. Hydrophilic water stops have been on the market for decades and have a proven track record. Water seepage through concrete construction joints, including those under high hydrostatic pressure and intermittent hydrostatic conditions, is effectively protected by hydrophilic water stops.
Hydrophilic waterstops are available in rolls or strips. The profile is usually a small rectangle and the two most common sizes are 20 × 25 mm (3/4 × 1 in.) and 20 × 10 mm (3/4 × 3/8 in.). Bentonite and rubber hydrophilic tape systems are primarily used in construction joints; most are not suitable for use in expansion joints. These systems are simple to install and do not require sections to be heat welded together prior to the initial concrete pour. To allow a 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 the hardened concrete. This adhesion is necessary to ensure that the waterstop does not move during the concrete pour. To secure the waterstop, stencil cover strips placed on the strip may be nailed 300 mm (12 in.) on center (oc).
Use only mechanical fasteners (i.e., nails without a stencil cover) to install hydrophilic strip waterstops along the length of the product. When installing waterstops using only screws, a small layer of concrete slurry may be extruded beneath the waterstop, thereby losing most, if not all, of its effectiveness.
Worse, concrete placement may tear the waterstop from the fastener, causing this component of the joint to move into the concrete and out of the joint plane. Therefore, these strip stops must always be specified and installed in the proper location or in conjunction with a stencil cover system.
Hydrophilic waterstops can be used not only for cast-in-place concrete construction joints. Hydrophilic waterstops are easy to place around pipe penetrations, I-beams, concrete piles and irregularly shaped surfaces because of their flexibility and compliance.
Hydrophilic waterstops are also used to seal new concrete to old concrete. They are also lightweight and adaptable and do not require any specific prefabricated T's, L's or crosses. This type of waterstop is popular among contractors because of its ease of installation.
For hydrophilic water stops, manufacturers typically require a minimum concrete cover depth of 50 to 75 mm (2 to 3 in.), depending on the profile size and material type. To avoid concrete spalling due to inadequate concrete coverage, these water stops must be installed in strict compliance with the manufacturer's minimum concrete coverage standards.
They must be inserted without overlapping the ends of adjacent strips and must be closely adjacent to produce a continuous system.
These items should not get wet prematurely as they will swell when exposed to water. This requires a second layer of concrete to be poured immediately after the waterstop; otherwise, the waterstop may swell in the presence of rain. There is not enough "free water" in the concrete mixture to physically expand the hydrophilic waterstop.
Once the concrete has cured, for the waterstop to truly expand, it requires a large supply of outside water that will migrate into and come into contact with the joints. If there is no external water source in contact with it, the hydrophilic waterstop will remain dormant.
Not all hydrophilic components in hydrophilic water stops are bentonite. When in contact with water, hydrophilic rubber stops will swell and maintain the integrity of the solid material and will not decompose due to uncontrolled swelling.
However, when they are exposed to water, they may have different swelling characteristics (in terms of rate and volume) because they are made with different types of hydrophilic agents. In addition, some are made with non-expandable rubber in part of the profile, which means that the whole profile does not activate and swell.
This type of hydrophilic stop has the same drawbacks as bentonite-based stops, such as the inability to expand in fluids other than water and the lack of expansion joint functionality.
Daye Lake Bridge
The use of hydrophilic waterstops effectively prevents water penetration through concrete construction joints, even under high pressure and intermittent hydrostatic pressure conditions. When hydrated in an unrestricted, free-swelling environment (e.g., a bowl of water), hydrophilic waterstops exhibit a significant degree of expansion due to their product design.
As the product approaches maximum expansion in an unrestricted state, it may rupture. Although cracking appears to be a drawback of the material, it is a positive performance indicator for cast-in-place concrete joint conditions.
This means that the waterstop can stretch and mold well to the inner surface of concrete joints, no matter how uneven they may be.
It also has the ability to extrude into cracks and transition through angles in joints due to its malleability and expansion capabilities. In addition to concrete interfaces that do not bond well with the waterstop, bentonite composite tapes have been observed to expand through narrow cracks to fill larger void areas.
This dynamic sealing ability is possible due to the swelling properties; an ability that is not possible with high tensile strength materials such as hydrophilic rubber waterstops. Due to their harder material quality, hydrophilic rubber water stops have been reported to limit expansion to the cracks, gaps and joints surrounding them in laboratory tests.
The hardness of the rubber may limit the expansion of the waterstop to a small raised amount above the crack opening, rather than squeezing to the depth of the crack.
In properly cemented concrete, the maximum expansion exhibited by hydrophilic materials under unconfined, free-expansion conditions will not be apparent. Hydrophilic water stops only need to expand slightly at the proper locations to provide a positive seal on the concrete interface.
This limited expansion provides the product with the reserve expansion potential to seal poorly consolidated concrete or to prevent subsequent concrete cracking due to building settlement or seismic activity.
Hydrophilic water stops rarely undergo a wet/dry cycle once they are wetted. The material maintains its hydration equilibrium when contained in concrete and below grade, and does not shrink under regular groundwater level changes or intermittent water conditions.
Interestingly, bentonite can be hydrated and dried numerous times without losing its natural swelling potential. It can be frozen and thawed many times without losing its outstanding efficacy. Finally, even when in-situ drying occurs (a very unlikely scenario), bentonite has been shown to rehydrate to its original performance level.
