In most of the construction project you might have already used the PVC Waterstop but did you know about Stainless Steel Waterstop and its benefits?
If not than this post is for you; as i am going to discuss in detail what is stainless steel waterstop? How it is fixed in the concrete? How stainless steel waterstop is spliced or welded?
Waterstop as the name suggests is an element embedded in concrete to avoid ingress of water through the construction joints, contraction and expansion joints. It is a must to use in water retaining structures or buildings subjected to heavy rainfalls.
A specially fabricated Stainless steel waterstop is sometimes used in concrete joints that are subjected to severe chemical, ozone, or high temperature exposure.
Embedded in concrete, stainless steel waterstops span the joint to form a continuous, watertight diaphragm that prevents the passage of fluids like water, grout etc.
The waterstop must be designed and installed properly to accommodate joint expansion, contraction and other lateral and transverse movements.
Forming and Positioning Requirements
Stainless steel waterstops are installed prior to the initial concrete pour to ensure proper positioning.
Split formwork is generally required. This allows half of the waterstop to be positioned inside the first pour with the other half projecting into the second pour.
The centerline of the waterstop should be aligned to coincide with the center of the joint. The split form should firmly hold the waterstop in position to prevent misalignment of the waterstop during concrete placement.
A tight fit is also necessary to prevent excessive leakage of concrete paste, which could lead to honeycombing of the concrete. When installed in joints with expected movement, a 2” wide strip of duct tape should be placed over the center V section to prevent concrete paste from filling the “V” area.
Once embedded in the first pour of concrete, the rigidity of the waterstop offers sufficient support to withstand the second placement of concrete. Attachment to surrounding formwork or reinforcing steel is not generally required.
Splicing Requirements for Stainless Steel Waterstop
Continuity of the waterstop, including the flanges and the centerline “V” section, is critical for optimum performance.
Continuity should be maintained through changes in direction, intersections, and transitions by the use of mitered welds.
Poorly constructed intersections and splices are prime locations for leaks. Riveting or bolting of the waterstop should never be permitted.
Properly constructed mitered welds should be performed by a qualified welder using proper TIG welding equipment.
TIG is extremely well suited to join thin sheets since the heat input in this process is small and the chance of “burn through” is minimal.
TIG welds do not create undercuts or excessive penetration, with lowest distortion when compared to any other welding process. For this reason, “Stick welding” or Shielded Metal Arc Welding (SMAW) are not recommended splicing methods.
Properly cutting and fitting mitered ends of the stainless steel waterstop is difficult and best performed under controlled conditions in a shop environment. It is therefore recommended that factory fabrications be used for all changes in direction, intersections and transitions, leaving only straight end-to-end splices for field welding.
In this way, the owner, engineer and contractor can be assured of a high quality waterstop system.
Execution and Installation
- Ensure steel reinforcing bars do not interfere with proper position of waterstop.
- Clean concrete joints and waterstop of dirt and construction debris prior to second pour of concrete.
- Lap metal waterstop at splices and continuously weld exposed edge on containment side. Use 0.35 diameter 316 stainless steel alloy filter rod for grade 316L stainless steel.
- Weld factory supplied intersections and directional changes to straight length sections described below.
- All welds to be made by qualified welder with TIG welding experience.
- Splices to be free from defects as defined in “Field Quality Control” in section 3.03.
- Center waterstop on joint with peak of “V” section oriented toward containment side. Seal base (open side) of “V” expansion area in metal waterstop with one layer of two-inch wide duct tape.
- At expansion joints keep “V” area unembedded.
- Place concrete without disturbing waterstop and thoroughly vibrate concrete to maximize intimate contact between waterstop and concrete.
- After first pour, clean protruding waterstop leg to ensure full contact of second pour.
Field Quality Control
- Waterstop splicing defects which are unacceptable include, but not limited to the following:-
- Tensile strength less than 80 percent of parent section.
- Misalignment of “V” section and flanges greater than 1/16 inch.
- Visible porosity or “burn-through” in the weld
- Adhesive bonds, free lap joint, or lap joints with mechanical fasteners.
- Misalignment of waterstop splices resulting in misalignment of waterstop in excess of ½ inch in 10 feet.