Although mastic tape waterstops, unlike bentonite or hydrophilic rubber materials, are not susceptible to pre-hydrated expansion, their dependence on concrete adhesion may prevent complete sealing of the joint if certain components are not properly bonded or joined together.
Most non-expandable mastic waterstops are made in rolls or strips, similar to hydrophilic waterstops. The profile is usually a small rectangle, with butyl rubber composites measuring 20 x 25 mm (34 x 1 in.) and asphalt-based tapes measuring 38 x 12 mm (1 12 x 12 in.) being the most common.
Waterstops made of mastic are usually made of adhesive, asphalt or butyl rubber-based composites. They are made to adhere to the pre-treated surface of cured concrete cold joints. The strips are attached to a minimum embedment depth according to the manufacturer's instructions, and then a second pour of concrete is placed to encapsulate the remaining three sides.
Due to the heat from the hydrated concrete, the substance becomes more viscous and seals the joint by acting as an internal adhesion sealant.
The importance of adhesion cannot be overemphasized. If the waterstop is moved during the concrete placement process, it can easily lose most, if not all, of its waterstop function. Waterstops made of mastic are only suitable for construction joints and should not be directed for expansion joints.
The only obstacle to fluid migration is the low-profile strip of adhesive to the concrete, so the hydrostatic resistance of cemented water stops is greatly limited.
Cementitious waterstops are the least effective of all commercially available waterstops, and therefore the least expensive.
Metal water stops restrict the passage of corrosive fluids even at extremely high temperatures. For this reason, metal water stops are often used in harsh chemical and high temperature environments where other materials would decay. There are many different metals, grades and sizes available.
Stainless steel has extensive corrosion resistance and is essentially unaffected by ozone, making it a suitable material for ozone contactor construction in modern water treatment plants. Stainless steel water stops are available in a wide range of standard shapes and sizes, as well as profiles suitable for new and retrofit applications. All variant fabrication should be completed in advance, leaving only straight butt welds for the job.
Metal water stops are the most difficult to install as split forming using tungsten inert gas (TIG) or metal inert gas (MIG) welding is always required. Edge-to-edge welding (no overlap) should be performed on any straight material.
The stiffness of a metal waterstop can cause cracking of adjacent concrete. Therefore, solid metal waterstops with proper concrete cover should be installed.
Injection hose waterstops are typically permeable or perforated hoses with numerous injection ports and valves added during new construction. These ports are exposed to the inner surface of the concrete for eventual entry. If a leak occurs after construction, a grout pump can be used to inject a resin (usually polyurethane) to seal the joint and fill any nearby voids in the concrete.
Some products are advertised as re-injectable, but this is often not the case, either because of cured resin around the hose or because the contractor failed to follow the manufacturer's instructions (primarily by not cleaning the hose properly after the initial resin injection).
Each injection hose system uses a permeable hose that is short in length (typically less than 9 m [30 ft]). A braided mesh casing surrounds the hose core, allowing resin injected under pressure to flow out of the tube and into the fitting while preventing cement particles and aggregates from entering the hose and clogging it.
Using mechanically fastened clamps, the hose is secured to the first pour of concrete once it has set (typically at 305 mm [12 in] on center).
At the end of each section, adjacent perforated hoses overlap by 150 to 300 mm (6 to 12 in.), and a small non-perforated tube is added inline, using the concrete as an injection port. After the structure is constructed, polyurethane resin is injected into the hoses to seal the joint and repair any cracks or cavities.
They can also be used to seal joints between old and new structures during construction. Secondary containment chambers, basements and tunnels are common uses.
Because waterstop systems are so affordable, installing ancillary products can be a prudent and low-cost investment. This raises the question, "If the concrete joint has the proper width clearance, why not use one waterstop as the primary barrier and the other as a secondary barrier as an insurance policy?"
If the primary system fails in any way due to material or installation failure, the second system provides liquid-tight integrity at the concrete joint.
To be clear, a secondary waterstop system is not required when a ribbed center bulb or hydrophilic waterstop is properly placed. These waterstop products, whether polymer or manufacturer, leak only due to installation errors and lack of quality assurance.
The use of a ribbed center bulb waterstop on the positive pressure side of the joint and hydrophilic or adhesive strip applied stops a few inches from the negative pressure side of the joint is a common strap and sling technique. An injection pipe system installed on the low pressure side can be used as a supplemental waterstop.
The redundancy of established waterstop systems provides significant benefits at low cost, especially when amortized over the life of the concrete structure in which they are installed.
Hydrophilic water stops can be used for concrete construction joints, while PVC hydrophobic water stops can be used for pipes and mechanical penetrations.
Three waterstop systems were specified and implemented in construction joints in thick concrete walls of critical infrastructure subway projects. A PVC rib center bulb on the positive pressure side, a bentonite hydrophilic strip in the center, and an injection hose waterstop closest to the inner surface of the concrete wall were all part of the installation.
The contractor is responsible for installing the waterstops, which may be their most important job. For the long-term success of the project, these systems should be considered as critical building envelope barrier materials. The function of any waterstop requires proper design, installation and concrete methods. First, select a product size and profile that is appropriate for predicting joint movement, hydrostatic head and chemical resistance.
